Hippocampal GABAergic Neurons Research Articles

Novel Nuclear Protein Complexes of Dystrophin 71 Isoforms in Rat Cultured Hippocampal GABAergic and Glutamatergic Neurons.

The precise functional role of the dystrophin 71 in neurons is still elusive. Previously, we reported that dystrophin 71d and dystrophin 71f are present in nuclei from cultured neurons. In the present work, we performed a detailed analysis of the intranuclear distribution of dystrophin 71 isoforms (Dp71d and Dp71f), during the temporal course of 7-day postnatal rats hippocampal neurons culture for 1h, 2, 4, 10, 15 and 21 days in vitro (DIV). By immunofluorescence assays, we detected the highest level of nuclear expression of both dystrophin Dp71 isoforms at 10 DIV, during the temporal course of primary culture. Dp71d and Dp71f were detected mainly in bipolar GABAergic (≥60%) and multipolar Glutamatergic (≤40%) neurons, respectively. We also characterized the existence of two nuclear dystrophin-associated protein complexes (DAPC): dystrophin 71d or dystrophin 71f bound to β-dystroglycan, α1-, β-, α2-dystrobrevins, α-syntrophin, and syntrophin-associated protein nNOS (Dp71d-DAPC or Dp71f-DAPC, respectively), in the hippocampal neurons. Furthermore, both complexes were localized in interchromatin granule cluster structures (nuclear speckles) of neuronal nucleoskeleton preparations. The present study evinces that each Dp71’s complexes differ slightly in dystrobrevins composition. The results demonstrated that Dp71d-DAPC was mainly localized in bipolar GABAergic and Dp71f-DAPC in multipolar Glutamatergic hippocampal neurons. Taken together, our results show that dystrophin 71d, dystrophin 71f and DAP integrate protein complexes, and both complexes were associated to nuclear speckles structures.

Regional and sub-regional differences in hippocampal GABAergic neuronal vulnerability in the TgCRND8 mouse model of Alzheimer's disease.

Hippocampal network activity is predominantly coordinated by γ-amino-butyric acid (GABA)ergic neurons. We have previously hypothesized that the altered excitability of hippocampal neurons in Alzheimer's disease (AD), which manifests as increased in vivo susceptibility to seizures in the TgCRND8 mouse model of AD, may be related to disruption of hippocampal GABAergic neurons. In agreement, our previous study in TgCRND8 mice has shown that hippocampal GABAergic neurons are more vulnerable to AD-related neuropathology than other types of neurons. To further explore the mechanisms behind the observed decrease of GABAergic neurons in 6 month-old TgCRND8 mice, we assessed the relative proportion of somatostatin (SOM), neuropeptide Y (NPY) and paravalbumin (PV) sub-types of GABAergic neurons at the regional and sub-regional level of the hippocampus. We found that NPY expressing GABAergic neurons were the most affected, as they were decreased in CA1-CA2 (pyramidal-, stratum oriens, stratum radiatum and molecular layers), CA3 (specifically in the stratum oriens) and dentate gyrus (specifically in the polymorphic layer) in TgCRND8 mice as compared to non-transgenic controls. SOM expressing GABAergic neurons were decreased in CA1-CA2 (specifically in the stratum oriens) and in the stratum radiatum of CA3, whereas PV neurons were significantly altered in stratum oriens sub-region of CA3. Taken together, these data provide new evidence for the relevance of hippocampal GABAergic neuronal network disruption as a mechanism underlying AD sequelae such as aberrant neuronal excitability, and further point to complex hippocampal regional and sub-regional variation in susceptibility to AD-related neuronal loss.

Neurogenesis and sensorimotor gating: bridging a microphenotype and an endophenotype.

