AMPA Subtype Of Glutamate Receptors Research Articles

Prolonged seizure activity leads to increased Protein Kinase A activation in the rat pilocarpine model of status epilepticus

Status epilepticus is a life-threatening form of seizure activity that represents a major medical emergency associated with significant morbidity and mortality. Protein Kinase A is an important regulator of synaptic strength that may play an important role in the development of status epilepticus-induced neuronal pathology. This study demonstrated an increase in PKA activity against exogenous and endogenous substrates during later stages of SE. As SE progressed, a significant increase in PKA-mediated phosphorylation of an exogenous peptide substrate was demonstrated in cortical structures. The increased activity was not due to altered expression of either regulatory or catalytic subunits of the enzyme. Through the use of phospho-specific antibodies, this study also investigated the effects of SE on the phosphorylation of the GluR1 subunit of the AMPA subtype of glutamate receptor. After the onset of continuous seizure activity, an increase in phosphorylation of the PKA site on the GluR1 subunit of the AMPA receptor was observed. These data suggest a potential mechanism by which SE may increase neuronal excitability in the cortex, potentially leading to maintenance of seizure activity or long-term neuronal pathology.

Mechanisms of neocortical development

Mechanisms of neocortical development

AMPA and ampakines as proneurogenic modulators of progenitors derived from subventricular zone

Event Abstract Back to Event AMPA and ampakines as proneurogenic modulators of progenitors derived from subventricular zone Clarissa De-Sampaio-Schitine1* 1 Universidade de Coimbra, Centro de Neurociencias e Biologia Celular, Portugal Neurogenesis in the brain of adult mammals occurs throughout life, and has been demonstrated at two locations under normal conditions: the subventricular zone (SVZ) of the lateral ventricles and the subgranular zone (SGZ) of the dentate gyrus in the hippocampus.AMPAkines are a group of chemical compounds that modulate the properties of ionotropic AMPA subtype of glutamate receptors, potentiating excitatory signals and enhancing cognitive properties. AMPAkine effects are presumably mediated through increase in synaptic efficiency of excited neuronal circuits. However, a positive effect on neurogenesis cannot be ruled out. Here, we propose to disclose the pro-neurogenic effects of an excitatory stimulation, through AMPA treatment, and AMPAkines in SVZ cell cultures derived from neonatal mice.SVZ cells were incubated in the presence of AMPA (1 to 50μM) and AMPAkine CX546 (5 to 150μM). Both treatments triggered a concentration-dependent increase in proliferation, evaluated in 48h treated cultures through the BrdU incorporation assay. AMPA and AMPAkines stimulated neuronal differentiation as the numbers of NeuN mature neurons increased in 7 days treated cultures. Moreover AMPA and AMPAkine treatments increased the numbers of functional neurons, evaluated by single cell calcium imaging. Immunoassays for the phosphorylated form of the JNK signaling were also performed in SVZ cell cultures treated with AMPA 1μM and AMPAKine CX546 5μM for 6h. AMPA and AMPAkine treatment promoted a five and six fold increase in the number and in the total length of the ramifications per neurosphere, respectively. Knowing that JNK signaling is involved in axonogenesis, these data show that AMPA and AMPAkine CX 546 improve neuronal maturation.Altogether, these data demonstrate that AMPA and AMPAkines CX 546 are positive modulators of neurogenesis in SVZ cell cultures and highlight the possible use of AMPAkines for future development of cell- based brain therapies.Acknowledgments: Convenio GRICES-CAPES and Fundacao para a Ciencia e Tecnologia: PTDC-SAU-NEU- 68465-2006 Conference: 11th Meeting of the Portuguese Society for Neuroscience, Braga, Portugal, 4 Jun - 6 Jun, 2009. Presentation Type: Poster Presentation Topic: Abstracts Citation: De-Sampaio-Schitine C (2009). AMPA and ampakines as proneurogenic modulators of progenitors derived from subventricular zone. Front. Neurosci. Conference Abstract: 11th Meeting of the Portuguese Society for Neuroscience. doi: 10.3389/conf.neuro.01.2009.11.037 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 06 Aug 2009; Published Online: 06 Aug 2009. * Correspondence: Clarissa De-Sampaio-Schitine, Universidade de Coimbra, Centro de Neurociencias e Biologia Celular, Alicante, Portugal, schitine@biof.ufrj.br Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Clarissa De-Sampaio-Schitine Google Clarissa De-Sampaio-Schitine Google Scholar Clarissa De-Sampaio-Schitine PubMed Clarissa De-Sampaio-Schitine Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Delivery of AMPA receptors to perisynaptic sites precedes the full expression of long-term potentiation

