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Other Publications (174)
- Science (New York, N.Y.)
- NeuroImage
- Neuroscience Research
- Brain and Nerve = Shinkei Kenkyu No Shinpo
- Biochemical and Biophysical Research Communications
- Biological & Pharmaceutical Bulletin
- British Journal of Pharmacology
- Journal of Neurocytology
- The European Journal of Neuroscience
- The Journal of Neuroscience : the Official Journal of the Society for Neuroscience
- Japanese Journal of Pharmacology
- The European Journal of Neuroscience
- Neuropharmacology
- The Journal of Cell Biology
- The European Journal of Neuroscience
- The Journal of Biological Chemistry
- Japanese Journal of Pharmacology
- The Journal of Physiology
- Glia
- Naunyn-Schmiedeberg's Archives of Pharmacology
- The Journal of Neuroscience : the Official Journal of the Society for Neuroscience
- Cellular and Molecular Neurobiology
- The Journal of Physiology
- Synapse (New York, N.Y.)
- Synapse (New York, N.Y.)
- Current Neurovascular Research
- Proceedings of the National Academy of Sciences of the United States of America
- The Journal of Physiology
- The Journal of Neuroscience : the Official Journal of the Society for Neuroscience
- Cerebral Cortex (New York, N.Y. : 1991)
- Science (New York, N.Y.)
- Biophysical Journal
- Tanpakushitsu Kakusan Koso. Protein, Nucleic Acid, Enzyme
- Developmental Biology
- The Journal of Biological Chemistry
- The Neuroscientist : a Review Journal Bringing Neurobiology, Neurology and Psychiatry
- Journal of Neurochemistry
- Neuroscience Research
- The Journal of Physiology
- Cell Calcium
- Cerebral Cortex (New York, N.Y. : 1991)
- Nihon Yakurigaku Zasshi. Folia Pharmacologica Japonica
- The Journal of Physiology
- Neuroreport
- Biological & Pharmaceutical Bulletin
- Neuroreport
- Cerebral Cortex (New York, N.Y. : 1991)
- PloS One
- Journal of Pharmacological Sciences
- Journal of Pharmacological Sciences
- Neuroscience Research
- The Journal of Neuroscience : the Official Journal of the Society for Neuroscience
- PloS One
- Yakugaku Zasshi : Journal of the Pharmaceutical Society of Japan
- Brain and Nerve = Shinkei Kenkyu No Shinpo
- Neural Plasticity
- Journal of Neurophysiology
- The Journal of Neuroscience : the Official Journal of the Society for Neuroscience
- Experimental Neurology
- Journal of Pharmacological Sciences
- The Journal of Biological Chemistry
- Tanpakushitsu Kakusan Koso. Protein, Nucleic Acid, Enzyme
- The European Journal of Neuroscience
- Nihon Yakurigaku Zasshi. Folia Pharmacologica Japonica
- Journal of Pharmacological Sciences
- Neuroscience Research
- Journal of Neurophysiology
- Cerebral Cortex (New York, N.Y. : 1991)
- Molecular Brain
- The International Journal of Neuroscience
- Biological & Pharmaceutical Bulletin
- The Journal of Physiology
- The Chinese Journal of Physiology
- Communicative & Integrative Biology
- Neural Networks : the Official Journal of the International Neural Network Society
- Proceedings of the National Academy of Sciences of the United States of America
- Biophysical Journal
- Analytical and Bioanalytical Chemistry
- Journal of Pharmacological Sciences
- Neural Networks : the Official Journal of the International Neural Network Society
- Current Protocols in Neuroscience
- The Journal of Neuroscience : the Official Journal of the Society for Neuroscience
- Journal of the American Chemical Society
- Neuroscience Research
- The Journal of Physiological Sciences : JPS
- Biological & Pharmaceutical Bulletin
- Journal of Integrative Neuroscience
- The Journal of Neuroscience : the Official Journal of the Society for Neuroscience
- Science (New York, N.Y.)
- Cerebral Cortex (New York, N.Y. : 1991)
- PloS One
- PloS One
- Nature Medicine
- Nihon Yakurigaku Zasshi. Folia Pharmacologica Japonica
- The Journal of Physiology
- The Journal of Physiology
- Nature Protocols
- Brain Research
- Neuroreport
- The Journal of Neuroscience : the Official Journal of the Society for Neuroscience
- The European Journal of Neuroscience
- Journal of Pharmacological Sciences
- Science (New York, N.Y.)
- Yakugaku Zasshi : Journal of the Pharmaceutical Society of Japan
- Conference Proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference
- Scientific Reports
- Brain and Nerve = Shinkei Kenkyu No Shinpo
- Frontiers in Neural Circuits
- Journal of Neurochemistry
- Angewandte Chemie (International Ed. in English)
- The Journal of Neuroscience : the Official Journal of the Society for Neuroscience
- Cerebral Cortex (New York, N.Y. : 1991)
- PLoS Computational Biology
- Neuroreport
- The Journal of Physiological Sciences : JPS
- PloS One
- Neuroreport
- The Journal of Neuroscience : the Official Journal of the Society for Neuroscience
- Molecular Brain
- The Journal of Physiology
- The Journal of Neuroscience : the Official Journal of the Society for Neuroscience
- The European Journal of Neuroscience
- Nature Neuroscience
- Neuroreport
- Scientific Reports
- Physiological Reports
- PLoS Biology
- ELife
- Proceedings of the National Academy of Sciences of the United States of America
- Neuroscience Research
- Neuron
- The European Journal of Neuroscience
- Cognitive Neurodynamics
- The European Journal of Neuroscience
- Brain and Nerve = Shinkei Kenkyu No Shinpo
- Scientific Reports
- Current Biology : CB
- Neuroscience Research
- The Journal of Neuroscience : the Official Journal of the Society for Neuroscience
- Current Biology : CB
- Neurogenesis (Austin, Tex.)
- The Journal of Neuroscience : the Official Journal of the Society for Neuroscience
- Hippocampus
- The Journal of Physiological Sciences : JPS
- EBioMedicine
- Nihon Yakurigaku Zasshi. Folia Pharmacologica Japonica
- Journal of Pharmacological Sciences
- Cell Calcium
- PloS One
- Glia
- Proceedings of the National Academy of Sciences of the United States of America
- Neuroscience Research
- BMC Neuroscience
- The European Journal of Neuroscience
- Anatomical Science International
- The European Journal of Neuroscience
- Chembiochem : a European Journal of Chemical Biology
- Neuroscience Research
- Scientific Reports
- Scientific Reports
- Cell Reports
- Scientific Reports
- PloS One
- Journal of Neuroscience Methods
- Anatomical Science International
- Frontiers in Neuroanatomy
- ENeuro
- Data in Brief
- Biological & Pharmaceutical Bulletin
- Brain and Nerve = Shinkei Kenkyu No Shinpo
- Scientific Reports
- Journal of Pharmacological Sciences
- Neural Development
- Cerebral Cortex (New York, N.Y. : 1991)
Articles by Yuji Ikegaya in JoVE
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Quadruple Immunostaining of the Olfactory Bulb for Visualization of Olfactory Sensory Axon Molecular Identity Codes
Naoki Ihara1, Yuji Ikegaya1,2, Haruki Takeuchi1,3
1Laboratory of Chemical Pharmacology, Graduate School of Pharmaceutical Sciences, The University of Tokyo, 2Center for Information and Neural Networks, National Institute of Information and Communications Technology, 3PRESTO, Japan Science and Technology Agency (JST)
Olfactory sensory neurons express a wide variety of axon-sorting molecules to establish proper neural circuitry. This protocol describes an immunohistochemical staining method to visualize combinatorial expressions of axon-sorting molecules at the axon termini of olfactory sensory neurons.
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Simultaneous Recordings of Cortical Local Field Potentials, Electrocardiogram, Electromyogram, and Breathing Rhythm from a Freely Moving Rat
Yu Shikano1, Takuya Sasaki1, Yuji Ikegaya1,2
1Graduate School of Pharmaceutical Sciences, The University of Tokyo, 2Center for Information and Neural Networks
This study introduces a method for the simultaneous recording of local field potentials in the brain, electrocardiograms, electromyograms, and breathing signals of a freely moving rat. This technique, which reduces experimental costs and simplifies data analysis, will contribute to the understanding of the interactions between the brain and peripheral organs.
Other articles by Yuji Ikegaya on PubMed
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Hippocampal Long-term Depression As an Index of Spatial Working Memory
The European Journal of Neuroscience.
Sep, 2002 |
Pubmed ID: 12372034 Long-term potentiation (LTP), a form of synaptic plasticity in the hippocampus, is a cellular model for the neural basis of learning and memory, but few studies have investigated the contribution of long-term depression (LTD), a counterpart of LTP. To address the possible relationship between hippocampal LTD and spatial performance, the spatial cognitive ability of a rat was assessed in a spontaneous alternation test and, thereafter, LTD in response to low-frequency burst stimulation (LFBS) was monitored in the dentate gyrus of the same rat under anaesthesia. To enhance a divergence in the ability for spatial performance, some of the animals received fimbria-fornix (FF) transection 14 days before the experiments. LTD was reliably induced by application of LFBS to the medial perforant path of intact rats, while no apparent LTD was elicited in rats with FF lesions. The behavioural parameters of spatial memory showed a significant correlation with the magnitude of LTD. We found no evidence that the cognitive ability correlated with other electrophysiological parameters, e.g. basal synaptic responses, stimulus intensity to produce half-maximal responses, paired-pulse facilitation or paired-pulse depression. These results suggest that the magnitude of LTD in the dentate gyrus serves as a reliable index of spatial cognitive ability, providing insights into the functional significance of hippocampal LTD.
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Brain-derived Neurotrophic Factor Promotes the Maturation of GABAergic Mechanisms in Cultured Hippocampal Neurons
The Journal of Neuroscience : the Official Journal of the Society for Neuroscience.
