Positive Modulator Of GABAA Receptors Research Articles

Neurosteroids and translocator protein 18kDa (TSPO) ligands as novel treatment options in depression.

Recently, the gamma-aminobutyric acid (GABA) system has come into focus for the treatment of anxiety, postpartum depression, and major depressive disorder. Endogenous 3α-reduced steroids such as allopregnanolone are potent positive allosteric modulators of GABAA receptors and have been known for decades. Current industry developments and first approvals by the U.S. food and drug administration (FDA) for the treatment of postpartum depression with exogenous analogues of these steroids represent a major step forward in the field. 3α-reduced steroids target both synaptic and extrasynaptic GABAA receptors, unlike benzodiazepines, which bind to synaptic receptors. The first FDA-approved 3α-reduced steroid for postpartum depression is brexanolone, an intravenous formulation of allopregnanolone. It has been shown to provide rapid relief of depressive symptoms. An orally available 3α-reduced steroid is zuranolone, which also received FDA approval in 2023 for the treatment of postpartum depression. Although a number of studies have been conducted, the efficacy data were not sufficient to achieve approval of zuranolone in major depressive disorder by the FDA in 2023. The most prominent side effects of these 3α-reduced steroids are somnolence, dizziness and headache. In addition to the issue of efficacy, it should be noted that current data limit the use of these compounds to two weeks. An alternative to exogenous 3α-reduced steroids may be the use of substances that induce endogenous neurosteroidogenesis, such as the translocator protein 18kDa (TSPO) ligand etifoxine. TSPO has been extensively studied for its role in steroidogenesis, in addition to other functions such as anti-inflammatory and neuroregenerative properties. Currently, etifoxine is the only clinically available TSPO ligand in France for the treatment of anxiety disorders. Studies are underway to evaluate its antidepressant potential. Hopefully, neurosteroid research will lead to the development of fast-acting antidepressants.

Neurosteroids and translocator protein 18kDa (TSPO) ligands as novel treatment options in depression.

Recently, the gamma-aminobutyric acid (GABA) system has come into focus for the treatment of anxiety, postpartum depression, and major depressive disorder. Endogenous 3α-reduced steroids such as allopregnanolone are potent positive allosteric modulators of GABAA receptors and have been known for decades. Current industry developments and first approvals by the U.S. food and drug administration (FDA) for the treatment of postpartum depression with exogenous analogues of these steroids represent a major step forward in the field. 3α-reduced steroids target both synaptic and extrasynaptic GABAA receptors, unlike benzodiazepines, which bind to synaptic receptors. The first FDA-approved 3α-reduced steroid for postpartum depression is brexanolone, an intravenous formulation of allopregnanolone. It has been shown to provide rapid relief of depressive symptoms. An orally available 3α-reduced steroid is zuranolone, which also received FDA approval in 2023 for the treatment of postpartum depression. Although a number of studies have been conducted, the efficacy data were not sufficient to achieve approval of zuranolone in major depressive disorder by the FDA in 2023. The most prominent side effects of these 3α-reduced steroids are somnolence, dizziness and headache. In addition to the issue of efficacy, it should be noted that current data limit the use of these compounds to two weeks. An alternative to exogenous 3α-reduced steroids may be the use of substances that induce endogenous neurosteroidogenesis, such as the translocator protein 18kDa (TSPO) ligand etifoxine. TSPO has been extensively studied for its role in steroidogenesis, in addition to other functions such as anti-inflammatory and neuroregenerative properties. Currently, etifoxine is the only clinically available TSPO ligand in France for the treatment of anxiety disorders. Studies are underway to evaluate its antidepressant potential. Hopefully, neurosteroid research will lead to the development of fast-acting antidepressants.

Neurosteroids as a possible new horizon in the treatment of fibromyalgia

Fibromyalgia (FM) is a central chronic pain syndrome with fatigue, sleep disorders, and other symptoms. It has 1–5 % worldwide prevalence, 3:1 female-to-male ratio, and shows correlation with stress. The pathogenic mechanism is unknown, biomarkers are missing, and patient management is extremely difficult due to the lack of resolutive therapies. We developed a pathogenic model of FM based on a thalamocortical loop network that shifts from monostability to bistability for decreasing GABAergic and increasing glutamatergic transmission, leading to the appearance of a high-firing-rate steady state that represents FM altered central pain processing. Here, we propose the hypothesis that the pathogenic GABA/Glutamate unbalance could be effectively counteracted by the use of neurosteroid drugs acting as positive allosteric modulators of both synaptic and extrasynaptic GABAA receptors. Our hypothesis is based on evidence suggesting the involvement of large fluctuations of gonadal neurosteroids (notably brain allopregnanolone withdrawal in perimenstrual/peripartum periods) and of adrenocortical hormones (notably cortisol rise during stress activation) in FM pathogenesis and in the regulation of central GABA/Glutamate balance. Therefore, our hypothesis provides a link between FM clinical features (such as female prevalence and correlation with stress) and endocrine influences on neurotransmission, suggesting the use of neurosteroid drugs for the treatment of the disease.

