GABAergic Effects of Etifoxine and Alprazolam Assessed by Double Pulse TMS.

INTRODUCTION: There is a need for novel anxiolytics with improved side effect profiles compared to benzodiazepines. A promising candidate with alternative pharmacodynamics is the translocator protein ligand, etifoxine. METHODS: To get further insight into its mechanisms of action and side effects compared to the benzodiazepine alprazolam, we performed a double-blind, placebo-controlled, repeated-measures study in 36 healthy male subjects. Participants were examined for trait anxiety and side effects and underwent repeated transcranial magnetic stimulation (TMS) assessments, including motor evoked potentials (MEP), short intracortical inhibition (SICI), intracortical facilitation (ICF), and cortical silent period (CSP). RESULTS: We observed attenuation of MEPs by alprazolam but not by etifoxine. SICI was not significantly affected by alprazolam or etifoxine. However, the response pattern indicated a lowered SICI threshold after the administration of etifoxine and alprazolam compared to the placebo. ICF and CSP were influenced by neither medication. Alprazolam led to higher sedation and subjective impairment of concentration compared to etifoxine. Individual anxiety trait scores did not affect TMS parameters. DISCUSSION: This study indicated a favorable side effect profile of etifoxine in healthy volunteers. Moreover, it revealed differential GABA-related effects on neuromuscular function by means of TMS. The side effects and TMS profile of etifoxine are compatible with the involvement of neurosteroidogenesis and a predominant α3 subunit modulation compared to alprazolam.

A Novel CCK Receptor GPR173 Mediates Potentiation of GABAergic Inhibition.

Cholecystokinin (CCK) enables excitatory circuit long-term potentiation (LTP). Here, we investigated its involvement in the enhancement of inhibitory synapses. Activation of GABA neurons suppressed neuronal responses in the neocortex to a forthcoming auditory stimulus in mice of both sexes. High-frequency laser stimulation (HFLS) of GABAergic neurons potentiated this suppression. HFLS of CCK interneurons could induce the LTP of their inhibition toward pyramidal neurons. This potentiation was abolished in CCK knock-out mice but intact in mice with both CCK1R and 2R knockout of both sexes. Next, we combined bioinformatics analysis, multiple unbiased cell-based assays, and histology examinations to identify a novel CCK receptor, GPR173. We propose GPR173 as CCK3R, which mediates the relationship between cortical CCK interneuron signaling and inhibitory LTP in the mice of either sex. Thus, GPR173 might represent a promising therapeutic target for brain disorders related to excitation and inhibition imbalance in the cortex.SIGNIFICANCE STATEMENT CCK, the most abundant and widely distributed neuropeptide in the CNS, colocalizes with many neurotransmitters and modulators. GABA is one of the important inhibitory neurotransmitters, and much evidence shows that CCK may be involved in modulating GABA signaling in many brain areas. However, the role of CCK-GABA neurons in the cortical microcircuits is still unclear. We identified a novel CCK receptor, GPR173, localized in the CCK-GABA synapses and mediated the enhancement of the GABA inhibition effect, which might represent a promising therapeutic target for brain disorders related to excitation and inhibition imbalance in the cortex.

GABA-ergic agents modulated the effects of histamine on the behaviour of male mice in the elevated plus maze test.

