GABA Modulation Research Articles

Association between Inhibitory-Excitatory Balance and Brain Activity Response during Cognitive Flexibility in Young and Older Individuals.

Cognitive flexibility represents the capacity to switch among different mental schemes, providing an adaptive advantage to a changing environment. The neural underpinnings of this executive function have been deeply studied in humans through fMRI, showing that the left inferior frontal cortex (IFC) and the left inferior parietal lobe (IPL) are crucial. Here, we investigated the inhibitory-excitatory balance in these regions by means of γ-aminobutyric acid (GABA+) and glutamate + glutamine (Glx), measured with magnetic resonance spectroscopy (MRS), during a cognitive flexibility task and its relationship with performance level and the local task-induced blood-oxygen level dependent (BOLD) response in 40 young (18-35 y.o.; 26 female) and 40 older (18-35 y.o.; 21 female) human adults. As the IFC and the IPL are richly connected regions, we also examined whole-brain effects associated with their local metabolic activity. Results did not show absolute metabolic modulations associated with flexibility performance, but performance level was related to the direction of metabolic modulation in the IPL with opposite patterns in young and older individuals. The individual inhibitory-excitatory balance modulation showed an inverse relationship with the local BOLD response in the IPL. Finally, the modulation of inhibitory-excitatory balance in IPL was related to whole-brain effects only in older individuals. These findings show disparities in the metabolic mechanisms underlying cognitive flexibility in young and older adults and their association with performance level and BOLD response. Such metabolic differences are likely to play a role in executive functioning during aging and specifically in cognitive flexibility.Significance Statement Cognitive flexibility provides an advantage in adapting to changing environments. We investigated the inhibitory-excitatory balance (GABA+/Glx) modulation in the frontal and parietal cortices during cognitive flexibility in young and older individuals through MRS. An increase in the excitatory tone during cognitive performance related to a better execution in younger adults. Interestingly, it was an increase in the inhibitory tone that was associated to a better performance in older adults. Furthermore, we revealed that an increased inhibitory tone in older adults related to a decreased oxygen consumption in remote brain areas (BOLD-fMRI). This may suggest that GABA modulation facilitates the segregation of neural networks, maximizing brain efficiency and cognitive performance. These findings underscore age-related disparities in the neurometabolic mechanisms underlying cognitive flexibility.

Age-Dependent Changes in the Occurrence and Segregation of GABA and Acetylcholine in the Rat Superior Cervical Ganglia.

The occurrence, inhibitory modulation, and trophic effects of GABA have been identified in the peripheral sympathetic nervous system. We have demonstrated that GABA and acetylcholine (ACh) may colocalize in the same axonal varicosities or be segregated into separate ones in the rat superior cervical ganglia (SCG). Neurotransmitter segregation varies with age and the presence of neurotrophic factors. Here, we explored age-dependent changes in the occurrence and segregation of GABA and ACh in rats ranging from 2 weeks old (wo) to 12 months old or older. Using immunohistochemistry, we characterized the expression of L-glutamic acid decarboxylase of 67 kDa (GAD67) and vesicular acetylcholine transporter (VAChT) in the rat SCG at 2, 4, 8, 12 wo and 12 months old or older. Our findings revealed that GAD67 was greater at 2 wo compared with the other ages, whereas VAChT levels were greater at 4 wo than at 12 wo and 12 months old or older. The segregation of these neurotransmitters was more pronounced at 2 and 4 wo. We observed a caudo-rostral gradient of segregation degree at 8 and 12 wo. Data point out that the occurrence and segregation of GABA and ACh exhibit developmental adaptative changes throughout the lifetime of rats. We hypothesize that during the early postnatal period, the increase in GABA and GABA-ACh segregation promotes the release of GABA alone which might play a role in trophic actions.

The metabolism of amino acids, AsA and abscisic acid induced by strigolactone participates in chilling tolerance in postharvest zucchini fruit.

