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Objective: Area tempestas, a functionally defined region in the anterior piriform cortex, was identified as a crucial ictogenic trigger zone in the rat brain in the 1980s. However, whether the primate piriform cortex can trigger seizures remains unknown. Here, in a nonhuman primate model, we aimed to localize a similar trigger zone in the piriform cortex and, subsequently, evaluated the ability of focal inhibition of the substantia nigra pars reticulata (SNpr) to suppress the evoked seizures., Methods: Focal microinjection of the γ-aminobutyric acid type A (GABA A ) antagonist bicuculline methiodide into the piriform cortex was performed, in macaque monkeys, on a within-subject basis to map the ictogenic regions within this area. Glutamate antagonists were used to characterize the local circuit pharmacology. Focal inhibition of the substantia nigra by infusion of the GABA A agonist muscimol suppressed seizures evoked from piriform cortex., Results: We documented a well-defined region highly susceptible to bicuculline-induced seizures in the piriform cortex, just posterior to the junction of the frontal and temporal lobes, indicating that a functional homolog to the rodent area tempestas is present in the primate brain. Focal infusion of glutamate receptor antagonists into the area tempestas revealed that α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor-mediated, but not N-methyl-D-aspartate-mediated, neurotransmission was necessary for the expression of seizures. Pharmacological inhibition of the SNpr robustly suppressed area tempestas-evoked seizures., Significance: Together, these data point to the area tempestas as a potent ictogenic zone in the primate brain and underscore the antiseizure effects of inhibition of the SNpr. Building on decades of studies in rodents, our present findings emphasize the relevance of these targets to the primate brain and provide further rationale for exploring these targets for clinical use., (© 2024 International League Against Epilepsy.)

A century of research established that GABA inhibits proprioceptive inputs presynaptically to sculpt spinal neural inputs into skilled motor output. Recent results in mice challenged this theory by showing that GABA can also facilitate action potential conduction in proprioceptive afferents. Here, we tackle this controversy in monkeys, the most human-relevant animal model, and show that GABA A receptors (GABA A Rs) indeed facilitate sensory inputs to spinal motoneurons and interneurons and that this mechanism also influences sensory transmission to supraspinal centers. We performed causal manipulations of GABA A Rs with intrathecal pharmacology in anesthetized monkeys while recording electrical signals in the muscles, spinal cord, thalamus, and cortex. We show that blocking GABA A Rs suppresses spinal reflexes to hand muscles, sensory-evoked single-unit firing in the spinal cord, and sensory-evoked potentials in the thalamus and somatosensory cortex. Our results portray a sophisticated picture of presynaptic modulation of sensory inputs by GABA in the spinal cord., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024. Published by Elsevier Inc.)

Panic disorder is more frequent in women than in men. In women, vulnerability to panic is enhanced during the late luteal phase of the menstrual cycle. At this time secretion of progesterone and its neuroactive metabolite allopregnanolone (ALLO), which acts as a positive allosteric modulator of the actions of GABA at GABA A receptors, decline sharply. In female rats, responsiveness to a hypoxic panicogenic challenge increases during the late diestrus (LD) phase as ALLO concentration in the brain falls. During LD, short-term treatment with fluoxetine at a low dose (1.75 mg/kg i.p.) blocked panic-related escape behavior in response to hypoxia. At this dose fluoxetine increases brain concentration of ALLO without affecting 5-HT levels, thereby stabilizing brain ALLO concentration. We here report that the panicolytic-like effect of fluoxetine during LD is prevented by microinjection of the GABA A receptor antagonist bicuculline (5 pmol) into the dorsal periaqueductal gray (dPAG), a key panic-related area. This result suggests that fluoxetine's effect is indirectly mediated via a GABAergic mechanism in the dPAG and highlights the important role of changes in GABAergic tone in regulating neuronal excitability in the panic circuitry during the estrous cycle. It also points to the potential for using short-term, low dose fluoxetine as an anti-panic medication in women., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. No generative AI and AI-assisted technologies were used in the preparation of this manuscript., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Abdominal aortic aneurysm is a potentially fatal vascular inflammatory disease characterized by infiltration of various inflammatory cells.The GABA-A receptor is expressed in many inflammatory cells such as macrophages and T cells and has anti-inflammatory and antioxidant effects. Therefore, the GABA-A receptor may become a potential therapeutic target for abdominal aortic aneurysms. The purpose of this study was to investigate the effect of regulating the activity of the GABA-A receptor on the formation of experimental abdominal aortic aneurysm in rats. In this study, the abdominal aortic aneurysm model of rats was established by aorta intracavitary perfusion of elastase combined with aorta extracavitary infiltration of calcium chloride. GABA-A receptor agonist (topiramate) and antagonist (bicuculline) were used to treating the abdominal aortic aneurysm model rats, which were divided into sham operation group, model group, topiramate group, and bicuculline group(n = 10). Histopathology, immunohistochemistry, fluorescence quantitative PCR, Western blotting, ELISA and Gelatine zymogram were used to study. Regulation of GABA-A receptor activity can interfere with the development and severity of abdominal aortic aneurysms in rats. The GABA-A receptor agonist topiramate reduces the infiltration of inflammatory cells, particularly T cells, into the abdominal aortic wall, while also modulating the balance of Th1/Th2 cytokines in peripheral blood, leading to a significant reduction in inflammatory responses. Additionally, topiramate decreases the secretion of matrix metalloproteinases MMP2 and MMP9, thereby inhibiting extracellular matrix degradation and slowing the progression of aneurysms. In contrast, the GABA-A receptor antagonist bicuculline exacerbates inflammation and promotes aneurysm development. At the molecular level, the mechanisms of action of the GABA-A receptor agonist topiramate and the antagonist bicuculline may involve inhibition or activation of the p38 MAPK signaling pathway. Regulation of GABA-A receptor activity can effectively intervene in the occurrence and development of abdominal aortic aneurysms in rats., Competing Interests: Declarations. Competing interests: The authors declare no competing interests. Ethics approval and consent to participate: All experiments were performed according to guidelines established by the Institutional Animal Care and Use Ethical Committee of North Sichuan Medical College (Sichuan, China). Consent for publication: The submission to this journal has been read and approved by all coauthors., (© 2024. The Author(s).)

The infralimbic (IL) division of the medial prefrontal cortex (mPFC) is a crucial site for the extinction of conditioned fear memories in rodents. Recent work suggests that neuronal plasticity in the IL that occurs during (or soon after) fear conditioning enables subsequent IL-dependent extinction learning. We therefore hypothesized that pharmacological activation of the IL after fear conditioning would promote the extinction of conditioned fear. To test this hypothesis, we characterized the effects of post-conditioning infusions of the GABA A receptor antagonist, picrotoxin, into the IL on the extinction of auditory conditioned freezing in male and female rats. In four experiments, we found that picrotoxin injections performed immediately, 24 h, or 13 days after fear conditioning reduced conditioned freezing to the auditory conditioned stimulus (CS) during both extinction training and extinction retrieval; this effect was observed up to two weeks after picrotoxin infusions. Interestingly, inhibiting protein synthesis inhibition in the IL immediately after fear conditioning prevented the inhibition of freezing by picrotoxin injected 24 h later. Our data suggest that the IL encodes an inhibitory memory during the consolidation of fear conditioning that is necessary for future fear suppression., (© 2024. The Author(s).)

Encephalopathy following sepsis is defined as life-threatening organ failure due to the irregular response of the host to infection and has high mortality and morbidity rates. The present study aimed to investigate the effects of inflammation and the gamma-aminobutyric acid-A (GABA A ) receptor antagonist, bicuculline, on brain tissue in rats with sepsis. Sepsis was experimentally generated using lipopolysaccharide (LPS). The rats were divided into four groups: control, LPS (10 mg/kg i.p.), bicuculline (1.5 mg/kg s.c.), and LPS+Bic. Electrophysiologic recordings and body temperature measurements were completed at the 24th hour, and samples were taken. TNF-α, IL-10, GABA, and MDA levels were measured. Tissue imaging was performed using S100-ß, NEUN, and synaptophysin antibodies. One-way ANOVA followed by the Tukey test was performed for statistical analysis. Inflammatory parameters significantly increased in brain tissue in the LPS group compared with the other groups (TNF-α, [F (3.14) = 6.015, p = 0.042]; IL-10, [F (3.15) = 9.013, p = 0.02]). Tissue imaging results were as follows: S100-ß involvement increased, and NeuN and synaptophysin involvement decreased in the LPS group [F (3.21) = 18.016, p = 0.006, for S100-ß; F (3.21) = 19.071, p = 0.003, for NeuN; F (3.21) = 18.098, p = 0.005, for synaptophysin]. In electrophysiologic recordings, we observed activity consistent with acute non-focal seizures in the LPS group. Contrarily, the control and other comparison groups exhibited normal resting neural activity. Bicuculline may be used as a therapeutic agent in sepsis to maintain the neurotransmitter and pro- and anti-inflammatory cytokine balance and reduce lipid peroxidation with its effects of acetylcholine esterase inhibition and GABA A receptor antagonism., Competing Interests: Declarations. Ethics Approval: Ethics committee approval for the study was obtained from the Local Ethics Committee of Animal Experiments of Istanbul Bagcilar Training and Research Hospital (2017/63). Consent to Participate: Not applicable. Consent for Publication: All the authors have declared their consent for publication. Competing Interests: The authors declare no competing interests., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

The midbrain dorsomedial periaqueductal grey column (dmPAG) is involved in the regulation of cardiovascular responses. Due to the presence of Gamma-Aminobutyric acid (GABA) receptors in the dmPAG, this study aimed to investigate the role of GABA A receptors in the dmPAG on cardiovascular parameters and its possible peripheral mechanisms. The left femoral artery was cannulated, and systolic arterial pressure (SAP), mean arterial pressure (MAP) and heart rate (HR) were recorded using a Power lab system. Microinjection of saline, muscimol and bicuculline (BIC) was done using a stereotaxic device. Also, the peripheral mechanisms dependent on GABA A receptors in the dmPAG were evaluated by intravenous (i.v.) injection of hexamethonium (Hexa) and atropine (Atr) 5 min before the BIC. Results showed that BIC significantly increased ∆SAP, ∆MAP and ∆HR than the control group, but muscimol had no significant effect. Injection of Hex significantly attenuates the effect of BIC on ∆SAP and ∆MAP. Atr (i.v) significantly increased the ∆HR, and when injected before BIC microinjection, it did not affect the cardiovascular responses induced by BIC. These findings show that GABA A receptors of the dmPAG have inhibitory effects on the cardiovascular system, which are mostly mediated by the sympathetic system., (© 2024 Nordic Association for the Publication of BCPT (former Nordic Pharmacological Society). Published by John Wiley & Sons Ltd.)

