Focal penicillin seizures--motor activity and cellular physiology and morphology

Two types of intracellular activity have been found in neurons in the cortical penicillin seizure focus during an interictal spike; a prolonged depolarization (PDS) followed by hyperpolarization or predominantly hyperpolarization. In the present study of a penicillin focus we have correlated the penicillin focus location with motor behavior and the cellular physiology with cellular morphology and location. Penicillin injection at the same location in the anterior sigmoid gyrus invariably resulted in focal seizures involving the contralateral shoulder. From the locations of the myoclonus and the focus, the character of the movements and the route of seizure spread we conclude that the same pathways mediate movement produced by penicillin seizures or by electrically stimulating the same motor cortex. Intracellular recordings and dye-marking of cells in and around the seizure focus revealed that PDS neurons were located within a 3 mm radius from the site of penicillin injection. All PDS neurons either lacked well filled processes or had abnormal dendrites. Inhibited neurons were all pyramidal neurons with normal dendrites. The dendritic abnormalities observed could be important in the genesis of the PDS.