PERINATAL STRUCTURAL SEX DIFFERENTIATION OF HYPOTHALAMUS IN RATS

During the last two days of fetal life, a significant increase of the nuclear volumes in the nerve cells of the preoptic area and the ventromedial nucleus, both of which are involved in the regulation of gonadotrophin release and sexual behavior, was observed in the female but not in the male rat. Significant sex-specific caryometric differences are, therefore, already present in the hypothalamus at birth. This observation suggests that the beginning of the hypothalamic organization phase in rats occurs during the late prenatal period. © 1969 S. Karger AG, Basel.