Graduate School Neurosciences Amsterdam, The Netherlands Institute for Brain Research. F.Kruijver@nih.knaw.nl
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.
Sex differences in androgen receptors of the human mamillary bodies are related to endocrine status rather than to sexual orientation or transsexuality.
Kruijver FP, Fernandez-Guasti A, Fodor M, Kraan EM, Swaab DF.
Graduate School of Neurosciences, Netherlands Institute for Brain Research, 1105 Amsterdam, The Netherlands. email@example.com
In a previous study we found androgen receptor (AR) sex differences in several regions throughout the human hypothalamus. Generally, men had stronger nuclear AR immunoreactivity (AR-ir) than women. The strongest nuclear labeling was found in the caudal hypothalamus in the mamillary body complex (MBC), which is known to be involved in aspects of cognition and sexual behavior. The present study was carried out to investigate whether the sex difference in AR-ir of the MBC is related to sexual orientation or gender identity (i.e. the feeling of being male or female) or to circulating levels of androgens, as nuclear AR-ir is known to be up-regulated by androgens. Therefore, we studied the MBC in postmortem brain material from the following groups: young heterosexual men, young homosexual men, aged heterosexual castrated and noncastrated men, castrated and noncastrated transsexuals, young heterosexual women, and a young virilized woman. Nuclear AR-ir did not differ significantly between heterosexual and homosexual men, but was significantly stronger than that in women. A female-like pattern of AR-ir (i.e. no to weak nuclear staining) was observed in 26- to 53-yr-old castrated male-to-female transsexuals and in old castrated and noncastrated men, 67--87 yr of age. In analogy with animal studies showing strong activational effects of androgens on nuclear AR-ir, the present data suggest that nuclear AR-ir in the human MBC is dependent on the presence or absence of circulating levels of androgen. The group data were, moreover, supported by the fact that a male-like AR-ir (i.e. intense nuclear AR-ir) was found in a 36-yr-old bisexual noncastrated male-to-female transsexual and in a heterosexual virilized woman, 46 yr of age, with high levels of circulating testosterone. In conclusion, the sexually dimorphic AR-ir in the MBC seemed to be clearly related to circulating levels of androgens and not to sexual orientation or gender identity. The functional implications of these alterations are discussed in relation to reproduction, cognition, and neuroprotection.
PMID: 11158052 [PubMed - indexed for MEDLINE]
See that so important paper, about two androgen insensitivity syndromes, one more hard, that caused an intersex genital situation (PAIS) and the other, no genital signs of strong problems (the genitals were male, but small). That MAIS situation (mild insensitivity) may sometimes be the cause of micropenis and transsexual gender dysphorias. That is one example of micropenis....and we dont know nothing if there was also a GID. You may read the FREE FULL PAPER !!!!! Click on the button below!
Discordant measures of androgen-binding kinetics in two mutant androgen receptors causing mild or partial androgen insensitivity, respectively.
Lady Davis Institute for Medical Research, Sir M. B. Davis-Jewish General Hospital, Montreal, Quebec, Canada.
We have characterized two different mutations of the human androgen receptor (hAR) found in two unrelated subjects with androgen insensitivity syndrome (AIS): in one, the external genitalia were ambiguous (partial, PAIS); in the other, they were male, but small (mild, MAIS). Single base substitutions have been found in both individuals: E772A in the PAIS subject, and R871G in the MAIS patient. In COS-1 cells transfected with the E772A and R871G hARs, the apparent equilibrium dissociation constants (Kd) for mibolerone (MB) and methyltrienolone are normal. Nonetheless, the mutant hAR from the PAIS subject (E772A) has elevated nonequilibrium dissociation rate constants (k(diss)) for both androgens. In contrast, the MAIS subject's hAR (R871G) has k(diss) values that are apparently normal for MB and methyltrienolone; in addition, the R871G hAR's ability to bind MB resists thermal stress better than the hAR from the PAIS subject. The E772A and R871G hARs, therefore, confer the same pattern of discordant androgen-binding parameters in transfected COS-1 cells as observed previously in the subjects' genital skin fibroblasts. This proves their pathogenicity and correlates with the relative severity of the clinical phenotype. In COS-1 cells transfected with an androgen-responsive reporter gene, trans-activation was 50% of normal in cells containing either mutant hAR. However, mutant hAR-MB binding is unstable during prolonged incubation with MB, whereas normal hAR-MB binding increases. Thus, normal equilibrium dissociation constants alone, as determined by Scatchard analysis, may not be indicative of normal hAR function. An increased k(diss) despite a normal Kd for a given androgen suggests that it not only has increased egress from a mutant ligand-binding pocket, but also increased access to it. This hypothesis has certain implications in terms of the three-dimensional model of the ligand-binding domain of the nuclear receptor superfamily.
