Emergence of deprivation-induced drinking: implications for hypothalamically elicited behavior

The possibility that 23-hr water deprived rats must learn to drink in response to thirst states was examined in subjects presented with consecutive days (CD), alternate days (AD), or no days (ND) of deprivation experience CD animals displayed a gradual rise in water intake; however, motivational factors seemed critical in producing this effect because CD rats drank more and weighed less than the AD animals. In addition, AD subjects always drank more than ND animals; thus, the gradual rise in drinking could not be attributed to an ad lib body water surplus that prevented subjects from being thirsty during the initial drinking session. All subjects were allowed to recover from the first phase of deprivation, and then each group was presented with the consecutive-day deprivation procedure. In this second phase, the groups did not differ in the amount of water drunk; so, learning factors once again were contraindicated because more "practiced" subjects did not ingest more. Habituation processes also were implicated in the gradual increase in drinking. These data contrast with those indicating that rats must "learn" to display consummatory responding during electrical stimulation of the lateral hypothalamus, and they strongly support the possibility that learning-like effects during water deprivation reflect the operation of motivational processes.