Papers of the Week

CB cannabinoid receptor activation suppresses pathological pain in animal models. CB agonists show promise as therapeutic agents because they lack unwanted side effects commonly associated with direct activation of CB receptors. However, the types of pain most responsive to CB agonists are incompletely understood and cell types which underlie CB-mediated anti-allodynic efficacy remain largely unknown. Our laboratory previously reported that the CB receptor agonist LY2828360 attenuated the maintenance of neuropathic pain induced by toxic challenge with chemotherapeutic and anti-retroviral agents in mice. Whether these findings generalize to models of inflammatory pain is not known. Here we show that LY2828360 (10 mg/kg i.p.) reversed the maintenance of carrageenan-induced mechanical allodynia in female mice. Anti-allodynic efficacy was fully preserved in global CB knock out (KO) mice but absent in CB KO mice. The anti-allodynic efficacy of LY2828360 was absent in conditional KO mice lacking CB receptors in peripheral sensory neurons (Advillin; CB). Intraplantar administration of LY2828360 (30 μg i.pl.) reversed carrageenan-induced mechanical allodynia in CB but not Advillin; CB mice of both sexes. Thus, CB receptors in peripheral sensory neurons underlie the therapeutic effects of LY2828360 injection in the paw. Lastly, qRT-PCR analyses revealed that LY2828360 reduced carrageenan-induced increases in IL-1β and IL-10 mRNA in paw skin. Our results provide evidence that LY2828360 suppresses inflammatory nociception in mice through a neuronal CB-dependent mechanism that requires peripheral sensory neuron CB receptors and suggest that the clinical applications of LY2828360 as an anti-hyperalgesic agent should be re-evaluated.