Fig. 5.

Activity-dependent plasticity and metaplasticity of excitatory synaptic inputs. Graphs showing the effects of 5 (A), 10 (B), and 20 (C) Hz stimulation of EINs on monosynaptic inputs in contralateral motor neurons. As in Figure 4, because the pattern of activity-dependent plasticity in control was similar, summed control data from EIN to motor neuron pairs before substance P (1 μm; ○; n = 5) and 5-HT (10 μm; ▪; n = 5) application are shown on the graphs. Di, Traces showing EIN inputs to a postsynaptic ipsilateral motor neuron at 20 Hz in control (black line) and the modulation of the effects by 1 μmsubstance P (gray line). The 1st and 5th EPSPs in a train from a different experiment to that in Di are also shown on an expanded time scale in control (black line) and in the presence of substance P (gray line). Dii, Traces showing plasticity of EIN inputs evoked at 20 Hz in control (black line) and its modulation by 10 μm 5-HT (gray line). The 1st and 5th EPSPs in a train from a different experiment to that in Di are also shown on an expanded time scale in control (black line) and in the presence of 5-HT (gray line). The horizontal lines on the traces in Di and Diiindicate the amplitude of the initial EPSP in control (black) and in substance P or 5-HT (gray). E, Graph showing the effects of stimulus trains at 5–20 Hz on EIN-evoked EPSPs. The first EPSP in the train (EPSP_initial), EPSPs during the early part of the train (EPSP_2–5), and during the final five EPSPs in the train (EPSP_15–20) are shown. These effects are shown for control cords, and in the presence of substance P (1 μm) or 5-HT (10 μm). Calibration: 0.5 mV, 200 msec (for the train), 20 msec (for the expanded trace).