Fig. 3. Augmentation caused an increase in EJP amplitudes even when stimuli were suspended for several seconds. (A) Original recording of the electrical response of the gm6 muscle to 20 Hz stimulation of LG with 10 trains of stimuli. Inter-train interval 4 s. The responses to the first, fifth and tenth stimulus trains are shown. Dotted lines indicate maximum depolarization and amplitude of test EJP. (B) Test EJPs increased in amplitude with repeated train stimulation. EJP amplitudes were normalized to the test EJP after the first stimulus train and plotted over the number of the stimulus train. 20 Hz stimulations were used. For further details and N numbers, see Table 1. Significances are shown for the test EJP after the tenth stimulus train. Significantly different from amplitude of test EJP after the first stimulus train, P<0.05. **Significantly different from amplitude of test EJP after the tenth stimulus train with longer inter-train durations, P<0.01. *Significantly different from amplitude of test EJP after the tenth stimulus train with longer inter-train durations, P<0.05. Significantly different from amplitude of test EJP after the tenth stimulus train with 32 s inter-train duration, P<0.05. (C) The first, fifth and tenth EJP increased in amplitude when stimulus trains (20 Hz) were repeated. EJP amplitudes were normalized to the tenth EJP of the first stimulus train. Average of N=11 animals. (D) Development of the amplitude of the tenth EJP during repeated train stimulation (20 Hz) with inter-train intervals of 1–32 s. EJP amplitudes were normalized to the tenth EJP of the first stimulus train. Significances as in B. For details and N numbers, see Table 2. (E) Exponential decay function fit of the augmentation index A (as revealed by the normalized amplitude of the tenth EJP of the tenth stimulus train during 20 Hz stimulation) over inter-train interval. Average of nine animals (32 s inter-train interval) and 11 animals (all other intervals), respectively. Significantly different from A of longer inter-train interval (P<0.05). (F) Decrement of EJP amplitudes after the end of a series of 10 train stimulations (20 Hz). EJPs were elicited at delays of 2, 4, 6, 8, 10, 12, 14, 16 and 18 s after the end (arrow) of the last stimulus train. Average of three sweeps. (G) Exponential decay function fit of decrement of EJP amplitudes after the tenth stimulus train (20 Hz). Average of N=14 animals. Arrow, first EJP of the first stimulus train (control EJP). For details see Table 3. Dotted line indicates amplitude of control EJP. **Significantly different from control, P<0.01. *Significantly different from control, P<0.05. Significantly different from EJP amplitudes with longer delays, P<0.05. (H) Development of EJP amplitudes (average of N=11 animals) during repetitive train stimulation (20 Hz). All EJPs of all stimulus trains are shown. Amplitudes were normalized to the last EJP of the first stimulus train. After the third stimulus train, no further enhancement of EJP amplitudes was obtained. (I) Within-train facilitation of EJP amplitudes is affected by augmentation. The amplitudes of all EJPs in each stimulus train are shown. Amplitudes were normalized separately to the last EJP of each particular stimulus train (20 Hz). Average of N=11 animals. F, facilitation index.