Behavioral and electrophysiological evidence for the differential functions of TRPV1 at early and late stages of chronic inflammatory nociception in rats.
We previously reported that vanilloid receptor type 1 (VR1, or TRPV1) was up-regulated in dorsal root ganglion (DRG) and the spinal dorsal horn after chronic inflammatory pain produced by complete Freund's adjuvant (CFA) injection into the plantar of rat hind paw. In the present study, we found that subcutaneous or intrathecal application of capsazepine (CPZ), a TRPV1 competitive antagonist, could inhibit thermal hyperalgesia on day 1 and on day 14 but not on day 28 after CFA injection. With extracellular electrophysiological recording, the effect of CPZ on noxious electrical or heat stimulation evoked responses of wide dynamic range (WDR) neurons in the deep layers of the spinal dorsal horn was evaluated. Under noxious electrical stimulation to sciatic nerve, CPZ applied to the spinal cord produced an inhibition on Adelta- and C-fiber evoked responses of WDR neurons on day 1 and 14, but not on day 28. Under radiant heat stimulation to the receptive field skin, subcutaneous application of CPZ significantly inhibited the background activity and extended the response latency of WDR neurons on day 14. These results provide new evidence for the functional significance of TRPV1 at the early stage, but not the late stage, in the rat model of CFA-induced inflammatory pain.
Luo
Hao
H
Neuroscience Research Institute, Peking University, 38 Xueyuan Road, Beijing 100083, China.
Xu
Isabella Shi
IS
Chen
Yi
Y
Yang
Fei
F
Yu
Lu
L
Li
Guang-Xin
GX
Liu
Feng-Yu
FY
Xing
Guo-Gang
GG
Shi
Yu-Shun
YS
Li
Tan
T
Han
Ji-Sheng
JS
Wan
You
Y
D000818:Animals; D002211:Capsaicin / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use; D002908:Chronic Disease; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects; D005620:Freund's Adjuvant; D006358:Hot Temperature; D006930:Hyperalgesia / Q000188:drug therapy*; D007249:Inflammation / Q000139:chemically induced / Q000503:physiopathology*; D007278:Injections, Spinal; D008297:Male; D010146:Pain; D010812:Physical Stimulation; D020671:Posterior Horn Cells / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012584:Sciatic Nerve / Q000187:drug effects / Q000502:physiology; D013116:Spinal Cord / Q000187:drug effects; D050916:TRPV Cation Channels / Q000502:physiology*
D050916:TRPV Cation Channels; C493922:Trpv1 protein, rat; D005620:Freund's Adjuvant; C071423:capsazepine; D002211:Capsaicin