Enhancement of Presynaptic Performance in Transgenic Drosophila Overexpressing Heat Shock Protein Hsp70

Synapse (New York, N.Y.). Apr, 2002  |  Pubmed ID: 11842441

Prior heat shock confers protection to Drosophila synapses during subsequent heat stress by stabilizing quantal size and reducing the decline of quantal emission at individual synaptic boutons. The major heat shock protein Hsp70, which is strongly induced by high temperatures in Drosophila, may be responsible for this synaptic protection. To test this hypothesis, we investigated synaptic protection and stabilization at larval neuromuscular junctions of transgenic Drosophila which produce more than the normal amount of Hsp70 in response to heat shock. Overexpression of Hsp70 coincides with enhanced protection of presynaptic performance, assayed by measuring mean quantal content and percentage success of transmission. Quantal size was not selectively altered, indicating no effects of overexpression on postsynaptic performance. Thus, presynaptic mechanisms can be protected by manipulating levels of Hsp70, which would provide stability to neural circuits otherwise susceptible to heat stress.

Diversification of Synaptic Strength: Presynaptic Elements

Nature Reviews. Neuroscience. Jul, 2002  |  Pubmed ID: 12094207

Synapses are not static; their performance is modified adaptively in response to activity. Presynaptic mechanisms that affect the probability of transmitter release or the amount of transmitter that is released are important in synaptic diversification. Here, we address the diversity of presynaptic performance and its underlying mechanisms: how much of the variation can be accounted for by variation in synaptic morphology and how much by molecular differences? Significant progress has been made in defining presynaptic structural contributions to synaptic strength; by contrast, we know little about how presynaptic proteins produce normally observed functional differentiation, despite abundant information on presynaptic proteins and on the effects of their individual manipulation. Closing the gap between molecular and physiological synaptic diversification still represents a considerable challenge.

Intracellular Ionic Concentration by Calibration from Fluorescence Indicator Emission Spectra, Its Relationship to the K(d), F(min), F(max) Formula, and Use with Na-Green for Presynaptic Sodium

Journal of Neuroscience Methods. Aug, 2002  |  Pubmed ID: 12204307

The emission spectra calibration curves for a fluorescence indicator and the F(min), F(max), and K(d) formula were shown to be related. Using the known calibrated fluorescence emitted by Sodium Green (Na-Green) and photo-multiplier-tube quantum efficiency, we calculated the detection signal over a range of sodium concentrations. The calculated calibration curves were compared for optical filters passing a narrow band, medium band or full spectrum. We found that a method based on the full emission spectrum was the most appropriate. Given a known resting concentration of intracellular sodium, calibrated readings can be converted to concentration values. This method is applicable to any fluorescence indicator when curves for emission spectra over a range of concentrations are available. We measured sodium concentration changes during trains of action potentials (APs) at a crayfish motor axon's presynaptic terminals injected with Na-Green. During low frequency AP trains, net sodium increases asymptotically with frequency. Average net Na-flux per AP decreases for increasing terminal size. The terminals of crayfish motor axon have surface area to volume ratio which is 7700 times larger than for squid. Thus, in comparison to squid, crayfish terminals exhibit a larger change in [Na(+)](i) during equivalent AP activity.

Presynaptic Regulation of Neurotransmission in Drosophila by the G Protein-coupled Receptor Methuselah

Neuron. Sep, 2002  |  Pubmed ID: 12367510

Regulation of synaptic strength is essential for neuronal information processing, but the molecular mechanisms that control changes in neuroexocytosis are only partially known. Here we show that the putative G protein-coupled receptor Methuselah (Mth) is required in the presynaptic motor neuron to acutely upregulate neurotransmitter exocytosis at larval Drosophila NMJs. Mutations in the mth gene reduce evoked neurotransmitter release by approximately 50%, and decrease synaptic area and the density of docked and clustered vesicles. Pre- but not postsynaptic expression of normal Mth restored normal release in mth mutants. Conditional expression of Mth restored normal release and normal vesicle docking and clustering but not the reduced size of synaptic sites, suggesting that Mth acutely adjusts vesicle trafficking to synaptic sites.

