Genetic Ablation of Dentate Hilar Somatostatin-Positive GABAergic Interneurons is Sufficient to Induce Cognitive Impairment.

Aging is often associated with a decline in cognitive function. A reduction in the number of somatostatin-positive (SOM+) interneurons in the dentate gyrus (DG) has been described in cognitively impaired but not in unimpaired aged rodents. However, it remains unclear whether the reduction in SOM + interneurons in the DG hilus is causal for age-related cognitive dysfunction. We hypothesized that hilar SOM+ interneurons play an essential role in maintaining cognitive function and that a reduction in the number of hilar SOM + interneurons might be sufficient to induce cognitive dysfunction. Hilar SOM+ interneurons were ablated by expressing a diphtheria toxin transgene specifically in these interneurons, which resulted in a reduction in the number of SOM+ /GAD-67+ neurons and dendritic spine density in the DG. C-fos and Iba-1 immunostainings were increased in DG and CA3, but not CA1, and BDNF protein expression in the hippocampus was decreased. Behavioral testing showed a reduced recognition index in the novel object recognition test, decreased alternations in the Y maze test, and longer latencies and path lengths in the learning and reversal learning phases of the Morris water maze. Our results show that partial genetic ablation of SOM+ hilar interneurons is sufficient to increase activity in DG and CA3, as has been described to occur with aging and to induce an impairment of learning and memory functions. Thus, partial ablation of hilar SOM + interneurons may be a significant contributing factor to age-related cognitive dysfunction. These mice may also be useful as a cellularly defined model of hippocampal aging.

GABAA receptors as targets for treating affective and cognitive symptoms of depression.

In the past 20 years, our understanding of the pathophysiology of depression has evolved from a focus on an imbalance of monoaminergic neurotransmitters to a multifactorial picture including an improved understanding of the role of glutamatergic excitatory and GABAergic inhibitory neurotransmission. FDA-approved treatments targeting the glutamatergic [esketamine for major depressive disorder (MDD)] and GABAergic (brexanolone for peripartum depression) systems have become available. This review focuses on the GABAA receptor (GABAAR) system as a target for novel antidepressants and discusses the mechanisms by which modulation of δ-containing GABAARs with neuroactive steroids (NASs) or of α5-containing GABAARs results in antidepressant or antidepressant-like actions and discusses clinical data on NASs. Moreover, a potential mechanism by which α5-GABAAR-positive allosteric modulators (PAMs) may improve cognitive deficits in depression is presented.

A marker chromosome in psychosis identifies glycine decarboxylase (GLDC) as a novel regulator of neuronal and synaptic function in the hippocampus.

The biological significance of a small supernumerary marker chromosome that results in dosage alterations to chromosome 9p24.1, including triplication of the GLDC gene encoding glycine decarboxylase, in two patients with psychosis is unclear. In an allelic series of copy number variant mouse models, we identify that triplication of Gldc reduces extracellular glycine levels as determined by optical fluorescence resonance energy transfer (FRET) in dentate gyrus (DG) but not in CA1, suppresses long-term potentiation (LTP) in mPP-DG synapses but not in CA3-CA1 synapses, reduces the activity of biochemical pathways implicated in schizophrenia and mitochondrial bioenergetics, and displays deficits in prepulse inhibition, startle habituation, latent inhibition, working memory, sociability and social preference. Our results thus provide a link between a genomic copy number variation, biochemical, cellular and behavioral phenotypes, and further demonstrate that GLDC negatively regulates long-term synaptic plasticity at specific hippocampal synapses, possibly contributing to the development of neuropsychiatric disorders.

Selective inhibition of somatostatin-positive dentate hilar interneurons induces age-related cellular changes and cognitive dysfunction.

The cellular basis of age-related impairments of hippocampal function is not fully understood. In order to evaluate the role of somatostatin-positive (Sst+) interneurons in the dentate gyrus (DG) hilus in this process, we chemogenetically inhibited Sst+ interneurons in the DG hilus. Chronic chemogenetic inhibition (CCI) of these neurons resulted in increased c-Fos staining in the DG hilus, a decrease in the percentage of GAD67- and of Sst-expressing interneurons in the DG, and increased microglial activation in DG, CA3, and CA1. Total dendritic length and spine density were reduced in DG and CA1, suggesting reduced dendritic complexity. Behaviorally, the recognition index in an object recognition task and the percentage of spontaneous alternations in the Y-maze were decreased, while in both initial and reversal learning in the Morris water maze, the latencies to find the hidden platform were increased, suggesting cognitive dysfunction. Our findings establish a causal role for a reduced function of Sst+ interneurons in the DG hilus for cognitive decline and suggest that this reduced function may contribute to age-related impairments of learning and memory. Furthermore, our CCI mice may represent a cellularly defined model of hippocampal aging.

