Parasites have been shown to permanently remove the innate fear that mice have towards cats, which could give us key information in the treatment against schizophrenia.
For as long as there have been mice, there have been cats to chase those mice around. Neither of them can help it, it's in the cats nature to chase, and the mouses to be chased. It's built into the mouses brain at a cellular level to fear cats, and run from any sign of them. This is a very important reaction for a mouse to have, as any other reaction would probably result in their untimely demise.
However, recent research has suggested that the parasite Toxoplasma, which is a very common infection in humans, may be able to alter the brains of mice and eradicate their innate fear. Not only this, but it has also been shown that the effect of Toxoplasma is retained in the mouse long after the infection has cleared, suggesting that this change in the mouses behaviour is permanent and causes structural changes within the brain.
An infection by Toxoplasma induces a disease called Toxoplasmosis. Whilst most mammals and birds can be infected by this disease, the fear eradicating side effect seen in mice is totally unique.
Now, one of the biggest questions is obvious, why? Why would a parasite want to make its host less scared of cats? This actually happens so that the parasite can compete its life cycle. The only place that Toxoplasma can sexually reproduce is inside the cats intestines, and the only way it can get there is for the mouse that it's living in to be eaten.
This could help put the cartoon Tom and Jerry into a brand new perspective. Whilst we all thought we were watching a cat and a mouse running around in a bitter rivalry, what we were actually witnessing was just one stage in a parasites life cycle who had evolved over millions of years to fill in that one particular niche. Who'd have thought it ay?
It's all good and well having this very interesting piece of information, but in what ways, if any, can it relate to us as humans to help us understand ourselves?
Well, it turns out that this parasite is also prevalent in a large number of patients with schizophrenia, one of the symptoms of which is an increase in the levels of neurotransmitter dopamine. It is thought that the parasite can induce this increase by forming microscopic cysts that grow inside a number of brain cells, which increases their production of dopamine. In actual fact, the treatment against schizophrenia usually involves treatment against this infection.
However, because this loss of fear in mice is persistant and retained long after the infection has cleared, the changed induced by Toxoplasma must occur before cysts are formed, and must adapt the brain at a very basic level. This calls into question the theory of cysts increasing dopamine release being the cause of this behavioural change, potentially nullifying treatment against schizophernia that target cysts.
As with most research, this has raised more questions that it has answered. However, it has given us more crucial information on schizophrenia, and allows us to take one more step toward the effective treatment of this disease.
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If you're particularly interested in this research then you can find the original paper here.
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