Toxoplasmosis and Brain Chemistry

Toxoplasma gondii is a fiendishly clever microbe that can only complete its life cycle if it gets eaten by a cat. When it finds itself in a rat or mouse, it exercises a malign influence on its host's survival instincts:

Infected mice and rats lose their innate fear of cats, increasing the chances of being caught and eaten, which enables the parasite to return to its main host to complete its life cycle.

About 20% of people in the US and Britain are infected with Toxoplasmosis, because we live so closely with cats. In humans , Toxoplasmosis is associated with schizophrenia, although it has not been definitely shown to be a cause.

Now research has shown one particular effect that Toxoplasma gondii has in the human brain: it can dramatically increase the amount of dopamine produced by infected cells. The impact of this would depend on which cells in the brain were infected, but it could be all sorts of bad.