Neurosteroids Mediate Neuroprotection in an In Vitro Model of Hypoxic/Hypoglycaemic Excitotoxicity via δ-GABAA Receptors without Affecting Synaptic Plasticity.

Neurosteroids and benzodiazepines are modulators of the GABAA receptors, thereby causing anxiolysis. Furthermore, benzodiazepines such as midazolam are known to cause adverse side-effects on cognition upon administration. We previously found that midazolam at nanomolar concentrations (10 nM) blocked long-term potentiation (LTP). Here, we aim to study the effect of neurosteroids and their synthesis using XBD173, which is a synthetic compound that promotes neurosteroidogenesis by binding to the translocator protein 18 kDa (TSPO), since they might provide anxiolytic activity with a favourable side-effect profile. By means of electrophysiological measurements and the use of mice with targeted genetic mutations, we revealed that XBD173, a selective ligand of the translocator protein 18 kDa (TSPO), induced neurosteroidogenesis. In addition, the exogenous application of potentially synthesised neurosteroids (THDOC and allopregnanolone) did not depress hippocampal CA1-LTP, the cellular correlate of learning and memory. This phenomenon was observed at the same concentrations that neurosteroids conferred neuroprotection in a model of ischaemia-induced hippocampal excitotoxicity. In conclusion, our results indicate that TSPO ligands are promising candidates for post-ischaemic recovery exerting neuroprotection, in contrast to midazolam, without detrimental effects on synaptic plasticity.

Control of contextual memory through interneuronal α5-GABAA receptors.

γ-Aminobutyric acid type A receptors that incorporate α5 subunits (α5-GABAARs) are highly enriched in the hippocampus and are strongly implicated in control of learning and memory. Receptors located on pyramidal neuron dendrites have long been considered responsible, but here we report that mice in which α5-GABAARs have been eliminated from pyramidal neurons (α5-pyr-KO) continue to form strong spatial engrams and that they remain as sensitive as their pseudo-wild-type (p-WT) littermates to etomidate-induced suppression of place cells and spatial engrams. By contrast, mice with selective knockout in interneurons (α5-i-KO) no longer exhibit etomidate-induced suppression of place cells. In addition, the strength of spatial engrams is lower in α5-i-KO mice than p-WT littermates under control conditions. Consistent with the established role of the hippocampus in contextual fear conditioning, α5-i-KO mice resisted etomidate's suppression of freezing to context, but so too did α5-pyr-KO mice, supporting a role for extra-hippocampal regions in the development of contextual fear memory. Overall, our results indicate that interneuronal α5-GABAARs serve a physiological role in promoting spatial learning and that they mediate suppression of hippocampus-dependent contextual memory by etomidate.

Midazolam at Low Nanomolar Concentrations Affects Long-term Potentiation and Synaptic Transmission Predominantly via the α1-γ-Aminobutyric Acid Type A Receptor Subunit in Mice.

