Gamma-aminobutyric Acid Neurons Research Articles

Pharmacological Antagonism of T-Type Calcium Channels Constrains Rebound Burst Firing in Two Distinct Subpopulations of GABA Neurons in the Rat Ventral Tegmental Area: Implications for α-Lipoic Acid.

The ventral tegmental area (VTA) is a midbrain region highly involved in motivation and reward. A large body of work has investigated synaptic plasticity and ion channel excitability in this area, which has strong implication in drug abuse. We recently provided electrophysiological and pharmacological evidence that the CaV3.1 isoform of T-type voltage-gated calcium channels contributes to the excitability of VTA dopamine (DA) neurons. However, the role of T-channels in excitability of VTA gamma-amino-butyric acid (GABA) neurons remained unaddressed. Here, with a population study of rat VTA GABA neurons, we provide evidence that T-channels contribute to rebound spiking activity in two phenotypically distinct subpopulations of GABAergic neurons, each with differing electrophysiological characteristics. Additionally, we provide the first study to investigate the effect of α-lipoic acid (ALA) on ion channels in mesolimbic reward circuitry. Taken together, our population study and pharmacology experiments implicate T-channels as a target for therapies aimed at tempering VTA and mesolimbic circuit excitability.

The undeveloped properties of GABA neurons in the ventral tegmental area promote energy intake for growth in juvenile rats

Juvenile animals show higher energy intake (EI) per body weight (BW) to meet the energy requirements for growth. However, the underlying mechanisms that induce high EI/BW in juvenile animals remain unknown. The EI from a control diet (CD) and high fat diet (HFD), as well as BW changes were compared between juvenile (3 weeks old) and adult (8 weeks old) rats. BW gain and EI were increased in the HFD-fed adult rats compared to the CD-fed adult rats. However, in the juvenile rats, there were no differences in BW gain and EI between the CD-fed and HFD-fed groups. The locomotor activity was significantly increased in HFD group compared with the CD group in juvenile, but not in adult rats. Gamma-aminobutyric acid (GABA) neurons in the VTA were found to remain undeveloped with less GABAergic input into dopamine neurons in the juvenile rats. The deletion of the VTA GABA neurons in the adult rats significantly increased CD consumption, but showed almost no change in HFD consumption. These data suggest that undeveloped properties of VTA GABA neurons in juvenile rats can promote higher EI regardless of high or less palatable feeding, and contribute to growth promotion.

Investigation of the Role of AT2 Receptors in the Nucleus Tractus Solitarii of Normotensive Rats in Blood Pressure Control.

AimThe nucleus tractus solitarii (NTS) densely expresses angiotensin II type 2 receptors (AT2R), which are mainly located on inhibitory gamma-aminobutyric acid (GABA) neurons. Central AT2R stimulation reduces blood pressure, and AT2R stimulation in the rostral ventrolateral medulla (RVLM), mediates a hypotensive response through a GABAergic mechanism. We aimed to test the hypothesis that an AT2R mediated inhibition of the GABA release within the NTS might be involved in this hypotensive response, by assessing possible alterations in blood pressure and heart rate, as well as in GABA levels in normotensive Wistar rats.MethodsIn vivo microdialysis was used for measurement of extracellular GABA levels and for perfusion of the selective AT2R agonist, Compound 21, within the NTS. Our set-up allowed to determine simultaneously the excitatory glutamate dialysate levels. The mean arterial pressure and heart rate responses were monitored with a pressure transducer.ResultsLocal perfusion of Compound 21 into the NTS did not modify blood pressure and heart rate, nor glutamate and GABA levels compared to baseline concentrations. A putative effect was also not unmasked by concomitant angiotensin II type 1 receptor blockade with candesartan. Positive control experiments confirmed that the experimental set up had enough sensitivity to detect a reduction in GABA dialysate levels and blood pressure.ConclusionThe results did not provide evidence for a role of the AT2R within the NTS in the control of blood pressure, nor for an interaction with local GABAergic signaling in normotensive rats.

Effects of GABA and Leptin Receptor-Expressing Neurons in the Lateral Hypothalamus on Feeding, Locomotion, and Thermogenesis.

