Figure 5. NGF effects on the discharge variability of axotomized motoneurons. A–C, Firing patterns of control (A), axotomized (B), and axotomized but NGF-treated (C) motoneurons. The firing rate (FR) in control and axotomized motoneurons showed a highly regular profile during spontaneous eye movements (EP). The single-unit discharge of action potentials (AP) is shown in the middle trace. D–F, Periods of 1 s of instantaneous firing rate in a control (D), axotomized (E), and NGF-treated (F) abducens motoneuron. Stationary periods were selected as having similar mean firing rate across groups. Note, however, the large increase of both the SD and the coefficient of variation (CV) in F. G–I, First-order ISI histograms from the corresponding cells shown in A–C, but constructed using a 2 s sample (bins of 0.1 ms). Distributions were normal except in I (Kolmogorov–Smirnov test; p > 0.05), which showed a high skew to the right. J, The control autocorrelogram (1 ms bin size) showed one clear peak, isolated from the base, and up to three clear peaks, fused in the base (same cell as in A, D, and G). K, The autocorrelogram of the axotomized motoneuron shown in B and E demonstrated a somewhat higher variability than the control motoneuron. L, The autocorrelogram of the NGF-treated motoneuron illustrated in C and F showed a complete absence of spike predictability.