Purpose: The infralimbic (IL) subregion of the medial prefrontal cortex (mPFC) regulates the extinction of conditioned fear memory. Glucocorticoid and gamma-aminobutyric acid (GABA) receptors are expressed in the mPFC and are also critical in fear extinction. This study investigated the possible interactive effects of the glucocorticoids and GABAergic system in the IL on the regulation of fear extinction., Method: The rats were trained using an auditory fear conditioning task during which they received three conditioned stimuli (tones, 30 s, 4 kHz, 80 dB), co-terminated with the three unconditioned stimuli (footshock, 0.8 mA, 1 s). Extinction testing was conducted over 3 days (Ext 1-3). Thirty minutes before the first extinction trial (Ext 1), the rats received bicuculline (BIC, 1 mg/kg/2 mL, intraperitoneal [i.p.]) as a GABA A receptor antagonist or CGP55845 (CGP, 0.1 mg/kg/2 ML, i.p.) as a GABA B receptor antagonist followed by systemic injection of corticosterone (CORT, 3 mg/kg/2 ML, i.p.). Furthermore, separate groups of rats received a bilateral intra-IL injection of BIC (100 ng/0.3 µL/side) or CGP (10 ng/0.3 µL/side) followed by a systemic injection of CORT (3 mg/kg/2 ML, i.p.) before the first extinction trial (Ext 1). The extracellular signal-regulated kinase (ERK1) and cAMP response element-binding (CREB) activity in the IL was examined by Western blot analysis after Ext 1., Finding: The results indicated that systemic CORT injection facilitated fear extinction and increased the expression of ERK1 but not CREB in the IL. Both systemic and intra-IL co-injection of BIC or CGP blocked the effects of CORT on fear extinction and ERK1 expression., Conclusion: These findings suggest that glucocorticoids and the GABAergic system may modulate fear extinction through the ERK pathway in the IL., (© 2024 The Author(s). Brain and Behavior published by Wiley Periodicals LLC.)

Homeostatic plasticity represents a set of mechanisms thought to stabilize some function of neural activity. Here, we identified the specific features of cellular or network activity that were maintained after the perturbation of GABAergic blockade in two different systems: mouse cortical neuronal cultures where GABA is inhibitory and motoneurons in the isolated embryonic chick spinal cord where GABA is excitatory (males and females combined in both systems). We conducted a comprehensive analysis of various spiking activity characteristics following GABAergic blockade. We observed significant variability in many features after blocking GABA A receptors (e.g., burst frequency, burst duration, overall spike frequency in culture). These results are consistent with the idea that neuronal networks achieve activity goals using different strategies (degeneracy). On the other hand, some features were consistently altered after receptor blockade in the spinal cord preparation (e.g., overall spike frequency). Regardless, these features did not express strong homeostatic recoveries when tracking individual preparations over time. One feature showed a consistent change and homeostatic recovery following GABA A receptor block. We found that spike rate within a burst (SRWB) increased after receptor block in both the spinal cord preparation and cortical cultures and then returned to baseline within hours. These changes in SRWB occurred at both single cell and population levels. Our findings indicate that the network prioritizes the burst spike rate, which appears to be a variable under tight homeostatic regulation. The result is consistent with the idea that networks can maintain an appropriate behavioral response in the face of challenges., Competing Interests: Theauthors declare no competing financial interests., (Copyright © 2024 Lakhani et al.)

The lateral parafacial area (pFL) is a crucial region involved in respiratory control, particularly in generating active expiration through an expiratory oscillatory network. Active expiration involves rhythmic abdominal (ABD) muscle contractions during late-expiration, increasing ventilation during elevated respiratory demands. The precise anatomical location of the expiratory oscillator within the ventral medulla's rostro-caudal axis is debated. While some studies point to the caudal tip of the facial nucleus (VIIc) as the oscillator's core, others suggest more rostral areas. Our study employed bicuculline (a γ-aminobutyric acid type A [GABA-A] receptor antagonist) injections at various pFL sites (-0.2 mm to +0.8 mm from VIIc) to investigate the impact of GABAergic disinhibition on respiration. These injections consistently elicited ABD recruitment, but the response strength varied along the rostro-caudal zone. Remarkably, the most robust and enduring changes in tidal volume, minute ventilation, and combined respiratory responses occurred at more rostral pFL locations (+0.6/+0.8 mm from VIIc). Multivariate analysis of the respiratory cycle further differentiated between locations, revealing the core site for active expiration generation with this experimental approach. Our study advances our understanding of neural mechanisms governing active expiration and emphasizes the significance of investigating the rostral pFL region., Competing Interests: AP, MP, CD, SP No competing interests declared, (© 2024, Pisanski et al.)

The reliable induction of long-term potentiation (LTP) in the dentate gyrus (DG) in vitro requires the blockade of the γ-aminobutyric acid A (GABA A ) receptor. In these studies we examined the effectiveness of the specific GABA A receptor antagonist bicuculline methiodide (BMI) in facilitating LTP in the DG from hippocampal slices obtained from either C57Bl/6 mice or Sprague-Dawley rats, two species commonly used for electrophysiology. In the C57Bl/6 mice, maximal short-term potentiation and LTP in the DG were produced with a concentration of 5 µM BMI. In contrast, a concentration of 10 μM BMI was required to produce maximal short-term potentiation and LTP in the DG of Sprague-Dawley rats. These results reveal that there are species differences in the optimal amount of BMI required to produce robust and reliable LTP in the rodent DG in vitro and highlight the need to take consideration of the species being used when choosing concentrations of pharmacological agents to employ for electrophysiological use. NEW & NOTEWORTHY In this report we provide specific neurophysiological evidence for concentrations of GABA A antagonist required to study long-term potentiation in the medial perforant pathway of the dentate gyrus. Two commonly used species, Sprague-Dawley rats and C57Bl/6 mice, require different concentrations of bicuculline methiodide to induce optimal short-term and long-term potentiation.

