Subcortical gray matter changes in transgender subjects after long-term cross-sex hormone administration
Introduction
Sex-steroid hormones are involved in sexual differentiation, development and behaviour (Zubiaurre-Elorza et al., 2014) and play a pivotal role in the development and function of the central nervous system (Paus et al., 2010, Peper et al., 2009). They exert varied effects on the brain and the body and are thought to alter several processes related to cognition and emotion (Höfer et al., 2013, Toffoletto et al., 2014). For example, higher levels of progesterone and estradiol during pregnancy have been associated with a worsening of mood and an impairment of memory performance (Buckwalter et al., 1999, van Wingen et al., 2008). Studies also revealed an impact on emotional processing, as indicated by alterations in amygdala activation due to changing hormonal levels during the menstrual cycle (Derntl et al., 2008). These results were also substantiated by the fact that cognitive changes have been associated with hormonal contraceptive use. Specifically, performance changes on verbal memory, verbal fluency and on the mental rotation task in woman using oral contraceptives have been observed (Griksiene and Ruksenas, 2011).
Gonadal hormones either act as neuroactive steroids by modulating ligand-gated ion channels and G-protein coupled receptors or by binding to nuclear androgen (Beyenburg et al., 2000, Finley and Kritzer, 1999, Puy et al., 1995) and estrogen receptors (González et al., 2007, Montague et al., 2008, Osterlund et al., 2000a), directly influencing gene expression (Brinton et al., 2008, Rupprecht and Holsboer, 1999). These receptors have been detected in gray matter (GM) cortical areas as well as in subcortical structures (Fernández-Guasti et al., 2000, Finley and Kritzer, 1999, Kruijver et al., 2002, Osterlund et al., 2000b, Puy et al., 1995).
Animal studies already indicated influences of sex-steroid exposure on brain morphology. In this regard, hippocampal synaptic plasticity and neurogenesis in rodents after testosterone and estrogen administration has been observed (Galea et al., 2006, Gould et al., 1990, MacLusky et al., 2006).
In addition, sex hormones influence neural development during puberty and in the adult human brain. For example, increasing levels of circulating testosterone during puberty in boys indicate a contribution to sex differences in the amygdala and hippocampus region during adolescence (Neufang et al., 2009). It was further shown that circulating sex hormones were related to GM structures in several areas of the brain, indicating an influence of steroid hormones on brain morphology in the human brain (Witte et al., 2010).
Treatment studies involving humans are scarce, due to ethical and methodological reasons. However, a unique model to study the influence of long-term high-dose sex-steroid hormone treatment onto the living human brain can be achieved by the investigation of Female-to-Male (FtM) and Male-to-Female (MtF) transgender people. These subjects are characterized by strong and persistent cross-gender identification, experience an incongruency between their biological sex and their gender identity, finally seeking hormonal treatment and in some cases sex reassignment surgery (Bao and Swaab, 2011).
First evidence for a putative influence of cross-sex hormone treatment on brain structures in transgender subjects was observed in post-mortem studies. It was shown that the bed nucleus of the stria terminalis of the hypothalamus was of female size in MtFs and of male size in one observed FtM subject, which may have been attributable to cross-sex hormone administration (Kruijver et al., 2000, Zhou et al., 1995). So far, only two studies have investigated the influence of long-term high-dose cross-sex hormone treatment on gray matter brain morphology in FtM and MtF transgender individuals in vivo. Pol et al. showed that testosterone in FtM subjects increased total brain volume and the hypothalamus, whereby estrogens and anti-androgens in MtF subjects led to decreases in brain volume and to an increase in the ventricles. Authors concluded that testosterone led to masculinization, whereby estradiol and anti-androgens to feminization of the brain (Pol et al., 2006). However, sample size was rather small, with only 8 MtF and 6 FtM transgender participants and a limited number of brain structures have been evaluated. Detailed results were delivered by a more recent study, where it was shown that testosterone therapy increases cortical thickness in FtM subjects (Zubiaurre-Elorza et al., 2014). The thickening in cortical regions was associated with changes in testosterone levels. On the other hand, estrogens and anti-androgen therapy in MtFs was associated with a decrease in cortical thickness. But also subcortical structures were affected in the form of GM increases in the thalamus after testosterone administration and decreases in the thalamus as well as in the pallidum due to estradiol and anti-androgen treatment. Interestingly, also an enlargement of the ventricles was observed in the MtF cohort.