Human genetic data on psychiatric disorders repeatedly demonstrate the involvement of various genes that are associated with neural development and neurogenesis. Neurogenesis is a biological process that is critical in brain development and continues throughout life. Neurogenesis is a multi-step process starting from the division of neural stem cells/progenitor cells, leading to self-renewal and simultaneously to the production of lineage-committed cells, including neurons and glial cells. Minor defects in the neurogenesis process, such as production of fewer new neurons and malformation of neural circuits, could represent phenotypes of psychiatric disorders at molecular and cellular levels in animal models (here termed as "microphenotypes"). However, microphenotypes are not easily used as biomarkers. We have focused on a physiological condition, sensorimotor gating deficits, that can be scored by a prepulse inhibition (PPI) test. Impaired PPI is considered to be one of the compelling endophenotypes (biological markers) of mental disorders such as schizophrenia, autism, and other neurodevelopmental disorders. Because the neural circuit for PPI involves the hippocampus, a unique brain region where neurogenesis occurs postnatally, we hypothesize that an impairment of preadolescent neurogenesis is critical for the onset of sensorimotor gating defects. To test this hypothesis, we investigated a critical period of neurogenesis that can affect PPI. In this paradigm, we introduced an enriched environment to restore neurogenesis, thereby recovering PPI deficits in mice. We noted impairments in the maturation of newborn neurons in the hippocampal dentate gyrus (DG) and GABAergic neurons in the hippocampus, which could be considered as microphenotypes associated with PPI defects. More precise genetically controlled neurogenesis models (with precise time points or periods) are needed to be studied in further investigation to support our hypothesis.

Interaction between CHL1 and serotonin receptor 2c regulates signal transduction and behavior in mice.

The serotonergic system plays important roles in multiple functions of the nervous system and its malfunctioning leads to neurological and psychiatric disorders. Here, we show that the cell adhesion molecule close homolog of L1 (CHL1), which has been linked to mental disorders, binds to a peptide stretch in the third intracellular loop of the serotonin 2c (5-HT2c) receptor through its intracellular domain. Moreover, we provide evidence that CHL1 deficiency in mice leads to 5-HT2c-receptor-related reduction in locomotor activity and reactivity to novelty, and that CHL1 regulates signaling pathways triggered by constitutively active isoforms of the 5-HT2c receptor. Furthermore, we found that the 5-HT2c receptor and CHL1 colocalize in striatal and hippocampal GABAergic neurons, and that 5-HT2c receptor phosphorylation and its association with phosphatase and tensin homolog (PTEN) and β-arrestin 2 is regulated by CHL1. Our results demonstrate that CHL1 regulates signal transduction pathways through constitutively active 5-HT2c receptor isoforms, thereby altering 5-HT2c receptor functions and implicating CHL1 as a new modulator of the serotonergic system.

Voltage-independent sodium channels emerge for an expression of activity-induced spontaneous spikes in GABAergic neurons.

BackgroundCerebral overexcitation needs inhibitory neurons be functionally upregulated to rebalance excitation vs. inhibition. For example, the intensive activities of GABAergic neurons induce spontaneous spikes, i.e., activity-induced spontaneous spikes (AISS). The mechanisms underlying AISS onset remain unclear. We investigated the roles of sodium channels in AISS induction and expression at hippocampal GABAergic neurons by electrophysiological approach.ResultsAISS expression includes additional spike capability above evoked spikes, and the full spikes in AISS comprise early phase (spikelets) and late phase, implying the emergence of new spikelet component. Compared with the late phase, the early phase is characterized as voltage-independent onset, less voltage-dependent upstroke and sensitivity to TTX. AISS expression and induction are independent of membrane potential changes. Therefore, AISS’s spikelets express based on voltage-independent sodium channels. In terms of AISS induction, the facilitation of voltage-gated sodium channel (VGSC) activation accelerates AISS onset, or vice versa.ConclusionAISS expression in GABAergic neurons is triggered by the spikelets based on the functional emergence of voltage-independent sodium channels, which is driven by intensive VGSCs’ activities.

