Selective and nonselective benzodiazepine agonists have different effects on motor cortex excitability

Transcranial magnetic stimulation (TMS) is a useful method to study pharmacological effects on motor cortex excitability. Zolpidem is a selective agonist of the benzodiazepine receptor subtype BZ(1) and has a distinct pharmacological profile compared to diazepam. To study the different effects of these two drugs on the cortical inhibitory system, TMS was performed before and after administration of a single oral dose of zolpidem (10 mg) and diazepam (5 mg) in six healthy volunteers. TMS tests included the determination of resting and active motor threshold (MT) and measurements of the amplitudes of motor evoked potentials, intracortical facilitation (ICF), short-latency intracortical inhibition (SICI), and long-latency intracortical inhibition (LICI), and determination of the cortical silent period (CSP). Both drugs were without effect on the active or resting MT and decreased the ICF. Prolongation of the CSP and enhancement of LICI only in the presence of zolpidem point to a specific BZ(1)-related mechanism underlying the long-lasting component of cortical inhibition. This selective modulation of the CSP and the LICI points to a specific role of BZ(1) receptors in the control of inhibitory neuronal loops within the primary motor cortex.