BACKGROUND: Midazolam amplifies synaptic inhibition via different γ-aminobutyric acid type A (GABAA) receptor subtypes defined by the presence of α1-, α2-, α3-, or α5-subunits in the channel complex. Midazolam blocks long-term potentiation and produces postoperative amnesia. The aims of this study were to identify the GABAA receptor subtypes targeted by midazolam responsible for affecting CA1 long-term potentiation and synaptic inhibition in neocortical neurons. METHODS: The effects of midazolam on hippocampal CA1 long-term potentiation were studied in acutely prepared brain slices of male and female mice. Positive allosteric modulation on GABAA receptor-mediated miniature inhibitory postsynaptic currents was investigated in organotypic slice cultures of the mouse neocortex. In both experiments, wild-type mice and GABAA receptor knock-in mouse lines were compared in which α1-, α5-, α1/2/3-, α1/3/5- and α2/3/5-GABAA receptor subtypes had been rendered benzodiazepine-insensitive. RESULTS: Midazolam (10 nM) completely blocked long-term potentiation (mean ± SD, midazolam, 98 ± 11%, n = 14/8 slices/mice vs. control 156 ± 19%, n = 20/12; P < 0.001). Experiments in slices of α1-, α5-, α1/2/3-, α1/3/5-, and α2/3/5-knock-in mice revealed a dominant role for the α1-GABAA receptor subtype in the long-term potentiation suppressing effect. In slices from wild-type mice, midazolam increased (mean ± SD) charge transfer of miniature synaptic events concentration-dependently (50 nM: 172 ± 71% [n = 10/6] vs. 500 nM: 236 ± 54% [n = 6/6]; P = 0.041). In α2/3/5-knock-in mice, charge transfer of miniature synaptic events did not further enhance when applying 500 nM midazolam (50 nM: 171 ± 62% [n = 8/6] vs. 500 nM: 175 ± 62% [n = 6/6]; P = 0.454), indicating two different binding affinities for midazolam to α2/3/5- and α1-subunits. CONCLUSIONS: These results demonstrate a predominant role of α1-GABAA receptors in the actions of midazolam at low nanomolar concentrations. At higher concentrations, midazolam also enhances other GABAA receptor subtypes. α1-GABAA receptors may already contribute at sedative doses to the phenomenon of postoperative amnesia that has been reported after midazolam administration.

Long-term diazepam treatment enhances microglial spine engulfment and impairs cognitive performance via the mitochondrial 18 kDa translocator protein (TSPO).

Benzodiazepines are widely administered drugs to treat anxiety and insomnia. In addition to tolerance development and abuse liability, their chronic use may cause cognitive impairment and increase the risk for dementia. However, the mechanism by which benzodiazepines might contribute to persistent cognitive decline remains unknown. Here we report that diazepam, a widely prescribed benzodiazepine, impairs the structural plasticity of dendritic spines, causing cognitive impairment in mice. Diazepam induces these deficits via the mitochondrial 18 kDa translocator protein (TSPO), rather than classical γ-aminobutyric acid type A receptors, which alters microglial morphology, and phagocytosis of synaptic material. Collectively, our findings demonstrate a mechanism by which TSPO ligands alter synaptic plasticity and, as a consequence, cause cognitive impairment.

Negative Allosteric Modulation of Gamma-Aminobutyric Acid A Receptors at α5 Subunit-Containing Benzodiazepine Sites Reverses Stress-Induced Anhedonia and Weakened Synaptic Function in Mice.

BACKGROUND: Abnormal reward processing, typically anhedonia, is a hallmark of human depression and is accompanied by altered functional connectivity in reward circuits. Negative allosteric modulators of GABAA (gamma-aminobutyric acid A) receptors (GABA-NAMs) have rapid antidepressant-like properties in rodents and exert few adverse effects, but molecular targets underlying their behavioral and synaptic effects remain undetermined. We hypothesized that GABA-NAMs act at the benzodiazepine site of GABAA receptors containing α5 subunits to increase gamma oscillatory activity, strengthen synapses in reward circuits, and reverse anhedonia. METHODS: Anhedonia was induced by chronic stress in male mice and assayed by preferences for sucrose and female urine (n = 5-7 mice/group). Hippocampal slices were then prepared for electrophysiological recording (n = 1-6 slices/mouse, 4-6 mice/group). Electroencephalography power was quantified in response to GABA-NAM and ketamine administration (n = 7-9 mice/group). RESULTS: Chronic stress reduced sucrose and female urine preferences and hippocampal temporoammonic-CA1 synaptic strength. A peripheral injection of the GABA-NAM MRK-016 restored hedonic behavior and AMPA-to-NMDA ratios in wild-type mice. These actions were prevented by pretreatment with the benzodiazepine site antagonist flumazenil. MRK-016 administration increased gamma power over the prefrontal cortex in wild-type mice but not α5 knockout mice, whereas ketamine promoted gamma power in both genotypes. Hedonic behavior and AMPA-to-NMDA ratios were only restored by MRK-016 in stressed wild-type mice but not α5 knockout mice. CONCLUSIONS: α5-Selective GABA-NAMs exert rapid anti-anhedonic actions and restore the strength of synapses in reward regions by acting at the benzodiazepine site of α5-containing GABAA receptors. These results encourage human studies using GABA-NAMs to treat depression by providing readily translatable measures of target engagement.