Zucchini fruit are notably susceptible to chilling injury when stored at low temperatures. The purpose of this experimental investigation was to assess the influence of strigolactone (ST) (5 μmol L-1) on mitigating chilling injury and the metabolic changes in amino acids, ascorbic acid, and abscisic acid in zucchini fruit stored at 4°C. Research findings demonstrated that ST-treated zucchini fruit displayed a significantly higher tolerance to chilling stress compared to the control group. Postharvest ST treatment led to a decrease in weight loss, accompanied by reduced levels of malondialdehyde and relative ion leakage compared to the untreated group. ST immersion significantly boosted the metabolic pathways associated with proline and arginine, affecting both the enzymatic reactions and gene expressions, thus cumulatively increasing the internal concentrations of these amino acids in zucchini fruit. Zucchini treated with ST exhibited an increased concentration of γ-aminobutyric acid (GABA) as a result of augmented activities and elevated transcriptional levels of glutamate decarboxylase (GAD), GABA transaminase (GAT), and succinate semialdehyde dehydrogenase (SSD). In the ST-treated sample, the elevated enzymatic activities and enhanced gene expressions within the ascorbic acid (AsA) biosynthesis pathway worked together to sustain AsA accumulation. The application of ST resulted in a rise in abscisic acid (ABA) concentration, which correspondingly correlated with the induction of both activities and gene expression levels of crucial enzymes involved in ABA metabolism. Our findings revealed that submerging zucchini fruit in ST could be a highly effective strategy for boosting their chilling tolerance. The alleviation in chilling injury induced by ST may be attributed to the modulation of proline, arginine, GABA, AsA and ABA metabolism.

Modulation of GABA by sodium butyrate ameliorates hypothalamic inflammation in experimental model of PCOS

Polycystic ovarian syndrome (PCOS) is a known endocrine disorder that has affected many women of childbearing age, and is accompanied by various neurodegenerative conditions. Hence, this study investigates the impact of butyrate in reversing hypothalamic-related disorder, possibly through γ aminobutyric acid (GABA) in a rat model of PCOS. Eight-week-old female Wistar rats were allotted into four groups (n = 5), which include control, butyrate, letrozole, and letrozole + butyrate groups. PCOS was induced by administering 1 mg/kg of letrozole (oral gavage) for 21 days. After confirmation of PCOS, 200 mg/kg of butyrate (oral gavage) was administered for 6 weeks. Rats with PCOS were characterized by elevated levels of plasma insulin and testosterone. Increases in plasma and hypothalamic triglyceride levels, inflammatory biomarker (SDF-1), apoptotic marker (caspase-6), and decreased plasma GnRH were observed. Additionally, a decrease in hypothalamic GABA was revealed. Nevertheless, the administration of butyrate attenuated these alterations. The present study suggests that butyrate ameliorates hypothalamic inflammation in an experimental model of PCOS, a beneficial effect that is accompanied by enhanced GABA production.

Pharmacotherapies Targeting GABA-Glutamate Neurotransmission for Treatment-Resistant Depression.

Treatment-resistant depression (TRD) is a term used to describe a particular type of major depressive disorder (MDD). There is no consensus about what defines TRD, with various studies describing between 1 and 4 failures of antidepressant therapies, with or without electroconvulsive therapy (ECT). That is why TRD is such a growing concern among clinicians and researchers, and it explains the necessity for investigating novel therapeutic targets beyond conventional monoamine pathways. An imbalance between two primary central nervous system (CNS) neurotransmitters, L-glutamate and γ-aminobutyric acid (GABA), has emerged as having a key role in the pathophysiology of TRD. In this review, we provide an evaluation and comprehensive review of investigational antidepressants targeting these two systems, accessing their levels of available evidence, mechanisms of action, and safety profiles. N-methyl-D-aspartate (NMDA) receptor antagonism has shown the most promise amongst the glutamatergic targets, with ketamine and esketamine (Spravato) robustly generating responses across trials. Two specific NMDA-glycine site modulators, D-cycloserine (DCS) and apimostinel, have also generated promising initial safety and efficacy profiles, warranting further investigation. Combination dextromethorphan-bupropion (AXS-05/Auvelity) displays a unique mechanism of action and demonstrated positive results in particular applicability in subpopulations with cognitive dysfunction. Currently, the most promising GABA modulators appear to be synthetic neurosteroid analogs with positive GABAA receptor modulation (such as brexanolone). Overall, advances in the last decade provide exciting perspectives for those who do not improve with conventional therapies. Of the compounds reviewed here, three are approved by the Food and Drug Administration (FDA): esketamine (Spravato) for TRD, Auvelity (dextromethorphan-bupropion) for major depressive disorder (MDD), and brexanolone (Zulresso) for post-partum depression (PPD). Notably, some concerns have arisen with esketamine and brexanolone, which will be detailed in this study.