ObjectiveThe lateral hypothalamus (LH) is known for its role in feeding, and it also regulates other aspects of energy homeostasis. How genetically defined LH neuronal subpopulations mediate LH effects on energy homeostasis remains poorly understood. The behavioral effects of chemogenetically activating LH gamma‐aminobutyric acid (GABA) and the more selective population of LH GABA neurons that coexpress the leptin receptor (LepR) were compared.MethodsLepR‐cre and VGAT‐cre mice were injected with AAV5‐hSyn‐DIO‐hM3DGq‐mCherry in the LH. The behavioral effects of LH GABA or LH LepR neuronal activation on feeding, locomotion, thermogenesis, and body weight were assessed.ResultsThe activation of LH GABA neurons increased body temperature (P ≤ 0.008) and decreased body weight (P ≤ 0.01) despite decreased locomotor activity (P = 0.03) and transiently increased chow intake (P ≤ 0.009). Also, similar to other studies, this study found that activation of LH GABA neurons induced gnawing on both food and nonfood (P = 0.001) items. Activation of LH LepR neurons decreased body weight (P ≤ 0.01) and chow intake when presented on the cage floor (P ≤ 0.04) but not when presented in the cage top and increased locomotor activity (P = 0.002) and body temperature (P = 0.03).ConclusionsLH LepR neurons are a subset of LH GABA neurons, and LH LepR activation more specifically regulates energy homeostasis to promote a negative energy balance.

Gamma amino-butyric acid and the control of GnRH secretion in sheep

The release of GnRH from nerve terminals in the median eminence into the portal vessels is influenced by factors in the internal and external environment of the animal. In the former category are the gonadal steroid hormones oestrogen and progesterone which alter the characteristics of GnRH secretion during the oestrous and seasonal cycles. These cannot exert their actions directly on the GnRH neurones as they do not possess hormone receptors. Therefore, some other steroid-sensitive neuronal system must relay this information to the GnRH neurones. Gamma amino-butyric acid (GABA) neurones are good candidates for this role as they contain steroid hormone receptors and synapse on GnRH neurones. Recent studies in ewes have sought to identify a role for GABA in mediating the actions of both oestrogen and progesterone on GnRH release. The technique of microdialysis was used to monitor GABA concentrations in areas containing GnRH cell bodies during the oestrogen-induced surge of GnRH and during progesterone negative feedback. Concentrations of this inhibitory neurotransmitter have been shown to fall in the former situation where GnRH release is being stimulated, but to be increased when progesterone is depressing GnRH release. GABA may also be important in mediating the seasonal switch in the negative feedback actions of oestradiol. During the anoestrous season, when oestradiol is a potent inhibitor of GnRH secretion, specific GABA receptor antagonists can stimulate neurohormone release, an action that is not observed in the breeding season when oestrogen is much less potent.

Блокада транспортеров гамма-аминомасляной кислоты в синапсах головного мозга предохраняет от развития судорог при дыхании кислородом под давлением

Hyperbaric oxygen (HBO2) causes inhibition of gamma-aminobutyric acid (GABA) synthesis in the brain, which leads to a decrease in GABAergic neurotransmission and the development of convulsive syndrome like epileptic seizures. We tested the hypothesis that inhibition of GABA transporters can compensate a decrease in GABA synthesis, enhance GABAergic transmission, and prevent against oxygen seizures. HBO2-induced seizures were analyzed in awake rats pretreated with GABA transporter inhibitors (NO-711, nipecotic acid) by intracerebroventricular injection and exposed to oxygen at 5 ATA (absolute atmospheres). In a separate group of rats, GABA was measured in the striatum using intracerebral microdialysis coupled with liquid chromatography. Inhibition of neuronal and glial GABA transporters increased extracerebral GABA content in the brain and protected against HBO2-induced seizures. A more effective anti-convulsive effect was observed after the treatment with a non-selective inhibitor of GABA transporters. The data obtained indicate that blocking the functions of neuronal and glial GABA transporters increases the level of extracellular GABA in the brain and prevent the development of convulsive syndrome in HBO2. The anti-convulsive effects of the GABA transporter inhibition in HBO2 are apparently due to the enhancement of GABA-mediated synaptic and extrasynaptic neurotransmissions. Inhibition of GABA transporters may be a promising approach for the development of effective methods to prevent oxygen seizures.

