有点意思。不知道人的gay & bi 能不能从这里找到根据。

Molecular regulation of sexual preference revealed by genetic studies of 5-HT in the brains of male mice

Yan Liu, Yun'ai Jiang, Yunxia Si,Ji-Young Kim,Zhou-Feng Chen & Yi Rao

Nature Volume: 472,Pages:95–99 Date published:(07 April 2011)
DOI:doi:10.1038/nature09822

Although the question of to whom a male directs his mating attempts is a critical one in social interactions, little is known about the molecular and cellular mechanisms controlling mammalian sexual preference. Here we report that the neurotransmitter 5-hydroxytryptamine (5-HT) is required for male sexual preference. Wild-type male mice preferred females over males, but males lacking central serotonergic neurons lost sexual preference although they were not generally defective in olfaction or in pheromone sensing. A role for 5-HT was demonstrated by the phenotype of mice lacking tryptophan hydroxylase 2 (Tph2), which is required for the first step of 5-HT synthesis in the brain. Thirty-five minutes after the injection of the intermediate 5-hydroxytryptophan (5-HTP), which circumvented Tph2 to restore 5-HT to the wild-type level, adult Tph2 knockout mice also preferred females over males. These results indicate that 5-HT and serotonergic neurons in the adult brain regulate mammalian sexual preference.