title: The pain pathway in the rat following noxious thermal stimulation: effect of morphine on pERK1/2 and TRPV1 at the dorsal horn level, and on hyperalgesia.
abstract: The aim of the present study was to investigate the phosphorylation of ERK1/2 in the lumbar dorsal horn of the rat by fluorescence immunohistochemistry following a noxious thermal stimulation of the hind paw. The protein level of TRPV1 in the dorsal spinal cord and the development of a heat hyperalgesia after the acute noxious thermal stimulation were also measured. The protein content of TRPV1 was determined by Western blot and heat hyperalgesia by the plantar test. At 2 and 10 min after the thermal stimulation a 4-fold increase in pERK1/2 immunoreactivity was observed in cells of lamina I/II of the L3-L5 dorsal horn. A pretreatment with the opioid analgesic morphine markedly attenuated ERK1/2 phosphorylation. The protein content of TRPV1 in the lumbar dorsal spinal cord was not significantly altered at 1 and 4 h after the thermal hind paw stimulation and by the morphine pretreatment. Heat hyperalgesia in the plantar test was observed at 8 h, but not at 24 h after the noxious stimulation. This temporary hyperalgesia was prevented by the morphine pretreatment. The present findings indicate that ERK1/2 activation in dorsal horn nociceptive neurons may be linked to the development of hyperalgesia, and that opioid analgesics are effective agents to prevent sensitization in the pain pathway at spinal level.
authors.affiliation: Institute of Experimental and Clinical Pharmacology, Medical University of Graz, Graz, Austria.
authors.forename: Josef
authors.initials: J
authors.lastname: Donnerer
authors.forename: Ingrid
authors.initials: I
authors.lastname: Liebmann
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D006358:Hot Temperature; D006930:Hyperalgesia / Q000188:drug therapy / Q000378:metabolism*; D008297:Male; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D048053:Mitogen-Activated Protein Kinase 6 / Q000378:metabolism*; D009020:Morphine / Q000494:pharmacology*; D010146:Pain / Q000188:drug therapy / Q000378:metabolism*; D020671:Posterior Horn Cells / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D050916:TRPV Cation Channels / Q000378:metabolism
chemical_list: D000701:Analgesics, Opioid; D050916:TRPV Cation Channels; C493922:Trpv1 protein, rat; D009020:Morphine; D048052:Mitogen-Activated Protein Kinase 3; D048053:Mitogen-Activated Protein Kinase 6