Targeted Subcutaneous Vibration With Single-Neuron Electrophysiology As a Novel Method for Understanding the Central Effects of Peripheral Vibrational Therapy in a Rodent Model.

Very little is known about the effects of whole body vibration on the supraspinal central nervous system. Though much clinical outcome data and mechanistic data about peripheral neural and musculoskeletal mechanisms have been explored, the lack of central understanding is a barrier to evidence-based, best practice guidelines in the use of vibrational therapy. Disparate methods of administration render study to study comparisons difficult. To address this lack of uniformity, we present the use of targeted subcutaneous vibration combined with simultaneous in vivo electrophysiological recordings as a method of exploring the central effects of peripheral vibration therapy. We used implanted motors driven by both Grass stimulators and programmed microcontrollers to vary frequency and location of stimulation in an anesthetized in vivo rat model while simultaneously recording firing rate from gamma-aminobutyric acid (GABA) neurons in the ventral tegmental area. We show that peripheral vibration can alter GABA neuron firing rate in a location- and frequency-dependent manner. We include detailed schematics and code to aid others in the replication of this technique. This method allows for control of previous weaknesses in the literature including variability in body position, vibrational intensity, node and anti-node interactions with areas of differing mechanoreceptor densities, and prefrontal cortex influence.

S58. Functional Characterization of Brain Organoids Derived From Human Pluripotent Stem Cells

Aberrant gamma-aminobutyric acid (GABA) system, the major inhibitory neurotransmitter in the CNS, is highly implicated in autism spectrum disorder (ASD). Development of the GABAergic neurons in human has only been recently examined, and the results unexpectedly show that GABA neurons are overproduced in ASD (Mariani et al 2015). It is essentially unknown as to how GABAergic transmission is perturbed in developing ASD circuitry.

The effect of hairy and enhancer of split 1 on human gamma aminobutyric acid neurons’ differentiation

Objective To investigate the effect of blocking hairy and enhancer of split 1 (Hes1) on gamma aminobutyric acid (GABA) neurons’ differentiation in human neural stem cells. Methods The human neural stem cells were cultured for 10 days and identified by nestin immunofluorescence stain, then using the human neural stem cells to differentiate GABA neurons. The design project of experiment was adopted completely random. The control cultured medium were the common differentiated medium added 10% bovine serum albumin. And the experimental cultured mediums were identical with the control excepted for the anti-Hes1. Anti-GABA immunofluorescence stain was carried out when most of the cells were differentiated. Results A lot of 150-200 μm diameter neurosphere which were identified when cultured for 10 days. The second generation of neurospheres were using for GABA neurons differentiation. At the sixth day, more than half of cells were differentiated and begin to concentrate. Digested and inoculated again, then 90%-95% cells were adherent and differentiated at day 14. Anti-GABA immuno-fluorescence stain showed that 55-70 positive cells were be found in 100 cells in every visual field, the rate was (64.0±0.6)% in anti-Hes1 differentiated group and in the same condition the positive cells were only 15-20 positive cells, the rat was (16.6±0.6)% in control group, there are significant difference between the two groups. Conclusion blocking Hes1 can significant increase the differentiation rate of GABA neurons in human neural stem cells. Key words: Hes1; Human neural stem cell; Gamma aminobutyric acid ergic neuron; Differentiation

Are there Sleep-promoting Neurons in the Mouse Parafacial Zone?

Although recent studies have reported that gamma-aminobutyric acid (GABA) neurons in the parafacial zone (PZ) of the rostral medulla are needed for the induction of slow-wave sleep (SWS) and that the PZ is a medullary SWS-promoting center, it remains unknown whether the PZ contains SWS-active or sleep-promoting neurons. In the present study, a total of 125 neurons were recorded, for the first time, in non-anesthetized, head-restrained mice during the complete wake–sleep cycle throughout the PZ of the rostral medulla. The vast majority (87.2%) of the neurons displayed increased activity during both wakefulness (W) and paradoxical (or rapid eye movement) sleep (PS) compared to during SWS (W/PS-active neurons) and a few (8.0%) discharged phasically and selectively during PS (PS-active neurons), but none discharged maximally during SWS (SWS-active neurons) or displayed a higher rate of spontaneous discharge during both SWS and PS than during W (SWS/PS-active neurons). These findings do not support the view that the GABAergic PZ is a medullary SWS-promoting center.