Transient expression of a GABA receptor subunit during early development is critical for inhibitory synapse maturation and function.

Developing neural circuits, including GABAergic circuits, switch receptor types. But the role of early GABA receptor expression for establishment of functional inhibitory circuits remains unclear. Tracking the development of GABAergic synapses across axon terminals of retinal bipolar cells (BCs), we uncovered a crucial role of early GABAA receptor expression for the formation and function of presynaptic inhibitory synapses. Specifically, early α3-subunit-containing GABAA (GABAAα3) receptors are a key developmental organizer. Before eye opening, GABAAα3 gives way to GABAAα1 at individual BC presynaptic inhibitory synapses. The developmental downregulation of GABAAα3 is independent of GABAAα1 expression. Importantly, lack of early GABAAα3 impairs clustering of GABAAα1 and formation of functional GABAA synapses across mature BC terminals. This impacts the sensitivity of visual responses transmitted through the circuit. Lack of early GABAAα3 also perturbs aggregation of LRRTM4, the organizing protein at GABAergic synapses of rod BC terminals, and their arrangement of output ribbon synapses.

α2-containing γ-aminobutyric acid type A receptors promote stress resiliency in male mice.

Brain α2-containing GABAA receptors play a critical role in the modulation of anxiety- and fear-like behavior. However, it is unknown whether these receptors also play a role in modulating resilience to chronic stress, and in which brain areas and cell types such an effect would be mediated. We evaluated the role of α2-containing GABAA receptors following chronic social defeat stress using male mice deficient in the α2 subunit globally or conditionally in dopamine D1- or D2-receptor-expressing neurons, e.g., within the nucleus accumbens (NAc). In addition, we examined the effect of the lack of the α2 subunit on intermediates of the glutathione synthesis pathway. We found that α2-containing GABAA receptors on D2-receptor-positive but not on D1-receptor-positive neurons promote resiliency to chronic social defeat stress, as reflected in social interaction tests. The pro-resiliency effects of α2-containing GABAA receptors on D2-receptor-positive neurons do not appear to be directly related to alterations in anxiety-like behavior, as reflected in the elevated plus-maze, light-dark box, and novel open field tests. Increases in indices of oxidative stress-reflected by increases in cystathionine levels and reductions in GSH/GSSG ratios-were found in the NAc and prefrontal cortex but not in the hippocampus of mice lacking α2-containing GABAA receptors. We conclude that α2-containing GABAA receptors within specific brain areas and cell populations promote stress resiliency independently of direct effects on anxiety-like behaviors. A potential mechanism contributing to this increased resiliency is the protection that α2-containing GABAA receptors provide against oxidative stress in NAc and the prefrontal cortex.

Organization and emergence of a mixed GABA-glycine retinal circuit that provides inhibition to mouse ON-sustained alpha retinal ganglion cells.

In the retina, amacrine interneurons inhibit retinal ganglion cell (RGC) dendrites to shape retinal output. Amacrine cells typically use either GABA or glycine to exert synaptic inhibition. Here, we combined transgenic tools with immunohistochemistry, electrophysiology, and 3D electron microscopy to determine the composition and organization of inhibitory synapses across the dendritic arbor of a well-characterized RGC type in the mouse retina: the ON-sustained alpha RGC. We find mixed GABA-glycine receptor synapses across this RGC type, unveiling the existence of "mixed" inhibitory synapses in the retinal circuit. Presynaptic amacrine boutons with dual release sites are apposed to ON-sustained alpha RGC postsynapses. We further reveal the sequence of postsynaptic assembly for these mixed synapses: GABA receptors precede glycine receptors, and a lack of early GABA receptor expression impedes the recruitment of glycine receptors. Together our findings uncover the organization and developmental profile of an additional motif of inhibition in the mammalian retina.

GABAA receptors in GtoPdb v.2021.3.

