The medicinal properties of marijuana have been recognized for centuries, but clinical and societal acceptance of this drug of abuse as a potential therapeutic agent remains fiercely debated. An attractive alternative to marijuana-based therapeutics would be to target the molecular pathways that mediate the effects of this drug. To date, these neural signaling pathways have been shown to comprise a cannabinoid receptor (CB1) that binds the active constituent of marijuana, tetrahydrocannabinol (THC), and a postulated endogenous CB1 ligand anandamide. Although anandamide binds and activates the CB1 receptor in vitro, this compound induces only weak and transient cannabinoid behavioral effects in vivo, possibly a result of its rapid catabolism. Here we show that mice lacking the enzyme fatty acid amide hydrolase (FAAH ؊/؊ ) are severely impaired in their ability to degrade anandamide and when treated with this compound, exhibit an array of intense CB1-dependent behavioral responses, including hypomotility, analgesia, catalepsy, and hypothermia. FAAH ؊/؊ -mice possess 15-fold augmented endogenous brain levels of anandamide and display reduced pain sensation that is reversed by the CB1 antagonist SR141716A. Collectively, these results indicate that FAAH is a key regulator of anandamide signaling in vivo, setting an endogenous cannabinoid tone that modulates pain perception. FAAH may therefore represent an attractive pharmaceutical target for the treatment of pain and neuropsychiatric disorders.T he endogenous cannabinoid system has been the focus of intense research over the past decade (1-3). Cannabinoid receptors that recognize the active component of marijuana, ⌬ 9 -tetrahydrocannabinol (THC) (4), have been identified in both the brain (CB 1 receptor) and immune system (CB 2 receptor) (5). Additionally, a natural brain lipid, N-arachidonoyl ethanolamine, or anandamide, has been characterized as a possible endogenous ligand for the CB 1 receptor (6). Consistent with its postulated role as an endocannabinoid, anandamide (i) binds and activates the CB 1 receptor in vitro (6, 7), (ii) is produced in the brain in response to peripheral pain stimuli (8), and (iii) induces some cannabinoid behavioral effects in vivo, including hypothermia, analgesia, and motor defects (9-11).Although a number of biochemical and cell biological studies have provided evidence that anandamide acts as an endogenous CB 1 ligand (6,7,12,13), the behavioral effects induced by this compound are very weak and transient, especially when compared with those elicited by exocannabinoids like THC (11). Additionally, efforts to block the behavioral effects of anandamide with the CB 1 antagonist SR141716A have met with mixed success (14, 15). Most recently, anandamide was found to produce significant behavioral effects in CB 1 receptor-knockout (CB 1 Ϫ/Ϫ ) mice (16), suggesting that an alternative site(s) of action for this compound may exist in vivo. On this note, anandamide affects multiple receptor systems in addition to the CB 1 receptor in vitro, i...

Cellular communication in the nervous system is mediated by chemical messengers that include amino acids, monoamines, peptide hormones, and lipids. An interesting question is how neurons regulate signals that are transmitted by membrane-embedded lipids. Here, we report the 2.8 angstrom crystal structure of the integral membrane protein fatty acid amide hydrolase (FAAH), an enzyme that degrades members of the endocannabinoid class of signaling lipids and terminates their activity. The structure of FAAH complexed with an arachidonyl inhibitor reveals how a set of discrete structural alterations allows this enzyme, in contrast to soluble hydrolases of the same family, to integrate into cell membranes and establish direct access to the bilayer from its active site.

Fatty acid amide hydrolase (FAAH) and monoglyceride lipase (MGL) catalyse the hydrolysis of the endocannabinoids anandamide and 2-arachidonoyl glycerol. We investigated their ultrastructural distribution in brain areas where the localization and effects of cannabinoid receptor activation are known. In the hippocampus, FAAH was present in somata and dendrites of principal cells, but not in interneurons. It was located mostly on the membrane surface of intracellular organelles known to store Ca 2+ (e.g. mitochondria, smooth endoplasmic reticulum), less frequently on the somatic or dendritic plasma membrane. MGL immunoreactivity was found in axon terminals of granule cells, CA3 pyramidal cells and some interneurons. In the cerebellum, Purkinje cells and their dendrites are intensively immunoreactive for FAAH, together with a sparse axon plexus at the border of the Purkinje cell ⁄ granule cell layers. Immunostaining for MGL was complementary, the axons in the molecular layer were intensively labelled leaving the Purkinje cell dendrites blank. FAAH distribution in the amygdala was similar to that of the CB 1 cannabinoid receptor: evident signal in neuronal somata and proximal dendrites in the basolateral nucleus, and hardly any labelling in the central nucleus. MGL staining was restricted to axons in the neuropil, with similar relative signal intensities seen for FAAH in different nuclei. Thus, FAAH is primarily a postsynaptic enzyme, whereas MGL is presynaptic. FAAH is associated with membranes of cytoplasmic organelles. The differential compartmentalization of the two enzymes suggests that anandamide and 2-AG signalling may subserve functional roles that are spatially segregated at least at the stage of metabolism.