EFFECTS OF CASTRATION AND TESTOSTERONE, DIHYDROTESTOSTERONE OR OESTRADIOL REPLACEMENT TREATMENT IN NEONATAL RATS ON MOUNTING BEHAVIOUR IN THE ADULT

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Abstract
Castration of rats on the day of birth abolished the capacity to ejaculate and reduced the capacity to show intromissions in response to testosterone propionate (TP) treatment in adults. Day 10 castrated rats treated daily with oil or day 0 castrated rats treated daily with testosterone benzoate (TB) during the first 10 days of life achieved intromissions and ejaculation after TP treatment in adulthood. Treatment of day 0 castrated rats with a high dose of TB during the first 10 days of life enhanced their capacity to ejaculate in response to TP treatment in adulthood to a level above that of day 10 castrated rats given oil in infancy and similarly treated with TP as adults. Castration on the day of birth greatly reduced the increase in penis weight and the development of cornified papillae on the glans penis which were seen in day 10 castrated rats after TP treatment in adulthood. These peripheral effects of neonatal testicular secretions are reversed by neonatal treatment of day 0 castrated rats with TB. Daily treatment of day 0 castrated rats with dihydrotestosterone benzoate (DHTB) during the first 10 days of life facilitated the increase in weight of the penis and the development of cornified papillae on the glans penis but did not enhance the capacity to ejaculate in response to TP treatment in adulthood. Daily treatment of day 0 castrated rats with oestradiol benzoate (OB) during the first 10 days of life facilitated ejaculation without increasing penis sensitivity to TP in adulthood. Combined treatment of the neonate with OB and DHTB was no more effective in facilitating ejaculation in the adult than was OB alone. Neonatal treatment with OB was considerably more potent than neonatal treatment with TB in enhancing ejaculatory behaviour in adulthood. It is suggested that both the inhibition of the development of lordosis behaviour and the facilitation of the development of mounting behaviour by testicular secretions in newborn rats may be dependent upon, but variously sensitive to, the amount of oestradiol formed in the brain from testosterone in the blood during the first 10 days of life.