Summary of different activation patterns of three MAPK family members (ERK, p38, and JNK) in the DRG and spinal cord in normal and nerve injury (SNL) conditions
| Dorsal root ganglion | Spinal cord dorsal horn (gray matter) | |||||
|---|---|---|---|---|---|---|
| Basal expression | Injured (L5) | Noninjured (L4) | Basal expression | 3 d | 21 d | |
| pERK | Small neurons (+) | Large neurons (+) | No significant change | Not detectable | Microglia (+++) | Astrocytes (+++) |
| Satellite cells (+) | Satellite cells (+++) | |||||
| p-p38 | Small neurons (++) | Small neurons (+++) | Small neurons (+++) | Microglia (+) | Microglia (+++) | Microglia (++) |
| Satellite cells (+) | Large neurons (++) | Large neurons (+) | ||||
| pJNK | Small neurons (+) | Small neurons (+++) | No significant change | Astrocytes (+) | Astrocytes (++) | Astrocytes (+++) |
| Nerve fibers (+) | Nerve fibers (++) | |||||
| Satellite cells (+) | ||||||
Activation of MAPK is revealed by the expression of pMAPK. There is a low-level, basal expression of pMAPK in normal non-injured condition. +, ++, and +++ indicate low, medium, and high levels of expression of pMAPK, respectively. Small and large neurons of the DRG are described as NF-200-negative (C-fiber) and NF-200-positive (A-fiber) neurons, respectively. Switch of MAPKs to different cell types at late times has not been clearly studied in the DRG. pERK is also transiently induced in dorsal horn neurons in the first several hours of nerve injury. See the related references of Kim et al., 2002; Jin et al., 2003; Obata et al., 2003, 2004a,b; Schafers et al., 2003; Tsuda et al., 2004; Zhuang et al., 2005.