The HPG axis can also be suppressed by GnRH antagonists or continuous administration of GnRH agonist, such as in the following applications Also as a result, many of the side effects are similar to the symptoms of pregnancy. Although often described as preventing pregnancy by mimicking the pregnancy state, hormonal birth control is effective because it works on the HPG axis to mimic the luteal phase of a woman's cycle. Hormone replacement can be used to initiate puberty and continue if the gene mutation occurs in the gene coding for the hormone. A mutation that causes a gain of function for LH receptors can result in a condition known as testotoxicosis, which causes puberty to occur between ages 2–3 years. For example, the male mutation of the GnRH coding gene could result in hypogonadotrophic hypogonadism. Interestingly, kisspeptin has been found to have an antidepressant action possibly by modulating brain serotonergic neurons . These meta-analyses further strengthen the concept that clinical hypogonadism confers a high risk for depression in men. Likewise, in an adjusted linear regression analysis, the prospective Longitudinal Aging Study Amsterdam observed greater depressive symptoms in men with the lowest quartile of calculated free testosterone compared to men in the highest free testosterone quartile . Furthermore, using a logistic regression, this study found that high depression scores were present in 61% of men with hypogonadism compared to only 14% of eugonadal men . Examples include genital virilisation such as midline fusion, phallic urethra, scrotal thinning and rugation, and phallic enlargement; although the role of testosterone is far smaller than that of dihydrotestosterone. The relative potency of these effects can depend on various factors and is a topic of ongoing research. Testosterone is a steroid hormone from the androstane class containing a ketone and a hydroxyl group at positions three and seventeen respectively. Chromosome idiogram map of gene variants that have significant genome-wide association with testosterone. Genome-wide association studies (GWAS) from the UK Biobank and other large cohorts have identified the SNP-based heritability for total testosterone to be ~ 20% and free testosterone to be ~ 15% 21–23, 127. Therefore, the benefits of testosterone replacement therapy on major depressive disorder in men with clinically defined hypogonadism remains uncertain and will hopefully be elucidated by the TRAVERSE Trial and other ongoing research.. Adiponectin inhibits both the basal and GnRH-stimulated LH secretion, and its effect is detected even after a short exposure with gonadotrophs 14, 144.|In accordance with sperm competition theory, testosterone levels are shown to increase as a response to previously neutral stimuli when conditioned to become sexual in male rats. Studies have shown small or inconsistent correlations between testosterone levels and male orgasm experience, as well as sexual assertiveness in both sexes. This is known as hormone replacement therapy (HRT) or testosterone replacement therapy (TRT), which maintains serum testosterone levels in the normal range. Some of these effects may decline as testosterone levels might decrease in the later decades of adult life.|In addition, the adiponectin receptors interact with APPL proteins (adaptor protein, phosphotyrosine interacting with plekstrin-homologous domain and leucine zipper), but not with heterotrimeric G-proteins. The tissues, the targets of adiponectin, express the adiponectin receptors AdipoR1 and AdipoR2, which bind specifically to various forms of adiponectin with different affinity 111, 125, 126, 127. Post-translational modifications of adiponectin and its oligomerization significantly affect the bioavailability, binding characteristics and pattern of specific activity of adiponectin 115, 120, 123, 124, 125. To form the trimeric complex, hydroxylation of the proline and lysine residues in the collagenous repeats is necessary, since the lack of this modification does not allow the formation of such complex and leads to a loss in the adiponectin activity 118, 119. In the testes of 30-day knockout mice with severe hyperleptinemia, the expression of the gene encoding leptin was increased, while the expression of the genes encoding StAR and P450scc was reduced.|There have been two meta-analyses strongly supporting the relationship of androgen deprivation therapy with depression. This study uniquely investigated the time-dependence for adverse effects of ADT on mood demonstrating a dose–response relationship of ADT duration and depression. The association of androgen deprivation therapy and depression represents the most extensively studied psychiatric outcome variable due to its detrimental impact on survivorship 49, 51. However, androgen deprivation therapy has been shown to have a substantially stronger induction of depression. Considering that the brain serotonergic neuronal system has a critical role in depression and antidepressant treatment, the interaction of testosterone and kisspeptin neurotransmission may have an unrecognized role in major depressive disorder. Testosterone feedback without interacting directly with GnRH neurons targets AR-expressing kisspeptin neurons in the arcuate nucleus of the hypothalamus to negatively regulate pulsatile GnRH release and the HPG axis 38, 40.} Women's level of testosterone is higher when measured pre-intercourse vs. pre-cuddling, as well as post-intercourse vs. post-cuddling. In non-human primates, it may be that testosterone in puberty stimulates sexual arousal, which allows the primate to increasingly seek out sexual experiences with females and thus creates a sexual preference for females. Regular monitoring during treatment typically includes hematocrit levels every 3-6 months to prevent polycythemia, along with PSA monitoring in men over 40. Serious side effects may include liver toxicity, heart disease (though a randomized trial found no evidence of major adverse cardiac events compared to placebo in men with low testosterone), and behavioral changes. Research on male twins has provided heritability estimates of 57–58% for total testosterone 125, 126. Furthermore, the Testosterone Trials and other studies have reported that testosterone replacement therapy may only be beneficial in men with dysthymic disorder or subsyndromal depression that does not meet criteria for major depressive syndrome. Using PET imaging, a recent study has reported that testosterone regulates hippocampal serotonin 5-HT4 receptors and increases brain serotonergic function . Testosterone treatment upregulates serotonin transporter expression and increases the firing rate of serotonergic dorsal raphe neurons 119, 120 which has been proposed to promote an antidepressant action. Deficient serotonergic neurotransmission and reduced serotonin 5-HT1A and 5-HT1B receptor signaling has an important role in the pathophysiology of major depressive disorder and form the basis of the serotonin hypothesis of depression .
