Both opioids and cannabinoids bind to G-protein-coupled receptors to inhibit adenylyl cyclase in neurons. These reactions were assayed in brain membranes, where maximal inhibitory activity occurred in the following regions: mu-opioid inhibition in rat thalamus, delta-opioid inhibition in rat striatum, kappa-opioid inhibition in guinea pig cerebellum, and cannabinoid inhibition in cerebellum. The inhibition of adenylyl cyclase by both cannabinoid and opioid agonists was typical of G-protein-linked receptors: they required GTP, they were not supported by non-hydrolyzable GTP analogs, and they were abolished (in primary neuronal cell culture) by pertussis toxin treatment. The immediate targets of this system were determined by assaying protein phosphorylation in the presence of receptor agonists and App(NH)p, a substrate for adenylyl cyclase. In striatal membranes, opioid agonists inhibited the phosphorylation of at least two bands of MW 85 and 63 kDa, which may be synapsins I and II, respectively. Other experiments determined the long-term effects of this second messenger system. In primary neuronal cultures, opioid-inhibited adenylyl cyclase attenuated forskolin-stimulated pro-enkephalin mRNA levels, thus providing a feedback regulation of opioid synthesis. Finally, in cerebellar granule cells, both cannabinoid and opioid receptors may exist on the same cells. In these cells, agonists which bind to different receptor types may produce similar biological responses.
Neuroactive steroids that allosterically modulate GABAA receptors have potential uses as anticonvulsants, anxiolytics, and sedative-hypnotic agents. Recently, a series of pregnanes substituted with simple alkyl groups at the 3 beta-position were synthesized and found to be active in vitro. The present report describes the synthesis of a series of substituted 3 alpha-hydroxy-3 beta-(phenylethynyl)pregnan-20-ones and their in vitro structure-activity relationship determined by their potency for inhibition of [35S]TBPS binding in rat brain membranes. Appropriate substitution of the phenyl group results in ligands with particularly high affinity for the neuroactive steroid site on GABAA receptors (e.g., 4-acetyl 28, IC50 10 nM). The potency of selected steroids was confirmed electrophysiologically in oocytes expressing cloned human GABAA alpha 1 beta 2 gamma 2L receptors (e.g., compound 28, EC50 6.6 nM). Consistent with their in vitro activity, some of the 3 beta-(phenylethynyl)-substituted steroids displayed anticonvulsant activity in the pentylenetetrazol (PTZ) and maximal electroshock (MES) tests following ip administration in mice. Notably, the 3 beta-[(4-acetylphenyl)ethynyl]-19-nor derivative 36 demonstrated an attractive anticonvulsant profile (PTZ and MES ED50 values of 2.8 and 9.2 mg/kg, respectively). A new pharmacophore for the neuroactive steroid site of GABAA receptors is proposed based upon the high affinity of certain substituted 3 beta-(phenylethynyl) steroids.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.