Penicillin-Induced Segmental Myoclonus

Abstract

Penicillin was applied to the cat spinal cord and the changes in membrane properties of motoneurons measured. Just prior to the appearance of the facilitated spontaneous synaptic potentials, there is a diminution of the resting potential of the motoneuron. This is not associated with a detectable change in membrane resistance or in time constant. The after-hyperpolarization of the action potential is decreased. The simplest explanation for these changes is a change in the potassium equilibrium potential (E_k). To test the possibility that the change in E_kis causally related to the appearance of the prolonged depolarization, the intracellular potassium of normal motoneurons was displaced with either choline or tetramethylammonium ions. In both cases a prolonged depolarization occurred similar to that produced by penicillin, and, moreover, this response was evoked by directly applied intracellular currents.