NEW FINDINGS: What is the central question of this study? Is there an interaction between histamine and the GABAergic system in modulation of anxiety in mice? What is the main finding and its importance? There is a synergistic anxiogenic effect between histamine and bicuculline in mice. This effect may be due to a direct or an indirect effect of the histaminergic system on the GABAergic system. ABSTRACT: It has been documented that both histaminergic and GABAergic systems participate in the neurobiology of anxiety behaviour. In the current research, we investigated the effects of the histaminergic system and GABAA receptor agents on anxiety-related behaviours and their interaction using the elevated plus maze test in mice. Intraperitoneal (i.p.) administration of muscimol (0.12 and 0.25 mg/kg) increased the open arm time (OAT) (P < 0.001) without affecting the open arm entries (OAE) and locomotor activity, showing an anxiolytic effect. i.p. injection of bicuculline (0.5 and 1 mg/kg) decreased OAT (P < 0.001) but not OAE and locomotor activity, suggesting an anxiogenic behaviour. Intracerebroventricular (i.c.v.) microinjection of histamine (2.5 and 5 µg/mouse) resulted in a decline in OAT (P < 0.001) but not OAE and locomotor activity, indicating an anxiogenic response. Co-administration of histamine with GABAergic agents, muscimol (0.06 mg/kg; i.p.) and bicuculline (0.25 mg/kg; i.p.), decreased (P < 0.001) and increased (P < 0.05), respectively, the anxiogenic-like response to the effective dose (5 µg/mouse; i.c.v.) of histamine. In addition, co-treatment of effective doses of histamine (2.5 and 5 µg/mouse;i.c.v.) with an effective dose of muscimol (0.12 mg/kg; i.p.) and a non-effective dose of bicuculline (0.25 mg/kg; i.p.) significantly decreased OAT (P < 0.001), suggesting a likely interaction between the histaminergic and GABAergic systems in the regulation of anxiety. The results demonstrated a synergistic anxiogenic-like effect between histamine and bicuculline in mice. In conclusion, our results present an interaction between the histaminergic and GABAergic systems in anxiolytic/anxiogenic-like behaviours in the elevated plus maze test.

The imidazodiazepine, KRM-II-81: An example of a newly emerging generation of GABAkines for neurological and psychiatric disorders.

GABAkines, or positive allosteric modulators of γ-aminobutyric acid-A (GABAA) receptors, are used for the treatment of anxiety, epilepsy, sleep, and other disorders. The search for improved GABAkines, with reduced safety liabilities (e.g., dependence) or side-effect profiles (e.g., sedation) constituted multiple discovery and development campaigns that involved a multitude of strategies over the past century. Due to the general lack of success in the development of new GABAkines, there had been a decades-long draught in bringing new GABAkines to market. Recently, however, there has been a resurgence of efforts to bring GABAkines to patients, the FDA approval of the neuroactive steroid brexanolone for post-partum depression in 2019 being the first. Other neuroactive steroids are in various stages of clinical development (ganaxolone, zuranolone, LYT-300, Sage-324, PRAX 114, and ETX-155). These GABAkines and non-steroid compounds (GRX-917, a TSPO binding site ligand), darigabat (CVL-865), an α2/3/5-preferring GABAkine, SAN711, an α3-preferring GABAkine, and the α2/3-preferring GABAkine, KRM-II-81, bring new therapeutic promise to this highly utilized medicinal target in neurology and psychiatry. Herein, we also discuss possible conditions that have enabled the transition to a new age of GABAkines. We highlight the pharmacology of KRM-II-81 that has the most preclinical data reported. KRM-II-81 is the lead compound in a new series of orally bioavailable imidazodiazepines entering IND-enabling safety studies. KRM-II-81 has a preclinical profile predicting efficacy against pharmacoresistant epilepsies, traumatic brain injury, and neuropathic pain. KRM-II-81 also produces anxiolytic- and antidepressant-like effects in rodent models. Other key features of the pharmacology of this compound are its low sedation rate, lack of tolerance development, and the ability to prevent the development of seizure sensitization.

Activation of the ABA Signal Pathway Mediated by GABA Improves the Drought Resistance of Apple Seedlings.

Drought seriously affects the yield and quality of apples. γ-aminobutyric acid (GABA) plays an important role in the responses of plants to various stresses. However, the role and possible mechanism of GABA in the drought response of apple seedlings remain unknown. To explore the effect of GABA on apple seedlings under drought stress, seedlings of Malus hupehensis were treated with seven concentrations of GABA, and the response of seedlings under 15-day drought stress was observed. The results showed that 0.5 mM GABA was the most effective at relieving drought stress. Treatment with GABA reduced the relative electrical conductivity and MDA content of leaves induced by drought stress and significantly increased the relative water content of leaves. Exogenous GABA significantly decreased the stomatal conductance and intercellular carbon dioxide concentration and transpiration rate, and it significantly increased the photosynthetic rate under drought. GABA also reduced the accumulation of superoxide anions and hydrogen peroxide in leaf tissues under drought and increased the activities of POD, SOD, and CAT and the content of GABA. Exogenous treatment with GABA acted through the accumulation of abscisic acid (ABA) in the leaves to significantly decrease stomatal conductance and increase the stomatal closure rate, and the levels of expression of ABA-related genes PYL4, ABI1, ABI2, HAB1, ABF3, and OST1 changed in response to drought. Taken together, exogenous GABA can enhance the drought tolerance of apple seedlings.

