Scientists in China say they have discovered that the sexual behaviour of male mice is influenced by a chemical in the brain.

They bred male mice without the neurotransmitter serotonin and found that these mice lost interest in females.

The modified mice appeared to show sexual behaviour towards other males instead and were far more likely to attempt to mount them and make ‘mating calls’.

A series of experiments were carried out. The modified mice showed no preference for either gender when presented with a choice of male and female partners. But when a single male was introduced, they were more likely to show sexual interest.

But sexual interest in females could be restored by injecting serotonin into the brain.

The report said: “Serotonergic signalling 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 experiment has not looked at the effects of serotonin in female mice.

Scientists have cautioned against relating these findings to human sexual behaviour. Although serotonin can affect libido in humans, no evidence has been found for any effect on sexual orientation.

Study co-author Zhou-Feng Chen, of the Washington University School of Medicine in St Louis, told Science News: “We have to be cautious because this is work done in mice. I would be extremely careful to extrapolate these results into humans. We just don’t know much about this.”

The study, led by Yi Rao of the National Institute of Biological Sciences and Peking University in Beijing, was published online in the journal Nature this week.