Timing of yawns induced by a small dose of apomorphine and its alteration by naloxone.

The report examines the temporal sequence of yawns induced by apomorphine and whether the opiate antagonist, naloxone, affects it. Before administering apomorphine (0.075 mg/kg) or saline, rats (n = 8) were pretreated with naloxone (1 mg/kg) or saline. Each subject received all 4 possible treatments (saline-saline, saline-apomorphine, naloxone-saline, and naloxone-apomorphine) in random order. Results indicate that yawning induced by apomorphine seems to come in fits; that is, there is a series of yawns spaced closely together and followed by a period of quiescence before the start of another cluster of yawns. Naloxone reduced the number of apomorphine-induced yawns, and the occurrence of very short inter-yawn intervals. It is suggested that the timing of yawns may provide useful information regarding some pathologies and that opiates may potentiate the action of dopaminergic systems.