Pharmacological modulation of fish-induced depth selection in D. magna: the role of cholinergic and GABAergic signalling.

Animal behaviour is closely related to individual fitness, which allows animals to choose suitable mates or avoid predation. The central nervous system regulates many aspects of animal behaviour responses. Therefore, behavioural responses can be especially sensitive to compounds with a neurodevelopmental or neurofunctional mode of action. Phototactic behavioural changes against fish in the freshwater crustacean Daphnia magna have been the subject of many ecological investigations. The aim of this study was to identify which neurotransmitter systems modulate phototactic behaviour to fish kairomones. We used a positive phototactic D. magna clone (P132,85) that shows marked negative phototactism after exposure to fish kairomones. Treatments included up to 16 known agonists and antagonists of the serotonergic, cholinergic, dopaminergic, histaminergic, glutamatergic and GABAergic systems. It was hypothesized that many neurological signalling pathways may modulate D. magna phototactic behaviour to fish kairomones. A new custom-designed device with vertically oriented chambers was used, and changes in the preferred areas (bottom, middle, and upper areas) were analysed using groups of animals after 24 h of exposure to the selected substance(s). The results indicated that agonists of the muscarinic acetylcholine and GABAA receptors and their equi-effective mixture ameliorated the negative phototactic response to fish kairomones, whereas antagonists and their mixtures increased the negative phototactism to fish kairomones. Interestingly, inhibition of the muscarinic acetylcholine receptor abolished positive phototaxis, thus inducing the phototactic response to fish kairomones. Analysis of the profile of neurotransmitters and their related metabolites showed that the D. magna behavioural responses induced by fish depend on changes in the levels of acetylcholine, dopamine and GABA.

Hidden pharmacological activities of valproic acid: A new insight.

Valproic acid (VPA) is an approved drug for managing epileptic seizures, bipolar disorders, and migraine. VPA has been shown to elevate the level of gamma-aminobutyric acid (GABA) in the brain through competitive inhibition of GABA transaminase, thus promoting the availability of synaptic GABA and facilitating GABA-mediated responses. VPA, which is a small chain of fatty acids, prevents histone deacetylases (HDACs). HDACs play a crucial role in chromatin remodeling and gene expression through posttranslational changes of chromatin-associated histones. Recent studies reported a possible effect of VPA against particular types of cancers. This effect was partially attributed to its role in regulating epigenetic modifications through the inhibition of HDACs, which affect the expression of genes associated with cell cycle control, cellular differentiation, and apoptosis. In this review, we summarize the current information on the actions of VPA in diseases such as diabetes mellitus, kidney disorders, neurodegenerative diseases, muscular dystrophy, and cardiovascular disorders.

Sustained treatment with an α5 GABA A receptor negative allosteric modulator delays excitatory circuit development while maintaining GABAergic neurotransmission.

