Abstract
Alterations in the intracellular signal transduction pathway in primary afferents may contribute to pain hypersensitivity. Recently, we have reported that the phosphorylation of extracellular signal-regulated protein kinase 1/2 (ERK1/2) and p38 mitogen-activated protein kinase (MAPK) occurs in primary afferent neurons in response to noxious stimulation of the peripheral tissue, i.e., activity-dependent activation of ERK1/2 and p38 MAPK in dorsal root ganglion (DRG) neurons. In the present study, we investigated the phosphorylation of ERK5, also known as big MAPK1, in the DRG by noxious stimulation using immunohistochemistry. Capsaicin injection induced phosphorylated ERK5 (p-ERK5) in small-to-medium diameter sensory neurons with a peak at 2 min after capsaicin injection. Furthermore, we examined the p-ERK5 labeling in the DRG after noxious heat and cold stimuli and found a stimulus intensity-dependent increase in the number of activated neurons. Most of these p-ERK5-immunoreactive neurons were small- and medium-sized neurons, which coexpressed transient receptor potential (TRP) ion channel TRPV1 and TRPA1 after noxious heat and cold stimuli, respectively. In contrast, there was no change in ERK5 phosphorylation in the spinal dorsal horn. The i.t. administration of ERK5 antisense oligodeoxynucleotide reversed heat hyperalgesia, but not mechanical allodynia, produced by capsaicin injection. Taken together, these findings suggest that the in vivo activation of the ERK5 signaling pathway in sensory neurons by noxious stimulation may be, at least in part, correlated with functional activity and, further, involved in the development of pain hypersensitivity.
Footnotes
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This work was supported in part by grants-in-aid for Scientific Research and the Open Research Center grant, Hyogo College of Medicine, both from the Japanese Ministry of Education, Science, and Culture. This work was also supported by a grant from the Japan Health Sciences Foundation.
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.106.116749.
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ABBREVIATIONS: MAPK, mitogen-activated protein kinase(s); ERK, extracellular signal-regulated protein kinase(s); DRG, dorsal root ganglion(s); MEK, mitogen-activated protein kinase kinase(s); PD98059, 2′-amino-3′-methoxyflavone; U0126, 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenyltio)butadiene; AS, antisense; ODN, oligodeoxynucleotide; MM, mismatch; FITC, fluorescein isothiocyanate; p-ERK5, phosphorylated ERK5; TSA, tyramide signal amplification; TRP, transient receptor potential; NF200, neurofilament 200; IR, immunoreactive; ANOVA, analysis of variance; ABC, avidin-biotin-peroxidase complex; ISHH, in situ hybridization histochemistry; TBS, Tris-HCl-buffered saline; TBST, Tris-buffered saline/Tween 20.
- Received November 6, 2006.
- Accepted January 18, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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