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Somatostatin cells are frequently described as a major population of GABAergic neurons in the cerebral cortex. In this study, we performed a comprehensive analysis of their molecular expression, morphological features, and laminar distribution. We provided a detailed description of somatostatin neurons in the human prefrontal cortex, including their proportion in the total neuron population, laminar distribution, neurotransmitter phenotype, as well as their molecular and morphological characteristics using immunofluorescence and RNAscope in situ hybridization. We found that somatostatin neurons comprise around 7% of neocortical neurons in the human Brodmann areas 9 and 14r, without significant difference between the two regions. Somatostatin cells were NeuN positive and synthesized vesicular GABA transporter and glutamate decarboxylase 1 and 2, confirming their neuronal nature and GABAergic phenotype. Somatostatin cells in the upper cortical layers were small, had a high expression of somatostatin mRNA, a relatively low expression of somatostatin peptide, and co-expressed calbindin. In the lower cortical layers, somatostatin cells were larger with complex somato-dendritic morphology, typically showed a lower expression of somatostatin mRNA and a high expression of somatostatin peptide, and co-expressed neuronal nitric oxide synthase (nNOS) and neuropeptide Y (NPY), but not calbindin. Somatostatin neurons in the white matter co-expressed MAP2. Based on their somato-dendritic morphology, cortical somatostatin neurons could be classified into at least five subtypes. The somatostatin neurons of the human prefrontal cortex show remarkable morphological and molecular complexity, which implies that they have equally complex and distinct functions in the human brain. [ABSTRACT FROM AUTHOR]

Several studies suggest that neurons from the lateral region of the SuM (SuML) innervating the dorsal dentate gyrus (DG) display a dual GABAergic and glutamatergic transmission and are specifically activated during paradoxical (REM) sleep (PS). The objective of the present study is to characterize the anatomical, neurochemical and electrophysiological properties of the SuML-DG projection neurons and to determine how they control DG oscillations and neuronal activation during PS and other vigilance states. For this purpose, we combine structural connectivity techniques using neurotropic viral vectors (rabies virus, AAV), neurochemical anatomy (immunohistochemistry, in situ hybridization) and imaging (light, electron and confocal microscopy) with in vitro (patch clamp) and in vivo (LFP, EEG) optogenetic and electrophysiological recordings performed in transgenic VGLUT2-cre male mice. At the cellular level, we show that the SuML-DG neurons co-release GABA and glutamate on dentate granule cells and increase the activity of a subset of DG granule cells. At the network level, we show that activation of the SuML-DG pathway increases theta power and frequency during PS as well as gamma power during PS and waking in the DG. At the behavioral level, we show that the activation of this pathway does not change animal behavior during PS, induces awakening during slow wave sleep and increases motor activity during waking. These results suggest that the SuML-DG pathway is capable of supporting the increase of theta and gamma power in the DG observed during PS and plays an important modulatory role of DG network activity during this state. [ABSTRACT FROM AUTHOR]

The striatum, the main input structure of the basal ganglia, is critical for action selection and adaptive motor control. To understand the neuronal mechanisms underlying these functions, an analysis of microcircuits that compose the striatum is necessary. Among these, cholinergic interneurons (ChIs) provide intrinsic striatal innervation whose dysfunction is implicated in neuropsychiatric diseases, such as Parkinson's disease and Tourette syndrome. The ability to experimentally manipulate the activity of ChIs is critical to gain insights into their contribution to the normal function of the striatum and the emergence of behavioral abnormalities in pathological states. In this study, we generated and tested CAV-pChAT-GFP, a replication-defective canine adenovirus type 2 (CAV-2) vector carrying the green fluorescent protein (GFP) sequence under the control of the human choline acetyltransferase (ChAT) promoter. We first tested the potential specificity of CAV-pChAT-GFP to label striatal ChIs in a rat before performing experiments on two macaque monkeys. In the vector-injected rat and monkey striatum, we found that GFP expression preferentially colocalized with ChAT-immunoreactivity throughout the striatum, including those from local circuit interneurons. CAV-2 vectors containing transgene driven by the ChAT promoter provide a powerful tool for investigating ChI contributions to circuit function and behavior in nonhuman primates. [ABSTRACT FROM AUTHOR]

