Injured nerve block alters adjacent nerves spinal interaction in neuropathic rats

Baseline activity and responses to simultaneous saphenous stimulation of pairs of neurones recorded from sciatic (L5-6) and saphenous (L2) spinal cord segments, in rats with thermal hyperalgesia following sciatic constriction, were analysed before, during and after a sciatic nerve block with a local anaesthetic. In sciatic neurones, during the block, reductions of baseline activity (p < 0.001), increases in threshold of saphenous electrical stimulation (p < 0.01) and reductions of responses to electrical and to natural noxious saphenous stimuli (p < 0.001) were consistently found. The neuronal baseline and evoked activities remained unmodified in saphenous neurones. The contribution of input from injured periphery to central neurone circuitry mechanisms underlying the unmasking of improper afferents is discussed.