More evidence that the immune system and behaviour are connected

Last week, NewScientist.com covered a paper about the psychological effects of the Toxoplasma parasite. We know that infected mice are fearless about approaching cats, and humans that are infected sometimes shows signs of reckless behaviour.

Picture of mouse

Watch out for immune hijackers, little mouse!
Photo: © Rgbspace | Stock Free Images

A new discovery by Antonio Barragan, however, now shows us that the mechanism linking the infection with the change in behaviour is the way that white blood cells (immune cells) are essentially “hijacked” by the parasite. It turns out that the parasite turns on a gene on the immune cells responsible for producing a neurotransmitter called GABA. We know that brain cells produce this neurotransmitter, but what these guys found is that the infected immune cells produce and also have receptors for GABA, which in turn makes them move around the body faster, which unfortunately spreads the parasite around the body faster.

GABA is also responsible for decreased fear – so really what this parasite is doing is making the immune system a) move faster, meaning the parasite gets spread within the body faster, and b) pump out fear-reducing chemicals, meaning that mice can get eaten by cats, further spreading the parasite among other species! How devious.

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