The first is the challenge hypothesis which states that testosterone would increase during puberty, thus facilitating reproductive and competitive behavior which would include aggression. Studies have found that testosterone facilitates aggression by modulating vasopressin receptors in the hypothalamus. About half of studies have found a relationship and about half, no relationship. have been undertaken on the relationship between more general aggressive behavior, and feelings, and testosterone. On the other hand, elevated testosterone in men may increase their generosity, primarily to attract a potential mate.|Specifically, testosterone, along with anti-Müllerian hormone (AMH) promote growth of the Wolffian duct and degeneration of the Müllerian duct respectively. The relative potency of these effects can depend on various factors and is a topic of ongoing research. It exerts its action through binding to and activation of the androgen receptor. 1-terrible, 9-excellent. Similarly, eliminating the hormonal stress response via adrenalectomy also eliminated sex differences in water maze performance . A variety of chronic stressors impair spatial working and reference memory in rodents 210,211,212, and the negative effects of stress on spatial memory seem to be caused by corticosterone binding to receptors in the hippocampus 213,214.|Acute injections of estradiol enhanced cell proliferation in female rats 122,123,124,125, while cell survival of new neurons can be enhanced or suppressed by chronic estradiol exposure in females contingent on the timing of estradiol replacement 43,126,127. Acute removal of estrogens reduced cell proliferation in female rats , whereas long-term ovariectomy has no effect on cell proliferation in female rats or mice 42,122. Testosterone could be influencing hippocampal neurogenesis in adult males via its metabolite, estradiol, but relatively few experiments have tested this idea.|This difference after training corresponded with better performance by females on the task, suggesting that a sex difference in hippocampal neurogenesis leads to a sex difference in cognitive ability. Without training on the task, males had higher levels of neurogenesis (12-day neuron survival) than did females, but after training the females had higher levels of neurogenesis than the males . A handful of experiments have more directly addressed the hypothesis that testosterone improves spatial memory by increasing adult neurogenesis in the dentate gyrus. Thus, testosterone enhances spatial working memory and some forms of spatial reference memory, but a critical question is whether these memory improvements are the result of changes in adult neurogenesis. A 30-day treatment with DHT that enhanced neurogenesis in male rats had no effect on neurogenesis in young or middle-aged female rats .|However, there are no guidelines advocating the use of TRT in men with hypogonadism for stroke prevention. Additionally, it has been shown to increase neurogenic output of excitatory progenitors in human brain organoids 10–12. A deeper understanding of the complex relationship between testosterone, DHEA, and neurodevelopment is essential to determining clinical applications. Elevations in prenatal testosterone have additionally demonstrated an inverse relationship with the development of pathways responsible for social communication and cognition 6, 7. ARs are also found in the dorsal horn of the spinal cord and various brain stem locations, predominating in the area postrema, motor nucleus of the vagus nerve, dorsal raphe nucleus, periaqueductal gray, retrorubral nucleus, retrotrapezoid nucleus, and substantia nigra.|Testosterone is a naturally occurring androgen that is produced in both men and women. Participants experienced improvements in ambulation, strength, muscle mass, and disease burden after receiving this study intervention. As such, combination therapy has the potential to limit disease progression and functional decline in individuals with muscular dystrophy. 5α-Reductase is highly expressed in the male reproductive organs (including the prostate gland, seminal vesicles, and epididymides), skin, hair follicles, and brain and aromatase is highly expressed in adipose tissue, bone, and the brain. Approximately 5 to 7% of testosterone is converted by 5α-reductase into 5α-DHT, with circulating levels of 5α-DHT about 10% of those of testosterone, and approximately 0.3% of testosterone is converted into estradiol by aromatase. Finally, increasing levels of testosterone through a negative feedback loop act on the hypothalamus and pituitary to inhibit the release of GnRH and FSH/LH, respectively. When testosterone levels are low, gonadotropin-releasing hormone (GnRH) is released by the hypothalamus, which in turn stimulates the pituitary gland to release FSH and LH.|Conversely, a retrospective analysis of five men with PD and testosterone deficiency did show significant improvement of refractory non-motor PD symptoms following TRT . Thus, there is no clear role for TRT in the prevention or treatment of MCI or dementia. Similarly, another study with a one-year follow-up reviewed the impact of TRT versus placebo in men with MCI and symptomatic hypogonadism and showed no improvement in cognitive function 47, 48. One study showed no difference in cognitive performance in hypogonadal men with mild cognitive impairment on TRT compared to those on placebo at 12 weeks follow-up. This was further confirmed by male animal models having higher amyloid beta protein deposition and lower hippocampal volume following castration when compared with the control group . Progressive testicular atrophy causing oligospermia is seen in 80% of men with DM1 along with reduced adrenal androgen synthesis . Furthermore, testosterone supplementation along with exercise in patients with IBM led to an additional decrease in inflammatory response when compared to exercise alone .}
In general, acute and chronic stress cause a decrease in adult neurogenesis , and this effect is likely mediated through elevated glucocorticoid levels caused by stress 218,219. In support of this hypothesis, castration of male rats was found to increase levels of multiple protein markers of apoptosis, including caspase-3 . Androgens may, therefore, activate the MAPK pathway to have anti-apoptotic effects , which, in turn, increase the survival of newly developing neurons in the adult brain.
