GABAA receptor: Positive and negative allosteric modulators

Interaction Between Allopregnanolone and Amiloride Binding Sites on the GABAA Receptor

Allopregnanolone (Allo) is a positive allosteric modulator of the GABAA receptor, and amiloride (Ami) is a competitive antagonist of the GABAA receptor. The purpose of this work was to study the combined effect of Allo and Ami on functional activity of GABAA receptor. The GABA-induced chloride current (IGABA) was measured in isolated Purkinje cells of rat cerebellum using the patch-clamp technique and a system of fast application. Our results indicate that Allo suppresses the inhibitory effect of Ami on IGABA, the IC50 value of Ami concentration-response curve was increased from 164 to 547 µM (P < 0.001) in the presence of Allo. Next, GABA concentration-response curves (EC50 = 5.8 µM) were constructed in the presence of Allo (EC50 = 1.2 µM), Ami (EC50 = 25.5 µM), and the combination of Allo+Ami (EC50 = 3.2 µM). Changes in EC50 values as a percentage relative to the control were calculated. The blocking effect of Ami is reduced in the presence of Allo (340% vs 150%, P < 0.01) and the potentiating effect of Allo does not change in the presence of Ami (78% vs 87%, P > 0.05). The results suggest that there is an allosteric relationship between the Allo and Ami binding sites on GABAA receptor that operates in one direction, from Allo sites to Ami site, but not vice versa.

Pharmacological therapies for early and long-term recovery in disorders of consciousness: current knowledge and promising avenues

INTRODUCTION

Disorders of consciousness (DoC) are characterized by impaired arousal and/or awareness, ranging from coma to unresponsive wakefulness syndrome, minimally conscious state, and cognitive motor dissociation. Pharmacological treatment options remain limited, complicated by the heterogeneity of etiologies, such as traumatic brain injury, stroke, and infections. The lack of rigorous clinical trials has led to off-label use of treatments, often without clear mechanistic understanding, posing challenges for effective patient care.

AREAS COVERED

In this perspective, the authors report on key studies concerning the effectiveness of pharmacological interventions, including dopaminergic and GABAergic agents, antidepressants, statins, and anticonvulsants, in promoting recovery of consciousness in DoC.

EXPERT OPINION

Robust longitudinal clinical trials are needed, with priority given to early subacute phase intervention. Outcomes should be better defined, considering immediate responses to medication while also increasing the emphasis on long-term quality of life. Unified functional and mechanistic frameworks are needed to guide research and foster collaboration. Furthermore, a shift toward personalized medicine would benefit this heterogeneous population. Moving forward, assessing the efficacy of more unconventional or 'paradoxical' pharmacological options in treatment plans will be essential. The authors also expect an increased use of AI tools to identify factors that best predict treatment responses.

Diagnosis and management of paroxysmal sympathetic hyperactivity: a narrative review of recent literature

Paroxysmal sympathoexcitatory syndrome is a clinical syndrome, recognized in a subgroup of survivors of severe acquired brain injury, of simultaneous, paroxysmal transient increases in sympathetic [elevated heart rate, blood pressure, respiratory rate, temperature, sweating] and motor [posturing] activity. Coupled with the absence of uniform treatment guidelines, it is prone to underdiagnosis and misdiagnosis, leading to the adoption of inappropriate treatment protocols, which may adversely affect the prognosis of patients. This narrative review summarized the existing literature and provided a comprehensive account of the research history and terminology of PSH, epidemiology and pathogenesis, diagnostic criteria, therapeutic options, and prognosis, hoping to bring new ideas to the clinical treatment of PSH.

Inhibition of NMDA receptors and other ion channel types by membrane-associated drugs

N-methyl-D-aspartate receptors (NMDARs) are ligand-gated ion channels present at most excitatory synapses in the brain that play essential roles in cognitive functions including learning and memory consolidation. However, NMDAR dysregulation is implicated in many nervous system disorders. Diseases that involve pathological hyperactivity of NMDARs can be treated clinically through inhibition by channel blocking drugs. NMDAR channel block can occur via two known mechanisms. First, in traditional block, charged drug molecules can enter the channel directly from the extracellular solution after NMDAR activation and channel opening. Second, uncharged molecules of channel blocking drug can enter the hydrophobic plasma membrane, and upon NMDAR activation the membrane-associated drug can transit into the channel through a fenestration within the NMDAR. This membrane-associated mechanism of action is called membrane to channel inhibition (MCI) and is not well understood despite the clinical importance of NMDAR channel blocking drugs. Intriguingly, a hydrophobic route of access for drugs is not unique to NMDARs. Our review will address inhibition of NMDARs and other ion channels by membrane-associated drugs and consider how the path of access may affect a drug's therapeutic potential.

Novel Spiro-Barbiturates Can Reverse the Action of General Anesthetics on the GABAAR

GABAARs are pentameric ligand-gated ion channels that play a major role in mediating inhibition in the CNS. They are the target of many widely used positive allosteric modulators (PAMs) of GABAARs such as general anesthetics, sedatives, antiepileptics, and anxiolytics. However, close structural analogs of these PAMs are negative allosteric modulators that cause excitation. Comparison of the SAR of inhibitory and excitatory barbiturates suggested that conformationally constrained spiro-analogs of phenobarbital might have intermediate allosteric activity. More than 50 spiro-analogs were synthesized and characterized for their ability to enhance desensitization and reverse the action of anesthetics. A number of these reversed the action of anesthetics without having any action on GABA-induced desensitization. These constitute a new class of GABA-ergic drugs that are null allosteric ligands. They offer the potential to reverse the sedative action of current PAMs and modulate the behavior of diseases resulting from mutations in GABAAR subunits.

Tangeretin enhances sedative activity of diazepam in Swiss mice through GABAA receptor interaction: In vivo and in silico approaches

The citrus peel flavonoid tangeretin (TAN) has diverse biological activities, including antioxidant, anti-inflammatory, antitumor, hepatoprotective, and neuroprotective effects. This study investigates the sedative effects of TAN, in Swiss albino mice using in vivo and in silico approaches. TAN (10 and 20 mg/kg, i.p.) was administered alone and in combination with diazepam (DZP, 2 mg/kg, i.p.) and flumazenil (FLU, 0.1 mg/kg, i.p.) to evaluate its impact on thiopental sodium (TS)-induced sleep, locomotor activity, and dark-light behavior. Results demonstrated that TAN at 10 mg/kg significantly (p < 0.05) reduced sleep onset latency and increased sleep duration, with a synergistic effect observed when combined with DZP. In locomotor activity tests, TAN dose-dependently decreased the distance traveled, while the combination with DZP further enhanced this effect. Dark-light tests revealed that TAN increased dark residence time, indicating potential anxiolytic properties. Molecular docking studies showed that TAN binds to the GABAA receptor (α1 and β2 subunits) with a binding affinity of -6.6 kcal/mol, suggesting its interaction with GABAergic pathways. Pharmacokinetic analysis indicated high intestinal absorption and compliance with Lipinski's rule of five, with a favorable safety profile (LD50 = 5000 mg/kg). Overall, TAN enhances the sedative effects of DZP through GABAA receptor modulation, highlighting its potential as a natural sedative agent. Further research should explore the long-term effects, bioavailability, blood-brain barrier permeability, and synergistic interactions of TAN, with comprehensive in vitro studies and clinical trials needed to validate its potential as a natural sedative.

Protein phosphatase 2A inhibitors: a possible pharmacotherapy for benzodiazepine dependence

OBJECTIVES

Benzodiazepines (BZDs) activate the γ-aminobutyric acid (GABA) subtype A (GABAA) receptors, and thus are widely used medicines for the treatment of anxiety and insomnia. For chronic use, tolerance to BZDs is a major problem. Patients with chronic insomnia that develop tolerance to BZDs lose therapeutic effects but also potentially suffer from BZD dependence resulting in BZD withdrawal. The development of such treatments is important for the appropriate use of BZDs.

METHODS

Research articles regarding investigation of BZD dependence were searched on PubMed, Embase, and Scopus databases using keywords "benzodiazepine", "dependence", "treatment".

KEY FINDINGS

When BZDs are taken chronically, continuous GABAA binding results in up-regulation of α-amino-3-hydroxy-5-methyl-4-lisoxazolepropionic acid (AMPA) glutamate receptor function and release of brain-derived neurotrophic factor (BDNF). Released BDNF binds to its specific receptor tropomyosin-related kinase receptor B (TrkB). Enhanced BDNF-TrkB signaling activates protein phosphatase 2A (PP2A). Activated PP2A dephosphorylates GABAA receptors, resulting in the downregulation of the GABAA receptor function. Reduced GABAA receptor function augments long-term potentiation (LTP), AMPA-mediated glutamatergic neuroplasticity, by reducing LTP inhibition by GABAA receptor function. Augmented LTP enhances extreme anxiety, which leads to BZD dependence.

