BACKGROUND AND PURPOSEAgonists selective for the a7 nicotinic acetylcholine (nACh) receptor produce anti-hyperalgesic effects in rodent models of inflammatory pain, via direct actions on spinal pain circuits and possibly via attenuated release of peripheral pro-inflammatory mediators. Increasingly, allosteric modulation of ligand-gated receptors is recognized as a potential strategy to obtain desired efficacy in the absence of the putative adverse effects associated with agonist activation. EXPERIMENTAL APPROACHWe compared the anti-hyperalgesic and anti-inflammatory effects of the a7 nACh receptor agonist compound B with the positive allosteric modulator (PAM) PNU-120596 and the standard non-steroidal anti-inflammatory drug (NSAID), diclofenac, in rats with hind paw inflammation induced by either formalin, carrageenan or complete Freund's adjuvant (CFA). KEY RESULTSWhen administered before carrageenan, both diclofenac (30 mg·kg ) also attenuated both measures of pain-like behaviour, albeit less robustly. Whereas compound B and PNU-120596 attenuated the carrageenan-induced increase in levels of TNF-a and IL-6 within the hind paw oedema, diclofenac only attenuated IL-6 levels. Established mechanical hyperalgesia induced by carrageenan or CFA was also partially reversed by compound B and PNU-120596. However, diclofenac was considerably more efficacious. Formalin-induced nocifensive behaviours were only reversed by compound B, albeit at doses which disrupted motor performance. CONCLUSIONS AND IMPLICATIONSa7 nACh receptor PAMs could prove to be useful in the treatment of inflammatory pain conditions, which respond poorly to NSAIDs or in situations where NSAIDs are contra-indicated. Abbreviations

Neuropathic pain is characterised by both positive (hyperalgesia and allodynia) and negative (sensory deficits) symptoms and remains intractable to many commonly used analgesics. Antiepileptics are increasingly utilised in the treatment of neuropathic pain. This class of drugs works via three major mechanisms of action in order to dampen neuronal hyperexcitability within the central nervous system: potentiation of GABA transmission, reduction of glutamate-mediated excitatory transmission, and block of voltage-activated ion channels. The latter mechanism of action in particular, is exemplified by the success of the newer generation of antiepileptics such as lamotrigine and gabapentin in the clinical treatment of neuropathic pain symptoms. In the current review article, we will examine in detail, the antinociceptive effects of a diverse range of antiepileptics as tested in animal models of nerve injury. Where appropriate, we will compare these findings with their analgesic efficacy in the clinical treatment of neuropathic pain.