AbstractNoxious cold sensation is commonly associated with peripheral neuropathies, however, there has been limited progress in understanding the mechanism of cold pain. Transient receptor potential (TRP) A1 channels facilitate the perception of noxious cold at the level of dorsal root ganglia (DRG), where kappa opioid receptors (KOR) are also expressed but have not previously been implicated in cold sensation. Here we identify a new role for KOR in enhancing cold hypersensitivity. First, we show that systemic KOR agonism (U50,488, KOR agonist), significantly potentiates the latency to jump and the number of jumps on the cold plate compared controls at 3°C. Importantly, NorBNI (KOR antagonist) attenuates U50,488-induced cold hypersensitivity. However, the central administration of NorBNI does not block U50,488-induced cold hypersensitivity suggesting that peripheral KOR likely modulate this effect. Furthermore, the peripherally-restricted KOR agonist, ff(nle)r-NH2 also induces cold hypersensitivity. Using fluorescent in situ hybridization, we show that KOR mRNA colocalizes with the transcripts for the cold-activated TRPA1 and TRPM8 channels in DRG. Finally, using calcium imaging in DRG, we show that intracellular calcium release is potentiated during the simultaneous application of a TRPA1 agonist, mustard oil (MO), and a KOR agonist (U50,488), when compared to MO alone. This potentiated calcium response is absent in TRPA1 KO mice. Together our data suggest that KOR-induces cold hypersensitivity through modulation of peripheral TRPA1 channels. These findings indicate that whether activation of peripheral KOR is protective or not may be dependent on the pain modality.
Odontoblast TRPC5 channels signal cold pain in teeth