Investigation of Synapse Formation and Function in a Glutamatergic-GABAergic Two-Neuron Microcircuit

Neural circuits are composed of mainly glutamatergic and GABAergic neurons, which communicate through synaptic connections. Many factors instruct the formation and function of these synapses; however, it is difficult to dissect the contribution of intrinsic cell programs from that of extrinsic environmental effects in an intact network. Here, we perform paired recordings from two-neuron microculture preparations of mouse hippocampal glutamatergic and GABAergic neurons to investigate how synaptic input and output of these two principal cells develop. In our reduced preparation, we found that glutamatergic neurons showed no change in synaptic output or input regardless of partner neuron cell type or neuronal activity level. In contrast, we found that glutamatergic input caused the GABAergic neuron to modify its output by way of an increase in synapse formation and a decrease in synaptic release efficiency. These findings are consistent with aspects of GABAergic synapse maturation observed in many brain regions. In addition, changes in GABAergic output are cell wide and not target-cell specific. We also found that glutamatergic neuronal activity determined the AMPA receptor properties of synapses on the partner GABAergic neuron. All modifications of GABAergic input and output required activity of the glutamatergic neuron. Because our system has reduced extrinsic factors, the changes we saw in the GABAergic neuron due to glutamatergic input may reflect initiation of maturation programs that underlie the formation and function of in vivo neural circuits.

Number and regional distribution of GAD65 mRNA-expressing interneurons in the rat hippocampal formation

In rodent models for neuropsychiatric disorders reduced number of hippocampal interneurons have been reported, but the total number of GABAergic neurons in the normal rat hippocampus is yet unknown. We used in situ hybridization method to label the 65 isoform of glutamic acid decarboxylase (GAD65) and counted the number of GAD65 mRNA-expressing neurons along the entire septo-temporal axis of the hippocampus. We found that 2/3 of the interneurons were in Ammon's horn (61,590) and 1/3 in the dentate gyrus (28,000). We observed the following numbers in Ammon's horn: CA3 area 33,400, CA2 area 4,190, CA1 area 24,000 and in the dentate gyrus: 6,000 in the molecular and 9,000 in the granule cell layers and 13,000 in the hilus. GAD65 mRNA-expressing neurons were significantly more numerous in dorsal than in ventral hippocampus. The ratio between interneurons and principal cells was lowest in the granule cell layer (0.9%) and highest in hilus (21%). In Ammon's horn this ratio was constant being 13% in CA3 and 8% in CA1-2 areas. In the entire hippocampal formation, the interneuron/principal cell ratio was 6%, with a significant difference between Ammon's horn (9.5%) and the dentate gyrus (2.8%) including the hilus. Such low ratios could suggest that even a limited loss of GABAergic neurons in the hippocampus may have a considerable functional impact.

Short-term episodes of hypoxia induce posthypoxic hyperexcitability and selective death of GABAergic hippocampal neurons

We have previously developed a rat hippocampal neuronal cell model for the registration of the preconditioning effect and posthypoxic hyperexcitability (Turovskaya et al., 2011). Repeated episodes of short-term hypoxia are reported to suppress the amplitude of Ca2+ response to NMDA in majority of neurons, reflecting the effect of preconditioning in the culture. In addition, exposure to hypoxia causes posthypoxic hyperexcitability: this is characterized by the onset of spontaneous synchronous Ca2+ transients in a population of neurons in a neural network during the period of reoxygenation after each hypoxic episode. The nature of this phenomenon is unknown, although it has been observed that there always exists a minority of neurons in which there is no effect of hypoxic preconditioning. In this small population of neurons, the amplitude of Ca2+ response to NMDA is not suppressed, but rather increases after each episode of hypoxia. Here we report the type of these neurons and their role in the generation of posthypoxic hyperexcitability. We compared the effect of short-term hypoxia on the amplitude of the Ca2+ response to NMDA and the Ca2+ transient generation in two populations of neurons — inhibitory GABAergic and excitatory glutamatergic. We have demonstrated that the neurons in which the preconditioning effect was not observed are GABAergic. Moreover at the instant moment of the posthypoxic synchronous Ca2+-transient generation (during reoxygenation) there is a global increase of [Ca2+]i and subsequent apoptosis in some GABAergic neurons. Anti-inflammatory cytokine interleukin-10 prevents the development of posthypoxic hyperexcitability, inhibiting the spontaneous synchronous Ca2+ transients. At the same time, interleukin-10 protects GABAergic neurons from death, by restoring the effect of hypoxic preconditioning in them. Activation of one of the signaling pathways initiated by interleukin-10 appears to be necessary for the development of hypoxic preconditioning in GABAergic neurons. Overall our results indicate that short-term episodes of hypoxia can damage GABAergic neurons and weaken the inhibitory action of GABAergic neurons in a neural network. Activation of PI3K-dependent survival signaling pathways in neurons of this type is a possible strategy to protect these cells against hypoxia.

