Physostigmine modulates hippocampal GABAergic neurotransmission via α7 nicotinic acetylcholine receptors.

Background: Epilepsy is a common and frequently devastating disorder affecting millions of people. According to a recent survey, 1-2% of the Indian population suffers from major mental disorders and 5% suffers from minor mental disorders. Epilepsy is among those mental disorders that affect 30 million people worldwide. Currently, the treatment of epilepsy involves agents which modulate sodium-ion channels, enhance GABAergic transmission, and agents with multiple modes of action. Various classes of synthetic drugs are used to treat epilepsy, but these drugs are often challenged due to their unwanted side effects. Medicinal plants have been a part of human society which combating diseases from the dawn of civilization. The plant Cyanthillium cinereum (L.) H. Rob. is mainly found in the Himalayas from Kashmir to Nepal at an altitude of 8000 m. Decoction of this plant is traditionally used as an anti-cancer, anti-malarial, anti-epileptic, and in neurosis and skin diseases. Objectives: The present study investigated the anti-epileptic activity of Cyanthillium cinereum leaves against pentylenetetrazole (PTZ)-induced epileptic model in mice. Methods: Plant extracts were prepared using solvents in increasing polarity viz., petroleum ether, chloroform, ethanol, and water, using a Soxhlet apparatus. The bio-active extract was characterized using FTIR and GC techniques. In vivo antioxidants like GSH and SOD level, oxidative stress markers- MDA and hemoglobin and platelet count were also estimated in the animal brain. Results: Amongst all extracts tested, only ethanol extract of Cyanthillium cinereum significantly (p<0.05) inhibited generalized tonic-clonic seizures in PTZ-induced epilepsy in mice in a dose (100 or 200 mg/kg., p.o.) dependent manner. The dose of 200 mg/kg of extract exhibited the most significant effect. It is also found that treatment with ethanol extract on PTZ-induced epilepsy in mice significantly (p<0.05) reduces the duration of convulsion and delays the onset of clonic convulsion. Conclusion: The present findings suggest that the high amounts of phenols and flavonoids in the ethanol extract could be responsible for the anti-epileptic effect. Moreover, the ethanol extract also restored GSH, SOD and hemoglobin and platelet level and decreased oxidative marker- MDA content in the mice brain.

Gastrointestinal motility is regulated primarily by the enteric and the central nervous systems. Our previous studies revealed that central circuits regulating colorectal motility partially overlap with those involved in pain modulation, suggesting functional interactions between the nociceptive modulatory pathway and the autonomic regulatory pathway of colorectal motility. Here, we examined whether peripheral inflammatory pain alters the neural components of the descending pathway regulating colorectal motility. Complete Freund's adjuvant (CFA) was administered unilaterally into the hind paw of rats to induce inflammation. Colorectal motility was assessed in vivo under anesthesia with α-chloralose and ketamine. In sham-treated rats, intraluminal administration of capsaicin, a noxious stimulus to the colorectal lumen, enhanced colorectal motility. In contrast, the capsaicin-induced colorectal motility response was suppressed in rats 3 days after CFA treatment. This suppression was rescued by the intrathecal administration of a GABAA receptor antagonist or an oxytocin (OXT) receptor antagonist. Furthermore, spinal OXT administration and chemogenetic activation of OXT neurons in naïve rats elicited a marked inhibition of capsaicin-induced motility responses of the colorectum. Notably, the inhibitory effect of activated OXT neurons was abolished by the intrathecal administration of a GABAA receptor antagonist. These results indicate that the descending OXT pathway becomes operative in response to persistent pain caused by peripheral inflammation and that the inhibitory effect on colorectal motility may involve local GABAergic transmission within the spinal cord. These changes may reduce parasympathetic outflow to the colorectum and contribute to defecation disorders involving central neural mechanisms.

