Ovarian influences on the development of sexual behavior in neonatally androgenized rats

Neonatal and pubertal, but not adult, ovarian steroids are necessary for the development of female-typical patterns of dodging to protect a food item

Rats protect food by dodging horizontally away from a conspecific. Females and males use different movement and stepping patterns to execute a dodge. An unresolved question is whether exposure to ovarian steroids in females is necessary for the development of the female-typical pattern. Females ovariectomized neonatally and prior to puberty use a combination of male and female tactics. Pregnant females, however, use a female-typical pattern of dodging, suggesting that the patterns used by prepubertal ovariectomized females are not due to their increase in body mass. Thus, the contribution of ovarian steroids to the development of female-typical patterns of behavior needs to be studied further at both a behavioral and neural level with regard to the organization of movement.

High fetal estrogen concentrations: correlation with increased adult sexual activity and decreased aggression in male mice

In the house mouse (Mus musculus), fetuses may develop in utero next to siblings of the same or opposite sex. The amniotic fluid of the female fetuses contains higher concentrations of estradiol than that of male fetuses. Male fetuses that developed in utero between female fetuses had higher concentrations of estradiol in their amniotic fluid than males that were located between other male fetuses during intrauterine development. They were also more sexually active as adults, less aggressive, and had smaller seminal vesicles than males that had developed between other male fetuses in utero. These findings raise the possibility that during fetal life circulating estrogens may interact with circulating androgens both in regulating the development of sex differences between males and females and in producing variation in phenotype among males and among females.

Organisational effects of neonatal and pubertal testosterone on sexually differentiated behaviours in the open-field and head-dip apparatus

On days 1 and 4 after birth rats were injected with 100 μg of testosterone propionate (TP) or vehicle, and at 35 days of age they were injected intramuscularly with 400 μg of testosterone oenanthate (TO), a long acting androgen, or the vehicle. There were four groups (oil-oil, TP-oil, oil-TO, TP-TO), each group subdivided by sex. Females treated with testosterone neonatally or at puberty were masculinised or defeminised on adult open-field behaviours, being less active and rearing less than oil-oil females; the oil-TO group also defaecated significantly more than controls. The TP-TO female group was indistinguishable from the oil-TO group. In a second experiment, sex differences were found in head-dipping behaviour as well as in activity and rearing. Females treated with TP or TO reared less and defaecated more than controls, and TP also decreased activity, but neither hormone treatment affected head-dipping behaviour. There is thus a peripubertal as well as a neonatal period when testosterone can act organisationally to masculinise or defeminise female rats. Potentiation between effects of neonatal and pubertal androgens was found on female body weights. TO alone had no effect, but TP-TO females were significantly heavier than controls at 90 days of age and by 130 days of age the TP-oil group was also heavier than controls.

Differentiation of coital behavior in mammals: a comparative analysis

The evidence reviewed suggests that in all mammalian species the adult male's ability to display masculine coital behavior depends in part on exposure of the developing brain to testicular testosterone or its metabolites. In many mammals, particularly rodents, ruminants, and some carnivores, perinatal exposure to androgen also causes behavioral defeminization, i.e., reduced capacity to display typically feminine coital behavior in response to gonadal hormones in adulthood. The data reviewed suggest that no such process occurs in certain other mammalian species, including ferret, rhesus monkey, marmoset, and man. Testicular androgen may cause behavioral defeminization only in those species in which expression of feminine sexual behavior normally depends on the neural action of progesterone, acting synergistically with estradiol; new data support this claim in the ferret. The possible contribution of estrogenic and 5 alpha-reduced androgenic metabolites of testosterone to the occurrence of behavioral masculinization and defeminization is considered in those mammalian species for which data are available.