Role of lever responding and water presentation in altering rat brain catecholamine metabolism

Alterations in rat brain catecholamine (CA) metabolism were found to be associated with water-reinforced lever-press responding under a variable-interval 30-second (VI 30-sec) schedule of water presentation. This alteration was not due to training alone since it did not occur if trained rats were not placed in the experimental chamber. Rats performing on the VI 30-sec schedule were compared with rats that were not performing the schedule-maintained behavior and it was found that the metabolism of NE in the pons-medulla and DA in the caudate was increased in the performing rats. In addition, yoked VI 30-sec rats (water presentation with no response contingencies) had an increased CA metabolism comparable to that of VI 30-sec performing rats. These results suggest that altered CA metabolism may be closely associated with periodic water presentation. Further experiments showed that water-deprived rats presented water for the first time did not have changes in CA metabolism, suggesting that water consumption per se is not responsible for altered CA metabolism. Rats with prior exposure to periodic water consumption under the experimental conditions showed increased CA metabolism when water was presented even if water consumption did not occur. Thus, although water deprivation and consumption are major factors in producing increased CA metabolism, other critical variables appear to include the presentation of stimuli previously associated with water presentation and/or water consumption. These results demonstrate that stimuli associated with previous behavior may alter the metabolism of CAs, and this phenomenon may provide a neurochemical explanation for the observation that many drugs affect behavior as a function of the behavior itself.