Obesity has risen at an epidemic rate during the past 20 years, according to the Centers for Disease Control and Prevention. More than 60 percent of adult Americans are overweight or obese. These people face an increased risk for a range of physical ailments, including high blood pressure, diabetes, and stroke.
"For many years anecdotal reports have described how marijuana use can increase appetite," says Cowley. "Some users describe these cravings as the munchies."
This and other work has prompted the development of drugs that combat appetite by blocking the cannabinoid receptors, which are activated by marijuana. "Some of these drugs are in late stage clinical trials," says Cowley. "How they are able to control eating, however, has been a mystery."
To shed some light on how they might work, Cowley and his colleagues gave mice a cannabinoid receptor blocker, termed AM251. "We found that the treated animals significantly reduced their food intake, as has been known for many years," says Cowley. "We also found evidence that the activity of brain cells involved in the melanocortin system, which is known to control food intake and energy balance, increased."
Several molecular measures signaled that there was increased activity in melanocortin brain cells. Included was the discovery that in treated animals there was a fourfold increase in the number of melanocortin brain cells that contained c-fos, a marker of cellular activation.
"These data show that cannabinoid receptor blockers can regulate the melanocortin pathways in animals and support the further development of cannabinoid blockers to help combat obesity in humans," says Cowley.