Date Published: 4 November 2011

Brain parasite toxoplasma gondii alters brain chemistry

Recent research conducted at Leeds University (England) indicates that infection by the brain parasite toxoplasma gondii, may directly affect the production of dopamine, an important chemical messenger in the brain.

Toxoplasmosis can be transmitted via cat faeces and is found on unwashed vegetables and raw or undercooked infected meat. It is relatively common, with 10-20% of the UK population and 22% of the US population estimated to carry the parasite as cysts. Most people with the parasite are healthy, but for some people, e.g. those who are immune-suppressed, there are thought to be significant health risks.

The work was carried out using rodents but researcher Dr Glenn McConkey of the University's Faculty of Biological Sciences, suggested that the results might in time provide useful information about the treatment of human neurological disorders that are dopamine-related such as schizophrenia, attention deficit hyperactivity disorder, and Parkinson's disease.

In this study the research team found that the parasite toxoplasma gondii causes production and release of many times the normal amount of dopamine in infected brain cells.

Dopamine is a natural chemical that relays messages in the brain controlling aspects of movement, cognition and behaviour. It helps control the brain's reward and pleasure centres and regulates emotional responses such as fear. The presence of a certain kind of dopamine receptor is also associated with sensation-seeking, whereas dopamine deficiency in humans results in Parkinson's disease.
These findings build on earlier studies in which Dr McConkey's group found that the parasite actually encodes the enzyme for producing dopamine in its genome.

" Based on these analyses, it was clear that T. gondii can orchestrate a significant increase in dopamine production in neural cells," says Dr McConkey.

" Humans are accidental hosts to T. gondii and the parasite could end up anywhere in the brain, so human symptoms of toxoplasmosis infection may depend on where parasite ends up. This may explain the observed statistical link between incidences of schizophrenia and toxoplasmosis infection." Dr McConkey says his next experiments will investigate how the parasite enzyme triggers dopamine production and how this may change behaviour.

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