Reduced Somatostatin Expression or Somatostatin-Positive Gamma-Aminobutyric Acid Neurons: A Shared Pathology Across Brain Disorders

The clinical and biological heterogeneity that pervades the field of neuropsychiatry has hindered progress in uncovering the pathophysiological mechanisms of psychiatric illnesses. Indeed, it is rare to come across well-replicated pathological findings within or across disorders, and when such findings do arise they merit our attention and focus. In this issue, Pantazopoulos et al. ( 1 Pantazopoulos H. Wiseman J.T. Markota M. Ehrenfeld L. Berretta S. Decreased numbers of somatostatin-expressing neurons in the amygdala of subjects with bipolar disorder or schizophrenia: Relationship to circadian rhythms. Biol Psychiatry. 2017; 81: 536-547 Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar ) bring forward a pathological feature that is common to postmortem brains of patients with schizophrenia and bipolar disorder and that is shared by other psychiatric or neurodegenerative brain disorders ( 2 Lin L.C. Sibille E. Reduced brain somatostatin in mood disorders: A common pathophysiological substrate and drug target?. Front Pharmacol. 2013; 4: 110 Crossref PubMed Scopus (81) Google Scholar ). Decreased Numbers of Somatostatin-Expressing Neurons in the Amygdala of Subjects With Bipolar Disorder or Schizophrenia: Relationship to Circadian RhythmsBiological PsychiatryVol. 81Issue 6PreviewGrowing evidence points to a key role for somatostatin (SST) in schizophrenia (SZ) and bipolar disorder (BD). In the amygdala, neurons expressing SST play an important role in the regulation of anxiety, which is often comorbid in these disorders. We tested the hypothesis that SST-immunoreactive (IR) neurons are decreased in the amygdala of subjects with SZ and BD. Evidence for circadian SST expression in the amygdala and disrupted circadian rhythms and rhythmic peaks of anxiety in BD suggest a disruption of rhythmic expression of SST in this disorder. Full-Text PDF

Modeling the differential phenotypes of spinal muscular atrophy with high-yield generation of motor neurons from human induced pluripotent stem cells.

Spinal muscular atrophy (SMA) is a devastating motor neuron disease caused by mutations of the survival motor neuron 1 (SMN1) gene. SMN2, a paralogous gene to SMN1, can partially compensate for the loss of SMN1. On the basis of age at onset, highest motor function and SMN2 copy numbers, childhood-onset SMA can be divided into three types (SMA I-III). An inverse correlation was observed between SMN2 copies and the differential phenotypes of SMA. Interestingly, this correlation is not always absolute. Using SMA induced pluripotent stem cells (iPSCs), we found that the SMN was significantly decreased in both SMA III and SMA I iPSCs derived postmitotic motor neurons (pMNs) and γ-aminobutyric acid (GABA) neurons. Moreover, the significant differences of SMN expression level between SMA III (3 copies of SMN2) and SMA I (2 copies of SMN2) were observed only in pMNs culture, but not in GABA neurons or iPSCs. From these findings, we further discovered that the neurite outgrowth was suppressed in both SMA III and SMA I derived MNs. Meanwhile, the significant difference of neurite outgrowth between SMA III and SMA I group was also found in long-term cultures. However, significant hyperexcitability was showed only in SMA I derived mature MNs, but not in SMA III group. Above all, we propose that SMN protein is a major factor of phenotypic modifier. Our data may provide a new insight into recognition for differential phenotypes of SMA disease.

Ketamine abuse potential and use disorder.

Ketamine is a noncompetitive antagonist of N-methyl-d-asparate (NMDA) receptor and has been long used as an anesthetic agent in humans and veterinary medicine. The present article reviews the epidemiology, pharmacology, neurochemistry, and treatment of ketamine abuse. Ketamine has a unique mood controlling property and a number of studies have demonstrated a significant and rapid antidepressant effect of ketamine. However, the therapeutic value of ketamine to treat psychiatric disorders faces a major challenge that ketamine also owns significant reinforcing and toxic effects. Its abuse has posted severe harms on individuals and society. Disrupted learning and memory processing has long been related with ketamine use. It is hypothesized that ketamine blocks NMDA receptors on gamma-aminobutyric acid (GABA) neurons inside the thalamic reticular nucleus, which leads to disinhibition of dopaminergic neurons and increased release of dopamine. Currently, there is no specific treatment for treating every ketamine patient presenting peripheral toxicity. Interestingly, ketamine psychotherapy has been suggested to be a promising approach to treat addiction of other drugs. Future research can continue to develop creative ways to investigate potential mechanism and treatments related to ketamine abuse that have posted severe individual and social harms.

