EFFECTS OF PHYSIOLOGICAL-STATE ON ORAL HABITUATION IN DEVELOPING RATS- CELLULAR AND EXTRACELLULAR DEHYDRATION

Hydrational state has been demonstrated to influence intake of various solutions in young rat pups. For instance, both cellular and extracel lular dehydration produce an enhancement of intake in pups tested at 6 days of age, However, the behavioral mechanisms that result in increa sed intake following manipulations of hydrational state have been less extensively studied. The impact of hydrational state on behavioral re sponsiveness in young rat pups was examined by assessing the pattern o f responding to a series of repeated oral infusions of diet. Pups were tested at 6, 12, or 18 days of age following either acute cellular de hydration produced by injection of 1 M NaCl or acute extracellular deh ydration produced by injection of 10% polyethylene glycol (PEG). Oral responsiveness to a series of 30 brief infusions of one of four taste solutions (water, 10% sucrose, 0.135 M NaCl, or 1 M NaCl) was measured . Each infusion lasted 3 s and there was 1 min between infusions. The pattern of oral responding to solutions was affected by the developmen tal age of the pup, the hydrational state of the pup, and the solution offered, with the largest effects of dehydration observed in the youn gest animals. In all conditions except one, pups habituated to repeate d infusions. The exception was the failure of extracellularly dehydrat ed 6-day-old pups to display habituation to oral infusions of sucrose. These results suggest that, although intake is enhanced by both cellu lar and extracellular dehydration in very young pups, the behavioral c hanges responsible for the enhancement of intake after cellular dehydr ation are different from the behavioral changes resulting from extrace llular dehydration. This dissociation of behavioral effects of dehydra tion in young pups demonstrates that intake measures alone may obscure subtle differences in behavior and argues for the utility of dissecti on of behavioral components in understanding the neural and physiologi cal control of behavior. (C) 1995 by John Wiley & Sons, Inc.