Researchers from Beijing's National Institute of Biological Sciences, China have found a chemical in the brain controls sexual preference in mice. The study published in the journal Nature said that male mice bred without serotonin lose their preference for females. This is the first study that shows that a neurotransmitter plays a role in sexual preference in mammals. However it is still a long way before similar conclusions can be drawn for humans the experts believe.
The team first bred male mice whose brains were not receptive to serotonin. Then they performed a series of experiments that demonstrated that these mice had lost the preference for females shown by unmodified males. The serotonin deficient mice were presented with a choice of partners; they showed no overall preference for either males or females. When just a male was introduced into the cage, the modified males were far more likely to mount the male and emit a "mating call" normally given off when encountering females than unmodified males were. They then repeated the experiments with a different set of mice that lacked the tryptonphan hydroxylase 2 gene, which is needed to produce serotonin. Similar results were seen.
However, a preference for females could be “restored” by injecting serotonin into the brain. Researchers conclude, “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.”
“Nobody thought that serotonin could be involved in this kind of sexual preference,” study co-author Zhou-Feng Chen of Washington University School of Medicine in St Louis said. Serotonin is a neurotransmitter that is connected to many behaviours and may play a role in cognitive processes, including moods. Several antidepressants increase the amount of serotonin in the brain and can have sexual side effects, typically leading to a decrease in libido. There is no evidence that they influence sexual orientation.
Professor Keith Kendrick, a neuroscientist at the Babraham Institute in Cambridge, said, “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….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…At this time therefore any potential links between serotonin and human sexual preferences must be considered somewhat tenuous.”