cannabinoid receptor
any of a family of specialized molecules in cell membranes that bind with cannabis-based compounds and similar bodily created substances (i.e., with cannabinoids and endogenous cannabinoids, respectively). There are two known types: CB1 receptors, first identified in 1988 by U.S. pharmacologists Allyn C. Howlett and William A. Devane and located primarily within the brain and spinal cord; and CB2 receptors, located primarily within the spleen and other tissues of the immune system. Findings from recent research indicate the existence of other types of cannabinoid receptors (e.g., GPR55), but their characteristics have yet to be completely elaborated. Both CB1 and CB2 receptors are coupled to G proteins, which affect levels of second messengers that act to open or close certain ion channels. CB1 receptors are the most prolific G-protein-coupled receptors in the
central nervous system and are concentrated particularly within the hippocampus, cerebellum, and basal ganglia, areas of the brain related to motor control, learning and memory, emotional responses, motivated behavior, and homeostasis. Their activation by endogenous cannabinoids causes short- or long-term suppression of neurotransmitter release by neighboring neurons, leading to pain reduction, smooth muscle relaxation, suppression of nausea and vomiting, enhanced appetite, reduced intraocular pressure, and a variety of other physiological and behavioral effects. Additionally, the CB1 receptor is responsible for the psychoactive and psychomotor effects of plant-based cannabinoids, and it has been implicated in the rewarding aspects associated with the use of such drugs as alcohol, cocaine, methamphetamine, and heroin.
In contrast, activation of CB2 receptors produces immunosuppressive, anti-inflammatory, and antiallergenic effects. Given this wide range of activity, efforts are ongoing to develop synthetic cannabinoid receptor agonists and antagonists for therapeutic purposes.