DIURNAL-VARIATION OF INTENSIVE RUNNING IN FOOD-DEPRIVED RATS

Manipulation of the food supply can induce either intense hyperactive wheel running or a fatal activity anorexia in rats that is strongly an alogous to that seen in humans. The abnormal behaviour is accompanied by alterations in the diurnal pattern of activity. As part of a detail ed study of hyperactivity and anorexia, spontaneous wheel running by m ale rats was studied under three conditions: ad libitum feeding; restr iction to 15 g of food per day; and restriction to a single 90-min mea l per day. Ad libitum fed rats increased their running at the rate of 440 +/- 60 m/day per day, stabilizing after day 10 at 6045 +/- 3010 m/ day. The running occurred in short bursts throughout the dark period a nd at the beginning of the light period. Rats restricted to 15 g/day i ncreased their running at the significantly greater (p < 0.001) rate o f 1230 +/- 120 m/day per day, reaching 12200 +/- 4090 miday by day 10 and thereafter stabilizing at 13600 +/- 4160 m/day. The running was in itially triphasic and confined to the dark period but eventually progr essed to a biphasic pattern. The rats restricted to a single 90-min ac cess period to food each day showed an even greater rate of increase i n running, attaining 1930 +/- 288 m/day per day (p < 0.02 vs. 15 g/day group). These animals decreased eating and decompensated by day 4. Th e diurnal pattern of activity was disturbed from day 1 of the protocol , and by day 4 the rats ran essentially continuously throughout the da ily cycle. The sensitivity to hyperactivity is a function of the sever ity of food restriction in this animal model of hyperactivity. It is p aralleled by a marked disturbance of the diurnal pattern of activity, suggesting that the hyperactivity is related to a basic central nervou s system dysfunction.