Morphometric analysis of the suprachiasmatic and paraventricular nuclei in the human brain: sex differences and age-dependent changes.

The size, shape and cellular morphology of the suprachiasmatic (SCN) and paraventricular nuclei (PVN) in the human hypothalamus were examined in relation to sex and age. In both nuclear regions the following parameters were determined: length of the rostrocaudal axis, maximum cross sectional area, volume, numerical cell density, total number of cells and the diameter of cell nuclei. No sexual difference was observed in any of these parameters, either in the SCN or in the PVN, with the exception of a sexual dimorphism in the shape of the SCN. In contrast to the absolute measurements, sexual differences were found in the internal structural organisation of these hypothalamic nuclei using multivariate regression analysis. Of the parameters measured only the volume of the SCN in females showed a continuous decrease with ageing, whereas the changes in the other variables were not consistent. Regression analysis revealed that this decrease in SCN volume is mainly caused by cell loss rather than by a reduction in cell size. Finally, a comparison of the volumetric measurements of the human SCN and PVN with those of the rat showed that the human SCN is reduced in size relative to other hypothalamic nuclei. Possible consequences of this phenomenon for the functional significance of the SCN in man are discussed.