Effects of adrenoceptor agents on apomorphine-induced licking behavior in rats

In the present study, intraperitoneal (IP) administration of the dopaminerg ic receptor agonist apomorphine (0.1, 0.25, and 0.5 mg/kg) induced a dose-d ependent licking in rats. The intraperitoneal injection of the alpha(1)"' a drenoceptor agonist phenylephrine (1-8 mg/kg) but not the alpha(2)-adrenoce ptor agonist clonidine (0.025-0.05 mg/kg) decreased licking induced by apom orphine. The alpha-adrenoceptor antagonists prazosin, phenoxybenzamine, and yohimbine also reduced the apomorphine response significantly. The respons e induced by phenylephrine was decreased by a dose of prazosin. The beta(1) -adrenenocepor agonist dobutamine and beta(2)-adrenenocepor agonist salbuta mol did not alter the apomorphine response. However, beta(2)-adrenenocepor antagonists atenolol and propranolol reduced the apomorphine effect. It may be concluded that alpha(1)- and possibly beta(1)-adrenoceptor mechanisms m ay be involved in modulation of licking behavior. (C) 2000 Elsevier Science Inc.