Bagdas_2015_Biochem.Pharmacol_97(4)_590

The aim of the present study was to determine the impact of alpha5 nicotinic acetylcholine receptor (nAChR) subunit deletion in the mouse on the development and intensity of nociceptive behavior in various chronic pain models. The role of alpha5-containing nAChRs was explored in mouse models of chronic pain, including peripheral neuropathy (chronic constriction nerve injury, CCI), tonic inflammatory pain (the formalin test) and short and long-term inflammatory pain (complete Freund's adjuvant, CFA and carrageenan tests) in alpha5 knock-out (KO) and wild-type (WT) mice. The results showed that paw-licking time was decreased in the formalin test, and the hyperalgesic and allodynic responses to carrageenan and CFA injections were also reduced. In addition, paw edema in formalin-, carrageenan- or CFA-treated mice were attenuated in alpha5-KO mice significantly. Furthermore, tumor necrosis factor-alpha (TNF-alpha) levels of carrageenan-treated paws were lower in alpha5-KO mice. The antinociceptive effects of nicotine and sazetidine-A but not varenicline were alpha5-dependent in the formalin test. Both hyperalgesia and allodynia observed in the CCI test were reduced in alpha5-KO mice. Nicotine reversal of mechanical allodynia in the CCI test was mediated through alpha5-nAChRs at spinal and peripheral sites. In summary, our results highlight the involvement of the alpha5 nAChR subunit in the development of hyperalgesia, allodynia and inflammation associated with chronic neuropathic and inflammatory pain models. They also suggest the importance of alpha5-nAChRs as a target for the treatment of chronic pain.