Sep, 2002 |
Pubmed ID: 12196581 Brain-derived neurotrophic factor (BDNF) has been implicated in activity-dependent plasticity of neuronal function and network arrangement. To clarify how BDNF exerts its action, we evaluated the physiological, histological, and biochemical characteristics of cultured hippocampal neurons after long-term treatment with BDNF. Here we show that BDNF facilitates high K(+)-elicited release of GABA but not of glutamate and induces an increase in immunoreactive signals of glutamic acid decarboxylase, a GABA-synthesizing enzyme. The soma size of GABAergic neurons was enlarged in BDNF-treated cultures, whereas the average soma size of all neurons was virtually unchanged. BDNF also upregulated protein levels of GABA(A) receptors but not of glutamate receptors. These data imply that BDNF selectively advances the maturation of GABAergic synapses. However, immunocytochemical analyses revealed that a significant expression of TrkB, a high-affinity receptor for BDNF, was detected in non-GABAergic as well as GABAergic neurons. BDNF also increased to total amount of synaptic vesicle-associated proteins without affecting the number of presynaptic vesicles that can be labeled with FM1-43 after K(+) depolarization. Together, our findings indicate that BDNF principally promotes GABAergic maturation but may also potentially contribute to excitatory synapse development via increasing resting synaptic vesicles.
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Cytoskeleton Disruption Causes Apoptotic Degeneration of Dentate Granule Cells in Hippocampal Slice Cultures
Neuropharmacology.
Jun, 2002 |
Pubmed ID: 12128012 Colchicine, a potent microtubule-depolymerizing agent, is well known to selectively kill dentate granule cells in the hippocampal formation in vivo. Using organotypic cultures of rat entorhino-hippocampal slices, we confirmed that in vitro exposure to 1 microM and 10 microM of colchicine reproduced a specific degeneration of the granule cells after 24 h. Similar results were obtained with other types of microtubule-disrupting agents, i.e., nocodazole, vinblastine, and Taxol. Interestingly, the actin-depolymerizing agents cytochalasin D and latrunculin A also elicited selective neurotoxicity in the dentate gyrus without affecting survival of hippocampal pyramidal cells. The selective pattern of degeneration was observable 24 h after a brief treatment with the toxins as short as 5 min, but this delayed neuronal death was unlikely to be a result of excitotoxicity because it was virtually unaffected by glutamate receptor antagonists, tetrodotoxin, or extracellular Ca(2+)-free conditions. The damaged tissues contained a large number of TUNEL-positive neurons and exhibited an increased level in caspase-3-like activity, suggesting that cytoskeleton disruption triggers an apoptosis-like process in dentate granule cells. Thus, this study may provide a basis for understanding the distinctive mechanism that supports granule cell survival.
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Mossy Fiber Zn2+ Spillover Modulates Heterosynaptic N-methyl-D-aspartate Receptor Activity in Hippocampal CA3 Circuits
The Journal of Cell Biology.
Jul, 2002 |
Pubmed ID: 12119362 Although Zn2+ is contained in large amounts in the synaptic terminals of hippocampal mossy fibers (MFs), its physiological role in synaptic transmission is poorly understood. By using the newly developed high-sensitivity Zn2+ indicator ZnAF-2, the spatiotemporal dynamics of Zn2+ was monitored in rat hippocampal slices. When high-frequency stimulation was delivered to the MFs, the concentration of extracellular Zn2+ was immediately elevated in the stratum lucidum, followed by a mild increase in the stratum radiatum adjacent to the stratum lucidum, but not in the distal area of stratum radiatum. The Zn2+ increase was insensitive to a non-N-methyl-d-aspartate (NMDA) receptor antagonist but was efficiently attenuated by tetrodotoxin or Ca2+-free medium, suggesting that Zn2+ is released by MF synaptic terminals in an activity-dependent manner, and thereafter diffuses extracellularly into the neighboring stratum radiatum. Electrophysiological analyses revealed that NMDA receptor-mediated synaptic responses in CA3 proximal stratum radiatum were inhibited in the immediate aftermath of MF activation and that this inhibition was no longer observed in the presence of a Zn2+-chelating agent. Thus, Zn2+ serves as a spatiotemporal mediator in imprinting the history of MF activity in contiguous hippocampal networks. We predict herein a novel form of metaplasticity, i.e., an experience-dependent non-Hebbian modulation of synaptic plasticity.
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Endothelin Downregulates the Glutamate Transporter GLAST in CAMP-differentiated Astrocytes in Vitro
Glia.
Feb, 2002 |
Pubmed ID: 11754215 Endothelin (ET) is a putative pathogenetic mediator associated with brain trauma and ischemia. Because a link between neuronal damage after these injuries and glial Na(+)-dependent L-glutamate transporter activity has been suggested, we investigated the effect of ET on the glutamate clearance ability of astrocytes. Dibutyryl cyclic adenosine monophosphate (dBcAMP), which is widely used to induce differentiation of cultured astrocytes, markedly increased [(3)H]glutamate transport activity in a concentration- and time-dependent manner. In the presence of ET, however, dBcAMP decreased the glutamate uptake. This effect was efficiently prevented by an antagonist of ET(B) receptor, but not of ET(A) receptor. ET per se was virtually ineffective. Eadie-Hofstee analysis demonstrated that dBcAMP increased the V(max) value of glutamate uptake activity by 43.4% in the absence of ET, but decreased it by 41.4% in the presence of ET, without apparent changes in the K(m) value. Accordingly, Western blot analysis indicated that the change in transport activity correlated closely with that in expression level of the glial glutamate transporter GLAST. These results may represent the mechanisms by which ET aggravates trauma- and ischemia-elicited neuronal damage.
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Activity-evoked Capacitative Ca2+ Entry: Implications in Synaptic Plasticity
The Journal of Neuroscience : the Official Journal of the Society for Neuroscience.
Aug, 2003 |
Pubmed ID: 12944501 The Ca2+ influx controlled by intracellular Ca2+ stores, called store-operated Ca2+ entry (SOC), occurs in various eukaryotic cells, but whether CNS neurons are endowed with SOC capability and how they may operate have been contentious issues. Using Ca2+ imaging, we present evidence for the presence of SOC in cultured hippocampal pyramidal neurons. Depletion of internal Ca2+ stores by thapsigargin caused intracellular Ca2+ elevation, which was prevented by SOC channel inhibitors 2-aminoethoxydiphenyl borate (2-APB), SKF96365, and La3+. Interestingly, these inhibitors also accelerated the decay of NMDA-induced Ca2+ transients without affecting their peak amplitude. In addition, SOC channel inhibitors attenuated tetanus-induced dendritic Ca2+ accumulation and long-term potentiation at Schaffer collateral-CA1 synapses in hippocampal slice preparations. These data suggest a novel link between ionotropic receptor-activated SOC and neuroplasticity.
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Mossy Fibre Synaptic NMDA Receptors Trigger Non-Hebbian Long-term Potentiation at Entorhino-CA3 Synapses in the Rat
The Journal of Physiology.
Feb, 2003 |
Pubmed ID: 12562995 Hippocampal CA3 pyramidal cells receive two independent afferents from the enthorinal cortex, i.e. a direct input via the temporoammonic pathway (TA, perforant path) and an indirect input via the mossy fibres (MF) of dentate granule cells. In spite of past suggestions that the TA is assigned an important role in exciting the pyramidal cells, little is known about their physiological properties. By surgically making an incision through the sulcus hippocampi and a small part of the dentate molecular layer, we succeeded in isolating TA-mediated monosynaptic responses in CA3 stratum lacunosum-moleculare. The TA-CA3 synaptic transmission was completely blocked by a combination of D,L-2-amino-5-phosphonopentanoic acid (AP5) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), NMDA and non-NMDA receptor antagonists, respectively, and displayed paired-pulse facilitation and NMDA receptor-dependent long-term potentiation, which are all typical of glutamatergic synapses. We next addressed the heterosynaptic interaction between TA-CA3 and MF-CA3 synapses. The TA-CA3 transmission was partially attenuated by single-pulse MF pre-stimulation at inter-pulse intervals of up to 70 ms. However, surprisingly, burst stimulation of the MF alone induced long-lasting facilitation of TA-CA3 synaptic efficacy. This non-Hebbian form of synaptic plasticity was efficiently prevented by local application of AP5 into the MF synapse-rich area. Therefore, MF-activated NMDA receptors are responsible for the heterosynaptic modification of TA-CA3 transmission, and thereby, the history of MF activity may be etched into TA-CA3 synaptic strength. Our findings predict a novel form of spatiotemporal information processing in the hippocampus, i.e. a use-dependent intersynaptic memory transfer.
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Fimbrial Control of Bidirectional Synaptic Plasticity of Medial Perforant Path-dentate Transmission
Synapse (New York, N.Y.).
Mar, 2003 |
Pubmed ID: 12494398 Lesions of the fimbria-fornix (FF) tract cause profound impairments of cognitive ability in animals. Our previous study showed that spatial performance correlates with long-term potentiation (LTP) of the dentate gyrus (DG), but not of the CA1 region, in rats with bilateral FF lesions, suggesting that FF lesions selectively inhibited LTP in the DG. The cortical input to the DG is anatomically and physiologically divided into two types of afferents, i.e., the medial perforant path (MPP) and the lateral perforant path (LPP), which show distinct synaptic properties. To elucidate the difference in the FF modulation of these two inputs, field responses were recorded from MPP- or LPP-DG synapses in anesthetized rats. MPP-DG synapses of rats with FF lesions displayed neither LTP in response to theta-burst stimulation nor long-term depression (LTD) in response to low-frequency burst stimulation. In contrast to the MPP, LPP-DG synapses showed normal LTP in rats with FF lesions. The low-frequency burst stimulation could not induce LTD at LPP-DG synapses in either intact or FF-lesioned rats. These results suggest that the FF pathway selectively supports the mechanisms of bidirectional synaptic plasticity at MPP-DG synapses. This study provides new insights into external control of information processing in the hippocampus.
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Interleukin-1beta Abrogates Long-term Depression of Hippocampal CA1 Synaptic Transmission
Synapse (New York, N.Y.).