Inverse Relationship Between Release Probability and Readily Releasable Vesicles in Depressing and Facilitating Synapses

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. Nov, 2002  |  Pubmed ID: 12427821

We tested the hypothesis that the probability of vesicular exocytosis at synapses is positively correlated with the pools of readily releasable synaptic vesicles, as shown for mammalian neurons grown in tissue culture. We compared synapses of two identified glutamatergic neurons: phasic (high-output, depressing) and tonic (low-output, facilitating) crustacean motor neurons, which differ 100- to 1000-fold in quantal content. Estimates of vesicles available for exocytosis were made from depletion during forced release and from electron microscopic observation of vesicles docked at synaptic membranes near active zones. Both measurements showed a significantly larger pool of readily releasable vesicles in facilitating synapses, despite their much lower quantal output during stimulation. Thus, the probability for release of docked vesicles is very much lower at facilitating synapses, and the presence of more docked vesicles does not predict higher synaptic release probability in these paired excitatory neurons.

Quantal Size and Variation Determined by Vesicle Size in Normal and Mutant Drosophila Glutamatergic Synapses

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. Dec, 2002  |  Pubmed ID: 12451127

Quantal size and variation at chemical synapses could be determined presynaptically by the amount of neurotransmitter released from synaptic vesicles or postsynaptically by the number of receptors available for activation. We investigated these possibilities at Drosophila glutamatergic neuromuscular synapses formed by two separate motor neurons innervating the same muscle cell. At wild-type synapses of the two neurons we found a difference in quantal size corresponding to a difference in mean synaptic vesicle volume. The same finding applied to two mutants (dlg and lap) in which synaptic vesicle size was altered. Quantal variances at wild-type and mutant synapses were similar and could be accounted for by variation in vesicular volume. The linear relationship between quantal size and vesicular volume for several different genotypes indicates that glutamate is regulated homeostatically to the same intravesicular concentration in all cases. Thus functional differences in synaptic strength among glutamatergic neurons of Drosophila result in part from intrinsic differences in vesicle size.

Synaptic Vesicles: Test for a Role in Presynaptic Calcium Regulation

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. Mar, 2004  |  Pubmed ID: 15014125

Membrane-bound organelles such as mitochondria and the endoplasmic reticulum play an important role in neuronal Ca(2+) homeostasis. Synaptic vesicles (SVs), the organelles responsible for exocytosis of neurotransmitters, occupy more of the volume of presynaptic nerve terminals than any other organelle and, under some conditions, can accumulate Ca(2+). They are also closely associated with voltage-gated Ca(2+) channels (VGCCs) that trigger transmitter release by admitting Ca(2+) into the nerve terminal in response to action potentials (APs). We tested the hypothesis that SVs can modulate Ca(2+) signals in the presynaptic terminal. This has been a difficult question to address because neither pharmacological nor genetic approaches to block Ca(2+) permeation of the SV membrane have been available. To investigate the possible role of SVs in Ca(2+) regulation, we used imaging techniques to compare Ca(2+) dynamics in motor nerve terminals before and after depletion of SVs. We used the temperature-sensitive Drosophila dynamin mutant shibire, in which SVs can be eliminated by stimulation. There was no difference in the amplitude or time course of Ca(2+) responses during high-frequency trains of APs, or single APs, in individual presynaptic boutons before and after depletion of SVs. SVs have a limited role, if any, in the rapid sequestration of Ca(2+) within the neuronal cytosol or the synaptic microdomain. We also conclude that SVs are not important for regulation of synaptic VGCCs.