Neuroinflammation accompanies several brain disorders, either as a secondary consequence or as a primary cause and may contribute importantly to disease pathogenesis. Neurosteroids which act as Positive Steroid Allosteric GABA-A receptor Modulators (Steroid-PAM) appear to modulate neuroinflammation and their levels in the brain may vary because of increased or decreased local production or import from the systemic circulation. The increased synthesis of steroid-PAMs is possibly due to increased expression of the mitochondrial cholesterol transporting protein (TSPO) in neuroinflammatory tissue, and reduced production may be due to changes in the enzymatic activity. Microglia and astrocytes play an important role in neuroinflammation, and their production of inflammatory mediators can be both activated and inhibited by steroid-PAMs and GABA. What is surprising is the finding that both allopregnanolone, a steroid-PAM, and golexanolone, a novel GABA-A receptor modulating steroid antagonist (GAMSA), can inhibit microglia and astrocyte activation and normalize their function. This review focuses on the role of steroid-PAMs in neuroinflammation and their importance in new therapeutic approaches to CNS and liver disease., Competing Interests: Declaration of Competing Interest TB and BFS are shareholders and Board Members of Umecrine Cognition AB (UCAB), MD is employed by UCAB.TPB is a Board Member of UCAB; VF has received research grant support from UCAB., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Rationale: Several lines of evidence have demonstrated that the cannabinoid type 1 receptor (CB 1 ) is found in the caudate nucleus and putamen (CPu) in addition to the substantia nigra pars reticulata (SNpr). Here, we investigated the role of endocannabinoid neuromodulation of striato-nigral disinhibitory projections on the activity of nigro-collicular GABAergic pathways that control the expression of unconditioned fear-related behavioural responses elicited by microinjections of the GABA A receptor selective antagonist bicuculline (BIC) in the deep layers of the superior colliculus (dlSC)., Methods: Fluorescent neural tract tracers were deposited in either CPu or in SNpr. Wistar rats received injection of vehicle, anandamide (AEA), either at low (50 pmol) or high (100 pmol) concentrations in CPu followed by bicuculline microinjections in dlSC., Results: Connections between CPu, the SNpr and dlSC were demonstrated. The GABA A receptor blockade in dlSC elicited panic-like behaviour. AEA at the lowest concentration caused a panicolytic-like effect that was antagonised by the CPu pretreatment with AM251 at 100 pmol. AEA at the highest concentration caused a panicogenic-like effect that was antagonised by the CPu pretreatment with 6-iodonordihydrocapsaicin (6-I-CPS) at different concentrations (0.6, 6, 60 nmol)., Conclusion: These findings suggest that while pre-synaptic CB1-signalling subserves an indirect facilitatory effect of AEA on striato-nigral pathways causing panicolytic-like responses through midbrain tectum enhanced activity, post-synaptic TRPV 1 -signalling in CPu mediates AEA direct activation of striato-nigral disinhibitory pathways resulting in increasing dlSC neurons activity and a panicogenic-like response. All these actions seem to depend on the interface with the nigro-collicular inhibitory GABAergic pathways., Competing Interests: Declaration of Competing Interest The authors declare that there are no conflicts of interest concerning the presented work., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Here we studied spinal neurotransmitter mechanisms involved in the reduction of mechanical hypersensitivity by inhibition of the amygdaloid central nucleus (CeA) in male and female rats with spared nerve injury (SNI) model of neuropathy. SNI induced mechanical hypersensitivity that was stronger in females. Reversible blocking of the CeA with muscimol (GABA A receptor agonist) induced a reduction of mechanical hypersensitivity that did not differ between males and females. Following spinal co-administration of atipamezole (α 2 -adrenoceptor antagonist), the reduction of mechanical hypersensitivity by CeA muscimol was attenuated more in males than females. In contrast, following spinal co-administration of raclopride (dopamine D2 receptor antagonist) the reduction of hypersensitivity by CeA muscimol was attenuated more in females than males. The reduction of mechanical hypersensitivity by CeA muscimol was equally attenuated in males and females by spinal co-administration of WAY-100635 (5-HT 1A receptor antagonist) or bicuculline (GABA A receptor antagonist). The CeA muscimol induced attenuation of ongoing pain-like behavior (conditioned place preference test) that was reversed by spinal co-administration of atipamezole in both sexes. The results support the hypothesis that CeA contributes to mechanical hypersensitivity and ongoing pain-like behavior in SNI males and females. Disinhibition of descending controls acting on spinal α 2 -adrenoceptors, 5-HT 1A , dopamine D2 and GABA A receptors provides a plausible explanation for the reduction of mechanical hypersensitivity by CeA block in SNI. The involvement of spinal dopamine D2 receptors and α 2 -adrenoceptors in the CeA muscimol-induced reduction of mechanical hypersensitivity is sexually dimorphic, unlike that of spinal α 2 -adrenoceptors in the reduction of ongoing neuropathic pain., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Author(s). Published by Elsevier B.V. All rights reserved.)

γ-Aminobutyric acid (GABA) is the main inhibitory neurotransmitter. GABA receptor type A (GABA A R) possesses binding sites for a large group of pharmacological agents which are supposed to interact allosterically with each other. The aim of this work was to study the interaction between the positive allosteric modulators (PAMs) and the competitive antagonists of GABA A Rs. The GABA-induced chloride current (I GABA ) was measured in isolated Purkinje cells of rat cerebellum using the patch-clamp technique. PAMs, neurosteroid allopregnanolone (Allo) and zolpidem (Zolp), a drug that positively modulates the GABA A R through interaction with the benzodiazepine (BDZ) site, doubled the I GABA amplitude in the control solution. Competitive antagonist of GABA A Rs, bicuculline (Bic, 5 µM) blocked the I GABA by 90%. The addition of 1 μM Allo or 0.5 µM Zolp to the Bic solution caused an unblocking effect, so that the I GABA amplitude increased 10 and 4 times from control value, correspondingly. This unblocking effect developed slowly, as evidenced by a threefold increase in the current rise time. Competitive antagonist of GABA A Rs, gabazine (GBZ, 0.5 µM) blocked the I GABA by 87%. The addition of 1 μM Allo to the GBZ solution caused an unblocking effect, so that the I GABA amplitude increased 7-fold. However, the addition of 0.5 µM Zolp to the GBZ solution did not cause an unblocking effect. So, Allo appeared to have a stronger unblocking potential than Zolp, and Bic binding site showed a higher sensitivity to the action of unblocking PAMs than GBZ binding site. The results indicate for the first time the existence of an allosteric relationship between the sites binding PAMs and the competitive antagonists of GABA A R., Competing Interests: Declarations of interest None., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Immediate early genes (IEGs) are transcribed in response to neuronal activity from sensory stimulation during multiple adaptive processes in the brain. The transcriptional profile of IEGs is indicative of the duration of neuronal activity, but its sensitivity to the strength of depolarization remains unknown. Also unknown is whether activity history of graded potential changes influence future neuronal activity. In this work with dissociated rat cortical neurons, we found that mild depolarization-mediated by elevated extracellular potassium (K + )-induces a wide array of rapid IEGs and transiently depresses transcriptional and signaling responses to a successive stimulus. This latter effect was independent of de novo transcription, translation, and signaling via calcineurin or mitogen-activated protein kinase. Furthermore, as measured by multiple electrode arrays and calcium imaging, mild depolarization acutely subdues subsequent spontaneous and bicuculline-evoked activity via calcium- and N-methyl-d-aspartate receptor-dependent mechanisms. Collectively, this work suggests that a recent history of graded potential changes acutely depress neuronal intrinsic properties and subsequent responses. Such effects may have several potential downstream implications, including reducing signal-to-noise ratio during synaptic plasticity processes., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter in adults, has a critical contribution to balanced excitatory-inhibitory networks in the brain. Alteration in depolarizing action of GABA during early life is connected to a wide variety of neurodevelopmental disorders. Additionally, the effects of postnatal GABA blockade on neuronal synaptic plasticity are not known and therefore, we set out to determine whether postnatal exposure to bicuculline, a competitive antagonist of GABA A receptors, affects electrophysiologic changes in hippocampal CA1 neurons later on. To this end, male and female Wistar rats received vehicle or bicuculline (300 μg/kg) on postnatal days (PNDs) 7, 9 and 11, and then underwent different behavioral and electrophysiological examinations in adulthood. Postnatal exposure to bicuculline did not affect basic synaptic transmission but led to a pronounced decrease in paired-pulse facilitation (PPF) in CA1 pyramidal neurons. Bicuculline treatment also attenuated the long-term potentiation (LTP) and long-term depression (LTD) of CA1 neurons accompanied by decreased theta-burst responses in male and female adult rats. These electrophysiology findings together with the reduced brain-derived neurotrophic factor (BDNF) levels in the hippocampus and prefrontal cortex reliably explain the disturbance in spatial reference and working memories of bicuculline-treated animals. This study suggests that postnatal GABA A blockade deteriorates short- and long-term synaptic plasticity of hippocampal CA1 neurons and related encoding of spatial memory in adulthood., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Antisecretory Factor (AF) is an endogenous peptide known for its powerful antisecretory and anti-inflammatory properties. We have previously shown that AF also acts as a neuromodulator of GABAergic synaptic transmission in rat hippocampus in a way that results in disinhibition of CA1 pyramidal neurons. Disinhibition is expected to facilitate the induction of long-term potentiation (LTP), and LTP is known to play a crucial role in learning and memory acquisition. In the present study we investigated the effect of AF on LTP in CA3-CA1 synapses in rat hippocampus. In addition, endogenous AF plasma activity was upregulated by feeding the rats with specially processed cereals (SPC) and spatial learning and memory was studied in the Morris Water Maze (MWM). We found that LTP was significantly enhanced in the presence of AF, both when added exogenously in vitro as well as when upregulated endogenously by SPC-feeding. In the presence of the GABA A -receptor antagonist picrotoxin (PTX) there was however no significant enhancement of LTP. Moreover, rats fed with SPC demonstrated enhanced spatial learning and short-term memory, compared with control animals. These results show that the disinhibition of GABAergic transmission in the hippocampus by the endogenous peptide AF enhances LTP as well as spatial learning and memory., (Copyright © 2022 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Cerebellar Purkinje cells (PCs) play critical roles in motor coordination and motor learning through their simple spike (SS) activity. Previous studies have shown that chronic ethanol exposure (CEE) in adolescents impairs learning, attention, and behavior, at least in part by impairing the activity of cerebellar PCs. In this study, we investigated the effect of CEE on the SS activity in urethane-anesthetized adolescent mice by in vivo electrophysiological recordings and pharmacological methods. Our results showed that the cerebellar PCs in CEE adolescent mice expressed a significant decrease in the frequency and an increase in the coefficient of variation (CV) of SS than control group. Blockade of ɤ-aminobutyric acid A (GABA A ) receptor did not change the frequency and CV of SS firing in control group but produced a significant increase in the frequency and a decrease in the CV of SS firing in CEE mice. The CEE-induced decrease in SS firing rate and increase in CV were abolished by application of an N-methyl-D-aspartate (NMDA) receptor blocker, D-APV, but not by anα-amino-3-hydroxy-5-methyl -4-isoxazolepropionic acid (AMPA) receptor antagonist, NBQX. Notably, the spontaneous spike rate of molecular layer interneurons (MLIs) in CEE mice was significantly higher than control group, which was also abolished by application of D-APV. These results indicate that adolescent CEE enhances the spontaneous spike firing rate of MLIs through activation of NMDA receptor, resulting in a depression in the SS activity of cerebellar PCs in vivo in mice., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Type A GABA (γ-aminobutyric acid) receptors represent a diverse population in the mammalian brain, forming pentamers from combinations of α-, β-, γ-, δ-, ε-, ρ-, θ- and π-subunits 1 . αβ, α4βδ, α6βδ and α5βγ receptors favour extrasynaptic localization, and mediate an essential persistent (tonic) inhibitory conductance in many regions of the mammalian brain 1,2 . Mutations of these receptors in humans are linked to epilepsy and insomnia 3,4 . Altered extrasynaptic receptor function is implicated in insomnia, stroke and Angelman and Fragile X syndromes 1,5 , and drugs targeting these receptors are used to treat postpartum depression 6 . Tonic GABAergic responses are moderated to avoid excessive suppression of neuronal communication, and can exhibit high sensitivity to Zn 2+ blockade, in contrast to synapse-preferring α1βγ, α2βγ and α3βγ receptor responses 5,7-12 . Here, to resolve these distinctive features, we determined structures of the predominantly extrasynaptic αβ GABA A receptor class. An inhibited state bound by both the lethal paralysing agent α-cobratoxin 13 and Zn 2+ was used in comparisons with GABA-Zn 2+ and GABA-bound structures. Zn 2+ nullifies the GABA response by non-competitively plugging the extracellular end of the pore to block chloride conductance. In the absence of Zn 2+ , the GABA signalling response initially follows the canonical route until it reaches the pore. In contrast to synaptic GABA A receptors, expansion of the midway pore activation gate is limited and it remains closed, reflecting the intrinsic low efficacy that characterizes the extrasynaptic receptor. Overall, this study explains distinct traits adopted by αβ receptors that adapt them to a role in tonic signalling., (© 2022. The Author(s).)