The GABAA receptor is a ligand-gated ion channel of the Cys-loop family that includes the nicotinic acetylcholine, 5-HT3 and strychnine-sensitive glycine receptors. GABAA receptor-mediated inhibition within the CNS occurs by fast synaptic transmission, sustained tonic inhibition and temporally intermediate events that have been termed 'GABAA, slow' [45]. GABAA receptors exist as pentamers of 4TM subunits that form an intrinsic anion selective channel. Sequences of six α, three ß, three γ, one δ, three ρ, one ε, one π and one θ GABAA receptor subunits have been reported in mammals [278, 235, 236, 283]. The π-subunit is restricted to reproductive tissue. Alternatively spliced versions of many subunits exist (e.g. α4- and α6- (both not functional) α5-, ß2-, ß3- and γ2), along with RNA editing of the α3 subunit [71]. The three ρ-subunits, (ρ1-3) function as either homo- or hetero-oligomeric assemblies [359, 50]. Receptors formed from ρ-subunits, because of their distinctive pharmacology that includes insensitivity to bicuculline, benzodiazepines and barbiturates, have sometimes been termed GABAC receptors [359], but they are classified as GABA A receptors by NC-IUPHAR on the basis of structural and functional criteria [16, 235, 236]. Many GABAA receptor subtypes contain α-, ß- and γ-subunits with the likely stoichiometry 2α.2ß.1γ [168, 235]. It is thought that the majority of GABAA receptors harbour a single type of α- and ß - subunit variant. The α1ß2γ2 hetero-oligomer constitutes the largest population of GABAA receptors in the CNS, followed by the α2ß3γ2 and α3ß3γ2 isoforms. Receptors that incorporate the α4- α5-or α 6-subunit, or the ß1-, γ1-, γ3-, δ-, ε- and θ-subunits, are less numerous, but they may nonetheless serve important functions. For example, extrasynaptically located receptors that contain α6- and δ-subunits in cerebellar granule cells, or an α4- and δ-subunit in dentate gyrus granule cells and thalamic neurones, mediate a tonic current that is important for neuronal excitability in response to ambient concentrations of GABA [209, 272, 83, 19, 288]. GABA binding occurs at the ß+/α- subunit interface and the homologous γ+/α- subunits interface creates the benzodiazepine site. A second site for benzodiazepine binding has recently been postulated to occur at the α+/ß- interface ([254]; reviewed by [282]). The particular α-and γ-subunit isoforms exhibit marked effects on recognition and/or efficacy at the benzodiazepine site. Thus, receptors incorporating either α4- or α6-subunits are not recognised by 'classical' benzodiazepines, such as flunitrazepam (but see [356]). The trafficking, cell surface expression, internalisation and function of GABAA receptors and their subunits are discussed in detail in several recent reviews [52, 140, 188, 316] but one point worthy of note is that receptors incorporating the γ2 subunit (except when associated with α5) cluster at the postsynaptic membrane (but may distribute dynamically between synaptic and extrasynaptic locations), whereas as those incorporating the δ subunit appear to be exclusively extrasynaptic. NC-IUPHAR [16, 235, 3, 2] class the GABAA receptors according to their subunit structure, pharmacology and receptor function. Currently, eleven native GABAA receptors are classed as conclusively identified (i.e., α1ß2γ2, α1ßγ2, α3ßγ2, α4ßγ2, α4ß2δ, α4ß3δ, α5ßγ2, α6ßγ2, α6ß2δ, α6ß3δ and ρ) with further receptor isoforms occurring with high probability, or only tentatively [235, 236]. It is beyond the scope of this Guide to discuss the pharmacology of individual GABAA receptor isoforms in detail; such information can be gleaned in the reviews [16, 95, 168, 173, 143, 278, 216, 235, 236] and [9, 10]. Agents that discriminate between α-subunit isoforms are noted in the table and additional agents that demonstrate selectivity between receptor isoforms, for example via ß-subunit selectivity, are indicated in the text below. The distinctive agonist and antagonist pharmacology of ρ receptors is summarised in the table and additional aspects are reviewed in [359, 50, 145, 223]. Several high-resolution cryo-electron microscopy structures have been described in which the full-length human α1ß3γ2L GABAA receptor in lipid nanodiscs is bound to the channel-blocker picrotoxin, the competitive antagonist bicuculline, the agonist GABA (γ-aminobutyric acid), and the classical benzodiazepines alprazolam and diazepam [198].

