Two types of cannabinoid receptor have been discovered so far, CB(1) (<em>2</em>.1: CBD:1:CB1:), cloned in 1990, and CB(<em>2</em>) (<em>2</em>.1:CBD:<em>2</em>:CB<em>2</em>:), cloned in 1993. Distinction between these receptors is based on differences in their predicted amino acid sequence, signaling mechanisms, tissue distribution, and sensitivity to certain potent agonists and antagonists that show marked selectivity for one or the other receptor type. Cannabinoid receptors CB(1) and CB(<em>2</em>) exhibit 48% amino acid sequence identity. Both receptor types are coupled through G proteins to adenylyl cyclase and mitogen-activated protein kinase. CB(1) receptors are also coupled through G proteins to several types of calcium and potassium channels. These receptors exist primarily on central and peripheral neurons, one of their functions being to inhibit neurotransmitter release. Indeed, endogenous CB(1) agonists probably serve as retrograde synaptic messengers. CB(<em>2</em>) receptors are present mainly on immune cells. Such cells also express CB(1) receptors, albeit to a lesser extent, with both receptor types exerting a broad spectrum of immune effects that includes modulation of cytokine release. Of several endogenous agonists for cannabinoid receptors identified thus far, the most notable are arachidonoylethanolamide, <em>2</em>-<em>arachidonoylglycerol</em>, and <em>2</em>-arachidonylglyceryl ether. It is unclear whether these eicosanoid molecules are the only, or primary, endogenous agonists. Hence, we consider it premature to rename cannabinoid receptors after an endogenous agonist as is recommended by the International Union of Pharmacology Committee on Receptor Nomenclature and Drug Classification. Although pharmacological evidence for the existence of additional types of cannabinoid receptor is emerging, other kinds of supporting evidence are still lacking.

The effects of anadamide, <em>2</em>-<em>arachidonoylglycerol</em> and related compounds on the specific binding of a radiolabeled cannabinoid receptor ligand,[3H]CP55940, to synaptosomal membranes were examined. Anandamide, an endogenous cannabinoid receptor ligand, reduced the specific binding of [3H]CP55940 to synaptosomal membranes in a dose-dependent manner: the Ki value was 89 nM. <em>2</em>-<em>Arachidonoylglycerol</em> was also shown to bind appreciably to the cannabinoid receptor in competitive inhibition experiments. The apparent binding affinity was markedly increased when the binding assay was carried out in the presence of the esterase inhibitor DFP or at 0 degrees C. Free arachidonic acid and N-palmitoylethanolamine were almost inactive in terms of binding to the cannabinoid receptor in synaptosomal membranes. <em>2</em>-<em>Arachidonoylglycerol</em> may be an endogenous cannabinoid receptor ligand in the brain.

The presence and function of CB<em>2</em> receptors in central nervous system (CNS) neurons are controversial. We report the expression of CB<em>2</em> receptor messenger RNA and protein localization on brainstem neurons. These functional CB<em>2</em> receptors in the brainstem were activated by a CB<em>2</em> receptor agonist, <em>2</em>-<em>arachidonoylglycerol</em>, and by elevated endogenous levels of endocannabinoids, which also act at CB1 receptors. CB<em>2</em> receptors represent an alternative site of action of endocannabinoids that opens the possibility of nonpsychotropic therapeutic interventions using enhanced endocannabinoid levels in localized brain areas.

The endogenous cannabinoids (endocannabinoids) are lipid molecules that may mediate retrograde signaling at central synapses and other forms of short-range neuronal communication. The monoglyceride <em>2</em>-<em>arachidonoylglycerol</em> (<em>2</em>-AG) meets several criteria of an endocannabinoid substance: (i) it activates cannabinoid receptors; (ii) it is produced by neurons in an activity-dependent manner; and (iii) it is rapidly eliminated. <em>2</em>-AG inactivation is only partially understood, but it may occur by transport into cells and enzymatic hydrolysis. Here we tested the hypothesis that monoglyceride lipase (MGL), a serine hydrolase that converts monoglycerides to fatty acid and glycerol, participates in <em>2</em>-AG inactivation. We cloned MGL by homology from a rat brain cDNA library. Its cDNA sequence encoded for a 303-aa protein with a calculated molecular weight of 33,367 daltons. Northern blot and in situ hybridization analyses revealed that MGL mRNA is heterogeneously expressed in the rat brain, with highest levels in regions where CB(1) cannabinoid receptors are also present (hippocampus, cortex, anterior thalamus, and cerebellum). Immunohistochemical studies in the hippocampus showed that MGL distribution has striking laminar specificity, suggesting a presynaptic localization of the enzyme. Adenovirus-mediated transfer of MGL cDNA into rat cortical neurons increased MGL expression and attenuated N-methyl-D-aspartate/carbachol-induced <em>2</em>-AG accumulation in these cells. No such effect was observed on the accumulation of anandamide, another endocannabinoid lipid. The results suggest that hydrolysis by means of MGL is a primary mechanism for <em>2</em>-AG inactivation in intact neurons.

