The effect of GABA on the binding of ³H-flunitrazepam in mouse brains during development

Studies of the benzodiazepine (BZD) and GABA receptors during development have shown similarities in their receptor densities (relative to adult levels) during the early neonatal period. GABA can increase the affinity of BZD receptor binding. It is important to know whether this functional relationship exists in the fetal and neonatal periods. Saturation isotherms for ³H-flunitrazepam (FLU) binding, using mouse brain homogenates from different ages, were assayed in the presence of either 10 μM GABA or 100 μM (+) bicuculline (BC). Clonazepam was used as the displacer. GABA increased the affinity of FLU binding, while BC decreased the affinity. An ANOVA indicated that there were no differences in the K_D's between ages and the pooled results are: 1.05 nM, for NO GABA; 0.51 nM for 10 μM GABA; 0.55 nM for NO BC; and 1.76 nM for 100 μM BC. To see if the BZD receptor was differentially sensitive to GABA during development, dose-response curves for the GABA effect were run at fetal, neonatal, and adult ages. The results show that the concentration of GABA causing a half maximal increase in FLU binding was nearly equal at all ages (≈1. μM). The dissociation kinetics of the GABA effect on FLU binding were also investigated. A significant decrease in k_-1 was seen: 0.055 min^-1 for NO GABA, and 0.030 min^-1 for 10 μM GABA.