Fig. 8.

Changes in spike amplitude and duration during repetitive firing. A, Data from a normally adapting (TML cell; top row) and a nonadapting (GCL cell;middle row) interneuron and from a granule cell (bottom row). For each cell, a spike train elicited by injected depolarizing current (left column), thesuperimposed traces of the first (solid line) and fifth (dotted line) spike of the train (middle column), and a graph of spike duration (A. P. Duration) versus spike number (A. P. Number) during the train is shown. The depolarizing current injection was 0.2 nA for the interneurons and 0.14 nA for the granule cell. Note that in the nonadapting cell neither the spike amplitude nor duration changed during the train. In contrast, marked changes in both of these parameters were apparent in all other cell types tested.B, Comparison of the effect of repetitive firing on the amplitude of the action potential. The bar graph depicts the amplitude of the fifth action potential of a train expressed as a percentage of the first action potential of the train in each of the three classes of interneurons and granule cells. In this figure, bars and error bars represent the mean ± SEM (**p< 0.01). C, Comparison of the effect of repetitive firing on the duration of the action potential. The bar graph represents the duration of the fifth spike of the train as a percentage of the duration of the first spike (**p < 0.01; ***p < 0.001). Note the striking lack of a change in the spike duration in nonadapting cells as compared with all other cell types.