Binding characteristics of [3H]flunitrazepam in pentobarbital-withdrawal rats

The effects of chronic pentobarbital (PB) treatment on the binding characteristics of [3H]flunitrazepam (FLU) in rat brain were examined. Saline or sodium PB (500 micrograms/10 microliters/hr) was infused into the lateral cerebral ventricles of rats for 6 days using osmotic pumps. Immediately before withdrawal, there were no significant differences in [3H]FLU binding constants (KD and Bmax) between saline and PB groups. However, 24 hr withdrawal caused an increase in Bmax with no changes in KD. The enhancement of [3H]FLU binding by in vitro addition of chloride ions and PB was not affected after the PB infusion. The PB enhancement of [3H]FLU binding was inhibited by the convulsant, picrotoxinin. PB withdrawal did not cause significant differences in the binding constants of [3H]Ro 15-1788, a benzodiazepine (BZ) antagonist, between the saline and PB groups. Pretreatment of membranes with 0.02 mM of 3-[(3-cholamidopropyl)-dimethylammonio]-1- propanesulfonate (CHAPS), a zwitterionic detergent, caused decreases in both KD and Bmax in FLU binding in PB-withdrawal membrane, but not in the saline-treated membrane. The enhancement of [3H]FLU binding by chloride ions and PB was not affected by the CHAPS treatment. These results suggest that the change in BZ receptors induced by PB withdrawal is functionally linked to the GABA-BZ-barbiturate receptor complex and that PB withdrawal induces some conformational changes in BZ receptors.