Crustacean Phasic and Tonic Motor Neurons

Integrative and Comparative Biology. Feb, 2004  |  Pubmed ID: 21680480

Crustacean motor neurons subserving locomotion are specialized for the type of activity in which they normally participate. Neurons responsible for maintained activity ('tonic' neurons) support moderate to high frequencies of nerve impulses intermittently or continuously during locomotion, while those recruited for short-lasting rapid responses ('phasic' neurons) generally fire a few impulses in a rapid burst during rapid locomotion and are otherwise silent. The synaptic responses of the two types, recorded at their respective neuromuscular junctions, differ enormously: phasic neurons exhibit much higher quantal release per synapse and per muscle fibre, along with more rapid synaptic depression and less short-term facilitation. We have analyzed the factors that are responsible for the large difference in initial release of neurotransmitter. Several possibilities, including synapse and active zone size differences, entry of calcium at active zones, and immediately releasable vesicle pools, could not account for the large phasic-tonic difference in initial transmitter output. The most likely feature that differentiates synaptic release is the sensitivity of the exocytotic machinery to intracellular calcium. Molecular features of the phasic and tonic presynaptic nerve terminals are currently under investigation.

The Multiple Functions of Cysteine-string Protein Analyzed at Drosophila Nerve Terminals

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. Mar, 2005  |  Pubmed ID: 15745946

The synaptic vesicle-associated cysteine-string protein (CSP) is important for synaptic transmission. Previous studies revealed multiple defects at neuromuscular junctions (NMJs) of csp null-mutant Drosophila, but whether these defects are independent of each other or mechanistically linked through J domain mediated-interactions with heat-shock cognate protein 70 (Hsc70) has not been established. To resolve this issue, we genetically dissected the individual functions of CSP by an in vivo structure/function analysis. Expression of mutant CSP lacking the J domain at csp null-mutant NMJs fully restored normal thermo-tolerance of evoked transmitter release but did not completely restore evoked release at room temperature and failed to reverse the abnormal intraterminal Ca2+ levels. This suggests that J domain-mediated functions are essential for the regulation of intraterminal Ca2+ levels but only partially required for regulating evoked release and not required for protecting evoked release against thermal stress. Hence, CSP can also act as an Hsc70-independent chaperone protecting evoked release from thermal stress. Expression of mutant CSP lacking the L domain restored neurotransmission and partially reversed the abnormal intraterminal Ca2+ levels, suggesting that the L domain is important, although not essential, for the role of CSP in regulating intraterminal Ca2+ levels. We detected no effects of csp mutations on individual presynaptic Ca2+ signals triggered by action potentials, suggesting that presynaptic Ca2+ entry is not primarily impaired. Both the J and L domains were also required for the role of CSP in synaptic growth. Together, these results suggest that CSP has several independent synaptic functions, affecting synaptic growth, evoked release, thermal protection of evoked release, and intraterminal Ca2+ levels at rest and during stimulation.

Calcium Sensitivity of Neurotransmitter Release Differs at Phasic and Tonic Synapses

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. Mar, 2005  |  Pubmed ID: 15788768

The efficacy of synaptic transmission varies greatly among synaptic contacts. We have explored the origins of differences between phasic and tonic crustacean neuromuscular junctions. Synaptic boutons of a phasic motor neuron release three orders of magnitude more quanta to a single action potential and show strong depression to a train, whereas tonic synapses are nearly unresponsive to single action potentials and display an immense facilitation. Phasic and tonic synapses display a similar nonlinear dependence on extracellular [Ca2+]. We imposed similar spatially uniform intracellular [Ca2+] ([Ca2+]i) steps in phasic and tonic synapses by photolysis of presynaptic caged calcium. [Ca2+]i was measured fluorometrically while transmitter release was monitored electrophysiologically from single boutons in which the [Ca2+]i was elevated. Phasic synapses released the readily releasable pool (RRP) of vesicles at a much higher rate and with a shorter delay than did tonic synapses. Comparison of several kinetic models of molecular events showed that a difference in Ca2+-sensitive priming of vesicles in the RRP combined with a revision of the kinetic Ca2+-binding sequence to the secretory trigger produced the best fit to the markedly different responses to Ca2+ steps and action potentials and of the characteristic features of synaptic plasticity in phasic and tonic synapses. The results reveal processes underlying one aspect of synaptic diversity that may also regulate changes in synaptic strength during development and learning and memory formation.

