Brain Parasite Directly Alters Brain Chemistry
Research shows infection by the brain parasite Toxoplasma gondii, found in 10-20 percent of the U.K.’s population, directly affects the production of dopamine, a key chemical messenger in the brain.
Findings from the University of Leeds research group are the first to demonstrate that a parasite found in the brain of mammals can affect dopamine levels.
While the work has been carried out with rodents, lead investigator Dr. Glenn McConkey of the University’s Faculty of Biological Sciences believes that the findings could ultimately shed new light on treating dopamine-related human neurological disorders, such as schizophrenia, attention deficit hyperactivity disorder, and Parkinson’s disease.
This research may explain how these parasites, remarkably, manipulate rodents’ behavior to their advantage. 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 primary host to complete its life cycle.
In this study, funded by the Stanley Medical Research Institute and Dunhill Medical Trust, the research team found that the parasite causes the production and release of many times the average amount of dopamine in infected brain cells.
Dopamine is a natural chemical that relays messages in the brain controlling aspects of movement, cognition, and behavior. It helps control the brain’s reward and pleasure centers and regulates emotional responses like 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 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 the parasite ends up. This may explain the observed statistical link between incidences of schizophrenia and toxoplasmosis infection.”
Dr. McConkey says his subsequent experiments will investigate how the parasite enzyme triggers dopamine production and how this may change behavior.
Toxoplasmosis, transmitted via cat feces (found on unwashed vegetables) and raw or undercooked infected meat, is relatively common, with 10-20% of the U.K. population and 22% of the U.S. population estimated to carry the parasite as cysts. Most people with the parasite are healthy, but for those who are immune-suppressed – and particularly for pregnant women – there are significant health risks that can occasionally be fatal.
The parasite infects the brain by forming a cyst within its cells and produces an enzyme called tyrosine hydroxylase, which is needed to make dopamine. Dopamine’s role in mood, sociability, attention, motivation, and sleep patterns is well documented, and schizophrenia has long been associated with dopamine, which is the target of all current schizophrenia drugs on the market.
The enzyme tyrosine hydroxylase is a crucial step in making L-DOPA (prescribed as levodopa for Parkinson’s Disease), a chemical that is readily converted to the neurotransmitter dopamine.
The U.S.-based Stanley Medical Research Institute focuses on mental health conditions and has a particular emphasis on bipolar illnesses. Dunhill Medical Trust supports research on diseases of aging.