GABA is the main inhibitory neurotransmitter in the brain and GABAergic transmission has been shown to be of importance for regulation of mood, memory and food intake. The progesterone metabolite allopregnanolone (Allo) is a positive GABA A receptor modulating steroid with potent effects. In humans, disorders such as premenstrual dysphoric disorder (PMDD), hepatic encephalopathy and polycystic ovarian syndrome are associated with elevated Allo levels and increased negative mood, disturbed memory and increased food intake in some individuals. This is surprising because Allo shares many properties with benzodiazepines and is mainly considered to be anxiolytic and anti-depressant. However, it is well established that, in certain individuals, GABA A receptor activating compounds could have paradoxical effects and thus be anxiogenic in low physiological plasma concentrations but anxiolytic at high levels. We have demonstrated that isoallopregnanolone (Isoallo), the 3β-OH sibling of Allo, functions as a GABA A receptor modulating steroid antagonist (GAMSA) but without any effects of its own on GABA A receptors. The antagonistic effect is noted in most GABA A subtypes investigated in vitro to date. In vivo, Isoallo can inhibit Allo-induced anaesthesia in rats, as well as sedation or saccadic eye velocity in humans. Isoallo treatment has been studied in women with PMDD. In a first phase II study, Isoallo (Sepranolone; Asarina Pharma) injections significantly ameliorated negative mood in women with PMDD compared with placebo. Several GAMSAs for oral administration have also been developed. The GAMSA, UC1011, can inhibit Allo induced memory disturbances in rats and an oral GAMSA, GR3027, has been shown to restore learning and motor coordination in rats with hepatic encephalopathy. In humans, vigilance, cognition and pathological electroencephalogram were improved in patients with hepatic encephalopathy on treatment with GR3027. In conclusion GAMSAs are a new possible treatment for disorders and symptoms caused by hyperactivity in the GABA A system., (© 2021 The Authors. Journal of Neuroendocrinology published by John Wiley & Sons Ltd on behalf of British Society for Neuroendocrinology.)

Synaptic plasticity is long-lasting changes in synaptic currents and structure. When neurons are exposed to signals that induce aberrant neuronal excitation, they increase the threshold for the induction of long-term potentiation (LTP), known as metaplasticity. However, the metaplastic regulation of structural LTP (sLTP) remains unclear. We investigate glutamate uncaging/photoactivatable (pa)CaMKII-dependent sLTP induction in hippocampal CA1 neurons after chronic neuronal excitation by GABA A receptor antagonists. We find that the neuronal excitation decreases the glutamate uncaging-evoked Ca 2+ influx mediated by GluN2B-containing NMDA receptors and suppresses sLTP induction. In addition, single-spine optogenetic stimulation using paCaMKII indicates the suppression of CaMKII signaling. While the inhibition of Ca 2+ influx is protein synthesis independent, the paCaMKII-induced sLTP suppression depends on it. Our findings demonstrate that chronic neuronal excitation suppresses sLTP in two independent ways (i.e., dual inhibition of Ca 2+ influx and CaMKII signaling). This dual inhibition mechanism may contribute to robust neuronal protection in excitable environments., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.)

Hypo-excitability was reported in the peri-infarct tissue following stroke, an effect counteracted by a blockage of α5-GABAA receptors in adult rodents. Our present study aims to evaluate the effect of a selective α5-GABAA receptor antagonist, S 44819, in stroke in juvenile animals. We have set up and characterized an original model of transient ischemic stroke in 28 day-old Sprague-Dawley rats (45-min occlusion of the middle cerebral artery by intraluminal suture). In this model, S 44819 (1, 3 and 10 mg/kg, b.i.d) was orally administered from day 3 to day 16 after stroke onset. Sensorimotor recovery was assessed on day 1, day 9 and day 16 after stroke onset. Results show that rats treated with S 44819 at the doses of 3 and 10 mg/kg displayed a significant improvement of the neurological deficits (neuroscore) on day 9 and day 16, when compared with animals treated with vehicle. Grip-test data analysis reveals that rats treated with S 44819 at the dose of 3 mg/kg displayed a better recovery on day 9 and day 16. These results are in agreement with those previously observed in adult rats, demonstrating that targeting α5-GABAA receptors improves neurological recovery after stroke in juvenile rats., (Copyright © 2021 Elsevier Inc. All rights reserved.)

The present study aimed to examine the synergistic effects of exercise and pharmacological inhibition of the α5 subunit-containing gamma-aminobutyric acid (GABA) A receptors (α5GABA A R) on motor function recovery after intracerebral hemorrhage (ICH). Wistar rats were divided into five groups (n = 8 per group): SHAM, ICH, ICH + exercise (ICH + EX), ICH + L-655,708 (ICH + L6), and ICH + L-655,708 and exercise (ICH + L6EX) groups. ICH was induced by microinjection of a collagenase solution. The ICH + EX and ICH + L6EX groups exercised on a treadmill (12 m/min for 30 min/day). L-655,708 (0.5 mg/kg), a negative allosteric modulator of α5GABA A R, was administered intraperitoneally to the ICH + L6 and ICH + L6EX groups. Each intervention was initiated 1 week after the ICH surgery and was performed for 3 weeks, followed by tissue collection, including the motor cortex and spinal cord. At 4 weeks after ICH, significant motor recovery was found in the ICH + L6EX group compared to the ICH group. L-655,708 administration increased brain-derived neurotrophic factor (BDNF) expression in the cortex. Regarding neuroplastic changes in the spinal cord, rats in the ICH + L6EX group showed a significant increase in several neuroplastic markers: 1) BDNF, 2) growth-associated protein 43 as an axonal sprouting marker, 3) synaptophysin as a synaptic marker, and 4) Nogo-A as an axonal growth inhibitor. This study is the first to demonstrate that combined treatment with exercise and α5GABA A R inhibitor effectively promoted motor function recovery after ICH. Regarding the underlying mechanism of post-ICH recovery with the combined treatment, the present study highlights the importance of both growth and inhibitory modification of axonal sprouting in the spinal cord., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Brainstem respiratory neuronal network significantly contributes to cough motor pattern generation. Neuronal populations in the pre-Bötzinger complex (PreBötC) represent a substantial component for respiratory rhythmogenesis. We studied the role of PreBötC neuronal excitation and inhibition on mechanically induced tracheobronchial cough in 15 spontaneously breathing, pentobarbital anesthetized adult cats (35 mg/kg, iv initially). Neuronal excitation by unilateral microinjection of glutamate analog d,l-homocysteic acid resulted in mild reduction of cough abdominal electromyogram (EMG) amplitudes and very limited temporal changes of cough compared with effects on breathing (very high respiratory rate, high amplitude inspiratory bursts with a short inspiratory phase, and tonic inspiratory motor component). Mean arterial blood pressure temporarily decreased. Blocking glutamate-related neuronal excitation by bilateral microinjections of nonspecific glutamate receptor antagonist kynurenic acid reduced cough inspiratory and expiratory EMG amplitude and shortened most cough temporal characteristics similarly to breathing temporal characteristics. Respiratory rate decreased and blood pressure temporarily increased. Limiting active neuronal inhibition by unilateral and bilateral microinjections of GABA A receptor antagonist gabazine resulted in lower cough number, reduced expiratory cough efforts, and prolongation of cough temporal features and breathing phases (with lower respiratory rate). The PreBötC is important for cough motor pattern generation. Excitatory glutamatergic neurotransmission in the PreBötC is involved in control of cough intensity and patterning. GABA A receptor-related inhibition in the PreBötC strongly affects breathing and coughing phase durations in the same manner, as well as cough expiratory efforts. In conclusion, differences in effects on cough and breathing are consistent with separate control of these behaviors. NEW & NOTEWORTHY This study is the first to explore the role of the inspiratory rhythm and pattern generator, the pre-Bötzinger complex (PreBötC), in cough motor pattern formation. In the PreBötC, excitatory glutamatergic neurotransmission affects cough intensity and patterning but not rhythm, and GABA A receptor-related inhibition affects coughing and breathing phase durations similarly to each other. Our data show that the PreBötC is important for cough motor pattern generation, but cough rhythmogenesis appears to be controlled elsewhere.

