<P> Cannabinoid receptors, located throughout the body, are part of the endocannabinoid system, which is involved in a variety of physiological processes including appetite, pain - sensation, mood, and memory . </P> <P> Cannabinoid receptors are of a class of cell membrane receptors in the G protein - coupled receptor superfamily . As is typical of G protein - coupled receptors, the cannabinoid receptors contain seven transmembrane spanning domains . Cannabinoid receptors are activated by three major groups of ligands: endocannabinoids, produced by the mammillary body; plant cannabinoids (such as cannabidiol, produced by the cannabis plant); and synthetic cannabinoids (such as HU - 210). All of the endocannabinoids and phytocannabinoids (plant based cannabinoids) are lipophilic, such as fat soluble compounds . </P> <P> There are currently two known subtypes of cannabinoid receptors, termed CB and CB . The CB receptor is expressed mainly in the brain (central nervous system or "CNS"), but also in the lungs, liver and kidneys . The CB receptor is expressed mainly in the immune system and in hematopoietic cells . Mounting evidence suggests that there are novel cannabinoid receptors that is, non-CB and non-CB, which are expressed in endothelial cells and in the CNS . In 2007, the binding of several cannabinoids to the G protein - coupled receptor GPR55 in the brain was described . </P> <P> The protein sequences of CB and CB receptors are about 44% similar . When only the transmembrane regions of the receptors are considered, amino acid similarity between the two receptor subtypes is approximately 68% . In addition, minor variations in each receptor have been identified . Cannabinoids bind reversibly and stereo - selectively to the cannabinoid receptors . Subtype selective cannabinoids have been developed which theoretically may have advantages for treatment of certain diseases such as obesity . </P>

Where are cannabinoid receptors located in the brain