Heterosexual or homosexual? The happiness hormone serotonin plays a crucial role in mice (Image: Thinkstock)
Read aloud Whether for flirting, for a short affair or "until death divides us" - the search for a partner is one of the driving forces of our behavior. Whether we find the other sex attractive or our own, probably depends on several factors. Of which exactly, however, so far only partially clarified. So one knows that the sex hormones play an important role. At least in animals, sexual manipulation can be altered by manipulating these hormones. A Chinese research team has now identified another messenger that determines, at least in mice, whether these males or females find sexually attractive: the happiness hormone serotonin. The hormone serotonin, chemically 5-hydroxytryptamine (5-HT), is an important component of our hormone system. Among other things, the messenger helps to regulate body temperature, blood pressure, appetite and digestion. But above all, the serotonin affects the mood: it awakens and is considered a happiness hormone. In 2011, Yi Rao and his colleagues from the University of Beijing found another effect of the hormone in experiments with mice: They blocked serotonin production in male mice, thus losing their usually pronounced interest in the opposite sex. Instead, they indiscriminately tagged any mouse they encountered, whether females or males. Apparently the happiness hormone is necessary for a degree of sexual preference, the researchers stated at that time.

When mouse ladies stand on ladies

In their current study, Rao and his colleagues continued to pursue this trail. This time they blocked the production of serotonin in female mice or the docking sites for the messenger substance. The mouse ladies manipulated in such a way then put them in cages with either a male or a female conspecific and observed what happened. The same thing they did with some non-manipulated mice. The control mice behaved as expected: Attracted by the scent of the males, they sniffed their head and genital region with preference, but left the females on the left. The manipulated mouse ladies, on the other hand, are different: they prefer the females and sniff them much longer and more extensively than the readily available males, as the researchers report.

And not only that: If the mouse ladies with serotonin blockade could do more than just sniff, they also promptly took action. "They tried to grab the other female around the waist and climbed from behind, " Rao and his colleagues report. Thus, the manipulated females behaved more typical male and showed a clear preference for their own sex. This rather homosexual sexual behavior, the researchers observed at least about 70 percent of the manipulated mouse ladies. The female control animals did not behave this way or only in exceptional cases. "These results show that serotonin controls sexual preference, " the researchers note. By manipulating this hormone, the sexual orientation of the animals was reversed, without the sex hormones playing a role. Because these were the same in manipulated and unmanipulated mice. display

Transferability to humans unclear

How important the happiness hormone itself is in the short term showed another attempt by the researchers. They administered a chemical substance to normal, fully-grown mouse ladies, which binds the serotonin and thus makes it unusable for the body in a short time. If these females were then allowed to sniff their conspecifics, they too suddenly preferred females instead of males. As the scientists explain, this proves that happiness hormone does not only affect sexual orientation if it is missing during development in the womb or during puberty. Apparently, the hormone also continues to play an active role in the regulation of the sexual preferences of females in adulthood.

Whether the happiness hormone serotonin plays a comparable role with us humans, about the researchers do not comment. However, they do not limit their conclusions on the effect of serotonin in their study by the afterthought "in mice" - which might suggest that they see the mice as a model for other mammals and also humans. Why serotonin in male mice at best bisexual, but not clearly homosexual behavior causes, they also do not explain - also here there is still a need for research. However, these findings once again show that the question of whether someone is attracted to women or men has a complex and as yet poorly understood biological basis.

Yi Rao (Beijing University, Beijing) et al., Proceedings of the National Academy of Sciences (PNAS), doi: 10.1073 / pnas.1220712110 science.de - === Nadja Podbregar

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