Journal
EXPERIMENTAL NEUROLOGY
Volume 212, Issue 2, Pages 337-347Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.expneurol.2008.04.009
Keywords
allodynia; p38; fractalkine; astrocytes; peripheral nerve injury
Categories
Funding
- NINDS NIH HHS [R01 NS043798, NS43798, F31 NS058138, R01 NS037846, P30-NS045758, F31 NS058138, P30 NS045758, NS37846, R01 NS043798-05S1, R01 NS043798-01] Funding Source: Medline
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Spinal cord injury (SCI) impairs sensory systems causing chronic allodynia. Mechanisms underlying neuropathic pain have been more extensively studied following peripheral nerve injury (PNI) than after central trauma. Microglial activation, pro-inflammatory cytokine production and activation of p38 MAP kinase pathways may induce at-level allodynia following PNI. We investigated whether midthoracic SCI elicits similar behavioral and cellular responses below the level of injury (lumbar spinal cord; L5). Importantly, we show that anatomical connections between L5 and supraspinal centers remain intact after moderate SCI allowing direct comparison to a well-established model of peripheral nerve injury. We found that SCI elicits below-level allodynia of similar magnitude to at-level pain caused by a peripheral nerve injury. Moreover, the presence of robust microglial activation in L5 cord predicted allodynia in 86% of rats. Also increased phosphorylation of p38 MAP kinase occurred in the L5 dorsal horn of allodynic rats. For below-level allodynia after SCI, TNF-alpha and IL-1 beta increased in the L5 dorsal horn by 7 dpo and returned to baseline by 35 dpo. Interestingly, IL-6 remains at normal levels early after SCI and increases at chronic time points. Increased levels of pro-inflammatory cytokines also occurred in the thalamus after SCI-induced allodynia. These data suggest that remote microglial activation is pivotal in the development and maintenance of below-level allodynia after SCI. Fractalkine, a known activator of microglia, and astrocytes were not primary modulators of below-level pain. Although the mechanisms of remote microglial activation are unknown, this response may be a viable target for limiting or preventing neuropathic pain after SCI in humans. (C) 2008 Elsevier Inc. All rights reserved.
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