Cannabinoid Receptors
Definition: Cannabinoid receptors are proteins on the surface of cells that respond to cannabinoids, both the body’s own endocannabinoids and plant compounds like THC. The two main types are CB1, found mostly in the brain, and CB2, found mostly on immune cells. Together they form the core of the endocannabinoid system (ECS).
What Is the Endocannabinoid System?
The endocannabinoid system is a cell-signaling network that helps regulate pain, mood, appetite, memory, sleep, stress, and immune responses. It has three parts:
- Receptors: mainly CB1 and CB2
- Endocannabinoids: molecules the body makes on demand, chiefly anandamide (discovered in 1992) and 2-AG (identified in 1995)
- Enzymes: FAAH and MAGL, which break endocannabinoids down once they’ve done their job
How Do Cannabinoid Receptors Work?
Both CB1 and CB2 are G protein-coupled receptors. When an endocannabinoid binds, it usually acts as a brake, reducing how much of a chemical messenger a nerve or immune cell releases. THC mimics this by binding CB1, which is why it changes mood, memory, and perception. CBD binds these receptors only weakly and works mostly through other targets.
When Were Cannabinoid Receptors Discovered?
Researchers identified the CB1 receptor in rat brain tissue in 1988 and cloned it in 1990. The CB2 receptor was cloned in 1993. Finding receptors that THC fit so precisely led scientists to search for, and find, the body’s own cannabinoids.
Are There Other Cannabinoid Receptors?
Possibly. Cannabinoids also act on other receptors, including GPR55 and TRPV1, the receptor that senses heat and capsaicin. Whether GPR55 should count as a third cannabinoid receptor is still debated.
Related terms: CB1 Receptor, CB2 Receptors, Cannabinoids, Caryophyllene
Sources: Lu HC, Mackie K, “An Introduction to the Endogenous Cannabinoid System,” Biological Psychiatry, 2016; National Institute on Drug Abuse: Cannabis (Marijuana).