PMID: 10022458 [PubMed - indexed for MEDLINE]
See those wonderfull Abstracts,
about human hypothalamus sex and gender differentiation. Click on RELATED ARTICLES and see!
Graduate School Neurosciences Amsterdam, Netherlands Institute for Brain Research,
Meibergdreef 33, Amsterdam, 1105 AZ The Netherlands. firstname.lastname@example.org
Sex differences in the brain may be the basis not only for sex differences in reproduction, gender
identity (the feeling of being male or female), and sexual orientation (heterosexuality vs
homosexuality), but also for the sex difference in prevalence of psychiatric and neurological
diseases ( Swaab and Hofman, 1995 ). In this brief article we discuss a few examples of structural
and functional sex differences in the human brain. Copyright 2001 Academic Press.
PMID: 11534968 [PubMed - indexed for MEDLINE]
1: Adv Exp Med Biol. 2002;511:75-100; discussion 100-5.
Swaab DF, Chun WC, Kruijver FP, Hofman MA, Ishunina TA.
Graduate School Neurosciences Amsterdam, Netherlands Institute for Brain Research, Meibergdreef 33, 1105 AZ Amsterdam, The Netherlands.
Functional sex differences in reproduction, gender and sexual orientation and in the incidence of neurological and psychiatric diseases are presumed to be based on structural and functional differences in the hypothalamus and other limbic structures. Factors influencing gender, i.e., the feeling to be male or female, are prenatal hormones and compounds that change the levels of these hormones, such as anticonvulsants, while the influence of postnatal social factors is controversial. Genetic factors and prenatal hormone levels are factors in the determination of sexual orientation, i.e. heterosexuality, bisexuality or homosexuality. There is no convincing evidence for postnatal social factors involved in the determination of sexual orientation. The period of overt sexual differentiation of the human hypothalamus occurs between approximately four years of age and adulthood, thus much later than is generally presumed, although the late sexual differentiation may of course be based upon processes that have already been programmed in mid-pregnancy or during the neonatal period. The recently reported differences in a number of structures in the human hypothalamus and adjacent structures depend strongly on age. Replication of these data is certainly necessary. Since the size of brain structures may be influenced by premortem factors (e.g. agonal state) and postmortem factors (e.g. fixation time), one should not only perform volume measurements, but also estimate a parameter that is not dependent on such factors as, i.e., total cell number of the brain structure in question. In addition, functional differences that depend on the levels of circulating hormones in adulthood have been observed in several hypothalamic and other brain structures. The mechanisms causing sexual differentiation of hypothalamic nuclei, the pre- and postnatal factors influencing this process, and the exact functional consequences of the morphological and functional hypothalamic differences await further elucidation.
PMID: 12575757 [PubMed - indexed for MEDLINE]
New!!! See those important papers,
about how the early stress in our life (mainly mother's stress during gestation in
humans), may disturb our sexual behavior.
Early social stress in female guinea pigs induces a masculinization of adult behavior
and corresponding changes in brain and neuroendocrine function.
Behav Brain Res. 2003 Sep 15;144(1-2):199-210. PMID: 12946610 [PubMed - in process]
Implications of natural selection in shaping 99.4% nonsynonymous DNA identity between humans and chimpanzees: enlarging genus Homo. Proc Natl Acad Sci U S A. 2003 Jun 10;100(12):7181-8. Epub 2003 May 23. PMID: 12766228 [PubMed - indexed for MEDLINE]