Munc13-Independent Vesicle Priming at Mouse Photoreceptor Ribbon Synapses

Munc13 proteins are essential regulators of exocytosis. In hippocampal glutamatergic neurons, the genetic deletion of Munc13s results in the complete loss of primed synaptic vesicles (SVs) in direct contact with the presynaptic active zone membrane, and in a total block of neurotransmitter release. Similarly drastic consequences of Munc13 loss are detectable in hippocampal and striatal GABAergic neurons. We show here that, in the adult mouse retina, the two Munc13-2 splice variants bMunc13-2 and ubMunc13-2 are selectively localized to conventional and ribbon synapses, respectively, and that ubMunc13-2 is the only Munc13 isoform in mature photoreceptor ribbon synapses. Strikingly, the genetic deletion of ubMunc13-2 has little effect on synaptic signaling by photoreceptor ribbon synapses and does not prevent membrane attachment of synaptic vesicles at the photoreceptor ribbon synaptic site. Thus, photoreceptor ribbon synapses and conventional synapses differ fundamentally with regard to their dependence on SV priming proteins of the Munc13 family. Their function is only moderately affected by Munc13 loss, which leads to slight perturbations of signal integration in the retina.

Nerve Growth Factor in the Hippocamposeptal System: Evidence for Activity-Dependent Anterograde Delivery and Modulation of Synaptic Activity

Neurotrophins have been implicated in regulating neuronal differentiation, promoting neuronal survival, and modulating synaptic efficacy and plasticity. The prevailing view is that, depending on the target and mode of action, most neurotrophins can be trafficked and released either anterogradely or retrogradely in an activity-dependent manner. However, the prototypic neurotrophin, nerve growth factor (NGF), is not thought to be anterogradely delivered. Here we provide the neuroanatomical substrate for an anterograde hippocamposeptal transport of NGF by demonstrating its presence in mouse hippocampal GABAergic neurons and in their hippocamposeptal axons that ramify densely and abut neurons in the medial septum/diagonal band of Broca (MS/DB). We also demonstrate an activity-dependent increase in septal NGF levels that is dependent on the pattern of intrahippocampal stimulation. In addition, we show that acute exposure to NGF, via activation of TrkA, attenuates GABA(A) receptor-mediated inhibitory synaptic currents and reduces sensitivity to exogenously applied GABA. These acute actions of NGF display cell type and functional selectivity insofar as (1) they were found in cholinergic, but not GABAergic, MS/DB neurons, and (2) glutamate-mediated excitatory synaptic activity as well as AMPA-activated current responses were unaffected. Our results advocate a novel anterograde, TrkA-mediated NGF signaling in the CNS.