An Update on Stiripentol Mechanisms of Action: A Narrative Review.

Stiripentol (Diacomit®) (STP) is an orally active antiseizure medication (ASM) indicated as adjunctive therapy, for the treatment of seizures associated with Dravet syndrome (DS), a severe form of childhood epilepsy, in conjunction with clobazam and, in some regions valproic acid. Since the discovery of STP, several mechanisms of action (MoA) have been described that may explain its specific effect on seizures associated with DS. STP is mainly considered as a potentiator of gamma-aminobutyric acid (GABA) neurotransmission: (i) via uptake blockade, (ii) inhibition of degradation, but also (iii) as a positive allosteric modulator of GABAA receptors, especially those containing α3 and δ subunits. Blockade of voltage-gated sodium and T-type calcium channels, which is classically associated with anticonvulsant and neuroprotective properties, has also been demonstrated for STP. Finally, several studies indicate that STP could regulate glucose energy metabolism and inhibit lactate dehydrogenase. STP is also an inhibitor of several cytochrome P450 enzymes involved in the metabolism of other ASMs, contributing to boost their anticonvulsant efficacy as add-on therapy. These different MoAs involved in treatment of DS and recent data suggest a potential for STP to treat other neurological or non-neurological diseases.

Ivermectin Exerts Anticonvulsant Effects Against Status Epilepticus Induced by Lithium-Pilocarpine in Rats via GABAA Receptor and Neuroinflammation Modulation: Possible Interaction of Opioidergic Pathways and KATP Channel with Nitrergic System.

Status epilepticus (SE) is a critical medical emergency marked by persistent or rapidly repeating seizures, posing a threat to life. Using the lithium-pilocarpine-induced SE model, we decide to evaluate the anti-seizure effects of ivermectin as a positive allosteric modulator of GABAA receptor and the underlying mechanisms involved. Lithium chloride was injected intraperitoneally at a dose of 127 mg/kg, followed by the administration of pilocarpine at a dose of 60 mg/kg after a 20-h interval in order to induce SE. Subsequently, the rats received varying amounts of ivermectin (0.3, 1, 3, 5, and 10 mg/kg, i.p.) 30 min before the onset of SE. To study the underlying molecular mechanisms, we had pharmacological interventions of diazepam (1 mg/kg), glibenclamide and nicorandil as ATP-sensitive potassium channel blocker and opener (both 1 mg/kg, i.p.), naltrexone and morphine, as opioid receptor antagonist and agonist (1 mg/kg and 0.5 mg/kg, i.p., respectively). In addition, three nitric oxide inhibitors, namely, L-NAME (10 mg/kg, i.p.), 7-NI (30 mg/kg, i.p.), and aminoguanidine (100 mg/kg, i.p.), were administered to the rats in the experiment. Finally, we use ELISA and western blotting, respectively, to examine the amounts of pro-inflammatory cytokines (TNF-α and IL-1β), nitrite, and GABAA receptors in the rat hippocampal tissue. The study found that ivermectin, at doses of 3, 5, and 10 mg/kg, exerts anti-seizure effects and decrease Racine's scale SE score. Interestingly glibenclamide and naltrexone reduced the anti-seizure effects of ivermectin, and from other hand diazepam, nicorandil, morphine, L-NAME, 7-NI, and aminoguanidine, enhance the effects when co-administrated with subeffective dose of ivermectin. Additionally, the study found that ivermectin decreased the elevated levels of TNF-α and IL-1β following SE, while increased the reduced expression of GABAA receptors. Overall, these findings suggest that ivermectin has anti-seizure effects in a SE seizure which may be mediated by the modulation of GABAergic, opioidergic, and nitrergic pathways and KATP channels.

