Up-regulation of acid-sensing ion channel 3 in dorsal root ganglion neurons following application of nucleus pulposus on nerve root in rats.
METHODS
Immunocytochemistry for acid-sensing ion channel 3 (ASIC3) in neurons of rat dorsal root ganglions (DRGs) from animals exposed to a model of lumbar disc herniation.


OBJECTIVE
To examine expression of ASIC3 in DRGs and the effect of a sodium channel blocker applied to the nerve root in a rat model of lumbar disc herniation.


BACKGROUND
Radicular pain is a common symptom of lumbar disc herniation in human beings. A depolarizing sodium channel gated by protons during tissue acidosis, ASIC3, is specifically expressed in sensory neurons. It has been associated with cardiac ischemic and inflammatory pain. We often perform spinal nerve root block for radicular pain using a sodium channel blocker, such as lidocaine; however, it has been unclear whether the effective period of this treatment is usually longer than the expected duration of efficacy.


METHODS
For the lumbar disc herniation model, nucleus pulposus was harvested from the tail and applied to the L5 nerve root, and the nerve roots were pinched. We evaluated mechanical allodynia in sham-operated animals and a disc herniation model. Immunohistochemistry was used to examine ASIC3 expression in L5 DRGs. Finally, the effect of lidocaine on pain and ASIC3 expression in the disc herniation model was examined.


RESULTS
Animals exposed to the lumbar disc herniation model showed allodynia for 8 days, and ASIC3 immunoreactivity was up-regulated in DRG neurons. After administration of lidocaine to spinal nerve roots affected by disc herniation, ASIC3 immunoreactivity was down-regulated in DRG neurons, and the level of mechanical allodynia was significantly decreased for 8 days.


CONCLUSIONS
Our results suggest that ASIC3 in DRG neurons may play an important role in nerve root pain caused by lumbar disc herniation. Lidocaine decreased ASIC3 expression in DRG neurons and pain associated with the disc herniation model.
Ohtori
Seiji
S
Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan. sohtori@faculty.chiba-u.jp
Inoue
Gen
G
Koshi
Takana
T
Ito
Toshinori
T
Doya
Hideo
H
Saito
Tomoko
T
Moriya
Hideshige
H
Takahashi
Kazuhisa
K
D062565:Acid Sensing Ion Channels; D000818:Animals; D004195:Disease Models, Animal; D005727:Ganglia, Spinal / Q000378:metabolism / Q000473:pathology*; D006930:Hyperalgesia / Q000209:etiology / Q000378:metabolism / Q000473:pathology; D007403:Intervertebral Disc / Q000473:pathology* / Q000637:transplantation; D007405:Intervertebral Disc Displacement / Q000150:complications / Q000378:metabolism / Q000473:pathology*; D008012:Lidocaine / Q000494:pharmacology; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism / Q000473:pathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015222:Sodium Channels / Q000378:metabolism*; D013126:Spinal Nerve Roots / Q000187:drug effects / Q000473:pathology*; D015854:Up-Regulation
C568269:ASIC3 protein, rat; D062565:Acid Sensing Ion Channels; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D015222:Sodium Channels; D008012:Lidocaine