Sex differences in rat brain oestrogen and progestin receptors

Abstract

The brains of both male and female rats possess specific cytoplasmic receptors for oestrogens and progestins¹, and it has been suggested that sex differences in the neuroendocrine and behavioural responses to these hormones result from differences in the number of steroid receptors in specific locations in the brain². Although there have been numerous comparisons of steroid receptors in male and female brains^3–9, the question of whether there are sex differences in these receptor systems remains unresolved, due in part to the inability of available biochemical techniques to achieve sufficiently high anatomical resolution. We have overcome this problem by applying the Palkovits punch-out technique¹⁰ to measure steroid receptors in hypothalamic nuclei known to be involved in behavioural and neuroendocrine control. We report here that castrated male rats have fewer oestrogen and progestin receptors in certain hypothalamic nuclei than females. This suggests that the relative insensitivity of male rats to feminine actions of gonadal steroids might be due in part to a lack of receptors for these steroids in highly localized brain regions.