A shielded microelectrode suitable for single-electrode voltage clamping of neurones in the CNS

The fabrication of a shielded microelectrode is described which has a time constant of about 3 microseconds, regardless of its depth in neural tissue. The shield is insulated from surrounding tissue with an insulation resistance which exceeds 1000 M omega, and the insulation will withstand +/- 15 V. Because of its narrow profile, the electrode is suitable for in vivo intracellular recordings from motoneurones and other large neurones of the CNS. The small time constant and the high breakdown resistance of the electrode make it suitable for use with single-electrode voltage clamp circuitry to voltage clamp motoneurone somata using switching rates in excess of 30 kHz.