Autism Spectrum Disorder and Role of the Inflammatory Theory: A Case Report

In this case study, an 8-year-old child from a consanguineous marriage with a complicated pregnancy due to maternal preeclampsia and a normal delivery experienced developmental delays, language problems, social challenges, and other autism spectrum disorder (ASD) symptoms. The child underwent various diagnostic tests, including the M-CHAT, ADI, and ADOS, which all supported an ASD diagnosis. Despite receiving psychomotor, speech, and ABA therapy, the child showed gradual improvement in language skills but continued to exhibit behavioral issues such as irritability, anger outbursts, and sleep disturbances. After experiencing a febrile episode with tonsillitis, followed by knee pain, walking difficulties, chest pain, and shortness of breath, the child was diagnosed with acute rheumatic fever and received corticosteroid therapy, resulting in significant clinical improvement in language, facial expressions, social interactions, and a renewed ASD assessment. The discussion focuses on the potential environmental factors contributing to ASD, emphasizing the role of shared environmental factors in twin studies and genetic factors. The study explores the inflammatory response as a possible common pathway for ASD development, particularly in cases where preeclampsia during pregnancy and its associated inflammation affect the mother and, subsequently, the placenta or fetus. Abnormal angiogenesis and elevated levels of soluble tyrosine kinase 1 (sFlt-1) are discussed as potential factors contributing to fetal neurodevelopmental abnormalities. The text also highlights the role of corticosteroid therapy in improving ASD symptoms, with references to previous studies showing positive responses to corticosteroid treatment in ASD patients. The impact of medications like prednisone and pregnenolone on ASD symptoms and their mechanisms of action, including potential modulation of GABA A receptors, is mentioned. In conclusion, the case study suggests a potential link between ........

Anxiolytic activity of Coconut water by GABA Modulation as Evidenced by Pharmacological Experiments and Molecular Docking Studies

Objective: To determine the anxiolytic activity of coconut water by pre-clinical studies. Materials and Methods: The anxiolytic activity of coconut water was screened by neuropharmacology and molecular docking studies. Twenty-four adult female rats of the Wistar strain were divided equally into four groups: Group I: Distilled water [3ml/Kg]; Group II: Coconut water [3ml/Kg]; Group III: Diazepam [5mg/Kg]; Group IV: Coconut water [3ml/Kg] + Diazepam [2.5mg/Kg]. All agents were administered orally for 15 days. Elevated plus maze and light/dark arena apparatus tests were used to assess anxiety in rats. Once the pharmacological screening was done, rats were sacrificed, and brains were removed out to estimate GABA levels. An insilico docking of bio-active components in coconut water was done to probe the possible mechanism of action. Results: This study showed coconut water produced significant anxiolytic activity in rats. Brain biochemical analysis revealed coconut water significantly increased GABA levels. Computational studies revealed that the phytocompound ‘Zeatin’ in coconut water could block gamma-aminobutyric acid transaminase, the enzyme responsible for GABA degradation, thereby increasing GABA levels. Conclusion: Coconut water has anxiolytic-like activity by modulating GABAergic neurotransmission.

Efficacy and safety of pharmacotherapy for refractory or unexplained chronic cough: a systematic review and network meta-analysis

Refractory chronic cough (RCC) has a significant impact on patient's health-related quality of life and represents a challenge in clinical management. However, the optimal treatment for RCC remains controversial. This study aimed to investigate and compare the efficacy and safety of the current pharmacological therapeutic options for RCC. A systematic review was performed by searching PubMed, Web of Science, Embase, and Ovid databases from January 1, 2008 to March 1, 2023. All randomised control trials (RCTs) reporting outcomes of efficacy or/and safety were included in the Bayesian network meta-analysis. Here, we compared the effects on Leicester Cough Questionnaire (LCQ), Visual Analogue Scale (VAS), and objective cough frequency of patients with RCC. Besides, we also compared the incidence of adverse events (AEs) for analysis of safety. PROSPERO registration: CRD42022345940. 19 eligible RCTs included 3326 patients and 7 medication categories: P2X3 antagonist, GABA modulator, Transient Receptor Potential (TRP) modulator, NK-1 agonist, opioid analgesic, macrolide, and sodium cromoglicate. Compared with placebo, mean difference (MD) of LCQ and 24 h cough frequency for P2X3 antagonist relief were 1.637 (95% CI: 0.887-2.387) and-11.042 (P=0.035). Compared with placebo, effect sizes (MD for LCQ and cough severity VAS) for GABA modulator were 1.347 (P=0.003) and-7.843 (P=0.003). In the network meta-analysis, gefapixant is the most effective treatment for patients with RCC (The Surface Under the Cumulative Ranking Curves (SUCRA) is 0.711 in LCQ, 0.983 in 24 h cough frequency, and 0.786 in cough severity VAS). Lesogaberan had better efficacy than placebo (SUCRA: 0.632 vs. 0.472) in 24 h cough frequency. Eliapixant and lesogaberan had better efficacy than placebo in cough severity VAS. However, TRP modulator had worse efficacy than placebo. In the meta-analysis of AEs, the present study found P2X3 antagonist had a significant correlation to AEs (RR: 1.129, 95% CI: 1.012-1.259), especially taste-related AEs (RR: 6.216, P<0.05). In this network meta-analysis, P2X3 antagonist showing advantages in terms of efficacy is currently the most promising medication for treatment of RCC. GABA modulator also showed potential efficacy for RCC but with AEs of the central system. Nevertheless, the role of TRP modulator needed to be revisited. Further research is needed to determine the potential beneficiary population for optimizing the pharmacological management of chronic cough. National Natural Science Foundation of China (81870079), Guangdong Science and Technology Project (2021A050520012), Incubation Program of National Science Foundation for Distinguished Young Scholars (GMU2020-207).