Psychoactive drugs used during pregnancy can affect the development of the brain of offspring, directly triggering neurological disorders or increasing the risk for their occurrence. Caffeine is the most widely consumed psychoactive drug, including during pregnancy. In Wild type mice, early life exposure to caffeine renders offspring more susceptible to seizures. Here, we tested the long-term consequences of early life exposure to caffeine in THY-Tau22 transgenic mice, a model of Alzheimer's disease-like Tau pathology. Caffeine exposed mutant offspring developed cognitive earlier than water treated mutants. Electrophysiological recordings of hippocampal CA1 pyramidal cells in vitro revealed that early life exposure to caffeine changed the way the glutamatergic and GABAergic drives were modified by the Tau pathology. We conclude that early-life exposure to caffeine affects the Tau phenotype and we suggest that caffeine exposure during pregnancy may constitute a risk-factor for early onset of Alzheimer's disease-like pathology. [ABSTRACT FROM AUTHOR]

Dopamine activity in anterior cingulate cortex (ACC) is essential for various aspects of instrumental behavior, including learning and effort based decision making. To dissociate learning from physical effort, we studied both observational (covert) learning, and trial-and-error (overt) learning. If ACC dopamine activity is required for task acquisition, its blockade should impair both overt and covert learning. If dopamine is not required for task acquisition, but solely for regulating the willingness to expend effort for reward, i.e., effort tolerance, blockade should impair overt learning but spare covert learning. Rats learned to push a lever for food rewards either with or without prior observation of an expert conspecific performing the same task. Before daily testing sessions, the rats received bilateral ACCmicroinfusions of SCH23390, a dopamine D1 receptor antagonist, or saline-control infusions. We found that dopamine blockade suppressed overt responding selectively, leaving covert task acquisition through observational learning intact. In subsequent testing sessions without dopamine blockade, rats recovered their overt-learning capacity but not their pre-treatment level of effort tolerance. These results suggest that ACC dopamine is not required for the acquisition of conditioned behaviors and that apparent learning impairments could instead reflect a reduced level of willingness to expend effort due to cortical dopamine blockade. [ABSTRACT FROM AUTHOR]

In mesial temporal lobe epilepsy (MTLE), spontaneous seizures likely originate from a multi-structural epileptogenic zone, including several regions of the limbic system connected to the hippocampal formation. In this study, we investigate the structural connectivity between the supramammillary nucleus (SuM) and the dentate gyrus (DG) in the model of MTLE induced by pilocarpine in the rat. This hypothalamic nucleus, which provides major extracortical projections to the hippocampal formation, plays a key role in the regulation of several hippocampus-dependent activities, including theta rhythms, memory function and emotional behavior, such as stress and anxiety, functions that are known to be altered in MTLE. Our findings demonstrate a marked reorganization of DG afferents originating from the SuM in pilocarpine-treated rats. This reorganization, which starts during the latent period, is massive when animals become epileptic and continue to evolve during epilepsy. It is characterized by an aberrant distribution and an increased number of axon terminals from neurons of both lateral and medial regions of the SuM, invading the entire inner molecular layer of the DG. This reorganization, which reflects an axon terminal sprouting from SuM neurons, could contribute to trigger spontaneous seizures within an altered hippocampal intrinsic circuitry. [ABSTRACT FROM AUTHOR]