CONCLUSION

Therefore, iInhibiting dephosphorylation of the GABAA receptor by PP2A, PP2A inhibitors could reduce LTP and anxiety, restoring BZD effectiveness and resulting in possible therapeutic effects for BZD dependence.

Expecting medication misuse: a proactive approach to drug discovery to prevent fatal overdose

Misuse of central nervous system (CNS) depressants (alprazolam, fentanyl, etc.) is a major cause of fatal overdose, with a high prevalence of deaths involving polydrug interactions from the victim's own prescriptions. Thus, there is an urgent need to improve the safety of CNS depressants to prevent fatalities. Pharmacological pursuits aiming to prevent harm through the design of non-addictive alternatives have either failed before clinical trials or produced mediocre treatment alternatives. Therefore, we propose a new perspective for medicinal chemists: rather than aiming to prevent misuse, we must design new central nervous system (CNS) depressants under the expectation of misuse. By shifting the design focus to partial modulators rather than full agonists, we can develop novel chemical entities (NCEs) that intrinsically minimize physical harm caused by misuse without sacrificing therapeutic efficacy. In this perspective, we provide an overview of the two most widely misused classes of medications (opioid and GABAA receptor modulators) in relation to pharmacodynamic properties and clinical outcomes. We then suggest a drug discovery pathway focused on physiological parameters. It is our opinion that this approach would dramatically decrease the lethality of overdose and improve outcomes of treatments for pain, anxiety, and withdrawal from alcohol, benzodiazepines, and opioids.

Experimental and Computational Investigation of the Target and Mechanisms of Gelsemium Alkaloids in the Central Nervous System

Gelsemium has a long history of medicinal use but is also a poisonous plant. Some low-toxicity alkaloids in Gelsemium exhibit anxiolytic, anti-inflammatory, analgesic, and other pharmacological effects; however, certain alkaloids in Gelsemium are highly toxic. Nevertheless, the molecular targets underlying the biological effects of Gelsemium alkaloids remain poorly understood. We employed electrophysiological techniques and molecular modeling to examine the modulatory effects of Gelsemium alkaloids on inhibitory neurotransmitter receptors, as well as to elucidate the mechanisms underlying their molecular interactions. Our findings indicate that low-toxicity alkaloids primarily exert their pharmacological effects through actions on glycine receptors, with the binding site located at the orthosteric site between two α-subunits. Both highly toxic and low-toxicity alkaloids target GABAA receptors, using the β+/α- interface transmembrane structural domains as common binding sites. These results identify the targets through which Gelsemium alkaloids affect the central nervous system and predict the binding modes and key amino acids involved from a computational modeling perspective. However, further experimental validation through mutational studies is necessary to strengthen these findings.

Decoding neural circuit dysregulation in bipolar disorder: Toward an advanced paradigm for multidimensional cognitive, emotional, and psychomotor treatment

Bipolar disorder (BD) is characterized by a complex constellation of emotional, cognitive, and psychomotor disturbances, each deeply intertwined with underlying dysfunctions in large-scale brain networks and neurotransmitter systems. This manuscript integrates recent advances in neuroimaging, neuromodulation, and pharmacological research to provide a comprehensive view of BD's pathophysiology, emphasizing the role of network-specific dysfunctions and their clinical manifestations. We explore how dysregulation within the fronto-limbic network, particularly involving the prefrontal cortex (PFC) and amygdala, underpins the emotional instability that defines both manic and depressive episodes. Additionally, impairments in the central executive network (CEN) and default mode network (DMN) are linked to cognitive deficits, with hyperactivity in the DMN driving rumination and cognitive inflexibility, while CEN underactivity contributes to attentional lapses and impaired executive function. Psychomotor symptoms, which oscillate between hyperactivity in mania and retardation in depression, are closely associated with imbalances in neurotransmitter systems, particularly dopamine and serotonin, within the basal ganglia-thalamo-cortical motor pathway. Recent studies indicate that these psychomotor disturbances are further exacerbated by disruptions in network connectivity, leading to impairments in both motor control and emotional regulation. Emerging therapeutic strategies are discussed, with a focus on neuromodulation techniques such as transcranial magnetic stimulation (TMS) and deep brain stimulation (DBS), which show promise in restoring balance within these critical networks. Furthermore, pharmacological interventions that modulate synaptic functioning and neuronal plasticity offer potential for addressing both the emotional and motor symptoms of BD. This manuscript underscores the need for an integrative treatment approach that simultaneously targets neural circuits and neurotransmitter systems to address the full spectrum of symptoms in BD. Drawing on recent advancements in neurobiological models and therapeutic frameworks, this proposal outlines a pathway for the development of precision-tailored interventions. These approaches are designed to optimize cognitive, emotional, and psychomotor outcomes, ultimately striving to elevate the quality of life for individuals living with bipolar disorder (BD), while remaining firmly grounded in the latest empirical evidence and theoretical insights.

Anxiolytic Activity of Morellic Acid: Modulation of Diazepam's Anxiolytic Effects, Possibly Through GABAergic Interventions

BACKGROUND

Numerous studies suggest that morellic acid (MOR), highly available in Garcinia plants, has different physiological activities, including anti-cancer, anti-oxidant, and anti-microbial activity.

AIM

In this investigation, we aimed to demonstrate the anxiolytic activity, along with the mechanism behind this activity of MOR, using in vivo and in silico studies.

METHODS

For this, we used different doses of MOR (5 and 10 mg/kg) and administered this drug intraperitoneally to Swiss albino mice (male and female). Diazepam (DZP), a positive allosteric modulator of the GABAA receptor, was used as a positive control at a dose of 2 mg/kg (i.p), and vehicle was used as a control group. In this test, various test protocols are used to assess the behavioral patterns of mice, including swing, hole cross, light-dark testing, and open field testing.

RESULTS

This investigation revealed that MOR remarkably reduced the locomotor activity of mice in a dose-dependent manner and produced calming behaviors like DZP. However, the findings showed that the combination of MOR and DZP synergistically reduced the locomotion of mice compared to the single therapy. On the other hand, from the computational study, the result demonstrated that MOR exhibited the highest binding scores (-9.2 kcal/mol) towards the GABAA receptor α3 subunit and -7.6 kcal/mol towards the GABAA α2 receptor. Whereas, DZP showed -6.6 and -7.3 kcal/mol docking affinity and FLU exerted -6.2 and -6.3 kcal/mol docking scores towards the GABAA receptor α2 and α3 subunits, respectively. The ligand interacted with the receptor by forming different hydrogen and hydrophobic bonds.

CONCLUSION

However, it is recommended that more precise and comprehensive preclinical investigations be required to demonstrate the exact mechanism behind the anxiolytic effects and conduct clinical trials to determine efficacy and safety.

Molecular mechanisms of the GABA type A receptor function

The GABA type A receptor (GABAAR) belongs to the family of pentameric ligand-gated ion channels and plays a key role in inhibition in adult mammalian brains. Dysfunction of this macromolecule may lead to epilepsy, anxiety disorders, autism, depression, and schizophrenia. GABAAR is also a target for multiple physiologically and clinically relevant modulators, such as benzodiazepines (BDZs), general anesthetics, and neurosteroids. The first GABAAR structure appeared in 2014, but the past years have brought a particularly abundant surge in structural data for these receptors with various ligands and modulators. Although the open conformation remains elusive, this novel information has pushed the structure-function studies to an unprecedented level. Electrophysiology, mutagenesis, photolabeling, and in silico simulations, guided by novel structural information, shed new light on the molecular mechanisms of receptor functioning. The main goal of this review is to present the current knowledge of GABAAR functional and structural properties. The review begins with an outline of the functional and structural studies of GABAAR, accompanied by some methodological considerations, especially biophysical methods, enabling the reader to follow how major breakthroughs in characterizing GABAAR features have been achieved. The main section provides a comprehensive analysis of the functional significance of specific structural elements in GABAARs. We additionally summarize the current knowledge on the binding sites for major GABAAR modulators, referring to the molecular underpinnings of their action. The final chapter of the review moves beyond examining GABAAR as an isolated macromolecule and describes the interactions of the receptor with other proteins in a broader context of inhibitory plasticity. In the final section, we propose a general conclusion that agonist binding to the orthosteric binding sites appears to rely on local interactions, whereas conformational transitions of bound macromolecule (gating) and allosteric modulation seem to reflect more global phenomena involving vast portions of the macromolecule.