Improvement in HAMD-17 Subscale Scores With 14-Day Treatment Course of Zuranolone in Postpartum Depression: Results From the SKYLARK Study [ID: 1372313

INTRODUCTION: Postpartum depression (PPD) is a serious perinatal complication. SKYLARK (phase 3, randomized, double-blind, placebo-controlled trial [NCT04442503]) evaluated zuranolone, an investigational, neuroactive steroid positive allosteric modulator of both synaptic and extrasynaptic GABA(A) receptors, in adult patients with PPD. The primary endpoint, change from baseline (CFB) in HAMD-17 total score at day 15, was met. Zuranolone was generally well tolerated. The HAMD-17 can be divided into subscales that group specific items from the HAMD-17 scale that measure different aspects of depression presentation. Here, we present HAMD-17 subscale data from SKYLARK. METHODS: Patients aged 18–45 years with severe PPD (HAMD 17 total score ≥26) were randomized 1:1 to oral, once-daily zuranolone 50 mg or placebo for 14 days. The secondary endpoint was day 15 CFB in HAMD-17 subscale (Core Depression, Anxiety, Bech-6, Maier) scores. Subscales were analyzed separately by a mixed-effects model for repeated measures. Institutional review board approval was obtained. RESULTS: One hundred ninety-five patients (zuranolone, 98; placebo, 97) were randomized, received study drug, and had valid baseline and one or more post-baseline efficacy assessments. At day 15, patients receiving a 14-day treatment course of zuranolone showed nominally significant improvements across all HAMD-17 subscales versus placebo (least squares mean [SE] CFB treatment difference: Core Depression, −5.9 [2.4], P=.0151; Anxiety, −5.7 [2.3], P=.0123; Bech-6, −8.6 [3.0], P=.0040; Maier, −7.6 [2.6], P=.0041). Improvement in all subscales was observed starting at day 3. CONCLUSION: In SKYLARK, zuranolone was associated with rapid improvement in depressive and anxiety symptoms in patients with PPD across multiple domains, supporting its development as a potential oral, rapid-acting treatment option for PPD.

Piracetam and Ginkgo biloba in the treatment of residual cognitive symptoms after the discontinuation of benzodiazepines in long-term users; case series and review of the literature

IntroductionLong-term benzodiazepine use is common although not routinely recommended. While their dependence potential is notorious, cognitive problems due to their chronic use have only recently been intensively studied. Residual cognitive symptoms may linger months after successful benzodiazepine discontinuation and significantly limit optimal functional outcome in abstinent individuals.ObjectivesWe present a series of cases, a 41-year-old man and a 33-year-old woman who successfully completed a ten-week benzodiazepine-dependence rehabilitation program at our hospital, including successful tapering and post-withdrawal integrative therapy. At subsequent monthly outpatient check-ups, abstinence was confirmed (including toxicology testing) and there was no residual anxiety or mood symptomatology. Still, patients complained of their suboptimal functioning due to residual cognitive problems, especially trouble concentrating and short-memory deficits, which were objectively confirmed via psychometric tests.MethodsDuring continuous outpatient treatment (monthly controls), patients were clinically and neurocognitively evaluated. They were reluctant to try conventional psychopharmacology agents but were open to supplement therapy. After thorough literature review, a trial of piracetam and Ginko biloba extract was suggested. Piracetam, a positive allosteric modulator of AMPA-receptors, has been used in the treatment of vascular neurocognitive changes in the elderly. Bilobalides from G. biloba, act as atypical antagonists of GABA-A receptors and were found to exert neuroprotective effects in animal models, without epileptogenic or anxiogenic risks.ResultsPatients were recommended piracetam (2.4 g a day) in divided doses and a once-daily dose of G. biloba extract (240 mg a day), in a standardized form containing 3.2% of bilobalides. No side effects were noticed. At subsequent monthly checkups, patients reported fewer cognitive problems and better everyday functioning. Neurocognitive testing confirmed subjective findings, with positive changes in all areas, but especially so in verbal memory, which may be due to this specific pharmacological combination. At the end of the observation period of sixth months, piracetam was gradually discontinued while patients were given free choice whether to continue with G. biloba supplementation.ConclusionsAccording to our findings, piracetam and G. biloba extract may prove beneficial in the treatment of residual cognitive symptoms after benzodiazepine discontinuation, in long-term benzodiazepine users. Other treatments, focusing not only on modulation of glutamate and GABA, but also on other pathways should be evaluated. Further clinical studies are warranted.Disclosure of InterestNone Declared

Histamine Release in the Prefrontal Cortex Excites Fast-Spiking Interneurons while GABA Released from the Same Axons Inhibits Pyramidal Cells.