The dorsoventral and developmental gradients of entorhinal layer II cell grid properties correlate with their resonance properties and with their hyperpolarization-activated cyclic nucleotide-gated (HCN) ion channel current characteristics. We investigated whether such correlation existed in rat hippocampal CA1 pyramidal cells, where place fields also show spatial and temporal gradients. Resonance was absent during the first postnatal week, and emerged during the second week. Resonance was stronger in dorsal than ventral cells, in accord with HCN current properties. Resonance responded to cAMP in ventral but not in dorsal cells. The dorsoventral distribution of HCN1 and HCN2 subunits and of the auxiliary protein tetratricopeptide repeat-containing Rab8b-interacting protein (TRIP8b) could account for these differences between dorsal and ventral cells. The analogous distribution of the intrinsic properties of entorhinal stellate and hippocampal cells suggests the existence of general rules of organization among structures that process complementary features of the environment. [ABSTRACT FROM AUTHOR]

We used a pathophysiological model of temporal lobe epilepsy induced by pilocarpine in adult rats in order to assess the in vivo role of drebrin A (DA), one of the major regulators of F-actin. This model displays a dynamic reorganization of the glutamatergic network including neo-spinogenesis, morphogenesis, and neo-synaptogenesis associated with an aberrant sprouting of granule cell axons in the dentate gyrus (DG). This reactive plasticity contributes in dentate granule-cell hyperexcitability that could lead to the emergence of recurrent spontaneous seizures. We investigated the hippocampal DA expression changes in pilocarpine animals using immunohistochemical, Western blot, and in situ hybridization analyses. We showed that DA immunoreactivity was decreased in the inner molecular layer (IML) and in the hilus (H) of the DG, at latent stage, when spinogenesis and morphogenesis occur. Western blot analysis confirmed these overall hippocampal decreases of DA protein expression. At chronic stage, when newly formed glutamatergic synapses are being established, the levels of immunolabeling for DA in the H and the IML were similar to control rats. This recovery is likely due to the increase of DA mRNA in perikarya of hilar and granule cells. Interestingly, our data showed that the changes pattern of labeling for Bassoon, a specific marker for presynaptic active zone, in the IML of pilocarpine-treated animals paralleled those found for DA at all time points examined. Furthermore, our double and triple immunofluorescence studies showed that the recovery in DA levels in the IML occurred within the dendritic spines involved in glutamatergic active synapses of presumed granule cells. Altogether, our results indicate that in vivo DA is not critical for spinogenesis and morphogenesis but instead is consistent with an involvement in synaptic structural integrity, stabilization, and function. Thus, DA appears as a novel modulator of reactive synaptic plasticity associated with epilepsy. © 2011 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Objective: Enduring, abnormal expression and function of the ion channel hyperpolarization-activated cyclic adenosine monophosphate gated channel type 1 (HCN1) occurs in temporal lobe epilepsy (TLE). We examined the underlying mechanisms, and investigated whether interfering with these mechanisms could modify disease course. Methods: Experimental TLE was provoked by kainic acid-induced status epilepticus (SE). HCN1 channel repression was examined at mRNA, protein, and functional levels. Chromatin immunoprecipitation was employed to identify the transcriptional mechanism of repressed HCN1 expression, and the basis for their endurance. Physical interaction of the repressor, NRSF, was abolished using decoy oligodeoxynucleotides (ODNs). Video/electroencephalographic recordings were performed to assess the onset and initial pattern of spontaneous seizures. Results: Levels of NRSF and its physical binding to the Hcn1 gene were augmented after SE, resulting in repression of HCN1 expression and HCN1-mediated currents (Ih), and reduced Ih-dependent resonance in hippocampal CA1 pyramidal cell dendrites. Chromatin changes typical of enduring, epigenetic gene repression were apparent at the Hcn1 gene within a week after SE. Administration of decoy ODNs comprising the NRSF DNA-binding sequence (neuron restrictive silencer element [NRSE]), in vitro and in vivo, reduced NRSF binding to Hcn1, prevented its repression, and restored Ih function. In vivo, decoy NRSE ODN treatment restored theta rhythm and altered the initial pattern of spontaneous seizures. Interpretation: Acquired HCN1 channelopathy derives from NRSF-mediated transcriptional repression that endures via chromatin modification and may provide insight into the mechanisms of a number of channelopathies that coexist with, and may contribute to, the conversion of a normal brain into an epileptic one. ANN NEUROL 2011;70: 454-464. [ABSTRACT FROM AUTHOR]

