RESEARCH ARTICLE


c-Fos or pERK, Which is a Better Marker for Neuronal Activation and Central Sensitization After Noxious Stimulation and Tissue Injury?



Yong-Jing Gao*, Ru-Rong Ji*
Department of Anesthesiology, Brigham and Women’s Hospital, 75 Francis Street,Medical Research Building, Room 604, Boston, MA 02115, USA;


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© 2009 Gao Yong-Jing and Ru-Rong Ji et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: https://creativecommons.org/licenses/by/4.0/legalcode. This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Department of Anesthesiology, Brigham and Women’s Hospital, 75 Francis Street,Medical Research Building, Room 604, Boston, MA 02115, USA; Tel: (617) 732-5500 Ext 32363; Fax: (617) 730-2801; E-mails: yjgao@partners.org , rrji@zeus.bwh.harvard.edu


Abstract

c-Fos, the protein of the protooncogene c-fos, has been extensively used as a marker for the activation of nociceptive neurons in the spinal cord for more than twenty years since Hunt et al. first reported that peripheral noxious stimulation to a hind paw of rats leads to a marked induction of c-Fos in superficial and deep dorsal horn neurons in 1987. In 1999, Ji et al. reported that phosphorylated extracellular signal-regulated kinase (pERK) is specifically induced by noxious stimulation in superficial dorsal horn neurons. Accumulating evidence indicates that pERK induction or ERK activation in dorsal horn neurons is essential for the development of central sensitization, increased sensitivity of dorsal horn neurons that is responsible for the generation of persistent pain. Further, molecular mechanisms underlying ERKmediated central sensitization have been revealed. In contrast, direct evidence for c-Fos-mediated central sensitization is not sufficient. After a noxious stimulus (e.g., capsaicin injection) or tissue injury, c-Fos begins to be induced after 30-60 minutes, whereas pERK can be induced within a minute, which can correlate well with the development of pain hypersensitivity. While c-Fos is often induced in the nuclei of neurons, pERK can be induced in different subcellular structures of neurons such as nuclei, cytoplasma, axons, and dendrites. pERK can even be induced in spinal cord microglia and astrocytes after nerve injury. In summary, both c-Fos and pERK can be used as markers for neuronal activation following noxious stimulation and tissue injury, but pERK is much more dynamic and appears to be a better marker for central sensitization.