Sex differences in the hypothalamus in the different stages of human life☆
Section snippets
Structural sex differences
Structural sex differences have been reported in a number of human hypothalamic nuclei ([95]; Fig. 1, Fig. 2) but the data from these studies are still controversial. Sex difference in the sexually dimorphic nucleus of the preoptic area (SDN-POA) that was first described in the rat by Gorski et al. [41] and is three to eight times larger in male rats than in female rats, is so evident that it can even be observed with the naked eye in Nissl-stained sections. We have found a sexually dimorphic
Development and sexual differentiation
Sexual dimorphism does not seem to be present in the human SDN-POA at the time of birth. At that moment, total cell numbers are still similar in boys and girls and the SDN-POA contains no more than some 20% of the total cell number found between 2 and 4 years of age. From birth up to this age, cell numbers increase equally rapidly in both sexes (Fig. 6). A sex difference in the SDN-POA does not occur until about the fourth year postnatally, when cell numbers start to decrease in girls, whereas
Sex differences in sleep
The sex difference in the shape of the vasopressinergic SCN and in VIP-expressing cell numbers [93], [101], [117] suggest the possibility of sex differences in circadian patterns. Moreover, in the human SCN, nuclear androgen receptor staining was more apparent in men than in women [34], while ERα and β staining was more pronounced in women [61], which also pointed to functional sex differences in this nucleus. Indeed, sex differences have been reported in sleep patterns that may be related to
Aging and sex differences
The sexually dimorphic pattern in aging of the SDN-POA has been discussed above.
In the mediobasal hypothalamus of aged subjects, a striking sex difference has been reported in neurofibrillary pathology associated with abnormally phosphorylated tau protein. The pathology in the median eminence and infundibular nucleus is characterized by a dense network of large dystrophic neurites with neurofibrillary tangles that are interspersed among them. The terminal-like processes contact the neurohaemal
Functional sex differences in the hypothalamus as revealed from postmortem tissue
Males have higher vasopressin levels than females, even though the number of vasopressin neurons in the supraoptic nucleus (SON) did not differ between men and women [91], [110]. This sex difference is explained by the higher activity we found in vasopressin neurons in the SON of young males as compared to females using the size of the Golgi apparatus as a measure for neuronal activity. In the course of aging, possibly triggered by the decrease in estrogen levels in postmenopausal women, the
Transsexuality and other gender identity problems
Transsexuality is a rare condition. The annual incidence of transsexuality in Sweden has been estimated to be 0.17 per 100,000 inhabitants. The sex ratio (genetic male:female) varies from country to country between 1.4:1 and 3:1 [37], [64]. There is only little information about the factors that may influence gender and cause transsexuality in humans (Table 2).
The disparate maternal aunt–uncle ratio in transsexual men has been hypothesized to be due to genomic imprinting [43]. There are only a
Homosexuality
Sexual orientation is influenced by quite a number of genetic as well as non-genetic factors (Table 2). Genetic factors appear from studies in families, twins and through molecular genetics [9], [10], [47], [51], [57], [78], [107]. Hamer and co-workers found linkage between DNA markers on the X-chromosome and male sexual orientation. Genetic linkage between the microsatellite markers on the X chromosome, i.e. Xq28, was detected for the families of gay males, but not for the families of lesbians
Acknowledgements
We would like to thank Ms. T. Eikelboom and Ms. W.T.P. Verweij for their excellent secretarial work. Brain material was obtained from the Netherlands Brain Bank (coordinator Dr. R. Ravid). Financial support was obtained from the Ter Meulen Fund, Hersenstichting Nederland, KNAW, Internationale Stichting Alzheimer Onderzoek, and NWO.
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Proceedings of the International Health Foundation on The Brain and Behavior in Different Stages of Life, April 18–19.