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How parasite tricks rats into becoming cat food


August 20, 2011 - Washington

A research has shed light on how a parasite uses the power of sexual attraction to trick rats into becoming cat food.

When a male rat senses the presence of a fetching female rat, a certain region of his brain lights up with neural activity, in anticipation of romance.

Now Stanford University researchers have discovered that in male rats infected with the parasite Toxoplasma, the same region responds just as strongly to the odour of cat urine.

"Well, we see activity in the pathway that normally controls how male rats respond to female rats, so it's possible the behaviour we are seeing in response to cat urine is sexual attraction behaviour, but we don't know that," said Patrick House, a PhD candidate in neuroscience in the School of Medicine.

"I would not say that they are definitively attracted, but they are certainly less afraid. Regardless, seeing activity in the attraction pathway is bizarre," added House.

For a rat, fear of cats is rational. But a cat's small intestine is the only environment in which Toxoplasma can reproduce sexually, so it is critical for the parasite to get itself into a cat's digestive system in order to complete its lifecycle.

Thus it benefits the parasite to trick its host rat into putting itself in position to get eaten by the cat.

For the experiments, he used cat urine he purchased in bulk from a wholesaler.

House analysed certain subregions of the amygdala that focus on innate fear and innate attraction.

In healthy male rats, cat urine activated the "fear' pathway.

But in the infected rats, although there was still activity in the fear pathway, the urine prompted quite a bit of activity in the "attraction" pathway as well.

"Exactly what you would see in a normal rat exposed to a female," said House, the lead author of a paper.

"Toxoplasma is altering these circuits in the amygdala, muddling fear and attraction," he added.

The findings confirmed observations that House made during the experiments, when he noticed that the infected rats did not run when they smelled cat urine, but actually seemed drawn to it and spent more time investigating it than they would just by chance.

Because Toxoplasma reproduces in the small intestine of cats, the parasites are excreted in feces, which is presumably how rats get infected.

Rats are known to be extremely curious, tasting almost everything they come in contact with. Toxoplasma is also frequently found in fertilizer and can infect virtually any mammal.

The research has been published in PLoS ONE.

ANI

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