The supramammillary nucleus (SuM) provides substantial projections to the hippocampal formation. This hypothalamic structure is involved in the regulation of hippocampal theta rhythm and therefore the control of hippocampal-dependent cognitive functions as well as emotional behavior. A major goal of this study was to characterize the neurotransmitter identity of the SuM–hippocampal pathways. Our findings demonstrate two distinct neurochemical pathways in rat. The first pathway originates from neurons in the lateral region of the SuM and innervates the supragranular layer of the dorsal dentate gyrus and, to a much lesser extent, the ventral dentate gyrus. This pathway displays a unique dual phenotype for GABAergic and glutamatergic neurotransmission. Axon terminals contain markers of GABAergic neurotransmission, including the synthesizing enzyme of GABA, glutamate decarboxylase 65, and the vesicular GABA transporter and also a marker of glutamatergic neurotransmission, the vesicular glutamate transporter 2. The second pathway originates from neurons in the most posterior and medial part of the SuM and innervates exclusively the inner molecular layer of the ventral dentate gyrus and the CA2/CA3a pyramidal cell layer of the hippocampus. The axon terminals from the medial part of the SuM contain the vesicular glutamate transporter 2 only. These data demonstrate for the first time the heterogeneity of the SuM–hippocampal pathways, not only from an anatomical but also a neurochemical point of view. These pathways, implicated in different neuronal networks, could modulate different hippocampal activities. They are likely to be involved differently in the regulation of hippocampal theta rhythm and associated cognitive functions as well as emotional behavior. [ABSTRACT FROM AUTHOR]

Patients with temporal lobe epilepsy (TLE), the most common form of epilepsy in adults, often display cognitive deficits. The time course and underlying mechanisms of cognitive decline remain unknown during epileptogenesis (the process leading to epilepsy). Using the rat pilocarpine model of TLE, we performed a longitudinal study to assess spatial and nonspatial cognitive performance during epileptogenesis. In parallel, we monitored interictal-like activity (ILA) in the hippocampal CA1 region, as well as theta oscillations, a brain rhythm central to numerous cognitive processes. Here, we report that spatial memory was altered soon after pilocarpine-induced status epilepticus, i.e., already during the seizure-free, latent period. Spatial deficits correlated with a decrease in the power of theta oscillations but not with the frequency of ILA. Spatial deficits persisted when animals had spontaneous seizures (chronic stage) without further modification. In contrast, nonspatial memory performances remained unaffected throughout. We conclude that the reorganization of hippocampal circuitry that immediately follows the initial insult can affect theta oscillation mechanisms, in turn, resulting in deficits in hippocampusdependent memory tasks. These deficits may be dissociated from the process that leads to epilepsy itself but could instead constitute, as ILA, early markers in at-risk patients and/or provide beneficial therapeutic targets. [ABSTRACT FROM AUTHOR]

Temporal Lobe Epilepsy (TLE) is often preceded by a latent (seizure-free) period during which complex network reorganizations occur. In experimental epilepsy, network hyperexcitability is already present during the latent period, suggesting a modification of information processing. The purpose of this study was to assess the input/output relationship in the hippocampal CA1 region during epileptogenesis. Field recordings in strata pyramidale and radiatum were used to measure the output of CA1 pyramidal cells as a function of the synaptic inputs they receive following the stimulation of Shaffer collaterals in slices obtained from sham and pilocarpine-treated animals during the latent and chronic periods. We show that there is a transient increase of the input and output field responses during the latent period as compared to sham and epileptic animals. The coupling between excitatory inputs and cell firing was also increased during the latent period. This increase persisted in epileptic animals, although to a lesser extent. We also confirm that paired-pulse facilitation occurs before the chronic phase. The present data further support the view that hyperexcitability is present at an early stage of epileptogenesis. Network output is more facilitated during the latent than during the chronic period. Hyperexcitability may participate to epileptogenesis, but it is not sufficient in itself to produce seizures. [ABSTRACT FROM AUTHOR]

