Editing Testosterone (section)

==== Early infancy ====
Early infancy androgen effects are the least understood.  In the first weeks of life for male infants, testosterone levels rise. The levels remain in a pubertal range for a few months, but usually reach the barely detectable levels of childhood by 4–7 months of age.<ref name="pmid4715291">{{cite journal | vauthors = Forest MG, Cathiard AM, Bertrand JA | title = Evidence of testicular activity in early infancy | journal = The Journal of Clinical Endocrinology & Metabolism| volume = 37 | issue = 1 | pages = 148–51 | date = July 1973 | pmid = 4715291 | doi = 10.1210/jcem-37-1-148 }}</ref><ref name="pmid1379488">{{cite journal | vauthors = Corbier P, Edwards DA, Roffi J | title = The neonatal testosterone surge: a comparative study | journal = Archives Internationales de Physiologie, de Biochimie et de Biophysique | volume = 100 | issue = 2 | pages = 127–31 | year = 1992 | pmid = 1379488 | doi = 10.3109/13813459209035274 }}</ref> The function of this rise in humans is unknown. It has been theorized that brain [[virilization|masculinization]] is occurring since no significant changes have been identified in other parts of the body.<ref name="pmid18445234">{{cite journal | vauthors = Dakin CL, Wilson CA, Kalló I, Coen CW, Davies DC | title = Neonatal stimulation of 5-HT(2) receptors reduces androgen receptor expression in the rat anteroventral periventricular nucleus and sexually dimorphic preoptic area | journal = The European Journal of Neuroscience | volume = 27 | issue = 9 | pages = 2473–80 | date = May 2008 | pmid = 18445234 | doi = 10.1111/j.1460-9568.2008.06216.x | s2cid = 23978105 }}</ref> The male brain is masculinized by the aromatization of testosterone into [[estradiol]],<ref name="HäggströmRichfield2014" /> which crosses the [[blood–brain barrier]] and enters the male brain, whereas female fetuses have [[α-fetoprotein]], which binds the estrogen so that female brains are not affected.<ref name="isbn0-495-60300-7">{{cite book | vauthors = Kalat JW | title = Biological psychology | publisher = Wadsworth, Cengage Learning | location = Belmont, Calif | year = 2009 | isbn = 978-0-495-60300-9 | chapter = Reproductive behaviors | chapter-url = https://books.google.com/books?id=ZlSbk5rUY60C&pg=PA321 | page = 321 | access-date = October 8, 2020 | archive-date = January 11, 2023 | archive-url = https://web.archive.org/web/20230111143031/https://books.google.com/books?id=ZlSbk5rUY60C&pg=PA321 | url-status = live }}</ref>