Contralateral inhibitory control of spinal nociceptive transmission in rats with chronic peripheral nerve injury.

The effects of contralateral homotopic noxious stimulation on the spinal neurons nociceptive responses were examined in rats with chronic constriction of one sciatic nerve, in intact and in sham operated rats. Wide dynamic range (WDR) neurons activity was recorded in the spinal sciatic territory in anesthetized, paralyzed rats. Noxious stimulation of the contralateral homologous area strongly reduced the WDR nociceptive responses, the inhibitory effect outlasting the conditioning stimulus duration by 20-40 s. During a reversible blockade of descending pathways the inhibitory effect, except for the overlasting component, was still present, after a spinal cord longitudinal cut at the lumbar level the inhibitory effect was powerfully attenuated. The role of propriospinal connections in this phenomenon and how the contralateral input contributes to the control of nociceptive transmission is discussed.