Pentobarbital and halothane hyperpolarize cat alpha-motoneurons.

The effect of anesthetics on the membrane potential of spinal alpha-motoneurons was studied in awake-intact cats that were sequentially anesthetized with either halothane or pentobarbital. Pentobarbital (35 mg/kg) and halothane (5%) both induced a 5 mV hyperpolarization and a reduction in spontaneous synaptic activity of motoneurons. We suggest that a reduction in the urinary EPSP frequencies contributes to the hyperpolarization and the membrane potential criterion of acceptable impalements of motoneurons in awake-intact preparations should be 5 mV more depolarized than that in anesthetized preparations.