Sex requires more than just testosterone…

There are few topics more exciting than anole reproduction, but there’s still much we have to learn about the neuroendocrine mechanisms that allow these creatures to do the deed.  We know that sex steroid hormones facilitate reproductive behaviors across a diversity of animals, and anoles are no exception.  In particular, an enzyme called aromatase regulates both male and female sexual behaviors by synthesizing estradiol from testosterone.  In a recent study using green anoles (Anolis carolinensis), Rachel Cohen and Juli Wade of Michigan State University examined whether lizard sex and season influenced the expression of aromatase in areas of the brain that are known to influence vertebrate reproductive behavior (the preoptic area (POA), the amygdala, and the ventromedial hypothalamus (VMH)).

Cohen and Wade (2011) used the technique of in situ hybridization to measure the number and density of cells in these brain regions that express aromatase mRNA.  Their results showed that males express aromatase in the POA more than females, and that breeding animals express more aromatase in the POA than non-breeding animals, consistent with findings that show that this region is important in male sexual behavior.  In the VMH, a region known to influence female receptivity, the density of aromatase-expressing cells was higher in females than males, although the number of aromatase-expressing cells did not differ between the sexes, and there was no effect of season.

What I find to be most intriguing in this study are aromatase expression patterns in the amygdala.  Surprisingly, Cohen and Wade found lateralization of aromatase expression in the amygdala – more and denser cells express aromatase in the left amygdala than the right amygdala.  At this point, there’s no clear hypothesis explaining the role of this lateralization (any ideas?), but I expect this will be the focus of future work in this area.

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