Casomorphins reduce separation distress in chicks.

Intraventricular administration of various chain length casomorphins (CM) reliably reduced separation induced distress vocalizations (DVs) in young domestic chicks. At a dose of 50 nanomoles, CM-5 was more potent than either CM-4 or CM-7, but for each the duration of action was approximately half an hour, with CM-7 having a somewhat longer effect. This suppression of DVs was partially antagonized by naloxone (1 mg/kg).