We studied how histamine and GABA release from axons originating from the hypothalamic tuberomammillary nucleus (TMN) and projecting to the prefrontal cortex (PFC) influence circuit processing. We optostimulated histamine/GABA from genetically defined TMN axons that express the histidine decarboxylase gene (TMNHDC axons). Whole-cell recordings from PFC neurons in layer 2/3 of prelimbic, anterior cingulate, and infralimbic regions were used to monitor excitability before and after optostimulated histamine/GABA release in male and female mice. We found that histamine-GABA release influences the PFC through actions on distinct neuronal types: the histamine stimulates fast-spiking interneurons; and the released GABA enhances tonic (extrasynaptic) inhibition on pyramidal cells (PyrNs). For fast-spiking nonaccommodating interneurons, histamine released from TMNHDC axons induced additive gain changes, which were blocked by histamine H1 and H2 receptor antagonists. The excitability of other fast-spiking interneurons in the PFC was not altered. In contrast, the GABA released from TMNHDC axons predominantly produced divisive gain changes in PyrNs, increasing their resting input conductance, and decreasing the slope of the input-output relationship. This inhibitory effect on PyrNs was not blocked by histamine receptor antagonists but was blocked by GABAA receptor antagonists. Across the adult life span (from 3 to 18 months of age), the GABA released from TMNHDC axons in the PFC inhibited PyrN excitability significantly more in older mice. For individuals who maintain cognitive performance into later life, the increases in TMNHDC GABA modulation of PyrNs during aging could enhance information processing and be an adaptive mechanism to buttress cognition.SIGNIFICANCE STATEMENT The hypothalamus controls arousal state by releasing chemical neurotransmitters throughout the brain to modulate neuronal excitability. Evidence is emerging that the release of multiple types of neurotransmitters may have opposing actions on neuronal populations in key cortical regions. This study demonstrates for the first time that the neurotransmitters histamine and GABA are released in the prefrontal cortex from axons originating from the tuberomammillary nucleus of the hypothalamus. This work demonstrates how hypothalamic modulation of neuronal excitability is maintained throughout adult life, highlighting an unexpected aspect of the aging process that may help maintain cognitive abilities.

Modulation of the mammalian GABAA receptor by type I and type II positive allosteric modulators of the α7 nicotinic acetylcholine receptor.

Positive allosteric modulators of the α7 nicotinic acetylcholine (nACh) receptor (α7-PAMs) possess promnesic and procognitive properties and have potential in the treatment of cognitive and psychiatric disorders including Alzheimer's disease and schizophrenia. Behavioural studies in rodents have indicated that α7-PAMs can also produce antinociceptive and anxiolytic effects that may be associated with positive modulation of the GABAA receptor. The overall goal of this study was to investigate the modulatory actions of selected α7-PAMs on the GABAA receptor. We employed a combination of cell fluorescence imaging, electrophysiology, functional competition and site-directed mutagenesis to investigate the functional and structural mechanisms of modulation of the GABAA receptor by three representative α7-PAMs. We show that the α7-PAMs at micromolar concentrations enhance the apparent affinity of the GABAA receptor for the transmitter and potentiate current responses from the receptor. The compounds were equi-effective at binary αβ and ternary αβγ GABAA receptors. Functional competition and site-directed mutagenesis indicate that the α7-PAMs bind to the classic anaesthetic binding sites in the transmembrane region in the intersubunit interfaces, which results in stabilization of the active state of the receptor. We conclude that the tested α7-PAMs are micromolar-affinity, intermediate- to low-efficacy allosteric potentiators of the mammalian αβγ GABAA receptor. Given the similarities in the in vitro sensitivities of the α7 nACh and α1β2γ2L GABAA receptors to α7-PAMs, we propose that doses used to produce nACh receptor-mediated behavioural effects in vivo are likely to modulate GABAA receptor function.

