[The role of capsaicin-sensitive primary afferents in experimental sciatic pain].
OBJECTIVE
To determine the effect of destroying capsaicin-sensitive primary afferents (CSPA) fibers on paw withdrawal mechanical threshold (PWMT) induced by the direct compression of L5 nerve root with autologous disc.


METHODS
The procedure used autologous disc of the rats from the coccygeal intervertebral discs to apply direct pressure to the L5 dorsal root. PWMT was measured at the different time points post-surgery and pre-surgery. 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
The study shows 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.
Department of Orthopaedic Surgery, First Hospital Affiliated to the General Hospital of the People's Liberation Army, Beijing 100048, China.
Jia-guang
JG
Tang
Shu-xun
SX
Hou
Wen-wen
WW
Wu
Wei-lin
WL
Shang
D000344:Afferent Pathways / Q000503:physiopathology*; D000818:Animals; D002211:Capsaicin / Q000494:pharmacology*; D004195:Disease Models, Animal; D006930:Hyperalgesia / Q000503:physiopathology*; D007405:Intervertebral Disc Displacement / Q000150:complications; D008297:Male; D017288:Pain Threshold / Q000187:drug effects; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012585:Sciatica / Q000209:etiology / Q000378:metabolism / Q000503:physiopathology*; D013126:Spinal Nerve Roots / Q000378:metabolism
D016760:Proto-Oncogene Proteins c-fos; D002211:Capsaicin