Trafficking of AMPA subtype glutamate receptors (AMPARs) from intracellular compartments to synapses is thought to be a major mechanism underlying the expression of long-term potentiation (LTP), a cellular substrate for learning and memory. However, it remains unclear whether the AMPAR trafficking that takes place during LTP is due to a targeted insertion of AMPARs directly into the synapse or delivery to extrasynaptic sites followed by translocation into the synapse. Here, we provide direct physiological evidence that LTP induced by a theta-burst pairing and tetanic stimulation protocols causes the rapid delivery of AMPARs to a perisynaptic site. Perisynaptic AMPARs do not normally detect synaptically released glutamate but can do so when the glial glutamate transporter EAAT1 is inhibited. AMPARs can be detected at this perisynaptic site before, but not after, the full expression of LTP. The appearance of perisynaptic AMPARs requires postsynaptic exocytosis, PKA signaling, and the C-terminal region of GluR1 subunit of AMPARs but not actin polymerization. Actin polymerization after LTP induction is required to retain AMPARs at the perisynaptic site after their appearance. Low-frequency stimulation given shortly after LTP induction leads to activity-dependent removal of perisynaptic AMPARs and suppresses the subsequent expression of LTP. These results demonstrate that AMPARs are rapidly trafficked to perisynaptic sites shortly after LTP induction and suggest that the delivery and maintenance of perisynaptic AMPARs may serve as a checkpoint in the expression of LTP.

CaM kinases and AMPA receptor subunit recomposition in hippocampal synaptic plasticity

It is broadly believed that synaptic plasticity is a neuronal mechanism for learning and memory in the mammalian brain. In the mature hippocampus, the expression of long-term potentiation (LTP) in Schaffer collateral-CA1 synapses requires a postsynaptic Ca2+ influx and the GluR1 subunit of the AMPA subtype of glutamate receptor (AMPAR). New findings indicate that the pattern of synaptic activity associated with exploratory behavior can induce LTP by changing the quality of synaptic AMPARs. This process is dynamic and requires activity of Ca2+/calmodulin dependent protein kinases (CaMKs), key transducers of postsynaptic Ca2+ changes into LTP. The two CaMKs, CaMKI and CaMKII target AMPARs and regulate synaptic strength differently, however. Under basal conditions, AMPARs in these synapses are heteromers composed of GluR1 and GluR2 subunits. CaMKI enhances synaptic strength by trafficking to synapses more functionally efficient and highly Ca2+-permeable GluR2-lacking AMPARs through a regulated actin dynamics. In contrast, CaMKII can enhance functional properties of these GluR2-lacking AMPARs by a direct phosphorylation of the C-terminus of GluR1 subunit. Taken together, these results argue for two distinct but orchestrated mechanisms in modification of synaptic strength during LTP. Results are discussed in terms of the role of AMPAR subunit recomposition for synaptic plasticity. from Seventeenth Annual Computational Neuroscience Meeting: CNS*2008 Portland, OR, USA. 19–24 July 2008

Learning-induced Glutamate Receptor Phosphorylation Resembles That Induced by Long Term Potentiation

Long term potentiation and long term depression of synaptic responses in the hippocampus are thought to be critical for certain forms of learning and memory, although until recently it has been difficult to demonstrate that long term potentiation or long term depression occurs during hippocampus-dependent learning. Induction of long term potentiation or long term depression in hippocampal slices in vitro modulates phosphorylation of the alpha-amino-3-hydrozy-5-methylisoxazole-4-propionic acid subtype of glutamate receptor subunit GluR1 at distinct phosphorylation sites. In long term potentiation, GluR1 phosphorylation is increased at the Ca2+/calmodulin-dependent protein kinase and protein kinase C site serine 831, whereas in long term depression, phosphorylation of the protein kinase A site serine 845 is decreased. Indeed, phosphorylation of one or both of these sites is required for long term synaptic plasticity and for certain forms of learning and memory. Here we demonstrate that training in a hippocampus-dependent learning task, contextual fear conditioning is associated with increased phosphorylation of GluR1 at serine 831 in the hippocampal formation. This increased phosphorylation is specific to learning, has a similar time course to that in long term potentiation, and like memory and long term potentiation, is dependent on N-methyl-D-aspartate receptor activation during training. Furthermore, the learning-induced increase in serine 831 phosphorylation is present at synapses and is in heteromeric complexes with the glutamate receptor subunit GluR2. These data indicate that a biochemical correlate of long term potentiation occurs at synapses in receptor complexes in a final, downstream, postsynaptic effector of long term potentiation during learning in vivo, further strengthening the link between long term potentiation and memory.