Adaptive sampling-based structural prediction reveals opening of a GABAA receptor through the αβ interface

γ-Aminobutyric acid type A (GABAA) receptors are ligand-gated ion channels in the central nervous system with largely inhibitory function. Despite being a target for drugs including general anesthetics and benzodiazepines, experimental structures have yet to capture an open state of classical synaptic α1β2γ2 GABAA receptors. Here, we use a goal-oriented adaptive sampling strategy in molecular dynamics simulations followed by Markov state modeling to capture an energetically stable putative open state of the receptor. The model conducts chloride ions with comparable conductance as in electrophysiology measurements. Relative to experimental structures, our open model is relatively expanded at both the cytoplasmic (-2') and central (9') gates, coordinated with distinctive rearrangements at the transmembrane αβ subunit interface. Consistent with previous experiments, targeted substitutions disrupting interactions at this interface slowed the open-to-desensitized transition rate. This work demonstrates the capacity of advanced simulation techniques to investigate a computationally and experimentally plausible functionally critical of a complex membrane protein yet to be resolved by experimental methods.

Evaluating Outcomes of Diazepam Administration in Gradual Steps Introductions of Adult Male and Female Rhesus Macaques (Macaca mulatta)

Social housing remains one of the best forms of environmental enhancement for nonhuman primates (NHPs). The gradual steps (GS) method, a 2-step plan involving an initial phase of limited physical contact (protected contact [PC]) prior to full contact (FC), is widely used for introducing macaque pairs. Recent evidence has suggested that administration of diazepam prior to FC introduction, without a PC phase, improves the success rate of pairings among adult male rhesus macaques (Macaca mulatta). Nevertheless, given the popularity of the standard GS method, there is considerable interest in using diazepam along with this technique. We hypothesized that administering a single dose of diazepam prior to the PC phase would improve the success rates of isosexual pairings of unfamiliar adult macaques. Twelve males and 12 females were studied in each of 3 groups, with 2 different doses of oral diazepam (2.5 or 3.2 mg/kg) and controls introduced without diazepam. Pairs were deemed successful after 14 consecutive days of compatible FC housing. Among males, success rates for the low diazepam, high diazepam, and control groups were 67%, 50%, and 67%, respectively. Among females, the corresponding values were 50%, 33%, and 17%. There were no significant differences in overall introduction success rates for either sex. However, among females, the success rates during the initial PC phase were significantly higher in introductions involving the lower dose of diazepam (83%) than among controls (33%). Descriptively, in both sexes, less severe wounding patterns were observed with the lower dose compared with either the high dose or control groups. Our results suggest that diazepam administration prior to the PC phase of the GS method does not improve pairing outcomes for either sex in rhesus macaques. However, diazepam may have some utility in moderating wounding during unsuccessful introductions.

Preferential Synaptic Type of GABA-A Receptor Ligands Enhancing Neuronal Survival and Facilitating Functional Recovery After Ischemic Stroke

Selective enhancement of synaptic GABA signaling mediated by GABA-A receptors has been previously reported to promote functional recovery after ischemic stroke, while tonic GABA signaling has been detrimental. To identify agents that enhance synaptic signaling, we synthesized GABA-A ligands based on three chemotypes with affinity values pKi= 6.44-8.32. Representative compounds showed a preference in functional responses toward synaptic type of GABA-A receptors, compared to the extrasynaptic ones. In a cellular ischemia model (OGD), selected compounds showed the potential to improve neuronal recovery. The selected lead, compound 4, demonstrated the ability to reduce mitochondrial dysfunction, regulate intracellular calcium levels, decrease caspase 3 levels, and promote neurite outgrowth in in vitro assays. In an animal model, compound 4 enhanced motor recovery and showed neuroprotective activity by reducing infarct volume and decreasing poststroke acidosis. These findings underscore the value of selective ligands modulating synaptic GABA-A receptors in promoting recovery from ischemic stroke.

GABA and its receptors' mechanisms in the treatment of insomnia

Insomnia has now become a major health problem of global concern, with about 1/3 of the population suffering from sleep problems, a proportion that is still rising year by year. Most of the therapeutic drugs for insomnia currently used in clinical practice are not developed in a targeted manner, but are discovered by chance, and have unavoidable side effects such as addiction. Finding a safer and more effective therapeutic drug has become an urgent need for current research. Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the central nervous system. It can ameliorate Insomnia, Alzheimer's disease, Parkinson's disease, Epilepsy, and other neurological disorders. Various mechanisms have been reported for GABA to ameliorate insomnia, such as GABAA receptor modulation, GABAB receptor modulation, inhibition of neuroinflammatory responses, repair of oxidative damage, and inter-regulation of the circadian rhythm hormone melatonin. GABA is a potential therapeutic target in the prevention and treatment of insomnia. This paper reviews mechanisms of GABA and its receptors in insomnia diseases and the potential of GABA analogs application and discusses the research progress of GABA as a promising therapeutic drug for insomnia diseases. This will help the development of novel targeted GABA-like drugs and provide new ideas and methods for the clinical treatment of insomnia.

Low-dose diazepam improves cognitive function in APP/PS1 mouse models: Involvement of AMPA receptors

Previous studies have indicated a close association between cognitive impairment in patients with neurodegenerative diseases, such as Alzheimer's disease (AD), and synaptic damage. Diazepam (DZP), a benzodiazepine class drug, is used to control symptoms such as seizures, anxiety, and sleep disorders. These symptoms can potentially manifest throughout the entire course of AD. Therefore, DZP may be utilized in the treatment of AD to manage these symptoms. However, the specific role and mechanisms of DZP in AD remain unclear. In this study, we discovered that long-term administration of a low dose of DZP (0.5  mg/kg) improved cognitive function and protected neurons from damage in APP/PS1 mice. Mechanistic investigations revealed that DZP exerted its neuroprotective effects and reduced Aβ deposition by modulating GluA1 (glutamate AMPA receptor subunit) to influence synaptic function. In conclusion, these findings highlight the potential benefits of DZP as a novel therapeutic approach, suggesting that long-term use of low-dose DZP in early-stage AD patients may be advantageous in slowing disease progression.

The Application and Pharmaceutical Development of Etomidate: Challenges and Strategies

Etomidate is a synthetic imidazole anesthetic that exerts hypnotic effects by potentiating the action of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) or directly activating the anionic GABA (GABAA) receptor. It stands out among many anesthetics because of its multiple advantages, such as good hemodynamic stability and minimal inhibition of spontaneous respiration. However, its low water solubility and side effects, such as adrenal cortex inhibition and myoclonus, have limited the clinical application of this drug. To address these issues, extensive research has been conducted on the drug delivery of etomidate in recent decades, which has led to the emergence of different etomidate preparations. Despite so many etomidate preparations, so far some of the toxic side effects have not yet been effectively addressed. Herein we discuss the pharmaceutical design of etomidate that may resolve the above problem. We also propose targeted strategies for future research on etomidate preparations and discuss the feasibility of different administration routes and dosage forms to expand the application of this drug. Through this review, we hope to draw more attention to the potential of etomidate and its application challenges and provide valuable insights into the development of new etomidate preparations.

GABA Receptors and Kv7 Channels as Targets for GABAergic Regulation of Acetylcholine Release in Frog Neuromuscular Junction

Effects of gamma-aminobutyric acid (GABA) and some selective GABAergic ligands on the quantal acetylcholine (ACh) release in the frog neuromuscular contacts were investigated using combination of microelectrode technique with fluorescent and immunohistochemical assays. Significant attenuation of ACh release was observed in the presence of GABA as well as selective GABAA and GABAB receptor agonists. Neither GABAA nor GABAB antagonists abolished to full extent this effect of GABA. Fluorescent assay allowed to detect the GABA-induced opening of K+ channels, which was inhibited by XE-991, a selective antagonist of Kv7 type. Electrophysiological recordings of endplate potentials in the presence of XE-991 confirmed the contribution of Kv7 type potassium channels to the effects of GABA on ACh release that was not associated with GABAA and GABAB receptors activation. Note that XE-991 effectively precluded the action of retigabine, neuronal Kv7 channel opener, on ACh release. Immunohistochemical assay revealed that frog mature skeletal muscle fibers contain a significant amount of GABA, and substantial amount of GABA can be released in the extracellular space at the muscle contractions induced by prolonged high-frequency nerve stimulation. Besides, some binding sites for exogenous GABA were detected on the plasma membranes. It is concluded that GABA, in addition to affecting GABAA and GABAB receptors, can directly activate Kv7 channels, thereby negatively modulating the evoked ACh release. Endogenous GABA may serve as a retrograde regulator of neurotransmitter exocytosis.

