Nitrous oxide inhibits glutamatergic transmission in spinal dorsal horn neurons☆

Abstract 

The effects of nitrous oxide (N₂O) are thought to be mediated by several pharmacological pathways at different levels of the central nervous system. Here, we focus on excitatory glutamatergic transmission in the superficial dorsal horn of the spinal cord with respect to its importance for the nociceptive processing. The effects of 50% N₂O on electrically evoked and spontaneous excitatory glutamatergic transmission and on the response to exogenous administration of N-methyl-d-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionic acid (AMPA) receptor agonists were examined in lamina II neurons of adult rat spinal cord slices using the whole-cell patch-clamp technique. Peak amplitudes of Aδ- and C-fiber evoked monosynaptic NMDA- and AMPA-receptor-mediated excitatory postsynaptic currents (EPSCs) were decreased in the presence of N₂O. N₂O reduced the peak amplitude and integrated area of exogenous NMDA- and AMPA-induced currents. Moreover N₂O changed the distribution of miniature EPSC amplitude, but not frequency distribution in most neurons. N₂O inhibits glutamatergic transmission in the superficial dorsal horn by modulating the NMDA- and AMPA-receptors. Our findings raise the possibility that the antinociceptive effect of N₂O may be directly mediated at the level of the spinal cord.

Keywords: Nitrous oxide, Analgesia, Glutamate receptors, Dorsal horn, Whole-cell patch-clamp