Science Cannabis

The Pharmacology ofTHC 57Figure 2.9. Distribution of cannabinoid CB! receptor in rat brain revealed byan autoradiograph of the binding of radioactively labelled CP-55940 to abrain section. The brain regions labelled are: Cb = cerebellum; CbN = deepcerebellar nucleus; cc = corpus callosum; EP = entopeduncular nucleus; fi= fimbria hippocampus; Fr = frontal cortex; FrPaM = frontoparietal cortexmotor area; GP = globus pallidus; Hi = hippocampus; 1C = inferior colliculus;LP = lateral posterior thalamus; Me = medial amygdaloid nucleus;PO = primary olfactory cortex; PCRt = parvocellular reticular nucleus; SNR= substantia nigra pars reticulata; Tu = olfactory tubercle; VP = ventroposteriorthalamus. Photograph kindly supplied by Dr. Miles Herkenham,National Institute of Mental Health, USA.from the CB-1 receptor in the brain (for review see Felder and Glass,1998). CB-2 receptors also bind radioactively tagged CP-55,940 and recognizemost of the cannabinoids that act at CB-1 sites. The CB-2 receptor,however, is clearly different and does not occur at all in the brain, beingfound only in peripheral tissues, particularly on white blood cells —thevarious components of the immune system of the body. It may be that theactions of THC on such CB-2 sites account for some of the effects ofcannabis on the immune system. Research on the CB-2 receptors will behelped by the recent availability of a drug that acts as a selective antagonistat these receptors (SR 144528), and by the development of a geneticallymodified strain of mice that lack CB-2 receptors.