Involvement of endorphins in the emotional behavior of pigs]

Social isolation and exposure to a new environment induce hyperactivity, vocalizations and ACTH release in weaned Piglets acutely submitted to this stress. These reactions are increased by pretreatment with morphine (0.5 and 1 mg/kg) and decreased by naloxone (1 mg/kg), suggesting that endogenous opiates modulate emotional behaviour in Pigs.