Hippocampal GABAergic Neurons are Susceptible to Amyloid-β Toxicity in vitro and are Decreased in Number in the Alzheimer's Disease TgCRND8 Mouse Model

The relevance of γ-amino-butyric acid (GABA)-ergic dysfunctions in the pathology of Alzheimer's disease (AD) remains a matter of debate. In the present study, we characterized the toxicity of amyloid-β (Aβ) on hippocampal GABAergic neurons both in vivo and in vitro. In the TgCRND8 mouse model of AD, we found a significant decrease in the number of hippocampal neurons immunoreactive for glutamate decarboxylase 67 (GAD67), the enzyme synthesizing GABA. This decrease, which was specific for hippocampal CA1-3 fields, was observed at 6 months of age, long after the overproduction of soluble Aβ42 (between 2 and 4 months) and accumulation of insoluble Aβ into amyloid plaques (between 4 and 6 months). In vitro, neurotoxicity was observed in primary hippocampal cultures 72 h following the addition of Aβ42 solutions containing a mixture of soluble oligomers. Taken together, our results suggest that when cultured and exposed to Aβ in vitro, GABAergic neurons are susceptible to Aβ42 neurotoxicity. However, in TgCRND8 mice, the number of GABAergic neurons is not altered up to 6 months, in spite of the massive Aβ load. Combined with the previously reported increased sensitivity to seizures observed in younger (1.5-2 month-old) TgCRND8 mice, it is likely that Aβ toxicity leads to GABAergic neuron dysfunction prior to their losses at a later stage.

Selective degeneration of septal and hippocampal GABAergic neurons in a mouse model of amyloidosis and tauopathy

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by brain accumulation of amyloid-β peptide and neurofibrillary tangles, which are believed to initiate a pathological cascade that results in progressive impairment of cognitive functions and eventual neuronal death. To obtain a mouse model displaying the typical AD histopathology of amyloidosis and tauopathy, we generated a triple-transgenic mouse line (TauPS2APP) by overexpressing human mutations of the amyloid precursor protein, presenilin2 and tau genes. Stereological analysis of TauPS2APP mice revealed significant neurodegeneration of GABAergic septo-hippocampal projection neurons as well as their target cells, the GABAergic hippocampal interneurons. In contrast, the cholinergic medial septum neurons remained unaffected. Moreover, the degeneration of hippocampal GABAergic interneurons was dependent on the hippocampal subfield and interneuronal subtype investigated, whereby the dentate gyrus and the NPY-positive interneurons, respectively, were most strongly affected. Neurodegeneration was also accompanied by a change in the mRNA expression of markers for inhibitory interneurons. In line with the loss of inhibitory neurons, we observed functional changes in TauPS2APP mice relative to WT mice, with strongly enhanced long-term potentiation in the medial-perforant pathway input to the dentate gyrus, and stereotypic hyperactivity. Our data indicate that inhibitory neurons are the targets of neurodegeneration in a mouse model of amyloidosis and tauopathy, thus pointing to a possible role of the inhibitory network in the pathophysiological and functional cascade of Alzheimer's disease.

Methamphetamine-Evoked Depression of GABAB Receptor Signaling in GABA Neurons of the VTA

Psychostimulants induce neuroadaptations in excitatory and fast inhibitory transmission in the ventral tegmental area (VTA). Mechanisms underlying drug-evoked synaptic plasticity of slow inhibitory transmission mediated by GABA(B) receptors and G protein-gated inwardly rectifying potassium (GIRK/Kir(3)) channels, however, are poorly understood. Here, we show that 1 day after methamphetamine (METH) or cocaine exposure both synaptically evoked and baclofen-activated GABA(B)R-GIRK currents were significantly depressed in VTA GABA neurons and remained depressed for 7 days. Presynaptic inhibition mediated by GABA(B)Rs on GABA terminals was also weakened. Quantitative immunoelectron microscopy revealed internalization of GABA(B1) and GIRK2, which occurred coincident with dephosphorylation of serine 783 (S783) in GABA(B2), a site implicated in regulating GABA(B)R surface expression. Inhibition of protein phosphatases recovered GABA(B)R-GIRK currents in VTA GABA neurons of METH-injected mice. This psychostimulant-evoked impairment in GABA(B)R signaling removes an intrinsic brake on GABA neuron spiking, which may augment GABA transmission in the mesocorticolimbic system.

