Roles of Substance P and Somatostatin on Transmission of Nociceptive Information Induced by Formalin in Spinal Cord

Nociceptive response induced by 0.5 % Formalin in the hindpaw of mice had two peaks, 0-5 mm (first phase) and 1 5-20 mm (second phase). By using the distmnct bmphasmc response, the nature of the transmitter systems activated by Formalmn in the spinal cord was studied for the purpose of determining the difference of the role of substance P (SP) and somatostatin (SST). The injection of (D-Pro2, D-Trp79)SP, (D-Arg1, D-Pro2, D-Trp79, Leu11)SP and SP antiserum inhibited only the first phase response. The i.t. injection of rAmiflOhePtanOYl-Phe-D-TrP-Ly5-(OBz)-Thr-i(an SST antagonist), SST antiserum and cysteamine (an SST depletor) inhibited only the second phase. This result indicates that SP is involved in the transmission of the first phase, and SST is involved in the transmission of the second phase of the Formalin-induced nociceptive response. With regar