Marijuana-Like Brain Chemicals Ease Parkinson's Symptoms in Mice

The treatment is much more targeted than smoking marijuana, researchers say.

By Ed Edelson
HealthDay Reporter
Wednesday, February 7, 2007; 12:00 AM

Copyright © 2007 ScoutNews, LLC. All rights reserved.

WEDNESDAY, Feb. 7 (HealthDay News) -- Manipulation of brain molecules similar to those found in marijuana provided dramatic relief of Parkinson's-like symptoms in mice, researchers report.

"This might be a target for treatment that could cure the motor deficits seen in Parkinson's disease," said lead researcher Anatol Kreitzer, whose team published the findings in the Feb. 8 issue of Nature.

Kreitzer emphasized two points, however -- that a lot of work must be done before human trials can begin, and that the study results do not support smoking marijuana as a way to help Parkinson's patients.

The study did involve cannabinoids, molecules that are similar to those found in marijuana. But these cannabinoids occur naturally in the brain, and the study hinged on targeting specific cannabinoids.

"When you smoke a joint, you activate cannabinoid receptors all over the brain," explained Kreitzer, who now is a postdoctoral fellow at Stanford University and will soon move to a research position at the University of California, San Francisco. "That is indiscriminate," Kreitzer said. "In general, you need more specific signaling. Our approach involved only regions of the brain or cells that release dopamine."

Dopamine is crucial, because a lack of that chemical produces the movement problems seen in Parkinson's disease. Kreitzer and Dr. Robert Malenka, professor in psychiatry and behavioral sciences at Stanford, focused on dopamine in the striatum, a region of the brain implicated in Parkinson's disease and a number of other disorders.

"This particular part of the brain doesn't have any obvious anatomy," Kreitzer said. "If you just look at the cells, they all look alike. But it turns out that there are two specific circuits there involved in the control of movement -- a direct pathway that activates motion and an indirect pathway that inhibits motion."

The researchers worked with mice engineered to have a fluorescent protein in one of those circuits. They found that dopamine acts differently in the two circuits. When dopamine is depleted in the pathway that inhibits movement, it becomes overly active.