March 24, 2011

Brain Chemical Controls Sexual Preference In Mice

Chinese scientists say they have found a chemical inside the brains of mice that controls sexual preference.

The researchers, reporting their findings in the journal Nature, said male mice bred without serotonin lose their preference for females. They said it is the first time that a neurotransmitter has been shown to play a role in sexual preference in mammals.

The team first bred male mice whose brains were not receptive to serotonin. Experiments showed that these mice had lost preference for females altogether. And when presented with a choice of partners, the modified mice showed no overall preference for either sex.

When only an unmodified male was introduced to a male without serotonin, it was far more likely to be mounted by the modified male -- which emitted a mating call while doing so -- then by another regular male.

The researchers got similar results when they bred another set of mice that lacked the tryptonphan hydroxylase 2 gene, which is needed to produce serotonin.

They said the males' preference for females would be "restored" by injecting serotonin into the brain.

"Serotonergic signaling is crucial for male sexual preference in mice. This is the first time, to our knowledge, that a neurotransmitter in the brain has been demonstrated to be important in mammalian sexual preference," the study report concluded.

Scientists believe, in mice, sexual behavior is driven mainly by their sense of smell.

"In terms of having potential relevance to understanding human sexual preference/orientation, we are of course far less influenced by odor cues in this context than mice are," Professor Keith Kendrick, a neuroscientist at the Babraham Institute in Cambridge, told BBC News.

"There is some very limited evidence for altered responses to selective serotonin uptake inhibitors (SSRIs) in the brains of homosexuals, but we have been using psychoactive drugs which either increase or decrease serotonin function for quite some time now, and while effects on sexual arousal, impulsivity and aggression have often been reported, no effects on sexual preference/orientation have," he said.

"At this time therefore any potential links between serotonin and human sexual preferences must be considered somewhat tenuous," noted Kendrick.


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