RUTHENIUM RED AND CAPSAZEPINE ANTINOCICEPTIVE EFFECT IN FORMALIN AND CAPSAICIN MODELS OF PAIN IN MICE

This study investigates the antinociception caused by intradermal (i.d ) or intracerebroventricular (i.c.v.) injection of the capsaicin recep tor antagonist capsazepine (CPZ), and ruthenium red (RR) (a cation-sel ective antagonist coupled to vanilloid receptor of capsaicin), on the chemical nociception caused by i.d. injection of formalin (FM) and cap saicin (CAP) into the mouse paw. The i.d. injection of either CPZ or R R in association with FM or CAP, inhibited the early phase, and to a l esser extent the late phase, of the FM, as well as CAP-induced nocicep tion. Given i.c.v., both CPZ and RR caused discrete antinociception in the FM (both phases), while producing graded inhibition of CAP. The a ctions of CPZ and RR were insensitive to i.p. injection of naloxone (5 mg/kg). These results indicate that i.d. injection of CPZ and RR prod uce marked antinociception in chemical models of neurogenic pain induc ed by CAP and FM in mice. However, administered by supraspinal site, b oth CPZ and RR were inactive in inhibiting FM, but prevented, in a gra ded manner, CAP-induced algesic response, suggesting the participation of distinct mechanisms in the nociception induced by FM and CAP. Thus , vanilloid selective antagonists seem to be useful tools for investig ating the nociception elicited by CAP and FM. (C) 1997 Elsevier Scienc e Ireland Ltd.