Different increase in C-fibre evoked responses after nociceptive conditioning stimulation in sham-operated and neuropathic rats.
Mechanisms of neuropathic pain are not clear. Recently we showed long-term potentiation (LTP) of wide dynamic range (WDR) neurones after electrical conditioning stimulation of the sciatic nerve in normal rats. In this study we investigated the effects of the same conditioning on both the evoked responses of WDR cells and on vital signs in neuropathic rats. Nerve injury was produced by tight ligation of the L5 and L6 spinal nerves and a control group received sham surgery. The electrical conditioning gave a significantly smaller LTP in neuropathic rats as compared to controls. Despite giving a smaller LTP in neuropathic rats, the rise in mean arterial blood pressure and heart rate induced by the conditioning was exactly the same as in the control group. The threshold for activating C-fibres was significantly lower and the baseline tended to be higher in neuropathic rats. Thus, it is suggested that the nerve injury itself is likely to induce an LTP-like state in the neurones studied. Further studies using the LTP-inducing model can provide new information on the mechanisms of neuropathic pain.
Rygh
L J
LJ
Neuropharmacology of Pain group, Department of Pharmacology, University College London, Gower Street, WC1 6BT, London, UK. lars.jorgen.ryghp@ki.uib.no
Kontinen
V K
VK
Suzuki
R
R
Dickenson
A H
AH
D000818:Animals; D003213:Conditioning, Psychological / Q000502:physiology*; D004558:Electric Stimulation; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D008026:Ligation; D017774:Long-Term Potentiation; D008297:Male; D009412:Nerve Fibers / Q000502:physiology*; D009619:Nociceptors / Q000503:physiopathology*; D010146:Pain / Q000503:physiopathology*; D010147:Pain Measurement; D010523:Peripheral Nervous System Diseases / Q000503:physiopathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013127:Spinal Nerves / Q000502:physiology