α5 subunit GABA type A receptor (GABAAR) preferring negative allosteric modulators (NAMs) are cognitive enhancers with antidepressant-like effects. α5-NAM success in treating mouse models of neurodevelopmental disorders with excessive inhibition have led to Phase 2 clinical trials for Down syndrome. Despite in vivo efficacy, no study has examined the effects of continued α5-NAM treatment on inhibitory and excitatory synapse plasticity to identify mechanisms of action. Here we used L-655,708, an imidazobenzodiazepine that acts as a highly selective but weak α5-NAM, to investigate the impact of sustained treatment on hippocampal neuron synapse and dendrite development. We show that 2-day pharmacological reduction of α5-GABAAR signaling from DIV12-14, when GABAARs contribute to depolarization, delays dendritic spine maturation and the NMDA receptor (NMDAR) GluN2B/GluN2A developmental shift. In contrast, α5-NAM treatment from DIV19-21, when hyperpolarizing GABAAR signaling predominates, enhances surface synaptic GluN2A while decreasing GluN2B. Despite changes in NMDAR subtype surface levels and localization, total levels of key excitatory synapse proteins were largely unchanged, and mEPSCs were unaltered. Importantly, 2-day α5-NAM treatment does not alter the total surface levels or distribution of α5-GABAARs, reduce the gephyrin inhibitory synaptic scaffold, or impair phasic or tonic inhibition. Furthermore, α5-NAM inhibition of the GABAAR tonic current in mature neurons is maintained after 2-day α5-NAM treatment, suggesting reduced tolerance liability, in contrast to other clinically relevant GABAAR-targeting drugs such as benzodiazepines. Together, these results show that α5-GABAARs contribute to dendritic spine maturation and excitatory synapse development via a NMDAR dependent mechanism without perturbing overall neuronal excitability.

GABAergic modulation of performance in response inhibition and interference control tasks.

BACKGROUND: Inhibitory control is a crucial executive function with high relevance to mental and physical well-being. However, there are still unanswered questions regarding its neural mechanisms, including the role of the major inhibitory neurotransmitter, γ-aminobutyric acid (GABA). AIMS: This study examined the effects of lorazepam (0.5 mg and 1 mg), a positive allosteric modulator at the GABAA receptor, on response inhibition and interference control. We also explored the heterogeneity of inhibitory control and calculated delta plots to explore whether lorazepam affects the gradual build-up of inhibition and activation over time. METHODS: N = 50 healthy participants performed antisaccade, Eriksen flanker and Simon tasks in a within-subjects, placebo-controlled, double-blind randomized design. RESULTS: Lorazepam increased reaction time (RT) and error rates dose dependently in all tasks (p ⩽ 0.005). In the antisaccade and Simon tasks, lorazepam increased congruency effects for error rate (p ⩽ 0.029) but not RT (p ⩾ 0.587). In the Eriksen flanker task, both congruency effects were increased by the drug (p ⩽ 0.031). Delta plots did not reflect drug-induced changes in inhibition and activation over time. Delta plots for RT in the Simon task were negative-going, as expected, whereas those for the antisaccade and flanker tasks were positive-going. CONCLUSIONS: This study provides evidence for GABAergic involvement in performance on response inhibition and interference control tasks. Furthermore, our findings highlight the diversity of the broader construct of inhibitory control while also pointing out similarities between different inhibitory control tasks. In contrast to RT and error rates, the cognitive processes indexed by delta plots may not be sensitive to GABAergic modulation.

Impaired inhibitory GABAergic synaptic transmission and transcription studied in single neurons by Patch-seq in Huntington's disease.

Transcriptional dysregulation in Huntington's disease (HD) causes functional deficits in striatal neurons. Here, we performed Patch-sequencing (Patch-seq) in an in vitro HD model to investigate the effects of mutant Huntingtin (Htt) on synaptic transmission and gene transcription in single striatal neurons. We found that expression of mutant Htt decreased the synaptic output of striatal neurons in a cell autonomous fashion and identified a number of genes whose dysregulation was correlated with physiological deficiencies in mutant Htt neurons. In support of a pivotal role for epigenetic mechanisms in HD pathophysiology, we found that inhibiting histone deacetylase 1/3 activities rectified several functional and morphological deficits and alleviated the aberrant transcriptional profiles in mutant Htt neurons. With this study, we demonstrate that Patch-seq technology can be applied both to better understand molecular mechanisms underlying a complex neurological disease at the single-cell level and to provide a platform for screening for therapeutics for the disease.

Gamma-aminobutyric acid attenuates insulin resistance in type 2 diabetic patients and reduces the risk of insulin resistance in their offspring.

