Age and sex do not affect the volume, cell numbers, or cell size of the suprachiasmatic nucleus of the rat: An unbiased stereological study

Abstract

The circadian rhythms displayed by numerous biological functions are known to be sex specific and affected by aging. It has not been settled yet whether the sex- and age-related characteristics of circadian rhythms derive from changes in the anatomy of the suprachiasmatic nucleus. To shed light on these issues, we applied unbiased stereological techniques to estimate the volume of the suprachiasmatic nucleus as well as the total number of its cells and the mean volume of their somata and 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 optical fractionator, and the mean somatic and nuclear volumes of cells were estimated by using isotropic, uniform random sections and the nucleator method. On average, the volume of the suprachiasmatic nucleus was 0.044 mm3, 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 microns3 and 400 microns3, 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 neither 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 suprachiasmatic nucleus at older ages cannot be ruled out. No effect of aging was observed in the total number of neurons or in the total number of astrocytes.

The role of androgen receptors in the masculinization of brain and behavior: What we've learned from the testicular feminization mutation

“…Regional volume and soma size of SDN-POA neurons are greater in male than in female rats (Gorski et al, 1980;Madeira et al, 1995), and perinatal hormone manipulations suggest that ERs, not ARs, are important in the masculinization of SDN-POA volume (Dohler et al, 1986). However, Tfm male rats show only a partial masculinization of the SDN-POA: volume is fully masculine but neuronal soma size is not, with Tfm males having smaller neurons in the SDN-POA than wt males .…”

“…The hippocampus is another sexually dimorphic area of the brain in which males show a greater overall volume than females (Madeira et al, 1995;Nunez et al, 2000). One area of the hippocampus, the dentate gyrus, is sexually dimorphic in some strains of mice in which males show a greater number, size, and density of cells within this region (Wimer and Wimer, 1984;Wimer et al, 1988;Wimer and Wimer, 1989).…”

“…Swaab and Hofman (1990) found the vasopressin subnucleus of the SCN of homosexual men to be 1.7 times as large and contain twice as many cells as that of heterosexual men. Studies of sex differences in the SCN of rats have yielded somewhat conflicting findings in which males have a greater SCN volume than females (Robinson et al, 1986;Gorski et al, 1978) or there were no differences (Madeira et al, 1995;Bloch and Gorski, 1988). These discrepancies suggest that sex differences in the rat SCN may either be small and/or strain dependent.…”

Aging in the circadian system: Considerations for health, disease prevention and longevity

“…Such age-related changes cannot be explained by cell death or atrophy in the SCN, as aging does not decrease cell size or numbers in the master pacemaker (Madeira et al, 1995). However, the aged SCN shows alterations in peptide expression (vasoactive intestinal polypeptide (VIP) (Kawakami et al, 1997); arginine vasopressin (AVP) (Roozendaal et al, 1987)), and a reduction in the amplitude of circadian rhythms of electrical activity (Satinoff et al, 1993;Watanabe et al, 1995).…”

Morphometry of ventral hippocampal neurons of CA1-CA4 fields in domestic cattle

“…W badaniach na dorosłych szczurach wykazano, że w wyniku procesu starzenia dochodzi do niejednakowej utraty liczby neuronów w różnych obszarach mózgowia, np. w podwzgórzu, w jądrze łukowatym (14). Na podstawie badań stereologicznych ludzkiego hipokampa wykazano spadek liczby neuronów w regionach podpory (subicular) oraz w DG, natomiast w polach CA1-CA2 i CA3 hipokampa nie zaobserwowano ich spadku (32--34).…”