AP180 Maintains the Distribution of Synaptic and Vesicle Proteins in the Nerve Terminal and Indirectly Regulates the Efficacy of Ca2+-triggered Exocytosis

Journal of Neurophysiology. Sep, 2005  |  Pubmed ID: 15888532

AP180 plays an important role in clathrin-mediated endocytosis of synaptic vesicles (SVs) and has also been implicated in retrieving SV proteins. In Drosophila, deletion of its homologue, Like-AP180 (LAP), has been shown to increase the size of SVs but decrease the number of SVs and transmitter release. However, it remains elusive whether a reduction in the total vesicle pool directly affects transmitter release. Further, it is unknown whether the lap mutation also affects vesicle protein retrieval and synaptic protein localization and, if so, how it might affect exocytosis. Using a combination of electrophysiology, optical imaging, electron microscopy, and immunocytochemistry, we have further characterized the lap mutant and hereby show that LAP plays additional roles in maintaining both normal synaptic transmission and protein distribution at synapses. While increasing the rate of spontaneous vesicle fusion, the lap mutation dramatically reduces impulse-evoked transmitter release at steps downstream of calcium entry and vesicle docking. Notably, lap mutations disrupt calcium coupling to exocytosis and reduce calcium cooperativity. These results suggest a primary defect in calcium sensors on the vesicles or on the release machinery. Consistent with this hypothesis, three vesicle proteins critical for calcium-mediated exocytosis, synaptotagmin I, cysteine-string protein, and neuronal synaptobrevin, are all mislocalized to the extrasynaptic axonal regions along with Dap160, an active zone marker (nc82), and glutamate receptors in the mutant. These results suggest that AP180 is required for either recycling vesicle proteins and/or maintaining the distribution of both vesicle and synaptic proteins in the nerve terminal.

The GTPase DMiro is Required for Axonal Transport of Mitochondria to Drosophila Synapses

Neuron. Aug, 2005  |  Pubmed ID: 16055062

We have identified EMS-induced mutations in Drosophila Miro (dMiro), an atypical mitochondrial GTPase that is orthologous to human Miro (hMiro). Mutant dmiro animals exhibit defects in locomotion and die prematurely. Mitochondria in dmiro mutant muscles and neurons are abnormally distributed. Instead of being transported into axons and dendrites, mitochondria accumulate in parallel rows in neuronal somata. Mutant neuromuscular junctions (NMJs) lack presynaptic mitochondria, but neurotransmitter release and acute Ca2+ buffering is only impaired during prolonged stimulation. Neuronal, but not muscular, expression of dMiro in dmiro mutants restored viability, transport of mitochondria to NMJs, the structure of synaptic boutons, the organization of presynaptic microtubules, and the size of postsynaptic muscles. In addition, gain of dMiro function causes an abnormal accumulation of mitochondria in distal synaptic boutons of NMJs. Together, our findings suggest that dMiro is required for controlling anterograde transport of mitochondria and their proper distribution within nerve terminals.

Thermoprotection of Synaptic Transmission in a Drosophila Heat Shock Factor Mutant is Accompanied by Increased Expression of Hsp83 and DnaJ-1

Physiological Genomics. May, 2006  |  Pubmed ID: 16595740

In Drosophila larvae, acquired synaptic thermotolerance after heat shock has previously been shown to correlate with the induction of heat shock proteins (Hsps) including HSP70. We tested the hypothesis that synaptic thermotolerance would be significantly diminished in a temperature-sensitive strain (Drosophila heat shock factor mutant hsf4), which has been reported not to be able to produce inducible Hsps in response to heat shock. Contrary to our hypothesis, considerable thermoprotection was still observed at hsf4 larval synapses after heat shock. To investigate the cause of this thermoprotection, we conducted DNA microarray experiments to identify heat-induced transcript changes in these organisms. Transcripts of the hsp83, dnaJ-1 (hsp40), and glutathione-S-transferase gstE1 genes were significantly upregulated in hsf4 larvae after heat shock. In addition, increases in the levels of Hsp83 and DnaJ-1 proteins but not in the inducible form of Hsp70 were detected by Western blot analysis. The mode of heat shock administration differentially affected the relative transcript and translational changes for these chaperones. These results indicate that the compensatory upregulation of constitutively expressed Hsps, in the absence of the synthesis of the major inducible Hsp, Hsp70, could still provide substantial thermoprotection to both synapses and the whole organism.

