EFFECT OF HYPOPHYSECTOMY ON DIURNAL RHYTHM OF SPONTANEOUS ACTIVITY IN THE RAT

Abstract

20 rats (11 albino and 9 half-wild) were hypophysectomized after preliminary adjustment to the activity recorded in continuous darkness and after the securing of records of normal spontaneous running. During the first 2 postoperative days, all animals exhibited little activity and no diurnal rhythm. During the next 10 days the amt. of activity increased and the rhythm reappeared. After the 2d wk. there was further increase in total activity, 1/3 to 1/2 that of the pre-operative level, and complete restoration of the diurnal rhythm. 2 hypophysectomized animals, 41 days after the operation, were exposed to periods of illumination corresponding to solar day and night for 6 days. Reversal of periods of illumination, resulted in a corresponding reversal of the diurnal activity rhythm of the animals, as would have occurred in intact animals.