Xenon blocks the induction of synaptic long-term potentiation in pain pathways in the rat spinal cord in vivo.

Abstract

Xenon's (Xe) mechanisms for producing anesthesia and analgesia are not fully understood. We tested the effect of Xe equilibrated in a lipid formulation or normal saline on spinal C-fiber-evoked potentials and on the induction of synaptic long-term potentiation (LTP). C-fiber-evoked field potentials were recorded in the superficial lumbar spinal cord in response to supramaximal electrical stimulation of the sciatic nerve. Anesthesia was maintained with isoflurane in one-third O2 and two-thirds N2O. Xe equilibrated at a concentration of 600 microL/mL of Lipofundin MCT(R) 20%, (n = 5) or solvent alone (n = 3), and Xe equilibrated at a concentration of 100 microL/mL of normal saline (n = 7) or saline alone (n = 7) was given IV under apnea. High-frequency stimulation of the sciatic nerve was applied 60 min after the injection of Xe-containing formulations or solvents [to induce LTP]. High-frequency stimulation potentiated C-fiber-evoked potentials to 156% +/- 14% (mean +/- sem) of control. Low-dose Xe in saline 0.9% blocked the induction of LTP. High-dose Xe equilibrated in MC(R) 20% showed no additional effect when compared with the solvent, which blocked the induction of LTP. Low-dose Xe in saline 0.9% revealed no antinociceptive, but preventive, action in spinal pain pathways.