In-silico testing of new pharmacology for restoring inhibition and human cortical function in depression

Reduced inhibition by somatostatin-expressing interneurons is associated with depression. Administration of positive allosteric modulators of α5 subunit-containing GABAA receptor (α5-PAM) that selectively target this lost inhibition exhibit antidepressant and pro-cognitive effects in rodent models of chronic stress. However, the functional effects of α5-PAM on the human brain in vivo are unknown, and currently cannot be assessed experimentally. We modeled the effects of α5-PAM on tonic inhibition as measured in human neurons, and tested in silico α5-PAM effects on detailed models of human cortical microcircuits in health and depression. We found that α5-PAM effectively recovered impaired cortical processing as quantified by stimulus detection metrics, and also recovered the power spectral density profile of the microcircuit EEG signals. We performed an α5-PAM dose-response and identified simulated EEG biomarker candidates. Our results serve to de-risk and facilitate α5-PAM translation and provide biomarkers in non-invasive brain signals for monitoring target engagement and drug efficacy.

A Randomized Phase 2 KINETIC Trial Evaluating SAGE-324/BIIB124 in Individuals with Essential Tremor.

SAGE-324/BIIB124 is an investigational positive allosteric modulator of GABAA receptors. KINETIC (NCT04305275), a double-blind, randomized, placebo-controlled, phase 2 study, evaluated SAGE-324/BIIB124 in individuals with essential tremor (ET). Individuals aged 18 to 80 years were randomly assigned 1:1 to orally receive 60 mg of SAGE-324/BIIB124 or placebo once daily for 28 days. The primary endpoint was change from baseline in The Essential Tremor Rating Assessment Scale-Performance Subscale (TETRAS-PS) Item 4 (upper-limb tremor) at day 29 with SAGE-324/BIIB124 versus placebo. Between May 2020 and February 2021, 69 U.S. participants were randomly assigned to receive SAGE-324/BIIB124 (n = 34) or placebo (n = 35). There was a significant reduction from baseline in TETRAS-PS Item 4 at day 29 with SAGE-324/BIIB124 versus placebo (least squares mean [standard error]: -2.31 [0.401] vs. -1.24 [0.349], P = 0.0491). The most common treatment-emergent adverse events included somnolence, dizziness, fatigue, and balance disorder. These results support further development of SAGE-324/BIIB124 for potential ET treatment. © 2024 Sage Therapeutics, Inc and The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Integrated workflow for the identification of new GABAA R positive allosteric modulators based on the in silico screening with further in vitro validation. Case study using Enamine's stock chemical space.

Numerous studies reported an association between GABAA R subunit genes and epilepsy, eating disorders, autism spectrum disorders, neurodevelopmental disorders, and bipolar disorders. This study was aimed to find some potential positive allosteric modulators and was performed by combining the in silico approach with further in vitro evaluation of its real activity. We started from the GABAA R-diazepam complexes and assembled a lipid embedded protein ensemble to refine it via molecular dynamics (MD) simulation. Then we focused on the interaction of α1β2γ2 with some Z-drugs (non-benzodiazepine compounds) using an Induced Fit Docking (IFD) into the relaxed binding site to generate a pharmacophore model. The pharmacophore model was validated with a reference set and applied to decrease the pre-filtered Enamine database before the main docking procedure. Finally, we succeeded in identifying a set of compounds, which met all features of the docking model. The aqueous solubility and stability of these compounds in mouse plasma were assessed. Then they were tested for the biological activity using the rat Purkinje neurons and CHO cells with heterologously expressed human α1β2γ2 GABAA receptors. Whole-cell patch clamp recordings were used to reveal the GABA induced currents. Our study represents a convenient and tunable model for the discovery of novel positive allosteric modulators of GABAA receptors. A High-throughput virtual screening of the largest available database of chemical compounds resulted in the selection of 23 compounds. Further electrophysiological tests allowed us to determine a set of 3 the most outstanding active compounds. Considering the structural features of leader compounds, the study can develop into the MedChem project soon.

Ivermectin ameliorates bleomycin-induced lung fibrosis in male rats by inhibiting the inflammation and oxidative stress

