Can Serotonin Levels Change the Sexual Orientation of Mice?

A new study published in the journal Proceedings of the National Academy of Science suggests that serotonin, which is usually linked to mood, has a significant role in determining sexual preferences in mice, Medical Daily reports.

Research led by Shasha Zhang, Yan Liu and Yi Rao of Peking University in China, which was reviewed by Dr. Catherine Ducal at Harvard, bred female mice to lack serotonin or specific neurons that release serotonin in parts of their brain. The scientists found mice with the mutations preferred to mount and sniff the genitals and heads of other female mice.

"The female mice without serotonergic neurons still responded to sexual attention from male mice, but when given a choice, it was clear to the researchers that they had a sexual preference toward other females," Medical Daily writes.

The researchers wrote the reversal of sexual preference in female mice was "more consistent with a central mechanism of 5HT [serotonin] in controlling sexual preference."

Medical Daily also notes that the genetic changes did not involve levels of sex hormones, like estrogen, which suggest that serotonin is plays an important role in sexual behavior. The results conclude "that serotonergic signaling is involved in controlling sexual preference in adult females." The site points out that the same scientists found in a different study that turning off serotonin activity all together, makes mice lose their libido completely.

The site also writes, "It's important to note that this is not a study that can be simply extrapolated to people - slapping human identity labels like 'gay' or 'lesbian' onto mice is immature. To start, we can watch the mating behavior of these animals, but we can't determine how they would self-identify."

Serotonin is a complex hormone and affects everything from sleep to mood to sex. Medical Daily stresses this is not a "gay cure" and says, "it should be clarified that the serotonin alterations were genetic - suggesting that, at least for these mice, sexual preference is something they were born with, not something that changed later in development."

Researcher Simon LeVay of Stanford University commented on the study in the New Scientist and wrote, "serotonin systems may be part of the cascade of signals that translate sex hormone levels during development into sexual partner preference in adulthood."

As the Atlantic points out, a recent Gallup poll found that 47 percent of people in the U.S. agree that sexual orientation is not a choice. In 1979 only 13 percent believed people are born gay.

The Atlantic added, "In the late 1990s, conversation around a 'gay gene' was very controversial. We won't likely trace human sexual orientation to a single gene, but research has made it apparent that sexuality can be influenced by manipulating genes, hormones, and neurotransmitters. Altering balances of testosterone and estrogen has been shown to affect sexuality, and imbalances of the neurotransmitter serotonin can make us hypersexual. In mice, serotonin has been tied to sexual preference -- mice bred without certain neurons have shown 'no sexual preference.' But scientists have never 'reversed' any species' sexual orientation by messing with their genes."