Freitas_2013_J.Pharmacol.Exp.Ther_344_264

The alpha7 nicotinic acetylcholine receptor (nAChR) subtype is abundantly expressed in the central nervous system and in the periphery. Recent evidence suggests that alpha7 nAChR subtypes, which can be activated by an endogenous cholinergic tone, comprising acetylcholine and the alpha7 nAChR agonist choline, play an important role in subchronic pain and inflammation. This study's objective was to test whether alpha7 nAChR positive allosteric modulators (PAMs) produce antinociception in in vivo mouse models of acute and persistent pain. Testing type I [N-(5-chloro-2-hydroxyphenyl)-N'-[2-chloro-5-(trifluoromethyl)phenyl] (NS1738)] and type II [1-(5-chloro-2,4-dimethoxy-phenyl)-3-(5-methyl-isoxazol-3-yl) (PNU-120596)] alpha7 nAChR PAMs in acute and persistent pain, we found that, although neither reduced acute thermal pain, only PNU-120596 dose-dependently attenuated paw-licking behavior in the formalin test. The long-acting effect of PNU-120596 in this test was in discordance with its pharmacokinetic profile in mice, which suggests the involvement of postreceptor signaling mechanisms. Our results with selective mitogen-activated protein kinase kinase inhibitor 1,4-diamino-2,3-dicyano-1,4-bis(o-aminophenylmercapto)butadiene monoethanolate (U0126) argues for an important role of extracellular signal-regulated kinase-1/2 pathways activation in PNU-120596's antinociceptive effects. The alpha7 antagonist MLA, administered intrathecally, reversed PNU-120596's effects, confirming PNU-120596's action, in part, through central alpha7 nAChRs. Importantly, tolerance to PNU-120596 was not developed after subchronic treatment of the drug. Surprisingly, PNU-120596's antinociceptive effects were blocked by NS1738. Our results indicate that type II alpha7 nAChR PAM PNU-120596, but not type I alpha7 nAChR PAM NS1738, shows significant antinociception effects in persistent pain models in mice.