The relationship between fetal hormones and the differentiation of the central nervous system in primates;

The effects of neonatal exposure to testosterone on the development of behaviour in female marmoset monkeys

Experimental investigations of sexual differentiation in primates have been mainly confined to the rhesus monkey, a highly polygamous species with marked anatomical and behavioural sexual dimorphism. The marmoset is a monogamous monkey which shows little anatomical or behavioural sexual dimorphism, and both sexes exhibit positive feedback in response to the administration of oestradiol. This monkey has a relatively short gestation period of 144 days and usually gives birth to dizygotic twins. These share a common placental circulation and hence develop as haematopoietic chimaeras. However, a female with a male co-twin is not adversely affected as a result of this and the freemartin condition does not occur. Since the newborn male experiences raised testosterone levels soon after birth it is possible that the 'critical period' for sexual marmosets were implanted with 25 mg of testosterone for 50 days after birth. After removal of the implants their genitalia remained partly masculinized and they initiated more masculine rough-and-tumble play than their controls. After puberty they exhibited a mixture of male and female sexual behaviour when presented with unfamiliar normal males and females during 15-minute behavioural trials. Four of the implanted females have also ovulated. Neonatal administration of testosterone therefore has had an organizing effect on female behaviour. Whether the marmoset is exceptional in this respect, or whether other primates which exhibit a male neonatal testosterone surge, such as man and the rhesus monkey, also undergo some postnatal behavioural differentation, remains to be seen.

Effects of neonatal testosterone and progesterone on open-field behaviour in the rat

Rats treated on the day of birth with progesterone (50 üg) or testosterone pro-pionate (200 üg) or the oil injection vehicle alone were tested in the open-field on four consectuve days at 45 days and 85 days of age. Averages across treatments showed that females ambulated more and reared more than males at both ages, that they groomed more than males at 45 days of age, and defaecated less at 85 days of age. Progesterone treatment significantly reduced defaecation in males at 45 days of age, and reduced grooming in both sexes. At 85 days of age progesterone significantly increased activity in females. Testosterone-treated animals of both sexes groomed significantly less than same-sex controls at 45 days of age, whereas at 85 days of age activity scores were significantly reduced only in females although testosterone treated males were less active on 2 test days and more active on 1. Early postnatal treatment with progesterone appeared to feminise male rats, and testosterone to masculinise female rats. Both hormones also altered the behaviour of opposite sexed rats, indicating that male rats may be further masculinised by exogenous testosterone and female rats further feminised by progesterone. Progesterone may have acted as an anti-androgenic agent by blocking gonadal and adrenal androgens in males and adrenal androgens in females.