“Excuse me my dear, but is that cat urine you're wearing?” said the Toxoplasma infected rat.
When male rats are infected with the Toxoplasma parasite, the smell of cat urine may become as sexy as the scent of a female rat. After the cat eats the confused and severely disappointed rat, the parasite continues its life cycle in the cat's intestines.
Researchers at Standford University found that the same section of an infected rat's brain light up when it smells cat urine as when it smells a female rat. Though this doesn't prove the rat is actually sexually attracted to the cat urine, it does mean that it loses its fear. And a rat that doesn't fear felines becomes an easy meal.
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The Toxoplasma then continues its life cycle in the cat's gut, until it is pooped out. Rats are notoriously curious and taste everything that crosses their paths. When they examine and taste a cat's poop, they accidentally ingest the parasite. Curiosity then kills the rat, as the parasite takes over the rat's brain and makes it lose its fear 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 behavior we are seeing in response to cat urine is sexual attraction behavior, but we don't know that," said Patrick House, a PhD candidate in neuroscience at the Stanford University School of Medicine in a press release. "I would not say that they are definitively attracted, but they are certainly less afraid. Regardless, seeing activity in the attraction pathway is bizarre."
Scientists have known about the strange affect of Toxoplama on rats for years, but they didn't know that the rat's sexual attraction pathways were affected. The recent research found that the parasite infects the amygdala, a region associated with emotional states.
House wanted to find out how the amygdala was affected by the parasite, so he ran experiments with both healthy and Toxoplasma-infected rats. Each male rat was exposed to either cat urine or a female rat in heat for 20 minutes.
House then analyzed its brains for evidence of excitation in the amygdala. He found that neural pathways in the infected rats' brains reacted to cat urine the same way they would to sexual arousal.
"Exactly what you would see in a normal rat exposed to a female," House said.
"Toxoplasma is altering these circuits in the amygdala, muddling fear and attraction," House said.
When exposed to the cat urine, the infected rats seemed drawn to it, and spent more time checking it out than they would just by chance. A healthy rat would have run from the cat pee, fearing the urine's maker.
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"In some ways, Toxoplasma knows more about the neurobiology of fear than we do, because it can specifically alter it," Robert Sapolsky, head of the Stanford lab where House works, said in the Stanford press release.
The researchers don't know precisely how the Toxoplasma is causing these behavioral changes. The parasite infects the whole brain, but especially the amygdala. Once in the brain, the parasite surrounds itself with a cyst, then seems to go dormant.
"There are not many organisms that can get into the brain, stay there and specifically perturb your behavior," House said.
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Toxoplasma aren't just a problem for rats. The parasite infects approximately one-third of the world's human population. Normally, the parasite is no big deal, but for people with compromised immune systems Toxoplasma can be deadly. Pregnant women are also cautioned not to clean kitty litter boxes because of the risk that Toxoplasma crossing the placental barrier and causing complications.
No one has ever shown that humans infected with Toxoplasma will suddenly find cat urine sexy, but...
"There are a couple dozen studies in the last few years showing that if you have schizophrenia, you are more likely to have Toxoplasma. The studies haven't shown cause and effect, but it's possible," House said. "Humans have amygdalae too. We are afraid of and attracted to things – it's similar circuitry."
The relationship between Toxoplasma and rats lends credence to the “manipulation hypothesis.” According to this hypothesis, some parasites alter the behavior of their hosts in ways that benefit the parasite.
For example another parasite infects freshwater snails and turns them into suicidal zombies. The infected snail develops a bulbous, pulsating eye stalk, and the insatiable urge to climb something tall. That leaves them exposed to predators, and the mutant eye stalk serves as a beacon attracting the attention of hungry birds. Once the snail is eaten, the parasite continues its life cycle in the bird's intestines.
Tags: Animal Behavior, Animals, Cats, Mammals, Parasites
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