NE contribution to rebooting unconsciousness caused by midazolam

The advent of midazolam holds profound implications for modern clinical practice. The hypnotic and sedative effects of midazolam afford it broad clinical applicability. However, the specific mechanisms underlying the modulation of altered consciousness by midazolam remain elusive. Herein, using pharmacology, optogenetics, chemogenetics, fiber photometry, and gene knockdown, this in vivo research revealed the role of locus coeruleus (LC)-ventrolateral preoptic nucleus noradrenergic neural circuit in regulating midazolam-induced altered consciousness. This effect was mediated by α1 adrenergic receptors. Moreover, gamma-aminobutyric acid receptor type A (GABAA-R) represents a mechanistically crucial binding site in the LC for midazolam. These findings will provide novel insights into the neural circuit mechanisms underlying the recovery of consciousness after midazolam administration and will help guide the timing of clinical dosing and propose effective intervention targets for timely recovery from midazolam-induced loss of consciousness.

Enabling systemic identification and functionality profiling for Cdc42 homeostatic modulators

Maintaining body homeostasis is the ultimate key to health. There are rich resources of bioactive materials for the functionality of homeostatic modulators (HMs) from both natural and synthetic chemical repertories1-3. HMs are powerful modern therapeutics for human diseases including neuropsychiatric diseases, mental disorders, and drug addiction (e.g. Buspirone and benzodiazepines)4-7. However, the identification of therapeutic HMs are often unpredictable and limited to membrane protein receptors and ion channels. Based on a serendipitously encountered small molecule ZCL278 with partial agonist (PA) profile as a model compound8-10, the Mant-GTP fluorophore-based Cdc42-GEF (guanine nucleotide exchange factor) screening uncovered a near holistic spectrum of HMs for Cdc42, a cytoplasmic small GTPase in the Ras superfamily11,12. We categorized these HMs as functionally distinct, with some previously understudied classes: Class I-competitive PAs, Class II-hormetic agonists, Class III-bona fide inhibitors, Class IV-bona fide activators, and Class V-ligand-enhanced agonists. The model HMs elicited striking biological functionalities in modulating bradykinin activation of Cdc42 signaling as well as actin remodeling while they ameliorated Alzheimer's disease-like social behavior in mouse model. Furthermore, molecular structural modeling analyses led to the concept of preferential binding pocket order (PBPO) for profiling HMs that target Cdc42 complexed with intersectin (ITSN), a GEF selectively activating Cdc42. Remarkably, the PBPO enabled a prediction of HM class that mimics the pharmacological functionality. Therefore, our study highlights a model path to actively capture different classes of HM to broaden therapeutic landscape.

The TMEM132B-GABAA receptor complex controls alcohol actions in the brain

Alcohol is the most consumed and abused psychoactive drug globally, but the molecular mechanisms driving alcohol action and its associated behaviors in the brain remain enigmatic. Here, we have discovered a transmembrane protein TMEM132B that is a GABAA receptor (GABAAR) auxiliary subunit. Functionally, TMEM132B promotes GABAAR expression at the cell surface, slows receptor deactivation, and enhances the allosteric effects of alcohol on the receptor. In TMEM132B knockout (KO) mice or TMEM132B I499A knockin (KI) mice in which the TMEM132B-GABAAR interaction is specifically abolished, GABAergic transmission is decreased and alcohol-induced potentiation of GABAAR-mediated currents is diminished in hippocampal neurons. Behaviorally, the anxiolytic and sedative/hypnotic effects of alcohol are markedly reduced, and compulsive, binge-like alcohol consumption is significantly increased. Taken together, these data reveal a GABAAR auxiliary subunit, identify the TMEM132B-GABAAR complex as a major alcohol target in the brain, and provide mechanistic insights into alcohol-related behaviors.

Improvement of sleep duration and quality through GABAA receptor by whey protein hydrolysate containing DIQK as the main active compound

This study characterized the sleep activity, sleep mechanism, and active peptides of whey protein hydrolysates selected through behavioral analysis of fruit flies (Drosophila melanogaster). Sleep-inducing whey protein (WP) hydrolysate was selected through fruit fly behavior analysis, and sleep activity was measured using a pentobarbital model and electroencephalographic analysis. The mechanism of action was confirmed using a γ-aminobutyric acid (GABA) receptor antagonist, and the active peptide was identified using liquid chromatography-mass spectrometry. Whey protein hydrolysate, prepared using Alcalase and Prozyme (WP-AP), increased sleep time in a dose-dependent manner. The WP-AP significantly increased not only sleep time but also slow-wave sleep and showed an insomnia-alleviating effect in a caffeine-induced insomnia mouse model. In addition, the gene and protein expression levels of GABA subtype A receptors increased in the brains of mice orally administered with WP-AP. Through peptide analysis, the mixture of DIQK, VPPF peptide, and GABA contained in WP-AP was estimated to exhibit sleep activity, and due to its high content, DIQK was speculated to be the main sleep-inducing ingredient. These results indicate that WP-AP has the potential to be used as a new ingredient to improve sleep quality.

Trans-Ferulic acid reduces the sedative activity of diazepam in thiopental sodium-induced sleeping mice: A potential GABAergic transmission

trans-Ferulic acid (TFA), a bioactive compound found in many plants, has been recognized for its diverse pharmacological activities, including potential neurological benefits. Previous studies suggest that TFA exerts anxiolytic effects via GABAergic pathways. This study aimed to investigate the sedative effects of TFA and its possible molecular mechanisms through in vivo and in silico approaches. Adult Swiss mice were randomly divided into six groups (n = 7): control (vehicle), standard (DZP: Diazepam at 3 mg/kg, p.o.), three test groups (TFA at 25, 50, and 75 mg/kg, p.o.), and a combination group (TFA: 50 mg/kg with DZP: 3 mg/kg, p.o.). Thirty minutes post-treatment, thiopental sodium (TS) at 40 mg/kg was administered to induce sedation, and latency as well as duration of sleep, were observed for up to 4 h. In silico studies were conducted with GABAA receptor subunits (α1 and β2) to elucidate the possible molecular interactions. The results demonstrated that TFA significantly reduced latency and extended sleep duration in a dose-dependent manner compared to the control. Additionally, TFA combined with DZP further significantly (p < 0.001) enhanced these effects. In silico analysis revealed that TFA and DZP exhibited strong binding affinities with the GABAA receptor subunits (α1 and β2) in the identical binding sites, with binding energies of -6.8 and - 8.7 kcal/mol, respectively. Collectively, TFA exerted a mild sedative effect in TS-induced sleeping mice and modulated the activity of DZP, likely through interactions with GABAA receptors. TFA showed promising activity as a potential candidate for managing sleep disorders such as insomnia.

GABA Type A receptors expressed in triple negative breast cancer cells mediate chloride ion flux

Triple negative breast cancer (TNBC) is known for its heterogeneous nature and aggressive onset, limited unresponsiveness to hormone therapies and immunotherapy as well as high likelihood of metastasis and recurrence. Since no targeted standard treatment options are available for TNBC, novel and effective therapeutic targets are urgently needed. Ion channels have emerged as possible novel therapeutic candidates for cancer therapy. We previously showed that GABAA β3 subunit are expressed at higher levels in TNBC cell lines than non-tumorigenic MCF10A cells. GABAA β3 subunit knockdown causes cell cycle arrest in TNBC cell lines via decreased cyclin D1 and increased p21 expression. However, it is not known if the upregulated GABAAR express at the cell-surface in TNBC and mediate Cl- flux. Cl- ions are known to play a role in cell-cycle progression in other cancers such as gastric cancer. Here, using surface biotinylation and (N-(Ethoxycarbonylmethyl)-6-Methoxyquinolinium Bromide) MQAE-dye based fluorescence quenching, we show that upregulated GABAAR are on the cell-surface in TNBC cell lines and mediate significantly higher chloride (Cl-) flux as compared to non-tumorigenic MCF10A cells. Moreover, this GABAAR mediated Cl- flux can be modulated by pharmacological agents and is decreased in TNBC cells with GABAA β3 subunit knockdown. Further, treatment of TNBC cells with bicuculline, a GABAAR antagonist reduced cell viability in TNBC cells Overall, these results point to an unexplored role of GABAAR mediated Cl- flux in TNBC.

The emergence of antidepressant drugs targeting GABAA receptors: A concise review

Depression is among the most common psychiatric illnesses, which imposes a major socioeconomic burden on patients, caregivers, and the public health system. Treatment with classical antidepressants (e.g. tricyclic antidepressants and selective serotonine reuptake inhibitors), which primarily affect monoaminergic systems has several limitations, such as delayed onset of action and moderate efficacy in a relatively large proportion of depressed patients. Furthermore, depression is highly heterogeneus, and its different subtypes, including post-partum depression, involve distinct neurobiology, warranting a differential approach to pharmacotherapy. Given these shortcomings, the need for novel antidepressants that are superior in efficacy and faster in onset of action is fully justified. The development and market introduction of rapid-acting antidepressants has accelerated in recent years. Some of these new antidepressants act through the GABAergic system. In this review, we discuss the discovery, efficacy, and limitations of treatment with classic antidepressants. We provide a detailed discussion of GABAergic neurotransmission, with a special focus on GABAA receptors, and possible explanations for the mood-enhancing effects of GABAergic medications (in particular neurosteroids acting at GABAA receptors), and, ultimately, we present the most promising molecules belonging to this family which are currently used in clinical practice or are in late phases of clinical development.