Background Idiopathic pulmonary fibrosis (IPF) is a pulmonary fibrotic disease characterized by a poor prognosis, which its pathogenesis involves the accumulation of abnormal fibrous tissue, inflammation, and oxidative stress. Ivermectin, a positive allosteric modulator of GABAA receptor, exerts anti-inflammatory and antioxidant properties in preclinical studies. The present study investigates the potential protective effects of ivermectin treatment in rats against bleomycin-induced IPF. Materials and Methods The present study involved 42 male Wistar rats, which were divided into five groups: control (without induction of IPF), bleomycin (IPF-induced by bleomycin 2.5 mg/kg, by intratracheal administration), and three fibrosis groups receiving ivermectin (0.5, 1, and 3 mg/kg). lung tissues were harvested for measurement of oxidative stress [via myeloperoxidase (MPO), superoxide dismutase (SOD), glutathione (GSH)] and inflammatory markers (tumor necrosis factor-α [TNF-α], interleukin-1β [IL-1β], and transforming growth factor-β [TGF-β]). Histological assessments of tissue damage were performed using hematoxylin–eosin (H&E) and Masson’s trichrome staining methods. Results The induction of fibrosis via bleomycin was found to increase levels of MPO as well as TNF-α, IL-1β, and TGF-β while decrease SOD activity and GSH level. Treatment with ivermectin at a dosage of 3 mg/kg was able to reverse the effects of bleomycin-induced fibrosis on these markers. In addition, results from H&E and Masson’s trichrome staining showed that ivermectin treatment at this same dose reduced tissue damage and pulmonary fibrosis. Conclusion The data obtained from this study indicate that ivermectin may have therapeutic benefits for IPF, likely due to its ability to reduce inflammation and mitigate oxidative stress-induced toxicity.

Distinct mechanisms of allopregnanolone and diazepam underlie neuronal oscillations and differential antidepressant effect.

The rapid relief of depressive symptoms is a major medical requirement for effective treatments for major depressive disorder (MDD). A decrease in neuroactive steroids contributes to the pathophysiological mechanisms associated with the neurological symptoms of MDD. Zuranolone (SAGE-217), a neuroactive steroid that acts as a positive allosteric modulator of synaptic and extrasynaptic δ-subunit-containing GABAA receptors, has shown rapid-onset, clinically effective antidepressant action in patients with MDD or postpartum depression (PPD). Benzodiazepines, on the other hand, act as positive allosteric modulators of synaptic GABAA receptors but are not approved for the treatment of patients with MDD. It remains unclear how differences in molecular mechanisms contribute to the alleviation of depressive symptoms and the regulation of associated neuronal activity. Focusing on the antidepressant-like effects and neuronal activity of the basolateral amygdala (BLA) and medial prefrontal cortex (mPFC), we conducted a head-to-head comparison study of the neuroactive steroid allopregnanolone and the benzodiazepine diazepam using a mouse social defeat stress (SDS) model. Allopregnanolone but not diazepam exhibited antidepressant-like effects in a social interaction test in SDS mice. This antidepressant-like effect of allopregnanolone was abolished in extrasynaptic GABAA receptor δ-subunit knockout mice (δko mice) subjected to the same SDS protocol. Regarding the neurophysiological mechanism associated with these antidepressant-like effects, allopregnanolone but not diazepam increased theta oscillation in the BLA of SDS mice. This increase did not occur in δko mice. Consistent with this, allopregnanolone potentiated tonic inhibition in BLA interneurons via δ-subunit-containing extrasynaptic GABAA receptors. Theta oscillation in the mPFC of SDS mice was also increased by allopregnanolone but not by diazepam. Finally, allopregnanolone but not diazepam increased frontal theta activity in electroencephalography recordings in naïve and SDS mice. Neuronal network alterations associated with MDD showed decreased frontal theta and beta activity in depressed SDS mice. These results demonstrated that, unlike benzodiazepines, neuroactive steroids increased theta oscillation in the BLA and mPFC through the activation of δ-subunit-containing GABAA receptors, and this change was associated with antidepressant-like effects in the SDS model. Our findings support the notion that the distinctive mechanism of neuroactive steroids may contribute to the rapid antidepressant effects in MDD.

Schisandrin B, a dual positive allosteric modulator of GABAA and glycine receptors, alleviates seizures in multiple mouse models.