The role of gamma-aminobutyric acid (GABA) in attenuates insulin resistance (IR) in type 2 diabetic (T2D) patients and the reduction of the risk of IR in their offspring, and the function of GLUT4, IRS1 and Akt2 genes expression were investigated. T2D was induced by high fat diet and 35 mg/kg of streptozotocin. The male and female diabetic rats were then divided into three groups: CD, GABA, and insulin. NDC group received a normal diet. All the animals were studied for a six-month. Their offspring were just fed with normal diet for four months. Blood glucose was measured weekly in patients and their offspring. Intraperitoneal glucose tolerance test (IPGTT), urine volume, and water consumption in both patients and their offspring were performed monthly. The hyperinsulinemic euglycemic clamp in both patients and their offspring was done and blood sample collected to measure Hemoglobin A1c (HbA1c). IRS1, Akt and GLUT4 gene expressions in muscle were evaluated in all the groups. GABA or insulin therapy decreased blood glucose, IPGTT, and HbA1c in patients and their offspring compared to DC group. They also increased GIR in patients and their offspring. IRS1, Akt and GLUT4 gene expressions improved in both patients in comparison with DC group. GABA exerts beneficial effects on IRS1 and Akt gene expressions in GABA treated offspring. GABA therapy improved insulin resistance in diabetic patients by increasing the expression of GLUT4. It is also indirectly able to reduce insulin resistance in their offspring possibly through the increased gene expressions of IRS1 and Akt.

The intracellular domain of homomeric glycine receptors modulates agonist efficacy.

Like other pentameric ligand-gated channels, glycine receptors (GlyRs) contain long intracellular domains (ICDs) between transmembrane helices 3 and 4. Structurally characterized GlyRs are generally engineered to have a very short ICD. We show here that for one such construct, zebrafish GlyREM, the agonists glycine, ß-alanine, taurine, and GABA have high efficacy and produce maximum single-channel open probabilities greater than 0.9. In contrast, for full-length human α1 GlyR, taurine and GABA were clearly partial agonists, with maximum open probabilities of 0.46 and 0.09, respectively. We found that the elevated open probabilities in GlyREM are not due to the limited sequence differences between the human and zebrafish orthologs, but rather to replacement of the native ICD with a short tripeptide ICD. Consistent with this interpretation, shortening the ICD in the human GlyR increased the maximum open probability produced by taurine and GABA to 0.90 and 0.70, respectively, but further engineering it to resemble GlyREM (by introducing the zebrafish transmembrane helix 4 and C terminus) had no effect. Furthermore, reinstating the native ICD to GlyREM converted taurine and GABA to partial agonists, with maximum open probabilities of 0.66 and 0.40, respectively. Structural comparison of transmembrane helices 3 and 4 in short- and long-ICD GlyR subunits revealed that ICD shortening does not distort the orientation of these helices within each subunit. This suggests that the effects of shortening the ICD stem from removing a modulatory effect of the native ICD on GlyR gating, revealing a new role for the ICD in pentameric ligand-gated channels.

Estrogen Receptors Alpha and Beta Mediate Synaptic Transmission in the PFC and Hippocampus of Mice.

Distinct from ovarian estradiol, the steroid hormone 17ß-estradiol (E2) is produced in the brain and is involved in numerous functions, particularly acting as a neurosteroid. However, the physiological role of E2 and the mechanism of its effects are not well known. In hippocampal slices, 17ß-estradiol has been found to cause a modest increase in fast glutamatergic transmission; because some of these effects are rapid and acute, they might be mediated by membrane-associated receptors via nongenomic action. Moreover, activation of membrane estrogen receptors can rapidly modulate neuron function in a sex-specific manner. To further investigate the neurological role of E2, we examined the effect of E2, as an estrogen receptor (ER) agonist, on synaptic transmission in slices of the prefrontal cortex (PFC) and hippocampus in both male and female mice. Whole-cell recordings of spontaneous excitatory postsynaptic currents (sEPSC) in the PFC showed that E2 acts as a neuromodulator in glutamatergic transmission in the PFC in both sexes, but often in a cell-specific manner. The sEPSC amplitude and/or frequency responded to E2 in three ways, namely by significantly increasing, decreasing or having no response. Additional experiments using an agonist selective for ERß, diarylpropionitrile (DPN) showed that in males the sEPSC and spontaneous inhibitory postsynaptic currents sIPSC responses were similar to their E2 responses, but in females the estrogen receptor ß (ERß) agonist DPN did not influence excitatory transmission in the PFC. In contrast, in the hippocampus of both sexes E2 potentiated the gluatmatergic synaptic transmission in a subset of hippocampal cells. These data indicate that activation of E2 targeting probably a estrogen subtypes or different downstream signaling affect synaptic transmission in the brain PFC and hippocampus between males versus females mice.

