Editing Testosterone (section)

==== Adult ====
Testosterone is necessary for normal [[sperm]] development. It activates genes in [[Sertoli cell]]s, which promote differentiation of [[spermatogonia]]. It regulates acute [[hypothalamic–pituitary–adrenal axis]] (HPA axis) response under dominance challenge.<ref name="pmid18505319">{{cite journal |vauthors=Mehta PH, Jones AC, Josephs RA |title=The social endocrinology of dominance: basal testosterone predicts cortisol changes and behavior following victory and defeat |journal=Journal of Personality and Social Psychology |volume=94 |issue=6 |pages=1078–1093 |date=Jun 2008 |pmid=18505319 |doi=10.1037/0022-3514.94.6.1078 |url=http://homepage.psy.utexas.edu/homepage/faculty/josephs/pdf_documents/index.cfm.pdf |archive-url=https://web.archive.org/web/20090419200557/http://homepage.psy.utexas.edu/homepage/faculty/josephs/pdf_documents/index.cfm.pdf |archive-date=April 19, 2009 |url-status=dead |citeseerx=10.1.1.336.2502}}</ref> Androgens including testosterone enhance muscle growth. Testosterone also regulates the population of [[Thromboxane A2|thromboxane A<sub>2</sub>]] receptors on [[megakaryocytes]] and [[platelets]] and hence platelet aggregation in humans.<ref name="pmid15820970">{{cite journal |vauthors=Ajayi AA, Halushka PV | title = Castration reduces platelet thromboxane A2 receptor density and aggregability |journal=QJM |volume=98 |issue=5 |pages=349–356 |date=May 2005 |pmid=15820970 |doi=10.1093/qjmed/hci054 |doi-access=free}}</ref><ref name="pmid7758179">{{cite journal |vauthors=Ajayi AA, Mathur R, Halushka PV |title=Testosterone increases human platelet thromboxane A2 receptor density and aggregation responses |journal=Circulation |volume=91 |issue=11 |pages=2742–2747 |date=Jun 1995 |pmid=7758179 |doi=10.1161/01.CIR.91.11.2742}}</ref>

Adult testosterone effects are more clearly demonstrable in males than in females, but are likely important to both sexes. Some of these effects may decline as testosterone levels might decrease in the later decades of adult life.<ref>{{cite journal | vauthors = Kelsey TW, Li LQ, Mitchell RT, Whelan A, Anderson RA, Wallace WH | title = A validated age-related normative model for male total testosterone shows increasing variance but no decline after age 40 years | journal = PLOS ONE | volume = 9 | issue = 10 | pages = e109346 | date = October 8, 2014 | pmid = 25295520 | pmc = 4190174 | doi = 10.1371/journal.pone.0109346 | bibcode = 2014PLoSO...9j9346K | doi-access = free }}</ref>

The brain is also affected by this sexual differentiation;<ref name="pmid19403051" /> the [[enzyme]] [[aromatase]] converts testosterone into [[estradiol]] that is responsible for [[masculinization]] of the brain in male mice. In humans, masculinization of the fetal brain appears, by observation of gender preference in patients with [[congenital disease|congenital]] disorders of androgen formation or androgen receptor function, to be associated with functional androgen receptors.<ref name="pmid11534997">{{cite journal |vauthors=Wilson JD |date=Sep 2001 |title=Androgens, androgen receptors, and male gender role behavior |department=Review |journal=Hormones and Behavior |volume=40 |issue=2 |pages=358–66 |doi=10.1006/hbeh.2001.1684 |pmid=11534997 |s2cid=20480423}}</ref>

There are some [[Neuroscience of sex differences|differences between a male and female brain]] that may be due to different testosterone levels, one of them being size: the male human brain is, on average, larger.<ref name="pmid17544382">{{cite journal |vauthors=Cosgrove KP, Mazure CM, Staley JK |date=Oct 2007 |title=Evolving knowledge of sex differences in brain structure, function, and chemistry |journal=Biological Psychiatry |volume=62 |issue=8 |pages=847–55 |doi=10.1016/j.biopsych.2007.03.001 |pmc=2711771 |pmid=17544382}}</ref>