Altered dopamine modulation of LTD-like plasticity in Alzheimer's disease patients.
BACKGROUND Experiments in animal models suggest that neuronal plasticity can be enhanced by dopaminergic receptor activation. The present study tested whether stimulation-induced plasticity of human motor cortex after low-frequency repetitive transcranial magnetic stimulation (rTMS) could be potentiated by a single oral dose of the combined D1/D2 receptor agonist pergolide. METHODS In a randomized, double-blind, placebo-controlled cross-over design, nine healthy young volunteers received .125 mg pergolide or placebo 2 hours before 1 Hz rTMS was applied for 20 min to the left primary motor cortex. In a control experiment 7 subjects received .125 mg pergolide 2 hours before sham rTMS. We used single-pulse TMS at rest to assess corticospinal excitability before and up to 24 min after rTMS. RESULTS Suppression of corticospinal excitability by 1 Hz rTMS was more pronounced after pergolide intake compared with placebo and lasted approximately 20 min after pergolide but only 5 min after placebo. No change of corticospinal excitability could be observed when sham rTMS was performed after pergolide intake. CONCLUSIONS The results suggest a possible role for dopaminergic potentiation of rTMS-induced neuroplasticity in experimental or therapeutic applications and should be considered when rTMS is applied in patients under medication with dopamine agonists or antagonists.