Glial phosphorylated p38 MAP kinase mediates pain in a rat model of lumbar disc herniation and induces motor dysfunction in a rat model of lumbar spinal canal stenosis.
METHODS
Immunohistochemical and behavioral study using rat models of lumbar disc herniation and cauda equina syndrome.


OBJECTIVE
To investigate the expression of activated p38 mitogen-activated protein kinases (p38 MAP kinase; p38) in the spinal cord and to determine the effect of intrathecal administration of a specific p38 inhibitor on pain in a lumbar disc herniation model and on motor function and hypoalgesia in a spinal canal stenosis (SCS) model.


BACKGROUND
In pathologic lumbar disc herniation-induced neuropathic pain and compression of cauda equina-induced motor dysfunction and hypoalgesia caused by SCS, glia are activated and produce certain cytokines, including tumor necrosis factor-alpha (TNF-alpha) and interleukins, which play a crucial role in the pathogenesis of nerve degeneration. p38 is phosphorylated by these cytokines, suggesting that it may play an important role in pain transmission and nerve degeneration. Here we have examined the role of p38 in rat models of lumbar disc herniation and SCS.


METHODS
Six-week-old male Sprague-Dawley rats were used. For the disc herniation model, autologous nucleus pulposus was applied to L5 nerve roots, which were then crushed. For the SCS model, a piece of silicon was placed under the lamina of the fourth lumbar vertebra. We assessed mechanical allodynia, hypoalgesia, and motor function using von Frey hairs, treadmill tests, and immunohistochemical localization of phosphorylated p38 (P-p38) in the cauda equina, dorsal root ganglion (DRG), and spinal cord, which were also double-stained with NeuN (neuronal marker), GFAP (astrocyte/Schwann cell marker), or isolectin B4 (IB4; microglia marker). We also examined the effects of intrathecal administration of a specific p38 inhibitor, FR167653, on nucleus pulposus-induced pain, hypoalgesia, and motor dysfunction following SCS.


RESULTS
We demonstrated that activated P-p38-immunoreactive cells in the spinal cord and cauda equina were not observed before nerve injury but appeared in the cauda equina, DRG, and spinal dorsal horn in the disc herniation and SCS models. Double-labeling revealed that most P-p38-immunoreactive cells were isolectin B4-labeled microglia and GFAP-immunoreactive Schwann cells. Intrathecal administration of the p38 inhibitor FR167653 decreased mechanical allodynia in the disc herniation model and improved hypoalgesia and intermittent motor dysfunction in the SCS model.


CONCLUSIONS
Our findings suggest that activated p38 may play an important role in the involvement of microglia in the pathophysiology of pain following lumbar disc herniation and mechanical hypoalgesia, and motor nerve dysfunction of cauda equina following SCS.
Ito
Toshinori
T
Department of Orthopedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
Ohtori
Seiji
S
Inoue
Gen
G
Koshi
Takana
T
Doya
Hideo
H
Ozawa
Tomoyuki
T
Saito
Tomoko
T
Moriya
Hideshige
H
Takahashi
Kazuhisa
K
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D002420:Cauda Equina / Q000201:enzymology / Q000503:physiopathology; D004791:Enzyme Inhibitors / Q000008:administration & dosage / Q000494:pharmacology; D005727:Ganglia, Spinal / Q000201:enzymology; D006987:Hypesthesia / Q000209:etiology / Q000503:physiopathology; D007150:Immunohistochemistry; D007278:Injections, Spinal; D007405:Intervertebral Disc Displacement / Q000150:complications* / Q000201:enzymology / Q000503:physiopathology*; D008159:Lumbar Vertebrae; D008297:Male; D017628:Microglia / Q000201:enzymology*; D009069:Movement Disorders / Q000209:etiology*; D009474:Neurons / Q000201:enzymology; D010146:Pain / Q000209:etiology / Q000503:physiopathology / Q000523:psychology; D010766:Phosphorylation; D011128:Polyradiculopathy / Q000209:etiology / Q000503:physiopathology; D011720:Pyrazoles / Q000008:administration & dosage / Q000494:pharmacology; D011725:Pyridines / Q000008:administration & dosage / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012583:Schwann Cells / Q000201:enzymology; D013116:Spinal Cord / Q000201:enzymology; D013130:Spinal Stenosis / Q000150:complications*; D013997:Time Factors; D016138:Walking; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
D004791:Enzyme Inhibitors; C104334:FR 167653; D011720:Pyrazoles; D011725:Pyridines; D048051:p38 Mitogen-Activated Protein Kinases