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Tuesday, February 12, 2013

Animals When a Rat Doesn't Fear a Cat

Posted by Charles Mudede on Tue, Feb 12, 2013 at 7:50 AM

After my post about why cats are so useful to us, a related post about why rats sometimes don't fear the smell of our cats. The idea is explained by, again, the great thinker and researcher of mammalian emotions Jaak Panksepp, but this time he is interviewed on Ginger Brown's other podcast, Brain Science Podcast. (I highly recommend it to those who are interested in the new developments in neuroscience.) The thing is this: Rats can become fearless if they are infected by a particular parasite.

Dr. Campbell: Is that toxoplasmosis?

Dr. Panksepp: Toxoplasma gondii... which is very prevalent in the world; many people are infected with it. France seems to have the highest level of infection. We get it from our cats. That's why mothers should not be cleaning cat poop out of a litter box.

It turns out that Toxoplasma gondii, in order to reproduce, the only place it reproduces is the stomach of a cat. So, how does Toxoplasma get into the stomach of a cat? Obviously by things cats eat. Cats like to prey on little rodents. Little rodents get exposed to Toxoplasma gondii. The cat eats it. And when the cat eats it, it eats rodents that aren't too scared of it. It turns out that Toxoplasma makes rats less fearful of cat smell.

Toxoplasma actually gets into the brain, as Sapolsky has shown, and blocks the cat smell from activating fear. Wow! That means these rats are more liable to end up in the stomach of a cat. So, that makes a wonderful evolutionary story: how a little bug outwitted the rat emotional system to get into the cat's stomach.

When reading passages like this, one has to wonder if lots of the things that we do as animals (things that are good or bad for us) have their roots in pathogens? Dawkins called us robots for the genes, but what if we are more robots (or better yet zombies) for parasites?

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The sacculina barnacle would seem to lie at an intersection of your interests:

http://en.wikipedia.org/wiki/Sacculina

Posted by Alden on February 12, 2013 at 8:38 AM

In my own readings on T.gondii, I found discussion that the flu virus allegedly makes us more social and likely to go out -- during our most contagious period before flu symptoms have manifested. Here's the article in the Atlantic.

Posted by treacle on February 12, 2013 at 8:55 AM

Thanks for the follow up.

When I first learned about toxoplasmosis, it caused me to question a lot of my preconceived notions regarding why I like the things that I like and dislike others. What sort of microscopic biological/organic/chemical reactions were happening that made my brain decide at some base level that I like or dislike something?

It's difficult to not slip into nihilistic lines of thought when one considers that ALL of our preferences and aversions may come down to either active infections, or vestigial bits of DNA from exposure to microbes that was left permanently in our ancestors' DNA and passed down to us.

We seem but mere puppets under the control of otherwise brainless, single-celled organisms.

Posted by Bored@School on February 12, 2013 at 9:06 AM

I like the Cowbird. Because it needs to follow herds to feed, it lays eggs in other birds nests. It doesn't infect a host to change it's behavior but uses other birds instincts and behaviors. And it's chicks are bigger than the others in the nest, so it can push the other nestlings out. Then the birds feed the Cowbird chick as if it's their own.

Posted by Pope Peabrain on February 12, 2013 at 9:07 AM

We aren't robots or zombies for parasites or single-celled organisms, but to their genes. This no more makes us puppets than being robots for "our" genes.

Posted by Dakn on February 12, 2013 at 9:39 AM

From what I read toxoplasmosis makes mice more likely to take risky chances. And the result of taking these chances is a greater likelihood of getting eaten and infecting a cat. And previous studies show that people who are infected take greater chances as well, and are more likely to have car accidents.

Posted by Dr.Duck on February 12, 2013 at 12:10 PM