A treatment for Parkinson’s disease has been dramatically improved by boosting the levels of natural marijuana-like chemicals in the brain.

Researchers combined a drug used to treat patients with another that prevents the breakdown of substances called cannabinoids in the brain and noticed an almost complete recovery in mice that developed a Parkinson’s-like disease.

The scientists focused on a region of the brain called the striatum, which has been linked to a range of brain disorders including Parkinson’s. They uncovered two distinct brain circuits they believe play a key role in Parkinson’s disease. The first brain circuit activates normal movement, while the second works to restrain unwanted movements.

In Parkinson’s disease, nerves that produce a brain chemical called dopamine die off, and with low levels of dopamine, the second brain circuit becomes overactive, making it difficult for people to move properly.

In tests, mice treated with quinpirole, a dopamine-mimicking drug, showed a small improvement, but when injected with a chemical that slows down the degradation of cannabinoids in the brain, the mice were able to move freely within 15 minutes.

“The dopamine drug alone did a little bit but it wasn’t great, and the drug that targeted the enzyme that degrades endocannabinoids basically did nothing alone,” said Anatol Kreitzer at Stanford University school of medicine whose study appears in Nature today. “But when we gave the two together, the animals really improved dramatically.”

“It’s a long, long way to go before this will be tested in humans, but none the less, we have identified a new way of potentially manipulating the circuits that are malfunctioning in this disease,” added co-author Robert Malenka.

Parkinson’s disease affects one in 500 people and there are around 120,000 cases in Britain. The latest study sought to boost only those regions of the brain where cannabinoids are found naturally. “That is a really important difference, and it’s why we think our manipulation of the chemicals is really different from smoking marijuana,” said Professor Malenka.

resource: Guardian UK, Ian Sample – Thursday 8 February 2007