Thyroid hormones (THs) are essential for foetal brain development. Because the gestating mother is the main source of THs to the foetus, maternal hypothyroidism and/or premature birth compromise neurological outcomes in the offspring. Respiratory instability and recurrent apneas due to immaturity of the respiratory control network are major causes of morbidity in infants. Inadequate TH supply may be sufficient to delay perinatal maturation of the respiratory control system; however, this hypothesis remains untested. To address this issue, maternal hypothyroidism was induced by adding methimazole (MMI; 0.02% w/v) to the drinking water of pregnant dams from conception to postpartum day 4 (P4). The effect of TH supplementation on respiratory function was tested by injecting levothyroxine (L-T4) in newborns at P1. Respiratory function was assessed by plethysmography (in vivo) and recording of phrenic output from medullary preparations (in vitro). By comparison with controls, TH deficiency increased the frequency of apneas and decreased basal ventilation in vivo and prevented the age-dependent increase in phrenic burst frequency normally observed in vitro. The effects of TH deficiency on GABAergic modulation of respiratory activity were measured by bath application of muscimol (GABA A agonist) or bicuculline (GABA A antagonist). The phrenic burst frequency responses to GABAergic agents were consistently greater in preparations from TH deficient pups. L-T4 supplementation reversed part of the respiratory anomalies related to MMI treatment in vitro. We conclude that TH deficiency during the perinatal period is sufficient to delay maturation of the respiratory control network development. Excessive GABAergic inhibition may contribute to this effect., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Naturally occurring compounds such as sesquiterpenes and sesquiterpenoids (SQTs) have been shown to modulate GABA A receptors (GABA A Rs). In this study, the modulatory potential of 11 SQTs at GABA A Rs was analyzed to characterize their potential neurotropic activity. Transfected HEK293 cells and primary hippocampal neurons were functionally investigated using electrophysiological whole-cell recordings. Significantly different effects of β-caryophyllene and α-humulene, as well as their respective derivatives β-caryolanol and humulol, were observed in the HEK293 cell system. In neurons, the concomitant presence of phasic and tonic GABA A R configurations accounts for differences in receptor modulation by SQTs. The in vivo presence of the γ 2 and δ subunits is important for SQT modulation. While phasic GABA A receptors in hippocampal neurons exhibited significantly altered GABA-evoked current amplitudes in the presence of humulol and guaiol, negative allosteric potential at recombinantly expressed α 1 β 2 γ 2 receptors was only verified for humolol. Modeling and docking studies provided support for the binding of SQTs to the neurosteroid-binding site of the GABA A R localized between transmembrane segments 1 and 3 at the ( + α)-( - α) interface. In sum, differences in the modulation of GABA A R isoforms between SQTs were identified. Another finding is that our results provide an indication that nutritional digestion affects the neurotropic potential of natural compounds., (© 2021 The Authors. Journal of Neurochemistry published by John Wiley & Sons Ltd on behalf of International Society for Neurochemistry.)

α5 subunit GABA type A receptor (GABA A R) 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-GABA A R signaling from DIV12-14, when GABA A Rs 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 GABA A R 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-GABA A Rs, reduce the gephyrin inhibitory synaptic scaffold, or impair phasic or tonic inhibition. Furthermore, α5-NAM inhibition of the GABA A R tonic current in mature neurons is maintained after 2-day α5-NAM treatment, suggesting reduced tolerance liability, in contrast to other clinically relevant GABA A R-targeting drugs such as benzodiazepines. Together, these results show that α5-GABA A Rs contribute to dendritic spine maturation and excitatory synapse development via a NMDAR dependent mechanism without perturbing overall neuronal excitability., (Copyright © 2021. Published by Elsevier Ltd.)

Presympathetic neurons in the paraventricular nucleus of the hypothalamus (PVN) play a key role in cardiovascular regulation. We have previously shown that brain-derived neurotrophic factor (BDNF), acting in the PVN, increases sympathetic activity and blood pressure and serves as a key regulator of stress-induced hypertensive responses. BDNF is known to alter glutamatergic and GABA-ergic signaling broadly in the central nervous system, but whether BDNF has similar actions in the PVN remains to be investigated. Here, we tested the hypothesis that increased BDNF expression in the PVN elevates blood pressure by enhancing N -methyl-d-aspartate (NMDA) receptor (NMDAR)- and inhibiting GABA A receptor (GABA A R)-mediated signaling. Sprague-Dawley rats received bilateral PVN injections of AAV2 viral vectors expressing green fluorescent protein (GFP) or BDNF. Three weeks later, cardiovascular responses to PVN injections of NMDAR and GABA A R agonists and antagonists were recorded under α-chloralose-urethane anesthesia. In addition, expressions of excitatory and inhibitory signaling components in the PVN were assessed using immunofluorescence. Our results showed that NMDAR inhibition led to a greater decrease in blood pressure in the BDNF vs. GFP group, while GABA A R inhibition led to greater increases in blood pressure in the GFP group compared to BDNF. Conversely, GABA A R activation decreased blood pressure significantly more in GFP vs. BDNF rats. In addition, immunoreactivity of NMDAR1 was upregulated, while GABA A R-α1 and K + /Cl - cotransporter 2 were downregulated by BDNF overexpression in the PVN. In summary, our findings indicate that hypertensive actions of BDNF within the PVN are mediated, at least in part, by augmented NMDAR and reduced GABA A R signaling. NEW & NOTEWORTHY We have shown that BDNF, acting in the PVN, elevates blood pressure in part by augmenting NMDA receptor-mediated excitatory input and by diminishing GABA A receptor-mediated inhibitory input to PVN neurons. In addition, we demonstrate that elevated BDNF expression in the PVN upregulates NMDA receptor immunoreactivity and downregulates GABA A receptor as well as KCC2 transporter immunoreactivity.

Entorhinal cortex neurons make monosynaptic connections onto distal apical dendrites of CA1 and CA2 pyramidal neurons through the perforant path (PP) projection. Previous studies show that differences in dendritic properties and synaptic input density enable the PP inputs to produce a much stronger excitation of CA2 compared with CA1 pyramidal neurons. Here, using mice of both sexes, we report that the difference in PP efficacy varies substantially as a function of presynaptic firing rate. Although a single PP stimulus evokes a 5- to 6-fold greater EPSP in CA2 compared with CA1, a brief high-frequency train of PP stimuli evokes a strongly facilitating postsynaptic response in CA1, with relatively little change in CA2. Furthermore, we demonstrate that blockade of NMDARs significantly reduces strong temporal summation in CA1 but has little impact on that in CA2. As a result of the differences in the frequency- and NMDAR-dependent temporal summation, naturalistic patterns of presynaptic activity evoke CA1 and CA2 responses with distinct dynamics, differentially tuning CA1 and CA2 responses to bursts of presynaptic firing versus single presynaptic spikes, respectively. SIGNIFICANCE STATEMENT Recent studies have demonstrated that abundant entorhinal cortical innervation and efficient dendritic propagation enable hippocampal CA2 pyramidal neurons to produce robust excitation evoked by single cortical stimuli, compared with CA1. Here we uncovered, unexpectedly, that the difference in efficacy of cortical excitation varies substantially as a function of presynaptic firing rate. A burst of stimuli evokes a strongly facilitating response in CA1, but not in CA2. As a result, the postsynaptic response of CA1 and CA2 to presynaptic naturalistic firing displays contrasting temporal dynamics, which depends on the activation of NMDARs. Thus, whereas CA2 responds to single stimuli, CA1 is selectively recruited by bursts of cortical input., (Copyright © 2021 the authors.)

Chronic pain easily leads to concomitant mood disorders, and the excitability of anterior cingulate cortex (ACC) pyramidal neurons (PNs) is involved in chronic pain-related anxiety. However, the mechanism by which PNs regulate pain-related anxiety is still unknown. The GABAergic system plays an important role in modulating neuronal activity. In this paper, we aimed to study how the GABAergic system participates in regulating the excitability of ACC PNs, consequently affecting chronic inflammatory pain-related anxiety. A rat model of CFA-induced chronic inflammatory pain displayed anxiety-like behaviors, increased the excitability of ACC PNs, and reduced inhibitory presynaptic transmission; however, the number of GAD65/67 was not altered. Interestingly, intra-ACC injection of the GABA A R agonist muscimol relieved anxiety-like behaviors but had no effect on chronic inflammatory pain. Intra-ACC injection of the GABA A R antagonist picrotoxin induced anxiety-like behaviors but had no effect on pain in normal rats. Notably, chemogenetic activation of GABAergic neurons in the ACC alleviated chronic inflammatory pain and pain-induced anxiety-like behaviors, enhanced inhibitory presynaptic transmission, and reduced the excitability of ACC PNs. Chemogenetic inhibition of GABAergic neurons in the ACC led to pain-induced anxiety-like behaviors, reduced inhibitory presynaptic transmission, and enhanced the excitability of ACC PNs but had no effect on pain in normal rats. We demonstrate that the GABAergic system mediates a reduction in inhibitory presynaptic transmission in the ACC, which leads to enhanced excitability of pyramidal neurons in the ACC and is associated with chronic inflammatory pain-related anxiety., (© 2021. The Author(s).)