Pharmacological chaperones restore proteostasis of epilepsy-associated GABAA receptor variants

Recent advances in genetic diagnosis identified variants in genes encoding GABAA receptors as causative for genetic epilepsy. Here, we selected eight disease-associated variants in the α1 subunit of GABAA receptors causing mild to severe clinical phenotypes and showed that they are loss of function, mainly by reducing the folding and surface trafficking of the α1 protein. Furthermore, we sought client protein-specific pharmacological chaperones to restore the function of pathogenic receptors. Applications of positive allosteric modulators, including Hispidulin and TP003, increase the functional surface expression of the α1 variants. Mechanism of action study demonstrated that they enhance the folding, assembly, and trafficking and reduce the degradation of GABAA variants without activating the unfolded protein response in HEK293T cells and human iPSC-derived neurons. Since these compounds cross the blood-brain barrier, such a pharmacological chaperoning strategy holds great promise to treat genetic epilepsy in a GABAA receptor-specific manner.

Alterations in GABAA receptor-mediated inhibition triggered by status epilepticus and their role in epileptogenesis and increased anxiety

The triggers of status epilepticus (SE) in non-epileptic patients can vary widely, from idiopathic causes to exposure to chemoconvulsants. Regardless of its etiology, prolonged SE can cause significant brain damage, commonly resulting in the development of epilepsy, which is often accompanied by increased anxiety. GABAA receptor (GABAAR)-mediated inhibition has a central role among the mechanisms underlying brain damage and the ensuing epilepsy and anxiety. During SE, calcium influx primarily via ionotropic glutamate receptors activates signaling cascades which trigger a rapid internalization of synaptic GABAARs; this weakens inhibition, exacerbating seizures and excitotoxicity. GABAergic interneurons are more susceptible to excitotoxic death than principal neurons. During the latent period of epileptogenesis, the aberrant reorganization in synaptic interactions that follow interneuronal loss in injured brain regions, leads to the formation of hyperexcitable, seizurogenic neuronal circuits, along with disturbances in brain oscillatory rhythms. Reduction in the spontaneous, rhythmic "bursts" of IPSCs in basolateral amygdala neurons is likely to play a central role in anxiogenesis. Protecting interneurons during SE is key to preventing both epilepsy and anxiety. Antiglutamatergic treatments, including antagonism of calcium-permeable AMPA receptors, can be expected to control seizures and reduce excitotoxicity not only by directly suppressing hyperexcitation, but also by counteracting the internalization of synaptic GABAARs. Benzodiazepines, as delayed treatment of SE, have low efficacy due to the reduction and dispersion of their targets (the synaptic GABAARs), but also because themselves contribute to further reduction of available GABAARs at the synapse; furthermore, benzodiazepines may be completely ineffective in the immature brain.

Local and global effects of sedation in resting-state fMRI: a randomized, placebo-controlled comparison between etifoxine and alprazolam

TSPO ligands are promising alternatives to benzodiazepines in the treatment of anxiety, as they display less pronounced side effects such as sedation, cognitive impairment, tolerance development and abuse potential. In a randomized double-blind repeated-measures study we compare a benzodiazepine (alprazolam) to a TSPO ligand (etifoxine) by assessing side effects and acquiring resting-state fMRI data from 34 healthy participants after 5 days of taking alprazolam, etifoxine or a placebo. To study the effects of the pharmacological interventions in fMRI in detail and across different scales, we combine in our study complementary analysis strategies related to whole-brain functional network connectivity, local connectivity analysis expressed in regional homogeneity, fluctuations in low-frequency BOLD amplitudes and coherency of independent resting-state networks. Participants reported considerable adverse effects such as fatigue, sleepiness and concentration impairments, related to the administration of alprazolam compared to placebo. In resting-state fMRI we found a significant decrease in functional connection density, network efficiency and a decrease in the networks rich-club coefficient related to alprazolam. While observing a general decrease in regional homogeneity in high-level brain networks in the alprazolam condition, we simultaneously could detect an increase in regional homogeneity and resting-state network coherence in low-level sensory regions. Further we found a general increase in the low-frequency compartment of the BOLD signal. In the etifoxine condition, participants did not report any significant side effects compared to the placebo, and we did not observe any corresponding modulations in our fMRI metrics. Our results are consistent with the idea that sedation globally disconnects low-level functional networks, but simultaneously increases their within-connectivity. Further, our results point towards the potential of TSPO ligands in the treatment of anxiety and depression.

GABAergic implications in anxiety and related disorders

Evidence indicates that anxiety disorders arise from an imbalance in the functioning of brain circuits that govern the modulation of emotional responses to possibly threatening stimuli. The circuits under consideration in this context include the amygdala's bottom-up activity, which signifies the existence of stimuli that may be seen as dangerous. Moreover, these circuits encompass top-down regulatory processes that originate in the prefrontal cortex, facilitating the communication of the emotional significance associated with the inputs. Diverse databases (e.g., Pubmed, ScienceDirect, Web of Science, Google Scholar) were searched for literature using a combination of different terms e.g., "anxiety", "stress", "neuroanatomy", and "neural circuits", etc. A decrease in GABAergic activity is present in both anxiety disorders and severe depression. Research on cerebral functional imaging in depressive individuals has shown reduced levels of GABA within the cortical regions. Additionally, animal studies demonstrated that a reduction in the expression of GABAA/B receptors results in a behavioral pattern resembling anxiety. The amygdala consists of inhibitory networks composed of GABAergic interneurons, responsible for modulating anxiety responses in both normal and pathological conditions. The GABAA receptor has allosteric sites (e.g., α/γ, γ/β, and α/β) which enable regulation of neuronal inhibition in the amygdala. These sites serve as molecular targets for anxiolytic medications such as benzodiazepine and barbiturates. Alterations in the levels of naturally occurring regulators of these allosteric sites, along with alterations to the composition of the GABAA receptor subunits, could potentially act as mechanisms via which the extent of neuronal inhibition is diminished in pathological anxiety disorders.

New epilepsy therapies in development

Epilepsy is a common brain disorder, characterized by spontaneous recurrent seizures, with associated neuropsychiatric and cognitive comorbidities and increased mortality. Although people at risk can often be identified, interventions to prevent the development of the disorder are not available. Moreover, in at least 30% of patients, epilepsy cannot be controlled by current antiseizure medications (ASMs). As a result of considerable progress in epilepsy genetics and the development of novel disease models, drug screening technologies and innovative therapeutic modalities over the past 10 years, more than 200 novel epilepsy therapies are currently in the preclinical or clinical pipeline, including many treatments that act by new mechanisms. Assisted by diagnostic and predictive biomarkers, the treatment of epilepsy is undergoing paradigm shifts from symptom-only ASMs to disease prevention, and from broad trial-and-error treatments for seizures in general to mechanism-based treatments for specific epilepsy syndromes. In this Review, we assess recent progress in ASM development and outline future directions for the development of new therapies for the treatment and prevention of epilepsy.

The Nicotinic Acetylcholine Receptor and Its Pentameric Homologs: Toward an Allosteric Mechanism of Signal Transduction at the Atomic Level

The nicotinic acetylcholine receptor has served, since its biochemical identification in the 1970s, as a model of an allosteric ligand-gated ion channel mediating signal transition at the synapse. In recent years, the application of X-ray crystallography and high-resolution cryo-electron microscopy, together with molecular dynamic simulations of nicotinic receptors and homologs, have opened a new era in the understanding of channel gating by the neurotransmitter. They reveal, at atomic resolution, the diversity and flexibility of the multiple ligand-binding sites, including recently discovered allosteric modulatory sites distinct from the neurotransmitter orthosteric site, and the conformational dynamics of the activation process as a molecular switch linking these multiple sites. The model emerging from these studies paves the way for a new pharmacology based, first, upon the occurrence of an original mode of indirect allosteric modulation, distinct from a steric competition for a single and rigid binding site, and second, the design of drugs that specifically interact with privileged conformations of the receptor such as agonists, antagonists, and desensitizers. Research on nicotinic receptors is still at the forefront of understanding the mode of action of drugs on the nervous system.