Jan, 2003 |
Pubmed ID: 12422373 Although interleukin-1beta (IL-1beta) is well known to modulate synaptic transmission and plasticity of the hippocampus, no study has yet evaluated how this cytokine affects long-term depression (LTD), one of the major forms of hippocampal synaptic plasticity. Here we report that at Schaffer collateral-CA1 synapses, bath application of IL-1beta induces a long-lasting decrease in synaptic strength in intact slices, but not in disinhibited slices in the presence of bicuculline, a gamma-aminobutyric acid receptor antagonist. The IL-1beta-induced synaptic depression efficiently foreclosed the subsequent induction of LTD in response to a 1-Hz tetanus and, conversely, it was also prevented by preexisting LTD. These results suggest that IL-1beta-induced, persistent depression of synaptic efficacy is required for GABAergic activation and shares, at least in part, a common cellular mechanism for LTD.
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Mossy Fiber Sprouting As a Potential Therapeutic Target for Epilepsy
Current Neurovascular Research.
Jan, 2004 |
Pubmed ID: 16181061 Hippocampal mossy fibers, axons of dentate granule cells, converge in the dentate hilus and run through a narrow area called the stratum lucidum to synapse with hilar and CA3 neurons. In the hippocampal formation of temporal lobe epilepsy patients, however, this stereotyped pattern of projection is often collapsed; the mossy fibers branch out of the dentate hilus and abnormally innervate the dentate inner molecular layer, a phenomenon that is termed mossy fiber sprouting. Experimental studies have replicated this sprouting in animal models of temporal lobe epilepsy, including kindling and pharmacological treatment with convulsants. Because these axon collaterals form recurrent excitatory inputs into dendrites of granule cells, the circuit reorganization is assumed to cause epileptiform activity in the hippocampus, whereas some recent studies indicate that the sprouting is not necessarily associated with early-life seizures. Here we review the mechanisms of mossy fiber sprouting and consider its potential contribution to epileptogenesis. Based on recent findings, we propose that the sprouting can be regarded as a result of disruption of the molecular mechanisms underlying the axon guidance. We finally focus on the possibility that prevention of the abnormal sprouting might be a new strategy for medical treatment with temporal lobe epilepsy.
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Chronometric Readout from a Memory Trace: Gamma-frequency Field Stimulation Recruits Timed Recurrent Activity in the Rat CA3 Network
The Journal of Physiology.
Nov, 2004 |
Pubmed ID: 15375190 Synchronous population activity is prevalent in neurones of the central nervous system and experimentally captured as oscillatory electric fields, the frequency of which can represent the state of the neural circuit, e.g. theta (approximately 5 Hz) and gamma (approximately 40 Hz). Such field oscillations, however, are not merely a result of coherent neuronal activity. They may also play active roles in information processing in the brain. In this study, we observed that, in cultured hippocampal slices, CA3 pyramidal cells responded to single-pulse stimuli with monosynaptic and polysynaptic potentials and firing spikes which occurred after variable latencies. The variability of the spike latencies was greatly reduced in the presence of weak electric field oscillations, especially the oscillation in the gamma-band frequency range, that per se induced only small fluctuations in the subthreshold membrane potential, and this effect was inhibited by blockade of NMDA receptor activity. Furthermore, the latency of the firing spikes changed if the stimulus was applied at a different phase of the imposed gamma oscillations. These results may suggest that the background field oscillations serve as an extracellular time reference and assure accurate and stable decoding of a memory trace present in cortical feedback networks.
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Brain-derived Neurotrophic Factor Induces Hyperexcitable Reentrant Circuits in the Dentate Gyrus
The Journal of Neuroscience : the Official Journal of the Society for Neuroscience.
Aug, 2004 |
Pubmed ID: 15317847 Aberrant sprouting and synaptic reorganization of the mossy fiber (MF) axons are commonly found in the hippocampus of temporal lobe epilepsy patients and result in the formation of excitatory feedback loops in the dentate gyrus, a putative cellular basis for recurrent epileptic seizures. Using ex vivo hippocampal cultures, we show that prolonged hyperactivity induces MF sprouting and the resultant network reorganizations and that brain-derived neurotrophic factor (BDNF) is necessary and sufficient to evoke these pathogenic plasticities. Hyperexcitation induced an upregulation of BDNF protein expression in the MF pathway, an effect mediated by L-type Ca2+ channels. The neurotrophin receptor tyrosine kinase (Trk)B inhibitor K252a or function-blocking anti-BDNF antibody prevented hyperactivity-induced MF sprouting. Even under blockade of neural activity, local application of BDNF to the hilus, but not other subregions, was capable of initiating MF axonal remodeling, eventually leading to dentate hyperexcitability. Transfecting granule cells with dominant-negative TrkB prevented axonal branching. Thus, excessive activation of L-type Ca2+ channels causes granule cells to express BDNF, and extracellularly released BDNF stimulates TrkB receptors present on the hilar segment of the MFs to induce axonal branching, which may establish hyperexcitable dentate circuits.
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BDNF Boosts Spike Fidelity in Chaotic Neural Oscillations
Biophysical Journal.
Mar, 2004 |
Pubmed ID: 14990508 Oscillatory activity and its nonlinear dynamics are of fundamental importance for information processing in the central nervous system. Here we show that in aperiodic oscillations, brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, enhances the accuracy of action potentials in terms of spike reliability and temporal precision. Cultured hippocampal neurons displayed irregular oscillations of membrane potential in response to sinusoidal 20-Hz somatic current injection, yielding wobbly orbits in the phase space, i.e., a strange attractor. Brief application of BDNF suppressed this unpredictable dynamics and stabilized membrane potential fluctuations, leading to rhythmical firing. Even in complex oscillations induced by external stimuli of 40 Hz (gamma) on a 5-Hz (theta) carrier, BDNF-treated neurons generated more precisely timed spikes, i.e., phase-locked firing, coupled with theta-phase precession. These phenomena were sensitive to K252a, an inhibitor of tyrosine receptor kinases and appeared attributable to BDNF-evoked Na(+) current. The data are the first indication of pharmacological control of endogenous chaos. BDNF diminishes the ambiguity of spike time jitter and thereby might assure neural encoding, such as spike timing-dependent synaptic plasticity.
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Developmental Switch in Axon Guidance Modes of Hippocampal Mossy Fibers in Vitro
Developmental Biology.
Mar, 2004 |
Pubmed ID: 14975715 Hippocampal mossy fibers (MFs), axons of dentate granule cells, run through a narrow strip, called the stratum lucidum, and make synaptic contacts with CA3 pyramidal cells. This stereotyped pathfinding is assumed to require a tightly controlled guidance system, but the responsible mechanisms have not been proven directly. To clarify the cellular basis for the MF pathfinding, microslices of the dentate gyrus (DG) and Ammon's horn (AH) were topographically arranged in an organotypic explant coculture system. When collagen gels were interposed between DG and AH slices prepared from postnatal day 6 (P6) rats, the MFs passed across this intervening gap and reached CA3 stratum lucidum. Even when the recipient AH was chemically pre-fixed with paraformaldehyde, the axons were still capable of accessing their normal target area only if the DG and AH slices were directly juxtaposed without a collagen bridge. The data imply that diffusible and contact cues are both involved in MF guidance. To determine how these different cues contribute to MF pathfinding during development, a P6 DG slice was apposed simultaneously to two AH slices prepared from P0 and P13 rats. MFs projected normally to both the host slices, whereas they rarely invaded P0 AH when the two hosts were fixed. Early in development, therefore, the MFs are guided mainly by a chemoattractant gradient, and thereafter, they can find their trajectories by a contact factor, probably via fasciculation with pre-established MFs. The present study proposes a dynamic paradigm in CNS axon pathfinding, that is, developmental changes in axon guidance cues.
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To BDNF or Not to BDNF: That is the Epileptic Hippocampus
The Neuroscientist : a Review Journal Bringing Neurobiology, Neurology and Psychiatry.
Aug, 2005 |
Pubmed ID: 16061515 Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, has drawn much attention as a potential therapeutic target for temporal lobe epilepsy (TLE). TLE seizures are produced by synchronized hyperactivity of neuron populations due to the disruption of a balance between excitatory and inhibitory synaptic transmissions. In epileptogenesis-related brain areas, including the hippocampus, BDNF is up-regulated in the course of the development of epilepsy and induces a collapse of balanced excitation and inhibition, eventually exerting its epileptogenic effects. On the other hand, several reports demonstrate that intrahippocampal infusion of BDNF can attenuate (or retard) the development of epilepsy. This antiepileptogenic effect seems to be mediated mainly by an increase in the expression of neuropeptide Y. These contrasting effects of BDNF have prevented us from concluding whether inhibition or enhancement of BDNF signaling finally achieves the prevention of TLE. To address this question, it is essential to evaluate how BDNF changes its influences depending on conditions, for example, cell specificity, neural networks, and expression timing and loci. In this article, the authors review BDNF-induced acute and long-lasting changes seen in epileptic circuits from the anatomical and functional points of view.
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Microglia-specific Expression of Microsomal Prostaglandin E2 Synthase-1 Contributes to Lipopolysaccharide-induced Prostaglandin E2 Production
Journal of Neurochemistry.
Sep, 2005 |
Pubmed ID: 16000148 Microsomal prostaglandin E2 synthase (mPGES)-1 is an inducible protein recently shown to be an important enzyme in inflammatory prostaglandin E2 (PGE2) production in some peripheral inflammatory lesions. However, in inflammatory sites in the brain, the induction of mPGES-1 is poorly understood. In this study, we demonstrated the expression of mPGES-1 in the brain parenchyma in a lipopolysaccharide (LPS)-induced inflammation model. A local injection of LPS into the rat substantia nigra led to the induction of mPGES-1 in activated microglia. In neuron-glial mixed cultures, mPGES-1 was co-induced with cyclooxygenase-2 (COX-2) specifically in microglia, but not in astrocytes, oligodendrocytes or neurons. In microglia-enriched cultures, the induction of mPGES-1, the activity of PGES and the production of PGE2 were preceded by the induction of mPGES-1 mRNA and almost completely inhibited by the synthetic glucocorticoid dexamethasone. The induction of mPGES-1 and production of PGE2 were also either attenuated or absent in microglia treated with mPGES-1 antisense oligonucleotide or microglia from mPGES-1 knockout (KO) mice, respectively, suggesting the necessity of mPGES-1 for microglial PGE2 production. These results suggest that the activation of microglia contributes to PGE2 production through the concerted de novo synthesis of mPGES-1 and COX-2 at sites of inflammation of the brain parenchyma.
