Intracellular potentials from "idle" cells in cerebral cortex of cat.

potentials were recorded from "idle" cells in the cerebral cortex of the cat. Records were made during repetitive stimulation of the cortical surface and during Metrazol induced paroxysmal activity. 2. The intraand extra-cellular potentials induced by either stimulation of cortical surface or Metrazol injection were of opposite polarity, revealing that the intracellularly recorded potential was a change in membrane potential of the impaled cell and not a field potential generated by other elements. 3. The extracellular potential elicited during stimulation of the cortical surface was an approximate mirror image of the intracellular one, and thus accounted for the slow depolarization of the "idle" cell. 4. Following Metrazol injection, the extracellular potential, although opposite in polarity to the intracellular one, showed oscillation which had no counterpart in the intracellular record. Similar recordings made from cortical neurons showed intracellularly recorded oscillations which corresponded to extracellular ones. Therefore, the extracellular potential recorded immediately outside an "idle" cell following Metrazol is viewed as reflecting a composite of both glial and neuronal membrane changes. 5. Iontophoretic staining of "idle" cells suggests that they are probably glia.