Effects of pertussis toxin on the alpha 2-adrenoceptor-inhibitory GTP-binding protein-adenylate cyclase system in rat brain: pharmacological and neurochemical studies

Abstract

Behavioral excitement and the increase in locomotion were observed in male adult rats four days after an intraventricular injection of 5 micrograms pertussis toxin (IAP). Clonidine (100 micrograms/kg s.c.)-induced locomotor hypoactivity was not observed in animals pretreated with 1 and 5 micrograms IAP. IAP caused a significant (P less than 0.05) decrease in the KD value of [3H]clonidine binding and enhanced GTP (1 microM)-induced decrease in the binding to cortical membranes from rat brain. In addition, the inhibition of adenylate cyclase induced by alpha 2-receptor stimulation (100 microM adrenaline plus 100 microM propranolol) was completely suppressed in the cerebral cortical membranes by IAP pretreatment. It is suggested that the system consisting of alpha 2-receptor, the inhibitory GTP-binding protein (Ni) and adenylate cyclase inhibits some animal behaviors and cyclic AMP formation. Moreover, IAP seems to inactivate Ni, subsequently producing behavioral excitement and it inhibits clonidine-induced sedation.