Testosterone Directly Amplifies but Does Not Program Male Behaviors

http://www.sciencedaily.com/releases/2010/04/100428142246.htm

ScienceDaily (May 3, 2010) — New research uncovers some surprising information about how sex hormones control masculinization of the brain during development and drive gender related behaviors in adult males. The study, published in the April 29 issue of the journal Neuron, demonstrates that direct action of testosterone, the prototypical male hormone, is unnecessary for masculinizing the brain and behavior.

Testosterone and estrogen are thought to play an essential role in organizing and activating gender-specific patterns of behavior in sexually reproducing animals. Testosterone is produced by the testes and directly activates the androgen receptor (AR) in target tissues such as muscle. Estrogen is produced by the ovaries and is nearly undetectable in the circulation of males of most species. However, circulating testosterone in males can be converted into estrogen in the brain, and this testosterone-derived estrogen has been shown to control many male behaviors.

"It was known that testosterone and estrogen are essential for typical male behaviors in many vertebrate species," explains the study's senior author, Dr. Nirao M. Shah from the Department of Anatomy at the University of California, San Francisco. "However, how these two hormones interact to control masculinization of the brain and behavior remained to be established."

Dr. Shah and colleagues found that during the neonatal testosterone surge there is very little AR expressed in the developing brain, making it unlikely that testosterone signaling via AR plays a major role in masculinizing neural pathways. Importantly, they went on to show that the male pattern of AR expression in the brain was dependent on testosterone-derived estrogen signaling.

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