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Friday, January 23, 2015

Medial Amygdalar Aromatase Neurons Regulate Aggression in Both Sexes

A miniscule cluster of estrogen-producing nerve cells in the mouse brain exerts highly specific effects on aggressive behavior in both males and females, according to new research .
As has been known for several decades ( estrogen signaling controls sex-typical behaviors in both sexes in rodents and many other vertebrates.
In particular, it is critical for male-typical ultrasonic courtship vocalizations, sexual displays, aggression, and territory marking
A role of estradiol in controlling male behaviors seems counterintuitive because it is essentially undetectable in the male mouse circulation. Estrogenic steroids in vivo are derived from testosterone or related androgens in a reaction catalyzed by aromatase, and aromatase+ cells in the male brain convert circulating androgens into estrogenic derivatives
It is this locally synthesized estradiol that is thought to control male-typical behaviors
Sex hormones exert global control over the display of sexually dimorphic social behaviors. For example, estrogen signaling in males governs vocalization, sexual displays, aggression, and territory marking.
By contrast, the authors find that aromatase+ MeApd neurons in this study are only required for WT levels of aggression
Although there is little circulating testosterone in female mice and the female brain is exposed to circulating estradiol secreted by ovaries, there is aromatase expression in the female rodent brain, albeit at lower levels than in males
The function, if any, of aromatase+ neurons in female mice has been unknown
There is much more here than meets the to just how and why aromatase functions in the brain....
•MeApd aromatase neurons regulate male aggression, but not marking, singing, or mating
•MeApd aromatase neurons regulate maternal aggression, but not female sexual behavior
•MeApd aromatase neurons regulate specific components of aggression in both sexes
•MeApd aromatase neurons control aggression in a modular manner
More broadly, the authors state that the findings suggest the possibility that a primordial neural pathway underlying aggression predates the divergent needs of the two sexes to fight in different contexts. Such a neural circuit could be modified during evolution and sexual selection such that it is activated by different stimuli and drives different motor programs in the two sexes.
but for now here is what the pop journalists say
"The cells in question, known as aromatase-expressing (aromatase+) cells, represent less than five one-hundredths of a percent of the neurons in the mouse brain, but they play crucial roles in sexual differentiation during early development and in regulating sexual and social behavior in adulthood.
Though estrogen is generally thought of as a female sex hormone, during the 1970s it was discovered that the male sex hormone testosterone can be converted to estrogen in the brain by aromatase, an enzyme also found in many other mouse and human tissues.
In the male mouse, estrogen, presumably synthesized by aromatase+ neurons in the brain, is known to be involved in diverse social behaviors, including the ultrasonic "singing" that males produce when courting females, and in mating, aggression, and the marking of territory.
Aromatase+ neurons are also present, in smaller numbers, in females. But because females produce high levels of circulating estrogen and very little testosterone, it has been unclear whether aromatase+ cells in the female brain are purely vestigial or serve some other function."