Direct evidence for involvement of dopaminergic inhibition and cholinergic activation in yawning.
A behavioral study was performed in an attempt to understand the neurological mechanism involved in yawning in rats. Intraperitoneal injections of low doses (0.25 mg/kg) of apomorphine, which preferentially activate presynaptic dopamine autoreceptors, elicited yawning. Whereas apomorphine, at a high dose of 2 mg/kg, produces stereotypy which has been thought to be mediated by stimulation of postsynaptic dopamine receptors. The yawning and stereotypy did not occur simultaneously in the rat. The apomorphine-induced yawning was completely inhibited by pretreatment with fluphenazine (9 mg/kg, IM) or scopolamine (0.5 mg/kg IP), but markedly increased by reserpine (5 mg/kg, SC), however it was not affected by methylscopolamine (0.5 mg/kg, IP). Both physostigmine (0.2 mg/kg, IP), an indirect acetylcholine agonist, and pilocarpine (4 mg/kg, IP), a direct acetylcholine agonist, also induced yawning. This was abolished by scopolamine (0.5 mg/kg, IP) and increased by reserpine (5 mg/kg, SC). Fluphenazine (9 mg/kg, IP) did not affect the pilocarpine-induced yawning but increased the physostigmine-induced yawning. The results indicate that apomorphine elicits yawning by stimulating presynaptic dopamine receptors, and that dopaminergic inhibition and cholinergic activation are concomitantly involved in the yawning.
D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D001522:Behavior, Animal / Q000187:drug effects*; D018492:Dopamine Antagonists; D005476:Fluphenazine / Q000494:pharmacology; D006801:Humans; D008297:Male; D010275:Parasympathetic Nervous System / Q000502:physiology*; D010830:Physostigmine / Q000494:pharmacology; D010862:Pilocarpine / Q000494:pharmacology; D051381:Rats; D012018:Reflex / Q000187:drug effects; D012110:Reserpine / Q000494:pharmacology; D012601:Scopolamine / Q000494:pharmacology; D013239:Stereotyped Behavior / Q000187:drug effects
D018492:Dopamine Antagonists; D010862:Pilocarpine; D012110:Reserpine; D010830:Physostigmine; D012601:Scopolamine; D001058:Apomorphine; D005476:Fluphenazine