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Dynamic Synapses As Archives of Synaptic History: State-dependent Redistribution of Synaptic Efficacy in the Rat Hippocampal CA1
The Journal of Physiology.
Jul, 2005 |
Pubmed ID: 15845579 Plastic modifications of synaptic strength are putative mechanisms underlying information processing in the brain, including memory storage, signal integration and filtering. Here we describe a dynamic interplay between short-term and long-term synaptic plasticity. At rat hippocampal CA1 synapses, induction of both long-term potentiation (LTP) and depression (LTD) was accompanied by changes in the profile of short-term plasticity, termed redistribution of synaptic efficacy (RSE). RSE was presynaptically expressed and associated in part with a persistent alteration in hyperpolarization-activated I(h) channel activity. Already potentiated synapses were still capable of showing RSE in response to additional LTP-triggering stimulation. Strikingly, RSE took place even after reversal of LTP or LTD, that is, the same synapse can display different levels of short-term plasticity without changing synaptic efficacy for the initial spike in burst presynaptic firing, thereby modulating spike transmission in a firing rate-dependent manner. Thus, the history of long-term synaptic plasticity is registered in the form of short-term plasticity, and RSE extends the information storage capacity of a synapse and adds another dimension of functional complexity to neuronal operations.
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BDNF Locally Potentiates GABAergic Presynaptic Machineries: Target-selective Circuit Inhibition
Cerebral Cortex (New York, N.Y. : 1991).
Mar, 2005 |
Pubmed ID: 15238431 Inhibitory neurotransmission is critical for neuronal circuit formation. To examine whether inhibitory neurotransmission receives target-selective modulation in the long term, we expressed the cDNA of brain-derived neurotrophic factor (BDNF), which has been shown to induce the augmentation of GABAergic synapses in vivo and in vitro, in a small population of cultured hippocampal neurons. At 48 h after transfection, the expression level of glutamic acid decarboxylase 65 (GAD65), a GABA synthetic enzyme that resides mainly in GABAergic terminals, was selectively enhanced around the BDNF-expressing neurons, in comparison with the neighboring control neurons interposed between the BDNF-expressing neurons and inhibitory neurons. Exogenous BDNF application for 48 h also increased the GAD level and enhanced the GABA release probability. These potentiating effects were attenuated in inhibitory synapses on neurons expressing a dominant negative form of the BDNF receptor (tTrkB). This suggests that postsynaptic BDNF-TrkB signaling contributes to the target-selective potentiation of inhibitory presynaptic machineries. Since BDNF is expressed in an activity-dependent manner in vivo, this selectivity may be one of the key mechanisms by which the independence of functional neuronal circuits is maintained.
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Integrative Spike Dynamics of Rat CA1 Neurons: a Multineuronal Imaging Study
The Journal of Physiology.
Jul, 2006 |
Pubmed ID: 16613875 The brain operates through a coordinated interplay of numerous neurons, yet little is known about the collective behaviour of individual neurons embedded in a huge network. We used large-scale optical recordings to address synaptic integration in hundreds of neurons. In hippocampal slice cultures bolus-loaded with Ca2+ fluorophores, we stimulated the Schaffer collaterals and monitored the aggregate presynaptic activity from the stratum radiatum and individual postsynaptic spikes from the CA1 stratum pyramidale. Single neurons responded to varying synaptic inputs with unreliable spikes, but at the population level, the networks stably output a linear sum of synaptic inputs. Nonetheless, the network activity, even though given constant stimuli, varied from trial to trial. This variation emerged through time-varying recruitment of different neuron subsets, which were shaped by correlated background noise. We also mapped the input-frequency preference in spiking activity and found that the majority of CA1 neurons fired in response to a limited range of presynaptic firing rates (20-40 Hz), acting like a band-pass filter, although a few neurons had high pass-like or low pass-like characteristics. This frequency selectivity depended on phasic inhibitory transmission. Thus, our imaging approach enables the linking of single-cell behaviours to their communal dynamics, and we discovered that, even in a relatively simple CA1 circuit, neurons could be engaged in concordant information processing.
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Single Neurons Can Induce Phase Transitions of Cortical Recurrent Networks with Multiple Internal States
Cerebral Cortex (New York, N.Y. : 1991).
May, 2006 |
Pubmed ID: 16093564 Fluctuations of membrane potential of cortical neurons, referred to here as internal states, are essential for brain function, but little is known about how these internal states emerge and are maintained, or what determines transitions between these states. We performed intracellular recordings from hippocampal CA3 pyramidal cells ex vivo and found that neurons display multiple and hierarchical internal states, which are linked to cholinergic activity and are characterized by several power law structures in membrane potential dynamics. Multiple recordings from adjacent neurons revealed that the internal states were coherent between neurons, indicating that the internal state of any given cell in a local network could represent the network activity state. Repeated stimulation of single neurons led over time to transitions to different internal states in both the stimulated neuron and neighboring neurons. Thus, single-cell activation is sufficient to shift the state of the entire local network. As the states shift to more active levels, theta- and gamma-frequency components developed in the form of subthreshold oscillations. State transitions were associated with changes in membrane conductance but were not accompanied by a change in reversal potential. These data suggest that the recurrent network organizes the internal states of individual neurons into synchronization through network activity with balanced excitation and inhibition, and that this organization is discrete, heterogeneous and dynamic in nature. Thus, neuronal states reflect the 'phase' of an active network, a novel demonstration of the dynamics and flexibility of cortical microcircuitry.
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Active Hippocampal Networks Undergo Spontaneous Synaptic Modification
PloS One.
Nov, 2007 |
Pubmed ID: 18043757 The brain is self-writable; as the brain voluntarily adapts itself to a changing environment, the neural circuitry rearranges its functional connectivity by referring to its own activity. How the internal activity modifies synaptic weights is largely unknown, however. Here we report that spontaneous activity causes complex reorganization of synaptic connectivity without any external (or artificial) stimuli. Under physiologically relevant ionic conditions, CA3 pyramidal cells in hippocampal slices displayed spontaneous spikes with bistable slow oscillations of membrane potential, alternating between the so-called UP and DOWN states. The generation of slow oscillations did not require fast synaptic transmission, but their patterns were coordinated by local circuit activity. In the course of generating spontaneous activity, individual neurons acquired bidirectional long-lasting synaptic modification. The spontaneous synaptic plasticity depended on a rise in intracellular calcium concentrations of postsynaptic cells, but not on NMDA receptor activity. The direction and amount of the plasticity varied depending on slow oscillation patterns and synapse locations, and thus, they were diverse in a network. Once this global synaptic refinement occurred, the same neurons now displayed different patterns of spontaneous activity, which in turn exhibited different levels of synaptic plasticity. Thus, active networks continuously update their internal states through ongoing synaptic plasticity. With computational simulations, we suggest that with this slow oscillation-induced plasticity, a recurrent network converges on a more specific state, compared to that with spike timing-dependent plasticity alone.
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Metastability of Active CA3 Networks
The Journal of Neuroscience : the Official Journal of the Society for Neuroscience.
Jan, 2007 |
Pubmed ID: 17234584 The brain is spontaneously active even in the absence of external input. This ongoing background activity impacts neural information processing. We used functional multineuron calcium imaging (fMCI) to analyze the net structure of spontaneous CA3 network activity in hippocampal slice cultures loaded with Oregon Green 488 BAPTA-1 using a spinning disk confocal microscope (10-30 frames/s). Principal component analysis revealed that network states, defined by active cell ensembles, were stable but heterogenous and discrete. These states were stabilized through synaptic activity and maintained against external perturbations. A few discrete states emerged during our observation period of up to 30 min. Networks tended to stay in a single state for tens of seconds and then suddenly jump to a new state. After a state transition, the old state was rarely, if ever, revisited by the network during our observation period. This temporal profile of state transitions could not be simulated by a hidden Markov model, indicating that the state dynamics is nonrandomly organized. Within each state, the pattern of network activity tended to stabilize in a specific configuration. Neither maintenance nor transition of the network states required NMDA receptor activity. These findings suggest that the network states are metastable, rather than multistable, and might be governed by local attractor-like dynamics. The fMCI data analyzed here are available at http://hippocampus.jp/data/
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Statistical Significance of Precisely Repeated Intracellular Synaptic Patterns
PloS One.
2008 |
Pubmed ID: 19096523 Can neuronal networks produce patterns of activity with millisecond accuracy? It may seem unlikely, considering the probabilistic nature of synaptic transmission. However, some theories of brain function predict that such precision is feasible and can emerge from the non-linearity of the action potential generation in circuits of connected neurons. Several studies have presented evidence for and against this hypothesis. Our earlier work supported the precision hypothesis, based on results demonstrating that precise patterns of synaptic inputs could be found in intracellular recordings from neurons in brain slices and in vivo. To test this hypothesis, we devised a method for finding precise repeats of activity and compared repeats found in the data to those found in surrogate datasets made by shuffling the original data. Because more repeats were found in the original data than in the surrogate data sets, we argued that repeats were not due to chance occurrence. Mokeichev et al. (2007) challenged these conclusions, arguing that the generation of surrogate data was insufficiently rigorous. We have now reanalyzed our previous data with the methods introduced from Mokeichev et al. (2007). Our reanalysis reveals that repeats are statistically significant, thus supporting our earlier conclusions, while also supporting many conclusions that Mokeichev et al. (2007) drew from their recent in vivo recordings. Moreover, we also show that the conditions under which the membrane potential is recorded contributes significantly to the ability to detect repeats and may explain conflicting results. In conclusion, our reevaluation resolves the methodological contradictions between Ikegaya et al. (2004) and Mokeichev et al. (2007), but demonstrates the validity of our previous conclusion that spontaneous network activity is non-randomly organized.