Taken together, studies on the influence of sex hormones in transgender individuals are scarce and limited by small sample sizes. Moreover, only uncorrected results have been reported so far in the literature. Here, we used the longitudinal processing stream implemented in FreeSurfer to increase statistical power by reducing the confounding effect of between-subject variability. Based on prior observations, we expected GM decreases due to estradiol and anti-androgen treatment and testosterone induced increases in gray matter structures, while for ventricular structures the opposite effect is expected.
Section snippets
Subjects
29 FtM and 21 MtF transgender participants underwent MRI assessment after the screening phase. However, 4 FtM (mean age ± SD = 28.5 ± 7.2) and 7 MtF (32.8 ± 10.0) subjects had to be excluded due to early study termination after the first measurement or movement artefacts during scanning. Hence, structural brain changes of 25 FtM (27.1 ± 6.0) and 14 MtF (26.9 ± 6.1) transgender participants were finally analysed in this longitudinal study. The second measurement was carried out at least after 4 months of
Study sample and scanning intervals
The transgender subjects (4 FtM, 7 MtF) excluded due to early study termination after the first measurement or movement artefacts during scanning did not differ significantly in terms of age compared to the final study sample (t-test; p > 0.05). The larger inter-scan variability of the FtM cohort compared to the MtF group was mainly driven by one of the 25 FtM participants. The re-analysis of the data excluding this participant did not change the main findings. As control subjects did not receive
Discussion
The analysis of brain structures in MtF subjects, receiving estradiol and anti-androgen treatment for a period of at least 4 months, revealed GM decreases in the right hippocampus and increases in the ventricular system (corr.). Our results are generally in line with previous studies investigating transgender participants, where estradiol and anti-androgens mainly induced decreases, while testosterone led to increases in subcortical brain areas after cross-sex hormone administration (Pol et
Conclusion
This study delivers evidence that cross-sex hormone therapy in transgender individuals leads to changes in subcortical brain areas. We showed that estradiol and anti-androgen treatment in MtF participants induced decreases in the hippocampus, while increases in the ventricles have been observed. While prior studies were limited by small sample sizes or presented uncorrected results, here we were able to show gray matter changes, corrected for multiple testing. Due to the use of the longitudinal
Conflict of interest
Without any relevance to this work, S. Kasper declares that he has received grant/research support from Bristol-Myers Squibb, Eli Lilly, GlaxoSmithKline, Lundbeck, Organon, Sepracor, and Servier; has served as a consultant or on advisory boards for AstraZeneca, Bristol-Myers Squibb, Eli Lilly, GlaxoSmithKline, Janssen, Lundbeck, Merck Sharp and Dome, Novartis, Organon, Pfizer, Schwabe, Sepracor, and Servier; and has served on speakers’ bureaus for Angelini, AstraZeneca, Bristol-Myers Squibb,
Contributors
R.L. and S.K. designed the study and R.Se., G.S.K., A.Ha. and R.L. wrote the manuscript. Authors A.K. and C.K. managed the literature searches and analyses. C.W., R.Sl., A.Hu. and M.W. performed the measurements. Authors R.Se., A.Ha., G.S.K. and S.G. undertook the statistical analysis, and R.Se. wrote the first draft of the manuscript. All authors contributed to and have approved the final manuscript.
Role of the funding source
This research was supported by the grant, Interdisciplinary translational brain research cluster (ITHC) with highfield MR’ from the Federal Ministry of Science, Research and Economy (BMWFW), Austria and by a grant of the Austrian Science Fund (FWF P23021) to R. Lanzenberger.
Acknowledgements
This scientific project was performed with the support of the Medical Imaging Cluster of the Medical University of Vienna.
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