Effect of Estradiol on Brain Maturation: Dose and Time Response Relationships1

Abstract

Single injections of estradiol dipropionate in the doses of 50, 100, 150, and 200 [mu]g/100 g body wt were administered postnatally to newborn rats beginning on day 4 and ending on day 12 of age. Brain maturation, assessed by maximal electroshock seizure responses, was significantly hastened by 200 [mu]g/100 g body wt administered on days 5, 6, 7 and 10, 150 [mu]g on day 10, 100 [mu]g on days 6 and 7, and 50 [mu]g on days 6 and 7 of age. Increased brain excitability was also observed for 6 months after estradiol administration (100 [mu]g/100 g body wt) by a lengthening of tonic extension and/or shortening of tonic flexion. Ovarian atrophy, hypophysial hypertrophy, adrenal atrophy and alterations in the estrous cycle were observed. These data show that a dose of 50 [mu]g/100 g body wt, administered to the infant rat at a critical period (6 and 7 days of age) during development, hastens brain maturation.