Tricyclic antipsychotics and antidepressants can inhibit α5-containing GABAA receptors by two distinct mechanisms

Background and Purpose: Many psychotherapeutic drugs, including clozapine, display polypharmacology and act on GABA receptors. Patients with schizophrenia show alterations in function, structure and molecular composition of the hippocampus, and a recent study demonstrated aberrant levels of hippocampal a5 subunit-containing GABA receptors. The purpose of this study is to investigate tricyclic compounds in a5 subunit-containing receptor subtypes. Experimental Approach: Functional studies of effects by seven antipsychotic and antidepressant medications were performed in several GABA receptor subtypes by two‐electrode voltage‐clamp electrophysiology using Xenopus laevis oocytes. Computational structural analysis was employed to design mutated constructs of the a5 subunit, probing a novel binding site. Radioligand displacement data complemented the functional and mutational findings. Key Results: We show that the antipsychotic drugs clozapine and chlorpromazine exert functional inhibition on multiple GABA receptor subtypes, including a5-containing ones. Based on a chlorpromazine binding site observed in a GABA-gated bacterial homologue, we identified a novel site in a5 GABA receptor subunits and demonstrate differential usage of this and the orthosteric sites by these ligands. Conclusion and Implications: Despite high molecular and functional similarities among the tested ligands, they reduce GABA currents by differential usage of allosteric and orthosteric sites. The CPZ site we describe here is a new potential target for optimizing antipsychotic medications with beneficial polypharmacology. Further studies in defined subtypes are needed to substantiate mechanistic links between the therapeutic effects of clozapine and its action on certain GABA receptor subtypes.

Tricyclic antipsychotics and antidepressants can inhibit α5-containing GABAA receptors by two distinct mechanisms

Background and Purpose: Many psychotherapeutic drugs, including clozapine, display polypharmacology and act on GABA receptors. Patients with schizophrenia show alterations in function, structure and molecular composition of the hippocampus, and a recent study demonstrated aberrant levels of hippocampal a5 subunit-containing GABA receptors. The purpose of this study is to investigate tricyclic compounds in a5 subunit-containing receptor subtypes. Experimental Approach: Functional studies of effects by seven antipsychotic and antidepressant medications were performed in several GABA receptor subtypes by two‐electrode voltage‐clamp electrophysiology using Xenopus laevis oocytes. Computational structural analysis was employed to design mutated constructs of the a5 subunit, probing a novel binding site. Radioligand displacement data complemented the functional and mutational findings. Key Results: We show that the antipsychotic drugs clozapine and chlorpromazine exert functional inhibition on multiple GABA receptor subtypes, including a5-containing ones. Based on a chlorpromazine binding site observed in a GABA-gated bacterial homologue, we identified a novel site in a5 GABA receptor subunits and demonstrate differential usage of this and the orthosteric sites by these ligands. Conclusion and Implications: Despite high molecular and functional similarities among the tested ligands, they reduce GABA currents by differential usage of allosteric and orthosteric sites. The C C C C C C site we describe here is a new potential target for optimizing antipsychotic medications with beneficial polypharmacology. Further studies in defined subtypes are needed to substantiate mechanistic links between the therapeutic effects of clozapine and its action on certain GABA receptor subtypes.

GABA receptors in the olfactory epithelium of the gilthead seabream (Sparus aurata)

Exposure to high PCO2/low pH seawater induces behavioural alterations in fish; a possible explanation for this is a reversal of Cl−/HCO3− currents through GABAA receptors (the GABAA receptor theory). However, the main evidence for this is that gabazine, a GABAA receptor antagonist, reverses these effects when applied to the water, assuming that exposure to systems other than the CNS would be without effect. Here, we show the expression of both metabotropic and ionotropic GABA receptors, and the presence of GABAA receptor protein, in the olfactory epithelium (OE) of gilthead seabream. Furthermore, exposure of the OE to muscimol (a specific GABAA receptor agonist) increases or decreases the apparent olfactory sensitivity to some odorants. Thus, although the exact function of GABAA receptors in the OE is not yet clear, this may complicate the interpretation of studies wherein water-borne gabazine is used to reverse the effects of high CO2 levels on olfactory-driven behaviour in fish.

nxiolytic Effect of the Hydro-alcoholic Extract of Anethum Graveolens Seed in Adult Female Wistar Rats: Modulation of GABA Receptors