Differential Regulation of AMPA Receptor Trafficking by Neurabin-Targeted Synaptic Protein Phosphatase-1 in Synaptic Transmission and Long-Term Depression in Hippocampus

Filamentous actin binding protein neurabin I (NrbI) targets protein phosphatase-1 (PP1) to specific postsynaptic microdomains, exerting critical control over AMPA receptor (AMPAR)-mediated synaptic transmission. NrbI-targeted synaptic PP1, which promotes synaptic depression upon long-term depression (LTD) stimuli, serves to prevent synaptic depression under basal conditions. The present studies investigate this opposite regulation of AMPAR trafficking during basal synaptic transmission and LTD by expressing NrbI or NrbI mutant, which is defective in PP1 binding, in hippocampal slice or neuron cultures. We find that expression of the NrbI mutant to interfere with PP1 targeting dramatically reduces basal synaptic transmission, which is correlated with the reduction in surface expression of AMPA subtype glutamate receptor (GluR) 1 and GluR2 subunits. Biochemical analysis demonstrates that the NrbI mutant selectively increases the phosphorylation of GluR2 at C-terminal consensus PKC site, serine 880, which is known to favor GluR2 interaction with PDZ (postsynaptic density 95/Discs large/zona occludens 1) protein PICK1 (protein interacting with C kinase-1). Inhibition of PKC activity or GluR2-PICK1 interaction completely reverses the synaptic depression in neurons expressing the NrbI mutant, suggesting that NrbI-targeted synaptic PP1 stabilizes the basal transmission by negatively controlling PKC phosphorylation of GluR2 and the subsequent PICK1-mediated decrease in GluR2-containing AMPAR surface expression. Distinct from basal transmission, blocking GluR2-PICK1 interaction or PKC activity produces minimal effects on LTD in NrbI-expressing neurons. Instead, NrbI-targeted PP1 facilitates LTD by dephosphorylating GluR1 at both serine 845 and serine 831, with GluR2 serine 880 phosphorylation unaltered. Our studies thus elucidate that NrbI-targeted PP1, in response to distinct synaptic activities, regulates the synaptic trafficking of specific AMPAR subunits.

Activity‐dependent formation and functions of chondroitin sulfate‐rich extracellular matrix of perineuronal nets

Extracellular matrix molecules--including chondroitin sulfate proteoglycans, hyaluronan, and tenascin-R--are enriched in perineuronal nets (PNs) associated with subsets of neurons in the brain and spinal cord. In the present study, we show that similar cell type-dependent extracellular matrix aggregates are formed in dissociated cell cultures prepared from early postnatal mouse hippocampus. Starting from the 5th day in culture, accumulations of lattice-like extracellular structures labeled with Wisteria floribunda agglutinin were detected at the cell surface of parvalbumin-expressing interneurons, which developed after 2-3 weeks into conspicuous PNs localized around synaptic contacts at somata and proximal dendrites, as well as around axon initial segments. Physiological recording and intracellular labeling of PN-expressing neurons revealed that these are large fast-spiking interneurons with morphological characteristics of basket cells. To study mechanisms of activity-dependent formation of PNs, we performed pharmacological analysis and found that blockade of action potentials, transmitter release, Ca2+ permeable AMPA subtype of glutamate receptors or L-type Ca2+ voltage-gated channels strongly decreased the extracellular accumulation of PN components in cultured neurons. Thus, we suggest that Ca2+ influx via AMPA receptors and L-type channels is necessary for activity-dependent formation of PNs. To study functions of chondroitin sulfate-rich PNs, we treated cultures with chondroitinase ABC that resulted in a prominent reduction of several major PN components. Removal of PNs did not affect the number and distribution of perisomatic GABAergic contacts but increased the excitability of interneurons in cultures, implicating the extracellular matrix of PNs in regulation of interneuronal activity.