Gamma band oscillations

We review our current understanding of abnormal γ band oscillations in schizophrenia, their association with symptoms and the underlying cortical circuit abnormality, with a particular focus on the role of fast-spiking parvalbumin gamma-aminobutyric acid (GABA) neurons in the disease state. Clinical electrophysiological studies of schizophrenia patients and pharmacological models of the disorder show an increase in spontaneous γ band activity (not stimulus-evoked) measures. These findings provide a crucial link between preclinical and clinical work examining the role of γ band activity in schizophrenia. MRI-based experiments measuring cortical GABA provides evidence supporting impaired GABAergic neurotransmission in schizophrenia patients, which is correlated with γ band activity level. Several studies suggest that stimulation of the cortical circuitry, directly or via subcortical structures, has the potential to modulate cortical γ activity, and improve cognitive function. Abnormal γ band activity is observed in patients with schizophrenia and disease models in animals, and is suggested to underlie the psychosis and cognitive/perceptual deficits. Convergent evidence from both clinical and preclinical studies suggest the central factor in γ band abnormalities is impaired GABAergic neurotransmission, particularly in a subclass of neurons which express parvalbumin. Rescue of γ band abnormalities presents an intriguing option for therapeutic intervention.

Gap Junctions Contribute to Ictal/Interictal Genesis in Human Hypothalamic Hamartomas

Human hypothalamic hamartoma (HH) is a rare subcortical lesion associated with treatment-resistant epilepsy. Cellular mechanisms responsible for epileptogenesis are unknown. We hypothesized that neuronal gap junctions contribute to epileptogenesis through synchronous activity within the neuron networks in HH tissue. We studied surgically resected HH tissue with Western-blot analysis, immunohistochemistry, electron microscopy, biocytin microinjection of recorded HH neurons, and microelectrode patch clamp recordings with and without pharmacological blockade of gap junctions. Normal human hypothalamus tissue was used as a control. Western blots showed increased expression of both connexin-36 (Cx36) and connexin-43 (Cx43) in HH tissue compared with normal human mammillary body tissue. Immunohistochemistry demonstrated that Cx36 and Cx43 are expressed in HH tissue, but Cx36 was mainly expressed within neuron clusters while Cx43 was mainly expressed outside of neuron clusters. Gap-junction profiles were observed between small HH neurons with electron microscopy. Biocytin injection into single recorded small HH neurons showed labeling of adjacent neurons, which was not observed in the presence of a neuronal gap-junction blocker, mefloquine. Microelectrode field recordings from freshly resected HH slices demonstrated spontaneous ictal/interictal-like discharges in most slices. Bath-application of gap-junction blockers significantly reduced ictal/interictal-like discharges in a concentration-dependent manner, while not affecting the action-potential firing of small gamma-aminobutyric acid (GABA) neurons observed with whole-cell patch-clamp recordings from the same patient's HH tissue. These results suggest that neuronal gap junctions between small GABAergic HH neurons participate in the genesis of epileptic-like discharges. Blockade of gap junctions may be a new therapeutic strategy for controlling seizure activity in HH patients.

GABBR1 and SLC6A1, Two Genes Involved in Modulation of GABA Synaptic Transmission, Influence Risk for Alcoholism: Results from Three Ethnically Diverse Populations.

