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SEXUAL DIMORPHISMS IN HUMAN BRAIN (Swaab et al., Hormones and Behavior, 2001 Problems to study humans • Use of bioptic material • No possibility of having homogenous groups • Difficulties to find the clinical history • Presence of brain pathologies • The legal period for autopsy is depending by the local laws (in Italy 48 hours postmortem, in Netherlands 8 hours) General features Woman Man • Weight: 1171 gr • Weight: 1308 gr • 19 mil of neurons • 23 mil of neurons • Higher cerebral metabolism • Higher cerebral volume in childrens • Higher linguistic capacities • Higher serotonin synthesis (+53%) Sexual dimorphism according to Swaab Sexual dimorphism according to Gorsky Sexually dimorphic nuclei of the human hypothalamus Differences in volume Allen et al., 1989 Swaab and Fliers, 1985 Comparison SDN-POA • volume 2.2 higher in man than in woman • Cell number about 2 times higher in man INAH • INAH1 8% > in HIV+ • INAH2 volume 2 times higher in man • INAH3 volume 3 times in man • INAH4 no dimorphism Development and sexual differentiation of the SDN-POA Cell number reach a peak value around 2-4 years postnatally, after which a sexual differentiation occurs due to a reduction in cell number in females, whereas cell number in males remains approximately unchanged up to age of 50 years (Hofman and Swaab, Exp Clin Endocrinol, 1991) Dimorphism of INAH in relation to gender and sexual orientation Individuals who died of complications of AIDS Individuals who died of causes other than AIDS An individual who was a bisexual man and died of AIDS (Le Vay, Science 1991) INAH 3 > in heterosexual men Homosexual men INAH 3 = Women INAH 3 INAH 3 is dimorphic with sexual orientation The sexual orientation has a biological substrate Comparison SDN-POA • volume 2.2 higher in man than in woman • Cell number about 2 times higher in man INAH • INAH1 8% > in HIV+ • INAH2 volume 2 times higher in man • INAH3 volume 3 times in man • INAH4 no dimorphism Dimorphism of INAH in relation to gender and sexual orientation Individuals who died of complications of AIDS Individuals who died of causes other than AIDS An individual who was a bisexual man and died of AIDS (Le Vay, Science 1991) INAH 3 > in heterosexual men Homosexual men INAH 3 = Women INAH 3 INAH 3 is dimorphic with sexual orientation The sexual orientation has a biological substrate Dimorphism in relation to gender and sexual orientation VOLUME Suprachiasmatic nucleus Swaab et al, Progr Brain Res, 1992 SDN-POA Dimorphism in relation to gender and sexual orientations Suprachiasmatic nucleus SDN-POA The nucleus of the Stria Terminalis The nucleus of the stria terminalis (BST) may be easily identifyed by means of Somatostatin distribution. men Homosexual men women transsexual men • Larger volume in men (a) than in women (b) • In homosexual men (c) the volume is similar to that of normal men • In transsexual men with female orientation (d) the nucleus has a volume similar to that of women The BST volume is reflecting the sexual orientation rather than the genetic sex. The nucleus of the Stria Terminalis men women The nucleus of the stria terminalis (BST) may be easily identifyed by means of VIP distribution. • Larger volume in men (a) than in women (b) • In homosexual men (c) the volume is similar to that of normal men • In transsexual men with female orientation (d) the nucleus has a volume similar to that of women Homosexual men transsexual men The BST volume is reflecting the sexual orientation rather than the genetic sex. Man Oxytocin neurons in the human SON Woman Oxytocin neurons do not shown any difference