Non-sedative cortical EEG signatures of allopregnanolone and functional comparators

Neurosteroids that positively modulate GABAA receptors are among a growing list of rapidly acting antidepressants, including ketamine and psychedelics. To develop increasingly specific treatments with fewer side effects, we explored the possibility of EEG signatures in mice, which could serve as a cross-species screening tool. There are few studies of the impact of non-sedative doses of rapid antidepressants on EEG in either rodents or humans. Here we hypothesize that EEG features may separate a rapid antidepressant neurosteroid, allopregnanolone, from other GABAA positive modulators, pentobarbital and diazepam. Further, we compared the actions GABA modulators with those of ketamine, an NMDA antagonist and prototype rapid antidepressant. We examined EEG spectra during active exploration at two cortical locations and examined cross-regional and cross-frequency interactions. We found that at comparable doses, the effects of allopregnanolone, despite purported selectivity for certain GABAAR subtypes, was indistinguishable from pentobarbital during active waking exploration. The actions of diazepam had recognizable common features with allopregnanolone and pentobarbital but was also distinct, consistent with subunit selectivity of benzodiazepines. Finally, ketamine exhibited no distinguishing overlap with allopregnanolone in the parameters examined. Our results suggest that rapid antidepressants with different molecular substrates may remain separated at the level of large-scale ensemble activity, but the studies leave open the possibility of commonalities in more discrete circuits and/or in the context of a dysfunctional brain.

High Fat Diet Increases [3H] Flunitrazepam Binding in the Mouse Brain that is Dependent on the Expression of the Dopamine D2 Gene.

Dopamine is an important neuromodulator in the brain that binds to dopamine D1-like receptors (D1, D5) as well as dopamine D2-like receptors (D2, D3, D4). The D2 receptor is known to play an integral role in a variety of physiological processes including addictive behaviors, locomotion, motivation, feeding behavior, and more. It was recently reported that dopamine is a direct-acting modulator of mammalian GABA(A) receptors. To this end, we wanted to examine how the expression of the dopamine D2 gene impacts the expression of GABA(A) receptors in the brain under different dietary conditions. Adult female Drd2 wild-type (WT), heterozygous (HT), and knockout (KO) mice were given either normal or high-fat diet for a period of 30weeks. Following this, their brains were collected for [3H] Flunitrazepam binding in order to assess GABA(A) receptor expression. A high fat diet significantly increased [3H] Flunitrazepam binding in the regions of the somatosensory cortex, striatum, and various other cortical areas within WT mice. In contrast, no effect of diet was observed in HT or KO mice. As such, HT and KO mice displayed reduced [3H] Flunitrazepam binding in these areas relative to WT mice under high-fat dietary conditions. The effect of a high-fat diet on [3H] Flunitrazepam binding is consistent with recent evidence showing increases in GABA neurotransmitter levels following a high-fat diet. We demonstrate for the first time that the expression of the D2 gene plays a prominent role in the ability of a high-fat diet to impact GABA(A) receptors in the mouse brain.

1470-P: GABA Stimulates or Inhibits Insulin and Somatostatin Secretion in Human Pancreatic Islets Depending on Glucose Concentration

GABA is an inhibitory neurotransmitter synthesized and secreted by β-cells that is reported to modulate glucagon, somatostatin (SST) , and insulin secretion. However, the direction of the effect of GABA, whether stimulatory or inhibitory, on insulin secretion is controversial. Our results from human islets show that GABA is inhibitory to insulin secretion under glucose-stimulating conditions. Further, islets from conditional knockout mice lacking the GABA-synthesizing enzymes GAD65 and GAD67 oversecrete insulin during glucose stimulation, consistent with GABA being inhibitory. However, the inhibitory effect of GABA is somewhat paradoxical as ligation of GABA-A receptor Cl channels are expected to depolarize the β-cell that should contribute to stimulating insulin secretion. It is also unclear if GABA signaling in β-cells is strictly autocrine or if the observed inhibition is mediated through an indirect effect of inducing SST secretion which, in turn, inhibits β-cells. Here, we improve understanding of GABA’s effect on insulin secretion by transiently applying 100 μM of GABA to human islets during perifusion with low (3 mM) and high glucose (16.7 mM) . GABA stimulated both insulin and SST in low glucose but inhibited insulin and SST when applied in high glucose. Thus, the modulation of GABA presents both stimulatory and inhibitory effects on β- and δ-cells depending on glucose concentration. In addition, the effect of GABA on β-cells appears to be direct and independent of SST signaling because SST and insulin secretion both change in the same direction with applied GABA. These results suggest the hypothesis that β-cell GABA-A receptors convey stimulatory responses to GABA under low glucose, but that G-protein coupled GABA-B receptors mediate inhibitory GABA signaling under high glucose. This mechanism would provide a consensus model that reconciles decades of seemingly antithetical studies where GABA is either inhibitory or stimulatory. Disclosure S.Ferreira: None. D.W.Hagan: None. E.Phelps: Research Support; Immunocore, Ltd. Funding National Institutes of Health (R01DK124267)

Cardiovascular deconditioning increases GABA signaling in the nucleus tractus solitarii.