Epilepsy is a prevalent and severe neurological disorder and approximately 30% of patients are resistant to existing medications. It is of utmost importance to develop alternative therapies to treat epilepsy. Schisandrin B (SchB) isa major bioactive constituent of Schisandra chinensis (Turcz.) Bailland has multiple neuroprotective effects, sedative and hypnotic activities.In this study, we investigated the antiseizure effect of SchB in various mouse models of seizure and explored the underlying mechanisms. Pentylenetetrazole (PTZ), strychnine (STR), and pilocarpine-induced mouse seizure models were established.We showed that injection ofSchB (10, 30, 60 mg/kg, i.p.) dose-dependentlydelayed the onset of generalized tonic-clonic seizures (GTCS), reduced the incidence of GTCS and mortality in PTZ and STR models. Meanwhile, injection ofSchB (30 mg/kg, i.p.) exhibited therapeutic potential in pilocarpine-induced status epilepticus model, which was considered as a drug-resistant model. In whole-cell recording from CHO/HEK-239 cells stably expressing recombinant human GABAA receptors (GABAARs) and glycine receptors (GlyRs) and cultured hippocampal neurons, co-application of SchB dose-dependently enhanced GABA or glycine-induced current with EC50 values at around 5 μM, and application of SchB (10 μM) alone did not activate the channels in the absence of GABA or glycine.Furthermore, SchB (10 μM) eliminated both PTZ-induced inhibition on GABA-induced current (IGABA) and strychnine (STR)-induced inhibition on glycine-induced current (Iglycine).Moreover, SchB(10 μM) efficiently rescued the impaired GABAARs associated with genetic epilepsies. In addition,the homologous mutants in both GlyRs-α1(S267Q) and GABAARs-α1(S297Q)β2(N289S)γ2L receptors by site-directed mutagenesis testsabolishedSchB-induced potentiation of IGABA and Iglycine. In conclusion, we have identified SchB as a natural positive allosteric modulator of GABAARs and GlyRs, supporting its potential as alternative therapies for epilepsy.

Research Trends and Hot Spots of Allopregnanolone Research in the Last 20 Years: A Bibliometric Analysis.

Allopregnanolone is a kind of neuroactive steroid or neurosteroid in the central nervous system that acts as an endogenenous GABAA receptor positive modulator. However, at present, no comprehensive bibliometric analysis regarding allopregnanolone research is available. In our study, we intend to analyze the research trends and hot spots related to allopregnanolone in the past 20 years. We searched for allopregnanolone related articles and reviews between 2004 and 2023 from the Web of Science Core Collection database. Then, the bibliometric analysis was conducted using VOSviewer, CiteSpace, Microsoft Excel 2019, as well as the online bibliometric analysis platform (http://bibliometric.com/). A total of 1841 eligible publications were identified. The number of annual publications and citations was generally on the rise. Among countries, the United States ranked first in overall publications, citations, international cooperation, and the number of research institutions. The University of North Carolina was the most active institution, conducting numerous preclinical and clinical work that focusing on allopregnanolone treatment for diverse psychiatric or neurologic disorders. As for authors, Dr. Frye CA, Morrow AL, and Pinna G were identified as the top three prolific scholars due to their great publications and citations. Based on the publication clusters and citation bursts analysis, the keyword co-occurrence network, the strongest citation bursts, and co-cited references analysis, the hot spots in recent years included "depression", "postpartum depression", "GABAA receptor", and so on. Allopregnanolone is still a popular area of research, and the United States leads the way in this area. Dr. Frye CA, Morrow AL, Pinna G, and their teams contributed greatly to the mechanism study and translation study of allopregnanolone. The use of allopregnanolone for the treatment of psychiatric or neurologic disorders, especially postpartum depression, is the current hot spot. However, the underlying mechanisms of anti-depression are still not clear, deserving more in-depth research.

Propofol mitigates brain injury and oxidative stress, and enhances GABAA receptor α1 subunit expression in a rat model of lithium chloride-pilocarpine induced status epilepticus.

Propofol is a positive allosteric modulator of GABAA receptor (GABAAR) and has potent antioxidant activity. The aim of this study was to investigate the effect of propofol on damage to the cerebral cortex and hippocampus in a lithium chloride (LiCl)-pilocarpine animal model of status epilepticus (SE). Adult male Sprague Dawley rats were injected with LiCl-pilocarpine to induce SE. They were then randomized and injected 30 min later with vehicle saline (SE+saline), propofol (SE+PPF, 50 mg/kg), Diazepam (SE+DZP, 10 mg/kg), Scopolamine (SE+SCOP, 10 mg/kg), or MK-801 (SE+MK-801, 2 mg/kg). Another group of rats received saline only and served as the naïve control (BLK). The levels of superoxide dismutase (SOD), glutathione (GSH) and malondialdehyde (MDA) in the serum, cortex and hippocampus were analyzed 2 and 24 h posttreatment. The degree of tissue damage in the cortex and hippocampus of individual rats was assessed 24 h posttreatment, together with expression of the GABAAR α1 subunit. The propofol group showed reduced levels of tissue damage in the cerebral cortex and hippocampus, decreased levels of MDA, and increased levels of GSH compared to the SE+saline group. No changes in SOD level were observed in serum and tissue samples from the cortex and hippocampus of SE+saline rats. Immunohistochemistry and Western blot assays showed that propofol treatment significantly increased the expression of GABAAR α1 subunit in the cortical and hippocampal tissues of SE rats. Propofol treatment protected against SE-induced tissue injury in the cortex and hippocampus of rats. This was due at least in part to its antioxidant activity and to its induction of GABAAR α1 subunit expression in the brain.