The origin of neocortical nitric oxide synthase-expressing inhibitory neurons

Inhibitory neurons are critical for regulating effective transfer of sensory information and network stability. The precision of inhibitory function likely derives from the existence of a variety of interneuron subtypes. Their specification is largely dependent on the locale of origin of interneuron progenitors. Neocortical and hippocampal inhibitory neurons originate the subpallium, namely in the medial and caudal ganglionic eminences (MGE and CGE), and in the preoptic area (POA). In the hippocampus, neuronal nitric oxide synthase (nNOS)-expressing cells constitute a numerically large GABAergic interneuron population. On the contrary, nNOS-expressing inhibitory neurons constitute the smallest of the known neocortical GABAergic neuronal subtypes. The origins of most neocortical GABAergic neuron subtypes have been thoroughly investigated, however, very little is known about the origin of, or the genetic programs underlying the development of nNOS neurons. Here, we show that the vast majority of neocortical nNOS-expressing neurons arise from the MGE rather than the CGE. Regarding their molecular signature, virtually all neocortical nNOS neurons co-express the neuropeptides somatostatin (SST) and neuropeptide Y (NPY), and about half of them express the calcium-binding protein calretinin (CR). nNOS neurons thus constitute a small cohort of the MGE-derived SST-expressing population of cortical inhibitory neurons. Finally, we show that conditional removal of the transcription factor Sox6 in MGE-derived GABAergic cortical neurons results in an absence of SST and CR expression, as well as reduced expression of nNOS in neocortical nNOS neurons. Based on their respective abundance, origin and molecular signature, our results suggest that neocortical and hippocampal nNOS GABAergic neurons likely subserve different functions and have very different physiological relevance in these two cortical structures.

Role of CB1 cannabinoid receptors on GABAergic neurons in brain aging

Brain aging is associated with cognitive decline that is accompanied by progressive neuroinflammatory changes. The endocannabinoid system (ECS) is involved in the regulation of glial activity and influences the progression of age-related learning and memory deficits. Mice lacking the Cnr1 gene (Cnr1(-/-)), which encodes the cannabinoid receptor 1 (CB1), showed an accelerated age-dependent deficit in spatial learning accompanied by a loss of principal neurons in the hippocampus. The age-dependent decrease in neuronal numbers in Cnr1(-/-) mice was not related to decreased neurogenesis or to epileptic seizures. However, enhanced neuroinflammation characterized by an increased density of astrocytes and activated microglia as well as an enhanced expression of the inflammatory cytokine IL-6 during aging was present in the hippocampus of Cnr1(-/-) mice. The ongoing process of pyramidal cell degeneration and neuroinflammation can exacerbate each other and both contribute to the cognitive deficits. Deletion of CB1 receptors from the forebrain GABAergic, but not from the glutamatergic neurons, led to a similar neuronal loss and increased neuroinflammation in the hippocampus as observed in animals lacking CB1 receptors in all cells. Our results suggest that CB1 receptor activity on hippocampal GABAergic neurons protects against age-dependent cognitive decline by reducing pyramidal cell degeneration and neuroinflammation.

Endogenous SNAP-25 Regulates Native Voltage-gated Calcium Channels in Glutamatergic Neurons