Purpose: To study the 24-hour expression of long noncoding RNAs (lncRNAs) in synaptic and extrasynaptic neurons expressing N-methyl-D-aspartate receptor (NMDAR), and normal neuronal cultures, via microarray analysis., Materials and Methods: Cortical neurons from embryonic (day E18) Sprague-Dawley rats were used for primary neuronal culture. NMDAR activation was blocked and the cells were then incubated for 6 hours. Total RNA was extracted, quantified, and analyzed for purity and integrity. Double-stranded cDNA was synthesized, followed by quantile normalization, quantitative polymerase chain reaction validation, and data analysis. The interactions between transcription factors and lncRNAs were analyzed by Pearson correlation., Results: The lncRNA profiles were obtained after synaptic and extrasynaptic NMDAR activation of rat cortical neuron cultures for 24 hours. In total, 251 lncRNAs were consistently upregulated, and 335 were downregulated, after extrasynaptic NMDAR activation compared with normal neurons. After synaptic NMDAR activation, only 9 lncRNAs were upregulated and 2 were downregulated., Conclusions: Differential expression of lncRNAs after synaptic and extrasynaptic NMDAR activation suggests that lncRNAs may be responsible for extrasynaptic NMDAR-induced neurodegeneration., (Copyright © 2021. Published by Elsevier Inc.)

Somatostatin-expressing interneurons (SOM-INs) are a major subpopulation of GABAergic cells in CA1 hippocampus that receive excitation from pyramidal cells (PCs), and, in turn, provide feedback inhibition onto PC dendrites. Excitatory synapses onto SOM-INs show a Hebbian long-term potentiation (LTP) mediated by type 1a metabotropic glutamate receptors (mGluR1a) that is implicated in hippocampus-dependent learning. The neuropeptide somatostatin (SST) is also critical for hippocampal long-term synaptic plasticity, as well as learning and memory. SST effects on hippocampal PCs are well documented, but its actions on inhibitory interneurons remain largely undetermined. In the present work, we investigate the involvement of SST in long-term potentiation of CA1 SOM-IN excitatory synapses using pharmacological approaches targeting the somatostatinergic system and whole cell recordings in slices from transgenic mice expressing eYFP in SOM-INs. We report that application of exogenous SST 14 induces long-term potentiation of excitatory postsynaptic potentials in SOM-INs via somatostatin type 1-5 receptors (SST 1-5 Rs) but does not affect synapses of PC or parvalbumin-expressing interneurons. Hebbian LTP in SOM-INs was prevented by inhibition of SSTRs and by depletion of SST by cysteamine treatment, suggesting a critical role of endogenous SST in LTP. LTP of SOM-IN excitatory synapses induced by SST 14 was independent of NMDAR and mGluR1a, activity-dependent, and prevented by blocking GABA A receptor function. Our results indicate that endogenous SST may contribute to Hebbian LTP at excitatory synapses of SOM-INs by controlling GABA A inhibition, uncovering a novel role for SST in regulating long-term synaptic plasticity in somatostatinergic cells that may be important for hippocampus-dependent memory processes., (© 2021. The Author(s).)

Benzodiazepine receptor agonists are widely prescribed therapeutic agents that alter gamma-aminobutyric acid (GABA) A receptor activity and have anxiolytic effects. Post-operative use of benzodiazepines is a risk factor of delirium. Inflammatory conditions alter the anxiolytic effects of benzodiazepine. We investigated the effect of diazepam, a typical benzodiazepine anxiolytic, on changes in the emotional behavior of mice in a hole-board test after lipopolysaccharide (LPS) treatment. Diazepam dose-dependently increased the number of head-dips at doses that did not alter locomotor activity; however, diazepam dose-dependently significantly decreased the number of head-dips at doses that did not alter locomotor activity in LPS-treated mice. Flumazenil, a benzodiazepine receptor antagonist, normalized the decrease in head-dipping behavior caused by diazepam treatment in normal and LPS-treated mice. The decrease of the head-dipping effect caused by diazepam was attenuated by minocycline in LPS-treated mice. We further found that the decrease in head-dipping behavior caused by diazepam was blocked by bumetanide, a Na + -K + -2Cl - cotransporter isoform 1 (NKCC1) antagonist, in LPS-treated mice. These findings suggest that diazepam induces the anxiety-like behavior under inflammation conditions, and may cause the GABA A receptor dysfunction associated with the chloride plasticity mediated by NKCC1, which contributes to benzodiazepine-induced delirium after surgery., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Synaptic and extrasynaptic GABA A receptor (GABA A R)-mediated neurotransmission is a critical component of the suprachiasmatic nucleus (SCN) neuronal network. However, the properties of the GABA A tonic current ( I tonic ) and its origin remain unexplored. Spontaneous GABA A postsynaptic currents (sGPSCs) and I tonic were recorded from SCN neurons with the whole cell voltage-clamp technique at different times of the day. GABA A R antagonists (bicuculline, gabazine, and picrotoxin) inhibited sGPSC and induced an outward shift of the holding current, which defined the I tonic amplitude. The sGPSC frequency, synaptic charge transfer, and I tonic amplitude all demonstrated significant diurnal rhythms, with peaks in the middle of the day [zeitgeber time (ZT)7-8] and nadirs at night (ZT19-20). The I tonic amplitude increased proportionally with the sGPSC frequency and synaptic charge transfer during the day and required action potential-mediated GABA release, which was confirmed by TTX application. The activation of presynaptic GABA B receptors by baclofen did not significantly alter the I tonic of neurons with low-frequency sGPSC. The equilibrium potential (Eq) for I tonic was similar to the Eq for chloride and GABA A receptor-activated currents. I tonic showed outward rectification at membrane potentials over the range of -70 to -10 mV and then was linear at voltages greater than -10 mV. GABA A R containing α4-, α5-, and δ-subunits were expressed in SCN, and their contribution to I tonic was confirmed by application of the GABA A R agonist 4,5,6,7-tetrahydroisoxazolo[5,4- c ]pyridin-3-ol (THIP) and the GABA A R inverse agonist 11,12,13,13 a -tetrahydro-7-methoxy-9-oxo-9 H -imidazo[1,5- a ]pyrrolo[2,1- c ][1,4]benzodiazepine-1-carboxylic acid ethyl ester (L655,708). Thus, the I tonic was mediated by extrasynaptic GABA A Rs activated predominantly by GABA diffusing out of GABAergic synapses. NEW & NOTEWORTHY A tonic current ( I tonic ) mediated by GABA A receptors (GABA A Rs) containing α4-, α5- and δ-subunits was observed in the suprachiasmatic nucleus. The I tonic amplitude strongly depended on the action potential-mediated synaptic release of GABA. The equilibrium potential for I tonic corresponds to that for GABA A currents. The frequency of GABA A postsynaptic currents and I tonic amplitude increased during the day, with peak in the middle of the day, and then gradually declined with a nadir at night, thus showing a diurnal rhythm.

Chronic pain is an incapacitating condition that affects a large population worldwide. Until now, there is no drug treatment to relieve it. The impairment of GABAergic inhibition mediated by GABA A receptors (GABA A R) is considered a relevant factor in mediating chronic pain. Even though both synaptic and extrasynaptic GABA A inhibition are present in neurons that process nociceptive information, the latter is not considered relevant as a target for the development of pain treatments. In particular, the extrasynaptic α 5 GABA A Rs are expressed in laminae I-II of the spinal cord neurons, sensory neurons, and motoneurons. In this review, we discuss evidence showing that blockade of the extrasynaptic α 5 GABA A Rs reduces mechanical allodynia in various models of chronic pain and restores the associated loss of rate-dependent depression of the Hoffmann reflex. Furthermore, in healthy animals, extrasynaptic α 5 GABA A R blockade induces both allodynia and hyperalgesia. These results indicate that this receptor may have an antinociceptive and pronociceptive role in healthy and chronic pain-affected animals, respectively. We propose a hypothesis to explain the relevant role of the extrasynaptic α 5 GABA A Rs in the processing of nociceptive information. The data discussed here strongly suggest that this receptor could be a valid pharmacological target to treat chronic pain states., (© 2021 The Authors. Physiological Reports published by Wiley Periodicals LLC on behalf of The Physiological Society and the American Physiological Society.)

Rosmarinic acid, a major component of rosemary, is a polyphenolic compound with potential neuroprotective effects. Asreducing the synaptic release of glutamate is crucial to achieving neuroprotectant's pharmacotherapeutic effects, the effect of rosmarinic acid on glutamate release was investigated in rat cerebrocortical nerve terminals (synaptosomes). Rosmarinic acid depressed the 4-aminopyridine (4-AP)-induced glutamate release in a concentration-dependent manner. The removal of extracellular calcium and the blockade of vesicular transporters prevented the inhibition of glutamate release by rosmarinic acid. Rosmarinic acid reduced 4-AP-induced intrasynaptosomal Ca 2+ elevation. The inhibition of N-, P/Q-type Ca 2+ channels and the calcium/calmodulin-dependent kinase II (CaMKII) prevented rosmarinic acid from having effects on glutamate release. Rosmarinic acid also reduced the 4-AP-induced activation of CaMKII and the subsequent phosphorylation of synapsin I, the main presynaptic target of CaMKII. In addition, immunocytochemistry confirmed the presence of GABA A receptors. GABA A receptor agonist and antagonist blocked the inhibitory effect of rosmarinic acid on 4-AP-evoked glutamate release. Docking data also revealed that rosmarinic acid formed a hydrogen bond with the amino acid residues of GABA A receptor. These results suggested that rosmarinic acid activates GABA A receptors in cerebrocortical synaptosomes to decrease Ca 2+ influx and CaMKII/synapsin I pathway to inhibit the evoked glutamate release.