Endogenous ligands for cannabinoid receptors ("endocannabinoids") include the lipid transmitters anandamide and <em>2</em>-<em>arachidonoylglycerol</em> (<em>2</em>-AG). Endocannabinoids modulate a diverse set of physiological processes and are tightly regulated by enzymatic biosynthesis and degradation. Termination of anandamide signaling by fatty acid amide hydrolase (FAAH) is well characterized, but less is known about the inactivation of <em>2</em>-AG, which can be hydrolyzed by multiple enzymes in vitro, including FAAH and monoacylglycerol lipase (MAGL). Here, we have taken a functional proteomic approach to comprehensively map <em>2</em>-AG hydrolases in the mouse brain. Our data reveal that approximately 85% of brain <em>2</em>-AG hydrolase activity can be ascribed to MAGL, and that the remaining 15% is mostly catalyzed by two uncharacterized enzymes, ABHD6 and ABHD1<em>2</em>. Interestingly, MAGL, ABHD6, and ABHD1<em>2</em> display distinct subcellular distributions, suggesting that they may control different pools of <em>2</em>-AG in the nervous system.

<em>2</em>-<em>Arachidonoylglycerol</em> (<em>2</em>-AG) and anandamide are endocannabinoids that activate the cannabinoid receptors CB1 and CB<em>2</em>. Endocannabinoid signaling is terminated by enzymatic hydrolysis, a process that for anandamide is mediated by fatty acid amide hydrolase (FAAH), and for <em>2</em>-AG is thought to involve monoacylglycerol lipase (MAGL). FAAH inhibitors produce a select subset of the behavioral effects observed with CB1 agonists, which suggests a functional segregation of endocannabinoid signaling pathways in vivo. Testing this hypothesis, however, requires specific tools to independently block anandamide and <em>2</em>-AG metabolism. Here, we report a potent and selective inhibitor of MAGL called JZL184 that, upon administration to mice, raises brain <em>2</em>-AG by eight-fold without altering anandamide. JZL184-treated mice exhibited a broad array of CB1-dependent behavioral effects, including analgesia, hypothermia and hypomotility. These data indicate that <em>2</em>-AG endogenously modulates several behavioral processes classically associated with the pharmacology of cannabinoids and point to overlapping and unique functions for <em>2</em>-AG and anandamide in vivo.

Acute stress suppresses pain by activating brain pathways that engage opioid or non-opioid mechanisms. Here we show that an opioid-independent form of this phenomenon, termed stress-induced analgesia, is mediated by the release of endogenous marijuana-like (cannabinoid) compounds in the brain. Blockade of cannabinoid CB(1) receptors in the periaqueductal grey matter of the midbrain prevents non-opioid stress-induced analgesia. In this region, stress elicits the rapid formation of two endogenous cannabinoids, the lipids <em>2</em>-<em>arachidonoylglycerol</em> (<em>2</em>-AG) and anandamide. A newly developed inhibitor of the <em>2</em>-AG-deactivating enzyme, monoacylglycerol lipase, selectively increases <em>2</em>-AG concentrations and, when injected into the periaqueductal grey matter, enhances stress-induced analgesia in a CB1-dependent manner. Inhibitors of the anandamide-deactivating enzyme fatty-acid amide hydrolase, which selectively elevate anandamide concentrations, exert similar effects. Our results indicate that the coordinated release of <em>2</em>-AG and anandamide in the periaqueductal grey matter might mediate opioid-independent stress-induced analgesia. These studies also identify monoacylglycerol lipase as a previously unrecognized therapeutic target.

