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In JoVE (2)
Other Publications (7)
- Neuron
- Neuron
- Journal of Neurophysiology
- Journal of Neurophysiology
- Proceedings of the National Academy of Sciences of the United States of America
- The Journal of Neuroscience : the Official Journal of the Society for Neuroscience
- The Journal of Neuroscience : the Official Journal of the Society for Neuroscience
Articles by Andres Barria in JoVE
JoVE Neuroscience
Organotypic Hippocampal Slice Cultures
Department of Physiology and Biophysics, University of Washington School of Medicine
We describe a method to prepare organotypic hippocampal slices that can be easily adapted to other brain regions. Brain slices are laid on porous membranes and culture media is allowed to form an interface. This method preserves the gross architecture of the hippocampus for up to 2 weeks in culture.
JoVE Neuroscience
Preparation and Culture of Chicken Auditory Brainstem Slices
1Department of Otolaryngology-Head and Neck Surgery, Virginia Merrill Bloedel Hearing Research Center, University of Washington, 2Department of Physiology and Biophysics, Virginia Merrill Bloedel Hearing Research Center, University of Washington
The chicken auditory brainstem is comprised of nuclei responsible for binaural sound processing. A single coronal slice preparation maintains the entire circuitry while the cultured approach provides a unique preparation to study the development of neuronal structure and auditory function at the molecular, cellular and network levels.
Other articles by Andres Barria on PubMed
Subunit-specific NMDA Receptor Trafficking to Synapses
To elucidate mechanisms controlling the number and subunit composition of synaptic NMDA-Rs in hippocampal slice neurons, the NR1, NR2A, and NR2B subunits were optically and electrophysiologically tagged. The NR2 subunit directs delivery of receptors to synapses with different rules controlling NR2A and NR2B. Synaptic incorporation of NR2B-containing receptors is not limited by synaptic transmission nor enhanced by increased subunit expression. NR2A-containing receptors whose expression normally increases with age replace synaptic NR2B-containing receptors. Replacement is enhanced by increased NR2A expression and requires synaptic activity. Surprisingly, spontaneously released transmitter acting on synaptic NMDA-Rs is sufficient for replacement and reduces NMDA-R responses. Thus, as with AMPA-Rs, synaptic trafficking of NMDA-Rs is tightly regulated and has subunit-specific rules with functionally important consequences.
NMDA Receptor Subunit Composition Controls Synaptic Plasticity by Regulating Binding to CaMKII
Calcium entry through postsynaptic NMDA-Rs and subsequent activation of CaMKII trigger synaptic plasticity in many brain regions. Active CaMKII can bind to NMDA-Rs, but the physiological role of this interaction is not well understood. Here, we test if association between active CaMKII and synaptic NMDA-Rs is required for synaptic plasticity. Switching synaptic NR2B-containing NMDA-Rs that bind CaMKII with high affinity with those containing NR2A, a subunit with low affinity for CaMKII, dramatically reduces LTP. Expression of NR2A with mutations that increase association to active CaMKII recovers LTP. Finally, driving into synapses NR2B with mutations that reduce association to active CaMKII prevents LTP. Spontaneous activity-driven potentiation shows similar results. We conclude that association between active CaMKII and NR2B is required for different forms of synaptic enhancement. The switch from NR2B to NR2A content in synaptic NMDA-Rs normally observed in many brain regions may contribute to reduced plasticity by controlling the binding of active CaMKII.
Development of Glutamatergic Synaptic Transmission in Binaural Auditory Neurons
Glutamatergic synaptic transmission is essential for binaural auditory processing in birds and mammals. Using whole cell voltage clamp recordings, we characterized the development of synaptic ionotropic glutamate receptor (iGluR) function from auditory neurons in the chick nucleus laminaris (NL), the first nucleus responsible for binaural processing. We show that synaptic transmission is mediated by AMPA- and N-methyl-d-aspartate (NMDA)-type glutamate receptors (AMPA-R and NMDA-R, respectively) when hearing is first emerging and dendritic morphology is being established across different sound frequency regions. Puff application of glutamate agonists at embryonic day 9 (E9) revealed that both iGluRs are functionally present prior to synapse formation (E10). Between E11 and E19, the amplitude of isolated AMPA-R currents from high-frequency (HF) neurons increased 14-fold. A significant increase in the frequency of spontaneous events is also observed. Additionally, AMPA-R currents become faster and more rectifying, suggesting developmental changes in subunit composition. These developmental changes were similar in all tonotopic regions examined. However, mid- and low-frequency neurons exhibit fewer spontaneous events and evoked AMPA-R currents are smaller, slower, and less rectifying than currents from age-matched HF neurons. The amplitude of isolated NMDA-R currents from HF neurons also increased, reaching a peak at E17 and declining sharply by E19, a trend consistent across tonotopic regions. With age, NMDA-R kinetics become significantly faster, indicating a developmental switch in receptor subunit composition. Dramatic increases in the amplitude and speed of glutamatergic synaptic transmission occurs in NL during embryonic development. These changes are first seen in HF neurons suggesting regulation by peripheral inputs and may be necessary to enhance coincidence detection of binaural auditory information.
