Cannabinoid Receptors - There are at least two cannabinoid receptor types, CB1 receptors, and CB2 receptors. CB1 receptors are found in high concentrations within the brain and spinal cord. Several cells in the brain and other organs contain specific protein receptors that recognize THC and some other cannabinoids and trigger cell responses. Other cannabinoids do not bind to these cannabinoid receptors and exert their effects by other ways.
The discovery of specific cannabinoid receptors prompted the search for naturally-occurring chemicals that interact with the receptors, the Endocannabinoids. (See defintion of Endocannabinoids in this glossary below.)
CB2 receptors are expressed primarily by immune cells and tissues (leukocytes, spleen and tonsils) but are also found in the brain.