Collectively, these results suggest that the presence of competitive activities rather than bond-maintenance activities is more relevant to changes in testosterone levels. Married men who engage in bond-maintenance activities such as spending the day with their spouse or child have no different testosterone levels compared to times when they do not engage in such activities. Single men who have not had relationship experience have lower testosterone levels than single men with experience. There has been speculation that these changes in testosterone result in the temporary reduction of differences in behavior between the sexes. Testosterone may prove to be an effective treatment in female sexual arousal disorders, and is available as a dermal patch. There is a time lag effect when testosterone is administered, on genital arousal in women. Androgens may modulate the physiology of vaginal tissue and contribute to female genital sexual arousal.
Similarly, castration did not cause a reduction in Ki67-expressing cells in the dentate gyrus of male mice or rats , supporting the general conclusion that testosterone does not play a significant role in regulating cell proliferation. Experiments with laboratory rodents support the general conclusion from the early studies with voles; namely, that testosterone enhances adult neurogenesis in the dentate gyrus by increasing cell survival, while having little or no effect on cell proliferation (Table 2). As one relevant example, transgenic mice (Sema7A knockout) that have reduced GnRH release from the hypothalamus, and therefore reduced testosterone levels from birth, showed no preference for female odors over male odors in adulthood (i.e., they lacked typical male sex preferences) . In contrast, castration caused a decrease in cell proliferation in the SVZ of juvenile male rats, and proliferation levels were restored by testosterone or estradiol injections but not by DHT injections , which suggests that testosterone is acting through an estrogen-dependent pathway. The study of the effects of testosterone upon adult neurogenesis was pioneered by researchers studying seasonal changes in the song-control nuclei of birds. Despite inconsistencies, initial findings suggesting sex differences in neurogenesis have led to productive research demonstrating that testosterone plays an important role in regulating adult neurogenesis. The effect of sex on cell proliferation has also been inconsistent, with studies with rodents showing no sex difference 42,43,45, higher levels in females 40,46, or higher levels in males 44,47.
Stroke occurring in patients aged 18–55 years is defined as stroke in young adults (15). These studies were limited to men above the age of 45 years using testosterone for hypogonadism (13, 14). Prior meta-analyses on this topic have shown conflicting data on the risk of cardiovascular events. However, data on trends of testosterone supplements usage from 2019 to 2024 is currently unavailable. A recent market analysis forecasts that the testosterone replacement therapy market in the US, UK, Canada, Germany, and China will expand by approximately 500 million USD over the next 4 years (7). Age-related testosterone decline may impair the brain’s ability to withstand and recover from injury.
Thus, it is hypothesized that alterations of ARs or androgen interactions with ARs located in the CNS may play a role in various neurological diseases and serve as a target for disease management. This androgen is responsible for masculine features and fertility in males while having positive effects on bone density, lean mass, mood, and libido in females. The primary function of androgens involves reproduction and the development of secondary sexual characters.
The same research found fathers (outside competitive environments) had the lowest testosterone levels compared to other males. Higher testosterone levels in men reduce the risk of becoming or staying unemployed. Testosterone levels play a major role in risk-taking during financial decisions. Physical presence may be required for women who are in relationships for the testosterone–partner interaction, where same-city partnered women have lower testosterone levels than long-distance partnered women. Falling in love has been linked with decreases in men's testosterone levels while mixed changes are reported for women's testosterone levels.
It fully manifests in men, typically in their third to fifth decades of life, while women with homozygous mutation have a subclinical disease course, indicating a role of androgen in pathogenesis as opposed to solely the mutant AR . The relationship between androgens and brain development highlights the need to understand their role in neuroplasticity. The outcomes of this open-label 36-week study of testosterone and rHGH in FSHD indicate that this treatment approach is safe and well tolerated over 24 weeks and is promising as a therapy to combat and reverse impaired ambulation, weakness, muscle loss, and symptomatic burden in FSHD.
In this study, we report the findings of a 36-week single-arm Study of Testosterone and rHGH in FSHD (STARFiSH). Facioscapulohumeral muscular dystrophy (FSHD) is the second most common form of adult-onset muscular dystrophy in the world.1,2 Clinically, FSHD is characterized by progressive weakness and atrophy of the face, shoulders, arms, and hip girdle muscles; impaired ambulation; and functional impairment related to muscle weakness. Combination therapy was safe and well tolerated in men with FSHD. The most common adverse event was mild injection site reaction at the rHGH and/or testosterone injection site. Nineteen of 20 participants completed the study, with no participants experiencing a serious adverse event. Participants were also evaluated for changes from baseline in lean body mass (LBM) and fat mass, measured by dual-energy X-ray absorptiometry; ambulation, measured by 6-minute walk distance; strength; clinical function, measured using the FSHD-Composite Outcome Measure (FSHD-COM); and patient-reported disease burden, measured by the FSHD Health Index (FSHD-HI).

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