Capsaicin‐ and Mustard Oil‐Induced Extracellular Signal‐Regulated Protein Kinase Phosphorylation in Sensory Neurons in vivo: Effects of Neurokinins 1 and 2 Receptor Antagonists and of a Nitric Oxide Synthase Inhibitor

Abstract: Stimulation of primary sensory neurons with capsaicin or mustard oil leads to phosphorylation of extracellular signal‐regulated protein kinase 1/2 (p‐ERK1/2) via activation of transient receptor potential V1 (TRPV1) or TRPA1, respectively. p‐ERK1/2 was determined by Western immunoblotting in the dorsal root ganglia and in the sciatic nerve of rats following either systemic or perineural capsaicin treatment, or mustard oil application to the hind paw skin. To investigate the possible involvement of neurokinin 1 (NK₁) and NK₂ receptors as well as of nitric oxide, the selective antagonists, SR140333 for NK₁ and SR48968 for NK₂, and the nitric oxide synthase inhibitor, N^G‐nitro‐L‐arginine methyl ester (L‐NAME), were employed. The increase of p‐ERK1/2 after systemic capsaicin treatment was markedly attenuated by SR140333, while only the increase in the dorsal root ganglia was impaired by SR48968; in contrast, inhibition of nitric oxide synthase had no effect. Perineural capsaicin induced an increase in p‐ERK1/2 in the ipsilateral sciatic nerve and in the dorsal root ganglia. This effect was not influenced by SR140333 or L‐NAME. We found for the first time that mustard oil application to the hind paw skin caused an increase in p‐ERK1/2 in the sciatic nerve and in the dorsal root ganglia and only the phosphorylation in the latter was attenuated by SR140333 while L‐NAME showed no effect. From the present results, it may be assumed that capsaicin‐ or mustard oil‐induced p‐ERK1/2 in sensory neurons is not solely directly linked to TRPV1 or TRPA1 channels, but under certain conditions NK₁‐ and NK₂‐mediated mechanisms are involved.