Search for Novel Therapies for Essential Tremor Based on Positive Modulation of α6-Containing GABAA Receptors.

Prior work using GABAA receptor subunit knockouts and the harmaline model has indicated that low-dose alcohol, gaboxadol, and ganaxolone suppress tremor via α6βδ GABAA receptors. This suggests that drugs specifically enhancing the action of α6βδ or α6βγ2 GABAA receptors, both predominantly expressed on cerebellar granule cells, would be effective against tremor. We thus examined three drugs described by in vitro studies as selective α6βδ (ketamine) or α6βγ2 (Compound 6, flumazenil) receptor modulators. In the first step of evaluation, the maximal dose was sought at which 6/6 mice pass straight wire testing, a sensitive test for psychomotor impairment. Only non-impairing doses were used to evaluate for anti-tremor efficacy in the harmaline model, which was assessed in wildtype and α6 subunit knockout littermates. Ketamine, in maximally tolerated doses of 2.0 and 3.5 mg/kg had minimal effect on harmaline tremor in both genotypes. Compound 6, at well-tolerated doses of 1-10 mg/kg, effectively suppressed tremor in both genotypes. Flumazenil suppressed tremor in wildtype mice at doses (0.015-0.05 mg/kg) far lower than those causing straight wire impairment, and did not suppress tremor in α6 knockout mice. Modulators of α6βδ and α6βγ2 GABAA receptors warrant attention for novel therapies as they are anticipated to be effective and well-tolerated. Ketamine likely failed to attain α6βδ-active levels. Compound 6 is an attractive candidate, but further study is needed to clarify its mechanism of action. The flumazenil results provide proof of principle that targeting α6βγ2 receptors represents a worthy strategy for developing essential tremor therapies. We tested for harmaline tremor suppression drugs previously described as in vitro α6βδ or α6βγ2 GABAA receptor-selective modulators. Well-tolerated flumazenil doses suppressed tremor in α6-wildtype but not α6-knockout mice. Compound 6 and ketamine failed to display this profile, likely from off-target effects. Selective α6 modulators hold promise as tremor therapy.

New GABA-Targeting Therapies for the Treatment of Seizures and Epilepsy: II. Treatments in Clinical Development.

The inhibitory neurotransmitter γ-aminobutyric acid (GABA) plays an important role in the modulation of neuronal excitability, and a disruption of GABAergic transmission contributes to the pathogenesis of some seizure disorders. Although many currently available antiseizure medications do act at least in part by potentiating GABAergic transmission, there is an opportunity for further research aimed at developing more innovative GABA-targeting therapies. The present article summarises available evidence on a number of such treatments in clinical development. These can be broadly divided into three groups. The first group consists of positive allosteric modulators of GABAA receptors and includes Staccato® alprazolam (an already marketed benzodiazepine being repurposed in epilepsy as a potential rescue inhalation treatment for prolonged and repetitive seizures), the α2/3/5 subtype-selective agents darigabat and ENX-101, and the orally active neurosteroids ETX155 and LPCN 2101. A second group comprises two drugs already marketed for non-neurological indications, which could be repurposed as treatments for seizure disorders. These include bumetanide, a diuretic agent that has undergone clinical trials in phenobarbital-resistant neonatal seizures and for which the rationale for further development in this indication is under debate, and ivermectin, an antiparasitic drug currently investigated in a randomised double-blind trial in focal epilepsy. The last group comprises a series of highly innovative therapies, namely GABAergic interneurons (NRTX-001) delivered via stereotactic cerebral implantation as a treatment for mesial temporal lobe epilepsy, an antisense oligonucleotide (STK-001) aimed at upregulating NaV1.1 currents and restoring the function of GABAergic interneurons, currently tested in a trial in patients with Dravet syndrome, and an adenoviral vector-based gene therapy (ETX-101) scheduled for investigation in Dravet syndrome. Another agent, a subcutaneously administered neuroactive peptide (NRP2945) that reportedly upregulates the expression of GABAA receptor α and β subunits is being investigated, with Lennox-Gastaut syndrome and other epilepsies as proposed indications. The diversity of the current pipeline underscores a strong interest in the GABA system as a target for new treatment development in epilepsy. To date, limited clinical data are available for these investigational treatments and further studies are required to assess their potential value in addressing unmet needs in epilepsy management.

