Body's 'internal marijuana': A new target for treatment of schizophrenia, Parkinson's?

“Endocannabinoids” is an impressive word that sounds like the name for a group of tribal warriors or an ancient people. Actually, it is the scientific term for beneficial molecules produced in the brain that act as “a sort of internal marijuana in our system,” says Andrea Giuffrida, Ph.D., assistant professor of pharmacology at The University of Texas Health Science Center at San Antonio.

Endocannabinoids stimulate the same nerve receptors (the cannabinoid or CB receptors) that the active ingredient in marijuana does. By regulating a chemical called dopamine, endocannabinoids seem to prevent psychosis. Increased dopamine activity is a brain abnormality documented in schizophrenics.

“In these subjects, the brain attempts to counterbalance this abnormality by producing more endocannabinoids,” Dr. Giuffrida says. “Thus, drugs that stimulate CB receptors may prove useful for the treatment of psychotic episodes.”

Dr. Giuffrida this week presented new data suggesting that activation of CB receptors might also protect against Parkinson’s disease. His report was part of the 34th Annual Meeting of the Society for Neuroscience Oct. 23-27 in San Diego.

Dr. Giuffrida discussed a study that was carried out in mice treated with MPTP, a compound that kills dopaminergic neurons – the same nerve cells that degenerate in Parkinson’s disease. The researchers found that administering a drug called WIN55212-2, which stimulates CB receptors, 30 minutes before MPTP sufficiently protected the neurons against MPTP injury.

Dr. Giuffrida cautioned that the result “may be limited to this mouse model, as the drug may interfere with the uptake of MPTP into dopaminergic cells. If that is the case, it may not prove to be a real anti-Parkinson’s therapy.”

However, he and his colleagues, James Roberts, Ph.D., professor of pharmacology at the Health Science Center, and Ph.D. student David Price, performed a second experiment in which they waited until MPTP was cleared out of the animal body before administering WIN55212-2. Even in this case, the marijuana-like compound proved effective.

“We saw a significant rescue of dopaminergic neurons, which tells us that WIN55212-2 might work in other models and in human Parkinson’s also, although we don’t know exactly through what mechanism,” Dr. Giuffrida said.