GABAA receptors are members of the Cys-loop family of ligand-gated ion channels which mediate most inhibitory neurotransmission in the central nervous system. These receptors are pentameric assemblies of individual subunits, including α1-6, β1-3, γ1-3, δ, ε, π, θ and ρ1-3. The majority of receptors are comprised of α, β and γ or δ subunits. Depending on the subunit composition, the receptors are located in either the synapses or extrasynaptic regions. The most abundant receptors are α1βγ2 receptors, which are activated and modulated by a variety of pharmacologically and clinically unrelated agents such as benzodiazepines, barbiturates, anaesthetics and neurosteroids, all of which bind at distinct binding sites located within the receptor complex. However, compared to αβγ, the binary αβ receptors lack a benzodiazepine α-γ2 interface. In pentameric αβ receptors, the third subunit is replaced with either an α1 or a β3 subunit leading to two distinct receptors that differ in subunit stoichiometry, 2α:3β or 3α:2β. The consequence of this is that 3α:2β receptors contain an α-α interface whereas 2α:3β receptors contain a β-β interface. Apart from the replacement of γ by α1 or β3 in binary receptors, the incorporation of ε subunit into GABAA receptors might be more complicated. As the ε subunit is not only capable of substituting the γ subunit, but also replacing the α/β subunits, receptors with altered stoichiometry and different pharmacological properties are produced. The different subunit arrangement of the receptors potentially constructs novel binding sites which may become new targets of the current or new drugs.
In the present study, a series of fourteen 5-benzoyl-4-methyl-1,3,4,5-tetrahydro-2H-1,5-benzodiazepin-2-one derivatives were designed, synthesized and characterized by appropriate spectral analysis. Further, titled compounds were in-vitro screened against wild HIV-1 RT enzyme using ELISA based colorimetric assay, in which four compounds significantly inhibited the RT activity with IC50≤25µM. Moreover, two significantly active compounds of the series, A10 and A11 exhibited IC50 values 8.62 and 6.87µM respectively, during the in-vitro assay. Structure Activity Relationship (SAR) studies were performed for the synthesized compounds in order to estimate the effect of substitution pattern on the RT inhibitory potency. The cytotoxicity of the synthesized compounds was evaluated against T lymphocytes. Further, putative binding modes of the significantly active (A11) and the least active (A4) compounds with wild HIV-1 RT were also investigated using docking studies.
This study presents anxiolytic- and antidepressant-like effects of a methanolic extract of Morinda citrifolia Linn. (noni) fruit (MMC) in well-established mouse models of anxiety and depression. The administration of MMC (1 g/kg, p.o.) and diazepam (1 mg/kg, i.p.) significantly attenuated anxiety-like behaviour in mice by increasing the percentage of time spent and number of entries in the open arms in the elevated plus maze (EPM), and significantly enhanced the exploration in the light box in the light/dark test (LDT). The pre-treatment with flumazenil (6 mg/kg, i.p.) or bicuculline (3 mg/kg, i.p.) or WAY 100635 (1 mg/kg, i.p.) antagonized the anxiolytic-like effect elicited by MMC (1 g/kg, p.o.). These results suggest the possible involvement of benzodiazepine-GABAAergic and serotonergic mechanisms in the anxiolytic-like effect of noni fruit. Meanwhile, in the antidepressant study, the administration of MMC (0.5 and 0.75 g/kg, p.o.) and desipramine (30 mg/kg, i.p.) significantly reduced the duration of immobility in the tail suspension test (TST). Furthermore, pre-treatment of mice with 4-chloro-DL-phenylalanine methyl ester hydrochloride (PCPA; 100 mg/kg, i.p., an inhibitor of serotonin synthesis) for four consecutive days or a single dose of WAY 100635 (1 mg/kg, i.p., 5HT1A receptor antagonist) or α-methyl-DL-tyrosine (AMPT; 100 mg/kg, i.p., an inhibitor of noradrenaline synthesis) significantly reversed the anti-immobility effect of MMC (0.5 g/kg, p.o.) in TST by indicating the specific involvement of the serotonergic and noradrenergic systems in the antidepressant-like effect of noni fruit. Taken together, these findings suggest that MMC has both anxiolytic- and antidepressant-like activities to be resorted as a valuable alternative therapy for comorbid anxiety and depressive conditions.
Novel treatments against migraine are an urgent medical requirement. The α6 subunit-containing GABAA receptors (α6GABAARs) are expressed in trigeminal ganglia (TG), the hub of the trigeminal vascular system (TGVS) that is involved in the pathogenesis of migraine. Here we reveal an unprecedented role of α6GABAARs in ameliorating TGVS activation using several pharmacological approaches in an animal model mimicking pathological changes in migraine. TGVS activation was induced by intra-cisternal (i.c.) instillation of capsaicin in Wistar rats. Centrally, i.c. capsaicin activated the trigeminal cervical complex (TCC) measured by the increased number of c-Fos-immunoreactive (c-Fos-ir) TCC neurons. Peripherally, it elevated calcitonin gene-related peptide immunoreactivity (CGRP-ir) in TG and depleted CGRP-ir in the dura mater. Pharmacological approaches included a recently identified α6GABAAR-selective positive allosteric modulator (PAM), the pyrazoloquinolinone Compound 6, two α6GABAAR-active PAMs (Ro15-4513 and loreclezole), an α6GABAAR-inactive benzodiazepine (diazepam), an α6GABAAR-selective antagonist (furosemide), and a clinically effective antimigraine agent (topiramate). We examined effects of these compounds on both central and peripheral TGVS responses induced by i.c. capsaicin. Compound 6 (3-10 mg/kg, i.p.) significantly attenuated the TCC neuronal activation and TG CGRP-ir elevation, and dural CGRP depletion induced by capsaicin. All these effects of Compound 6 were mimicked by topiramate, Ro15-4513 and loreclezole, but not by diazepam. The brain-impermeable furosemide antagonized the peripheral, but not central, effects of Compound 6. These results suggest that the α6GABAAR in TG is a novel drug target for TGVS activation and that α6GABAAR-selective PAMs have the potential to be developed as a novel pharmacotherapy for migraine.