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Did Scientists Really Make Those Mice Gay? Or Just Horny?

Those scientists who were able to modify the sexual orientation of mice by changing their serotonin levels had us all excited that the research would lead to the ability to ensure we give birth to gaybies. But as with all things biological and sexual, going from straight to bi or gay isn’t always so easily explained.

The physiology PhD and post-doc researcher who goes by SciCurious is out to see whether the data holds up in humans. Let’s get all sciencey:

Many people are aware, to some extent, that serotonin has something to do with sexual behavior. We’ve all heard about the sexual side effects of antidepressants. Many of these drugs are known as selective serotonin reuptake inhibitors (SSRIs). In the brain, serotonin is recycled back into the cell after release by serotonin transporters, so that it can be broken down or used again. When antidepressants like Prozac block these transporters, serotonin remains in the synapses between cells, and it builds up, resulting in more serotonin signaling in the brain. This affects sexual behavior. Generally speaking, high levels of serotonin (either administered directly into the brain, or as the result of genetic absence of the transporter), inhibit sexual behavior. This means that antidepressants which increase serotonin cause problems like longer time to ejaculate in men.

Of course, if HIGH levels of serotonin cause decreases in sexual behavior, what do LOW levels of serotonin do? Pretty much what you’d expect. Stimulating an inhibitory receptor that decreases serotonin neuron signaling will increase sexual behavior. Stopping the synthesis of serotonin (resulting in a massive serotonin decrease) also increases sexual behavior. The literature seems pretty clear. In general: high serotonin = low sexual behavior, and low serotonin = high sexual behavior. This is all in males, though some research in females suggests that similar effects may be in play.

But does any of this have to do with sexual orientation?

The interesting data is when the animals are exposed to male mice. While normal mice show basically no mounting of other males, the mice with low serotonin (either due to absence of serotonin neurons or the absence of the rate limiting enzyme to make serotonin), showed large amounts of mounting. Again the numbers are almost at ceiling, with the low serotonin animals mounting almost 100% of the time. In fact, low serotonin animals of both types mounted males and females with roughly equal preference. The question then becomes whether we are seeing a switch in sexual preference (not to preferring males, but to having no preference between sexes), an inability to distinguish the difference between male and female mice, or simply an increase in sexual activity. There is presumably an increase in sexual activity present, though it appears to hit the ceiling.

First they ran a large number of odor tests, for things like food substances, aversive smells (like predators) or other unfamiliar mice. The low serotonin animals passed all of those tests. But when given male or female genital scents or urine, they show no preference for the male or female. But what is also interesting is that they show large decreases in sniffing. So it appears that the the mice with reduced serotonin show a lack of sexual preference. The authors then found that they could RESTORE the sexual preference for females by administered serotonin to the low serotonin animals (you’ll notice below that this increase in serotonin produced a drastic decrease in sexual behavior in normal mice).

The authors conclude that the presence or absence of serotonin in these mice controls sexual preference. But based on the work in this paper and the literature on serotonin and sexual behavior, I think this conclusion may be premature. The proposed mechanism is a good hypothesis, but is what we are seeing in these data really a change in sexual PREFERENCE? Or is it merely a drastic increase in sexual behavior in low serotonin mice, one so profound that sexual activity will occur regardless of the target? Perhaps when the authors increased serotonin in these mice, they were decreasing sexual behavior to normal levels rather than changing preference.

And when they decreased the serotonin, they turned the mice into walking hard-ons willing to screw anything and everything.

[Scientific American]

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