Antiaggressive effects of topiramate in agonistic encounters between male mice

Topiramate, an antiepileptic drug, has been found to be useful for the treatment of aggression in clinical populations. However, no studies have explored the action of this compound on aggressive behavior in laboratory animals. This work examined the effects of topiramate (10, 20, 40 and 80 mg/kg, i.p.) on agonistic interactions between male mice, using an ethopharmacological approach. Individually housed mice were exposed to anosmic "standard opponents" 30 min after drug administration. Ten minutes of diadic interactions were staged between a singly housed and an anosmic mouse in a neutral area. The encounters were videotaped and the accumulated time allocated by subjects to 10 broad behavioral categories was estimated using an ethologically based analysis. Results showed that topiramate (20-80 mg/kg) produced a significant reduction of offensive behaviors (threat and attack), without affecting immobility. Digging behavior (all doses) was also significantly decreased. The antiaggressive effects of topiramate could be related to its ability for modulating positively GABA-A receptors and/or blocking AMPA subtype of glutamate receptors.

Synapse-specific regulation of AMPA receptor function by PSD-95

PSD-95 is a major protein found in virtually all mature excitatory glutamatergic synapses in the brain. Here, we have addressed the role of PSD-95 in controlling glutamatergic synapse function by generating and characterizing a PSD-95 KO mouse. We found that the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)subtype of glutamate receptor (AMPAR)-mediated synaptic transmission was reduced in these mice. Two-photon (2P) uncaging of MNI-glutamate onto individual spines suggested that the decrease in AMPAR function in the PSD-95 KO mouse stems from an increase in the proportion of "silent" synapses i.e., synapses containing N-methyl-d-aspartate (NMDA) receptors (NMDARs) but no AMPARs. Unexpectedly, the silent synapses in the KO mouse were located onto morphologically mature spines. We also observed that a significant population of synapses appeared unaffected by PSD-95 gene deletion, suggesting that the functional role of PSD-95 displays synapse-specificity. In addition, we report that the decay of NMDAR-mediated current was slower in KO mice: The contribution of NR2B subunit containing receptors to the NMDAR-mediated synaptic current was greater in KO mice. The greater occurrence of silent synapses might be related to the greater magnitude of potentiation after long-term potentiation induction observed in these mice. Together, these results suggest a synapse-specific role for PSD-95 in controlling synaptic function that is independent of spine morphology.

Down-regulation of glutaredoxin by estrogen receptor antagonist renders female mice susceptible to excitatory amino acid mediated complex I inhibition in CNS

β- N-oxalyl-amino- l-alanine, ( l-BOAA), an excitatory amino acid, acts as an agonist of the AMPA subtype of glutamate receptors. It inhibits mitochondrial complex I in motor cortex and lumbosacral cord of male mice through oxidation of critical thiol groups, and glutaredoxin, a thiol disulfide oxido-reductase, helps maintain integrity of complex I. Since incidence of neurolathyrism is less common in women, we examined the mechanisms underlying the gender-related effects. Inhibition of complex I activity by l-BOAA was seen in male but not female mice. Pretreatment of female mice with estrogen receptor antagonist ICI 182,780 or tamoxifen sensitizes them to l-BOAA toxicity, indicating that the neuroprotection is mediated by estrogen receptors. l-BOAA triggers glutathione (GSH) loss in male mice but not in female mice, and only a small but significant increase in oxidized glutathione (GSSG) was seen in females. As a consequence, up-regulation of γ-glutamyl cysteinyl synthase (the rate-limiting enzyme in glutathione synthesis) was seen only in male mouse CNS but not in females. Both glutathione reductase and glutaredoxin that reduce oxidized glutathione and protein glutathione mixed disulfides, respectively, were constitutively expressed at higher levels in females. Furthermore, glutaredoxin activity in female mice was down-regulated by estrogen antagonist indicating its regulation by estrogen receptor. The higher constitutive expression of glutathione reductase and glutaredoxin could potentially confer neuroprotection to female mice.

Modulation of GABAergic Transmission by Activity via Postsynaptic Ca2+-Dependent Regulation of KCC2 Function

Activity-induced modification of GABAergic transmission contributes to the plasticity of neural circuits. In the present work we found that prolonged postsynaptic spiking of hippocampal neurons led to a shift in the reversal potential of GABA-induced Cl- currents (E(Cl)) toward positive levels in a duration- and frequency-dependent manner. This effect was abolished by blocking cytosolic Ca2+ elevation and mimicked by releasing Ca2+ from internal stores. Activity- and Ca2+-induced E(Cl) shifts were larger in mature neurons, which express the K-Cl cotransporter KCC2 at high levels, and inhibition of KCC2 occluded the shifts. Overexpression of KCC2 in young cultured neurons, which express lower levels of KCC2 and have a more positive E(Cl), resulted in hyperpolarized E(Cl) similar to that of mature cells. Importantly, these young KCC2-expressing neurons became responsive to neuronal spiking and Ca2+ elevation by showing positive E(Cl) shifts. Thus, repetitive postsynaptic spiking reduces the inhibitory action of GABA through a Ca2+-dependent downregulation of KCC2 function.