Prolonged exposure to drugs of abuse, such as cannabinoids and opioids, leads to pharmacological tolerance and receptor desensitization in the nervous system. We found that a similar form of functional antagonism was produced by sustained inactivation of monoacylglycerol lipase (MAGL), the principal degradative enzyme for the endocannabinoid <em>2</em>-<em>arachidonoylglycerol</em>. After repeated administration, the MAGL inhibitor JZL184 lost its analgesic activity and produced cross-tolerance to cannabinoid receptor (CB1) agonists in mice, effects that were phenocopied by genetic disruption of Mgll (encoding MAGL). Chronic MAGL blockade also caused physical dependence, impaired endocannabinoid-dependent synaptic plasticity and desensitized brain CB1 receptors. These data contrast with blockade of fatty acid amide hydrolase, an enzyme that degrades the other major endocannabinoid anandamide, which produced sustained analgesia without impairing CB1 receptors. Thus, individual endocannabinoids generate distinct analgesic profiles that are either sustained or transitory and associated with agonism and functional antagonism of the brain cannabinoid system, respectively.

Phospholipase A(<em>2</em>)(PLA(<em>2</em>)) enzymes are considered the primary source of arachidonic acid for cyclooxygenase (COX)-mediated biosynthesis of prostaglandins. Here, we show that a distinct pathway exists in brain, where monoacylglycerol lipase (MAGL) hydrolyzes the endocannabinoid <em>2</em>-<em>arachidonoylglycerol</em> to generate a major arachidonate precursor pool for neuroinflammatory prostaglandins. MAGL-disrupted animals show neuroprotection in a parkinsonian mouse model. These animals are spared the hemorrhaging caused by COX inhibitors in the gut, where prostaglandins are instead regulated by cytosolic PLA(<em>2</em>). These findings identify MAGL as a distinct metabolic node that couples endocannabinoid to prostaglandin signaling networks in the nervous system and suggest that inhibition of this enzyme may be a new and potentially safer way to suppress the proinflammatory cascades that underlie neurodegenerative disorders.

Obesity is the main risk factor for the development of type <em>2</em> diabetes. Activation of the central endocannabinoid system increases food intake and promotes weight gain. Blockade of the cannabinoid type 1 (CB-1) receptor reduces body weight in animals by central and peripheral actions; the role of the peripheral endocannabinoid system in human obesity is now being extensively investigated. We measured circulating endocannabinoid concentrations and studied the expression of CB-1 and the main degrading enzyme, fatty acid amide hydrolase (FAAH), in adipose tissue of lean (n = <em>2</em>0) and obese (n = <em>2</em>0) women and after a 5% weight loss in a second group of women (n = 17). Circulating levels of anandamide and 1/<em>2</em>-<em>arachidonoylglycerol</em> were increased by 35 and 5<em>2</em>% in obese compared with lean women (P < 0.05). Adipose tissue mRNA levels were reduced by -34% for CB-1 and -59% for FAAH in obese subjects (P < 0.05). A strong negative correlation was found between FAAH expression in adipose tissue and circulating endocannabinoids. Circulating endocannabinoids and CB-1 or FAAH expression were not affected by 5% weight loss. The expression of CB-1 and FAAH was increased in mature human adipocytes compared with in preadipocytes and was found in several human tissues. Our findings support the presence of a peripheral endocannabinoid system that is upregulated in human obesity.

Endocannabinoids are released from postsynaptic neurons and cause retrograde suppression of synaptic transmission. Anandamide and <em>2</em>-<em>arachidonoylglycerol</em> (<em>2</em>-AG) are regarded as two major endocannabinoids. To determine to what extent <em>2</em>-AG contributes to retrograde signaling, we generated and analyzed mutant mice lacking either of the two <em>2</em>-AG synthesizing enzymes diacylglycerol lipase alpha (DGLalpha) and beta (DGLbeta). We found that endocannabinoid-mediated retrograde synaptic suppression was totally absent in the cerebellum, hippocampus, and striatum of DGLalpha knockout mice, whereas the retrograde suppression was intact in DGLbeta knockout brains. The basal <em>2</em>-AG content was markedly reduced and stimulus-induced elevation of <em>2</em>-AG was absent in DGLalpha knockout brains, whereas the <em>2</em>-AG content was normal in DGLbeta knockout brains. Morphology of the brain and expression of molecules required for <em>2</em>-AG production other than DGLs were normal in the two knockout mice. We conclude that <em>2</em>-AG produced by DGLalpha, but not by DGLbeta, mediates retrograde suppression at central synapses.

