ARCUATE NUCLEUS OF THE HYPOTHALAMUS - EFFECTS OF AGE AND SEX

The arcuate nucleus of the hypothalamus (ARN) is involved in a variety of functions known to be sexually dimorphic and altered by aging. Alt hough the effects of sex and age on the synaptic organization and neur ochemistry of the ARN have been extensively analyzed, data regarding s ex-related differences and age-induced effects on the total number of neurons and volume of the ARN in adult and aged male and female rats a re controversial. To address this issue, we have quantitatively analyz ed the ARN of male and female Wistar rats aged 6 and 24 months. The op tical fractionator, the optical rotator, and the Principle of Cavalier i were used as the estimators of the total number of neurons, mean nuc lear volume of ARN neurons, and volume of the ARN, respectively. In ad dition, a Golgi study was carried out to analyze the dendritic trees o f its neurons. We found that in young adult rats, the volume of the AR N is 0.9 mm(3) in males and 0.7 mm(3) in females, whereas the total nu mber of neurons is 100 x 10(3) in males and 86 x 10(3) in females. ARN neurons of males and females have identical mean nuclear volumes, whi ch we estimated to be 300 mu m(3). No significant effects of age were found in these parameters, both in males and in females. In adult rats , no sex-related differences were detected in the number of dendritic segments and in the total dendritic length, but the dendritic branchin g density and the spine density were greater in females than in males. In aged rats there was a significant reduction in the number of dendr itic segments, in the total dendritic length, and in the branching and spine densities that, although evident in both sexes, was more marked in females. Our results show that the total number of neurons and the volume of the ARN are sexually dimorphic in adult and aged rats and t hat neither of these parameters is altered by aging. Conversely, aging induces regressive changes in the dendritic arborizations of ARN neur ons of males and females and abolishes the sexual dimorphic pattern of their organization. (C) 1998 Wiley-Liss, Inc.