Coassembly of Two GluR6 Kainate Receptor Splice Variants within a Functional Protein Complex

Kainate receptors (KAR) are composed of several distinct subunits and splice variants, but the functional relevance of this diversity remains largely unclear. Here we show that two splice variants of the GluR6 subunit, GluR6a and GluR6b, which differ in their C-terminal domains, do not show distinct functional properties, but coassemble as heteromers in vitro and in vivo. Using a proteomic approach combining affinity purification and MALDI-TOF mass spectrometry, we found that GluR6a and GluR6b interact with two distinct subsets of cytosolic proteins mainly involved in Ca(2+) regulation of channel function and intracellular trafficking. Guided by these results, we provide evidence that the regulation of native KAR function by NMDA receptors depends on the heteromerization of GluR6a and GluR6b and interaction of calcineurin with GluR6b. Thus, GluR6a and GluR6b bring in close proximity two separate subsets of interacting proteins that contribute to the fine regulation of KAR trafficking and function.

Calcium-Permeable AMPA Receptor Plasticity Is Mediated by Subunit-Specific Interactions with PICK1 and NSF

A recently described form of synaptic plasticity results in dynamic changes in the calcium permeability of synaptic AMPA receptors. Since the AMPA receptor GluR2 subunit confers calcium permeability, this plasticity is thought to occur through the dynamic exchange of synaptic GluR2-lacking and GluR2-containing receptors. To investigate the molecular mechanisms underlying this calcium-permeable AMPA receptor plasticity (CARP), we examined whether AMPA receptor exchange was mediated by subunit-specific protein-protein interactions. We found that two GluR2-interacting proteins, the PDZ domain-containing Protein interacting with C kinase (PICK1) and N-ethylmaleimide sensitive fusion protein (NSF), are specifically required for CARP. Furthermore, PICK1, but not NSF, regulates the formation of extrasynaptic plasma membrane pools of GluR2-containing receptors that may be laterally mobilized into synapses during CARP. These results demonstrate that PICK1 and NSF dynamically regulate the synaptic delivery of GluR2-containing receptors during CARP and thus regulate the calcium permeability of AMPA receptors at excitatory synapses.

Crystal Structures of the GluR5 and GluR6 Ligand Binding Cores: Molecular Mechanisms Underlying Kainate Receptor Selectivity

Little is known about the molecular mechanisms underlying differences in the ligand binding properties of AMPA, kainate, and NMDA subtype glutamate receptors. Crystal structures of the GluR5 and GluR6 kainate receptor ligand binding cores in complexes with glutamate, 2S,4R-4-methylglutamate, kainate, and quisqualate have now been solved. The structures reveal that the ligand binding cavities are 40% (GluR5) and 16% (GluR6) larger than for GluR2. The binding of AMPA- and GluR5-selective agonists to GluR6 is prevented by steric occlusion, which also interferes with the high-affinity binding of 2S,4R-4-methylglutamate to AMPA receptors. Strikingly, the extent of domain closure produced by the GluR6 partial agonist kainate is only 3 degrees less than for glutamate and 11 degrees greater than for the GluR2 kainate complex. This, together with extensive interdomain contacts between domains 1 and 2 of GluR5 and GluR6, absent from AMPA receptors, likely contributes to the high stability of GluR5 and GluR6 kainate complexes.

Rapid BDNF-induced retrograde synaptic modification in a developing retinotectal system.

In cultures of hippocampal neurons, induction of long-term synaptic potentiation or depression by repetitive synaptic activity is accompanied by a retrograde spread of potentiation or depression, respectively, from the site of induction at the axonal outputs to the input synapses on the dendrites of the presynaptic neuron. We report here that rapid retrograde synaptic modification also exists in an intact developing retinotectal system. Local application of brain-derived neurotrophic factor (BDNF) to the Xenopus laevis optic tectum, which induced persistent potentiation of retinotectal synapses, led to a rapid modification of synaptic inputs at the dendrites of retinal ganglion cells (RGCs), as shown by a persistent enhancement of light-evoked excitatory synaptic currents and spiking activity of RGCs. This retrograde effect required TrkB receptor activation, phospholipase Cgamma activity and Ca2+ elevation in RGCs, and was accounted for by a selective increase in the number of postsynaptic AMPA-subtype glutamate receptors at RGC dendrites. Such retrograde information flow in the neuron allows rapid regulation of synaptic inputs at the dendrite in accordance to signals received at axon terminals, a process reminiscent of back-propagation algorithm for learning in neural networks.