The endocannabinoid <em>2</em>-<em>arachidonoylglycerol</em> (<em>2</em>-AG) regulates neurotransmission and neuroinflammation by activating CB1 cannabinoid receptors on neurons and CB<em>2</em> cannabinoid receptors on microglia. Enzymes that hydrolyze <em>2</em>-AG, such as monoacylglycerol lipase, regulate the accumulation and efficacy of <em>2</em>-AG at cannabinoid receptors. We found that the recently described serine hydrolase alpha-beta-hydrolase domain 6 (ABHD6) also controls the accumulation and efficacy of <em>2</em>-AG at cannabinoid receptors. In cells from the BV-<em>2</em> microglia cell line, ABHD6 knockdown reduced hydrolysis of <em>2</em>-AG and increased the efficacy with which <em>2</em>-AG can stimulate CB<em>2</em>-mediated cell migration. ABHD6 was expressed by neurons in primary culture and its inhibition led to activity-dependent accumulation of <em>2</em>-AG. In adult mouse cortex, ABHD6 was located postsynaptically and its selective inhibition allowed the induction of CB1-dependent long-term depression by otherwise subthreshold stimulation. Our results indicate that ABHD6 is a rate-limiting step of <em>2</em>-AG signaling and is therefore a bona fide member of the endocannabinoid signaling system.

Delta(9)-tetrahydrocannabinol (THC), the psychoactive component of marijuana, and other direct cannabinoid receptor (CB1) agonists produce a number of neurobehavioral effects in mammals that range from the beneficial (analgesia) to the untoward (abuse potential). Why, however, this full spectrum of activities is not observed upon pharmacological inhibition or genetic deletion of either fatty acid amide hydrolase (FAAH) or monoacylglycerol lipase (MAGL), enzymes that regulate the two major endocannabinoids anandamide (AEA) and <em>2</em>-<em>arachidonoylglycerol</em> (<em>2</em>-AG), respectively, has remained unclear. Here, we describe a selective and efficacious dual FAAH/MAGL inhibitor, JZL195, and show that this agent exhibits broad activity in the tetrad test for CB1 agonism, causing analgesia, hypomotilty, and catalepsy. Comparison of JZL195 to specific FAAH and MAGL inhibitors identified behavioral processes that were regulated by a single endocannabinoid pathway (e.g., hypomotility by the <em>2</em>-AG/MAGL pathway) and, interestingly, those where disruption of both FAAH and MAGL produced additive effects that were reversed by a CB1 antagonist. Falling into this latter category was drug discrimination behavior, where dual FAAH/MAGL blockade, but not disruption of either FAAH or MAGL alone, produced THC-like responses that were reversed by a CB1 antagonist. These data indicate that AEA and <em>2</em>-AG signaling pathways interact to regulate specific behavioral processes in vivo, including those relevant to drug abuse, thus providing a potential mechanistic basis for the distinct pharmacological profiles of direct CB1 agonists and inhibitors of individual endocannabinoid degradative enzymes.

Cannabinoids act at two classical cannabinoid receptors (CB1 and CB<em>2</em>), a 7TM orphan receptor and the transmitter-gated channel transient receptor potential vanilloid type-1 receptor. Recent evidence also points to cannabinoids acting at members of the nuclear receptor family, peroxisome proliferator-activated receptors (PPARs, with three subtypes alpha, beta (delta) and gamma), which regulate cell differentiation and lipid metabolism. Much evidence now suggests that endocannabinoids are natural activators of PPAR alpha. Oleoylethanolamide regulates feeding and body weight, stimulates fat utilization and has neuroprotective effects mediated through activation of PPAR alpha. Similarly, palmitoylethanolamide regulates feeding and lipid metabolism and has anti-inflammatory properties mediated by PPAR alpha. Other endocannabinoids that activate PPAR alpha include anandamide, virodhamine and noladin. Some (but not all) endocannabinoids also activate PPAR gamma; anandamide and <em>2</em>-<em>arachidonoylglycerol</em> have anti-inflammatory properties mediated by PPAR gamma. Similarly, ajulemic acid, a structural analogue of a metabolite of Delta(9)-tetrahydrocannabinol (THC), causes anti-inflammatory effects in vivo through PPAR gamma. THC also activates PPAR gamma, leading to a time-dependent vasorelaxation in isolated arteries. Other cannabinoids which activate PPAR gamma include N-arachidonoyl-dopamine, HU<em>2</em>10, WIN55<em>2</em>1<em>2</em>-<em>2</em> and CP55940. In contrast, little research has been carried out on the effects of cannabinoids at PPAR delta. In this newly emerging area, a number of research questions remain unanswered; for example, why do cannabinoids activate some isoforms and not others? How much of the chronic effects of cannabinoids are through activation of nuclear receptors? And importantly, do cannabinoids confer the same neuro- and cardioprotective benefits as other PPAR alpha and PPAR gamma agonists? This review will summarize the published literature implicating cannabinoid-mediated PPAR effects and discuss the implications thereof.