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Long-range Axonal Calcium Sweep Induces Axon Retraction
The Journal of Neuroscience : the Official Journal of the Society for Neuroscience.
Apr, 2008 |
Pubmed ID: 18448637 Axon guidance molecules trigger a cascade of local signal in growth cones and evoke various morphologic responses, including axon attraction, repulsion, elongation, and retraction. However, little is known about whether subcellular compartments, other than axonal growth cones, control axon outgrowth. We found that in isolated dentate granule cells, local application of glutamate to the somatodendritic areas, but not the axon itself, induced rapid axon retraction, during which a calcium wave propagated from the somata to the axon terminals. The calcium wave and axon retraction were both inhibited by blockade of voltage-sensitive calcium channels and intracellular calcium dynamics. A combination of perisomatic application of calcium ionophore and depolarizing current injection induced axonal calcium sweep and axon retraction. Thus, perisomatic environments can modulate axon behavior through long-range intracellular communication.
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Early-life Status Epilepticus Induces Ectopic Granule Cells in Adult Mice Dentate Gyrus
Experimental Neurology.
Jun, 2008 |
Pubmed ID: 18420198 A large number of aberrant hilar granule cells (GCs) are found in the patients and animal models of adult temporal lobe epilepsy (TLE), and these "ectopic" GCs have synchronous epileptiform bursting with other hippocampal neurons. In this study, we investigated whether early-life status epilepticus (SE) induces hilar ectopic GCs that remain in the adulthood because TLE patients frequently experience seizures in the early childhood when a large number of postnatally born GCs migrate in the hilus. To label newborn GCs, bromodeoxyuridine (BrdU) was injected daily for three consecutive days to C57BL/6J mice at different postnatal days starting at postnatal-0-day-old (P0) (Group1), P7 (Group2), or P35 (Group3). Mice in each group underwent pilocarpine-induced SE at P14. Six months later, to determine whether SE induces ectopic GCs, we plotted the distribution of postnatally born GCs which were immunohistochemically defined as BrdU- and the GC marker Prox1-colabeled cells. We also examined whether SE causes the granule cell layer (GCL) dispersion and/or the mossy fiber (MF) sprouting, other representative pathologies of TLE hippocampus. Only SE-experiencing mice in Group1 had significantly more neonatally born ectopic GCs compared with control mice. Neither control nor SE mice had dispersed GCL. All mice that underwent SE had sprouted MFs in CA3. We conclude that early-life SE disrupts a normal incorporation of GCs born pre-SE but not post-SE, inducing ectopic GCs in the adult hilus. Interestingly, the results also indicate that developmentally earlier born GCs are more responsive to early-life SE in terms of the emergence of ectopic GCs.
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Differential Involvement of Cell Cycle Reactivation Between Striatal and Cortical Neurons in Cell Death Induced by 3-nitropropionic Acid
The Journal of Biological Chemistry.
Mar, 2008 |
Pubmed ID: 18182390 Recent evidence suggests that unscheduled cell cycle activity leads to neuronal cell death. 3-Nitropropionic acid (3-NP) is an irreversible inhibitor of succinate dehydrogenase and induces cell death in both striatum and cerebral cortex. Here we analyzed the involvement of aberrant cell cycle progression in 3-NP-induced cell death in these brain regions. 3-NP reduced the level of cyclin-dependent kinase inhibitor p27 in striatum but not in cerebral cortex. 3-NP also induced phosphorylation of retinoblastoma protein, a marker of cell cycle progression at late G(1) phase, only in striatum. Pharmacological experiments revealed that cyclin-dependent kinase activity and N-methyl-d-aspartate (NMDA) receptor were cooperatively involved in cell death by 3-NP in striatal neurons, whereas only NMDA receptor was involved in 3-NP-induced neurotoxicity in cortical neurons. Death of striatal neurons was preceded by elevation of somatic Ca(2+) and activation of calpain, a Ca(2+)-dependent protease. Both striatal p27 down-regulation and cell death provoked by 3-NP were dependent on calpain activity. Moreover, transfection of p27 small interfering RNA reduced striatal cell viability. In cortical neurons, however, there was no change in somatic Ca(2+) and calpain activity by 3-NP, and calpain inhibitors were not protective. These results suggest that 3-NP induces aberrant cell cycle progression and neuronal cell death via p27 down-regulation by calpain in striatum but not in the cerebral cortex. This is the first report for differential involvement of cell cycle reactivation in different brain regions and lightens the mechanism for region-selective vulnerability in human disease, including Huntington disease.
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High-temperature, but Not High-pressure, Conditions Alter Neuronal Activity
Journal of Pharmacological Sciences.
May, 2009 |
Pubmed ID: 19430196 We describe the effect of high pressure and high temperature on neuronal activity. Increased intracranial pressure is generally a pathological sign observed in intracerebral hemorrhage, brain edema, and brain tumor, yet little is known about how the hyperbaric pressure per se affects neuronal activity. Using a pressure/temperature-changeable perfusion chamber, we carried out functional multineuron calcium imaging to record spontaneous spiking activity simultaneously from about 100 neurons in hippocampal slice cultures. High-pressure conditions (up to 100 mmHg) did not alter the network excitability, whereas high-temperature conditions (up to 40 degrees C) increased synchronized network activity. Thus, neurons are sensitive to feverish conditions, but the acute hyperbaric circumstance itself is unlikely to exert a detrimental effect on neuronal function.
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Influence of Brain-derived Neurotrophic Factor on Pathfinding of Dentate Granule Cell Axons, the Hippocampal Mossy Fibers
Molecular Brain.
Jan, 2009 |
Pubmed ID: 19183490 Mossy fibers, the dentate granule cell axons, are generated throughout an animal's lifetime. Mossy fiber paths and synapses are primarily restricted to the stratum lucidum within the CA3 region. Brain-derived neurotrophic factor (BDNF), a neurotrophin family protein that activates Trk neurotrophin receptors, is highly expressed in the stratum lucidum in an activity-dependent manner. The addition of a Trk neurotrophin receptor inhibitor, K252a, to cultured hippocampal slices induced aberrant extension of mossy fibers into ectopic regions. BDNF overexpression in granule cells ameliorated the mossy fiber pathway abnormalities caused by a submaximal dose of K252a. A similar rescue was observed when BDNF was expressed in CA3 pyramidal cells, most notably in mossy fibers distal to the expression site. These findings are the first to clarify the role of BDNF in mossy fiber pathfinding, not as an attractant cue but as a regulator, possibly acting in a paracrine manner. This effect of BDNF may be as a signal for new fibers to fasciculate and extend further to form synapses with neurons that are far from active BDNF-expressing synapses. This mechanism would ensure the emergence of new independent dentate gyrus-CA3 circuits by the axons of new-born granule cells.
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Regional Difference in Stainability with Calcium-sensitive Acetoxymethyl-ester Probes in Mouse Brain Slices
The International Journal of Neuroscience.
2009 |
Pubmed ID: 19125375 Loading neurons with membrane permeable Ca2+ indicators is a core experimental procedure in functional multineuron Ca2+ imaging (fMCI), an optical technique for monitoring multiple neuronal activities. Although fMCI has been applied to several brain networks, including cerebral cortex, hippocampus, and cerebellum, no studies have systematically addressed the dye-loading efficiency in different brain regions. Here, we describe the stainability of Oregon Green 488 BAPTA-1AM in mouse acute brain slice preparations. The data are suggestive of the potential usability of fMCI in many brain regions, including olfactory bulb, thalamus, dentate gyrus, habenular nucleus, and pons.
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Circuit Topology for Synchronizing Neurons in Spontaneously Active Networks
Proceedings of the National Academy of Sciences of the United States of America.
Jun, 2010 |
Pubmed ID: 20479225 Spike synchronization underlies information processing and storage in the brain. But how can neurons synchronize in a noisy network? By exploiting a high-speed (500-2,000 fps) multineuron imaging technique and a large-scale synapse mapping method, we directly compared spontaneous activity patterns and anatomical connectivity in hippocampal CA3 networks ex vivo. As compared to unconnected pairs, synaptically coupled neurons shared more common presynaptic neurons, received more correlated excitatory synaptic inputs, and emitted synchronized spikes with approximately 10(7) times higher probability. Importantly, common presynaptic parents per se synchronized more than unshared upstream neurons. Consistent with this, dynamic-clamp stimulation revealed that common inputs alone could not account for the realistic degree of synchronization unless presynaptic spikes synchronized among common parents. On a macroscopic scale, network activity was coordinated by a power-law scaling of synchronization, which engaged varying sets of densely interwired (thus highly synchronized) neuron groups. Thus, locally coherent activity converges on specific cell assemblies, thereby yielding complex ensemble dynamics. These segmentally synchronized pulse packets may serve as information modules that flow in associatively parallel network channels.
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Scale-free Topology of the CA3 Hippocampal Network: a Novel Method to Analyze Functional Neuronal Assemblies
Biophysical Journal.
May, 2010 |
Pubmed ID: 20441736 Cognitive mapping functions of the hippocampus critically depend on the recurrent network of the CA3 pyramidal cells. However, it is still not known in detail how network activity patterns emerge, or how they encode information. By using functional multineuron calcium imaging, we simultaneously recorded the activity of >100 neurons in the CA3 region of hippocampal slice cultures. We utilized a novel computational method to analyze the multichannel spike trains and to depict functional neuronal assemblies. By means of event synchronization and the correlation matrix analysis method, we found that: 1), the average functional neuronal cluster consists of 23 neurons, and neurons could be part of multiple assemblies; 2), the clustering strength, size, and mean distance among cells in neuronal assemblies follow a power-law-like distribution; 3), the clustering strength and size of neuronal assemblies are not correlated with the total number of neurons and their physical distance; and 4), the clustering distance of neuronal assemblies is weakly correlated with the total number of neurons and their physical distance. These findings suggest that the functional organization of the spontaneously firing CA3 hippocampal network is a scale-free structure in slice culture.