Structure-based functional design of chemical ligands for AMPA-subtype glutamate receptors.

Ionotropic glutamate receptors (GluRs) function as an excitatory transmitter system in the human brain, particularly in learning and memory. Development of small molecules that are capable of selectively potentiating the ion channel activity of AMPA-subtype GluRs holds promise for potential new treatment of neurodegenerative diseases such as Alzheimer's. In working towards this goal, we obtained main-chain nuclear magnetic resonance (NMR) assignments of the extracellular ligand-binding domain of GluR2 that enables us to investigate receptor-ligand interactions in physiological conditions at atomic detail. With NMR structure-based methods, chemical compounds that can selectively modulate the ion chancel activity of GluR2 alone or synergistically with glutamate or kainate were identified. Our NMR structural analysis of GluR2 S1S2 further reveals that the regions of the receptor dimer interface exhibit distinct conformational dynamics, which we hypothesize to be linked to receptor functions in interactions with an agonist or antagonist. This coupling of ligand binding to receptor dimerization, gating, and desensitization may serve as an in vitro biophysical parameter to evaluate potential biological effects of the chemical ligands being developed here.

Disinhibition of ventrolateral preoptic area sleep-active neurons by adenosine: a new mechanism for sleep promotion

The ventrolateral preoptic area of the hypothalamus (VLPO) contains a population of sleep-active neurons and is hypothesized to be an important part of the somnogenic process. Adenosine (AD) is an endogenous sleep-promoting factor and may play an important role in promoting natural sleep. We hypothesize that AD may promote sleep, in part, by activating the VLPO sleep-active neurons. Although, in the CNS, AD is generally regarded as an inhibitory neuromodulator, it is possible for AD to be directly excitatory via A2 receptors or indirectly via disinhibition. In order to test the hypotheses that AD can excite VLPO neurons we made intracellular recordings from the VLPO in vitro and examined the effects of AD on VLPO neural activity. Whole cell patch-clamp recordings were obtained from rat brain slices and drugs were bath applied. VLPO neurons were electrophysiologically heterogeneous. Depolarizing current steps elicited rhythmic firing (25 of 57), spike frequency adaptation or accommodation (24 of 57), or an unusual burst firing response (eight of 57). Spontaneous synaptic activity was pronounced in most recorded neurons and consisted of either fast excitatory post-synaptic potentials/currents (EPSP/C's) and/or fast inhibitory post-synaptic potentials/currents (IPSP/C's). The IPSC's were fully blocked by 30 μM bicuculline suggesting they are GABA A-mediated events, and the EPSC's were blocked by 40 μM DNQX suggesting they are mediated by the AMPA subtype of glutamate receptor (five of five). AD (20–100 μM) reduced the frequency of spontaneous IPSC's in 11 of 17 VLPO neurons (28–100%; mean reduction=63%) without significant effects on resting membrane potential. IPSC was unaffected in five neurons and one neuron displayed increases in spontaneous IPSC's. In contrast, AD decreased EPSC frequency in seven cells (36–73%; mean=59%), increased frequency in five cells (30–236%; mean 83%) and had no effect in six cells. AD application increased the firing rate in two of four cells tested. These data are consistent with the hypothesis that one mechanism which AD may promote sleep is by blocking inhibitory inputs on VLPO sleep-active neurons.

Emerging roles for endocannabinoids in long‐term synaptic plasticity

British Journal of Pharmacology (2003) 140, 781–789. doi:10.1038/sj.bjp.0705466

Structural basis for partial agonist action at ionotropic glutamate receptors.

An unresolved problem in understanding neurotransmitter receptor function concerns the mechanism(s) by which full and partial agonists elicit different amplitude responses at equal receptor occupancy. The widely held view of 'partial agonism' posits that resting and active states of the receptor are in equilibrium, and partial agonists simply do not shift the equilibrium toward the active state as efficaciously as full agonists. Here we report findings from crystallographic and electrophysiological studies of the mechanism of activation of an AMPA-subtype glutamate receptor ion channel. In these experiments, we used 5-substituted willardiines, a series of partial agonists that differ by only a single atom. Our results show that the GluR2 ligand-binding core can adopt a range of ligand-dependent conformational states, which in turn control the open probability of discrete subconductance states of the intact ion channel. Our findings thus provide a structure-based model of partial agonism.