Unraveling the identity of benzodiazepine binding sites in rat hipppocampus and olfactory bulb

The goals of the work reported here were (i) to identify distinct GABA(A)/b enzodiazepine receptors in the rat hippocampus and olfactory bulb using rec eptor binding assays, and (ii) to determine the affinities and selectivitie s of benzodiazepine receptor ligands from structurally diverse chemical fam ilies at each site identified. These studies were aided by the use of softw are AFFINITY ANALYSIS SYSTEM, developed in our laboratory for analysis of r eceptor binding data that allows the determination of receptor heterogeneit y using non-selective radioligands. Saturation binding assays using [H-3]RO 15-4513 (ethyl 8-azido-6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a]-[1,4]benz odiazepine-3-carboxylate) revealed two binding sites in each of these two t issues. The higher affinity site corresponds to alpha(5) subunit-containing GABA(A) receptor and the lower affinity site to a combination of alpha(1), alpha(2), and alpha(3) subunit-containing receptors. These results should be useful in the challenging task of identifying the various functional GAB A, receptors in the central nervous system, and in providing a link between receptor affinities and in vivo activities of the GABA(A)/benzodiazepine r eceptor ligands studied. (C) 2000 Elsevier Science B.V. All rights reserved .