In people with schizophrenia, a brain circuit that regulates emotion is overwhelmed by a chemical messenger called dopamine. The new discovery confirms a long-standing hypothesis about schizophrenia and provides the most direct evidence to date on why schizophrenics lose touch with reality.
The devastating symptoms of schizophrenia include delusions, hallucinations and paranoia. Like all effective antipsychotic drugs block a receptor for the neurotransmitter dopamine, the researchers guessed there are more than 30 years that dopamine circuits were overactive in people with the disease. This could be caused by an excess of dopamine, a too large number of dopamine receptors, or both. Indeed, the autopsies showed schizophrenics an overabundance of one type of dopamine receptors in the striatum, a part of the brain that helps to regulate emotion. But because most people with schizophrenia were treated with antipsychotic drugs, some researchers have argued that it was a result of drug treatment rather than the disease.
To measure whether the circuitry of dopamine-sensitive were overactive in schizophrenia, Anissa Abi-Dargham of Columbia University College of Physicians and Surgeons in New York and colleagues compared 18 schizophrenia with 18 normal subjects . First they treated patients and controls for 2 days with a drug that knocks off dopamine receptors. Then they gave the patients a mimetic radiolabeled dopamine which could accumulate on dopamine receptors emptied. Using a brain imaging method called emission tomography single photon, they compared the amount of dopamine molecules like landed on the receptors in the two groups.
In people with schizophrenia, the amount of dopamine-like molecules bound to the receptors increased twice that in controls, they report in the edition July 5 of Proceedings of the national Academy of sciences . It most likely means that schizophrenics have both more dopamine available and most of the dopamine receptors. In addition, the increase occurred in the October 2 chronic patients - who had used antipsychotic drugs in the past -. And in the eight newly diagnosed patients who had never been treated with medication
The search for "can potentially help us understand how antipsychotic drugs work," says psychiatrist and neuroscientist Francine Benes from Harvard Medical School in Boston. But psychiatrist Shitij Kapur of the University of Toronto is warning that researchers still need a way to measure dopamine directly into the brains of live schizophrenic. But "assuming this is in place," dit- it, "the whole story [dopamine] will start to come together."
For more information on schizophrenia of the National Institute of Mental Health: www.nimh.nih. gov / publicat / schizoph.htm
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