Nitrous oxide suppresses the electromyographic response evoked by electrical stimulation of the motor cortex

The influence of nitrous oxide on motor evoked potential (MEP) elicited in rats by cortical and midcervical electrical stimulation was studied and compared with early components of somatosensory evoked potential (SEP) following stimulation of the posterior tibial nerve in 6 rats. We found that nitrous oxide gradually suppresses MEP, depending on the concentration of this inhalation agent. At a concentration of 66 vol% of nitrous oxide, the MEP was completely abolished, whereas the initial component N1-P1 of the SEP was only slightly reduced. We conclude that the descending impulse elicited by electrical stimulation of the corticospinal tract is mainly inhibited at the level of the spinal neuronal or interneuronal system, since (1) neuromuscular transmission is not blocked by nitrous oxide, and (2) MEP suppression is the same following cortical and midcervical stimulation.