Effects of Adult Female Rat Androgenization on Brain Morphology and Metabolomic Profile

Testosterone administration affects 1H-MRS metabolite spectra in transgender men

BACKGROUND

Recently, a variety of studies using different neuroimaging techniques attempted to identify the existence of a brain endophenotype in people with gender dysphoria (GD). However, despite mounting neuroimaging work, brain gender differences and effects of gender-affirming hormone therapy (GAHT) at the metabolite level remain understudied.

METHODS

Thirty-one transgender men (TM) before and after testosterone administration (7.7 months ± 3.5 months), relative to 30 cisgender men (CM) and 35 cisgender women (CW) underwent magnetic resonance spectroscopy (1H-MRS) at two time points. Two brain regions were assessed, i.e. the lateral parietal cortex and the amygdala/anterior hippocampus. Associated metabolites that were measured include N-acetyl aspartate (NAA), creatine (Cr), choline (Cho), glutamate and glutamine (Glx), myo-inositol (mI), glycine (Gly) and their respective ratios.

RESULTS

A critical time by group interaction revealed an effect of GAHT in the lateral parietal cortex of TM. MI+Gly/Cr ratios decreased upon initiation of GAHT. In addition, NAA/Cr and Cho/Cr ratios were lower in CW when compared to CM in the lateral parietal cortex. Glx levels and Glx/Cr ratios in TM differed from those in CW in the amygdala/anterior hippocampus. Interestingly, pubertal age of onset of gender dysphoria (i.e. GD) in TM differentially affected testosterone-mediated effects on Cr concentration and NAA/Cr ratios when compared to childhood and adult GD onset in the amygdala/anterior hippocampus.

CONCLUSION

This 1H-MRS study demonstrated that testosterone administration shifts mI+Gly/Cr ratios in the parietal cortex. In the amygdala/anterior hippocampus, modulation of metabolite concentrations by age of onset of GD is suggestive for a possible developmental trend.

Genetic and Epigenetic Sexual Dimorphism of Brain Cells during Aging

In recent years, much of the attention paid to theoretical and applied biomedicine, as well as neurobiology, has been drawn to various aspects of sexual dimorphism due to the differences that male and female brain cells demonstrate during aging: (a) a dimorphic pattern of response to therapy for neurodegenerative disorders, (b) different age of onset and different degrees of the prevalence of such disorders, and (c) differences in their symptomatic manifestations in men and women. The purpose of this review is to outline the genetic and epigenetic differences in brain cells during aging in males and females. As a result, we hereby show that the presence of brain aging patterns in males and females is due to a complex of factors associated with the effects of sex chromosomes, which subsequently entails a change in signal cascades in somatic cells.

Gender-affirming hormonal treatment changes neural processing of emotions in trans men: An fMRI study

BACKGROUND

Some transgender people desire a transition through gender-affirming hormone treatment (GAHT). To date, it is unknown how GAHT changes emotion perception in transgender people.

METHODS

Thirty transgender men (TM), 30 cisgender men (CM), and 35 cisgender women (CW) underwent 3 Tesla functional magnetic resonance imaging (fMRI) while passively viewing emotional faces (happy, angry, surprised faces) at two timepoints (T0 and T1). At T0 all participants were hormone-naïve, while TM immediately commenced testosterone supplementation at T0. The second scanning session (T1) occurred after 6-10 months of GAHT in TM. All 3 groups completed both T0 and T1 RESULTS: GAHT in TM shifted the neural profile whilst processing emotions from a sex-assigned at birth pattern at T0 (similar to CW) to a consistent with gender identity pattern at T1 (similar to CM). Overall, the brain patterns stayed the same for the cis people at T0 and T1.

CONCLUSIONS

These findings document the impact of hormone treatment, and testosterone supplementation specifically, on emotion perception in TM.

Estradiol Replacement as a Potential Enhancer of Working Memory and Neuroplasticity in Hypogonadal Trans Women

INTRODUCTION

The cognitive effects of cross-sex hormone therapy (CSHT) are not well understood. In cisgender individuals, sex hormone therapy can impact neurotransmitter levels and structural anatomy. Similarly, in gender-diverse persons, CSHT has been associated with neural adaptations, such as growth in brain structures resembling those observed in cisgender individuals of the same sex. Hormone-related changes in learning and memory, as seen in menopause, are associated with physiological hypogonadism or a decline in hormones, such as estradiol. The present study examined the effect of estradiol administration in humans on glutamate concentration in brain regions involved in semantic and working memory (i.e., the dorsolateral prefrontal cortex [DLPFC], the posterior hippocampus, and the pregenual anterior cingulate cortex) and its relationship with memory.

METHODS

Eighteen trans women (male biological sex assigned at birth) ceased CSHT for 30 days for a washout phase (t1) upon study enrollment to reach a hypogonadal state. Working and semantic memory, cognition, hormonal assays, and brain imaging were assessed. Participants resumed CSHT for 60 days for a replacement phase (t2), after which the same evaluations from t1 were repeated.

RESULTS

Estradiol increased among trans women after 60 days of resumed CSHT with significant improvements in semantic memory compared to the hypogonadal phase. Working memory recall was significantly and positively correlated to glutamate in the DLPFC during the reinstatement phase, although the relationship was not moderated by levels of estradiol.