GABAA receptor subunit composition regulates circadian rhythms in rest-wake and synchrony among cells in the suprachiasmatic nucleus

The mammalian circadian clock located in the suprachiasmatic nucleus (SCN) produces robust daily rhythms including rest-wake. SCN neurons synthesize and respond to γ-aminobutyric acid (GABA), but its role remains unresolved. We tested the hypothesis that γ2- and δ-subunits of the GABAA receptor in the SCN differ in their regulation of synchrony among circadian cells. We used two approaches: 1) shRNA to knock-down (KD) the expression of either γ2 or δ subunits in the SCN or 2) knock-in mice harboring a point mutation in the M2 domains of the endogenous GABAA γ2 or δ subunits. KD of either γ2 or δ subunits in the SCN increased daytime running and reduced nocturnal running by reducing their circadian amplitude by a third. Similarly, δ subunit knock-in mice showed decreased circadian amplitude, increased duration of daily activity, and decreased total daily activity. Reduction, or mutation of either γ2 or δ subunits halved the synchrony among, and amplitude of, circadian SCN cells as measured by firing rate or expression of the PERIOD2 protein, in vitro. Surprisingly, overexpression of the γ2 subunit rescued these phenotypes following KD or mutation of the δ subunit, and overexpression of the δ subunit rescued deficiencies due to γ2 subunit KD or mutation. We conclude that γ2 and δ GABAA receptor subunits play similar roles in maintaining circadian synchrony in the SCN and amplitude of daily rest-wake rhythms, but that modulation of their relative densities can change the duration and amplitude of daily activities.

Forskolin reverses the O-GlcNAcylation dependent decrease in GABAAR current amplitude at hippocampal synapses possibly at a neurosteroid site on GABAARs

GABAergic transmission is influenced by post-translational modifications, like phosphorylation, impacting channel conductance, allosteric modulator sensitivity, and membrane trafficking. O-GlcNAcylation is a post-translational modification involving the O-linked attachment of β-N-acetylglucosamine on serine/threonine residues. Previously we reported an acute increase in O-GlcNAcylation elicits a long-term depression of evoked GABAAR inhibitory postsynaptic currents (eIPSCs) onto hippocampal principal cells. Importantly, O-GlcNAcylation and phosphorylation can co-occur or compete for the same residue; whether they interact in modulating GABAergic IPSCs is unknown. We tested this by recording IPSCs from hippocampal principal cells and pharmacologically increased O-GlcNAcylation, before or after increasing serine phosphorylation using the adenylate cyclase activator, forskolin. Although forskolin had no significant effect on baseline eIPSC amplitude, we found that a prior increase in O-GlcNAcylation unmasks a forskolin-dependent increase in eIPSC amplitude, reversing the O-GlcNAc-induced eIPSC depression. Inhibition of adenylate cyclase or protein kinase A did not prevent the potentiating effect of forskolin, indicating serine phosphorylation is not the mechanism. Surprisingly, increasing O-GlcNAcylation also unmasked a potentiating effect of the neurosteroids 5α-pregnane-3α,21-diol-20-one (THDOC) and progesterone on eIPSC amplitude in about half of the recorded cells, mimicking forskolin. Our findings show that under conditions of heightened O-GlcNAcylation, the neurosteroid site on synaptic GABAARs is possibly accessible to agonists, permitting strengthening of synaptic inhibition.

Discovering the Intriguing Properties of Extrasynaptic γ-Aminobutyric Acid Type A Receptors

Tonic inhibition in mouse hippocampal CA1 pyramidal neurons is mediated by α5 subunit-containing γ-aminobutyric acid type A receptors. By Caraiscos VB, Elliott EM, You-Ten KE, Cheng VY, Belelli D, Newell JG, Jackson MF, Lambert JJ, Rosahl TW, Wafford KA, MacDonald JF, Orser BA. Proc Natl Acad Sci U S A 2004; 101:3662-7. Reprinted with permission. In this Classic Paper Revisited, the author recounts the scientific journey leading to a report published in the Proceedings of the National Academy of Sciences (PNAS) and shares several personal stories from her formative years and "research truths" that she has learned along the way. Briefly, the principal inhibitory neurotransmitter in the brain, γ-aminobutyric acid (GABA), was conventionally thought to regulate cognitive processes by activating synaptic GABA type A (GABAA) receptors and generating transient inhibitory synaptic currents. However, the author's laboratory team discovered a novel nonsynaptic form of tonic inhibition in hippocampal pyramidal neurons, mediated by extrasynaptic GABAA receptors that are pharmacologically distinct from synaptic GABAA receptors. This tonic current is highly sensitive to most general anesthetics, including sevoflurane and propofol, and likely contributes to the memory-blocking properties of these drugs. Before the publication in PNAS, the subunit composition of GABAA receptors that generate the tonic current was unknown. The team's research showed that GABAA receptors containing the α5 subunit (α5GABAARs) generated the tonic inhibitory current in hippocampal neurons. α5GABAARs are highly sensitive to GABA, desensitize slowly, and are thus well suited for detecting low, persistent, ambient concentrations of GABA in the extracellular space. Interest in α5GABAARs has surged since the PNAS report, driven by their pivotal roles in cognitive processes and their potential as therapeutic targets for treating various neurologic disorders.

Factors promoting the release of picrotoxin from the trap in the GABA(A) receptor pore

Picrotoxin (PTX), a convulsant of plant origin, has been used in many studies as research tool. PTX is the open channel blocker of the GABAA receptor (GABAAR). Being in the pore, PTX initiates transfer of the channel to the closed state and thus it falls into the "trap". The consequence of this PTX trapping is so-called aftereffect, i.e. continuation of the blockade of the GABA-induced chloride current (IGABA) after removal of PTX from the external solution. The present work shows that the positive allosteric modulators (PAMs) of the GABAA receptor, allopregnanolone (Allo) and zolpidem (Zolp) as well as a high concentration of GABA shortened the PTX aftereffect. Experiments were carried out on isolated Purkinje neurons of the rat cerebellum using the whole-cell patch-clamp method. IGABA was induced by applications of 5 μM GABA (EC30) for 1 s with 30 s intervals. 50 μM PTX completely blocked IGABA, and recovery upon PTX washout occurred with a time constant (τrec) of 20.2 min. 1 μM Allo reduced the blocking effect of PTX by 30% and accelerated the recovery of IGABA by almost 10 times (τrec = 2.4 min). 0.5 μM Zolp did not change the IGABA block in the presence of PTX but accelerated the recovery of IGABA by more than 3 times (τrec = 5.6 min). Increasing the GABA concentration to 20 μM did not change the blocking effect of PTX, but accelerated recovery by 6 times (τrec = 3.3 min). The mechanism of the shortening of the PTX aftereffect is presumably the expansion of the GABAAR pore in the presence of PAMs and a high concentration of the agonist and, as a consequence, the escape of PTX from the "trap". The work describes new pharmacological properties of Allo and Zolp.

A review of the direct targets of the cannabinoids cannabidiol, Δ9-tetrahydrocannabinol, N-arachidonoylethanolamine and 2-arachidonoylglycerol

Marijuana has been used by humans for thousands of years for both medicinal and recreational purposes. This included the treatment of pain, inflammation, seizures, and nausea. In the 1960s, the structure of the principal psychoactive ingredient Δ9-tetrahydrocannabinol was determined, and over the next few decades, two cannabinoid receptors were characterized along with the human endocannabinoid system and what it affects. This includes metabolism, the cardiovascular and reproductive systems, and it is involved in such conditions as inflammation, cancer, glaucoma, and liver and musculoskeletal disorders. In the central nervous system, the endocannabinoid system has been linked to appetite, learning, memory, and conditions such as depression, anxiety, schizophrenia, stroke, multiple sclerosis, neurodegeneration, addiction, and epilepsy. It was the profound effectiveness of cannabidiol, a non-psychoactive ingredient of marijuana, to relieve the symptoms of Dravet syndrome, a severe form of childhood epilepsy, that recently helped spur marijuana research. This has helped substantially to change society's attitude towards this potential source of useful drugs. However, research has also revealed that the actions of endocannabinoids, such as anandamide and 2-arachidonoylglycerol, and the phytocannabinoids, tetrahydrocannabinol and cannabidiol, were not just due to interactions with the two cannabinoid receptors but by acting directly on many other targets including various G-protein receptors and cation channels, such as the transient receptor potential channels for example. This mini-review attempts to survey the effects of these 4 important cannabinoids on these currently identified targets.