Background: Along with industrial development and the increasing social complexity of societies, anxiety is one of the most prevalent psychological disorders. Medicinal plants are considered as an enrichment source of ingredients with biological activity. Objectives: The aim of this study was to evaluate the anxiolytic effect of Anethum Graveolens seed (AGS) and the possible involvement of Gamma-Aminobutyric Acid (GABA)-ergic system in the AGS effect. Materials & Methods: In the present experimental study, 64 female Wistar rats were divided into eight groups and received various concentrations of hydroalcoholic extract of AGS. To measure the level of anxiety, an elevated plus maze was used in a way that the animal’s head turned to an open arm. Prior to the injections of AGS extract, the GABA receptor antagonist was used. The results were analyzed by one-way analysis of variance using IBM SPSS v. 16. Results: Dose-response experiments showed that the AGS extract significantly decreased the anxiety indices compared to the control group (P<0.05). To analyze locomotor activity, our data showed that AGS extract at 0.1, 1, and 10 mg/kg could significantly increase locomotor activity compared to the control group (P<0.001). Pentylenetetrazol (PTZ (+extract significantly decreased the anxiolytic effect of AGS extract (P<0.01). Conclusion: Considering the anti-anxiety effects of AGS extract and a reduction in this effect caused by PTZ, part of the anti-anxiety effect of extract might be assumed via its interaction with GABA-ergic receptors. Further experimental trials; however, are required for the establishment of the anti-anxiety impact of AGS.

The effects of moxidectin nicotine-conditioned cue on nicotine-seeking behavior in mice

Current pharmacotherapies for nicotine abuse are few and relatively inefficient demonstrating the need for the development of new, effective remedies. Moxidectin is used as an anti-parasitic agent in both animals and humans, it also activates GABA receptors. The objective of the present investigation was to study the effect of moxidectin on nicotine-induced conditioned place preference (CPP) in male Swiss mice. Intraperitoneal (i.p.) route was used for nicotine (0.5mg/kg) administration for a 3-day conditioning program. The influences of moxidectin on the reinforcing characteristics of nicotine were tested in mice given i.p. treatment of moxidectin (5 and 10mg/kg) 30 minutes prior to per nicotine administration. CPP was extinguished by repeated testing, through which conditioned mice were daily given two doses of moxidectin (5 and 10mg/kg, i.p.). Subsequently, the potency of moxidectin in blocking the reinstatement of CPP provoked by priming given low-dose nicotine (0.1mg/kg, i.p.) was also evaluated. Moxidectin treatment illustrated a reserve of acquisition of nicotine-induced CPP. It was reduced priming nicotine-induced reinstatement and accelerated the extinction of CPP. Relatively nicotine enhanced the locomotor, motor activity but was not statistically significant. In conclusion, the outcomes demonstrate the potential for the development of moxidectin as a new pharmacotherapy for the treatment of nicotine addiction.

Inhibitory co-transmission from midbrain dopamine neurons relies on presynaptic GABA uptake

Dopamine (DA)-releasing neurons in the substantia nigra pars compacta (SNcDA) inhibit target cells in the striatum through postsynaptic activation of γ-aminobutyric acid (GABA) receptors. However, the molecular mechanisms responsible for GABAergic signaling remain unclear, as SNcDA neurons lack enzymes typically required to produce GABA or package it into synaptic vesicles. Here we show that aldehyde dehydrogenase 1a1 (Aldh1a1), an enzyme proposed to function as a GABA synthetic enzyme in SNcDA neurons does not produce GABA for synaptic transmission. Instead, we demonstrate that SNcDA axons obtain GABA exclusively through presynaptic uptake using the membrane GABA transporter Gat1 (encoded by Slc6a1). GABA is then packaged for vesicular release using the vesicular monoamine transporter Vmat2. Our data therefore show that presynaptic transmitter recycling can substitute for de novo GABA synthesis and that Vmat2 contributes to vesicular GABA transport, expanding the range of molecular mechanisms available to neurons to support inhibitory synaptic communication.

