Thursday, April 3, 2008

Mind control

Yesterday, I wrote about how male mice respond to the smell of the urine of female mice—they sing.

The subject for today is bobcat urine and how an infection can change a mouse’s response to it.

Normally, when a mouse smells a cat (or a fox), it runs away. I mean, it makes sense, given the gustatory preferences of cats. It’s pretty Darwinian, too. Mice that run away when they smell a cat are more likely to survive than mice that hang around.

Toxoplasma gondii is a parasite that can infect mice, cats, and humans. It’s the reason pregnant women are advised not to change their cat’s litter box. Here’s why:

The life cycle of the parasite requires that it spend some time in cats, to undergo the sexual portion of its reproductive cycle. Normally it gets into cats when cats eat an infected mouse.

This paper describes how Toxoplasma gondii makes it more likely that it will complete its life cycle. It controls the minds of mice. The investigators studied both rats and mice infected with Toxoplasma gondii. Control animals spent as little time as possible near bobcat urine or a collar that had been worn by a cat. Infected animals spent more time near the catty items. Not only were they not afraid of cat smells, they were attracted to them.

This wasn’t just a generalized anxiety effect, and it was specific for predator smells. Infection didn’t affect their behavior around rabbit urine or novel foods.

The parasite changes the brains of mice in such a way that the mouse is attracted to the very predator that is required for the parasite to reproduce.

There is even some evidence that Toxoplasma gondii infection affects human behavior, and that it may play a role in schizophrenia.

Yet another reason to stay away from cat poop.