Spinal expansion of saphenous afferents after sciatic nerve constriction in rats

In rats with chronic constriction of one sciatic nerve, neurone pair responses to saphenous electrical stimulation were simultaneously recorded in sciatic (L5-6) and in saphenous (L2) spinal areas. In 16 rats with thermal hyperalgesia, 43 pairs of neurons were recorded, 4 and 14 days after constriction, on both sides of the spinal cord. On the side ipsilateral to nerve constriction, stimulation of the saphenous evoked excitatory responses in 90% of neurones recorded in the L5-L6 sciatic area, regardless of the post-constriction time. No responses were evoked by saphenous stimulation of the L5-L6 contralateral spinal cord neurones. The possibility that pre-existing connections are unmasked after nerve injury and impinge on sensitized neurones, contributing to abnormal pain sensations such as, for instance, extraterritorial pain, is discussed.