Animal and human studies indicate that GABBR1, encoding the GABAB1 receptor subunit, and SLC6A1, encoding the neuronal gamma-aminobutyric acid (GABA) transporter GAT1, play a role in addiction by modulating synaptic GABA. Therefore, variants in these genes might predict risk/resilience for alcoholism. This study included 3 populations that differed by ethnicity and alcoholism phenotype: African American (AA) men: 401 treatment-seeking inpatients with single/comorbid diagnoses of alcohol and drug dependence, 193 controls; Finnish Caucasian men: 159 incarcerated alcoholics, half with comorbid antisocial personality disorder, 181 controls; and a community sample of Plains Indian (PI) men and women: 239 alcoholics, 178 controls. Seven GABBR1 tag single nucleotide polymorphisms were genotyped in the AA and Finnish samples; rs29220 was genotyped in the PI for replication. Also, a uniquely African, functional SLC6A1 insertion promoter polymorphism (IND) was genotyped in the AAs. We found a significant and congruent association between GABBR1 rs29220 and alcoholism in all 3 populations. The major genotype (heterozygotes in AAs, Finns) and the major allele in PIs were significantly more common in alcoholics. Moreover, SLC6A1 IND was more abundant in controls, that is, the major genotype predicted alcoholism. An analysis of combined GABBR1 rs29220 and SLC6A1 IND genotypes showed that rs29220 heterozygotes, irrespective of their IND status, had an increased risk for alcoholism, whereas carriers of the IND allele and either rs29220 homozygote were more resilient. Our results show that with both GABBR1 and SLC6A1, the minor genotypes/alleles were protective against risk for alcoholism. Finally, GABBR1 rs29220 might predict treatment response/adverse effects for baclofen, a GABAB receptor agonist.

G Protein-Gated K+ Channel Ablation in Forebrain Pyramidal Neurons Selectively Impairs Fear Learning

BackgroundCognitive dysfunction occurs in many debilitating conditions including Alzheimer’s disease, Down syndrome, schizophrenia, and mood disorders. The dorsal hippocampus is a critical locus of cognitive processes linked to spatial and contextual learning. G protein-gated inwardly rectifying potassium ion (GIRK/Kir3) channels, which mediate the postsynaptic inhibitory effect of many neurotransmitters, have been implicated in hippocampal-dependent cognition. Available evidence, however, derives primarily from constitutive gain-of-function models that lack cellular specificity. MethodsWe used constitutive and neuron-specific gene ablation models targeting an integral subunit of neuronal GIRK channels (GIRK2) to probe the impact of GIRK channels on associative learning and memory. ResultsConstitutive Girk2–/– mice exhibited a striking deficit in hippocampal-dependent (contextual) and hippocampal-independent (cue) fear conditioning. Mice lacking GIRK2 in gamma-aminobutyric acid neurons (GAD-Cre:Girk2flox/flox mice) exhibited a clear deficit in GIRK-dependent signaling in dorsal hippocampal gamma-aminobutyric acid neurons but no evident behavioral phenotype. Mice lacking GIRK2 in forebrain pyramidal neurons (CaMKII-Cre(+):Girk2flox/flox mice) exhibited diminished GIRK-dependent signaling in dorsal, but not ventral, hippocampal pyramidal neurons. CaMKII-Cre(+):Girk2flox/flox mice also displayed a selective impairment in contextual fear conditioning, as both cue fear and spatial learning were intact in these mice. Finally, loss of GIRK2 in forebrain pyramidal neurons correlated with enhanced long-term depression and blunted depotentiation of long-term potentiation at the Schaffer collateral/cornu ammonis 1 synapse in the dorsal hippocampus. ConclusionsOur data suggest that GIRK channels in dorsal hippocampal pyramidal neurons are necessary for normal learning involving aversive stimuli and support the contention that dysregulation of GIRK-dependent signaling may underlie cognitive dysfunction in some disorders.

Tlx3 promotes glutamatergic neuronal subtype specification through direct interactions with the chromatin modifier CBP.

