Brain Parasite Influences Rats’ Attraction to Cats

Researchers believe the parasite taxoplasma gondii hijacks brain circuits in the amygdala, making the rat exhibit attraction when it should show fear.

Sometimes the introduction of a foreign body such as a parasite can cause typical behaviors to go haywire. Patrick House, a neuroscientist at Stanford University in Palo Alto, Calif., studies the behavioral manipulation of fear in rats by the parasite toxoplasma gondii. House found that rats infected with the parasite were curious about, even attracted to, cat odor. Because taxoplasma gondii can only reproduce in the guts of cats, the parasite is dependent on rats to spread itself from feline to feline. To overcome this obstacle, the parasite leads the rat to do some strange things. In studies, House observed that both the fear and attraction pathways in the brain of taxo-infected rats “light up” after they smell cat urine. The researchers believe the parasite hijacks brain circuits in the amygdala, making the rat exhibit attraction when it should show fear, House said. Many humans carry the taxoplasma gondii parasite, said House. They can get it from eating uncooked meat and unwashed vegetables, or from handling a cat litter box. The parasite can be harmful to developing fetuses, and expectant mothers have been advised to avoid contact with cat litter. While the presence of the parasite has been considered harmless, some epidemiological research suggests that the parasite may have an association with schizophrenia and risk-taking behavior, House said. House presented his research at the Society for Neuroscience annual meeting.