Synthesis, In Vivo Anticonvulsant Activity Evaluation and In Silico Studies of Some Quinazolin-4(3H)-One Derivatives

Two series, "a" and "b", each consisting of nine chemical compounds, with 2,3-disubstituted quinazolin-4(3H)-one scaffold, were synthesized and evaluated for their anticonvulsant activity. They were investigated as dual potential positive allosteric modulators of the GABAA receptor at the benzodiazepine binding site and inhibitors of carbonic anhydrase II. Quinazolin-4(3H)-one derivatives were evaluated in vivo (D1-3 = 50, 100, 150 mg/kg, administered intraperitoneally) using the pentylenetetrazole (PTZ)-induced seizure model in mice, with phenobarbital and diazepam, as reference anticonvulsant agents. The in silico studies suggested the compounds act as anticonvulsants by binding on the allosteric site of GABAA receptor and not by inhibiting the carbonic anhydrase II, because the ligands-carbonic anhydrase II predicted complexes were unstable in the molecular dynamics simulations. The mechanism targeting GABAA receptor was confirmed through the in vivo flumazenil antagonism assay. The pentylenetetrazole experimental anticonvulsant model indicated that the tested compounds, 1a-9a and 1b-9b, present a potential anticonvulsant activity. The evaluation, considering the percentage of protection against PTZ, latency until the onset of the first seizure, and reduction in the number of seizures, revealed more favorable results for the "b" series, particularly for compound 8b.

Forskolin reverses the O-GlcNAcylation dependent decrease in GABAAR current amplitude at hippocampal synapses possibly at a neurosteroid site on GABAARs

GABAergic transmission is influenced by post-translational modifications, like phosphorylation, impacting channel conductance, allosteric modulator sensitivity, and membrane trafficking. O-GlcNAcylation is a post-translational modification involving the O-linked attachment of β-N-acetylglucosamine on serine/threonine residues. Previously we reported an acute increase in O-GlcNAcylation elicits a long-term depression of evoked GABAAR inhibitory post synaptic currents (eIPSCs) onto hippocampal principal cells. Importantly, O-GlcNAcylation and phosphorylation can co-occur or compete for the same residue; whether they interact in modulating GABAergic IPSCs is unknown. We tested this by recording IPSCs from hippocampal principal cells and pharmacologically increased O-GlcNAcylation, before or after increasing serine phosphorylation using the adenylate cyclase activator, forskolin. Although forskolin had no significant effect on baseline eIPSC amplitude, we found that a prior increase in O-GlcNAcylation unmasks a forskolin-dependent increase in eIPSC amplitude, reversing the O-GlcNAc-induced eIPSC depression. Inhibition of adenylate cyclase or protein kinase A did not prevent the potentiating effect of forskolin, indicating serine phosphorylation is not the mechanism. Surprisingly, increasing O-GlcNAcylation also unmasked a potentiating effect of the neurosteroids 5α-pregnane-3α,21-diol-20-one (THDOC) and progesterone on eIPSC amplitude, mimicking forskolin. Our findings show under conditions of heightened O-GlcNAcylation, the neurosteroid site on synaptic GABAARs is accessible to agonists, permitting strengthening of synaptic inhibition.

Neurosteroids and their potential as a safer class of general anesthetics

Neurosteroids (NS) are a class of steroids that are synthesized within the central nervous system (CNS). Various NS can either enhance or inhibit CNS excitability and they play important biological roles in brain development, brain function and as mediators of mood. One class of NS, 3α-hydroxy-pregnane steroids such as allopregnanolone (AlloP) or pregnanolone (Preg), inhibits neuronal excitability; these endogenous NS and their analogues have been therapeutically applied as anti-depressants, anti-epileptics and general anesthetics. While NS have many favorable properties as anesthetics (e.g. rapid onset, rapid recovery, minimal cardiorespiratory depression, neuroprotection), they are not currently in clinical use, largely due to problems with formulation. Recent advances in understanding NS mechanisms of action and improved formulations have rekindled interest in development of NS as sedatives and anesthetics. In this review, the synthesis of NS, and their mechanism of action will be reviewed with specific emphasis on their binding sites and actions on γ-aminobutyric acid type A (GABAA) receptors. The potential advantages of NS analogues as sedative and anesthetic agents will be discussed.

Mechanistic and therapeutic relationships of traumatic brain injury and γ-amino-butyric acid (GABA)

Traumatic brain injury (TBI) is a highly prevalent medical condition for which no medications specific for the prophylaxis or treatment of the condition as a whole exist. The spectrum of symptoms includes coma, headache, seizures, cognitive impairment, depression, and anxiety. Although it has been known for years that the inhibitory neurotransmitter γ-amino-butyric acid (GABA) is involved in TBI, no novel therapeutics based upon this mechanism have been introduced into clinical practice. We review the neuroanatomical, neurophysiological, neurochemical, and neuropharmacological relationships of GABA neurotransmission to TBI with a view toward new potential GABA-based medicines. The long-standing idea that excitatory and inhibitory (GABA and others) balances are disrupted by TBI is supported by the experimental data but has failed to invent novel methods of restoring this balance. The slow progress in advancing new treatments is due to the complexity of the disorder that encompasses multiple dynamically interacting biological processes including hemodynamic and metabolic systems, neurodegeneration and neurogenesis, major disruptions in neural networks and axons, frank brain lesions, and a multitude of symptoms that have differential neuronal and neurohormonal regulatory mechanisms. Although the current and ongoing clinical studies include GABAergic drugs, no novel GABA compounds are being explored. It is suggested that filling the gap in understanding the roles played by specific GABAA receptor configurations within specific neuronal circuits could help define new therapeutic approaches. Further research into the temporal and spatial delivery of GABA modulators should also be useful. Along with GABA modulation, research into the sequencing of GABA and non-GABA treatments will be needed.

GABA co-released from striatal dopamine axons dampens phasic dopamine release through autoregulatory GABAA receptors

Striatal dopamine axons co-release dopamine and gamma-aminobutyric acid (GABA), using GABA provided by uptake via GABA transporter-1 (GAT1). Functions of GABA co-release are poorly understood. We asked whether co-released GABA autoinhibits dopamine release via axonal GABA type A receptors (GABAARs), complementing established inhibition by dopamine acting at axonal D2 autoreceptors. We show that dopamine axons express α3-GABAAR subunits in mouse striatum. Enhanced dopamine release evoked by single-pulse optical stimulation in striatal slices with GABAAR antagonism confirms that an endogenous GABA tone limits dopamine release. Strikingly, an additional inhibitory component is seen when multiple pulses are used to mimic phasic axonal activity, revealing the role of GABAAR-mediated autoinhibition of dopamine release. This autoregulation is lost in conditional GAT1-knockout mice lacking GABA co-release. Given the faster kinetics of ionotropic GABAARs than G-protein-coupled D2 autoreceptors, our data reveal a mechanism whereby co-released GABA acts as a first responder to dampen phasic-to-tonic dopamine signaling.

Assessment of the anxiolytic, antidepressant, and antioxidant potential of Parquetina nigrescens (Afzel.) Bullock in Wistar rats

ETHNOPHARMACOLOGICAL RELEVANCE

The recent growing concerns about the multisystemic nature of mental health conditions in the global population are facilitating a new paradigm involving alternative natural, nutritional, and complementary therapies. Herbal remedies despite accounts in literature of their ethnobotanical as alternative remedies for diverse ailments, remain underexplored for psychiatric disorders like anxiety, depression, and insomnia.

AIM OF THE STUDY

Hence, the anxiolytic, antidepressant, and antioxidant properties of a hydro-ethanolic leaf extract of Parquetina nigrescens (PN) in male Wistar rats were investigated.

MATERIALS AND METHODS

The sedative effect was evaluated using the Diazepam sleeping time test while anxiety was induced with a single intraperitoneal injection of 20 mg/kg pentylenetetrazol (PTZ). This was after pre-treatment with 100, 150, and 250 mg/kg of PN or the standard drugs (1 mg/kg diazepam and 30 mg/kg imipramine) for 14 consecutive days. Behavioral tests (Open Field test, Elevated Plus-Maze test, and Forced Swim test) were performed on days 1 and 14, to evaluate the antidepressant and anxiolytic activities of PN. Oxidative stress and neurochemical markers were determined in the brain homogenates of the animals.

RESULTS

The duration of sleep was significantly (p < 0.001) increased in the PN-administered group compared to the control. The behavioral models showed that PN exhibited antidepressant and anxiolytic properties in PTZ-induced animals. Significant reductions were observed in GSH level and SOD activity while MDA, nitrite, and GPx levels were significantly increased in PTZ-induced rats. However, treatment with PN significantly improved brain antioxidant status by ameliorating the PTZ-induced oxidative stress. Dopamine, cortisol, and acetylcholine esterase activity levels were significantly (p < 0.05) elevated while serotonin and brain-derived neurotrophic factors were reduced in PTZ-induced rats compared with the control.

CONCLUSION

The PN demonstrated neurotransmitter modulatory ability by ameliorating the PTZ-induced neurochemical dysfunction. Findings from this study showed that PN exhibited sedative, antidepressant, and anxiolytic activities in rats.

