Patterns of drinking in the rat following the administration of opiate antagonists

Durations of drinking were recorded for water-deprived rats as they drank to satiety, following SC injections of naloxone (0.1-10.0 mg/kg), naltrexone (0.1-10.0 mg/kg) or saline vehicle. The results provided evidence for the effects of opiate antagonists on the temporal pattern of drinking exhibited by water-deprived animals. A separate, time-sampling procedure was used to supplement the drinking duration data, and showed that the opiate antagonists may suppress water consumption during a period 2.5-7.5 min after the start of the initial drinking bout. A second experiment confirmed that the pattern of drinking displayed during schedule-induced polydipsia in the rat is resistant to any suppressant effect of a moderate dose of an opiate antagonist. The similarity between opiate receptor blockade and water preloading in their effect on drinking in response to water deprivation, and lack of effect on schedule-induced polydipsia is discussed. Opiate antagonists may affect drinking principally by imposing a thirst satiety signal.