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Asynchronously Enhanced Spiking Activity of Ischemic Neuronal Networks
Biological & Pharmaceutical Bulletin.
2011 |
Pubmed ID: 21532170 Cerebral ischemia causes the depletion of oxygen and nutrition from brain tissues, and when persistent, results in irreversible damage to the cell function and survival. The cellular response to ischemic conditions and its mechanisms have been investigated widely in in vivo and in vitro experimental models, yet no study has addressed the response of a whole neuronal network to energy deprivation with the single-cell resolution. Observations at the level of network are necessary, because the activity of individual neurons is nonlinearly integrated through a network and thereby gives rise to unexpectedly complex dynamics. Here we used functional multineuron calcium imaging (fMCI), an optical recording technique with high temporal and spatial resolution, to visualize the activity of neuron populations in hippocampus CA1 region under ischemia-like conditions ex vivo. We found that, although neurons responded to oxygen and glucose deprivation with an increase in the event frequency, they maintained an asynchronous network state. This is in contrast with other well known pathological states, in which the network hyperexcitability is usually accompanied by an increase in synchrony. We suggest that under ischemic conditions, at least to some time point, the neuronal network maintains the excitatory and inhibitory balance as a whole, whether actively or as a consequence of the cellular response to energy deprivation.
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Genetically Encoded Green Fluorescent Ca2+ Indicators with Improved Detectability for Neuronal Ca2+ Signals
PloS One.
2012 |
Pubmed ID: 23240011 Imaging the activities of individual neurons with genetically encoded Ca(2+) indicators (GECIs) is a promising method for understanding neuronal network functions. Here, we report GECIs with improved neuronal Ca(2+) signal detectability, termed G-CaMP6 and G-CaMP8. Compared to a series of existing G-CaMPs, G-CaMP6 showed fairly high sensitivity and rapid kinetics, both of which are suitable properties for detecting subtle and fast neuronal activities. G-CaMP8 showed a greater signal (F(max)/F(min) = 38) than G-CaMP6 and demonstrated kinetics similar to those of G-CaMP6. Both GECIs could detect individual spikes from pyramidal neurons of cultured hippocampal slices or acute cortical slices with 100% detection rates, demonstrating their superior performance to existing GECIs. Because G-CaMP6 showed a higher sensitivity and brighter baseline fluorescence than G-CaMP8 in a cellular environment, we applied G-CaMP6 for Ca(2+) imaging of dendritic spines, the putative postsynaptic sites. By expressing a G-CaMP6-actin fusion protein for the spines in hippocampal CA3 pyramidal neurons and electrically stimulating the granule cells of the dentate gyrus, which innervate CA3 pyramidal neurons, we found that sub-threshold stimulation triggered small Ca(2+) responses in a limited number of spines with a low response rate in active spines, whereas supra-threshold stimulation triggered large fluorescence responses in virtually all of the spines with a 100% activity rate.
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Subicular Activation Preceding Hippocampal Ripples in Vitro
Scientific Reports.
2013 |
Pubmed ID: 24045268 Sharp wave-ripple complexes (SW-Rs), a transient form of high-frequency field oscillations observed in the hippocampus, are thought to mediate memory consolidation. They are initiated mainly in hippocampal CA3 area and propagate to the entorhinal cortex through the subiculum; however, little is known about how SW-Rs are initiated and propagate. Here, we used functional multineuronal calcium imaging to monitor SW-R-relevant neuronal activity from the subiculum at single-cell resolution. An unexpected finding was that a subset of subicular neurons was activated immediately before hippocampal SW-Rs. The SW-R-preceding activity was not abolished by surgical lesion of the CA1-to-subiculum projection, and thus, it probably arose from entorhinal inputs. Therefore, SW-Rs are likely to be triggered by entorhinal-to-CA3/CA1 inputs. Moreover, the subiculum is not merely a passive intermediate region that SW-Rs pass through, but rather, it seems to contribute to an active modification of neural information related to SW-Rs.
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Layer III Neurons Control Synchronized Waves in the Immature Cerebral Cortex
The Journal of Neuroscience : the Official Journal of the Society for Neuroscience.
Jan, 2013 |
Pubmed ID: 23325237 Correlated spiking activity prevails in immature cortical networks and is believed to contribute to neuronal circuit maturation; however, its spatiotemporal organization is not fully understood. Using wide-field calcium imaging from acute whole-brain slices of rat pups on postnatal days 1-6, we found that correlated spikes were initiated in the anterior part of the lateral entorhinal cortex and propagated anteriorly to the frontal cortex and posteriorly to the medial entorhinal cortex, forming traveling waves that engaged almost the entire cortex. The waves were blocked by ionotropic glutamatergic receptor antagonists but not by GABAergic receptor antagonists. During wave events, glutamatergic and GABAergic synaptic inputs were balanced and induced UP state-like depolarization. Magnified monitoring with cellular resolution revealed that the layer III neurons were first activated when the waves were initiated. Consistent with this finding, layer III contained a larger number of neurons that were autonomously active, even under a blockade of synaptic transmission. During wave propagation, the layer III neurons constituted a leading front of the wave. The waves did not enter the parasubiculum; however, in some cases, they were reflected at the parasubicular border and propagated back in the opposite direction. During this reflection process, the layer III neurons in the medial entorhinal cortex maintained persistent activity. Thus, our data emphasize the role of layer III in early network behaviors and provide insight into the circuit mechanisms through which cerebral cortical networks maturate.
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Interpyramid Spike Transmission Stabilizes the Sparseness of Recurrent Network Activity
Cerebral Cortex (New York, N.Y. : 1991).
Feb, 2013 |
Pubmed ID: 22314044 Cortical synaptic strengths vary substantially from synapse to synapse and exhibit a skewed distribution with a small fraction of synapses generating extremely large depolarizations. Using multiple whole-cell recordings from rat hippocampal CA3 pyramidal cells, we found that the amplitude of unitary excitatory postsynaptic conductances approximates a lognormal distribution and that in the presence of synaptic background noise, the strongest fraction of synapses could trigger action potentials in postsynaptic neurons even with single presynaptic action potentials, a phenomenon termed interpyramid spike transmission (IpST). The IpST probability reached 80%, depending on the network state. To examine how IpST impacts network dynamics, we simulated a recurrent neural network embedded with a few potent synapses. This network, unlike many classical neural networks, exhibited distinctive behaviors resembling cortical network activity in vivo. These behaviors included the following: 1) infrequent ongoing activity, 2) firing rates of individual neurons approximating a lognormal distribution, 3) asynchronous spikes among neurons, 4) net balance between excitation and inhibition, 5) network activity patterns that was robust against external perturbation, 6) responsiveness even to a single spike of a single excitatory neuron, and 7) precise firing sequences. Thus, IpST captures a surprising number of recent experimental findings in vivo. We propose that an unequally biased distribution with a few select strong synapses helps stabilize sparse neuronal activity, thereby reducing the total spiking cost, enhancing the circuit responsiveness, and ensuring reliable information transfer.
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Operant Conditioning of Synaptic and Spiking Activity Patterns in Single Hippocampal Neurons
The Journal of Neuroscience : the Official Journal of the Society for Neuroscience.
Apr, 2014 |
Pubmed ID: 24695722 Learning is a process of plastic adaptation through which a neural circuit generates a more preferable outcome; however, at a microscopic level, little is known about how synaptic activity is patterned into a desired configuration. Here, we report that animals can generate a specific form of synaptic activity in a given neuron in the hippocampus. In awake, head-restricted mice, we applied electrical stimulation to the lateral hypothalamus, a reward-associated brain region, when whole-cell patch-clamped CA1 neurons exhibited spontaneous synaptic activity that met preset criteria. Within 15 min, the mice learned to generate frequently the excitatory synaptic input pattern that satisfied the criteria. This reinforcement learning of synaptic activity was not observed for inhibitory input patterns. When a burst unit activity pattern was conditioned in paired and nonpaired paradigms, the frequency of burst-spiking events increased and decreased, respectively. The burst reinforcement occurred in the conditioned neuron but not in other adjacent neurons; however, ripple field oscillations were concomitantly reinforced. Neural conditioning depended on activation of NMDA receptors and dopamine D1 receptors. Acutely stressed mice and depression model mice that were subjected to forced swimming failed to exhibit the neural conditioning. This learning deficit was rescued by repetitive treatment with fluoxetine, an antidepressant. Therefore, internally motivated animals are capable of routing an ongoing action potential series into a specific neural pathway of the hippocampal network.
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Subtle Modulation of Ongoing Calcium Dynamics in Astrocytic Microdomains by Sensory Inputs
Physiological Reports.
Oct, 2015 |
Pubmed ID: 26438730 Astrocytes communicate with neurons through their processes. In vitro experiments have demonstrated that astrocytic processes exhibit calcium activity both spontaneously and in response to external stimuli; however, it has not been fully determined whether and how astrocytic subcellular domains respond to sensory input in vivo. We visualized the calcium signals in astrocytes in the primary visual cortex of awake, head-fixed mice. Bias-free analyses of two-photon imaging data revealed that calcium activity prevailed in astrocytic subcellular domains, was coordinated with variable spot-like patterns, and was dominantly spontaneous. Indeed, visual stimuli did not affect the frequency of calcium domain activity, but it increased the domain size, whereas tetrodotoxin reduced the sizes of spontaneous calcium domains and abolished their visual responses. The "evoked" domain activity exhibited no apparent orientation tuning and was distributed unevenly within the cell, constituting multiple active hotspots that were often also recruited in spontaneous activity. The hotspots existed dominantly in the somata and endfeet of astrocytes. Thus, the patterns of astrocytic calcium dynamics are intrinsically constrained and are subject to minor but significant modulation by sensory input.
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Neocortical Rebound Depolarization Enhances Visual Perception
PLoS Biology.