We investigated the correlation between increased gene copy number of gamma aminobutyric acid type A (GABAA) receptor α5-containing subunits and electrophysiological and behavioral phenotypes in a mouse model of Dup15q syndrome (15q dup) and tested the hypothesis that selectively inhibiting the activity of GABAA-α5 receptors may have therapeutic effects. Dup15q syndrome is a rare neurodevelopmental disorder caused by copy number gains of the 15q11.2-q13.1 chromosomal region, which includes UBE3A and a cluster of three genes (GABRA5, GABRB3, and GABRG3) encoding GABAA receptor subunits, all of which are critical for neural development and function. Most affected children display hypotonia, motor delays, intellectual disability, and epilepsy, as well as a characteristic electroencephalography (EEG) beta-band phenotype. There is no disease-modifying therapy available. Autoradiography showed increased density of GABAA-α5 receptors in the brains of 15q dup mice, while electrophysiology revealed enhanced GABAergic transmission in hippocampal slices from these mice. A GABAA-α5 negative allosteric modulator, RO4938581, decreased inhibitory synaptic charge transfer in 15q dup hippocampal slices. The behavioral analyses confirmed inflexibility in learning and abnormal social behaviors in 15q dup mice, and both phenotypes were normalized following chronic treatment with RO4938581. EEG recordings showed increased beta-power in 15q dup mice - which resembled the spectral signature of subjects with Dup15q - and was partially normalized following RO4938581 treatment. Our results suggest that excessive expression and function of the GABAA-α5 receptor subtype plays a key role in the pathophysiology of Dup15q and GABAA-α5 NAMs may represent a potential precision medicine therapeutic option.

Non-neuronal mechanisms in autism spectrum disorder (ASD): Microglia and astrocytes at the crossroads with neurons.

Altered somatostatin receptor 3 expression and functional dysregulation in tuberous sclerosis complex.

Noradrenaline Modulates Central Amygdala GABA Transmission and Alcohol Drinking in Female Rats.

Seizure syndrome is one of the most common and complex neurological complications in patients with acute brain injuries, particularly following stroke and traumatic brain injury. This complication significantly worsens clinical outcomes, increases the risk of mortality, and prolongs patients’ length of stay in the intensive care unit. This study aimed to determine the frequency of seizure syndrome in patients with stroke and traumatic brain injury, to analyse the main causes of its development, and to evaluate the efficacy and safety of antiepileptic therapy in order to improve treatment approaches and clinical outcomes. A comprehensive literature review was conducted using 50 relevant scientific publications from PubMed, Scopus, Web of Science and Google Scholar databases. The selection was carried out in accordance with PRISMA guidelines and included studies with clearly defined patient populations with stroke or traumatic brain injury, data on seizure frequency, antiepileptic drug use, and statistically analysed results published in peer reviewed journals. Published studies indicated that seizure syndrome occurs in approximately 15%- 30% of patients after stroke and in 20%-40% of individuals with traumatic brain injury. Early seizures (within the first seven days) are consistently reported in approximately 7% of patients after stroke and are associated with a poorer prognosis. The literature review identified multifactorial pathophysiological mechanisms, including primary structural brain tissue damage, secondary metabolic disorders, neuroinflammation, and an imbalance of neurotransmitter systems. Data from numerous studies demonstrated a high efficacy of modern antiepileptic therapy – particularly levetiracetam and lorazepam – estimated at 70%-85% with a favourable safety profile. The binding of levetiracetam to synaptic vesicle protein 2A is widely regarded as a key mechanism of seizure control, while lorazepam remains a first-line drug for the acute management of seizures due to its enhancement of GABAergic transmission

Anorexia nervosa (AN) has the highest mortality among psychiatric disorders, with hyperactivity being one of the most persistent and deleterious symptoms. Increased dopamine transmission is linked to AN and hyperactivity, though the underlying mechanisms remain unclear. Local GABAergic neurons powerfully regulate the dopamine system but their involvement in AN is unknown. Using the activity-based anorexia (ABA) mouse model, we found that GABAergic transmission onto ventral tegmental area dopamine (VTADA) neurons modulates hyperactivity in female mice. Indeed, female mice exposed to the ABA model displayed higher firing rates in VTADA compared to controls, along with reduced GABAergic transmission onto VTADA cells and decreased excitability of VTAGABA neurons. Chemogenetic stimulation of GABA neurons excitability in the midbrain reduced hyperactivity and body weight loss in ABA mice, while reducing GABA neuron activity worsened this phenotype. In summary, decreased GABAergic control over VTA dopamine neurons contributes to development of hyperactivity in the ABA model.

