REPETITIVE TRANSCRANIAL MAGNETIC STIMULATIONS OF THE RAT - EFFECT OF ACUTE AND CHRONIC STIMULATIONS ON PENTYLENETETRAZOLE-INDUCED CLONIC SEIZURES

Repetitive transcranial magnetic stimulation (RTMS) has been reported to induce epileptic seizures in normal control and in epileptic patien ts. Therefore we characterized the effect of acute or chronic stimulat ions with RTMS on the induction of pentylenetetrazole (PTZ)-induced cl onic seizures in the rat. Male Wistar rats were stimulated with a 13-c m coil with a stimulus frequency of 50 Hz. The motor threshold (T-m) w as determined by a single transcranial stimulus. Acute stimulation was performed with a stimulus intensity of 0.9 x T-m and 1.5 x T-m using a duration of the train of stimuli of five seconds. Chronic stimulatio n was performed with a duration of the train of stimuli of one and fiv e seconds using a stimulus intensity of 1.8 x T-m, every day for 30 da ys. Time to onset of PTZ-induced clonic seizure was determined after t he acute stimulation or the last stimulation in chronic RTMS. In the g roups of rats receiving acute RTMS (0.9 and 1.5 x T-m) no seizures dev eloped. No differences were observed in time to onset of clonic seizur es after PTZ injection compared to control rats. In the group of rats receiving chronic RTMS some rats showed facial contractions, chewing o r head movements during or immediately after the stimulations. None of the rats developed tonic or clonic seizures in relation to RTMS. Time to onset of PTZ clonic seizures was reduced in both groups receiving RTMS with a stimulus duration of one (P < 0.01) and five (P < 0.05) se conds compared to control rats. The results from this study suggest th at acute suprathreshold stimulation with a stimulus frequency of 50 Hz does not affect the induction of clonic PTZ seizures, whereas chronic (daily) stimulations have a facilitatory effect. This indicates that chronic stimulation with RTMS may induce a kindling process in the rat . Chronic RTMS stimulation may therefore represent an interesting alte rnative non-invasively kindling model to chemical and electrical stimu lations.