Figure 4.

Dose-dependent effect of D₂-like receptor activation on focal plasticity induced by PAS25 and PAS10 (experiment 2). The time course plots showing the effect of different doses of RP on PAS-induced focal neuroplasticity. Shown are baseline-standardized MEP amplitudes after plasticity induction by ePAS (ISI of 25 ms) and iPAS (ISI of 10 ms) under 0.125 (A), 0.5 (B), and 1.0 mg (C) of ropinirole up to the evening of the poststimulation day. Under placebo medication, ePAS enhances while iPAS diminishes excitability significantly for up to 30 min after stimulation. Under the medium ropinirole dosage, the PAS-generated excitability enhancement remains largely unaffected, whereas the high and low doses abolish this excitatory effect. For iPAS-induced excitability reduction, no significant dose-dependent effect was observed. A prolonged inhibition was observed until 60 min after stimulation in the iPAS condition under 0.125 mg. Filled symbols indicate significant deviations of the poststimulation MEP amplitudes from baseline with regard to each drug dose. The “#” symbols indicate significant differences of the drug versus PLC conditions with regard to identical time points (Student's t test, two-tailed, paired samples, p < 0.05). Error bars indicate SEM. ne, Next evening; nm, next morning; na, next afternoon; se, same evening.