Suppression of schedule-induced drinking and food-reinforced bar pressing by tail-pinch is not reversed by naloxone.

In Experiment 1 eleven food-deprived rats were tested in a schedule-induced drinking paradigm under both tail-pinch and non-tail-pinch conditions. Tail-pinch produced a strong suppression of schedule-induced drinking, licking, licks per milliliter, bar presses, and number of reinforcers received during 30-min test sessions. Experiment 2 showed that the narcotic antagonist naloxone (2 and 4 mg/kg) did not reverse the tail-pinch suppression of schedule-induced drinking and food-reinforced bar pressing. Experiment 3 demonstrated that the suppression of schedule-induced drinking by tail-pinch could not be attributed to a suppression of drinking behavior in general, as tail-pinch had no effect on deprivation-induced drinking. The failure of naloxone to reverse this blockade suggests that endogenous opiate systems do not play a very important role in the suppression of schedule-induced polydipsia by tail-pinch. It was suggested that the combination of both the schedule-induction paradigm and the tail-pinch procedure increased arousal levels to such a high level that all behaviors were suppressed.