Influence of different adrenoceptor agonists and antagonists on physostigmine-induced yawning in rats

In the present study, effects of adrenoceptor agonists and antagonists on physostigmine-induced yawning was investigated. Intraperitoneal (IP) injection of different doses of physostigmine (0.03, 0.05, 0.1, and 0.2 mg/kg) induced yawning in rats. The maximum response was obtained by 0.2 mg/kg of the drug. The alpha(1)-adrenoceptor agonist, phenylephrine, and the alpha(2)-adrenoceptor agonist, clonidine, decreased yawning induced by physostigmine. Prazosin and higher doses of phenoxybenzamine reduced the inhibitory effect of phenylephrine. Higher doses of yohimbine also reduced the clonidine response. The adrenoceptor antagonists, prazosin, phenoxybenzamine, and propranolol, did not significantly alter the physostigmine response. However, yohimbine, or lower doses of prazosin, decreased the physostigmine response. It may be concluded that alpha(1)- and alpha(2)-adrenoceptor stimulation decreases the physostigmine-induced yawning behavior in rats. (C) 1998 Elsevier Science Inc.