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

In the present study, effects of adrenoceptor agonists and antagonists on p hysostigmine-induced yawning was investigated. Intraperitoneal (IP) injecti on of different doses of physostigmine (0.03, 0.05, 0.1, and 0.2 mg/kg) ind uced 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)-a drenoceptor agonist, clonidine, decreased yawning induced by physostigmine. Prazosin and higher doses of phenoxybenzamine reduced the inhibitory effec t of phenylephrine. Higher doses of yohimbine also reduced the clonidine re sponse. The adrenoceptor antagonists, prazosin, phenoxybenzamine, and propr anolol, did not significantly alter the physostigmine response. However, yo himbine, or lower doses of prazosin, decreased the physostigmine response. It may be concluded that alpha(1)- and alpha(2)-adrenoceptor stimulation de creases the physostigmine-induced yawning behavior in rats. (C) 1998 Elsevi er Science Inc.