Effects of neonatal thyroxine stimulation on adult open-field behavior and thyroid activity in rats

Abstract

Three experiments are reported in which small groups of rats, given either thyroxine (T4) or triiodothyronine (T3) in large doses on Day 3 or Day 4 after birth, were tested in an open-field situation as adults. Ambulation and rearing were significantly increased by neonatal thyroid hormone treatment in both male and female rats. The effects were more pronounced among males than among females and were reduced by adult handling in the female group. With advancing age, hormone-treated rats showed a progressively lower body weight than controls. No consistent effect on thyroid uptake of radioiodine was noticed. The results are discussed with respect to possible implications for the reported adult learning deficit s in rats treated in a comparable manner.