A novel neuroimmune mechanism in cannabinoid-mediated attenuation of nerve growth factor-induced hyperalgesia.
BACKGROUND
Nerve growth factor (NGF) is central to processes involved in an inflammatory hyperalgesia. Administration of exogenous NGF induces a hyperalgesia that is dependent on local neutrophil influx. The effects of administration of the cannabinoid anandamide and the cannabimimetic palmitoylethanolamide on an NGF-induced hyperalgesia and neutrophil accumulation were examined in this study.


METHODS
Baseline hind limb withdrawal latencies to a noxious heat stimulus were recorded before intraplantar administration of NGF (1 microg in 0.05 ml) to the hind paw of 75 male Wistar rats. Anandamide or palmitoylethanolamide (a substance that has cannabinoid-like actions but little affinity for cannabinoid receptors) at doses of 10 and 25 mg/kg were given (intraperitoneally) immediately after NGF. CB1 (SR141716A) and CB2 (SR144528) receptor antagonists were coadministered with the higher dose of cannabinoids. Withdrawal latencies were expressed as difference from baseline. Seventy rats received intraplantar NGF and intraperitoneal treatments. Neutrophil accumulation in the injected paw was assessed using a myeloperoxidase assay.


RESULTS
Administration of NGF reduced latencies consistent with hyperalgesia. Anandamide and palmitoylethanolamide significantly reduced this hyperalgesia. The action of anandamide was CB1 receptor-mediated. SR144528 abrogated the action of palmitoylethanolamide. NGF also provoked neutrophil accumulation in the injected paw, denoted by an increase in myeloperoxidase. Palmitoylethanolamide significantly reduced neutrophil accumulation by an SR144528-sensitive action, whereas anandamide was without effect.


CONCLUSIONS
NGF induced a thermal hyperalgesia that was attenuated by anandamide and palmitoylethanolamide. Only palmitoylethanolamide reduced neutrophil influx. Thus, cannabinoids show a neuronal CB1 receptor-mediated antihyperalgesic action and a separate inhibition of a proinflammatory neuroimmune process. Such a mechanism suggests a therapeutic site of analgesic action separable from central side effects.
Farquhar-Smith
W Paul
WP
Pain Research, Imperial College, Chelsea and Westminster Campus, London, United Kingdom. paul.farquhar-smith@rmh.nthames.nhs.uk
Rice
Andrew S C
AS
D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D001095:Arachidonic Acids / Q000494:pharmacology; D002186:Cannabinoids / Q000494:pharmacology*; D002211:Capsaicin / Q000031:analogs & derivatives* / Q000494:pharmacology; D002465:Cell Movement / Q000187:drug effects; D063388:Endocannabinoids; D006930:Hyperalgesia / Q000188:drug therapy* / Q000209:etiology; D008297:Male; D020932:Nerve Growth Factor / Q000494:pharmacology*; D009504:Neutrophils / Q000187:drug effects / Q000502:physiology; D010880:Piperidines / Q000494:pharmacology; D053284:Polyunsaturated Alkamides; D011720:Pyrazoles / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D000077285:Rimonabant
D000700:Analgesics; D001095:Arachidonic Acids; D002186:Cannabinoids; D063388:Endocannabinoids; D010880:Piperidines; D053284:Polyunsaturated Alkamides; D011720:Pyrazoles; D020932:Nerve Growth Factor; C071423:capsazepine; D000077285:Rimonabant; D002211:Capsaicin; C078814:anandamide