The effects of thyroidectomy on the wheel running activity of female rats.

STERN, J.J. The effects of thyroidectomy on the wheel running activity of female rats.-The wheel running activity of female rats was observed prior to and following thyroidectomy. Thyroidectomy significantly reduced overall activity and increased the interval between activity peaks; thyroid feeding corrected these effects. Thyroid feeding did not correct the effects in ovariectomized rats. The continued administration of estradiol benzoate and progesterone increased activity in ovariectomized-thyroidectomized rats. The results suggest that the activity reduction consequent to thyroidectomy is not a direct result of thyroid removal but an indirect result mediated by altered ovarian functioning. Thyroidectomy Wheel running activity Activity Ovariectomy Sex hormones THE THYROID gland influences the wheel running activity of female rats. Total thyroidectomy reduces the activity of the female, abolishes its cycles, and the administration of thyroid extract corrects these effects [6]. Thriouracil, a thyroid inhibiting drug, abolishes the females' cycles and reduces wheel running activity [5]. Removal of the thyroid affects the functioning of the ovary. Following thyroidectomy the appearance of vaginal cornifica-tion is irregular and the intervals between estrus are lengthened [5]. Since the ovary is known to influence activity [8], the possibility exists that the activity changes consequent to thyroidectomy are not a direct result of thyroid removal but an indirect result mediated by altered ovarian functioning. The present study tested this possibility by examining the effects of thyroid feeding and subsequent ovarian hormone administration on the wheel running activity of thyroidec-tomized and ovariectomized rats. METHOD The animals were 12 virgin female albino rats. At the start of the experiment the females ranged in age from 90 to 117 days and weighed 197-227 g. Rat chow and water were constantly available. The laboratory had a thermostat which maintained the temperature at approximately 74°F. The rats were on a reversed 12 hr on-12 hr off light cycle with lights offat 10 a.ln. The females were initially given an adjustment period of 10-14 days in the activity cages. Following this and continuing throughout the experiment, revolutions per day (RPD) were recorded daily at approximately 9:30 p.m. On the 29th recorded day (Table 1) 9 females were thyroidectomized while 3 were sham operated. These operations and those to ~This research was funded by a University of Michigan Horace generously supplied by the Schering Corp., Bloomfield, N.J. follow were conducted under Nembutal anesthesia. Three weeks after the thyroidectomies (Day 50) the females in Groups l, 3 and 4 had …