Effects of neonatal testosterone and estrogen on open-field behaviour in rats

Abstract

On days 1 and 4 after birth male and female rats from the same litter were injected with either testosterone propionate (TP), or estradiol benzoate (EB) or oil. Subjects were tested in the open-field for 2 minutes per day, for 4 successive days at 45 and 85 days of age. Adult females were significantly more active than males in the outer and inner fields, reared more and defecated less. Neonatal TP and EB treatments reduced activity in females, but only EB increased defaecation in females. EB and TP treated females were heavier than controls at 125 days of age but non-significantly so in the case of TP. Gonadal weights in males and females were reduced in EB and TP treatment, as were penile diameter, number of penile papillae and anogenital spacing in EB treated males. Some of these results are consistent with the argument that androgens defeminize or masculinize certain neural mechanisms in the neonate after first being converted to estrogens, but both EB and TP have anomalous effects on males in producing morphological demasculinization.