Induction of long-term potentiation of single wide dynamic range neurones in the dorsal horn is inhibited by descending pathways

Previous studies have shown that long-term potentiation (LTP) in the dorsal horn may be induced by noxious stimuli. In this study it is investigated w hether induction of LTP in the dorsal horn may be affected by the descendin g pathways. Extracellular recordings of wide dynamic range (WDR) neurones i n the lumbar dorsal horn in intact urethane-anaesthetized Sprague-Dawley ra ts were performed, and the electrically evoked neuronal responses in these neurones were defined as A-fibre and C-fibre responses according to latenci es. Using a short-term cold block of the thoracic spinal cord. which produc ed a completely reversible increase of the A-fibre and C-fibre responses, t he influence of the descending inhibitory system on the induction of LTP by electrical high-frequency conditioning applied to the sciatic nerve was ex amined. As previously shown the A-fibre responses were almost unchanged fol lowing the conditioning. In contrast, the C-fibre responses following the s ame conditioning were strongly increased. Thus, a clear LTP of the nocicept ive transmission in the dorsal horn was observed following electrical high- frequency conditioning. interestingly, we found that the LTP was more power ful when the effects of the descending pathways were temporarily eliminated during conditioning. It is concluded that induction of LTP by electrical h igh-frequency conditioning stimulation, which may be part of the wider term central sensitization. is inhibited by descending pathways. (C) 2001 Inter national Association for the Study of Pain. Published by Elsevier Science B .V. All rights reserved.