SEXUAL DIMORPHISMSSEXUAL DIMORPHISMSININ

HUMAN BRAINHUMAN BRAIN(Swaab et al., Hormones and Behavior, 2001(Swaab et al., Hormones and Behavior, 2001

Problems to study humansProblems 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 featuresGeneral features

Woman

• Weight: 1171 gr

• 19 mil of neurons

• Higher cerebral metabolism

• Higher linguistic capacities

Man

• Weight: 1308 gr

• 23 mil of neurons

• Higher cerebral volume in childrens

• Higher serotonin synthesis (+53%)

Sexual dimorphism according to SwaabSexual dimorphism according to Swaab

.

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--

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VO

LUM

E

MALE

FEMALE

10-

40

41-

70

71-

100

YEARS

SEXUALLY DIMORPHIC NUCLEUSIN THE HUMAN HYPOTHALAMUS(Swaab and Fliers, 1985)

SDN

SDN

SDN

Sexual dimorphism according to GorskySexual dimorphism according to Gorsky

SEXUALLY DIMORPHIC CELL GROUPS (INAH 3 and 2)IN THE HUMAN HYPOTHALAMUS

Allen et al., 1989

2

33 3

Sexually dimorphic nucleiof the human hypothalamus

Allen et al., 1989 Swaab and Fliers, 1985

Differences in volume

Sexually dimorphic nucleiof the human hypothalamus

Allen et al., 1989 Swaab and Fliers, 1985

Differences in volume

ComparisonComparison

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 orientationDimorphism of INAH in relation to gender and sexual orientation

Individuals who died of complications of AIDSIndividuals who died of causes other than AIDSAn individual who was a bisexual man and died of AIDS

(Le Vay, Science 1991)

INAH 3 > in heterosexual menINAH 3 > in heterosexual menHomosexual men INAH 3 = Women INAH 3Homosexual men INAH 3 = Women INAH 3INAH 3 is dimorphic with sexual orientation INAH 3 is dimorphic with sexual orientation The sexual orientation has a biological The sexual orientation has a biological substratesubstrate

ComparisonComparison

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 orientationDimorphism of INAH in relation to gender and sexual orientation

Individuals who died of complications of AIDSIndividuals who died of causes other than AIDSAn individual who was a bisexual man and died of AIDS

(Le Vay, Science 1991)

INAH 3 > in heterosexual menINAH 3 > in heterosexual menHomosexual men INAH 3 = Women INAH 3Homosexual men INAH 3 = Women INAH 3INAH 3 is dimorphic with sexual orientation INAH 3 is dimorphic with sexual orientation The sexual orientation has a biological The sexual orientation has a biological substratesubstrate

Dimorphism in relation to gender and sexual orientationDimorphism in relation to gender and sexual orientation

SDN-POASDN-POASuprachiasmatic nucleusSuprachiasmatic nucleusSwaab et al, Progr Brain Res, 1992

VOLUMEVOLUME

Dimorphism in relation to gender and sexual orientationsDimorphism in relation to gender and sexual orientations

Suprachiasmatic nucleusSuprachiasmatic nucleus SDN-POASDN-POA

The nucleus The nucleus of the Stria of the Stria TerminalisTerminalis

The nucleus of the stria terminalis (BST) may be easily identifyed by means of Somatostatin 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

The BST volume is reflecting the sexual orientation rather than the genetic sex.

men women

Homosexual men transsexual men

The nucleus The nucleus of the Stria of the Stria TerminalisTerminalis

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

The BST volume is reflecting the sexual orientation rather than the genetic sex.

menwomen

Homosexual men transsexual men

Man

Woman

Oxytocin neurons in Oxytocin neurons in the human SONthe human SON

Oxytocin neurons do not shown any difference