Abstracts

We tested the effects of TMS using a model MagPro X100 (Medtronic Canada Inc., Toronto, ON) on well-established kindled seizures in rats as there seems to be no studies in this area. First we determined whether 60 Hz TMS could evoked seizures in kindled rats. Second, we determined whether low frequency (1 Hz) TMS (LFTMS) had any effect on the threshold or performance of kindled seizures., Since kindling was originally established in 21 rats using 2 sec of low intensity 60Hz sinusoidal electrical stimulation, we set the TMS parameters to 2 sec of 60Hz, biphasic, magnetic stimulation at 100%. The 21 rats, 7 amygdala and 14 ventral hippocampal kindled, previously received more than 10 generalized seizures and their thresholds were stabile. These 21 rats were also from 3 selectively bred groups, 6 [quot]Fast kindler[quot], 5 [quot]Slow kinders [quot] and 10 [quot]F1 hybrids[quot]. Two types of TMS coils were used to stimulate the rats, the round and the figure 8. The round coil had a central-hole that was positioned over the rats[apos] implanted headplug connector, when the kindling leads to the rat were not attached. The figure 8 coil was used when the leads were attached. In 12 ventral hippocampal kindled rats, we tested the efficacy of LFTMS against the kindled seizures in two experiments, A) 1Hz, 70%, for 30sec, wait 1min and determine the seizure threshold and behavioral profile, and B) 1Hz, 70%, for 5min, wait 24hrs before testing., No TMS protocol alone triggered a convulsive seizure or focal after-discharge in any rat. Further the focal after-discharge threshold to the kindling stimulus was not affected by LFTMS. However, the latency to forelimb clonus of the kindled seizure was significantly lengthened by both LFTMS protocols, indicating a delay in the recruitment of the convulsive kindled seizure. Surprisingly, TMS did not block or even marginally obscure the online EEG from the implanted bipolar Nichrome electrodes., TMS alone does not trigger seizures in seizure-prone or -resistant rats with a well-established kindled focus in either the amygdala or hippocampus. 1Hz TMS does not effect the AD threshold, but significantly affects the recruitment of the convulsive seizure, which is an anti-epileptic effect., (Supported by Medtronic of Canada for loan of TMS equipment.)