Phosphorylation of ERK in the Spinal Dorsal Horn Following Pancreatic Pronociceptive Stimuli With Proteinase-Activated Receptor-2 Agonists and Hydrogen Sulfide in Rats: Evidence for Involvement of Distinct Mechanisms

Noxious stimuli cause prompt phosphorylation of extracellular signal-regulated kinase (ERK) in the spinal dorsal horn that contributes to facilitation of pain sensation and is often used as an immediate marker for excitation of spinal neurons following somatic and colonic nociception. Here we asked whether two distinct pronociceptive stimuli with proteinase-activated receptor-2 (PAR2) agonists and hydrogen sulfide (H2S) in the pancreas cause phosphorylation of ERK in the spinal dorsal horn and also examined involvement of their possible downstream signaling molecules, transient receptor potential vanilloid-1 (TRPV1) and T-type Ca2+ channels, respectively. Capsaicin (a TRPV1 agonist), trypsin (an endogenous PAR2 agonist), SLIGRL-NH2 (a PAR2-activating peptide), and NaHS (an H2S donor) were infused into the pancreatic duct in anesthetized rats, and phosphorylated ERK in the spinal cord was detected by immunohistochemistry. Intraductal administration of capsaicin and trypsin caused prompt phosphorylation of ERK in the superficial layers of T9, but not T5 or T12, spinal dorsal horn. SLIGRL-NH2 and NaHS, administered in the same manner, also produced ERK phosphorylation in the corresponding spinal regions. Mibefradil, a T-type Ca2+ channel blocker, abolished the phosphorylation of ERK caused by intraductal NaHS but not SLIGRL-NH2. In contrast, capsazepine, an inhibitor of TRPV1, suppressed the phosphorylation of ERK caused by intraductal SLIGRL-NH2 but not NaHS. Our data thus demonstrate that pancreatic pronociceptive stimuli with PAR2 agonists and H2S cause ERK phosphorylation in the spinal dorsal horn, through activation of TRPV1 and T-type Ca2+ channels, respectively, and that those two pronociceptive pathways are independent of each other. (c) 2010 Wiley-Liss, Inc.