Identification of intraneuronal amyloid beta oligomers in locus coeruleus neurons of Alzheimer's patients and their potential impact on inhibitory neurotransmitter receptors and neuronal excitability.

AIMS: Amyloid ß-oligomers (AßO) are potent modulators of Alzheimer's pathology, yet their impact on one of the earliest brain regions to exhibit signs of the condition, the locus coeruleus (LC), remains to be determined. Of particular importance is whether AßO impact the spontaneous excitability of LC neurons. This parameter determines brain-wide noradrenaline (NA) release, and thus NA-mediated brain functions, including cognition, emotion and immune function, which are all compromised in Alzheimer's patients. Therefore, the aim of the study was to determine the expression profile of AßO in the LC of Alzheimer's patients and to probe their potential impact on the molecular and functional correlates of LC excitability, using a mouse model of increased Aß production (APP-PSEN1). METHODS AND RESULTS: Immunohistochemistry and confocal microscopy, using AßO-specific antibodies, confirmed LC AßO expression both intraneuronally and extracellularly in both Alzheimer's and APP-PSEN1 samples. Patch clamp electrophysiology recordings revealed that APP-PSEN1 LC neuronal hyperexcitability accompanied this AßO expression profile, arising from a diminished inhibitory effect of GABA due to impaired expression and function of the GABA-A receptor (GABAA R) α3 subunit. This altered LC α3-GABAA R expression profile overlapped with AßO expression in samples from both APP-PSEN1 mice and Alzheimer's patients. Finally, strychnine-sensitive glycine receptors (GlyRs) remained resilient to Aß-induced changes and their activation reversed LC hyperexcitability. CONCLUSIONS: The data suggest a close association between AßO and α3-GABAA Rs in the LC of Alzheimer's patients, and their potential to dysregulate LC activity, thereby contributing to the spectrum of pathology of the LC-NA system in this condition.

Bidirectional regulation of distinct memory domains by α5-subunit-containing GABAA receptors in CA1 pyramidal neurons.

Reduction in the expression or function of α5-subunit-containing GABAA receptors (α5GABAARs) leads to improvement in several hippocampus-dependent memory domains. However, studies thus far mostly lack anatomical specificity in terms of neuronal circuits and populations. We demonstrate that mice with a selective knockdown of α5GABAARs in CA1 pyramidal neurons (α5CA1KO mice) show improved spatial and trace fear-conditioning memory. Unexpectedly, α5CA1KO mice were comparable to controls in contextual fear-conditioning but showed an impairment in context discrimination, suggesting fine-tuning of activity in CA1 pyramidal cell dendrites through α5-mediated inhibition might be necessary for distinguishing highly similar contexts.

Propofol Affects Cortico-Hippocampal Interactions via ß3 Subunit-Containing GABAA Receptors.

BACKGROUND: General anesthetics depress neuronal activity. The depression and uncoupling of cortico-hippocampal activity may contribute to anesthetic-induced amnesia. However, the molecular targets involved in this process are not fully characterized. GABAA receptors, especially the type with ß3 subunits, represent a main molecular target of propofol. We therefore hypothesized that GABAA receptors with ß3 subunits mediate the propofol-induced disturbance of cortico-hippocampal interactions. METHODS: We used local field potential (LFP) recordings from chronically implanted cortical and hippocampal electrodes in wild-type and ß3(N265M) knock-in mice. In the ß3(N265M) mice, the action of propofol via ß3subunit containing GABAA receptors is strongly attenuated. The analytical approach contained spectral power, phase locking, and mutual information analyses in the 2-16 Hz range to investigate propofol-induced effects on cortico-hippocampal interactions. RESULTS: Propofol caused a significant increase in spectral power between 14 and 16 Hz in the cortex and hippocampus of wild-type mice. This increase was absent in the ß3(N265M) mutant. Propofol strongly decreased phase locking of 6-12 Hz oscillations in wild-type mice. This decrease was attenuated in the ß3(N265M) mutant. Finally, propofol reduced the mutual information between 6-16 Hz in wild-type mice, but only between 6 and 8 Hz in the ß3(N265M) mutant. CONCLUSIONS: GABAA receptors containing ß3 subunits contribute to frequency-specific perturbation of cortico-hippocampal interactions. This likely explains some of the amnestic actions of propofol.

