Yawning elicited by systemic and intrastriatal injection of piribedil and apomorphine in the rat.

The behavioural effects of systemic and intrastriatal injections of the dopamine agonists piribedil and apomorphine in male rats were examined. Bilateral application of piribedil (50 and 100 micrograms) or apomorphine (5, 10 and 20 micrograms) to the striatum produced yawning and chewing mouth movements accompanied by intermittent stretching and sexual arousal. Low doses of piribedil (1.25 and 2.5 mg/kg) and apomorphine (0.1 and 0.2 mg/kg) injected SC produced an identical yawning syndrome. Previous work has suggested that yawning elicited by systemic dopamine agonist treatment is a consequence of dopamine autoreceptor stimulation. Similarly, the most likely explanation of the present data is that yawning elicited by systemic and central dopamine agonist treatment was due to activation of dopamine autoreceptors. Systemic injection of haloperidol and scopolamine abolished yawning induced by intrastriatal piribedil and these data provide tentative support for the proposal that a dopamine-acetylcholine link may be involved in the expression of yawning.