Arcuate nucleus of the hypothalamus: Effects of age and sex

Abstract

The arcuate nucleus of the hypothalamus (ARN) is involved in a variety of functions known to be sexually dimorphic and altered by aging. Although the effects of sex and age on the synaptic organization and neurochemistry of the ARN have been extensively analyzed, data regarding sex-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 are controversial. To address this issue, we have quantitatively analyzed the ARN of male and female Wistar rats aged 6 and 24 months. The optical fractionator, the optical rotator, and the Principle of Cavalieri were used as the estimators of the total number of neurons, mean nuclear volume of ARN neurons, and volume of the ARN, respectively. In addition, a Golgi study was carried out to analyze the dendritic trees of its neurons. We found that in young adult rats, the volume of the ARN is 0.9 mm3 in males and 0.7 mm3 in females, whereas the total number 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, which we estimated to be 300 microm3. 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 branching density and the spine density were greater in females than in males. In aged rats there was a significant reduction in the number of dendritic 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 that neither of these parameters is altered by aging. Conversely, aging induces regressive changes in the dendritic arborizations of ARN neurons of males and females and abolishes the sexual dimorphic pattern of their organization.

Sex differences in synaptic plasticity in stress-responsive brain regions following chronic variable stress

“…Previous studies support sexual dimorphisms in synaptic innervation, as females have a greater density of dendritic branching and spines in the arcuate nucleus of the hypothalamus [62] and more dendritic spines and axospinous synapses in the hippocampal subiculum [63]. Increased availability of post-synaptic structures support our findings that females may have increased pre-synaptic innervation in stress-related brain regions, and further implicate differences in brain organization in the sexual dimorphism of behaviors.…”

Sexually Dimorphic Neurons in the Ventromedial Hypothalamus Govern Mating in Both Sexes and Aggression in Males

“…The sex differences in PR expression cannot result solely from sex differences in neuronal numbers. Indeed, no sex difference in neuronal number has been reported in the basal forebrain or VMHvl, and in the POA and arcuate nucleus, which contain more neurons in males (Gorski et al, 1980; Leal et al, 1998), we find more PR+ neurons in females. Finally, the 3–4 fold more PR+ neurons in the male BNSTmpm and MeApd exceeds the <2-fold more neurons in these regions in males (Morris et al, 2008; Shah et al, 2004; Wu et al., 2009).…”

Stereologic Characterization of Bovine (Bos taurus) Cumulus-Oocyte Complexes Aspirated from Small Antral Follicles During the Diestrous Phase1

“…For future studies, the mixed criteria could be adopted for estimating the volumes of COCs, oocytes, and nuclei of oocytes. Based on our results and on the previous use of virtual points by other authors [37][38][39], our strategy of using only a virtual reference for estimating cumulus cell volume seems adequate for providing unbiased data.…”

“…However, such a substitution was recently discussed and advanced for another volume estimator, the spatial rotator [37]. The use of a virtual central point was also recently implemented using both the nucleator [38] and the rotator [39] for estimating the nuclear volume of neurones deprived of well-defined nucleoli and thus of identifiable physical points. However, in these studies no attempt was made to evaluate the potential bias caused by choosing a virtual point.…”