AGE AND SEX DO NOT AFFECT THE VOLUME, CELL NUMBERS, OR CELL-SIZE OF THE SUPRACHIASMATIC NUCLEUS OF THE RAT - AN UNBIASED STEREOLOGICAL STUDY

The circadian rhythms displayed by numerous biological functions are k nown to be sex specific and affected by aging. It has not been settled yet whether the sex- and age-related characteristics of circadian rhy thms derive from changes in the anatomy of the suprachiasmatic nucleus . To shed light on these issues, we applied unbiased stereological tec hniques to estimate the volume of the suprachiasmatic nucleus as well as the total number of its cells and the mean volume of their somata a nd nuclei in progressively older groups of male and female Wistar rats (aged 1, 6, 12, 18, 24, and 30 months). The volume of the nucleus was estimated with the Cavalieri principle on serial sections. The total numbers of neurons and astrocytes were estimated by applying the optic al fractionator, and the mean somatic and nuclear volumes of cells wer e estimated by using isotropic, uniform random sections and the nuclea tor method. On average, the volume of the suprachiasmatic nucleus was 0.044 mm(3), and the total number of neurons and astrocytes was 17,400 . Cells of the dorsomedial and ventrolateral components of the nucleus , which are morphologically different, have identical mean perikaryal and nuclear volumes, which we estimated to be 750 mu m(3) and 400 mu m (3), respectively. We further demonstrated that, at all ages analysed, the volume of the suprachiasmatic nucleus, the total cell number, and the mean somatic and nuclear volumes of its cells are affected neithe r by the age nor by the sex of the animal, regardless of the presence of sex- and age-related variations in circadian rhythms. However, the possibility that females may display changes in the volume of the supr achiasmatic nucleus at older ages cannot be ruled out. No effect of ag ing was observed in the total number of neurons or in the total number of astrocytes. (C) 1995 Wiley-Liss, Inc.