The effects of various narcotic agonists and antagonists on deprivation-induced fluid consumption

When rats in a standardized deprivation-induced fluid consumption test system were given single doses of a variety of narcotic antagonists, dose-dependent reductions in fluid intake were obtained, once a threshold level was reached. Sub-threshold doses of the antagonists were without effect. In contrast, a variety of narcotic agonists, produced biphasic responses, with an initial dipsogenic effect followed by a subsequent dose-dependent decrease in fluid consumption as doses were increased.