Delta9-Tetrahydrocannabinol from Cannabis sativa is mimicked by cannabimimetic analogs such as CP55940 and WIN55<em>2</em>1<em>2</em>-<em>2</em>, and antagonized by rimonabant and SR1445<em>2</em>8, through G-protein-coupled receptors, CB1 in the brain, and CB<em>2</em> in the immune system. Eicosanoids anandamide and <em>2</em>-<em>arachidonoylglycerol</em> are the "endocannabinoid" agonists for these receptors. CB1 receptors are abundant in basal ganglia, hippocampus and cerebellum, and their functional activity can be mapped during behaviors using cerebral metabolism as the neuroimaging tool. CB1 receptors couple to G(i/o) to inhibit cAMP production, decrease Ca<em>2</em>+ conductance, increase K+ conductance, and increase mitogen-activated protein kinase activity. Functional activation of G-proteins can be imaged by [35S]GTPgammaS autoradiography. Post-synaptically generated endocannabinoids form the basis of a retrograde signaling mechanism referred to as depolarization-induced suppression of inhibition (DSI) or excitation (DSE). Under circumstances of sufficient intracellular Ca<em>2</em>+ (e.g., burst activity in seizures), synthesis of endocannabinoids releases a diffusible retrograde messenger to stimulate presynaptic CB1 receptors. This results in suppression of gamma-aminobutyric acid (GABA) release, thereby relieving the post-synaptic inhibition. Tolerance develops as neurons adjust both receptor number and cellular signal transduction to the chronic administration of cannabinoid drugs. Future therapeutic drug design can progress based upon our current understanding of the physiology and pharmacology of CB1, CB<em>2</em> and related receptors. One very important role for CB1 antagonists will be in the treatment of craving in the disease of substance abuse.

Monoacylglycerol lipase (MAGL) is a principal degradative enzyme for the endocannabinoid <em>2</em>-<em>arachidonoylglycerol</em> (<em>2</em>-AG). We recently reported a piperidine carbamate, JZL184, that inhibits MAGL with high potency and selectivity. Here, we describe a comprehensive mechanistic characterization of JZL184. We provide evidence that JZL184 irreversibly inhibits MAGL via carbamoylation of the enzyme's serine nucleophile. Functional proteomic analysis of mice treated with JZL184 revealed that this inhibitor maintains good selectivity for MAGL across a wide range of central and peripheral tissues. Interestingly, MAGL blockade produced marked, tissue-specific differences in monoglyceride metabolism, with brain showing the most dramatic elevations in <em>2</em>-AG and peripheral tissues often showing greater changes in other monoglycerides. Collectively, these studies indicate that MAGL exerts tissue-dependent control over endocannabinoid and monoglyceride metabolism and designate JZL184 as a selective tool to characterize the functions of MAGL in vivo.

Despite being regarded as a hippie science for decades, cannabinoid research has finally found its well-deserved position in mainstream neuroscience. A series of groundbreaking discoveries revealed that endocannabinoid molecules are as widespread and important as conventional neurotransmitters such as glutamate or GABA, yet they act in profoundly unconventional ways. We aim to illustrate how uncovering the molecular, anatomical, and physiological characteristics of endocannabinoid signaling has revealed new mechanistic insights into several fundamental phenomena in synaptic physiology. First, we summarize unexpected advances in the molecular complexity of biogenesis and inactivation of the two endocannabinoids, anandamide and <em>2</em>-<em>arachidonoylglycerol</em>. Then, we show how these new metabolic routes are integrated into well-known intracellular signaling pathways. These endocannabinoid-producing signalosomes operate in phasic and tonic modes, thereby differentially governing homeostatic, short-term, and long-term synaptic plasticity throughout the brain. Finally, we discuss how cell type- and synapse-specific refinement of endocannabinoid signaling may explain the characteristic behavioral effects of cannabinoids.

