Physiological correlates of schedule-induced activities in rats

Oxygen consumption and heart rate as well as a range of behavior variables were tracked continuously as rats adapted to a schedule of food delivery. Over 15 days of observation a majority of the subjects developed characteristic patterns of schedule-induced polydipsia (SIP) in which bouts of drinking reliably followed food delivery. Variations in food tray entries, oxygen consumption, heart rate, and, in the final stage of the experiment, rates of general activity were also time locked to food delivery in both rats exhibiting SIP and nondrinkers. However, the patterns of variation in these measures differed consistently between these two groups. Oxygen consumption varied over a wider range and reached higher levels in drinkers than nondrinkers. Additionally, heart rate was lower in the drinkers, which, in the final stage of the experiment, also exhibited depressed rates of food tray entries and general activity relative to the nondrinkers. Each of these between-subject differences was paralleled by differences within the drinking group between trials on which drinking occurred and trials on which it did not occur. The implications of these results on the utility of unidimensional energetic constructs are discussed.