TRPA1 and chronic cystitis: Taken together with the present results showing the loss of c-fos mRNA upregulation in the spinal cord of H2O2-injected TRPA1-KO mice, this suggests that activation of C-fibers through TRPA1 stimulation enhances the activity of spinal cord neurons, resulting in frequent urination and abdominal visceral pain during the initial phase of long-lasting cystitis.