Abstract
Mammalian glial cells were identified and studied in the optic nerves of anaesthetized rats. Cells with membrane potentials of 77-85 mV were located in the optic nerve with capillary micropipettes. These were shown to be neuroglia by iontophoretic injection of a fluorescent dye through the recording electrode, followed by histological verification of the location of the dye. No distinction was made between astroglia and oligodendroglia. Neuroglial cells gave no impulse activity. Their membrane potential was studied in isolated optic nerves by varying the ionic composition of the bathing fluid. The glial membrane potential depends predominantly on a transmembrane gradient of potassium ions.