Aug, 2015 |
Pubmed ID: 26274866 Animals are constantly exposed to the time-varying visual world. Because visual perception is modulated by immediately prior visual experience, visual cortical neurons may register recent visual history into a specific form of offline activity and link it to later visual input. To examine how preceding visual inputs interact with upcoming information at the single neuron level, we designed a simple stimulation protocol in which a brief, orientated flashing stimulus was subsequently coupled to visual stimuli with identical or different features. Using in vivo whole-cell patch-clamp recording and functional two-photon calcium imaging from the primary visual cortex (V1) of awake mice, we discovered that a flash of sinusoidal grating per se induces an early, transient activation as well as a long-delayed reactivation in V1 neurons. This late response, which started hundreds of milliseconds after the flash and persisted for approximately 2 s, was also observed in human V1 electroencephalogram. When another drifting grating stimulus arrived during the late response, the V1 neurons exhibited a sublinear, but apparently increased response, especially to the same grating orientation. In behavioral tests of mice and humans, the flashing stimulation enhanced the detection power of the identically orientated visual stimulation only when the second stimulation was presented during the time window of the late response. Therefore, V1 late responses likely provide a neural basis for admixing temporally separated stimuli and extracting identical features in time-varying visual environments.
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Heterogeneous Effects of Antiepileptic Drugs in an in Vitro Epilepsy Model--a Functional Multineuron Calcium Imaging Study
The European Journal of Neuroscience.
Jul, 2015 |
Pubmed ID: 25967117 Epilepsy is a chronic brain disease characterised by recurrent seizures. Many studies of this disease have focused on local neuronal activity, such as local field potentials in the brain. In addition, several recent studies have elucidated the collective behavior of individual neurons in a neuronal network that emits epileptic activity. However, little is known about the effects of antiepileptic drugs on neuronal networks during seizure-like events (SLEs) at single-cell resolution. Using functional multineuron Ca(2+) imaging (fMCI), we monitored the activities of multiple neurons in the rat hippocampal CA1 region on treatment with the proconvulsant bicuculline under Mg(2+) -free conditions. Bicuculline induced recurrent synchronous Ca(2+) influx, and the events were correlated with SLEs. Other proconvulsants, such as 4-aminopyridine, pentetrazol, and pilocarpine, also induced synchronous Ca(2+) influx. We found that the antiepileptic drugs phenytoin, flupirtine, and ethosuximide, which have different mechanisms of action, exerted heterogeneous effects on bicuculline-induced synchronous Ca(2+) influx. Phenytoin and flupirtine significantly decreased the peak, the amount of Ca(2+) influx and the duration of synchronous events in parallel with the duration of SLEs, whereas they did not abolish the synchronous events themselves. Ethosuximide increased the duration of synchronous Ca(2+) influx and SLEs. Furthermore, the magnitude of the inhibitory effect of phenytoin on the peak synchronous Ca(2+) influx level differed according to the peak amplitude of the synchronous event in each individual cell. Evaluation of the collective behavior of individual neurons by fMCI seems to be a powerful tool for elucidating the profiles of antiepileptic drugs.
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Frontal Association Cortex is Engaged in Stimulus Integration During Associative Learning
Current Biology : CB.
Jan, 2015 |
Pubmed ID: 25496961 The frontal association cortex (FrA) is implicated in higher brain function. Aberrant FrA activity is likely to be involved in dementia pathology. However, the functional circuits both within the FrA and with other regions are unclear. A recent study showed that inactivation of the FrA impairs memory consolidation of an auditory fear conditioning in young mice. In addition, dendritic spine remodeling of FrA neurons is sensitive to paired sensory stimuli that produce associative memory. These findings suggest that the FrA is engaged in neural processes critical to associative learning. Here we characterize stimulus integration in the mouse FrA during associative learning. We experimentally separated contextual fear conditioning into context exposure and shock, and found that memory formation requires protein synthesis associated with both context exposure and shock in the FrA. Both context exposure and shock trigger Arc, an activity-dependent immediate-early gene, expression in the FrA, and a subset of FrA neurons was dually activated by both stimuli. In addition, we found that the FrA receives projections from the perirhinal (PRh) and insular (IC) cortices and basolateral amygdala (BLA), which are implicated in context and shock encoding. PRh and IC neurons projecting to the FrA were activated by context exposure and shock, respectively. Arc expression in the FrA associated with context exposure and shock depended on PRh activity and both IC and BLA activities, respectively. These findings indicate that the FrA is engaged in stimulus integration and contributes to memory formation in associative learning.
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Microglia and Neurogenesis in the Epileptic Dentate Gyrus
Neurogenesis (Austin, Tex.).
2016 |
Pubmed ID: 27928548 Microglia are recognized as major immune cells in the brain. They have been traditionally studied in various contexts of disease, where their activation has been assumed to induce mostly detrimental effects. Recent studies, however, have challenged the current view of microglia, clarifying their essential contribution to the development of neural circuits and brain function. In this review, we particularly discuss the role of microglia as the major orchestrators that regulate adult neurogenesis in the hippocampus. We also review the roles of microglia in seizure-induced adult neurogenesis in the epileptic dentate gyrus. Specifically, we introduce our recent study, in which we identified a novel mechanism by which viable newborn cells in the adult dentate gyrus are phagocytosed and eliminated by microglia after status epilepticus, maintaining homeostasis of the dentate circuitry. This review aims to reconsider the microglial function in adult neurogenesis, especially when they are activated during epileptogenesis, challenging the dogma that microglia are harmful neurotoxic cells.
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Functional Organization of Flash-Induced V1 Offline Reactivation
The Journal of Neuroscience : the Official Journal of the Society for Neuroscience.
Nov, 2016 |
Pubmed ID: 27852780 The primary visual cortex exhibits a late, long response with a latency of >300 ms and an immediate early response that occurs ∼100 ms after a visual stimulus. The late response is thought to contribute to visual functions such as sensory perception, iconic memory, working memory, and forming connections between temporally separated stimuli. However, how the visual late response is generated and organized is not completely understood. In the mouse primary visual cortex in vivo, we isolated long-delayed responses by using a brief light-flash stimulus for which the stimulus late response occurred long after the stimulus offset and was not contaminated by the instantaneous response evoked by the stimulus. Using whole-cell patch-clamp recordings, we demonstrated that the late rebound response was shaped by a net-balanced increase in excitatory and inhibitory synaptic conductances, whereas transient imbalances were caused by intermittent inhibitory barrage. In contrast to the common assumption that the neocortical late response reflects a feedback signal from the downstream higher-order cortical areas, our pharmacological and optogenetic analyses demonstrated that the late responses likely have a thalamic origin. Therefore, the late component of a sensory-evoked cortical response should be interpreted with caution.
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3-Hz Subthreshold Oscillations of CA2 Neurons In Vivo
Hippocampus.
Dec, 2016 |
Pubmed ID: 27650674 The CA2 region is unique in the hippocampus; it receives direct synaptic innervations from several hypothalamic nuclei and expresses various receptors of neuromodulators, including adenosine, vasopressin, and oxytocin. Furthermore, the CA2 region may have distinct brain functions, such as the control of instinctive and social behaviors; however, little is known about the dynamics of the subthreshold membrane potentials of CA2 neurons in vivo. We conducted whole-cell current-clamp recordings from CA2 pyramidal cells in urethane-anesthetized mice and monitored the intrinsic fluctuations in their membrane potentials. The CA2 pyramidal cells emitted spontaneous action potentials at mean firing rates of ∼0.8 Hz. In approximately half of the neurons, the subthreshold membrane potential oscillated at ∼3 Hz. In two neurons, we obtained simultaneous recordings of local field potentials from the CA1 stratum radiatum and demonstrated that the 3-Hz oscillations of CA2 neurons were not correlated with CA1 field potentials. In tetrodotoxin-perfused acute hippocampal slices, the membrane potentials of CA2 pyramidal cells were not preferentially entrained to 3-Hz sinusoidal current inputs, which suggest that intracellular 3-Hz oscillations reflect the neuronal dynamics of the surrounding networks. © 2016 Wiley Periodicals, Inc.
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Selective Attenuation of Electrophysiological Activity of the Dentate Gyrus in a Social Defeat Mouse Model
The Journal of Physiological Sciences : JPS.
Aug, 2016 |
Pubmed ID: 27573168 Current research on stress pathology has revealed a set of molecular and cellular mechanisms through which psychosocial stress impairs brain function. However, there are few studies that have examined how chronic stress exposure alters neuronal activity patterns at a network level. Here, we recorded ensemble neuronal activity patterns of the cortico-hippocampal network from urethane-anesthetized mice that were subjected to repeated social defeat stress. In socially defeated mice, the magnitudes of local field potential signals, including theta, slow gamma, and fast gamma oscillations, were significantly reduced in the dentate gyrus, whereas they remained unchanged in the hippocampus and somatosensory cortex. In accordance with the vast majority of histological and biochemical studies, our evidence from electrophysiological investigations highlights the dentate gyrus as a key brain area that is primarily susceptible to stress-induced dysfunction.
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Nitric Oxide-induced Activation of the Type 1 Ryanodine Receptor Is Critical for Epileptic Seizure-induced Neuronal Cell Death
EBioMedicine.
Aug, 2016 |
Pubmed ID: 27544065 Status epilepticus (SE) is a life-threatening emergency that can cause neurodegeneration with debilitating neurological disorders. However, the mechanism by which convulsive SE results in neurodegeneration is not fully understood. It has been shown that epileptic seizures produce markedly increased levels of nitric oxide (NO) in the brain, and that NO induces Ca(2+) release from the endoplasmic reticulum via the type 1 ryanodine receptor (RyR1), which occurs through S-nitrosylation of the intracellular Ca(2+) release channel. Here, we show that through genetic silencing of NO-induced activation of the RyR1 intracellular Ca(2+) release channel, neurons were rescued from seizure-dependent cell death. Furthermore, dantrolene, an inhibitor of RyR1, was protective against neurodegeneration caused by SE. These results demonstrate that NO-induced Ca(2+) release via RyR is involved in SE-induced neurodegeneration, and provide a rationale for the use of RyR1 inhibitors for the prevention of brain damage following SE.