An increased ratio of the glutamatergic drive to the overall glutamatergic/GABAergic drive characterizes the chronic stage of temporal lobe epilepsy (TLE), but it is unclear whether this modification is present during the latent period that often precedes the epileptic stage. Using the pilocarpine model of TLE in rats, we report that this ratio is decreased in hippocampal CA1 pyramidal cells during the early phase of the latent period (3–5 days post pilocarpine). It is, however, increased during the late phase of the latent period (7–10 days post pilocarpine), via cell domain-dependent alterations in synaptic current properties, concomitant with the occurrence of interictal-like activity in vivo. During the late latent period, the glutamatergic drive was increased in somata via an enhancement in EPSC decay time constant and in dendrites via an increase in EPSC frequency and amplitude. The GABAergic drive remained unchanged in the soma but was decreased in dendrites, since the drop off in IPSC frequency was more marked than the increase in IPSC kinetics. Theoretical considerations suggest that these modifications are sufficient to produce interictal-like activity. In epileptic animals, the ratio of the glutamatergic drive to the overall synaptic drive was not further modified, despite additional changes in synaptic current frequency and kinetics. These results show that the global changes to more glutamatergic and less GABAergic activities in the CA1 region precede the chronic stage of epilepsy, possibly facilitating the occurrence and/or the propagation of interictal activity. [ABSTRACT FROM AUTHOR]

GABAergic interneurons play diverse and important roles in controlling neuronal network dynamics. They are characterized by an extreme heterogeneity morphologically, neurochemically, and physiologically, but a functionally relevant classification is still lacking. Present taxonomy is essentially based on their postsynaptic targets, but a physiological counterpart to this classification has not yet been determined. Using a quantitative analysis based on multidimensional clustering of morphological and physiological variables, we now demonstrate a strong correlation between the kinetics of glutamate and GABA miniature synaptic currents received by CA1 hippocampal interneurons and the laminar distribution of their axons: neurons that project to the same layer(s) receive synaptic inputs with similar kinetics distributions. In contrast, the kinetics distributions of GABAergic and glutamatergic synaptic events received by a given interneuron do not depend upon its somatic location or dendritic arborization. Although the mechanisms responsible for this unexpected observation are still unclear, our results suggest that interneurons may be programmed to receive synaptic currents with specific temporal dynamics depending on their targets and the local networks in which they operate. © 2006 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