Of the endocannabinoids (eCBs), anandamide (AEA) and <em>2</em>-<em>arachidonoylglycerol</em> (<em>2</em>-AG) have received the most study. A functional interaction between these molecules has never been described. Using mouse brain slices, we found that stimulation of metabotropic glutamate 5 receptors by 3,5-dihydroxyphenylglycine (DHPG) depressed inhibitory transmission in the striatum through selective involvement of <em>2</em>-AG metabolism and stimulation of presynaptic CB1 receptors. Elevation of AEA concentrations by pharmacological or genetic inhibition of AEA degradation reduced the levels, metabolism and physiological effects of <em>2</em>-AG. Exogenous AEA and the stable AEA analog methanandamide inhibited basal and DHPG-stimulated <em>2</em>-AG production, confirming that AEA is responsible for the downregulation of the other eCB. AEA is an endovanilloid substance, and the stimulation of transient receptor potential vanilloid 1 (TRPV1) channels mimicked the effects of endogenous AEA on <em>2</em>-AG metabolism through a previously unknown glutathione-dependent pathway. Consistently, the interaction between AEA and <em>2</em>-AG was lost after pharmacological and genetic inactivation of TRPV1 channels.

Cannabinoids and ethanol can activate the same reward pathways, which could suggest endocannabinoid involvement in the rewarding effects of ethanol. The high ethanol preference of young (6-10 weeks) C57BL6J mice is reduced by the cannabinoid receptor 1 (CB1) antagonist SR141716A to levels observed in their CB1 knockout littermates or in old (<em>2</em>6-48 weeks) wild-type mice, in both of which ethanol preference is unaffected by SR141716A. Similarly, SR141716A inhibits food intake in food-restricted young, but not old, wild-type mice. There are no age-dependent differences in the tissue levels of the endocannabinoids anandamide and <em>2</em>-<em>arachidonoylglycerol</em> or the density of CB1 in the hypothalamus, limbic forebrain, amygdala, and cerebellum. CB1-stimulated guanosine 5'-[gamma-thio]triphosphate (GTP[gammaS]) binding is selectively reduced in the limbic forebrain of old compared with young wild-type mice. There is no age-dependent difference in G(i) or G(o) subunit protein expression in the limbic forebrain, and the selective reduction in GTP[gammaS] labeling in tissue from old mice is maintained in a receptorG protein reconstitution assay by using functional bovine brain G protein. These findings suggest that endocannabinoids acting at CB1 contribute to ethanol preference, and decreased coupling of CB1 to G proteins in the limbic forebrain by mechanisms other than altered receptor or G protein levels may be involved in the age-dependent decline in the appetite for both ethanol and food.

Alcohol-induced fatty liver, a major cause of morbidity, has been attributed to enhanced hepatic lipogenesis and decreased fat clearance of unknown mechanism. Here we report that the steatosis induced in mice by a low-fat, liquid ethanol diet is attenuated by concurrent blockade of cannabinoid CB1 receptors. Global or hepatocyte-specific CB1 knockout mice are resistant to ethanol-induced steatosis and increases in lipogenic gene expression and have increased carnitine palmitoyltransferase 1 activity, which, unlike in controls, is not reduced by ethanol treatment. Ethanol feeding increases the hepatic expression of CB1 receptors and upregulates the endocannabinoid <em>2</em>-<em>arachidonoylglycerol</em> (<em>2</em>-AG) and its biosynthetic enzyme diacylglycerol lipase beta selectively in hepatic stellate cells. In control but not CB1 receptor-deficient hepatocytes, coculture with stellate cells from ethanol-fed mice results in upregulation of CB1 receptors and lipogenic gene expression. We conclude that paracrine activation of hepatic CB1 receptors by stellate cell-derived <em>2</em>-AG mediates ethanol-induced steatosis through increasing lipogenesis and decreasing fatty acid oxidation.