Involvement of opioidergic and GABAergic systems in the anti-nociceptive activity of the methanolic extract of Cuscuta Epithymum Murr. in mice.

ETHNOPHARMACOLOGICAL RELEVANCE: Cuscuta epithymum Murr. (CE) is a parasitic plant used as a traditional medicine to treat various diseases such as muscle and joint pains and headache different parts of the world, Europe in the north, Asia in the east. AIM OF THE STUDY: In this study, we aimed to investigate the anti-nociceptive effect of the methanolic extract of the aerial parts of CE and its probable mechanism(s) in mice. MATERIALS AND METHODS: The anti-nociceptive activity of different doses of CE methanolic extract (2.5, 5, 10, 25, 50 and 100 mg/kg, i.p.) was assessed using tail flick, formalin and writhing tests. Morphine (5 mg/kg, s.c.) was used as positive control drug. The possible mechanisms were evaluated by using naloxone (4 mg/kg, i.p.), ondansetron (4 mg/kg, i.p.), picrotoxin (0.6 mg/kg, i.p.) and MK-801 (0.03 mg/kg, i.p.). RESULTS: GC-MS analysis indicated that one of the main components of CE extract was terpenoid compounds. The CE extract (25-100 mg/kg), like morphine, reduced tail flick latency and nociceptive response in both phases of the formalin test. We also observed that the extract significantly decreased the number of abdominal contractions dose-dependently from 5 to 100 mg/kg. The results of tail flick and the first phase of formalin test proved that unlike ondansetron and MK-801, naloxone and picotroxin were able to reverse the anti-nociceptive effect of CE extract. CONCLUSION: Our observations showed the anti-nociceptive potential of the CE extract, which may be mediated by opioidergic and GABAergic systems.

Behavioral Deficits Induced by Somatostatin-Positive GABA Neuron Silencing Are Rescued by Alpha 5 GABA-A Receptor Potentiation.

INTRODUCTION: Deficits in somatostatin-positive gamma-aminobutyric acid interneurons (SST+ GABA cells) are commonly reported in human studies of mood and anxiety disorder patients. A causal link between SST+ cell dysfunction and symptom-related behaviors has been proposed based on rodent studies showing that chronic stress, a major risk factor for mood and anxiety disorders, induces a low SST+ GABA cellular phenotype across corticolimbic brain regions; that lowering Sst, SST+ cell, or GABA functions induces depressive-/anxiety-like behaviors (a rodent behavioral construct collectively defined as "behavioral emotionality"); and that disinhibiting SST+ cells has antidepressant-like effects. Recent studies found that compounds preferentially potentiating receptors mediating SST+ cell functions, α5-GABAA receptor positive allosteric modulators (α5-PAMs), achieved antidepressant-like effects. Together, the evidence suggests that SST+ cells regulate mood and cognitive functions that are disrupted in mood disorders and that rescuing SST+ cell function via α5-PAM may represent a targeted therapeutic strategy. METHODS: We developed a mouse model allowing chemogenetic manipulation of brain-wide SST+ cells and employed behavioral characterization 30 minutes after repeated acute silencing to identify contributions to symptom-related behaviors. We then assessed whether an α5-PAM, GL-II-73, could rescue behavioral deficits. RESULTS: Brain-wide SST+ cell silencing induced features of stress-related illnesses, including elevated neuronal activity and plasma corticosterone levels, increased anxiety- and anhedonia-like behaviors, and impaired short-term memory. GL-II-73 led to antidepressant- and anxiolytic-like improvements among behavioral deficits induced by brain-wide SST+ cell silencing. CONCLUSION: Our data validate SST+ cells as regulators of mood and cognitive functions and demonstrate that bypassing low SST+ cell function via α5-PAM represents a targeted therapeutic strategy.

