The effects of naloxone on body rotation-induced analgesia and anorexia in male mice.

The effects of body rotation in a horizontal plane and the opiate antagonist, naloxone, on the nociceptive responses and the feeding behavior of male mice were examined. In the first experiment the mice were rotated (70 rpm, schedule of 15 sec on; 5 sec off) for 60 minutes or exposed to sham rotation for the same duration. Midway through the rotation or sham procedure the mice were either injected with naloxone (1 mg/kg) or isotonic saline. At the end of the 60-minute treatment period the animals were placed on a warm surface (47.5 degrees C) and their latency to show a foot-licking response was measured. The rotation procedure produced a significant (p less than 0.01) increase in response latency in the saline-injected mice and the naloxone injections blocked this analgesic effect. This finding provides evidence for opioid involvement in the rotation-induced analgesia. In Experiment 2 mice on a food restriction schedule were rotated (70 rpm, 15 sec on; 5 sec off) or sham exposed for 60 minutes. Midway through this treatment period the mice were either injected with naloxone (1 mg/kg) or isotonic saline. Following the treatment period the mice were given access to food for 2 hours. The rotation procedure produced a significant (p less than 0.01) reduction in feeding (anorexia) in the first 30 minutes of food access for the saline-injected mice. Injections of naloxone significantly (p less than 0.05) enhanced the rotation-induced anorexia. These experiments demonstrate that rotation-induced analgesia in mice is blocked by the opiate antagonist, naloxone, whereas rotation-induced anorexia is not.(ABSTRACT TRUNCATED AT 250 WORDS)