Bilateral lesions of the striatum induced with 6-hydroxydopamine abolish apomorphine-induced yawning in rats.

The subcutaneous injection of 0.1 mg/kg apomorphine induced a syndrome consisting of yawning, chewing and sexual arousal in male rats. Bilateral lesions of the striatum induced with 6-hydroxydopamine abolished the drug-induced yawning, chewing and sexual arousal and produced a 58% depletion of the concentrations of dopamine in the striatum. These data suggest that apomorphine-induced yawning is mediated by presynaptic dopamine receptors (which may be autoreceptors). Furthermore, it appears that dopaminergic innervation of the striatum may play an important role in the production of yawning elicited by small doses of dopamine agonists.