Pheremones Decide Mice Sexuality
Sexual Behaviour and Genetics Study Reveals Causes of Bisexuality
Sep 27, 2007
Life is predictable in the mouse world. If you’re a male and you meet another male, you attack. If you meet a female, well, then you try to get intimate.
If you’re a female, you’ll be welcoming to a male. Unless you are nursing pups in which case you will attack.
Smell you later
A mouse’s social interaction is determined primarily through its sense of smell. More specifically, through an organ found in the nose called the vomeronasal organ (VNO).
Mice put out chemicals called pheromones. Male mice put out one kind and females put out another. The VNO is where mice are able to detect the presence of these pheromones.
A critical part of this detection is the TRPC2 receptor. This receptor recognizes which pheromone is present and alerts the brain. Scientists were curious about how mice would behave without the TRPC2 receptor. So they eliminated the TRPC2 gene which has the instructions for making this receptor.
Dominant bisexual mice
Knocking the TRPC2 gene out in mice had the same effect on both males and females. Both mice stopped fighting and started loving. These mice could not tell the difference between males and females and tried to get intimate with both.
The weird part was that females started acting like bisexual males. This was completely unexpected given what scientists thought they knew about how mammalian brains work.
Scientists have thought for a long time that mammalian brains are hard wired as either male or female. So they expected males to either fight with any mouse they encounter or try to get intimate if they can’t tell the males and females apart. And that female mice would either fight or be receptive to any mouse they encountered.
In this light, the result with males makes sense. Loving is stronger than fighting. But female mice did not behave as expected. Females acted like males who had found a female. In other words, both males and females became like dominant bisexual males.
If mice brains are really hard wired as a male or a female, then this is not the result we'd expect. Unless TRPC2 is somehow involved in hard wiring the brain. But the researchers also eliminated the VNO (and the TRPC2 receptor there) in adult female and male mice. And got the same results. This means that TRPC2 is not involved in hardwiring the brain.
The default brain and human sexuality
The result with the female mice suggests that the default brain of mice is actually that of a male who is a lover, not a fighter. In other words, the brain is not hard wired in mice as either male or female.
Instead, there must be something different about the way males and a females use the TRPC2 receptor. And it is this difference that determines how a male and a female will react.
So can we translate any of this to humans? That is hard to say. Humans are much more complex and so smell isn’t dominant. But it does play a role. A recent study with lesbian women, for example, showed that their brains responded to possible human pheromones similarly to that of heterosexual males.
What we don’t yet know is whether human brains are hard wired as male or female. One current theory states that homosexuality can arise when someone is physically of one sex but their brain is hardwired as the other sex. It will be interesting to see if scientists will be able to figure out if this is true or not. Or even possible given the mouse result.
 |