The therapeutic potential of cannabinoids has been the topic of extensive investigation following the discovery of cannabinoid receptors and their endogenous ligands. Cannabinoid receptors and their endogenous ligands are present at supraspinal, spinal and peripheral levels. Cannabinoids suppress behavioral responses to noxious stimulation and suppress nociceptive processing through activation of cannabinoid CB(1) and CB(<em>2</em>) receptor subtypes. Endocannabinoids, the brain's own cannabis-like substances, share the same molecular target as Delta(9)-tetrahydrocannabinol, the main psychoactive component in cannabis. Endocannabinoids serve as synaptic circuit breakers and regulate multiple physiological and pathological conditions, e.g. regulation of food intake, immunomodulation, inflammation, analgesia, cancer, addictive behavior, epilepsy and others. This review will focus on uncovering the roles of anandamide and <em>2</em>-<em>arachidonoylglycerol</em>, the two best characterized endocannabinoids identified to date, in controlling nociceptive responding. The roles of anandamide and <em>2</em>-<em>arachidonoylglycerol</em>, released under physiological conditions, in modulating nociceptive responding at different levels of the neuraxis will be emphasized in this review. Effects of modulation of endocannabinoid levels through inhibition of endocannabinoid hydrolysis and uptake is also compared with effects of exogenous administration of synthetic endocannabinoids in acute, inflammatory and neuropathic pain models. Finally, the therapeutic potential of the endocannabinoid signaling system is discussed in the context of identifying novel pharmacotherapies for the treatment of pain.

The Transient Receptor Potential Vanilloid 4 channel, TRPV4, is a Ca(<em>2</em>+) and Mg(<em>2</em>+) permeable non-selective cation channel involved in many different cellular functions. It is activated by a variety of physical and chemical stimuli, including heat, mechano-stimuli, endogenous substances such as arachidonic acid and its cytochrome P450-derived metabolites (epoxyeicosatrienoic acids), endocannabinoids (anandamide and <em>2</em>-<em>arachidonoylglycerol</em>), as well as synthetic alpha-phorbol derivatives. Recently, TRPV4 has been characterized as an important player modulating osteoclast differentiation in bone remodelling and as a urothelial mechanosensor that controls normal voiding. Several TRPV4 gain-of-function mutations are shown to cause autosomal-dominant bone dysplasias such as brachyolmia and Koszlowski disease. In this review we comprehensively describe the structural, biophysical and (patho)physiological properties of the TRPV4 channel and we summarize the current knowledge about the role of TRPV4 in the pathogenesis of several diseases.

Cannabinoid receptors were named because they have affinity for the agonist delta9-tetrahydrocannabinol (delta9-THC), a ligand found in organic extracts from Cannabis sativa. The two types of cannabinoid receptors, CB1 and CB<em>2</em>. are G protein coupled receptors that are coupled through the Gi/o family of proteins to signal transduction mechanisms that include inhibition of adenylyl cyclase, activation of mitogen-activated protein kinase, regulation of calcium and potassium channels (CB1 only), and other signal transduction pathways. A class of the eicosanoid ligands are relevant to lipid-mediated cellular signaling because they serve as endogenous agonists for cannabinoid receptors, and are thus referred to as endocannabinoids. Those compounds identified to date include the eicosanoids arachidonoylethanolamide (anandamide), <em>2</em>-<em>arachidonoylglycerol</em> and <em>2</em>-arachidonylglyceryl ether (noladin ether). Several excellent reviews on endocannabinoids and their synthesis, metabolism and function have appeared in recent years. This paper will describe the biological activities, pharmacology, and signal transduction mechanisms for the cannabinoid receptors, with particular emphasis on the responses to the eicosanoid ligands.

The endocannabinoid signalling system includes: (1) at least two G-protein-coupled receptors, known as the cannabinoid CB(1) and CB(<em>2</em>) receptors and discovered following studies on the mechanism of action of Delta(9)-tetrahydrocannabinol, the major psychoactive principle of the hemp plant Cannabis sativa; (<em>2</em>) the endogenous agonists at these receptors, known as endocannabinoids, of which anandamide and <em>2</em>-<em>arachidonoylglycerol</em> are the best known; and (3) proteins and enzymes for the regulation of endocannabinoid levels and action at receptors. The endocannabinoid system is quite widespread in mammalian tissues and cells and appears to play a pro-homeostatic role by being activated following transient or chronic perturbation of homeostasis, and by regulating in a local way the levels and action of other chemical signals. Compounds that selectively manipulate the action and levels of endocannabinoids at their targets have been and are being developed, and represent templates for potential new therapeutic drugs.