Intravenous clomipramine decreases excitability of human motor cortex: a study with paired magnetic stimulation

Several recent reports suggest the possibility of monitoring pharmacological effects on brain excitability through transcranial magnetic stimulation (TMS). In these studies, paired magnetic stimulation has been used in normal subjects and on patients who were taking different antiepileptic drugs. The aim of our study was to investigate motor area excitability on depressed patients after intravenous administration of a single dose of clomipramine, a tricyclic antidepressant. Motor cortex excitability was studied by single and paired transcranial magnetic stimulation (TMS) before and after 4, 8 and 24 h from intravenous administration of 25 mg of clomipramine. Cortical excitability was measured using different TMS parameters: motor threshold (MT), motor evoked potential (MEP) amplitude, duration of cortical silent period (CSP), intracortical inhibition (ICI) and intracortical facilitation (ICF). Spinal excitability and peripheral nerve conduction was measured by F response and M wave. A temporary but significant increase of motor threshold and intracortical inhibition and a decrease of intracortical facilitation were observed 4 h following drug administration. MEP amplitude, cortical silent period, F response and M wave were not significantly affected by drug injection. Our findings suggest that a single intravenous dose of clomipramine can exert a significant but transitory suppression of motor cortex excitability in depressed patients. TMS represents a useful research tool in assessing the effects of motor cortical excitability of neuropsychiatric drugs used in psychiatric disease.