Midazolam (MDZ) could affect lymphocyte immune functions. However, the influence of MDZ on cell's K + currents has never been investigated. Thus, in the present study, the effects of MDZ on Jurkat T lymphocytes were studied using the patch-clamp technique. Results showed that MDZ suppressed the amplitude of delayed-rectifier K + current ( I K(DR) ) in concentration-, time-, and state-dependent manners. The IC 50 for MDZ-mediated reduction of I K(DR) density was 5.87 μM. Increasing MDZ concentration raised the rate of current-density inactivation and its inhibitory action on I K(DR) density was estimated with a dissociation constant of 5.14 μM. In addition, the inactivation curve of I K(DR) associated with MDZ was shifted to a hyperpolarized potential with no change on the slope factor. MDZ-induced inhibition of I K(DR) was not reversed by flumazenil. In addition, the activity of intermediate-conductance Ca 2+ -activated K + (IK Ca ) channels was suppressed by MDZ. Furthermore, inhibition by MDZ on both I K(DR) and IK Ca -channel activity appeared to be independent from GABAA receptors and affected immune-regulating cytokine expression in LPS/PMA-treated human T lymphocytes. In conclusion, MDZ suppressed current density of I K(DR) in concentration-, time-, and state-dependent manners in Jurkat T-lymphocytes and affected immune-regulating cytokine expression in LPS/PMA-treated human T lymphocytes.

Benzodiazepines bind to and act on α1-3 and α5-containing GABAA receptors. Previous studies suggest that different GABAA receptor α-subtypes mediate the various behavioral effects of benzodiazepines, which raises the possibility of combining benzodiazepines with subtype-selective GABAA receptor antagonists to improve the therapeutic profiles of benzodiazepines. This study examined the GABAA receptor subtype mediation of the tolerance to midazolam-induced antinociception in rats. Midazolam (3.2 mg/kg) significantly reduced the locomotion in rats which was prevented by the selective α1-preferring GABAA receptor antagonist β-carboline-3-carboxylate-t-butyl ester (βCCt) (3.2 mg/kg). Midazolam increased the paw withdrawal threshold as tested by the von Frey filament assay in the complete Freund's adjuvant-induced inflammatory pain model in rats, and this effect was not altered by βCCt or another α1-preferring GABAA receptor antagonist 3-propoxy-β-carboline hydrochloride (3PBC). Repeated treatment with midazolam in combination with vehicle, βCCt or 3PBC (twice daily) for 7 days led to a progressive increase of the ED50 values in the midazolam- and vehicle-treated rats, but not in other rats, suggesting the development of tolerance to midazolam but not to the combination of midazolam with α1-preferring GABAA receptor antagonists. These results suggest the essential role of the α1-subtype of GABAA receptors in mediating the development of tolerance to midazolam-induced antinociceptive effects and raise the possibility of increasing therapeutic profiles of benzodiazepines by selectively blocking specific α-subtypes of GABAA receptors., (Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.)

Rationale: Nucleus cuneiformis (NC), a reticular nucleus of the midbrain, is a part of the descending pain modulatory system and therefore has an important role in pain perception., Objectives: Considering the abundance of GABA A and cannabinoid receptors in the NC and also the bidirectional roles for GABA in controlling nociception, the present study examined the effects of bilateral intra-NC microinjection of different doses of the GABA A receptor agonist, muscimol, and the GABA A receptor antagonist, bicuculline, on pain modulation using formalin test. We also assessed interaction between canabinergic and GABAergic systems in the NC during this test., Methods: Rats were exposed to intra-NC microinjection of bicuculline (50,100, and 200 ng/side) or muscimol (60, 120, and 240 ng/side) and then subjected to the formalin test. In another set of experiments, the effects of muscimol (60 ng/side) or bicuculline (50 ng/side) administration 5 min before a cannabinoid receptor agonist WIN 55,212-2 (5, 10, and 20 μg/side) microinjection into NC on the formalin test were evaluated., Results: Microinjection of bicuculline and muscimol into the NC decreased and increased pain responses, respectively, in a dose-dependent manner during both phases of the test. Microinjection of WIN 55,212-2 into the NC significantly reduced pain responses in a dose-dependent manner. Microinjection of bicuculline or muscimol in combination with WIN 55,212-2 into the NC respectively potentiated and attenuated WIN 55,212-2-induced antinociception in the formalin test., Conclusions: This study shows that GABA in the NC is involved in pain modulation and suggests the existence of a GABA A -mediated inhibitory system in the NC on pain control. Furthermore, it seems that the antinociceptive effect of WIN 55,212-2 in the formalin test is mediated partly by the activity of local GABA A receptors in the NC.

CDKL5 (cyclin-dependent kinase-like 5) deficiency disorder (CDD) is a severe neurodevelopmental encephalopathy characterized by early-onset epilepsy and intellectual disability. Studies in mouse models have linked CDKL5 deficiency to defects in neuronal maturation and synaptic plasticity, and disruption of the excitatory/inhibitory balance. Interestingly, increased density of both GABAergic synaptic terminals and parvalbumin inhibitory interneurons was recently observed in the primary visual cortex of Cdkl5 knockout (KO) mice, suggesting that excessive GABAergic transmission might contribute to the visual deficits characteristic of CDD. However, the functional relevance of cortical GABAergic circuits abnormalities in these mutant mice has not been investigated so far. Here we examined GABAergic circuits in the perirhinal cortex (PRC) of Cdkl5 KO mice, where we previously observed impaired long-term potentiation (LTP) associated with deficits in novel object recognition (NOR) memory. We found a higher number of GABAergic (VGAT)-immunopositive terminals in the PRC of Cdkl5 KO compared to wild-type mice, suggesting that increased inhibitory transmission might contribute to LTP impairment. Interestingly, while exposure of PRC slices to the GABA A receptor antagonist picrotoxin had no positive effects on LTP in Cdkl5 KO mice, the selective GABA B receptor antagonist CGP55845 restored LTP magnitude, suggesting that exaggerated GABA B receptor-mediated inhibition contributes to LTP impairment in mutants. Moreover, acute in vivo treatment with CGP55845 increased the number of PSD95 positive puncta as well as density and maturation of dendritic spines in PRC, and restored NOR memory in Cdkl5 KO mice. The present data show the efficacy of limiting excessive GABA B receptor-mediated signaling in improving synaptic plasticity and cognition in CDD mice., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Myocardial macrophages have key roles in cardiac remodeling and dysfunction. The gamma-aminobutyric acid subtype A (GABA A ) receptor was recently found to be distributed in macrophages, allowing regulation of inflammatory responses to various diseases. This study aimed to clarify the role of GABA A receptor-mediated macrophage responses in pressure overload-induced heart failure., Methods and Results: C57BL/6J mice underwent transverse aortic constriction for pressure-overload hypertrophy (POH) and were intraperitoneally treated with a specific GABA A receptor agonist (topiramate) or antagonist (bicuculline). Echocardiography, histology, and flow cytometry were performed to evaluate the causes and effects of myocardial hypertrophy and fibrosis. Activation of the GABA A receptor by topiramate reduced ejection fraction and fractional shortening, enlarged the end-diastolic and end-systolic left ventricular internal diameter, aggravated myocardial hypertrophy and fibrosis, and accelerated heart failure in response to pressure overload. Mechanistically, topiramate increased the number of Ly6C low macrophages in the heart during POH and circulating Ly6C high classic monocyte infiltration in late-phase POH. Further, topiramate drove Ly6C low macrophages toward MHCII high macrophage polarization. As a result, Ly6C low macrophages activated the amphiregulin-induced AKT/mTOR signaling pathway, and Ly6C low MHCII high macrophage polarization increased expression levels of osteopontin and TGF-β, which led to myocardial hypertrophy and fibrosis. Conversely, GABA A receptor blockage with bicuculline reversed these effects., Conclusions: Control of the GABA A receptor activity in monocytes/macrophages plays an important role in myocardial hypertrophy and fibrosis after POH. Blockade of the GABA A receptor has the potential to improve pressure overload-induced heart failure., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Bu, Huang, Wang, Xia, Liu, You, Wang and Liu.)

The regulation of protein synthesis is a vital and finely tuned process in cellular physiology. In neurons, this process is very precisely regulated, as which mRNAs undergo translation is highly dependent on context. One of the most prominent regulators of protein synthesis is the enzyme eukaryotic elongation factor kinase 2 (eEF2K) that regulates the elongation stage of protein synthesis. This kinase and its substrate, eukaryotic elongation factor 2 (eEF2) are important in processes such as neuronal development and synaptic plasticity. eEF2K is regulated by multiple mechanisms including Ca 2+ -ions and the mTORC1 signaling pathway, both of which play key roles in neurological processes such as learning and memory. In such settings, the localized control of protein synthesis is of crucial importance. In this work, we sought to investigate how the localization of eEF2K is controlled and the impact of this on protein synthesis in neuronal cells. In this study, we used both SH-SY5Y neuroblastoma cells and mouse cortical neurons, and pharmacologically and/or genetic approaches to modify eEF2K function. We show that eEF2K activity and localization can be regulated by its binding partner Homer1b/c, a scaffolding protein known for its participation in calcium-regulated signaling pathways. Furthermore, our results indicate that this interaction is regulated by the mTORC1 pathway, through a known phosphorylation site in eEF2K (S396), and that it affects rates of localized protein synthesis at synapses depending on the presence or absence of this scaffolding protein., (© 2020 International Society for Neurochemistry.)