Shank3 deletion in PV neurons is associated with abnormal behaviors and neuronal functions that are rescued by increasing GABAergic signaling

BackgroundPhelan–McDermid syndrome (PMS) is a neurodevelopmental disorder characterized by developmental delay, intellectual disability, and autistic-like behaviors and is primarily caused by haploinsufficiency of SHANK3 gene. Currently, there is no specific treatment for PMS, highlighting the need for a better understanding of SHANK3 functions and the underlying pathophysiological mechanisms in the brain. We hypothesize that SHANK3 haploinsufficiency may lead to alterations in the inhibitory system, which could be linked to the excitatory/inhibitory imbalance observed in models of autism spectrum disorder (ASD). Investigation of these neuropathological features may shed light on the pathogenesis of PMS and potential therapeutic interventions.MethodsWe recorded local field potentials and visual evoked responses in the visual cortex of Shank3∆11−/− mice. Then, to understand the impact of Shank3 in inhibitory neurons, we generated Pv-cre+/−Shank3Fl/Wt conditional mice, in which Shank3 was deleted in parvalbumin-positive neurons. We characterized the phenotype of this murine model and we compared this phenotype before and after ganaxolone administration.ResultsWe found, in the primary visual cortex, an alteration of the gain control of Shank3 KO compared with Wt mice, indicating a deficit of inhibition on pyramidal neurons. This alteration was rescued after the potentiation of GABAA receptor activity by Midazolam. Behavioral analysis showed an impairment in grooming, memory, and motor coordination of Pv-cre+/−Shank3Fl/Wt compared with Pv-cre+/−Shank3Wt/Wt mice. These deficits were rescued with ganaxolone, a positive modulator of GABAA receptors. Furthermore, we demonstrated that treatment with ganaxolone also ameliorated evocative memory deficits and repetitive behavior of Shank3 KO mice.LimitationsDespite the significant findings of our study, some limitations remain. Firstly, the neurobiological mechanisms underlying the link between Shank3 deletion in PV neurons and behavioral alterations need further investigation. Additionally, the impact of Shank3 on other classes of inhibitory neurons requires further exploration. Finally, the pharmacological activity of ganaxolone needs further characterization to improve our understanding of its potential therapeutic effects.ConclusionsOur study provides evidence that Shank3 deletion leads to an alteration in inhibitory feedback on cortical pyramidal neurons, resulting in cortical hyperexcitability and ASD-like behavioral problems. Specifically, cell type-specific deletion of Shank3 in PV neurons was associated with these behavioral deficits. Our findings suggest that ganaxolone may be a potential pharmacological approach for treating PMS, as it was able to rescue the behavioral deficits in Shank3 KO mice. Overall, our study highlights the importance of investigating the role of inhibitory neurons and potential therapeutic interventions in neurodevelopmental disorders such as PMS.

CNSC-01. GABAERGIC NEURON-TO-GLIOMA SYNAPSES IN DIFFUSE MIDLINE GLIOMAS

Abstract High-grade gliomas include clinically and molecularly distinct subtypes that stratify by anatomical location into diffuse midline gliomas (DMG) such as diffuse intrinsic pontine glioma (DIPG) and hemispheric high-grade gliomas. Neuronal activity drives high-grade glioma progression both through paracrine signaling and direct neuron-to-glioma synapses. Glutamatergic, AMPA receptor-dependent synapses between neurons and malignant glioma cells have been demonstrated in both pediatric and adult high-grade gliomas, but neuron-to-glioma synapses mediated by other neurotransmitters remain largely unexplored. Using whole-cell patch clamp electrophysiology, in vivo optogenetics and patient-derived glioma xenograft models, we have now identified functional, tumor-promoting GABAergic neuron-to-glioma synapses mediated by GABAA receptors in DMGs. GABAergic input has a depolarizing effect on DMG cells due to NKCC1 expression and consequently elevated intracellular chloride concentration in DMG tumor cells. As membrane depolarization increases glioma proliferation, we find that the activity of GABAergic interneurons promotes DMG proliferation in vivo. Increasing GABA signaling with the benzodiazepine lorazepam – a positive allosteric modulator of GABAA receptors commonly administered to children with DMG for nausea or anxiety - increases GABAA receptor conductance and increases glioma proliferation in orthotopic xenograft models of DMG. Conversely, levetiracetam, an anti-epileptic drug that attenuates GABAergic neuron-to-glioma synaptic currents, reduces glioma proliferation in patient-derived DMG xenografts and extends survival of mice bearing DMG xenografts. Concordant with gene expression patterns of GABAA receptor subunit genes across subtypes of glioma, depolarizing GABAergic currents were not found in hemispheric high-grade gliomas. Accordingly, neither lorazepam nor levetiracetam influenced the growth rate of hemispheric high-grade glioma patient-derived xenograft models. Retrospective real-world clinical data are consistent with these conclusions and should be replicated in future prospective clinical studies. Taken together, these findings uncover GABAergic synaptic communication between GABAergic interneurons and DMG cells, underscoring a tumor subtype-specific mechanism of brain cancer neurophysiology with important potential implications for commonly used drugs in this disease context.

