Oleylethanolamide (OEA) is a natural analogue of the endogenous cannabinoid anandamide. Like anandamide, OEA is produced in cells in a stimulus-dependent manner and is rapidly eliminated by enzymatic hydrolysis, suggesting a function in cellular signalling 1. However, OEA does not activate cannabinoid receptors and its biological functions are still unknown 2. Here we show that, in rats, food deprivation markedly reduces OEA biosynthesis in the small intestine. Administration of OEA causes a potent and persistent decrease in food intake and gain in body mass. This anorexic effect is behaviourally selective and is associated with the discrete activation of brain regions (the paraventricular hypothalamic nucleus and the nucleus of the solitary tract) involved in the control of satiety. OEA does not affect food intake when injected into the brain ventricles, and its anorexic actions are prevented when peripheral sensory fibres are removed by treatment with capsaicin. These results indicate that OEA is a lipid mediator involved in the peripheral regulation of feeding

Severe pain remains a major area of unmet medical need. Here we report that agonists of the nuclear receptor PPAR-␣ (peroxisome proliferator-activated receptor-␣) suppress pain behaviors induced in mice by chemical tissue injury, nerve damage, or inflammation. The PPAR-␣ agonists GW7647 [2-(4-(2-(1-cyclohexanebutyl)-3-cyclohexylureido)ethyl)phenylthio)-2-methylpropionic acid], Wy-14643 [4-chloro-6-(2,3-xylidino)-2-pyrimidinylthioacetic acid], and palmitoylethanolamide (PEA) reduced nocifensive behaviors elicited in mice by intraplantar (i.pl.) injection of formalin or i.p. injection of magnesium sulfate. These effects were absent in PPAR-␣-null mice yet occurred within minutes of agonist administration in wild-type mice, suggesting that they were mediated through a transcriptionindependent mechanism. Consistent with this hypothesis, blockade of calcium-operated IK ca (K Ca 3.1) and BK ca (K Ca 1.1) potassium channels prevented the effects of GW7647 and PEA in the formalin test. Three observations suggest that PPAR-␣ agonists may inhibit nocifensive responses by acting on peripheral PPAR-␣. (i) PEA reduced formalin-induced pain at i.pl. doses that produced no increase in systemic PEA levels; (ii) PPAR-␣ was expressed in dorsal root ganglia neurons of wildtype but not PPAR-␣-null mice; and (ii) GW7647 and PEA prevented formalin-induced firing of spinal cord nociceptive neurons in rats. In addition to modulating nociception, GW7647 and PEA reduced hyperalgesic responses in the chronic constriction injury model of neuropathic pain; these effects were also contingent on PPAR-␣ expression and were observed following either acute or subchronic PPAR-␣ agonist administration. Finally, acute administration of GW7647 and PEA reduced hyperalgesic responses in the complete Freund's adjuvant and carrageenan models of inflammatory pain. Our results suggest that PPAR-␣ agonists may represent a novel class of analgesics.Current therapies do not control safely and effectively severe pain states-a broad spectrum of debilitating conditions that comprises acute, persistent inflammatory, and neuropathic pain. Even widely used drugs, such as opiates (e.g., morphine) or anticonvulsants (e.g., gabapentin), are only active in a fraction of the patient population and produce multiple, often serious, side effects. Thus, despite continuing progress in analgesic drug discovery, the need for therapeutic agents capable of blocking abnormal pain sensation without impairing normal abilities remains largely unmet.PPAR-␣ is a nuclear receptor that serves important functions in lipid nutrient utilization and inflammation (Taylor et al., 2002;Kostadinova et al., 2005). Like other members of the nuclear receptor superfamily, PPAR-␣ is activated

Palmitoylethanolamide (PEA), the naturally occurring amide of ethanolamine and palmitic acid, is an endogenous lipid that modulates pain and inflammation. Although the anti-inflammatory effects of PEA were first characterized nearly 50 years ago, the identity of the receptor mediating these actions has long remained elusive. We recently identified the ligand-activated transcription factor, peroxisome proliferator-activated receptor-alpha (PPAR-a), as the receptor mediating the anti-inflammatory actions of this lipid amide. Here we outline the history of PEA, starting with its initial discovery in the 1950s, and discuss the pharmacological properties of this compound, particularly in regards to its ability to activate PPAR-a. Discovery of PEAThe discovery of naturally occurring fatty acid ethanolamides (FAEs) (Fig. 1) stems from an interesting clinical finding in the early 1940s, when investigators noted that supplementing the diets of 0024-3205/$ -see front matter D

