A long-term analysis of the spinal somatosensory evoked potential of rats with sciatic constriction injury.
BACKGROUND
This study was undertaken to evaluate the long-term effect of a peripheral neuropathic pain model, chronic constriction injury (CCI) of the sciatic nerve, through analyses of electrophysiologic change, sciatic nerve function, and pain behavior.


METHODS
CCI of the sciatic nerve was induced in twelve rats as described by Bennett and Xie. Three parameters were monitored: spinal somatosensory evoked potential (SSEP) elicited by supramaximal stimulation of the posterior tibial nerve and recorded from the thoracolumbar junctional space; thermal hyperalgesia assessed by measuring paw withdrawal latency (PWL); and sciatic function index (SFI). All the values of these parameters were obtained before the CCI procedure (day 1 as a preoperative baseline, and again on days 5, 12, 19, 26, 33, 47, 61, 75, and 89). SSEP was also measured 3 hr after the CCI operation. Data were also obtained from contralateral limbs.


RESULTS
All rats with CCI developed thermal hyperalgesia on day 5, as indicated by a significant reduction in PWL in the CCI limbs and a deterioration of the SFI compared with baseline values. These effects persisted to day 89. In the electrophysiologic study, 3 hrs after the CCI operation, the amplitude significantly decreased and latency significantly increased in all SSEP recordings. The changes persisted and showed no further statistically significant deterioration or recovery. The data demonstrated that the major electrophysiologic change after a constriction injury was the loss of conduction ability across the injury site in the fast-conducting fibers, but in the slow-conducting fibers the conduction ability was still preserved, which occurred immediately after the operation and persisted consistently for 89 days in the rats with behavior manifestations of neuropathic pain.


CONCLUSIONS
Our findings suggest that SSEP is simple to obtain and sensitive in the acute phase of electrophysiological changes, but is limited for long-term evaluation after CCI.
Jou
I-Ming
IM
Department of Orthopedics, National Cheng Kung University Medical Center, Tainan, Taiwan, R.O.C.
Chang
Pei-Jung
PJ
Wu
Hsin-Huei
HH
Wang
Po-Jen
PJ
Chu
Koung-Shing
KS
Lin
Ruey-Mo
RM
Tsai
Yu-Chuan
YC
D000818:Animals; D002908:Chronic Disease; D003251:Constriction, Pathologic; D005073:Evoked Potentials, Somatosensory; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D020426:Sciatic Neuropathy / Q000473:pathology / Q000503:physiopathology*; D013116:Spinal Cord / Q000503:physiopathology*