Carrageenan-induced thermal hyperalgesia in the mouse: role of nerve growth factor and the mitogen-activated protein kinase pathway.

ABSTRACT

NGF is an important link between inflammation and hyperalgesia and interacts with many different mediators of inflammation, including the MAPK signaling pathway. In these studies, carrageenan-induced thermal hyperalgesia was evaluated in the mouse and the role of NGF and the MAPK pathway investigated. Carrageenan induced a time-dependent inflammation and thermal hyperalgesia, which was maximal 4 h post administration. Both indomethacin (0.3, 1.0 and 10 mg/kg s.c., 30 min pre-carrageenan) and morphine (0.4, 1.2, 4.0 mg/kg; s.c., 30 min pre-hyperalgesia measurement) significantly inhibited carrageenan-induced thermal hyperalgesia and indomethicin inhibited paw inflammation, demonstrating the model as suitable for the assessment of anti-hyperalgesic and anti-inflammatory agents. Anti-NGF (0.67 mg/kg sc, 60 min pre-carrageenan) produced a significant inhibition of thermal hyperalgesia, but not inflammation. NGF itself produced a time-dependent hyperalgesia, but not inflammation, following intraplantar injection. The specific MAPK pathway inhibitor, PD98059 (0.1, 0.3 and 1 mg/kg sc, 30 min pre-carrageenan) significantly inhibited carrageenan-induced hyperalgesia, but not inflammation. These data demonstrate a role for both NGF and the MAPK signaling pathway in the production of thermal hyperalgesia, but not inflammation, in the mouse.