title: Role of mitogen-activated protein kinase activation in injured and intact primary afferent neurons for mechanical and heat hypersensitivity after spinal nerve ligation.
abstract: To investigate whether activation of mitogen-activated protein kinase (MAPK) in damaged and/or undamaged primary afferents participates in neuropathic pain after partial nerve injury, we examined the phosphorylation of extracellular signal-regulated protein kinase (ERK), p38 MAPK, and c-Jun N-terminal kinase (JNK) in the L4 and L5 dorsal root ganglion (DRG) in the L5 spinal nerve ligation (SNL) model. We first confirmed, using activating transcription factor 3 and neuropeptide Y immunoreactivity, that virtually all L4 DRG neurons are spared from axotomy in this model. In the injured L5 DRG, the L5 SNL induced the activation of ERK, p38, and JNK in different populations of DRG neurons. In contrast, in the uninjured L4 DRG, the L5 SNL induced only p38 activation in tyrosine kinase A-expressing small- to medium-diameter neurons. Intrathecal ERK, p38, and JNK inhibitor infusions reversed SNL-induced mechanical allodynia, whereas only p38 inhibitor application attenuated SNL-induced thermal hyperalgesia. Furthermore, the L5 dorsal rhizotomy did not prevent SNL-induced thermal hyperalgesia. We therefore hypothesized that p38 activation in the uninjured L4 DRG might be involved in the development of heat hypersensitivity in the L5 SNL model. In fact, the treatment of the p38 inhibitor and also anti-nerve growth factor reduced SNL-induced upregulation of brain-derived neurotrophic factor and transient receptor potential vanilloid type 1 expression in the L4 DRG. Together, our results demonstrate that the L5 SNL induces differential activation of MAPK in injured and uninjured DRG neurons and, furthermore, that MAPK activation in the primary afferents may participate in generating pain hypersensitivity after partial nerve injury.
authors.affiliation: Department of Anatomy and Neuroscience, Hyogo College of Medicine, Hyogo 663-8501, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Obata
authors.forename: Hiroki
authors.initials: H
authors.lastname: Yamanaka
authors.forename: Kimiko
authors.initials: K
authors.lastname: Kobayashi
authors.forename: Yi
authors.initials: Y
authors.lastname: Dai
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Mizushima
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Katsura
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Fukuoka
authors.forename: Atsushi
authors.initials: A
authors.lastname: Tokunaga
authors.forename: Koichi
authors.initials: K
authors.lastname: Noguchi
mesh_terms: D000818:Animals; D000873:Anthracenes / Q000494:pharmacology; D019208:Brain-Derived Neurotrophic Factor / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D002070:Butadienes / Q000494:pharmacology; D004789:Enzyme Activation; D005727:Ganglia, Spinal / Q000166:cytology* / Q000201:enzymology; D005786:Gene Expression Regulation / Q000502:physiology; D006358:Hot Temperature / Q000009:adverse effects; D006930:Hyperalgesia / Q000209:etiology / Q000503:physiopathology*; D007093:Imidazoles / Q000494:pharmacology; D007473:Ion Channels / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D048031:JNK Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology; D008026:Ligation; D008159:Lumbar Vertebrae; D020935:MAP Kinase Signaling System / Q000502:physiology*; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000502:physiology; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000502:physiology; D009475:Neurons, Afferent / Q000502:physiology*; D009570:Nitriles / Q000494:pharmacology; D010812:Physical Stimulation / Q000009:adverse effects; D011720:Pyrazoles / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D019051:Rhizotomy; D013127:Spinal Nerves / Q000293:injuries*; D013314:Stress, Mechanical; D050916:TRPV Cation Channels; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology
chemical_list: D000873:Anthracenes; D019208:Brain-Derived Neurotrophic Factor; D002070:Butadienes; C104334:FR 167653; D007093:Imidazoles; D007473:Ion Channels; D009570:Nitriles; D011720:Pyrazoles; D011725:Pyridines; D050916:TRPV Cation Channels; C493922:Trpv1 protein, rat; C113580:U 0126; C432165:pyrazolanthrone; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases; C093642:SB 203580