Neuroscience. Gatekeeper at the Synapse

Science (New York, N.Y.). May, 2006  |  Pubmed ID: 16709774

Modular Neuropile Organization in the Drosophila Larval Brain Facilitates Identification and Mapping of Central Neurons

The Journal of Comparative Neurology. Dec, 2006  |  Pubmed ID: 17029252

Elucidating how neuronal networks process information requires identification of critical individual neurons and their connectivity patterns. For this purpose, we used the third-instar Drosophila larval brain and applied reverse-genetic tools, immunolabeling procedures, and 3D digital reconstruction software. Consistent topological definition of neuropile compartments in the larval brain can be obtained through simple fluorescence-immunolabeling methods. The modular neuropiles can be used as a fiducial framework for mapping the projection patterns of individual neurons labeled with green fluorescent protein (GFP). GFP-labeled neurons often exhibit dendrite-like arbors as well as clustered varicose terminals on neurite branches that innervate identifiable neuropile compartments. We identified candidate cholinergic interneurons in genetic mosaic brains that overlap with the larval optic nerve terminus. By using the neuropile framework, we demonstrate that the candidate visual interneurons are not a subset of the previously identified circadian pacemaker neurons that also contact the larval optic nerve terminus; they may represent parallel pathways in the processing of visual inputs. Thus, in the Drosophila larval brain, modular neuropiles can be used as a framework for systematically identifying, mapping, and classifying interneurons; understanding their roles in behavior can then be pursued further.

Morphological and Functional Effects of Altered Cysteine String Protein at the Drosophila Larval Neuromuscular Junction

Synapse (New York, N.Y.). Jan, 2007  |  Pubmed ID: 17068777

The synaptic vesicle-associated cysteine string protein (CSP) is critical for neurotransmitter release at the neuromuscular junction (NMJ) of Drosophila, where the approximately 4% of mutant flies lacking CSP that survive to adulthood exhibit spastic jumping and shaking, temperature-sensitive paralysis, and premature death. Previously, it has been shown that CSP is also required for nerve terminal growth and the prevention of neurodegeneration in Drosophila and mice. At larval csp null mutant NMJs of Drosophila, intracellular recordings from the muscle showed that evoked release is significantly reduced at room temperature. However, it remained unclear whether the reduction in evoked release might be due to a loss of synaptic boutons, loss of synapses, and alterations in trafficking of vesicles to synapses. To resolve these issues, we have examined synaptic structure and function of csp null mutant NMJs at the level of single boutons. csp null mutations proportionally reduce the number of synaptic boutons of both motor neurons (1s and 1b) innervating larval muscles 6 and 7, while the number of synapses per bouton remains normal. However, focal recordings from individual synaptic boutons show that nerve-evoked neurotransmitter release is also impaired in both 1s and 1b boutons. Further, our ultrastructural analyses show that the reduction in evoked release at low stimulation frequencies is not due to a loss of synapses or to alterations in docked vesicles at synapses. Together, these data suggest that CSP promotes synaptic growth and evoked neurotransmitter release by mechanistically independent signaling pathways.