Inhibitory control of external urethral sphincter motor neurons (EUS‐MNs) in the spinal dorsolateral nucleus (DLN), which corresponds to a portion of Onuf's nucleus in humans, is essential for normal micturition by inducing EUS relaxation during voiding; yet synaptic mechanisms remain poorly characterized. Using neonatal mice P8‐P12, we developed a slicing technique—cutting spinal cords at 150° from the coronal plane (30° from the horizontal plane in the agarose block), for maximizing EUS‐MNs captured per slice. Using transgenic mice co‐expressing channelrhodopsin‐2 in inhibitory interneurons (VGAT‐ChR2) and GFP in cholinergic neurons (ChAT‐GFP), we investigated inhibitory synaptic transmission onto EUS‐MNs. Optogenetic activation evoked robust inhibitory postsynaptic potentials (IPSPs), classified as sustained or transient based on temporal profiles. Pharmacology revealed that sustained IPSPs contained both glycinergic and GABAergic components, while GABAA receptors predominantly mediated transient IPSPs. Strychnine (1 μM) selectively blocked glycinergic transmission, while bicuculline (10 μM) eliminated GABAergic components. Insensitivity to glutamatergic antagonists (CNQX and AP5) confirmed purely inhibitory responses. Our findings demonstrate segregation of inhibitory inputs onto EUS‐MNs, with glycinergic and GABAergic transmission contributing to sustained and transient inhibition, respectively, establishing the methodological foundation for investigating inhibitory circuit dynamics in pathological conditions such as spinal cord injury with deficient inhibitory control.

Chronic alcohol consumption sex-dependently affects IL-6 modulation of GABAergic synapses in the central amygdala of rhesus macaques.

Prenatal exposure to alcohol (PAE) increases the risk for misusing alcohol and/or developing an alcohol use disorder (AUD) by adulthood. The corticotropin releasing factor (CRF) system is a major target of pre- and post-natal ethanol (EtOH) exposure. CRF and its receptor (CRFR1), in part, mediate EtOH potentiated GABA release in the medial nucleus of the central amygdala (CeM) of adult male rodents. Interestingly, our lab has shown a disruption in the function and expression of CeM CRFR1 and acute EtOH’s effects on GABA transmission in PAE adolescent animals, but it is unknown whether these alterations to the CRF system persist into adulthood or alter the actions of acute EtOH on GABAergic transmission in the CeM. Using CRF1-Cre-tdTomato rats, this study examined how moderate PAE alters acute EtOH modulation of GABAergic neurotransmission onto CRFR1+ and CRFR1− CeM neurons in adult offspring (P80–105). Pregnant dams were exposed to vaporized ethanol or room air (control) on gestational day 12 (G12) for 6 hours and whole-cell electrophysiology was performed in the CeM to assess the actions of acute EtOH (44, 66, & 88 mM) on GABAergic transmission onto CRFR1+ and CRFR1− neurons. We found unique effects of PAE that were cell type- and concentration-dependent in males and females, suggesting PAE dysregulates acute EtOH’s modulation of GABA transmission within the CeM in a sex-specific manner. This study contributes to the expanding body of research exploring the effects of PAE and how a single exposure can impact neurophysiological mechanisms in brain regions associated with AUD.

Chronic stress disrupts skeletal homeostasis, yet central neural mechanisms remain unclear. In this study, we demonstrated that hyperactivation of locus coeruleus noradrenergic (LCNE+) neurons was both necessary and sufficient to drive bone loss in a mouse model of chronic social defeat stress (CSDS). Mechanistically, CSDS induced a bidirectional imbalance in the central amygdala corticotropin-releasing hormone (CRH)–expressing (CeACRH+) neurons to LCNE+ circuit, characterized by enhanced CRH release and suppressed GABAergic transmission. A CeACRH+-LCNE+-paraventricular hypothalamic CRH–expressing (PVHCRH+) pathway was identified, which propagated stress signals to bone via sympathetic outflows. These findings redefine central bone metabolism control by establishing LCNE+ neurons as key stress-responsive hubs. Restoration of CRH/γ-aminobutyric acid balance within the CeACRH+-LCNE+ circuit reversed CSDS-induced bone loss. Targeted inhibition of the CeACRH+-LCNE+-PVHCRH+ pathway effectively mitigated stress-related osteoporosis, suggesting neural pathway–directed interventions as a promising therapeutic strategy for stress-induced bone pathology.

Intractable forms of recurrent seizures occur in approximately 30% of epileptic patients. Therefore, development of new antiseizure therapies is of special urgency. Improvement of inhibition in epileptic circuitries is currently believed to be a promising strategy for treating epilepsy. This is mainly due to the following observations. A deficit of GABAergic transmission has been documented in epileptic patients and various animal models of epilepsy, and a pharmacological increase of synaptic GABA produces an anticonvulsive effect. Genetic intervention of GABAergic interneurons offers an opportunity to selectively modulate their activity. In recent years, the efficiency of on-demand control of seizures via opto- or chemogenetic modulation of inhibitory networks has been confirmed in various in vivo and acute brain slice models of epilepsy. It was found that suppression of seizures can be achieved by opto- or chemogenetic modulation of local and distant inhibitory neurons, and recruitment of a mixed population of GABAergic interneurons results in more potent seizure suppression than recruitment of their single subclasses. The major advantage of this strategy is that the activity of neuronal networks outside the epileptic zone and during interseizure intervals remains intact, thus preserving normal brain function. However, the dual role of inhibitory networks in ictogenesis may compromise the future development of this approach. In this review, we focus on recent advances in developing therapies for epilepsy treatment by genetic intervention of GABAergic INs, caveats to consider when manipulating the function of GABAergic INs using genetic tools, and considerations to overcome these caveats.

