Endocrinology
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The vasopressin-immunoreactive (AVP-ir) projections of the bed nucleus of the stria terminalis (BST) and medial amygdaloid nucleus (MA) are much denser in males than in females even if males and females are treated with similar amounts of testosterone. Previous studies have established that testosterone influences AVP-ir projections during development, but not whether these effects of testosterone were permanent. This study tested the effects of various hormonal manipulations during development on the ability of testosterone to influence the AVP immunostaining in cells of the BST and MA and of fibers in the lateral septum of adult rats. ⋯ This indicated that testicular secretions influenced the differentiation of AVP-ir pathways around postnatal day 7. This was further confirmed in the third experiment, in which testosterone propionate treatment at the seventh postnatal day significantly raised AVP-ir fiber density in the lateral septum of neonatally gonadectomized male and female rats and fully restored the number of AVP-ir cells in the BST of neonatally castrated males. Combined, these data suggest that testosterone levels around the seventh postnatal day determine the sexual differentiation of AVP-ir projections to the lateral septum.