In addition to its primary role as a fundamental component of the SNARE complex, SNAP-25 also modulates voltage-gated calcium channels (VGCCs) in various overexpression systems. Although these studies suggest a potential negative regulatory role of SNAP-25 on VGCC activity, the effects of endogenous SNAP-25 on native VGCC function in neurons are unclear. In the present study, we investigated the VGCC properties of cultured glutamatergic and GABAergic rat hippocampal neurons. Glutamatergic currents were dominated by P/Q-type channels, whereas GABAergic cells had a dominant L-type component. Also, glutamatergic VGCC current densities were significantly lower with enhanced inactivation rates and shifts in the voltage dependence of activation and inactivation curves compared with GABAergic cells. Silencing endogenous SNAP-25 in glutamatergic neurons did not alter P/Q-type channel expression or localization but led to increased VGCC current density without changes in the VGCC subtype proportions. Isolation of the P/Q-type component indicated that increased current in the absence of SNAP-25 was correlated with a large depolarizing shift in the voltage dependence of inactivation. Overexpressing SNAP-25 in GABAergic neurons reduced current density without affecting the VGCC subtype proportion. Accordingly, VGCC current densities in glutamatergic neurons from Snap-25(+/-) mice were significantly elevated compared with wild type glutamatergic neurons. Overall, this study demonstrates that endogenous SNAP-25 negatively regulates native VGCCs in glutamatergic neurons which could have important implications for neurological diseases associated with altered SNAP-25 expression.

NaV1.1 channels and epilepsy

Voltage-gated sodium channels initiate action potentials in brain neurons, and sodium channel blockers are used in therapy of epilepsy. Mutations in sodium channels are responsible for genetic epilepsy syndromes with a wide range of severity, and the NaV1.1 channel encoded by the SCN1A gene is the most frequent target of mutations. Complete loss-of-function mutations in NaV1.1 cause severe myoclonic epilepsy of infancy (SMEI or Dravet's Syndrome), which includes severe, intractable epilepsy and comorbidities of ataxia and cognitive impairment. Mice with loss-of-function mutations in NaV1.1 channels have severely impaired sodium currents and action potential firing in hippocampal GABAergic inhibitory neurons without detectable effect on the excitatory pyramidal neurons, which would cause hyperexcitability and contribute to seizures in SMEI. Similarly, the sodium currents and action potential firing are also impaired in the GABAergic Purkinje neurons of the cerebellum, which is likely to contribute to ataxia. The imbalance between excitatory and inhibitory transmission in these mice can be partially corrected by compensatory loss-of-function mutations of NaV1.6 channels, and thermally induced seizures in these mice can be prevented by drug combinations that enhance GABAergic neurotransmission. Generalized epilepsy with febrile seizures plus (GEFS+) is caused by missense mutations in NaV1.1 channels, which have variable biophysical effects on sodium channels expressed in non-neuronal cells, but may primarily cause loss of function when expressed in mice. Familial febrile seizures is caused by mild loss-of-function mutations in NaV1.1 channels; mutations in these channels are implicated in febrile seizures associated with vaccination; and impaired alternative splicing of the mRNA encoding these channels may also predispose some children to febrile seizures. We propose a unified loss-of-function hypothesis for the spectrum of epilepsy syndromes caused by genetic changes in NaV1.1 channels, in which mild impairment predisposes to febrile seizures, intermediate impairment leads to GEFS+ epilepsy, and severe or complete loss of function leads to the intractable seizures and comorbidities of SMEI.

Cell Type-Specific Long-Term Plasticity at Glutamatergic Synapses onto Hippocampal Interneurons Expressing either Parvalbumin or CB1Cannabinoid Receptor

Different GABAergic interneuron types have specific roles in hippocampal function, and anatomical as well as physiological features vary greatly between interneuron classes. Long-term plasticity of interneurons has mostly been studied in unidentified GABAergic cells and is known to be very heterogeneous. Here we tested whether cell type-specific plasticity properties in distinct GABAergic interneuron types might underlie this heterogeneity. We show that long-term potentiation (LTP) and depression (LTD), two common forms of synaptic plasticity, are expressed in a highly cell type-specific manner at glutamatergic synapses onto hippocampal GABAergic neurons. Both LTP and LTD are generated in interneurons expressing parvalbumin (PV+), whereas interneurons with similar axon distributions but expressing cannabinoid receptor-1 show no lasting plasticity in response to the same protocol. In addition, LTP or LTD occurs in PV+ interneurons with different efferent target domains. Perisomatic-targeting PV+ basket and axo-axonic interneurons express LTP, whereas glutamatergic synapses onto PV+ bistratified cells display LTD. Both LTP and LTD are pathway specific, independent of NMDA receptors, and occur at synapses with calcium-permeable (CP) AMPA receptors. Plasticity in interneurons with CP-AMPA receptors strongly modulates disynaptic GABAergic transmission onto CA1 pyramidal cells. We propose that long-term plasticity adjusts the synaptic strength between pyramidal cells and interneurons in a cell type-specific manner and, in the defined CA1 interneurons, shifts the spatial pattern of inhibitory weight from pyramidal cell dendrites to the perisomatic region.

