Zhao T J, Li M, Chiu T H, Rosenberg H C
Department of Pharmacology and Therapeutics, Medical College of Ohio, Toledo, Ohio, USA.
J Pharmacol Exp Ther. 1998 Nov;287(2):752-9.
Benzodiazepine potentiation of gamma-aminobutyric acid (GABA) neurotransmission is associated with the presence of a gamma-2 subunit in the GABAA 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 oligodeoxynucleotide (ASO) was performed every 12 hr for 3 days. Controls were treated with a sense oligodeoxynucleotide. Parasagittal brain sections were used for quantitative autoradiographic analysis of radioligand binding. ASO treatment caused a 15% to 25% decrease of specific [3H]flunitrazepam binding in most brain areas, with statistically significant decreases in frontal cortex, cerebellar molecular layer, zona reticulata of substantia nigra and CA3 of hippocampus. In contrast, [3H]muscimol binding was not changed. [3H]GABA binding was also unchanged, except for a 10% decrease in cerebellar granule cell layer. The effect on the chloride channel of the GABAA receptor complex was examined by 4'-ethynyl-4-n-[2, 3-3H2]propylbicycloorthobenzoate binding; most brain areas showed small decreases in 4'-ethynyl-4-n-[2, 3-3H2]propylbicycloorthobenzoate binding. However, hippocampal regions showed much larger decreases. Binding of the adenosine A1 receptor antagonist [3H]8-cyclopentyl-1,3-dipropylxanthine was used to examine possible secondary effects of the ASO. There was a decrease in [3H]8-cyclopentyl-1,3-dipropylxanthine binding, but this was much smaller than the change in [3H]flunitrazepam binding, and no area showed a significant effect. Quantitative immunoblotting with a monoclonal antibody that recognizes GABAA receptor beta-2 and beta-3 subunits showed no change in immunoreactivity in cerebellar tissue after ASO treatment. The results indicate a selective effect on benzodiazepine binding to GABAA receptors and a possible change in receptor subunit composition.
