The role of capsaicin-sensitive primary afferents in experimental sciatica induced by disc herniation in rats.
METHODS
The topical capsaicin treatment of the sciatic nerve, which was proved to destroy capsaicin-sensitive primary afferent (CSPA) fibers, was performed to determine the effect on decreases in paw withdrawal mechanical threshold (PWMT) and changes in spatial expression pattern of spinal c-Fos protein induced by the direct compression of L5 nerve root with autologous disc.


OBJECTIVE
To investigate the role of CSPA fibers in the development of mechanical hyperalgesia in the new sciatica model.


BACKGROUND
To date, CSPA fibers have been shown to be involved in development of thermal hyperalgesia in various pain models. But the controversy still exists as to whether CSPA fibers are involved in the development of mechanical hyperalgesia in different pain models. To our best knowledge, the role of CSPA in sciatica was not investigated. Therefore, the present study was designed to determine the role of CSPA fibers in the newly developed sciatica model.


METHODS
All surgeries were performed in Sprague-Dawley rats. PWMT was measured at the different time points postsurgery and presurgery. The changes in spatial expression pattern of c-Fos protein in the spinal cord were also determined at 3 weeks when PWMT decreased to the peak.


RESULTS
The pretreatment with capsaicin produced a complete prevention of mechanical hyperalgesia induced by disc compression. The direct compression of L5 nerve root produced an obvious expression of Fos-like immunoreactivity neurons in the dorsal horn of the spinal cord, which was significantly decreased by pretreatment with capsaicin.


CONCLUSIONS
We conclude that CSPA fibers, which mainly terminated in superficial layers of dorsal horn, may play a key role in mechanical hyperalgesia in the new sciatica model.
Tang
Jia-Guang
JG
Institute of Orthopedics, Changzheng Hospital of PLA, Shanghai, Peoples Republic of China.
Chen
Hui-Sheng
HS
Yuan
Wen
W
Hou
Shuxun
S
Wang
Xinwei
X
Zhou
Xuhui
X
D000287:Administration, Topical; D000818:Animals; D002211:Capsaicin / Q000494:pharmacology; D002452:Cell Count; D004195:Disease Models, Animal; D006358:Hot Temperature; D006930:Hyperalgesia / Q000209:etiology / Q000503:physiopathology* / Q000517:prevention & control; D007124:Immunoenzyme Techniques; D007405:Intervertebral Disc Displacement / Q000150:complications / Q000503:physiopathology; D009408:Nerve Compression Syndromes / Q000150:complications / Q000503:physiopathology; D009412:Nerve Fibers / Q000187:drug effects / Q000502:physiology*; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology*; D009619:Nociceptors / Q000187:drug effects / Q000503:physiopathology*; D010147:Pain Measurement; D017288:Pain Threshold; D010812:Physical Stimulation; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time; D012584:Sciatic Nerve / Q000187:drug effects / Q000502:physiology*; D012585:Sciatica / Q000209:etiology / Q000503:physiopathology; D018689:Sensory System Agents / Q000494:pharmacology; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism / Q000473:pathology
D016760:Proto-Oncogene Proteins c-fos; D018689:Sensory System Agents; D002211:Capsaicin