Endocannabinoid regulation of spinal nociceptive processing in a model of neuropathic pain.
Models of neuropathic pain are associated with elevated spinal levels of endocannabinoids (ECs) and altered expression of cannabinoid receptors on primary sensory afferents and post-synaptic cells in the spinal cord. We investigated the impact of these changes on the spinal processing of sensory inputs in a model of neuropathic pain. Extracellular single-unit recordings of spinal neurones were made in anaesthetized neuropathic and sham-operated rats. The effects of spinal administration of the cannabinoid CB(1) receptor antagonist N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251) and the cannabinoid receptor type 2 (CB(2)) receptor antagonist N-[(1S)-endo-1,3,3-trimethylbicycloheptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide (SR144528) on mechanically-evoked responses of spinal neurones were determined. The effects of spinal administration of (5Z,8Z11Z,14Z)-N-(3-furanylmethyl)-5,8,11,14-eicosatetraenamide (UCM707), which binds to CB(2) receptors and alters transport of ECs, on evoked responses of spinal neurones and spinal levels of ECs were also determined. The cannabinoid CB(1) receptor antagonist AM251, but not the CB(2) receptor antagonist, significantly facilitated 10-g-evoked responses of spinal neurones in neuropathic, but not sham-operated, rats. Spinal administration of UCM707 did not alter spinal levels of ECs but did significantly inhibit mechanically-evoked responses of neurones in neuropathic, but not sham-operated, rats. Pharmacological studies indicated that the selective inhibitory effects of spinal UCM707 in neuropathic rats were mediated by activation of spinal CB(2) receptors, as well as a contribution from transient receptor potential vanilloid 1 (TRPV1) channels. This work demonstrates that changes in the EC receptor system in the spinal cord of neuropathic rats influence the processing of sensory inputs, in particular low-weight inputs that drive allodynia, and indicates novel effects of drugs acting via multiple elements of this receptor system.
Sagar
Devi Rani
DR
School of Biomedical Sciences, University of Nottingham, Medical School, Queen's Medical Centre, Nottingham, UK. devi.sagar@nottingham.ac.uk
Jhaveri
Maulik D
MD
Richardson
Denise
D
Gray
Roy A
RA
de Lago
Eva
E
Fernández-Ruiz
Javier
J
Barrett
David A
DA
Kendall
David A
DA
Chapman
Victoria
V
D000758:Anesthesia; D000818:Animals; D001095:Arachidonic Acids / Q000494:pharmacology; D001892:Camphanes / Q000494:pharmacology; D063385:Cannabinoid Receptor Modulators / Q000378:metabolism*; D002491:Central Nervous System Agents / Q000494:pharmacology; D004195:Disease Models, Animal; D063388:Endocannabinoids; D005073:Evoked Potentials, Somatosensory / Q000187:drug effects; D005663:Furans / Q000494:pharmacology; D008297:Male; D008839:Microelectrodes; D009437:Neuralgia / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D010812:Physical Stimulation; D010880:Piperidines / Q000494:pharmacology; D053284:Polyunsaturated Alkamides / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D043884:Receptor, Cannabinoid, CB1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D043885:Receptor, Cannabinoid, CB2 / Q000037:antagonists & inhibitors / Q000378:metabolism; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism*; D050916:TRPV Cation Channels / Q000378:metabolism
D001095:Arachidonic Acids; D001892:Camphanes; D063385:Cannabinoid Receptor Modulators; D002491:Central Nervous System Agents; D063388:Endocannabinoids; D005663:Furans; C443680:N-(3-furylmethyl)eicosa-5,8,11,14-tetraenamide; D010880:Piperidines; D053284:Polyunsaturated Alkamides; D011720:Pyrazoles; D043884:Receptor, Cannabinoid, CB1; D043885:Receptor, Cannabinoid, CB2; C110630:SR 144528; D050916:TRPV Cation Channels; C493922:Trpv1 protein, rat; C103505:AM 251