DECREASED BENZODIAZEPINE BINDING WITH LITTLE EFFECT ON GAMMA-AMINOBUTYRIC-ACID BINDING IN RAT-BRAIN AFTER TREATMENT WITH ANTISENSE OLIGODEOXYNUCLEOTIDE TO THE GAMMA-AMINOBUTYRIC ACID(A) RECEPTOR GAMMA-2 SUBUNIT

Benzodiazepine potentiation of gamma-aminobutyric acid (GABA) neurotra nsmission is associated with the presence of a gamma-2 subunit in the GABA(A) receptor. A method was developed to modify the gamma-2 subunit expression in adult rat brain. Unilateral intracerebroventricular (i. c.v.) infusion of a 17-base phosphorothioate-modified antisense oligod eoxynucleotide (ASO) was performed every 12 hr for 3 days. Controls we re treated with a sense oligodeoxynucleotide. Parasagittal brain secti ons were used for quantitative autoradiographic analysis of radioligan d binding. ASO treatment caused a 15% to 25% decrease of specific [H-3 ]flunitrazepam binding in most brain areas, with statistically signifi cant decreases in frontal cortex, cerebellar molecular layer, zona ret iculata of substantia nigra and CA3 of hippocampus. In contrast, [H-3] muscimol binding was not changed. [H-3]GABA binding was also unchanged , except for a 10% decrease in cerebellar granule cell layer. The effe ct on the chloride channel of the GABA(A) receptor complex was examine d by ethynyl-4-n-[2,3-H-3(2)]propylbicycloorthobenzoate binding; most brain areas showed small decreases in ethynyl-4-n-[2,3-H-3(2)]propylbi cycloorthobenzoate binding. However, hippocampal regions showed much l arger decreases, Binding of the adenosine A(1) receptor antagonist [H- 3]8-cyclopentyl-1,3-dipropylxanthine was used to examine possible seco ndary effects of the ASO. There was a decrease in [H-3]8-cyclopentyl-1 ,3-dipropylxanthine binding, but this was much smaller than the change in [H-3]flunitrazepam binding, and no area showed a significant effec t. Quantitative immunoblotting with a monoclonal antibody that recogni zes GABA(A) receptor beta-2 and beta-3 subunits showed no change in im munoreactivity in cerebellar tissue after ASO treatment. The results i ndicate a selective effect on benzodiazepine binding to GABA(A) recept ors and a possible change in receptor subunit composition.