IN-SITU HYBRIDIZATION EVIDENCE OF DIFFERENTIAL MODULATION BY PENTOBARBITAL OF GABA(A) RECEPTOR ALPHA(1)-SUBUNIT AND BETA(3)-SUBUNIT MESSENGER-RNAS

Tolerance to and withdrawal from pentobarbital were induced in rats by continuous intracerebroventricular infusion via subcutaneously implan ted osmotic minipumps. In situ hybridization of GABA(A) receptor alpha (1)- and beta(3)-subunit mRNA was conducted using synthetic 3'-end S-3 5-dATP-labeled oligodeoxynucleotide probes. Results were quantified by film densitometry. In animals that were tolerant to pentobarbital, le vels of alpha(1)-subunit mRNA were decreased in hippocampus, superior colliculus, and inferior colliculus, but levels of beta(3)-subunit mRN A were not affected. Dramatically increased levels of GABA(A) receptor subunit mRNA were observed in animals 24 h after withdrawal from chro nic pentobarbital treatment. These increases occurred in cerebral cort ex and cerebellum for the alpha(1) subunit and in cerebral cortex only for the beta(3)-subunit. These data provide further support to the st ructural and pharmacological GABA(A) receptor heterogeneity in discret e brain areas. The observed changes of subunit expression may underlie , at least in part, the receptor up- and down-regulation observed in r eceptor ligand binding studies.