Developmental effects of neonatal sex hormones on spatial and activity skills in the white rat

The purpose of this experiment is to extend these experiments by using varying neonatal hormonal differentiation processes and to examine the effects of these different methods of neonatal feminization on changes in spatial and activity skills. The experiment involved three neonatally feminized groups of male rats: 'castration alone', 'estrogen alone', and 'estrogen injected castrates' together with one female sample, 'testosterone injected castrates', while treated and untreated male and female controls were also used. The data provide partial support for the major hypotheses that neonatal gonadectomy and opposite sex hormones administered to male and female castrated rats (together and independently for males) would reverse the normal sex-associated abilities of the white rate (higher male spatial learning and higher female activity). However, the feminization effect for the male 'estrogen alone' and 'castration alone' experimental groups was much greater than for the male estrogen injected castrates. The masculinized females, testosterone injected castrates, also had higher spatial learning and lower activity levels, while the feminized male's spatial and activity skills were also reversed. This confirmed in part the extent to which neonatal gonadal sex hormones are effective at critical periods of development in programming the brain in terms of sex-associated spatial and activity skills. Adult hormonal replacement therapy was also administered at 12 months and supported the hypothesis that sex hormones in adults would be mainly activational and have less marked effects than the significant directional changes obtained by these neonatal sex hormones and castration techniques.