Abstract
We investigated the effects of various concentrations of halothane (0.2, 0.5 and 1.0%) on the excitation and inhibition of dorsal horn wide dynamic range (WDR) neuronal activity induced by bradykinin (BK) in spinal cordtransected cat. Extracellular activity was recorded from a single WDR neuron in the dorsal horn when noxious and non-noxious stimuli were applied to the cutaneous receptive fields on the left hind paw footpads of decerebrate, and spinal cord-transected (L1-2) cats. Injection of 10 μg of BK (used as the noxious stimulus) into the femoral artery ipsilateral to the recording site resulted in excitatory response in 13 of 13 (100%) WDR neurons. On the other hand, when the same dose of BK was injected into the femoral artery contralateral to the recording site, 7 of 13 (54%) WDR neurons showed inhibitory responses and 6 showed no response. Halothane at 1.0% concentration, but not at lower concentrations (0.2 or 0.5%) significantly depressed the excitatory neuronal activity recorded in WDR neurons. Furthermore, halothane at 0.2, 0.5 and 1.0% significantly depressed the inhibitory neuronal activity in WDR neurons. Our results indicated that halothane reduces the excitation as well as inhibition of dorsal horn WDR neuronal activity induced by BK injection, suggesting that this anesthetic agent reduces the excitatory and inhibitory responses produced by noxious stimuli at spinal cord level.
