The distributions of apoptotic cells in the medial preoptic areas of male and female neonatal rats.

The medial preoptic area (MPA) of the hypothalamus of the rat contains two sexually dimorphic nuclei, the periventricular preoptic nucleus (PVpo) and the medial preoptic nucleus (MPN). To examine the relationship between sexual dimorphism and neuronal death, we examined the number of apoptotic cells in the subdivisions of the MPA in neonatal rats of postnatal days 1 (P1), 4 (P4), 7 (P7) and 14 (P14). Apoptotic cells in these areas were classified according to their progression into three stages. P1 and P4 rats contained many apoptotic cells in the subfield along the third ventricle, including the PVpo, and their number was significantly larger in P1 males: in particular, the number of early-stage cells was larger in males than females. The number of apoptotic cells in the MPN was increased in P4 and P7 rats, although no significant sexual differences were seen in the total number or in the number of each progressive stage of apoptotic cells. In P14 rats, very few apoptotic cells were seen in the MPA. Our data revealed that the distribution of apoptotic cells in the MPA of developing rats depends on the sexuality, subdivision of the area and postnatal period.