Valproic acid treated female Long-Evans rats are impaired on attentional set-shifting.

Autism spectrum disorder (ASD), is a neurodevelopmental disorder characterized by social deficits, communication impairments, restrictive behaviors, and cognitive flexibility deficits. The valproic acid (VPA) model of autism has been widely used to examine changes in rodent behavior and neurobiology to better understand ASD. This study examined social and anxiety behavior as well as cognitive flexibility in VPA and control offspring. Results for social behavior were consistent with prior studies showing reduced sociability in VPA rats and increased self-grooming, which may be viewed as a repetitive behavior. VPA rats also had deficits in performing the set-shifting task, with female VPA rats demonstrating greater impairment compared to female control rats and male VPA rats. These results support the hypothesis that females diagnosed with ASD may suffer from different symptoms and present a unique behavioral profile compared to males with ASD. Female VPA rats were also less likely to form an attentional set; offering evidence that the VPA model of autism is encompassing executive function deficits similar to those observed in humans with ASD.

Combined use of GABA and sitagliptin promotes human ß-cell proliferation and reduces apoptosis.

γ-Aminobutyric acid (GABA) and glucagon-like peptide-1 receptor agonist (GLP-1RA) improve rodent ß-cell survival and function. In human ß-cells, GABA exerts stimulatory effects on proliferation and anti-apoptotic effects, whereas GLP-1RA drugs have only limited effects on proliferation. We previously demonstrated that GABA and sitagliptin (Sita), a dipeptidyl peptidase-4 inhibitor which increases endogenous GLP-1 levels, mediated a synergistic ß-cell protective effect in mice islets. However, it remains unclear whether this combination has similar effects on human ß-cell. To address this question, we transplanted a suboptimal mass of human islets into immunodeficient NOD-scid-gamma mice with streptozotocin-induced diabetes, and then treated them with GABA, Sita, or both. The oral administration of either GABA or Sita ameliorated blood glucose levels, increased transplanted human ß-cell counts and plasma human insulin levels. Importantly, the combined administration of the drugs generated significantly superior results in all these responses, as compared to the monotherapy with either one of them. The proliferation and/or regeneration, improved by the combination, were demonstrated by increased Ki67+, PDX-1+, or Nkx6.1+ ß-cell numbers. Protection against apoptosis was also significantly improved by the drug combination. The expression level of α-Klotho, a protein with protective and stimulatory effects on ß cells, was also augmented. Our study indicates that combined use of GABA and Sita produced greater therapeutic benefits, which are likely due to an enhancement of ß-cell proliferation and a decrease in apoptosis.

Lateral septum microglial changes and behavioral abnormalities of mice exposed to valproic acid during the prenatal period.

Most animal model studies of autism spectrum disorder (ASD) have been performed in males, which may be a reflex of the 3-times higher prevalence in boys than in girls. For this reason, little is known about the mechanisms underlying disease progression in females, and nothing is known about potential associations between microglial changes in the lateral septum (LS) and adult female cognition. Prenatal exposure to valproic acid (VPA) in mice has been widely used as an experimental model of autism-like behaviors associated with cellular changes. However, no study has reported the influence of VPA exposure in utero and its consequences on limbic system-dependent tasks or the microglial response in the LS in adult female mice. We compared the exploratory activity and risk assessment in novel environments of BALB/c control mice to mice exposed in utero to VPA and estimated the total number of microglia in the LS using an optical fractionator. On day 12.5 of pregnancy, females received diluted VPA or saline by gavage. After weaning, VPA exposed or control pups were separately housed in standard laboratory cages. At 5 months of age, all mice underwent behavioral testing and their brain sections were immunolabelled using IBA-1 antibody. In the open field test, VPA group showed a greater distance traveled, which was accompanied by less immobility, less time spent on the periphery and a greater number, crossed lines. Similar findings were found in the elevated plus maze test, where VPA mice traveled greater distances, immobility was significantly higher than that of control and VPA group spent less time on the closed arms of apparatus. Stereological analysis demonstrated higher microglial total number and density in the LS of VPA mice, as the cell count was greater, but the volume was similar. Therefore, we suggest that an increase in microglia in the LS may be part of the cellular changes associated with behavioral dysfunction in the VPA model of ASD.