Fatty acid amide hydrolase (FAAH) is an intracellular serine hydrolase that catalyzes the cleavage of bioactive fatty acid ethanolamides, such as the endogenous cannabinoid agonist anandamide. Genetic deletion of the faah gene in mice elevates brain anandamide levels and amplifies the antinociceptive effects of this compound. Likewise, pharmacological blockade of FAAH activity reduces nocifensive behavior in animal models of acute and inflammatory pain. In the present study, we investigated the effects of the selective FAAH inhibitor URB597 (KDS-4103, cyclohexylcarbamic acid 3Ј-carbamoylbiphenyl-3-yl ester) in the mouse chronic constriction injury (CCI) model of neuropathic pain. Oral administration of URB597 (1-50 mg/kg, once daily) for 4 days produced a dose-dependent reduction in nocifensive responses to thermal and mechanical stimuli, which was prevented by a single i.p. administration of the cannabinoid CB 1 receptor antagonist rimonabant (1 mg/kg). The antihyperalgesic effects of URB597 were accompanied by a reduction in plasma extravasation induced by CCI, which was prevented by rimonabant (1 mg/kg i.p.) and attenuated by the CB 2 antagonist SR144528 (1 mg/kg i.p.). Oral dosing with URB597 achieved significant, albeit transient, drug levels in plasma, inhibited brain FAAH activity, and elevated spinal cord anandamide content. The results provide new evidence for a role of the endocannabinoid system in pain modulation and reinforce the proposed role of FAAH as a target for analgesic drug development.

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Cannabinoid CB1 receptor antagonists reduce body weight in rodents and humans, but their clinical utility as anti-obesity agents is limited by centrally mediated side effects. Here, we describe the first mixed CB1 antagonist/CB2 agonist, URB447 ([4-amino-1-(4-chlorobenzyl)-2-methyl-5-phenyl-1H-pyrrol-3-yl](phenyl)methanone), which lowers food intake and body-weight gain in mice without entering the brain or antagonizing central CB1-dependent responses. URB447 may provide a useful pharmacological tool for investigating the cannabinoid system, and might serve as a starting point for developing clinically viable CB1 antagonists devoid of central side effects.

We discuss and present new data regarding the physiological and molecular mechanisms of nuclear receptor activation in pain control, with a particular emphasis on non-genomic effects of ligands at peroxisome proliferator-activated receptor (PPAR), GPR30, and classical estrogen receptors. PPARα agonists rapidly reduce both acute and chronic pain in a number of pain assays. These effects precede transcriptional anti-inflammatory actions, and are mediated in part by IKca and BKca channels on DRG neurons. In contrast to the peripheral site of action of PPARα ligands, the dorsal horn supports the expression of PPARγ. Intrathecal administration of PPARγ ligands rapidly (≤5 minutes) attenuated mechanical and thermal hypersensitivity associated with nerve injury in a dose-dependent manner that could be blocked with PPARγ antagonists. By contrast, a PPARγ antagonist itself rapidly increased the mechanical allodynia associated with nerve injury. These data suggest that ligand-dependent, non-genomic activation of spinal PPARγ decreases behavioral signs of inflammatory and neuropathic pain. We also report that the GPR30 is expressed on cultured sensory neurons, that activation of the receptor elicits signaling to increase calcium accumulation and PKCε translocation, and that this signaling may contribute to increased neuronal sensitivity as treatment with the GPR30 agonist induces hyperalgesia. Finally, application of the membrane-impermeable 17ß-E2-BSA rapidly (within 15 min) enhanced BK-stimulated inositol phosphate (IP) accumulation and PGE2-mediated cAMP accumulation in trigeminal ganglion cultures. We conclude that nuclear receptor ligands may operate through rapid, non-genomic mechanisms to modulate inflammatory and neuropathic pain.

The analgesic properties of cannabinoid receptor agonists are well characterized. However, numerous side effects limit the therapeutic potential of these agents. Here we report a synergistic antinociceptive interaction between the endogenous cannabinoid receptor agonist anandamide and the synthetic peroxisome proliferator-activated receptor-α (PPAR-α) agonist 2-(4-(2-(1-Cyclohexanebutyl)-3-cyclohexylureido)ethyl)phenylthio)-2-methylpropionic acid (GW7647) in a model of acute chemical-induced pain. Moreover, we show that anandamide synergistically interacts with the largeconductance potassium channel (K Ca 1.1, BK) activator isopimaric acid. These findings reveal a synergistic interaction between the endocannabinoid and PPAR-α systems that might be exploited clinically and identify a new pharmacological effect of the BK channel activator isopimaric acid.