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Development of Practical Red Fluorescent Probe for Cytoplasmic Calcium Ions with Greatly Improved Cell-membrane Permeability
Cell Calcium.
Oct, 2016 |
Pubmed ID: 27349490 Fluorescence imaging of calcium ions (Ca(2+)) has become an essential technique for investigation of signaling pathways involving Ca(2+) as a second messenger. But, Ca(2+) signaling is involved in many biological phenomena, and therefore simultaneous visualization of Ca(2+) and other biomolecules (multicolor imaging) would be particularly informative. For this purpose, we set out to develop a fluorescent probe for Ca(2+) that would operate in a different color region (red) from that of probes for other molecules, many of which show green fluorescence, as exemplified by green fluorescent protein (GFP). We previously developed a red fluorescent probe for monitoring cytoplasmic Ca(2+) concentration, based on our established red fluorophore, TokyoMagenta (TM), but there remained room for improvement, especially as regards efficiency of introduction into cells. We considered that this issue was probably mainly due to limited water solubility of the probe. So, we designed and synthesized a red-fluorescent probe with improved water solubility. We confirmed that this Ca(2+) red-fluorescent probe showed high cell-membrane permeability with bright fluorescence. It was successfully applied to fluorescence imaging of not only live cells, but also brain slices, and should be practically useful for multicolor imaging studies of biological mechanisms.
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Microglia Engulf Viable Newborn Cells in the Epileptic Dentate Gyrus
Glia.
Sep, 2016 |
Pubmed ID: 27301702 Microglia, which are the brain's resident immune cells, engulf dead neural progenitor cells during adult neurogenesis in the subgranular zone (SGZ) of the dentate gyrus (DG). The number of newborn cells in the SGZ increases significantly after status epilepticus (SE), but whether and how microglia regulate the number of newborn cells after SE remain unclear. Here, we show that microglia rapidly eliminate newborn cells after SE by primary phagocytosis, a process by which viable cells are engulfed, thereby regulating the number of newborn cells that are incorporated into the DG. The number of newborn cells in the DG was increased at 5 days after SE in the adult mouse brain but rapidly decreased to the control levels within a week. During this period, microglia in the DG were highly active and engulfed newborn cells. We found that the majority of engulfed newborn cells were caspase-negative viable cells. Finally, inactivation of microglia with minocycline maintained the increase in the number of newborn cells after SE. Furthermore, minocycline treatment after SE induced the emergence of hilar ectopic granule cells. Thus, our findings suggest that microglia may contribute to homeostasis of the dentate neurogenic niche by eliminating excess newborn cells after SE via primary phagocytosis. GLIA 2016;64:1508-1517.
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Structural Insight into Photoactivation of an Adenylate Cyclase from a Photosynthetic Cyanobacterium
Proceedings of the National Academy of Sciences of the United States of America.
06, 2016 |
Pubmed ID: 27247413 Cyclic-AMP is one of the most important second messengers, regulating many crucial cellular events in both prokaryotes and eukaryotes, and precise spatial and temporal control of cAMP levels by light shows great promise as a simple means of manipulating and studying numerous cell pathways and processes. The photoactivated adenylate cyclase (PAC) from the photosynthetic cyanobacterium Oscillatoria acuminata (OaPAC) is a small homodimer eminently suitable for this task, requiring only a simple flavin chromophore within a blue light using flavin (BLUF) domain. These domains, one of the most studied types of biological photoreceptor, respond to blue light and either regulate the activity of an attached enzyme domain or change its affinity for a repressor protein. BLUF domains were discovered through studies of photo-induced movements of Euglena gracilis, a unicellular flagellate, and gene expression in the purple bacterium Rhodobacter sphaeroides, but the precise details of light activation remain unknown. Here, we describe crystal structures and the light regulation mechanism of the previously undescribed OaPAC, showing a central coiled coil transmits changes from the light-sensing domains to the active sites with minimal structural rearrangement. Site-directed mutants show residues essential for signal transduction over 45 Å across the protein. The use of the protein in living human cells is demonstrated with cAMP-dependent luciferase, showing a rapid and stable response to light over many hours and activation cycles. The structures determined in this study will assist future efforts to create artificial light-regulated control modules as part of a general optogenetic toolkit.
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Homeostatic Changes in Neuronal Network Oscillations in Response to Continuous Hypoperfusion in the Mouse Forebrain
Neuroscience Research.
Aug, 2016 |
Pubmed ID: 26945618 Neuronal activity is highly sensitive to changes in oxygen tension. In this study, we examined the impact of hypoxic/ischemic conditions on neuronal ensemble activity patterns in the mouse brain using in vivo extracellular electrophysiological recordings from up to 8 sites in the thalamus, dorsal hippocampus, and neocortex, while cerebral hypoperfusion was induced by unilateral carotid artery occlusion. After a few minutes, the occlusion triggered a rapid change in the power of the local field oscillations. In the hippocampus, but not in the neocortex, the absolute power changes at all frequency ranges (relative to the baseline) became less pronounced with time, and no significant changes were observed 30min after the occlusion-induced hypoperfusion. We also tested whether continuous hypoperfusion induced by the occlusion for up to 1 week alters neuronal activity. In the hippocampus and the thalamus, the chronic occlusion did not lead to a reduction in the power of the local field oscillations. These results indicate that certain neuronal populations have the ability to maintain internal neurophysiological homeostasis against continuous hypoperfusion.
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Late Arc/Arg3.1 Expression in the Basolateral Amygdala is Essential for Persistence of Newly-acquired and Reactivated Contextual Fear Memories
Scientific Reports.
Feb, 2016 |
Pubmed ID: 26880136 A feature of fear memory is its persistence, which could be a factor for affective disorders. Memory retrieval destabilizes consolidated memories, and then rapid molecular cascades contribute to early stabilization of reactivated memories. However, persistence of reactivated memories has been poorly understood. Here, we discover that late Arc (also known as Arg3.1) expression in the mouse basolateral amygdala (BLA) is involved in persistence of newly-acquired and reactivated fear memories. After both fear learning and retrieval, Arc levels increased at 2 h, returned to basal levels at 6 h but increased again at 12 h. Inhibiting late Arc expression impaired memory retention 7 d, but not 2 d, after fear learning and retrieval. Moreover, blockade of NR2B-containing N-methyl-D-aspartate receptors (NMDARs) prevented memory destabilization and inhibited late Arc expression. These findings indicate that NR2B-NMDAR and late Arc expression plays a critical role in the destabilization and persistence of reactivated memories.
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Photoactivated Adenylyl Cyclase (PAC) Reveals Novel Mechanisms Underlying CAMP-dependent Axonal Morphogenesis
Scientific Reports.
Jan, 2016 |
Pubmed ID: 26795422 Spatiotemporal regulation of axonal branching and elongation is essential in the development of refined neural circuits. cAMP is a key regulator of axonal growth; however, whether and how intracellular cAMP regulates axonal branching and elongation remain unclear, mainly because tools to spatiotemporally manipulate intracellular cAMP levels have been lacking. To overcome this issue, we utilized photoactivated adenylyl cyclase (PAC), which produces cAMP in response to blue-light exposure. In primary cultures of dentate granule cells transfected with PAC, short-term elevation of intracellular cAMP levels induced axonal branching but not elongation, whereas long-term cAMP elevation induced both axonal branching and elongation. The temporal dynamics of intracellular cAMP levels regulated axonal branching and elongation through the activation of protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac), respectively. Thus, using PAC, our study for the first time reveals that temporal cAMP dynamics could regulate axonal branching and elongation via different signaling pathways.
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Machine Learning-based Prediction of Adverse Drug Effects: An Example of Seizure-inducing Compounds
Journal of Pharmacological Sciences.
Feb, 2017 |
Pubmed ID: 28215473 Various biological factors have been implicated in convulsive seizures, involving side effects of drugs. For the preclinical safety assessment of drug development, it is difficult to predict seizure-inducing side effects. Here, we introduced a machine learning-based in vitro system designed to detect seizure-inducing side effects. We recorded local field potentials from the CA1 alveus in acute mouse neocortico-hippocampal slices, while 14 drugs were bath-perfused at 5 different concentrations each. For each experimental condition, we collected seizure-like neuronal activity and merged their waveforms as one graphic image, which was further converted into a feature vector using Caffe, an open framework for deep learning. In the space of the first two principal components, the support vector machine completely separated the vectors (i.e., doses of individual drugs) that induced seizure-like events and identified diphenhydramine, enoxacin, strychnine and theophylline as "seizure-inducing" drugs, which indeed were reported to induce seizures in clinical situations. Thus, this artificial intelligence-based classification may provide a new platform to detect the seizure-inducing side effects of preclinical drugs.
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CAMP-Dependent Calcium Oscillations of Astrocytes: An Implication for Pathology
Cerebral Cortex (New York, N.Y. : 1991).
Feb, 2017 |
Pubmed ID: 26803165 Astrocytes in various brain regions exhibit spontaneous intracellular calcium elevations both in vitro and in vivo; however, neither the temporal pattern underlying this activity nor its function has been fully evaluated. Here, we utilized a long-term optical imaging technique to analyze the calcium activity of more than 4000 astrocytes in acute hippocampal slices as well as in the neocortex and hippocampus of head-restrained mice. Although astrocytic calcium activity was largely sparse and irregular, we observed a subset of cells in which the fluctuating calcium oscillations repeated at a regular interval of ∼30 s. These intermittent oscillations i) depended on type 2 inositol 1,4,5-trisphosphate receptors; ii) consisted of a complex reverberatory interaction between the soma and processes of individual astrocytes; iii) did not synchronize with those of other astrocytes; iv) did not require neuronal firing; v) were modulated through cAMP-protein kinase A signaling; vi) were facilitated under pathological conditions, such as energy deprivation and epileptiform hyperexcitation; and vii) were associated with enhanced hypertrophy in astrocytic processes, an early hallmark of reactive gliosis, which is observed in ischemia and epilepsy. Therefore, calcium oscillations appear to be associated with a pathological state in astrocytes.
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