Fig. 9.

The delayed current transient can be obtained by extracellular stimulation. A, Morphology of the recorded interneuron (a basket cell) with Lucifer yellow staining. The Purkinje cell layer (PCL) corresponds roughly to the lower border of the field. The location of the stimulation pipette was alternated between a position 160 μm left of the soma of the recorded cell (Site 1) and another position 160 μm right of the soma of the recorded cell (Site 2; data not shown). B, Current traces obtained for different stimulation conditions. Series of pulses of 0.2 msec in duration and of various amplitudes were delivered with a frequency of 0.25 Hz at each site. Between each series of pulses, responses to somatic depolarizations were recorded. B1, A 600 μA stimulation at Site 1 failed to elicit any response. Only the stimulation artifact is obtained. B2, Increasing the stimulation intensity to 700 μA resulted in a large Na⁺ current (which just saturated the recording amplifier at 2 nA; data not shown) and a 90 pA delayed current transient. B3, Response to somatic stimulation. Na⁺ current amplitude = 1.75 nA (data not shown). Note the similarity of the amplitude and time course of the delayed current transient with that obtained by direct axon stimulation. B4, Lack of response at Site 2, with a stimulation intensity largely beyond the threshold at Site 1.