Effects of intracerebroventricular injection of naloxone on operant feeding and drinking in pigs

Operant feeding and drinking to satiation were studied in prepubertal pigs deprived of food or water for 18 hours and then given intracerebroventricular (ICV) injections of a solution of naloxone hydrochloride. In feeding tests there was no difference in the amount of food consumed, or in the rate at which reinforcements were obtained, between pigs given ICV injections of 0.4 or 0.8 mg naloxone and those receiving a control injection of saline. However, in drinking tests, injection of both 0.2 and 0.4 mg naloxone significantly (p less than 0.01) reduced the quantity of water drunk and slowed the rate at which reinforcements were obtained. No significant effects on operant water intake were seen after intravenous injection of 0.4 mg naloxone.