Orally administered atropine enhances motor cortex excitability: a transcranial magnetic stimulation study in human subjects

Oral application of atropine was used to test if a modulation of cholinergi c neurotransmission changed motor excitability. Healthy volunteers received either 1 or 2 mg atropine. Paired transcranial magnetic stimulation was us ed to study intracortical inhibition and intracortical facilitation before, 1 h and 24 h after ingestion of atropine. In addition, the silent period, motor threshold, F wave and motor response amplitudes were measured. The 1 mg dose of atropine induced a loss of intracortical inhibition, the 2 mg do se produced an intracortical disinhibition and enhanced intracortical facil itation. These changes returned to baseline after 24 h. Other electrophysio logical parameters remained unchanged. Thus, an antagonist of pre- and post synaptic muscarinic receptors increased excitability in the human motor cor tex in a dose-dependent manner, indicating an influence of the cholinergic system on motor cortex excitation. (C) 2001 Published by Elsevier Science I reland Ltd.