In the brains of mice the activation of receptors can counteract the behavioral and addictive effects of cocaine, finds American and Chinese scientists. This major finding paves way for new treatments of drug addiction.
There are two major cannabinoid receptor types: CB1 and CB2.
CB1 receptors, which are found in large numbers in the brain activated by drugs such as marijuana. They are known to stimulate the brain's reward system, which is why they have been the focus of addiction research.
CB2 receptors are primarily located on the body's immune cells. They are also known to be involved in pain perception.
Until recently, it was thought that CB2 receptors were not present in the brain or that, if they were, it was in such low density that they were not involved in drug addiction.
Now for the first time, a research led by Dr Zheng-Xiong Xi of the National Institute on Drug Abuse in the US, has identified that CB2 plays a vital role in controlling the reward mechanism responsible for drug addiction.
In their study, Xi and colleagues trained mice to self-administer cocaine intravenously. The researchers found that activating CB2 receptors with two different 'agonists' reduced drug-induced behaviour such as hyperactivity.
In addition, the CB2 receptor agonists reduced the bouts and amount of drug intake in normal (wild type) mice and mice who lacked the CB1 receptors, but not those that lacked CB2 receptors.
Further experiments showed the observed effects were mediated by the brain's CB2 receptors and that the rewarding effects of cocaine were blocked.
"Taken all together, the present findings, for the first time suggest that brain CB2 receptors functionally modulate the acute rewarding and locomotor-stimulating effects of cocaine in mice," ABC Science quoted Xi as saying.
"Our findings open a new field; CB2 agonists have a very high potential for treating addiction," he added.
Xi and his colleagues are now focusing on finding the mechanism by which activation of CB2 receptors inhibits dopamine release.
The results are published online in Nature Neuroscience.