gamma-Aminobutyric acid directly depolarizes cultured oligodendrocytes

gamma-Aminobutyric acid (GABA) depolarizes in a dose-dependent manner approximately one-third of all immunologically identified oligodendrocytes in cultures of mouse spinal cord. Measurements of [K+]o indicate that the response to GABA is not due to K+ released from active neurons. The depolarization is not accompanied by a change in cell input resistance. Replacement of sodium in the bathing solution abolishes the entire response, whereas ouabain only inhibits the repolarization phase. Current clamp experiments with two separate intracellular electrodes show that the depolarization increases at more positive potentials while the repolarization increases at more negative potentials. Bicuculline and picrotoxin but not nipecotic acid reduce the GABA effect. Pentobarbital and chlordiazepoxid also reduce the GABA-induced depolarization. Muscimol produces a depolarization similar to that of GABA. Heterogeneity in the oligodendrocyte population is indicated by the observation that some cells respond to both GABA and glutamate, while others respond only to one and some are not responsive to either.