Involvement of catecholamine receptor activities in modulating the incidence of yawning in rats

Possible involvement of catecholamine receptor activities in modulating the incidence of yawning, which involves activation of dopaminergic-cholinergic linked neuronal mechanism, was investigated in rats. Subcutaneous injection of talipexole (B-HT 920), a selective dopamine D2-receptor-agonist, elicited yawning behavior. This behavior was increased by prazosin and bunazosin, alpha 1-adrenoceptor antagonists, and by pindolol, a beta-adrenoceptor antagonist. The yawning induced by physostigmine, an anticholinesterase agent, and pilocarpine, a direct muscarinic receptor agonist, was increased by pindolol, but was unaffected by prazosin and bunazosin. In addition, the yawning induced by the dopaminergic agonists, but not by the cholinergic agonists, was markedly suppressed by ST587, an alpha 1-adrenoceptor agonist. All the yawning responses to dopaminergic and cholinergic agents were reduced not only by scopolamine, a muscarinic receptor antagonist, but also by idazoxan, rauwolscine, and yohimbine, alpha 2-adrenoceptor antagonists. The results suggest that catecholamine receptor activities seem to play different roles in inhibitory modulation of the occurrence of yawning caused by dopaminergic and cholinergic stimulation.