Researchers at the University of California San Francisco have shown in rats that a synthetic drug that mimics the principal active ingredient in marijuana has an effect similar to that of morphine on an area of the brain that modulates pain.
The finding, reported in the September 24 issue of Nature, raises the possibility that marijuana-like drugs could be used to treat pain, said the lead author of the study, Ian Meng, PhD, a postdoctoral fellow in the laboratory of Howard Fields, PhD, a professor of neurology and physiology and a research scientist in the W.M. Keck Foundation Center for Integrative Neuroscience at UCSF.
While opioids such as morphine provide strong analgesic effects for many types of pain, they produce side effects such as nausea and respiratory depression. In contrast, marijuana, a type of cannabinoid drug, actually increases appetite. In the future, says Meng, it may be possible to use a lower dose of opioids if they are used in combination with a cannabinoid, producing fewer side effects and increasing the pain relieving effects.
The researchers focused their study on a region of the brain known as the rostral ventromedial medulla (RVM) which modulates pain by either increasing or decreasing the amount of pain signals that pass through the spinal cord. They tested the effects of the synthetic cannabinoid, WIN555, 212-2, on this region by measuring the time it took for rats to move their tails away from a heat source.
In the first experiment, rats that were given WIN55,212-2 kept their tails on the heat source much longer than rats that were not given the drug, indicating the drug reduced pain. However, after the researchers shut down the RVM, rats that were given WIN55,212-2 no longer demonstrated insensitivity to pain, moving their tails from the heat source as quickly as the rats who had not received the drug. The test demonstrated that the RVM was critical for producing the pain-relieving effects of cannabinoids.