Reflex sympathetic activities during inhalation of anaesthetics in cats: nitrous oxide

The effects of nitrous oxide on the late reflex potential, a medullary component of somato-sympathetic reflex potentials, induced from the lumbar sympathetic trunk by electrical stimulation of the femoral nerve was investigated in brain intact cats and midbrain decerebrated cats under adequate anaesthesia with intravenous urethane and alpha-chloralose. The late reflex potential was depressed by inhalation of 75% nitrous oxide in oxygen in brain intact cats. Midbrain decerebration itself caused marked potentiation of the late reflex potential, although subsequent inhalation of 75% nitrous oxide did not cause any depressive effect on the potentiated late reflex potential. No significant changes in arterial pressure and heart rate were seen during the experiments. From these results, we concluded that anaesthetic concentrations of nitrous oxide might activate the descending inhibitory system from higher areas in the central nervous system.