Effect of different frequencies of repetitive transcranial magnetic stimulation (rTMS) on acquisition of chemical kindling seizures in rats

IIntroduction: Repetitive transcranial magnetic stimulation (rTMS) modulates the excitability of cortical neural networks. The effect of rTMS on excitability of cortical networks depends on its frequency. According to the previous reports, a distinction is made between low (<1Hz) and high frequencies of rTMS. Low frequencies of rTMS inhibit seizure but high frequencies increase it. In the current study we tried to investigate the effect of different frequencies of rTMS on chemical kindling induced seizure in rats. Methods: Chemical kindling was induced by i.p. injections of penthylentetrazol (PTZ) 45 mg/kg, 3 times per week.Effect of different frequencies of rTMS (0.25, 1 and 5 Hz) on kindling acquisition was investigated. rTMS was applied 30 minutes after PTZ injections. Stimulation was delivered at motor threshold intensity (4s, 4 stimulus interval of 10 s). Results: Maximum stage of behavioral seizure decreased by 0.25 Hz rTMS and increased by 5 Hz rTMS. Stages 4 and 5 latencies were increased by 0.25 Hz rTMS and decreased by 5 Hz rTMS. Stage 5 duration was decreased by0.25Hz rTMS and increased by 5 Hz rTMS. Discussion: Our results showed that application of rTMS had significant effect on seizure parameters in acquisition period. Lower frequencies of rTMS seem to be more effective.