OBTURATOR NERVE INJURY DURING ROBOTIC ASSISTED RADICAL CYSTECTOMY: RECOGNITION OF INJURY AND ROBOTIC REPAIR

Citron-N (citron) binds activated Rho and concentrates at excitatory postsynaptic densities on the smooth dendritic shafts of hippocampal GABAergic neurons. Since little is known about how cytoplasmic proteins become targeted and retained at synapses, we asked how citron attains this discrete distribution. We first sought to determine whether the synaptic localization machinery is unique to GABAergic interneurons, but in neurons cultured from either cerebral cortex or hippocampus, low levels of citron are found in a small population of glutamatergic neurons concentrated at the tips of dendritic spines in addition to shaft synapses. These data suggest that the targeting domains in citron can be utilized appropriately by any neuron, and consistent with this idea, tagged, exogenous, full-length citron becomes concentrated at postsynaptic sites in all hippocampal neurons in which it is introduced. Citron contains multiple sites for protein–protein interaction, including coiled-coil, pleckstrin homology, cysteine-rich zinc binding and CMG domains, as well as a proline-rich region and a PDZ binding tail that is known to interact with PSD-95/SAP90. Using citron deletion mutants, we find that the coiled-coil (CC) domain, located in the N-terminal half of the protein, mediates somatodendritic targeting, self-oligomerization and puncta formation independent of the Rho binding domain, while regions in the C-terminal half of citron are responsible for precise alignment of postsynaptic citron clusters at sites apposing presynaptic boutons. Rho binding and activation regulate membrane targeting and the number of synapses containing citron. Thus, citron's clustering at postsynaptic membranes is mediated by multiple domains, and its synaptic distribution is modified in response to Rho activation.

Distribution and neurochemical characterization of neurons expressing GIRK channels in the rat brain

G-protein inwardly rectifying potassium (GIRK) channels mediate the synaptic actions of numerous neurotransmitters in the mammalian brain and play an important role in the regulation of neuronal excitability in most brain regions through activation of various G-protein-coupled receptors such as the serotonin 5-HT(1A) receptor. In this report we describe the localization of GIRK1, GIRK2, and GIRK3 subunits and 5-HT(1A) receptor in the rat brain, as assessed by immunohistochemistry and in situ hybridization. We also analyze the co-expression of GIRK subunits with the 5-HT(1A) receptor and cell markers of glutamatergic, gamma-aminobutyric acid (GABA)ergic, cholinergic, and serotonergic neurons in different brain areas by double-label in situ hybridization. The three GIRK subunits are widely distributed throughout the brain, with an overlapping expression in cerebral cortex, hippocampus, paraventricular nucleus, supraoptic nucleus, thalamic nuclei, pontine nuclei, and granular layer of the cerebellum. Double-labeling experiments show that GIRK subunits are present in most of the 5-HT(1A) receptor-expressing cells in hippocampus, cerebral cortex, septum, and dorsal raphe nucleus. Similarly, GIRK mRNA subunits are found in glutamatergic and GABAergic neurons in hippocampus, cerebral cortex, and thalamus, in cholinergic cells in the nucleus of vertical limb of the diagonal band, and in serotonergic cells in the dorsal raphe nucleus. These results provide a deeper knowledge of the distribution of GIRK channels in different cell subtypes in the rat brain and might help to elucidate their physiological roles and to evaluate their potential involvement in human diseases.