Naked mole-rats ( Heterocephalus glaber ) have adaptations within their pain pathway that are beneficial to survival in large colonies within unventilated burrow systems, with lower O 2 and higher CO 2 ambient levels than ground-level environments. These adaptations ultimately lead to a partial disruption of the C-fiber pain pathway, which enables naked mole-rats to not feel pain from the acidosis associated with CO 2 accumulation. One hallmark of this disruption is that naked mole-rats do not express neuropeptides, such as Substance P and calcitonin gene- related peptide in their cutaneous C-fibers, therefore, effectively making the peptidergic pain pathway hypofunctional. One C-fiber pathway that remains unstudied in the naked mole-rat is the non-peptidergic, purinergic pathway, despite this being a key pathway for inflammatory pain. The current study aimed to establish the functionality of the purinergic pathway in naked mole-rats and the effectiveness of cannabinoids in attenuating pain through this pathway. Cannabinoids can manage chronic inflammatory pain in both humans and mouse models, and studies suggest a major downstream role for the purinergic receptor, P2X3, in this treatment. Here we used Ca 2+ -imaging of cultured dorsal root ganglion neurons and in vivo behavioral testing to demonstrate that the P2X3 pathway is functional in naked mole-rats. Additionally, formalin-induced inflammatory pain was reduced by the cannabinoid receptor agonist, WIN55 (inflammatory, but not acute phase) and the P2X3 receptor antagonist A- 317491 (acute and inflammatory phases). This study establishes that the non- peptidergic, purinergic C-fiber pathway is present and functional in naked mole-rats and that cannabinoid-mediated analgesia also occurs in this species.
