Cannabinoid receptor surprise

© Dr Neal Scolding / Photo Researchers, Inc.

The paper:

The finding:

While studying the anti-emetic effects of endogenous cannabinoids in ferrets, Keith Sharkey at the University of Calgary, Canada and colleagues found that agonists to the CB2 cannabinoid receptor reduced emetic events, even though only CB1 receptors were thought to be present in neurons. Probing further, Sharkey's group found CB2 messenger RNA and protein in three areas of rat brain.

The surprise:

CB2 receptors had "been identified before in the immune system," Sharkey says. "They were considered to be the peripheral CB receptors," with all effects of cannabinoids in the brain attributed to the CB1 receptor.

The brain:

This paper is only "half of the story," says Emmanuel Onaivi, assistant professor at William Patterson University, who was not an author of the paper. His and others' follow-up work has confirmed the presence of CB2 in rat cortex and cerebellum, and shown CB2 levels increase in areas associated with depression and addiction, when triggered by substances such as marijuana and alcohol.

The gut:

New research by Sharkey and others on CB2 receptors in the gut suggests that CB2 is activated in times of inflammation. CB2 receptors "seem to be an interesting braking system," Sharkey says. They are "able to regulate certain gut functions to try to restore normal physiology."