Astrocytic GABA controls fidelity of temporal cortical processing in Fragile X Syndrome.

The amino acid neurotransmitter gamma-aminobutyric acid (GABA) reportedly acts by unidentified ventromedial hypothalamic mechanisms to suppress hypoglycemia-associated counterregulatory endocrine function in male rats. Present studies addressed the premise that GABAergic transmission of ventromedial hypothalamic nucleus (VMN) origin may regulate dorsomedial VMN (VMNdm) growth hormone-releasing hormone (Ghrh)/steroidogenic factor-1 (SF-1) neuron counterregulatory signaling to control this hormone outflow. VMN glutamate decarboxylase-2 (GAD2/GAD65) gene knockdown increased basal but inhibited insulin-induced hypoglycemia (IIH)-associated augmentation of corticosterone and glucagon secretion, while suppressing growth hormone secretion regardless of glucose status. Multiplex qPCR analysis of laser-catapult-microdissected VMNdm Ghrh-immunoreactive neurons showed that GAD2 siRNA pretreatment intensified IIH-associated upregulation of mRNAs that encode the counterregulatory-enhancing neurochemicals nitric oxide and glutamate, and exacerbated hypoglycemic downregulation of GAD1, GAD2, and SF-1 transcription. VMN GAD2 gene silencing augmented hypoglycemic enhancement of Ghrh neuron 5'-AMP-activated protein kinase alpha-1 and alpha-2 gene expression. VMN GAD2 gene knockdown exacerbated both positive lactate receptor and negative estrogen receptor transcriptional reactivity to IIH. Study outcomes provide novel evidence for bidirectional, glucose status-specific VMN GABAergic control of corticosterone and glucagon secretion in male rats, which is not documented in the other sex. Data verify GABA regulation of VMN dorsomedial Ghrh neuron metabolic and hormonal signal reception, energy screening, and counterregulatory neurochemical release. Further effort is needed to characterize the impact of GABA-dependent neurotransmission by this discrete VMN neuron population on neural circuitries that govern glucose homeostasis.

Electroencephalographic (EEG) recordings in individuals with Fragile X Syndrome (FXS) and the mouse model of FXS (Fmr1 KO) display cortical hyperexcitability at rest, as well as deficits in sensory-driven cortical network synchrony. A form of circuit hyperexcitability is observed in ex vivo cortical slices of Fmr1 KO mice as prolonged persistent activity, or Up, states. It is unknown if the circuit mechanisms that cause prolonged Up states contribute to FXS-relevant EEG phenotypes. Here we examined the role of endocannabinoids (eCB) in prolonged Up states in slices and resting and sensory-driven EEG phenotypes in awake Fmr1 KO mice. Bidirectional changes in eCB function are reported in the Fmr1 KO that depend on synapse type (excitatory or inhibitory). We demonstrate that pharmacological or genetic reduction of Cannabinoid Receptor 1 (CB1R) in GABAergic neurons rescues prolonged cortical Up states and deficits in sensory-driven cortical synchrony in Fmr1 KO mice. In support of these findings, recordings from Fmr1 KO cortical Layer (L) 2/3 pyramidal neurons revealed enhanced CB1R-mediated suppression of inhibitory synaptic currents. In contrast, genetic reduction of Cnr1 in glutamatergic neurons did not affect Up state duration, but deletion of Fmr1 in the same neurons was sufficient to cause long Up states. These findings support a model where loss of Fmr1 in glutamatergic neurons leads to enhanced CB1R-mediated suppression of GABAergic synaptic transmission, prolonged cortical circuit activation and reduced sensory-driven circuit synchronization. Results suggest that antagonism of CB1Rs may be a therapeutic strategy to correct sensory processing deficits in FXS.

