Xenon Has Greater Inhibitory Effects on Spinal Dorsal Horn Neurons than Nitrous Oxide in Spinal Cord Transected Cats

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Abstract
Xenon (Xe) suppresses wide dynamic range neurons in cat spinal cord to a similar extent as nitrous oxide (N2 O).The antinociceptive action of N2 O involves the descending inhibitory system. To clarify whether the descending inhibitory system is also involved in the antinociceptive action of Xe, we compared the effects of Xe on the spinal cord dorsal horn neurons with those of N2 O in spinal cord-transected cats anesthetized with alpha-chloralose and urethane. We investigated the change of wide dynamic range neuron responses to touch and pinch by both anesthetics. Seventy percent Xe significantly suppressed both touch- and pinch-evoked responses in all 12 neurons. In contrast, 70% N2 O did not show significant suppression in touch- and pinch-evoked responses. These results suggest that the antinociceptive action of Xe might not be mediated by the descending inhibitory system, but instead may be produced by the direct effect on spinal dorsal horn neurons. Implications: Xenon (Xe) is an inert gas with anesthetic properties. We examined the antinociceptive effects of Xe and nitrous oxide (N2 O) in spinal cordtransected cats. Our studies indicate that Xe has a direct antinociceptive action on the spinal cord that is greater than that of N2 O. (Anesth Analg 1999;88:893-7)