CB1 is the main cannabinoid receptor in the brain but is also found in other tissues. CB1 is a G protein-coupled receptor which inhibits adenylyl cyclase and consequently reduces cAMP upon activation. This in turn regulates many second messenger pathways. 

CB2 is primarily expressed in the immune cells and tissues of the body. Like CB1, CB2 is a G protein-coupled receptor which inhibits adenylyl cyclase and consequently lowers cAMP upon activation. This, in turn, regulates many second messenger pathways.