Presynaptic Plasticity and Associative Learning Are Impaired in a Drosophila Presenilin Null Mutant

Developmental Neurobiology. Oct, 2007  |  Pubmed ID: 17562530

Alzheimer's disease is a neurodegenerative disorder characterized by progressive memory and cognitive decline that is associated with changes in synaptic plasticity and neuronal cell loss. Recent evidence suggests that some of these defects may be due to a loss of normal presenilin activity. Here, we have examined the effect of loss of Drosophila presenilin (psn) function on synaptic plasticity and learning. Basal transmitter release was elevated in psn mutants while both paired pulse synaptic plasticity and post-tetanic potentiation were impaired. These defects in synaptic strength and plasticity were not due to developmental defects in NMJ morphology. We also found that psn null terminals take up significantly less FM 4-64 than control terminals when loaded with high frequency stimulation, suggesting a defect in synaptic vesicle availability or mobilization. To determine whether these reductions in synaptic plasticity had any impact on learning, we tested the larvae for defects in associative learning. Using both olfactory and visual learning assays, we found that associative learning is impaired in psn mutants compared with controls. Both the learning and synaptic defects could be rescued by expression of a full length psn transgene suggesting the defects are specifically due to a loss of psn function. Taken together, these results provide the first evidence of learning and synaptic defects in a Drosophila psn mutant and strongly suggest a presynaptic role for presenilin in normal neuronal function.

Presynaptic Ryanodine Receptor-activated Calmodulin Kinase II Increases Vesicle Mobility and Potentiates Neuropeptide Release

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. Jul, 2007  |  Pubmed ID: 17634373

Although it has been postulated that vesicle mobility is increased to enhance release of transmitters and neuropeptides, the mechanism responsible for increasing vesicle motion in nerve terminals and the effect of perturbing this mobilization on synaptic plasticity are unknown. Here, green fluorescent protein-tagged dense-core vesicles (DCVs) are imaged in Drosophila motor neuron terminals, where DCV mobility is increased for minutes after seconds of activity. Ca2+-induced Ca2+ release from presynaptic endoplasmic reticulum (ER) is shown to be necessary and sufficient for sustained DCV mobilization. However, this ryanodine receptor (RyR)-mediated effect is short-lived and only initiates signaling. Calmodulin kinase II (CaMKII), which is not activated directly by external Ca2+ influx, then acts as a downstream effector of released ER Ca2+. RyR and CaMKII are essential for post-tetanic potentiation of neuropeptide secretion. Therefore, the presynaptic signaling pathway for increasing DCV mobility is identified and shown to be required for synaptic plasticity.

Chronic and Acute Alterations in the Functional Levels of Frequenins 1 and 2 Reveal Their Roles in Synaptic Transmission and Axon Terminal Morphology

The European Journal of Neuroscience. Nov, 2007  |  Pubmed ID: 17970740

Frequenin (Frq) and its mammalian homologue, neuronal calcium sensor 1 (NCS-1), are important calcium-binding proteins which enhance neurotransmitter release and facilitation. Here, we report the discovery of a second Frq-encoding gene (frq2) in Drosophila. The temporal and spatial expression patterns of the two genes are very similar, and the proteins they encode, Frq1 and Frq2, are 95% identical in amino acid sequence. Frq1 is more abundant than Frq2, and is most highly expressed in larva. Loss-of-function phenotypes were studied using dominant negative peptides to prevent Frq target binding, RNAi to reduce gene transcription, or both methods. To discriminate chronic from acute loss-of-function effects, we compared the effects of transgenic expression and forward-filling the dominant-negative peptide into presynaptic terminals. In both cases, a 70% reduction in quantal content per bouton occurred, demonstrating that this trait does not result from homeostatic adaptations of the synapse during development. The chronic treatment also produced more synaptic boutons from MNSNb/d-Is motorneurons, but fewer active zones per bouton. By contrast, excess-of-function conditions yielded a 1.4- to 2-fold increase in quantal content and fewer boutons in the same motorneuron. These synaptic effects resulted in behavioural changes in the Buridan locomotion assay, showing that walking speed is dependent on Frq activity in the nervous system. All the effects were identical for both Frqs, and consistent with excess- and loss-of-function genotypes. We conclude that Frqs have two distinct functions: one in neurotransmission, regulating the probability of release per synapse, and another in axonal growth and bouton formation.