Molecular Dynamic Simulations to Probe Stereoselectivity of Tiagabine Binding with Human GAT1.

The human gamma aminobutyric acid transporter subtype 1 (hGAT1) located in the nerve terminals is known to catalyze the neuronal function by the electrogenic reuptake of γ-aminobutyric acid (GABA) with the co-transport of Na+ and Cl- ions. In the past, there has been a major research drive focused on the dysfunction of hGAT1 in several neurological disorders. Thus, hGAT1 of the GABAergic system has been well established as an attractive target for such diseased conditions. Till date, there are various reports about stereo selectivity of -COOH group of tiagabine, a Food and Drug Administration (FDA)-approved hGAT1-selective antiepileptic drug. However, the effect of the stereochemistry of the protonated -NH group of tiagabine has never been scrutinized. Therefore, in this study, tiagabine has been used to explore the binding hypothesis of different enantiomers of tiagabine. In addition, the impact of axial and equatorial configuration of the-COOH group attached at the meta position of the piperidine ring of tiagabine enantiomers was also investigated. Further, the stability of the finally selected four hGAT1-tiagabine enantiomers namely entries 3, 4, 6, and 9 was evaluated through 100 ns molecular dynamics (MD) simulations for the selection of the best probable tiagabine enantiomer. The results indicate that the protonated -NH group in the R-conformation and the -COOH group of Tiagabine in the equatorial configuration of entry 4 provide maximum strength in terms of interaction within the hGAT1 binding pocket to prevent the change in hGAT1 conformational state, i.e., from open-to-out to open-to-in as compared to other selected tiagabine enantiomers 3, 6, and 9.

Cortical Control of Subthalamic Neuronal Activity through the Hyperdirect and Indirect Pathways in Monkeys.

The subthalamic nucleus (STN) plays a key role in the control of voluntary movements and basal ganglia disorders, such as Parkinson's disease and hemiballismus. The STN receives glutamatergic inputs directly from the cerebral cortex via the cortico-STN hyperdirect pathway and GABAergic inputs from the external segment of the globus pallidus (GPe) via the cortico-striato-GPe-STN indirect pathway. The STN then drives the internal segment of the globus pallidus, which is the output nucleus of the basal ganglia. Thus, clarifying how STN neuronal activity is controlled by the two inputs is crucial. Cortical stimulation evokes early excitation and late excitation in STN neurons, intervened by a short gap. Here, to examine the origin of each component of this biphasic response, we recorded neuronal activity in the STN, combined with electrical stimulation of the motor cortices and local drug application in two male monkeys (Macaca fuscata) in the awake state. Local application of glutamate receptor antagonists, a mixture of an AMPA/kainate receptor antagonist and an NMDA receptor antagonist, into the vicinity of recorded STN neurons specifically diminished early excitation. Blockade of the striatum (putamen) or GPe with local injection of a GABAA receptor agonist, muscimol, diminished late excitation in the STN. Blockade of striato-GPe transmission with local injection of a GABAA receptor antagonist, gabazine, into the GPe also abolished late excitation. These results indicate that cortically evoked early and late excitation in the STN is mediated by the cortico-STN glutamatergic hyperdirect and the cortico-striato-GPe-STN indirect pathways, respectively.SIGNIFICANCE STATEMENT Here we show that the subthalamic nucleus (STN), an input station of the basal ganglia, receives cortical inputs through the cortico-STN hyperdirect and cortico-striato-external pallido-STN indirect pathways. This knowledge is important for understanding not only the normal functions of the STN, but also the pathophysiology of STN-related disorders and therapy targeting the STN. Lesions or application of high-frequency stimulation in the STN ameliorates parkinsonian symptoms. These procedures could affect all components in the STN, such as afferent inputs through the hyperdirect and indirect pathways, and STN neuronal activity. If we can understand which component is most affected by such procedures, we may be able to identify more effective manipulation targets or methods to treat Parkinson's disease.