Dynamic Regulation of NMDA Receptor Transmission
N-methyl-D-aspartate receptors (NMDARs) are critical for establishing, maintaining, and modifying glutamatergic synapses in an activity-dependent manner. The subunit composition, synaptic expression, and some of the properties of NMDARs are regulated by synaptic activity, affecting processes like synaptic plasticity. NMDAR transmission is dynamic, and we were interested in studying the effect of acute low or null synaptic activity on NMDA receptors and its implications for synaptic plasticity. Periods of no stimulation or low-frequency stimulation increased NMDAR transmission. Changes became stable after periods of 20 min of low or no stimulation. These changes in transmission have a postsynaptic origin and are explained by incorporation of GluN2B-containing receptors to synapses. Importantly, periods of low or no stimulation facilitate long-term potentiation induction. Moreover, recovery after a weak preconditioning stimulus that normally blocks subsequent potentiation is facilitated by a nonstimulation period. Thus synaptic activity dynamically regulates the level of NMDAR transmission adapting constantly the threshold for plasticity.
NMDA Receptor Subunit Composition Controls Synaptogenesis and Synapse Stabilization
During early postnatal development in the rat hippocampus, synaptogenesis occurs in parallel with a developmental switch in the subunit composition of NMDA receptors from NR2B to NR2A. It is unclear how this switch affects the process of synaptogenesis, synapse maturation, and synapse stabilization. We investigated the role of NR2 subunits in synaptogenesis during the period in which expression and synaptic incorporation of the NR2A protein begins through the time when it reaches adult levels. We found that early expression of NR2A in organotypic hippocampal slices reduces the number of synapses and the volume and dynamics of spines. In contrast, overexpression of NR2B does not affect the normal number and growth of synapses; however, it does increase spine motility, adding and retracting spines at a higher rate. The C terminus of NR2B, and specifically its ability to bind CaMKII, is sufficient to allow proper synapse formation and maturation. Conversely, the C terminus of NR2A was sufficient to stop the development of synapse number and spine growth. Our results indicate that the ratio of synaptic NR2B over NR2A controls spine motility and synaptogenesis, and suggest a structural role for the intracellular C terminus of NR2 in recruiting the signaling and scaffolding molecules necessary for proper synaptogenesis.
Molecular Determinants Controlling NMDA Receptor Synaptic Incorporation
Synaptic incorporation of NMDA receptors (NMDARs) is regulated by GluN2 subunits with different rules controlling GluN2A- and GluN2B-containing receptors; whereas GluN2B-containing receptors are constitutively incorporated into synapses, GluN2A incorporation is activity-dependent. We expressed electrophysiologically tagged NMDARs in rat hippocampal slices to identify the molecular determinants controlling the mode of synaptic incorporation of NMDARs. Expressing chimeric GluN2 subunits, we identified a putative N-glycosylation site present in GluN2B, but not in GluN2A, as necessary and sufficient to drive NMDARs into synapses in an activity-independent manner. This suggests a novel mechanism for regulating activity-driven changes and trafficking of NMDARs to the synapse.
Regulation of NMDA-receptor Synaptic Transmission by Wnt Signaling
Wnt ligands are secreted glycoproteins controlling gene expression and cytoskeleton reorganization involved in embryonic development of the nervous system. However, their role in later stages of brain development, particularly in the regulation of established synaptic connections, is not known. We found that Wnt-5a acutely and specifically upregulates synaptic NMDAR currents in rat hippocampal slices, facilitating induction of long-term potentiation, a cellular model of learning and memory. This effect requires an increase in postsynaptic Ca(2+) and activation of noncanonical downstream effectors of the Wnt signaling pathway. In contrast, Wnt-7a, an activator of the canonical Wnt signaling pathway, has no effect on NMDAR-mediated synaptic transmission. Moreover, endogenous Wnt ligands are necessary to maintain basal NMDAR synaptic transmission, adjusting the threshold for synaptic potentiation. This novel role for Wnt ligands provides a mechanism for Wnt signaling to acutely modulate synaptic plasticity and brain function in later stages of development and in the mature organism.
