Riluzole suppresses motor cortex facilitation in correlation to its plasmalevel - A study using transcranial magnetic stimulation

The aim of our study was to measure the effects of the glutamate antagonist riluzole on different parameters of motor excitability, using transcranial magnetic stimulation (TMS) during 7 days of riluzole administration, and t o correlate these effects with riluzole plasma levels. Nine healthy volunte ers received a dose of 100 mg riluzole from day 1 to 7 of the study period. Electrophysiological examinations were performed on day 1 before and 2 h, 5 h and 8 h after riluzole administration, on day 2, day 3 and day 5 before riluzole administration, and on day 8. Plasma samples were taken simultane ously. The excitability of the motor cortex, supraspinal and spinal motor p athways was tested by studying intracortical facilitation and inhibition, t he cortical silent period and motor threshold after TMS, as well as the per ipheral silent period and F-wave amplitudes after electrical peripheral ner ve stimulation. We found a significant reduction of intracortical facilitat ion, which correlated significantly with riluzole plasma levels. To a lesse r extent, intracortical inhibition was enhanced on day I, motor threshold w as increased on day 8 and F-wave amplitudes were reduced. These changes did not correlate with riluzole plasma levels. We conclude that the main effec t of riluzole in vivo is a reduction of intracortical facilitation, which i s closely related to the drug's level in the plasma. The most probable mech anism involves an effect on glutamatergic synaptic transmission.