Actions of the Antiseizure Drug Carbamazepine in the Thalamic Reticular Nucleus: Potential Mechanism of Aggravating Absence Seizures Jang SS, Agranonik N, Huguenard JR. Proc Natl Acad Sci USA. 2025;122(31):e2500644122. Carbamazepine (CBZ) is a widely used antiepileptic drug effective in managing partial and generalized tonic-clonic seizures. Despite its established therapeutic efficacy, CBZ has been reported to worsen seizures in another form of epilepsy, generalized absence seizures, in both clinical and experimental settings. In this study, we focused on thalamic reticular (RT) neurons, which regulate thalamocortical network activity in absence seizures, to investigate whether CBZ alters their excitability, thereby contributing to the exacerbation of seizures. Using ex vivo whole-cell patch-clamp electrophysiology, we found that CBZ selectively inhibits the tonic firing of RT neurons in a dose-dependent manner without affecting burst firing. At the RT-thalamocortical synapse, CBZ significantly increases the failure rate of GABAergic synaptic transmission, with greater effects on somatostatin—than parvalbumin-expressing RT neurons. In vivo EEG recordings and open-field behavior in Scn8a med± mouse model confirmed that CBZ treatment exacerbates absence seizures, increasing both seizure frequency and duration while reducing locomotor activity. In addition, CBZ further amplifies the preexisting reduction in tonic firing of RT neurons in Scn8a med± mice. These findings uncover a mechanism by which CBZ exacerbates absence seizures through selective inhibition of RT neuron excitability and disruption of GABAergic synaptic transmission. This work provides mechanistic insights into the paradoxical effects of CBZ and suggests potential avenues for optimizing epilepsy treatment strategies.

Abstract BACKGROUND Diffuse hemispheric high-grade gliomas with H3G34 mutations (DHG-H3G34) are among the most lethal brain tumors affecting adolescents and young adults. Our recent work revealed that DHG-H3G34 tumors contain cancer cells resembling both neuronal progenitors and more differentiated GABAergic interneuron-like (eIN-like) cells. However, the spatial organization of these cell types within the tumor and their functional roles remain unclear. This study therefore aims to characterize the spatial distribution and abundance of eIN-like cells in DHG-H3G34 tumor tissue, as well as investigate their connectivity and communication with each other. METHODS Spatial Transcriptomics: A custom gene panel tailored to DHG-H3G34 cell states was developed for 10x Genomics Xenium spatial profiling of FFPE samples. Calcium Imaging: The genetically encoded calcium indicator GCaMP8s was used to assess neuronal network dynamics. RESULTS We identified GABAergic tumor cell niches containing rare eIN-like cells enriched for SLC32A1 and GABRA4, encoding the vesicular GABA transporter (vGAT) and the GABA(A) receptor subunit α4, respectively. In DHG-H3G34 in vitro models, protein expression of vGAT and GABA(A)α4 was confirmed, which may suggest GABAergic transmission between cancer cells. To determine tumor-cell intrinsic connectivity further, as well as characterize the network dynamics of DHG-H3G34 tumors, we performed live-cell calcium imaging. We found that DHG-H3G34 models (n=3) indeed exhibit autonomous rhythmic activity at two distinct frequencies, different from other gliomas examined: a faster, burst-like pattern and a slower rhythm around 10 millihertz. CONCLUSION DHG-H3G34 tumors harbor GABAergic/eIN-like niches exhibiting network dynamics with dual frequency rhythmic activity. Ongoing work is functionally dissecting the role of GABA receptors in H3G34-mutant tumors, and exploring its biological implications.

For over four decades, the substantia nigra pars reticulata (SNr) has been recognized as a critical structure in the modulation of seizure activity. Pharmacological and optogenetic inhibition of the SNr produces robust seizure suppression in a range of seizure models. These findings have given rise to a longstanding, yet unresolved question: do seizures involve a failure of inhibition within the SNr? We recorded single-unit activity in the SNr during spike-and-wave discharges (SWDs) in male and female WAG/Rij rats, a model of genetic absence epilepsy. We monitored extracellular γ-aminobutyric acid (GABA) levels using intensity-based GABA sensing fluorescence reporter (iGABASnFR). To emphasize the multi-modal efficacy of SNr inhibition on seizure suppression, we optogenetically inhibited the SNr. Fifty percent of recorded neurons exhibited a marked increase in firing at SWD onset, with activity returning to baseline at SWD termination. Extracellular GABA levels revealed a decrease in fluorescence during SWDs, consistent with reduced GABAergic transmission. Optogenetic inhibition of SNr neurons using continuous (open-loop) inhibition, but not closed-loop (responsive) inhibition, significantly reduced SWD incidence. These data suggest that a loss of GABAergic input to the SNr is associated with increased neuronal activity. Optogenetically restoring inhibition effectively reduced seizure burden. Together, these findings address a long-standing gap in the literature and provide compelling evidence that impaired inhibition within the SNr contributes to seizure expression.