Cerebral serotonin transporter asymmetry in females, males and male-to-female transsexuals measured by PET in vivo
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The serotonergic system modulates brain functions that are considered to underlie affective states, emotion and cognition. Several lines of evidence point towards a strong lateralization of these mental processes, which indicates similar asymmetries in associated neurotransmitter systems. Here, our aim was to investigate a potential asymmetry of the serotonin transporter distribution using positron emission tomography and the radioligand [11C]DASB in vivo. As brain asymmetries may differ between sexes, we further aimed to compare serotonin transporter asymmetry between females, males and male-to-female (MtF) transsexuals whose brains are considered to be partly feminized. Voxel-wise analysis of serotonin transporter binding in all groups showed both strong left and rightward asymmetries in several cortical and subcortical structures including temporal and frontal cortices, anterior cingulate, hippocampus, caudate and thalamus. Further, male controls showed a rightward asymmetry in the midcingulate cortex, which was absent in females and MtF transsexuals. The present data support the notion of a lateralized serotonergic system, which is in line with previous findings of asymmetric serotonin-1A receptor distributions, extracellular serotonin concentrations, serotonin turnover and uptake. The absence of serotonin transporter asymmetry in the midcingulate in MtF transsexuals may be attributed to an absence of brain masculinization in this region.
KeywordsSerotonin transporter Cerebral asymmetry Lateralization Gender dysphoria Transsexual
This research was funded by Austrian National Bank Grant P 13214 (to R. L.) and P 13675 (to M.M.). A. Hahn is a recipient of a DOC fellowship of the Austrian Academy of Sciences at the Department of Psychiatry and Psychotherapy. The authors are especially grateful to all transsexual subjects for participating in this study and to the clinical staff at the PET centre, the Department of Psychiatry and Psychotherapy for their technical and medical support and to Marie Spies for linguistic support.
Conflict of interest
The authors declare no conflict of interest related to this work.
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