The nucleus tractus solitarii (nTS) is the major integrative brainstem region for autonomic modulation and processing of cardiovascular reflexes. GABA and glutamate are the main inhibitory and excitatory neurotransmitters, respectively, within this nucleus. Alterations in the GABA-glutamate regulation in the nTS are related to numerous cardiovascular comorbidities. Bedridden individuals and people exposed to microgravity exhibit dysautonomia and cardiovascular deconditioning that are mimicked in the hindlimb unloading (HU) rat model. We have previously shown in the nTS that HU increases glutamatergic neurotransmission yet decreases neuronal excitability. In this study, we investigated the effects of HU on nTS GABAergic neurotransmission. We hypothesized that HU potentiates GABA signaling via increased GABAergic release and postsynaptic GABA receptor expression. Following HU or control postural exposure, GABAergic neurotransmission was assessed using whole cell patch clamp whereas the magnitude of GABA release was evaluated via an intensity-based GABA sensing fluorescence reporter (iGABASnFR). In response to GABA interneuron stimulation, the evoked inhibitory postsynaptic current (nTS-IPSC) amplitude and area, as well as iGABASnFR fluorescence, were greater in HU than in control. HU also elevated the frequency but not the amplitude of spontaneous miniature IPSCs. Picoapplication of GABA produced similar postsynaptic current responses in nTS neurons of HU and control. Moreover, HU did not alter GABAA receptor α1 subunit expression, indicating minimal alterations in postsynaptic membrane receptor expression. These results indicate that HU increases GABAergic signaling in the nTS likely via augmented release of GABA from presynaptic terminals. Altogether, our data indicate GABA plasticity contributes to the autonomic and cardiovascular alterations following cardiovascular deconditioning (CVD).NEW & NOTEWORTHY Gravity influences distribution of blood volume and autonomic function. Microgravity and prolonged bed rest induce cardiovascular deconditioning (CVD). We used hindlimb unloading (HU), a rat analog for bed rest, to investigate CVD-induced neuroplasticity in the brainstem. Our data demonstrate that HU increases GABA modulation of nucleus tractus solitarii (nTS) neurons via presynaptic plasticity. Given the importance of nTS in integrating cardiovascular reflexes, this study provides new evidence on the central mechanisms behind CVD following HU.

157 Efficacy of adjunctive cenobamate: post-hoc analysis in patients grouped by concomitant anti-epileptic drug type

PurposeThere has been little success with polytherapy for patients with drug-resistant epilepsy. The need for optimizing AED combinations is high. Cenobamate is a novel AED with a unique, dual, complementary mechanism of action (MoA) combining GABA-A positive allosteric modulation (via a binding site different from benzodiazepines) together with broad spectrum sodium channel blockage. Here we assessed the efficacy of cenobamate when combined with AEDs grouped by MoA.MethodsA post-hoc exploratory analysis of the study C017, in adult epilepsy patients with uncontrolled focal onset seizures who had ≥4 seizures/month despite treatment with stable doses of 1–3 AEDs.ResultsIn the maintenance phase, 183/397 (46%) patients were receiving at least one GABA modulator (felbamate, valproate, topiramate, tiagabine, vigabatrin) and 329/397 (82%) a sodium channel blockers (carbamazepine, oxcarbazepine, lamotrigine, lacosamide, eslicarbazepine). Added onto GABA modu- lators, cenobamate 100/200/400mg achieved seizure freedom rates (SFR) of 7.3%/15.6%/30.6% vs 2.1% for placebo; when added onto sodium channel blockers, cenobamate 100/200/400mg/day showed SFR of 2.3%/9.3%/17.5% vs 1.2% for placebo. Both results were statistically significant for 200 and 400mg. A consistent SFR with cenobamate for a subset of patients receiving background levetiracetam (11% 200mg and 25% 400 mg vs 2.5% placebo) as well as those with background benzodiazepines (20% 400 mg vs 0% placebo) occurred.ConclusionsAdjunctive cenobamate achieved significant dose-dependent SFR when combined with AEDs across multiple MoAs in patients with uncontrolled FOS.lee.finlan@arvelletx.com

Phenolics as GABAA Receptor Ligands: An Updated Review.

