Fig. 4.
Metaplasticity of inhibitory CCIN-evoked inputs. Graphs showing the effects of 5 (A), 10 (B), and 20 (C) Hz stimulation of CCINs on monosynaptic inputs to contralateral motor neurons. Because the pattern of activity-dependent plasticity seen in this study occurred consistently, control responses before application of the neuromodulators were similar. Thus, control responses before substance P and 5-HT application are combined on the graphs to simplify comparison of their effects (substance P, 1 μm; ○;n = 5; 5-HT, 10 μm; ▪;n = 4). Di, Traces showing the effects of 20 Hz stimulation on the CCIN input to a contralateral motor neuron in control (black line) and in the same cell after the application of 1 μm substance P (gray line). At the end of trace, the 1st and 5th IPSPs in a train from a different experiment are shown on an expanded time scale in control (black line) and in the presence of substance P (gray line). Dii, Traces showing the effects of 5 Hz stimulation on the CCIN input (black line) and in the same cell after application of 10 μm 5-HT (gray line). The 1st and 5th IPSPs from a separate experiment are again shown in control (black line) and in the presence of 5-HT (gray line). Horizontal lines inDi and Dii indicate the amplitude of the initial IPSP in control (black line) and in substance P or 5-HT (gray line), the overlap of the lines indicating that there was no effect of 5-HT on the amplitude of the initial IPSP in the train. E, Graph showing the effects of stimulus trains at 5–20 Hz on CCIN IPSPs. Averages of the first IPSP in the train (IPSPinitial), IPSPs during the early part of the train (IPSP2–5), and the final five IPSPs in the train (IPSP15–20) are shown at each frequency in control and in the presence of substance P (1 μm) or 5-HT (10 μm). Calibration: 1 mV, 200 msec (for the train), 20 msec (for the expanded trace).