O-GlcNAc transferase OGT-1 and the ubiquitin ligase EEL-1 modulate seizure susceptibility in C. elegans

Neurodevelopmental disorders such as epilepsy and autism have been linked to an imbalance of excitation and inhibition (E/I) in the central nervous system. The simplicity and tractability of C. elegans allows our electroconvulsive seizure (ES) assay to be used as a behavioral readout of the locomotor circuit and neuronal function. C. elegans possess conserved nervous system features such as gamma-aminobutyric acid (GABA) and GABA receptors in inhibitory neurotransmission, and acetylcholine (Ach) and acetylcholine receptors in excitatory neurotransmission. Our previously published data has shown that decreasing inhibition in the motor circuit, via GABAergic manipulation, will extend the time of locomotor recovery following electroshock. Similarly, mutations in a HECT E3 ubiquitin ligase called EEL-1 leads to impaired GABAergic transmission, E/I imbalance and altered sensitivity to electroshock. Mutations in the human ortholog of EEL-1, called HUWE1, are associated with both syndromic and non-syndromic intellectual disability. Both EEL-1 and its previously established binding protein, OGT-1, are expressed in GABAergic motor neurons, localize to GABAergic presynaptic terminals, and function in parallel to regulate GABA neuron function. In this study, we tested behavioral responses to electroshock in wildtype, ogt-1, eel-1 and ogt-1; eel-1 double mutants. Both ogt-1 and eel-1 null mutants have decreased inhibitory GABAergic neuron function and increased electroshock sensitivity. Consistent with EEL-1 and OGT-1 functioning in parallel pathways, ogt-1; eel-1 double mutants showed enhanced electroshock susceptibility. Expression of OGT-1 in the C. elegans nervous system rescued enhanced electroshock defects in ogt-1; eel-1 double mutants. Application of a GABA agonist, Baclofen, decreased electroshock susceptibility in all animals. Our C. elegans electroconvulsive seizure assay was the first to model a human X-linked Intellectual Disability (XLID) associated with epilepsy and suggests a potential novel role for the OGT-1/EEL-1 complex in seizure susceptibility.

Vitamin A Deficiency Exacerbates Gut Microbiota Dysbiosis and Cognitive Deficits in Amyloid Precursor Protein/Presenilin 1 Transgenic Mice

Vitamin A deficiency (VAD) plays an essential role in the pathogenesis of Alzheimer’s disease (AD). However, the specific mechanism by which VAD aggravates cognitive impairment is still unknown. At the intersection of microbiology and neuroscience, the gut-brain axis is undoubtedly contributing to the formation and function of neurological systems, but most of the previous studies have ignored the influence of gut microbiota on the cognitive function in VAD. Therefore, we assessed the effect of VAD on AD pathology and the decline of cognitive function in AD model mice and determined the role played by the intestinal microbiota in the process. Twenty 8-week-old male C57BL/6J amyloid precursor protein/presenilin 1 (APP/PS1) transgenic mice were randomly assigned to either a vitamin A normal (VAN) or VAD diet for 45 weeks. Our results show that VAD aggravated the behavioral learning and memory deficits, reduced the retinol concentration in the liver and the serum, decreased the transcription of vitamin A (VA)-related receptors and VA-related enzymes in the cortex, increased amyloid-β peptides (Aβ40 and Aβ42) in the brain and gut, upregulate the translation of beta-site APP-cleaving enzyme 1 (BACE1) and phosphorylated Tau in the cortex, and downregulate the expression of brain-derived neurotrophic factor (BDNF) and γ-aminobutyric acid (GABA) receptors in the cortex. In addition, VAD altered the composition and functionality of the fecal microbiota as exemplified by a decreased abundance of Lactobacillus and significantly different α- and β-diversity. Of note, the functional metagenomic prediction (PICRUSt analysis) indicated that GABAergic synapse and retinol metabolism decreased remarkably after VAD intervention, which was in line with the decreased expression of GABA receptors and the decreased liver and serum retinol. In summary, the present study provided valuable facts that VAD exacerbated the morphological, histopathological, molecular biological, microbiological, and behavioral impairment in the APP/PS1 transgenic mice, and the intestinal microbiota may play a key mediator role in this mechanism.

Potential action on the central nervous system of neroli oil extracted from Citrus aurantium

The essential oil from C. aurantium has been widely studied due to its potential anxiolytic action on several receptors in the Central Nervous System (CNS). Although it presents variations in its phytochemical composition depending on its origin, we can highlight that many compounds remain present, such as linalool that demonstrated antagonistic activity on glutamatergic receptors, possible inhibitory action of noradrenaline and serotonin receptors, besides the ability to activate GABA receptors in association with some flavonoids present in the oil. It is globally known that the underlying pathology called anxiety influences worldwide as an antecedent of conflicting psychological and physical disorders, which are associated with various neuronal disorders. In this regard, the oil extracted from C. aurantium flowers shows a potential therapeutic application for the treatment of anxiety disorders. However, more studies are needed to elucidate its complete role on the CNS and to verify and prove its safety and efficacy profile.