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.