The sexually dimorphic nucleus of the preoptic area in the human brain: a comparative morphometric study.

The sexually dimorphic nucleus of the preoptic area (SDN-POA) in the human hypothalamus is an ovoid, densely packed collection of large cells. The size, shape and cellular morphology of the SDN-POA was examined in relation to sex and age in adult human subjects. In this region the following parameters were measured: length of the rostrocaudal axis, maximum cross-sectional area, volume, numerical cell density, total number of cells, and the diameter of the cell nucleus. The SDN-POA was elongated in females and more spherical in males. The mean volume and total cell number were markedly sexually dimorphic: the volume of the SDN-POA was 2.2 times as large in males as in females and contained 2.1 times as many cells. No sex differences were observed in either cell density or mean diameter of the cell nuclei. Furthermore, multivariate regression analysis revealed that there are also sex-linked differences in the structural organisation of the human SDN-POA, finding expression in the way the morphometric parameters are interrelated. Of the parameters measured, only the volume and cell number of the SDN-POA showed a dramatic decrease with ageing. The reduction in cell number, however, was not constant throughout adulthood but was found to depend upon sex and age. In males, a major reduction in SDN-POA cell number was observed between the age of 50-60 years. In females, cell death was found to be more prominent than in males, especially among old people (t greater than 70 years), dropping to values which were only 10-15% of the cell number found in early childhood. In conclusion, the human SDN-POA has a sex-dependent pattern of ageing. Finally, the morphology of the SDN-POA was compared with that of other hypothalamic regions--the suprachiasmatic nucleus (SCN) and the paraventricular nucleus (PVN)--both in man and in rat. Species-specific differences in the dimensions of these nuclear regions are discussed in the light of their assumed functional significance.