Inhibitory action of sensory transmission by inhalational anesthetics in the spinal cord

This review article focuses on the suppression of sensory transmission by inhalational anesthetics at the spinal cord level. Volatile anesthetics (e.g. halothane and isoflurane) suppress neuronal responses evoked by both noxious and non-noxious stimuli. This suppression is mediated largely by activation of GABA_A and glycine receptors systems in the spinal dorsal horn. Depression of spinal glutamate receptor systems is also probably involved. The analgesic action of nitrous oxide is produced by activation of supra-spinal descending inhibitory systems, not by direct action on the spinal cord. Activation of the descending inhibitory systems by nitrous oxide causes release of noradrenaline in the spinal dorsal horn, and activates α₂ adrenergic receptor systems, resulting in depression of neuronal responses evoked by noxious stimuli. GABA_A and glycine receptor systems in the spinal dorsal horn are also important components of nitrous oxide anesthesia in depressing neuronal responses evoked by non-noxious stimuli. Although excitation or inhibition of GABA_A, glycine, α₂ adrenergic and glutamate receptors systems is an important action of inhalational anesthetics, influence of inhalational anesthetics on interactions among these receptor systems has yet to be studied.