Antidipsogenic action of naloxone under different water deprivation conditions

Naloxone (1 mg/Kg s.c.), in the light phase of the daily light-dark cycles during the 30 and 60 min of the test, shows an antidipsogenic effect of the same intensity in chronically water-deprived rats which drink more (+ 176% and + 162%) than the acutely water-deprived animals. In chronically water-deprived rats, the time interval from the drug introduction (5, 30, 60 and 90 min) is not critical for the intensity of the antidipsogenic action of naloxone. When water intake is controlled by a 20% variable ratio schedule that does not allow the animals to satisfy, during the session, more than 50% of their thirst, the time interval from the introduction of naloxone is critical. When the rats can drink freely for 30 min in their home-cage after they satisfied their thirst partially by means of bar-pressing, naloxone, paradoxically shows a weaker and not significant antidipsogenic action. The results and the usefulness of the behavioural test are briefly discussed.