Are beta- and alpha 2-adrenoceptors co-regulated during their stimulation? Behavioral studies.

The effects of beta-, and alpha 1-antagonists on the clenbuterol- and clonidine-induced depression of the exploratory activity was measured in rats in the open field test. The ability of clenbuterol (0.5 mg/kg) to reduce exploration was antagonized by 1-propranolol, significantly reduced by rauwolscine and unchanged by corynanthine and prazosin. Clonidine (0.2 mg/kg)-induced hypoactivity was significantly reduced by all the used adrenergic antagonists. A combined treatment with non-sedative doses of clenbuterol and clonidine significantly reduced exploration. Results suggest that both beta- and alpha 2-adrenoceptors are involved in clenbuterol- and clonidine-induced sedation. Moreover, they may indicate the existence of beta- and alpha 2-adrenoceptor interaction.