Nuclear and cytosolic androgen receptor levels in the limbic brain of neonatal male and female rats.

Nuclear and cytosolic androgen receptors in the limbic brain were measured in neonatal male and female rat pups. There were no sex differences in cytosolic receptor concentrations during the neonatal period in any of the regions studied (hypothalamus, amygdala, preoptic area and septum). Receptor concentrations in all 4 regions increase gradually over the first 10 days of life, with no change in the affinity for 5-alpha-dihydrotestosterone. Nuclear receptor levels in intact pups, measured using an exchange assay, are highest between days 4 and 8 of life. In general, nuclear receptor levels are higher in males than in females; however, this sex difference is most consistently seen in the amygdala. These results are discussed in relation to sex differences in circulating testosterone levels and with respect to the contribution of androgens to the sexual differentiation of behavior.