We have previously shown that, in HEK 293 cells, overexpression of acidic calponin, an actin-binding protein, induces remodeling of actin filaments, leading to a change in cell morphology. In addition, this protein is found in dendritic spines of adult hippocampal neurons. We hypothesized that this protein plays a role in regulating actin-based filaments during dendritic spine plasticity. To assess this hypothesis, the pilocarpine model of temporal lobe epilepsy was selected because an important reorganization of the glutamatergic network, which includes an aberrant sprouting of granule cell axons, neo-synaptogenesis, and dendritic spine remodeling, is well established in the dentate gyrus. This reorganization begins after the initial period of status epilepticus after pilocarpine injection, during the silent period when animals display a normal behavior, and reaches a plateau at the chronic stage when the animals have developed spontaneous recurrent seizures. Our data show that the intensity of immunolabeling for acidic calponin was clearly increased in the inner one-third of the molecular layer of the dentate gyrus, the site of mossy fiber sprouting, and neo-synaptogenesis, at 1 and 2 weeks after pilocarpine injection (silent period) when the reorganization was taking place. In contrast, in chronic pilocarpine-treated animals, when the reorganization was established, the levels of labeling for acidic calponin in the inner molecular layer were similar to those observed in control rats. In addition, double immunostaining studies suggested that the increase in acidic calponin levels occurred within the dendritic spines. Altogether, these results are consistent with an involvement of acidic calponin in dendritic spine plasticity. © 2003 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Specific subunits of γ-aminobutyric acid (GABA)A receptors may be regulated differentially in animal models of temporal lobe epilepsy during the chronic stage. Although several subunits may be upregulated, other subunits may be downregulated in the hippocampal formation. The α5 subunit is of particular interest because of its relatively selective localization in the hippocampus and its potential role in tonic inhibition. In normal rats, immunolabeling of the α5 subunit was high in the dendritic layers of CA1 and CA2 and moderate in these regions of CA3. In chronic pilocarpine-treated rats displaying recurrent seizures, α5 subunit-labeling was substantially decreased in CA1 and nearly absent in CA2. Only slight decreases in immunolabeling were evident in CA3. In situ hybridization studies demonstrated that the α5 subunit mRNA was also strongly decreased in stratum pyramidale of CA1 and CA2. Thus, the alterations in localization of the α5 subunit peptide and its mRNA were highly correlated. The large decreases in labeling of the α5 subunit did not appear to be related to loss of pyramidal neurons in CA1 or CA2 since these neurons were generally preserved in pilocarpine-treated animals. No comparable decreases in labeling of the α2 subunit of the GABAA receptor were detected. These findings indicate that the α5 subunit of the GABAA receptor is capable of substantial and prolonged downregulation in remaining pyramidal neurons in a model of temporal lobe epilepsy. The results raise the possibility that presumptive extrasynaptic GABAA receptor subunits, such as the α5 subunit, may be regulated differently than synaptically located subunits, such as the α2 subunit, within the same brain regions in some pathological conditions. Hippocampus 2003;13:633-645. © 2003 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

We studied the modulation of GABAergic inhibition by glutamate and kainate acting on GluR5-containing kainate receptors in the CA1 hippocampal region. Glutamate, kainate or ATPA, a selective agonist of GluR5-containing receptors, generates an inward current in inhibitory interneurons and cause repetitive action potential firing. This results in a massive increase of tonic GABAergic inhibition in the somata and apical dendrites of pyramidal neurons. These effects are prevented by the GluR5 antagonist LY 293558. Electrical stimulation of excitatory afferents generates kainate receptor-mediated excitatory postsynaptic currents (EPSCs) and action potentials in identified interneurons that project to the dendrites and somata of pyramidal neurons. Therefore glutamate acting on kainate receptors containing the GluR5 subunit may provide a protective mechanism against hyperexcitability. [ABSTRACT FROM AUTHOR]

Drebrin A, one of the most abundant neuron-specific F-actin-binding proteins, is found exclusively in dendrites and is particularly concentrated in dendritic spines receiving excitatory inputs. We investigated the role of drebrin A in synaptic transmission and found that overexpression of drebrin A augmented the glutamatergic synaptic transmission, probably through an increase of active synaptic site density. Interestingly, overexpression of drebrin A also affected the frequency, amplitude and kinetics of miniature inhibitory postsynaptic currents (mIPSCs), despite the fact that GABAergic synapse density and transmission efficacy were not modified. Downregulation of drebrin A led to a decrease of both glutamatergic and GABAergic synaptic activity. In heterologous cells, drebrin A reorganized and stabilized F-actin and these effects were mediated by its actin-binding domain. Thus, drebrin A might regulate dendritic spine morphology via regulation of actin cytoskeleton remodeling and dynamics. Our data demonstrate for the first time that drebrin A modulates glutamatergic and GABAergic synaptic activities. [ABSTRACT FROM AUTHOR]