Nervous system development relies on the generation of precise numbers of excitatory and inhibitory neurons. The homeodomain transcription factor, T-cell leukemia 3 (Tlx3), functions as the master neuronal fate regulator by instructively promoting the specification of glutamatergic excitatory neurons and suppressing the specification of gamma-aminobutyric acid (GABAergic) neurons. However, how Tlx3 promotes glutamatergic neuronal subtype specification is poorly understood. In this study, we found that Tlx3 directly interacts with the epigenetic co-activator cyclic adenosine monophosphate (cAMP)-response element-binding protein (CREB)-binding protein (CBP) and that the Tlx3 homeodomain is essential for this interaction. The interaction between Tlx3 and CBP was enhanced by the three amino acid loop extension (TALE)-class homeodomain transcription factor, pre-B-cell leukemia transcription factor 3 (Pbx3). Using mouse embryonic stem (ES) cells stably expressing Tlx3, we found that the interaction between Tlx3 and CBP became detectable only after these Tlx3-expressing ES cells were committed to a neural lineage, which coincided with increased Pbx3 expression during neural differentiation from ES cells. Forced expression of mutated Tlx3 lacking the homeodomain in ES cells undergoing neural differentiation resulted in significantly reduced expression of glutamatergic neuronal subtype markers, but had little effect on the expression on pan neural markers. Collectively, our results strongly suggest that functional interplay between Tlx3 and CBP plays a critical role in neuronal subtype specification, providing novel insights into the epigenetic regulatory mechanism that modulates the transcriptional efficacy of a selective set of neuronal subtype-specific genes during differentiation.

Markedly Lower Glutamic Acid Decarboxylase 67 Protein Levels in a Subset of Boutons in Schizophrenia

BackgroundConvergent findings indicate that cortical gamma-aminobutyric acid (GABA)ergic circuitry is altered in schizophrenia. Postmortem studies have consistently found lower levels of glutamic acid decarboxylase 67 (GAD67) messenger RNA (mRNA) in the prefrontal cortex (PFC) of subjects with schizophrenia. At the cellular level, the density of GABA neurons with detectable levels of GAD67 mRNA is ~30% lower across cortical layers. Knowing how this transcript deficit translates to GAD67 protein levels in axonal boutons is important for understanding the impact it might have on GABA synthesis. In addition, because reductions in GAD67 expression before, but not after, the maturation of GABAergic boutons results in a lower density of GABAergic boutons in mouse cortical cultures, knowing if GABAergic bouton density is altered in schizophrenia would provide insight into the timing of the GAD67 deficit. MethodsPFC tissue sections from 20 matched pairs of schizophrenia and comparison subjects were immunolabeled for the vesicular GABA transporter (vGAT) and GAD67. ResultsvGAT+ bouton density did not differ between subject groups, consistent with findings that vGAT mRNA levels are unaltered in the illness and confirming that the number of cortical GABAergic boutons is not lower in schizophrenia. In contrast, in schizophrenia subjects, the proportion of vGAT+ boutons with detectable GAD67 levels (vGAT+/GAD67+ boutons) was 16% lower and mean GAD67 levels were 14% lower in the remaining vGAT+/GAD67+ boutons. ConclusionsOur findings suggest that GABA production is markedly reduced in a subset of boutons in the PFC of schizophrenia subjects and that this reduction likely occurs after the maturation of GABAergic boutons.

Optogenetic Stimulation of GABA Neurons can Decrease Local Neuronal Activity While Increasing Cortical Blood Flow

We investigated the link between direct activation of inhibitory neurons, local neuronal activity, and hemodynamics. Direct optogenetic cortical stimulation in the sensorimotor cortex of transgenic mice expressing Channelrhodopsin-2 in GABAergic neurons (VGAT-ChR2) greatly attenuated spontaneous cortical spikes, but was sufficient to increase blood flow as measured with laser speckle contrast imaging. To determine whether the observed optogenetically evoked gamma aminobutyric acid (GABA)-neuron hemodynamic responses were dependent on ionotropic glutamatergic or GABAergic synaptic mechanisms, we paired optogenetic stimulation with application of antagonists to the cortex. Incubation of glutamatergic antagonists directly on the cortex (NBQX and MK-801) blocked cortical sensory evoked responses (as measured with electroencephalography and intrinsic optical signal imaging), but did not significantly attenuate optogenetically evoked hemodynamic responses. Significant light-evoked hemodynamic responses were still present after the addition of picrotoxin (GABA-A receptor antagonist) in the presence of the glutamatergic synaptic blockade. This activation of cortical inhibitory interneurons can mediate large changes in blood flow in a manner that is by and large not dependent on ionotropic glutamatergic or GABAergic synaptic transmission. This supports the hypothesis that activation of inhibitory neurons can increase local cerebral blood flow in a manner that is not entirely dependent on levels of net ongoing neuronal activity.