A new imaging method could show how cannabinoids affect diseases like schizophrenia.

Scientists have long known that the brain possesses natural chemicals similar to marijuana. While little is known about their precise function in the brain, studies suggest that these compounds, known as cannabinoids, and the receptors they bind to, play a role in diseases, including schizophrenia, Parkinson’s disease, and obesity.

Now researchers at Johns Hopkins University have developed a way to image cannabinoid receptors in living animals. The tool will help scientists figure out how these receptors are altered in drug addiction and disease, as well as helping pharmaceutical companies to design drugs that better target this system.

“This is a real breakthrough,” says Richard Frank, vice president of medical affairs at GE Healthcare in Princeton, NJ. “Scientists have long believed that the cannabinoid system is involved in diseases, but they’ve never been able to measure the receptor in living people’s brains.” The tracer is very specific, and can therefore be used in low doses. That’s important, says Frank, because the compound has no pharmacologic effect. In other words, it doesn’t make the user feel “high.”

Scientists will also be able to study disorders that have been linked to the cannabinoid system, such as schizophrenia and Parkinson’s disease. For example, smoking marijuana appears to precipitate symptoms of schizophrenia. Furthermore, schizophrenics seem to have higher levels of cannabinoids in their brains. But animal studies of these diseases have produced conflicting results, says Andrea Giuffrida, a neuroscientist at the University of Texas Health Science Center in San Antonio. The new imaging method, he says, “will be useful to understand exactly what’s going on.”

The same is true for Parkinson’s disease. Some scientists speculate that cannabinoids play a protective role in the brain, slowing the rate of disease. But knowing exactly what happens to patients as the disease progresses is crucial, says Giuffrida. The new tracer could also aid in drug development. Marijuana is already used to help cancer and AIDS patients with chronic pain or nausea.

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