Sex-specific schedule in steroid response of rhombencephalic catecholaminergic neurons in vitro.

Morphological differentiation of tyrosine hydroxylase-immunoreactive neurons was investigated in dissociated cell cultures of rhombencephalon of male and female day 14 rat embryos grown in the presence or absence of sex steroids. Numbers of cells were counted and morphometrical measurements carried out of soma size and length of tyrosine hydroxylase-immunoreactive neurites (processes). Subtle sex differences in length of stained neurites, which were not yet present after 3 days in vitro, were observed after 6 days in cultures grown in the absence of sex steroids. Female tyrosine hydroxylase-immunoreactive neurites could be traced over longer distances than male ones. Daily treatment of cultures with testosterone or 17 beta-estradiol resulted in an increase of lengths of stained neurites of female neurons after 3 days and of male neurons after 6 days in vitro. Regarding cell numbers or soma size, there were no differences between genders or between controls and hormone-treated cultures. It is concluded that sex steroids promote the outgrowth of neurites from noradrenergic neurons within a gender-specific time frame. It appears that the critical period for developmental effects of sex steroids differs between males and females.