Rett syndrome (RTT) is a neurodevelopmental disease caused mostly by mutations in the MECP2 gene. People with RTT show breathing dysfunction attributable to the high rate of sudden death. Previous studies have shown that insufficient GABA synaptic inhibition contributes to the breathing abnormalities in mouse models of RTT, while it remains elusive how the glycine system is affected. We found that optogenetic stimulation of GAD-expressing neurons in mice produced GABAergic and glycinergic postsynaptic inhibitions of neurons in the hypoglossal nucleus (XII) and the dorsal motor nucleus of vagus (DMNV). By sequential applications of bicuculline and strychnine, such inhibition appeared approximately 44% GABA A ergic and 52% glycinergic in XII neurons, and approximately 49% GABA A ergic and 46% glycinergic in DMNV neurons. Miniature inhibitory postsynaptic potentials (mIPSCs) in these neurons were approximately 47% GABA A ergic and 49% glycinergic in XII neurons, and approximately 48% versus 50% in DMNV neurons, respectively. Consistent with the data, our single-cell polymerase chain reaction studies indicated that transcripts of GABA A receptor γ2 subunit (GABA A Rγ2) and glycine receptor β subunit (GlyRβ) were simultaneously expressed in these cells. In MeCP2 R168X mice, proportions of GABA A ergic and glycinergic mIPSCs became approximately 28% versus 69% in XII neurons, and approximately 31% versus 66% in DMNV cells. In comparison with control mice, the GABA A ergic and glycinergic mIPSCs decreased significantly in the XII and DMNV neurons from the MeCP2 R168X mice, so did the transcripts of GABA A Rγ2 and GlyRβ. These results suggest that XII and DMNV neurons adopt dual GABA A ergic and glycinergic synaptic inhibitions, and with Mecp2 disruption these neurons rely more on glycinergic synaptic inhibition., (© 2020 Wiley Periodicals LLC.)

Chronic pain is a significant public health problem that afflicts nearly 30% of the global population, but current pharmacotherapies are insufficient. Previous report indicated that N-demethylsinomenine, an active metabolite of sinomenine, is efficacious against postoperative pain. The present study investigated whether N-demethylsinomenine is effective for chronic painful conditions or whether repeated treatment alters its effect. Both chronic constriction injury (CCI) surgery and complete Freund's adjuvant (CFA) intraplantar injection induced significant and reliable mechanical allodynia at least for 7 days. Acute treatment with N-demethylsinomenine (10-40 mg/kg, i.p.) dose-dependently attenuated the mechanical allodynia both in CCI-induced neuropathic pain and CFA-induced inflammatory pain in mice. The potency of N-demethylsinomenine for reducing CFA-induced mechanical allodynia was slightly higher than sinomenine. During the period of repeated treatment, N-demethylsinomenine maintained its anti-allodynic effect against both neuropathic and inflammatory pain without producing carry-over effect. Pretreatment with bicuculline, a selective γ-aminobutyric acid type A (GABA A ) receptor antagonist, almost completely blocked the anti-allodynia of N-demethylsinomenine (40 mg/kg) both in CCI and CFA-treated mice. Our findings indicated that N-demethylsinomenine exhibits GABA A receptor-mediated anti-allodynic effects in mouse models of neuropathic and inflammatory pain, suggesting it may be a useful novel pharmacotherapy for the control of chronic pain.

Output signals of neural circuits, including the retina, are shaped by a combination of excitatory and inhibitory signals. Inhibitory signals can act presynaptically on axon terminals to control neurotransmitter release and regulate circuit function. However, it has been difficult to study the role of presynaptic inhibition in most neural circuits due to lack of cell type-specific and receptor type-specific perturbations. In this study, we used a transgenic approach to selectively eliminate GABA A inhibitory receptors from select types of second-order neurons - bipolar cells - in mouse retina and examined how this affects the light response properties of the well-characterized ON alpha ganglion cell retinal circuit. Selective loss of GABA A receptor-mediated presynaptic inhibition causes an enhanced sensitivity and slower kinetics of light-evoked responses from ON alpha ganglion cells thus highlighting the role of presynaptic inhibition in gain control and temporal filtering of sensory signals in a key neural circuit in the mammalian retina., Competing Interests: JN, BE, MH, RS No competing interests declared, (© 2021, Nagy et al.)

Gamma-aminobutyric acid (GABA) is an important inhibitory neurotransmitter in the mature brain. At an early developmental period, it acts in an excitatory manner that influences many processes of proliferation, migration, and differentiation of the neurons. Previous evidence indicated that manipulation of the GABAergic system function by activation or blockade of its receptors during developmental periods leads to behavioral and cognitive abnormality in adulthood. Therefore, we examined the effects of neonatal blockade of GABA-A receptors by bicuculline on behavior, cognitive function, and hippocampal and prefrontal cortex (PFC) brain-derived neurotrophic factors level (BDNF) in adulthood. As a result, neonatal rats were treated with either bicuculline (75,150, and 300 μg/kg) or DMSO on postnatal days 7,9, and 11. These groups underwent the behavioral (open field, elevated plus maze, and hot plate) and learning and memory (passive avoidance learning and memory) tests in postnatal days (PNDs) 61-70. After the ending of the behavioral tests, the rats were sacrificed under deep anesthesia and the hippocampi and prefrontal cortex (PFC) of the brain were removed for assessing the BDNF mRNA expression. Our results indicated that neonatal administration of bicuculline at the highest dose increased passive avoidance memory and hippocampal BDNF level. Meanwhile, this drug at a low dose impaired this type of memory and increased PFC BDNF level. Besides, treatment with bicuculline during postnatal days increased anxiety and pain sensitivity in a dose-dependent manner. Taken together, these findings confirmed the notion that GABA-A receptors during the developmental period are important for programming neurobehavioral phenotypes in adult life., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Background: Multiple cognitive and psychiatric disorders are associated with an increased tonic inhibitory conductance that is generated by α5 subunit-containing γ-aminobutyric acid type A (α5 GABA A ) receptors. Negative allosteric modulators that inhibit α5 GABA A receptors (α5-NAMs) are being developed as treatments for these disorders. The effects of α5-NAMs have been studied on recombinant GABA A receptors expressed in non-neuronal cells; however, no study has compared drug effects on the tonic conductance generated by native GABA A receptors in neurones, which was the goal of this study., Methods: The effects of five α5-NAMs (basmisanil, Ono-160, L-655,708, α5IA, and MRK-016) on tonic current evoked by a low concentration of GABA were studied using whole-cell recordings in cultured mouse hippocampal neurones. Drug effects on current evoked by a saturating concentration of GABA and on miniature inhibitory postsynaptic currents (mIPSCs) were also examined., Results: The α5-NAMs caused a concentration-dependent decrease in tonic current. The potencies varied as the inhibitory concentration for 50% inhibition (IC 50 ) of basmisanil (127 nM) was significantly higher than those of the other compounds (0.4-0.8 nM). In contrast, the maximal efficacies of the drugs were similar (35.5-51.3% inhibition). The α5-NAMs did not modify current evoked by a saturating GABA concentration or mIPSCs., Conclusions: Basmisanil was markedly less potent than the other α5-NAMs, an unexpected result based on studies of recombinant α5 GABA A receptors. Studying the effects of α5 GABA A receptor-selective drugs on the tonic inhibitory current in neurones could inform the selection of compounds for future clinical trials., (Copyright © 2020 British Journal of Anaesthesia. Published by Elsevier Ltd. All rights reserved.)

Cobra venoms contain three-finger toxins (TFT) including α-neurotoxins efficiently binding nicotinic acetylcholine receptors (nAChRs). As shown recently, several TFTs block GABA A receptors (GABA A Rs) with different efficacy, an important role of the TFTs central loop in binding to these receptors being demonstrated. We supposed that the positive charge (Arg36) in this loop of α-cobratoxin may explain its high affinity to GABA A R and here studied α-neurotoxins from African cobra N. melanoleuca venom for their ability to interact with GABAARs and nAChRs. Three α-neurotoxins, close homologues of the known N. melanoleuca long neurotoxins 1 and 2, were isolated and sequenced. Their analysis on Torpedo californica and α7 nAChRs, as well as on acetylcholine binding proteins and on several subtypes of GABA A Rs, showed that all toxins interacted with the GABA A R much weaker than with the nAChR: one neurotoxin was almost as active as α-cobratoxin, while others manifested lower activity. The earlier hypothesis about the essential role of Arg36 as the determinant of high affinity to GABA A R was not confirmed, but the results obtained suggest that the toxin loop III may contribute to the efficient interaction of some long-chain neurotoxins with GABA A R. One of isolated toxins manifested different affinity to two binding sites on Torpedo nAChR.

The postpartum period is commonly accompanied by emotional changes, which for many new mothers includes a reduction in anxiety. Previous research in rodents has shown that the postpartum attenuation in anxiety is dependent on offspring contact and has further implicated enhanced GABAergic neurotransmission as an underlying mechanism. However, the specific brain regions where GABA acts to regulate the offspring-induced reduction in postpartum anxiety requires further investigation. Here, we test the hypothesis that offspring interactions suppress anxiety-like behavior in postpartum female rats via GABA signaling in the medial prefrontal cortex (mPFC). Our results show a postpartum reduction in anxiety-like behavior, an effect which was abolished by localized infusion of the GABA A receptor antagonist bicuculline in the mPFC. We also show that activation of GABA A receptors in the mPFC by the agonist muscimol was effective in restoring anxiolyisis in mothers separated from their pups. Lastly, we show that heightened anxiety-like behavior in pup-separated mothers was accompanied by a lower number and percentage of activated GABAergic neurons within the mPFC. Together, these results suggest that mother-offspring interactions reduce anxiety-like behavior in postpartum females via GABA A neurotransmission in the mPFC and in doing so provide insight into mechanisms that may become dysfunctional in mothers who experience high postpartum anxiety., (Copyright © 2020 Elsevier B.V. All rights reserved.)