Objective: To investigate by means of transcranial magnetic stimulation (TMS) the effect of a single oral dose of the GABA derivate piracetam on intracortical facilitatory I-wave interaction.
Methods: The study was performed in 8 healthy volunteers. Before, 1, 3, 6, and 24 h after intake of 4000 mg piracetam, MEPs in the relaxed abductor digiti minimi muscle were elicited by a recently introduced double pulse TMS technique with a suprathreshold first and a subthreshold second stimulus. From interstimulus intervals of 0.5-5.1 ms 3 periods were observed in which MEP facilitation showed maxima - so-called peaks of I-wave interaction - and which were separated by two troughs with no facilitation. We studied the changes in timing and size of the peaks over time.
Results: With piracetam, I-wave peaks showed a reduction in size as well as a shortening of the latencies at which the peaks occurred. Both changes were significant at 6 h after drug intake compared to baseline. The effects were partially reversible after 24 h.
Conclusions: The mode of action of piracetam within the nervous system is almost unknown. The peak size reduction was similar to effects that were seen under GABAergic drugs, although GABAergic properties of piracetam have not been observed so far. Shortening of the I-wave peak latencies is a new phenomenon. The results are discussed on the basis of the known therapeutic effects of piracetam in cortical myoclonus and as nootropic agent.