DISCUSSION

These results may have clinical implications for the therapeutic effects of estradiol replacement, serving as a protective factor against cognitive decline and impairment for trans women post-gonadectomy.

The Effects of Testosterone on the Brain of Transgender Men

Transgender men (TM) experience an incongruence between the female sex assigned when they were born and their self-perceived male identity. Some TM seek for a gender affirming hormone treatment (GAHT) to induce a somatic transition from female to male through continuous administration of testosterone. GAHT seems to be relatively safe. However, testosterone produces structural changes in the brain as detected by quantitative magnetic resonance imaging. Mainly, it induces an increase in cortical volume and thickness and subcortical structural volume probably due to the anabolic effects. Animal models, specifically developed to test the anabolic hypothesis, suggest that testosterone and estradiol, its aromatized metabolite, participate in the control of astrocyte water trafficking, thereby controlling brain volume.

Characterization of the 1H-MRS Metabolite Spectra in Transgender Men with Gender Dysphoria and Cisgender People

Much research has been conducted on sexual differences of the human brain to determine whether and to what extent a brain gender exists. Consequently, a variety of studies using different neuroimaging techniques attempted to identify the existence of a brain phenotype in people with gender dysphoria (GD). However, to date, brain sexual differences at the metabolite level using magnetic resonance spectroscopy (1H-MRS) have not been explored in transgender people. In this study, 28 cisgender men (CM) and 34 cisgender women (CW) and 29 transgender men with GD (TMGD) underwent 1H-MRS at 3 Tesla MRI to characterize common brain metabolites. Specifically, levels of N-acetyl aspartate (NAA), choline (Cho), creatine (Cr), glutamate and glutamine (Glx), and myo-inositol + glycine (mI + Gly) were assessed in two brain regions, the amygdala-anterior hippocampus and the lateral parietal cortex. The results indicated a sex-assigned at birth pattern for Cho/Cr in the amygdala of TMGD. In the parietal cortex, a sex-assigned at birth and an intermediate pattern were found. Though assessed post-hoc, exploration of the age of onset of GD in TMGD demonstrated within-group differences in absolute NAA and relative Cho/Cr levels, suggestive for a possible developmental trend. While brain metabolite levels in TMGD resembled those of CW, some interesting findings, such as modulation of metabolite concentrations by age of onset of GD, warrant future inquiry.

Anabolic steroids and their effects of on neuronal density in cortical areas and hippocampus of mice

Anabolic substances have been increasingly used by bodybuilders and athletes with the goal of improving performance and aesthetics. However, this practice has caused some concern to physicians and researchers because of unknowledge of consequences that the indiscriminate and illicit use of these substances can cause. Thus, this study analyzed the effects of two commercially available anabolic steroids (AS), Winstrol Depot® (Stanozolol) and Deposteron® (Testosterone Cypionate), in the neuronal density of limbic, motor and sensory regions on the cerebral cortex and in CA1, CA2, CA3 regions of the hippocampus. A total of 60 Swiss mice were used (30 males and 30 females), separated into three groups: control and two experimental groups, which received the AAS. From each brain, homotypic and semi-serial samples were taken in frontal sections from areas established for the study. The results showed that females treated with testosterone cypionate presented a reduction in all regions tested and the ones treated with Stanozolol showed a decrease in some hippocampal areas. Regarding male animals, stanozolol led to a decrease in neuron number in one hippocampal region. These data allow us to conclude that supra-physiological doses of steroids used in this study, can cause considerable damage to nervous tissue with ultrastructural and consequently behavioral impairment. These changes could interfere with the loss of physical yield and performance of athletes and non-athletes and may cause irreparable damage to individuals making irresponsible use of anabolic steroids.

Effects of adult male rat feminization treatments on brain morphology and metabolomic profile

Body feminization, as part of gender affirmation process of transgender women, decreases the volume of their cortical and subcortical brain structures. In this work, we implement a rat model of adult male feminization which reproduces the results in the human brain and allows for the longitudinal investigation of the underlying structural and metabolic determinants in the brain of adult male rats undergoing feminization treatments. Structural MRI and Diffusion Tensor Imaging (DTI) were used to non-invasively monitor in vivo cortical brain volume and white matter microstructure over 30 days in adult male rats receiving estradiol (E₂), estradiol plus cyproterone acetate (CA), an androgen receptor blocker and antigonadotropic agent (E₂ + CA), or vehicle (control). Ex vivo cerebral metabolic profiles were assessed by ¹H High Resolution Magic Angle Spinning NMR (¹H HRMAS) at the end of the treatments in samples from brain regions dissected after focused microwave fixation (5 kW). We found that; a) Groups receiving E₂ and E₂ + CA showed a generalized bilateral decrease in cortical volume; b) the E₂ + CA and, to a lesser extent, the E₂ groups maintained fractional anisotropy values over the experiment while these values decreased in the control group; c) E₂ treatment produced increases in the relative concentration of brain metabolites, including glutamate and glutamine and d) the glutamine relative concentration and fractional anisotropy were negatively correlated with total cortical volume. These results reveal, for the first time to our knowledge, that the volumetric decreases observed in trans women under cross-sex hormone treatment can be reproduced in a rat model. Estrogens are more potent drivers of brain changes in male rats than anti-androgen treatment.