Effect of nocistatin and its interaction with nociceptin/orphanin FQ on the rat formalin test.

Nocistatin is a 17 amino acid peptide and is processed from prepronociceptin. Nocistatin does not bind to the nociceptin receptor, but nocistatin blocks allodynia induced by nociceptin/orphanin FQ. In this study, we examined the effect of intrathecal nocistatin and its interaction with nociceptin/orphanin FQ in the rat formalin test and the hot plate test. Intrathecal nocistatin attenuated the formalin induced phase 1, but not phase 2, flinching behavior. Coadministration of nocistatin with nociceptin/orphanin FQ did not block the analgesic effect of nociceptin/orphanin FQ. Nocistatin had no effect on the hot plate test. These data suggest that nocistatin produces analgesic effect in the formalin test, but not in the hot plate test, and that the mechanisms underlying the analgesic effect of nocistatin is complex.