There is no doubt that sexual desire depends on many processes within the body and that the libido varies according to several factors. But it seems that a particular gene regulates the desire for reproducing in males, or at least in male mice.
Testosterone flows in the body of a male mammal. A hormone, secreted mostly by the gonads – the testicles in men, the ovaries in women – can be transformed into estradiol. In the case of mice, this conversion takes place in the testicles and the brain with the help of aromatase.
So far, it is not very exciting. But with this point in mind, we can look at what would be “the first key discovery to explain how testosterone stimulates sexual desire,” in the words of one of the study’s authors, Serdar Bulun. The study, published in Endocrinology, states that aromatase is very essential for male sexual desire.
A conclusion that required some genetic engineering. The researchers modified male mice to disable the genetic coding of aromatase in the brain, which is called Cyp19a1. And in other male mice, they turned off Cyp19a1, in their entire body. So the latter went on living peacefully, without aromatase. This however caused an increase in testosterone, for these two types of mice, since it was no longer converted to estradiol to the same extent.
A molecular conversion, a change of attitude
Next, the researchers introduced their male mice to female mice. Under normal circumstances, the former would have diligently pursued the latter, for mating. But here, the male mice without brain aromatase – called ArKo – showed a 50% reduction in sexual activity. And the administration of testosterone only partially restored their libido.
However, if testosterone administration was accompanied by estradiol, ArKo males regained the desire to mate. And this is how testosterone would, in part, activate male sexual behavior by converting estradiol inside the brain.
“For the first time, we have conclusively demonstrated that the conversion of testosterone into estradiol in the brain is essential to maintain a full activity or sexual desire in males,” says Bulun. Aromatase is the driving force! ”
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