Depolarization of cortical glial cells during electrocortical activity

Intracellular recordings were obtained from 257 inexcitable cells in the sigmoid gyri of the cat. Inexcitable cells were characterized electrophysiologically by an absence of postsynaptic and depolarizing potentials following thalamo-cortical and intracellular stimulation with current strengths adequate to evoke responses in neurons. Iontophoretic deposit of dye successfully marked 6 inexcitable cells, and revealed them to be small cells which had strongly marked oval nuclei surrounded by a small amount of lightly marked cytoplasm. These cells had the dimensions and appearance of cortical glial cells. One third of the inexcitable cells penetrated had membrane potentials ranging from -80 mV to -95 mV and 22% of the cells penetrated exhibited slow depolarizations of membrane potential which followed electrocortical spindle bursts. Some cells undergoing slow depolarization were found to be adjacent to active neurons. It is suggested that depolarization of some glial cells occurs as a normal physiological event during electrocortical activity.