Neither spinal γ-aminobutyric acid-A nor strychnine-sensitive glycine receptor systems are the sole mediators of halothane depression of spinal dorsal horn sensory neurons

Inhaled anesthetics depress the response of spinal dorsal horn low-threshold (LT) neurons to peripheral receptive field stimulation. Part of that depression may be mediated by anesthetic interactions with γ-aminobutyric acid type A (GABA_A) and strychnine-sensitive glycine inhibitory neurotransmitter systems. In this electrophysiological study, we attempted to antagonize halothane depression of LT neurons by administering bicuculline (a competitive GABA_A antagonist) and/or strychnine (a competitive glycine antagonist) systemically, alone or in combination, to decerebrate, spinal cord-transected rats. We observed that both bicuculline and strychnine, alone or in combination, significantly but only partially reversed halothane depression of LT neuronal responses to receptive field stimulation. The inability of bicuculline and strychnine, alone or in combination, to completely reverse halothane depression suggests that although GABA_A and glycine systems are involved in the observed halothane depression, additional mechanisms of action are also required for halothane depression of LT spinal sensory neurons.