Cannabinoid
Cannabinoids are a class of diverse chemical compounds that act on cannabinoid receptors on cells that repress neurotransmitter release in the brain. These receptor proteins include the endocannabinoids (produced naturally in the body by humans and animals),[1] the phytocannabinoids (found in cannabis and some other plants), and synthetic cannabinoids (manufactured chemically). The most notable cannabinoid is the phytocannabinoid ∆9-tetrahydrocannabinol (THC), the primary psychoactive compound of cannabis.[2][3] Cannabidiol (CBD) is another major constituent of the plant, representing up to 40% in extracts of the plant resin.[4] There are at least 85 different cannabinoids isolated from cannabis, exhibiting varied effects.[5]
Synthetic cannabinoids encompass a variety of distinct chemical classes: the classical cannabinoids structurally related to THC, the nonclassical cannabinoids (cannabimimetics) including the aminoalkylindoles, 1,5-diarylpyrazoles, quinolines, and arylsulphonamides, as well as eicosanoids related to the endocannabinoids.[2]
Cannabinoid receptors
Before the 1980s, it was often speculated that cannabinoids produced their physiological and behavioral effects via nonspecific interactions, instead of interacting with specific receptors directly. The discovery of the first cannabinoid receptors in the 1980s helped to resolve this debate. These receptors are common in animals, and have been found in mammals, birds, fish, and reptiles. At present, there are two known types of cannabinoid receptors, termed CB1 and CB2,[1] with mounting evidence of more.[6] The human brain has more cannabinoid receptors than any other G protein-coupled receptor (GPCR) type.[7]
Cannabinoid receptor type 1
CB1 receptors are found primarily in the brain, more specifically in the basal ganglia and in the limbic system, including the hippocampus.[1] They are also found in the cerebellum and in both male and female reproductive systems. CB1 receptors are absent in the medulla oblongata, the part of the brain stem responsible for respiratory and cardiovascular functions. Thus, there is not the risk of respiratory or cardiovascular failure that can be produced by some drugs. CB1 receptors appear to be responsible for the euphoric and anticonvulsive effects of cannabis.
Cannabinoid receptor type 2
CB2 receptors are predominantly found in the immune system, or immune-derived cells[8] with the greatest density in the spleen. While found only in the peripheral nervous system, a report does indicate that CB2 is expressed by a subpopulation of microglia in the human cerebellum.[9] CB2 receptors appear to be responsible for the anti-inflammatory and possibly other therapeutic effects of cannabis.[8]