Effects of Diazepam on Low-Frequency and High-Frequency Electrocortical γ-Power Mediated by α1- and α2-GABAA Receptors.

Patterns of spontaneous electric activity in the cerebral cortex change upon administration of benzodiazepines. Here we are testing the hypothesis that the prototypical benzodiazepine, diazepam, affects spectral power density in the low (20-50 Hz) and high (50-90 Hz) γ-band by targeting GABAA receptors harboring α1- and α2-subunits. Local field potentials (LFPs) and action potentials were recorded in the barrel cortex of wild type mice and two mutant strains in which the drug exclusively acted via GABAA receptors containing either α1- (DZα1-mice) or α2-subunits (DZα2-mice). In wild type mice, diazepam enhanced low γ-power. This effect was also evident in DZα2-mice, while diazepam decreased low γ-power in DZα1-mice. Diazepam increased correlated local LFP-activity in wild type animals and DZα2- but not in DZα1-mice. In all genotypes, spectral power density in the high γ-range and multi-unit action potential activity declined upon diazepam administration. We conclude that diazepam modifies low γ-power in opposing ways via α1- and α2-GABAA receptors. The drug's boosting effect involves α2-receptors and an increase in local intra-cortical synchrony. Furthermore, it is important to make a distinction between high- and low γ-power when evaluating the effects of drugs that target GABAA receptors.

Targeted Treatment of Individuals With Psychosis Carrying a Copy Number Variant Containing a Genomic Triplication of the Glycine Decarboxylase Gene.

BACKGROUND: The increased mutational burden for rare structural genomic variants in schizophrenia and other neurodevelopmental disorders has so far not yielded therapies targeting the biological effects of specific mutations. We identified two carriers (mother and son) of a triplication of the gene encoding glycine decarboxylase, GLDC, presumably resulting in reduced availability of the N-methyl-D-aspartate receptor coagonists glycine and D-serine and N-methyl-D-aspartate receptor hypofunction. Both carriers had a diagnosis of a psychotic disorder. METHODS: We carried out two double-blind, placebo-controlled clinical trials of N-methyl-D-aspartate receptor augmentation of psychotropic drug treatment in these two individuals. Glycine was used in the first clinical trial, and D-cycloserine was used in the second one. RESULTS: Glycine or D-cycloserine augmentation of psychotropic drug treatment each improved psychotic and mood symptoms in placebo-controlled trials. CONCLUSIONS: These results provide two independent proof-of-principle demonstrations of symptom relief by targeting a specific genotype and explicitly link an individual mutation to the pathophysiology of psychosis and treatment response.

TP003 is a non-selective benzodiazepine site agonist that induces anxiolysis via α2GABAA receptors.

Benzodiazepines (BDZ), which potentiate the action of GABA at four subtypes of GABAA receptors (α1, α2, α3, and α5GABAARs), are highly effective against anxiety disorders, but also cause severe side effects greatly limiting their clinical application. Both, preclinical studies in genetically engineered mice, and preclinical and clinical trials with subtype-selective compounds indicate that undesired effects can in principle be avoided by targeting specific GABAAR subtypes. While there is general consensus that activity at α1GABAARs should be avoided, controversy exists as to whether α2 or α3GABAARs need to be targeted for anxiolysis. While previous experiments in GABAAR point-mutated mice demonstrated a critical role of α2GABAARs, studies solely relying on pharmacological approaches suggested a dominant contribution of α3GABAARs. As most α1GABAAR-sparing BDZ site agonists discriminate little between α2 and α3GABAARs, these claims rest almost exclusively on a single compound, TP003, that has been reported to be a selective α3GABAAR modulator. Here, we have revisited the in vitro pharmacological profile of TP003 and, in addition, tested TP003 in GABAAR triple point-mutated mice, in which only either α1, α2, or α3GABAARs were left BDZ sensitive. These experiments revealed that TP003 behaves as a partial, rather non-selective BDZ site agonist in vitro that acts in vivo through α1, α2, and α3GABAARs (α5GABAAR-mediated effects were not tested). With respect to anxiolysis, our results support a critical contribution of α2GABAARs, but not of α3GABAARs. TP003 should therefore not be considered an α3GABAAR selective agent. Previously published studies using TP003 should be interpreted with caution.