A paper titled “Mast Cells in the Developing Brain Determine Adult Sexual Behavior” by Kathrin Lenz et al.,  was published recently in http://www.biorxiv.org. The paper, through experiments with rats, reveals that mast cell activation in the brain pre-optical area (POA) during the prenatal period masculinizes sexual behavior of females and de-masculinizes the sexual behavior of males. As I read the study, it is saying that prenatal inflammation in the brain center responsible for the thrusting heterosexual movements may cause homosexuality.

According to the study the male POA during the sexual differentiation stage has more mast cells than the female POA. A  gestational allergic challenge significantly increased the number of mast cells in the female POA to male-typical levels . Prenatal allergic challenge also increased the proportion of degranulated mast cells.   The females born to allergic challenged dams when adults, under treatment with testosterone, mounted more quickly and more often than control females, such that their overall performance was equivalent to males. They also trended towards a preference for olfactory investigation of female versus male soiled bedding. Males gestated in an allergic challenged dam showed the opposite, a loss of female partner preference, suggesting demasculinization.

The authors of the study propose that there may be an optimal threshold for inflammatory signaling in the male brain, beyond which there is dysregulated sociosexual development.

In the experiment the inflammation was induced prenatally, during the period of sexual differentiation of the brain. In humans, the brain pre-optical area continues to sexually differentiate during adolescence, hence it is possible that inflammation in the POA during adolescence could also affect its sexual differentiation and contribute to homosexuality.

1 hour ago, ritastrakosha said:

As I read the study, it is saying that prenatal inflammation in the brain center responsible for the thrusting heterosexual movements may cause homosexuality.

That's interesting, because the paper doesn't mention mate selection, sexuality or homosexuality.

In the real world, at most, this effect might be one of many factors  involved in rat sexuality.

There may even be a parallel in humans.

interesting read