Recent Developments in Pharmacotherapy of Depression: Bench to Bedside.

For the last 70 years, we did not move beyond the monoamine hypothesis of depression until the approval of the S-enantiomer of ketamine, an N-methyl-D-aspartate (NMDA) receptor blocker and the first non-monoaminergic antidepressant characterized by rapid antidepressant and antisuicidal effects. A similar profile has been reported with another NMDA receptor antagonist, dextromethorphan, which has also been approved to manage depression in combination with bupropion. More recently, the approval of a positive allosteric modulator of GABA-A receptors, brexanolone, has added to the list of recent breakthroughs with the relatively rapid onset of antidepressant efficacy. However, multiple factors have compromised the clinical utility of these exciting discoveries in the general population, including high drug acquisition costs, mandatory monitoring requirements, parenteral drug administration, lack of insurance coverage, indirect COVID-19 effects on healthcare systems, and training gaps in psychopharmacology. This narrative review aims to analyze the clinical pharmacology of recently approved antidepressants and discuss potential barriers to the bench-to-bedside transfer of knowledge and clinical application of exciting recent discoveries. Overall, clinically meaningful advances in the treatment of depression have not reached a large proportion of depressed patients, including those with treatment-resistant depression, who might benefit the most from the novel antidepressants.

Saying goodbye to an unwelcome guest: Towards robust methods for controlling multi-sensory confounds in TMS-EEG research.

Saying goodbye to an unwelcome guest: Towards robust methods for controlling multi-sensory confounds in TMS-EEG research.

Untangling TMS-EEG responses caused by TMS versus sensory input using optimized sham control and GABAergic challenge.

The combination of transcranial magnetic stimulation (TMS) and electroencephalography (EEG) elegantly probes the excitability and connectivity of the human brain. However, TMS-EEG signals inevitably also contain sensory-evoked responses caused by TMS-associated auditory and somatosensory inputs, constituting a substantial confounding factor. Here we applied our recently established optimized SHAM protocol (Gordon etal., Neuroimage 2021:118708) to disentangle TMS-EEG responses caused by TMS vs. sensory input. One unresolved question is whether these responses superimpose without relevant interaction, a requirement for their disaggregation by the optimized SHAM approach. We applied in 20 healthy subjects a pharmacological intervention using a single oral dose of 20mg of diazepam, a positive modulator of GABAA receptors. Diazepam decreased the amplitudes of the P60 and P150 components specifically in the ACTIVE TMS and/or the ACTIVE TMS minus SHAM conditions but not in the SHAM condition, pointing to a response caused by TMS. In contrast, diazepam suppressed the amplitude of the N100 component indiscriminately in the ACTIVE TMS and SHAM conditions but not in the ACTIVE TMS minus SHAM condition, pointing to a response caused by sensory input. Moreover, diazepam suppressed the beta-band response observed in the motor cortex specifically after ACTIVE TMS and ACTIVE TMS minus SHAM. These findings demonstrate a lack of interaction of TMS-EEG responses caused by TMS vs. sensory input and validate optimized SHAM-controlled TMS-EEG as an appropriate approach to untangle these TMS-EEG responses. This knowledge will enable the proficient use of TMS-EEG to probe the physiology of the human cortex. KEY POINTS: Optimized SHAM disentangles TMS-EEG responses caused by TMS vs. sensory input. Diazepam differentially modulates TMS-EEG responses caused by TMS vs. sensory input. Diazepam modulation of P60 and P150 indicate TMS-EEG responses caused by TMS. Diazepam modulation of N100 indicate a TMS-EEG response caused by sensory input.