Role of β3 subunit of the GABA type A receptor in triple negative breast cancer proliferation, migration, and cell cycle progression

Triple negative breast cancer (TNBC) is known for its heterogeneous nature and aggressive onset. The unresponsiveness to hormone therapies and immunotherapy and the toxicity of chemotherapeutics account for the limited treatment options for TNBC. Ion channels have emerged as possible therapeutic candidates for cancer therapy, but little is known about how ligand gated ion channels, specifically, GABA type A ligand-gated ion channel receptors (GABAAR), affect cancer pathogenesis. Our results show that the GABAA β3 subunit is expressed at higher levels in TNBC cell lines than non-tumorigenic cells, therefore contributing to the idea that limiting the GABAAR via knockdown of the GABAA β3 subunit is a potential strategy for decreasing the proliferation and migration of TNBC cells. We employed pharmacological and genetic approaches to investigate the role of the GABAA β3 subunit in TNBC proliferation, migration, and cell cycle progression. The results suggest that pharmacological antagonism or genetic knockdown of GABAA β3 subunit decreases TNBC proliferation and migration. In addition, GABAA β3 subunit knockdown causes cell cycle arrest in TNBC cell lines via decreased cyclin D1 and increased p21 expression. Our findings suggest that membrane bound GABAA receptors containing the β3 subunit can be further developed as a potential novel target for the treatment of TNBC.

Ethanol's interaction with BK channel α subunit residue K361 does not mediate behavioral responses to alcohol in mice

Large conductance potassium (BK) channels are among the most sensitive molecular targets of ethanol and genetic variations in the channel-forming α subunit have been nominally associated with alcohol use disorders. However, whether the action of ethanol at BK α influences the motivation to drink alcohol remains to be determined. To address this question, we first tested the effect of systemically administered BK channel modulators on voluntary alcohol consumption in C57BL/6J males. Penitrem A (blocker) exerted dose-dependent effects on moderate alcohol intake, while paxilline (blocker) and BMS-204352 (opener) were ineffective. Because pharmacological manipulations are inherently limited by non-specific effects, we then sought to investigate the behavioral relevance of ethanol's direct interaction with BK α by introducing in the mouse genome a point mutation known to render BK channels insensitive to ethanol while preserving their physiological function. The BK α K361N substitution prevented ethanol from reducing spike threshold in medial habenula neurons. However, it did not alter acute responses to ethanol in vivo, including ataxia, sedation, hypothermia, analgesia, and conditioned place preference. Furthermore, the mutation did not have reproducible effects on alcohol consumption in limited, continuous, or intermittent access home cage two-bottle choice paradigms conducted in both males and females. Notably, in contrast to previous observations made in mice missing BK channel auxiliary β subunits, the BK α K361N substitution had no significant impact on ethanol intake escalation induced by chronic intermittent alcohol vapor inhalation. It also did not affect the metabolic and locomotor consequences of chronic alcohol exposure. Altogether, these data suggest that the direct interaction of ethanol with BK α does not mediate the alcohol-related phenotypes examined here in mice.

Transcriptional Dysregulation of Cholesterol Synthesis Underlies Hyposensitivity to GABA in the Ventral Tegmental Area During Acute Alcohol Withdrawal

BACKGROUND

The ventral tegmental area (VTA) is a dopaminergic brain area that is critical in the development and maintenance of addiction. During withdrawal from chronic ethanol exposure, the response of VTA neurons to GABA (gamma-aminobutyric acid) is reduced through an epigenetically regulated mechanism. In the current study, a whole-genome transcriptomic approach was used to investigate the underlying molecular mechanism of GABA hyposensitivity in the VTA during withdrawal after chronic ethanol exposure.

METHODS

We performed RNA sequencing of the VTA of Sprague Dawley male rats withdrawn for 24 hours from a chronic ethanol diet as well as sequencing of the VTA of control rats fed the Lieber-DeCarli diet. RNA sequencing data were analyzed using weighted gene coexpression network analysis to identify modules that contained coexpressed genes. Validation was performed with quantitative polymerase chain reaction, gas chromatography-mass spectrometry, and electrophysiological assays.

RESULTS

Pathway and network analysis of weighted gene coexpression network analysis module 1 revealed a significant downregulation of genes associated with the cholesterol synthesis pathway. Consistent with this association, VTA cholesterol levels were significantly decreased during withdrawal. Chromatin immunoprecipitation indicated a decrease in levels of acetylated H3K27 at the transcriptional control regions of these genes. Electrophysiological studies in VTA slices demonstrated that GABA hyposensitivity during withdrawal was normalized by addition of exogenous cholesterol. In addition, inhibition of cholesterol synthesis produced GABA hyposensitivity, which was reversed by adding exogenous cholesterol to VTA slices.

CONCLUSIONS

These results suggest that decreased expression of cholesterol synthesis genes may regulate GABA hyposensitivity of VTA neurons during alcohol withdrawal. Increasing cholesterol levels in the brain may be a novel avenue for therapeutic intervention to reverse detrimental effects of chronic alcohol exposure.

Application of ensemble learning for predicting GABAA receptor agonists

BACKGROUND

Over the past few decades, agonists binding to the benzodiazepine site of the GABAA receptor have been successfully developed as clinical drugs. Different modulators (agonist, antagonist, and reverse agonist) bound to benzodiazepine sites exhibit different or even opposite pharmacological effects, however, their structures are so similar that it is difficult to distinguish them based solely on molecular skeleton. This study aims to develop classification models for predicting the agonists.

METHODS

306 agonists or non-agonists were collected from literature. Six machine learning algorithms including RF, XGBoost, AdaBoost, GBoost, SVM, and ANN algorithms were employed for model development. Using six descriptors including 1D/2D Descriptors, ECFP4, 2D-Pharmacophore, MACCS, PubChem, and Estate fingerprint to characterize chemical structures. The model interpretability was explored by SHAP method.

RESULTS

The best model demonstrated an AUC value of 0.905 and an MCC value of 0.808 for the test set. The PubMac-based model (PubMac-GB) achieved best AUC values of 0.935 for test set. The SHAP analysis results emphasized that MaccsFP62, ECFP_624, ECFP_724, and PubchemFP213 were the crucial molecular features. Applicability domain analysis was also performed to determine reliable prediction boundaries for the model. The PubMac-GB model was applied to virtual screening for potential GABAA agonists and the top 100 compounds were given.

CONCLUSION

Overall, our ensemble learning-based model (PubMac-GB) achieved comparable performance and would be helpful in effectively identifying agonists of GABAA receptors.

Preventing Long-Term Brain Damage by Nerve Agent-Induced Status Epilepticus in Rat Models Applicable to Infants: Significant Neuroprotection by Tezampanel Combined with Caramiphen but Not by Midazolam Treatment

Acute exposure to nerve agents induces a peripheral cholinergic crisis and prolonged status epilepticus (SE), causing death or long-term brain damage. To provide preclinical data pertinent to the protection of infants and newborns, we compared the antiseizure and neuroprotective effects of treating soman-induced SE with midazolam (MDZ) versus tezampanel (LY293558) in combination with caramiphen (CRM) in 12- and 7-day-old rats. The anticonvulsants were administered 1 hour after soman exposure; neuropathology data were collected up to 6 months postexposure. In both ages, the total duration of SE within 24 hours after soman exposure was significantly shorter in the LY293558 plus CRM groups compared with the MDZ groups. Neuronal degeneration was substantial in the MDZ-treated groups but absent or minimal in the groups treated with LY293558 plus CRM. Loss of neurons and interneurons in the basolateral amygdala and CA1 hippocampal area was significant in the MDZ-treated groups but virtually absent in the LY293558 plus CRM groups. Atrophy of the amygdala and hippocampus occurred only in MDZ-treated groups. Neuronal/interneuronal loss and atrophy of the amygdala and hippocampus deteriorated over time. Reduction of inhibitory activity in the basolateral amygdala and increased anxiety were found only in MDZ groups. Spontaneous recurrent seizures developed in the MDZ groups, deteriorating over time; a small percentage of rats from the LY293558 plus CRM groups also developed seizures. These results suggest that brain damage can be long lasting or permanent if nerve agent-induced SE in infant victims is treated with midazolam at a delayed timepoint after SE onset, whereas antiglutamatergic treatment with tezampanel and caramiphen provides significant neuroprotection. SIGNIFICANCE STATEMENT: To protect the brain and the lives of infants in a mass exposure to nerve agents, an anticonvulsant treatment must be administered that will effectively stop seizures and prevent neuropathology, even if offered with a relative delay after seizure onset. The present study shows that midazolam, which was recently approved by the Food and Drug Administration for the treatment of nerve agent-induced status epilepticus, is not an effective neuroprotectant, whereas brain damage can be prevented by targeting glutamate receptors.