Natural products can act as potential GABA modulators, avoiding the undesirable effects of traditional pharmacology used for the inhibition of the central nervous system such as benzodiazepines (BZD). Phenolics, especially flavonoids and phlorotannins, have been considered as modulators of the BZD-site of GABAA receptors (GABAARs), with sedative, anxiolytic or anticonvulsant effects. However, the wide chemical structural variability of flavonoids shows their potential action at more than one additional binding site on GABAARs, which may act either negatively, positively, by neutralizing GABAARs, or directly as allosteric agonists. Therefore, the aim of the present review is to compile and discuss an update of the role of phenolics, namely as pharmacological targets involving dysfunctions of the GABA system, analyzing both their different compounds and their mechanism as GABAergic modulators. We focus this review on articles written in English since the year 2010 until the present. Of course, although more research would be necessary to fully establish the type specificity of phenolics and their pharmacological activity, the evidence supports their potential as GABAAR modulators, thereby favoring their inclusion in the development of new therapeutic targets based on natural products. Specifically, the data compiled in this review allows for the directing of future research towards ortho-dihydroxy diterpene galdosol, the flavonoids isoliquiritigenin (chalcone), rhusflavone and agathisflavone (biflavonoids), as well as the phlorotannins, dieckol and triphlorethol A. Clinically, flavonoids are the most interesting phenolics due to their potential as anticonvulsant and anxiolytic drugs, and phlorotannins are also of interest as sedative agents.

Differentiation of PANC-1 ductal cells to β-like cells via cellular GABA modulation by Magainin and CPF-7 peptides

Some of the antimicrobial peptides induce insulin release and improve glucose tolerance while their effects on pancreatic cell differentiation have remained unresolved. In this report, we evaluated the effects of two of these peptides, Magainin-II and CPF-7, and also GABA, on PANC-1 ductal cells' differentiation. Based on immunofluorescence and qRT-PCR analyses the expression levels of some of the Epithelial to Mesenchymal transition (EMT)-related factors such as Snai1 and Ngn3, as two biomarkers of alpha and beta cells, were increased. Our findings also revealed a drastic increase in Arx, Pax4, Dnmt-1 and Glucagon expressions associated with dedifferentiation of PANC-1 cells into pancreatic endocrine progenitor cells. Futhermore, Magainin-II and CPF-7 exerted their roles partly via influencing the GABA cellular content. These data would undoubtedly provide a suitable ground for further investigation to guide these cells toward transplantable insulin producing beta cells.

Microtubule Disruption Without Learning Impairment in the Unicellular Organism, Paramecium: Implications for Information Processing in Microtubules.

Information processing in microtubules is an open question that has not been adequately addressed. It was suggested that microtubules could store and process information in the nervous system or even support consciousness. The unicellular organism, Paramecium caudatum, has a microtubular structure but lacks a neuron or neural network. However, it shows intelligent behaviors such as associative learning. This property may suggest that the microtubules are involved in intelligent behavior, information storage, or information processing in this organism. To test this hypothesis and study the role of microtubules in P. caudatum learning, we utilized a learning task in which the organism associates brightness in its swimming medium with attractive cathodal shocks. To see if microtubules are an integral part of information storage and processing in P. caudatum, we disrupted the microtubular dynamics in the organism using an antimicrotubular agent (parbendazole). We observed that while a partial allosteric modulator of GABA (midazolam) could disrupt the learning process in P. caudatum, the antimicrotubular agent could not interfere with the learning. Microtubules are probably not vital for the learning behavior in P. caudatum. Consequently, our results call for further investigation of the microtubular information processing hypothesis. Importance of Information processing in microtubules;Microtubules could store and process information in the nervous system;Unicellular organism, Paramecium caudatum, has a microtubular structure but lacks a neuron or neural network. Information processing in microtubules is an open question that has not been adequately addressed. It was suggested that microtubules could store and process information in the nervous system or even support consciousness. The unicellular organism, Paramecium caudatum, has a microtubular structure but lacks a neuron or neural network. However, it shows intelligent behaviors such as associative learning. This property may suggest that the microtubules are involved in intelligent behavior, information storage, or information processing in this organism. To test this hypothesis and study the role of microtubules in P. caudatum learning, we utilized a learning task in which the organism associates brightness in its swimming medium with attractive cathodal shocks. To see if microtubules are an integral part of information storage and processing in P. caudatum, we disrupted the microtubular dynamics in the organism using an antimicrotubular agent (parbendazole). We observed that while a partial allosteric modulator of GABA (midazolam) could disrupt the learning process in P. caudatum, the antimicrotubular agent could not interfere with the learning. Microtubules are probably not vital for the learning behavior in P. caudatum. Consequently, our results call for further investigation of the microtubular information processing hypothesis.