By Nancy Deutsch
NEW YORK, Jul 07 (Reuters Health) - For the first time, researchers have
managed to prove what has long been suspected: people with schizophrenia have
receptors in the brain that are chemically overstimulated.
Investigators from Columbia University College of Physicians and Surgeons in
New York City have performed the first study in humans to show that the
neurochemical dopamine is more active in schizophrenics than in people without
the psychiatric disorder.
"We suspected it. This is the first time it's been measured," said Dr.
Anissa Abi-Dargham, lead author of the study published in the July 5th issue of
the Proceedings of the National Academy of Sciences.
Measuring the dopamine in the brain is a difficult task, she admitted. The
researchers relied on brain imaging scans to assess the dopamine receptors
(areas where dopamine attaches) in the brains of 18 people with schizophrenia.
The team performed similar scans on 18 healthy individuals. The percentage
of dopamine receptors active in schizophrenics were found to be much higher than
in healthy individuals, Abi-Dargham told Reuters Health. Patients with
schizophrenia had a dopamine receptor availability of 19%, versus 9% in healthy
controls. While the number of individuals in the study was small, these people
were not taking any antipsychotic medication at the time, showing that the
dopamine receptors were more active without any outside intervention, she said.
When the system regulating dopamine transmission is interrupted, it makes
sense that psychotic symptoms would be reduced in these patients, explaining the
success of antipsychotics, Abi-Dargham said. These findings show that "patients
with higher levels of dopamine are most likely to improve with antipsychotic
treatment," she commented. "It makes sense. It's nice to demonstrate that it
makes sense."
About 20% to 30% of schizophrenic patients do not have high levels of
dopamine, she noted, and do not respond to antipsychotic treatment,
demonstrating that for some patients, other factors are involved in the disease
process. "We have to find out what it is that would work in other patients."
Furthermore, the researcher added, in patients with high levels of dopamine,
antipsychotics stem the more dramatic symptoms, such as hearing voices. But
these people still have altered cognitive functioning and cannot relate well to
others, indicating that other processes are involved in schizophrenia, not just
dopamine reception, she explained.
The team next plans to conduct a similar study using better imaging
equipment that has since become available, Abi-Dargham said. With better tools,
they hope to detect changes in smaller structures of the brain.