Frequenin/NCS-1 and the Ca2+-channel Alpha1-subunit Co-regulate Synaptic Transmission and Nerve-terminal Growth

Journal of Cell Science. Nov, 2009  |  Pubmed ID: 19861494

Drosophila Frequenin (Frq) and its mammalian and worm homologue, NCS-1, are Ca(2+)-binding proteins involved in neurotransmission. Using site-specific recombination in Drosophila, we created two deletions that removed the entire frq1 gene and part of the frq2 gene, resulting in no detectable Frq protein. Frq-null mutants were viable, but had defects in larval locomotion, deficient synaptic transmission, impaired Ca(2+) entry and enhanced nerve-terminal growth. The impaired Ca(2+) entry was sufficient to account for reduced neurotransmitter release. We hypothesized that Frq either modulates Ca(2+) channels, or that it regulates the PI4Kbeta pathway as described in other organisms. To determine whether Frq interacts with PI4Kbeta with consequent effects on Ca(2+) channels, we first characterized a PI4Kbeta-null mutant and found that PI4Kbeta was dispensable for synaptic transmission and nerve-terminal growth. Frq gain-of-function phenotypes remained present in a PI4Kbeta-null background. We conclude that the effects of Frq are not due to an interaction with PI4Kbeta. Using flies that were trans-heterozygous for a null frq allele and a null cacophony (encoding the alpha(1)-subunit of voltage-gated Ca(2+) channels) allele, we show a synergistic effect between these proteins in neurotransmitter release. Gain-of-function Frq phenotypes were rescued by a hypomorphic cacophony mutation. Overall, Frq modulates Ca(2+) entry through a functional interaction with the alpha(1) voltage-gated Ca(2+)-channel subunit; this interaction regulates neurotransmission and nerve-terminal growth.

Biphasic Effects of the Cholinergic Agonist Carbachol on Long-term Potentiation in the Dentate Gyrus of the Mammalian Hippocampus

Neuroscience Letters. Jul, 2010  |  Pubmed ID: 20510338

The dentate gyrus, an integral part of the hippocampal circuit, is capable of producing new neurons in adulthood, some of which become integrated into neuronal circuits that participate in processes underlying learning and memory. Acetylcholine (Ach) is an important neuromodulator of synaptic activity in the hippocampus but its action on activity-dependent plasticity of mature and young neurons has not been studied. Using standard hippocampal slice preparations and a functional assay for distinguishing young and mature neuronal populations, we found that Ach has a preferential stimulatory effect on long-term synaptic plasticity of mature neurons. This is in contrast to its inhibitory effect on synaptic plasticity of immature, adult-born neurons. This differential effect of Ach may contribute to differences in learning and memory in young and old brains, particularly in tasks that are sensitive to adult neurogenesis.

Peptide-induced Modulation of Synaptic Transmission and Escape Response in Drosophila Requires Two G-protein-coupled Receptors

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. Nov, 2010  |  Pubmed ID: 21048131

Neuropeptides are found in both mammals and invertebrates and can modulate neural function through activation of G-protein-coupled receptors (GPCRS). The precise mechanisms by which many of these GPCRs modulate specific signaling cascades to regulate neural function are not well defined. We used Drosophila melanogaster as a model to examine both the cellular and behavioral effects of DPKQDFMRFamide, the most abundant peptide encoded by the dFMRF gene. We show that DPKQDFMRFamide enhanced synaptic transmission through activation of two G-protein-coupled receptors, Fmrf Receptor (FR) and Dromyosupressin Receptor-2 (DmsR-2). The peptide increased both the presynaptic Ca(2+) response and the quantal content of released transmitter. Peptide-induced modulation of synaptic function could be abrogated by depleting intracellular Ca(2+) stores or by interfering with Ca(2+) release from the endoplasmic reticulum through disruption of either the ryanodine receptor or the inositol 1,4,5-trisphosphate receptor. The peptide also altered behavior. Exogenous DPKQDFMRFamide enhanced fictive locomotion; this required both the FR and DmsR-2. Likewise, both receptors were required for an escape response to intense light exposure. Thus, coincident detection of a peptide by two GPCRs modulates synaptic function through effects of Ca(2+)-induced Ca(2+) release, and we hypothesize that these mechanisms are involved in behavioral responses to environmental stress.