Figure 1.

SNHL increases membrane excitability. The resting membrane potential of SNHL neurons is significantly depolarized (A), and the input resistance is significantly higher (B) compared with neurons recorded in normal animals. In this and subsequent figures, each open symbol represents the measurement from one neuron (n values shown on the x-axis). Filled symbols are mean ± SEM. C, Examples of neurons that respond to suprathreshold current injection with an onset (top), sustained (middle trace), and adapting (bottom trace) response. Five suprathreshold pulses (10 pA, 1500 ms) were injected, and firing pattern was established if the fifth pulse did not alter the firing pattern. D, Bar graphs of firing patterns in normal and SNHL neurons show percentile distribution. After SNHL, onset-type neurons were not observed, and there was a significant rise in the sustained and a decrease in adapting neuron patterns, suggesting greater excitability. E, Linear fit of number of spikes by depolarizing current injection. Five 10 pA, 1500 ms depolarizing current steps were injected, and the resultant spikes were counted. The fit shows no significant difference between the stimulus-response characteristics of normal and SNHL adapting neurons; the SNHL sustained neuron fits had a greater correlation coefficient, similar to the correlation in sustained neuron fits of normal neurons (see Results). Therefore, the characteristics of firing patterns did not change; rather, the incidence of sustained firing increased and adapting neurons decreased in SNHL neurons, as shown in D.