Differential timing and sexual dimorphism in the expression of the vasopressin gene in the developing rat brain

The ontogeny of vasopressin (VP) gene expression in extrahypothalamic neurons of the bed nucleus of the stria terminalis (BNST) and medial amygdala (MA) was investigated using in situ hybridization. In both the BNST and MA, VP mRNA-positive cell profiles were only detected a few days after birth. In males, VP mRNA-expressing cell profiles appear in the BNST on day 3 and in the MA on day 5. In contrast, hybridization signals could not be detected in the female brain until day 14 in the BNST and day 35 in the MA. Adult VP mRNA levels are attained by day 35 in the BNST and day 60 in the MA for both sexes. From this data, it is apparent that development of the VP system is delayed in females compared to the males. Therefore, these data suggest that the sexual dimorphic pattern in the expression of VP mRNA in these nuclei of the adult brain is evident early in the development process.