Male-to-Female Transsexuals Have Female Neuron Numbers in a Limbic Nucleus

Abstract

Transsexuals experience themselves as being of the opposite sex, despite having the biological characteristics of one sex. A crucial question resulting from a previous brain study in male-to-female transsexuals was whether the reported difference according to gender identity in the central part of the bed nucleus of the stria terminalis (BSTc) was based on a neuronal difference in the BSTc itself or just a reflection of a difference in vasoactive intestinal polypeptide innervation from the amygdala, which was used as a marker. Therefore, we determined in 42 subjects the number of somatostatin-expressing neurons in the BSTc in relation to sex, sexual orientation, gender identity, and past or present hormonal status. Regardless of sexual orientation, men had almost twice as many somatostatin neurons as women (P < 0.006). The number of neurons in the BSTc of male-to-female transsexuals was similar to that of the females (P = 0.83). In contrast, the neuron number of a female-to-male transsexual was found to be in the male range. Hormone treatment or sex hormone level variations in adulthood did not seem to have influenced BSTc neuron numbers. The present findings of somatostatin neuronal sex differences in the BSTc and its sex reversal in the transsexual brain clearly support the paradigm that in transsexuals sexual differentiation of the brain and genitals may go into opposite directions and point to a neurobiological basis of gender identity disorder.

Regional volumes and spatial volumetric distribution of gray matter in the gender dysphoric brain

“…Postmortem studies have observed sex-atypical volumes and neuronal numbers in hypothalamic nuclei in the brains of individuals with GD (Garcia-Falgueras and Swaab, 2008;Kruijver et al, 2000;Zhou et al, 1995). Brain structure in individuals with GD has also been investigated in vivo.…”

Sexual Differentiation of the Bed Nucleus of the Stria Terminalis in Humans May Extend into Adulthood

“…Clear anatomical sex differences have also been described in the human bed nucleus of the stria terminalis (BST). The darkly staining posteromedial component of the BST (BST-dspm) and the central subdivision of the BST (BSTc) are both larger in men than in women (Allen and Gorski, 1990;Zhou et al, 1995;Kruijver et al, 2000). Differences in the size of the human BSTc have been related to the gender identity disorder transsexuality, in which subjects voice the strong feeling of being born in the wrong sex.…”

Where medicine meets the boundaries of manhood and womanhood

“…[18][19][20] This observation was refined, and it could further be shown that the one brain of a female-to-male transsexual available for post-mortem examination showed a male differentiation of the bed nucleus of the stria terminalis. 20 This finding of a biological index of female brain differentiation in male-to-female transsexuals could mark a conceptual turning point in the approach to transsexualism.…”