The Effects Of Low-frequency Repetitive Transcranial Magnetic Stimulation On The Local Field Potentials Of Hippocampus In Rats

Background: Repetitive transcranial magnetic stimulation(r TMS)is a kind of noninvasive stimulation of brain which has been widely applied in the field of neurology,psychology,rehabilitation and so on. Among them.Low-frequency r TMS has been proved to have better anti-epileptic effects,but the exact mechanism is not fully understood,stimulation parameters and times has not yet reached consensus.Multi-channel in vivo recording techniques is a new electrophysiological techniques which are used to record local field potentials(LFPs) of deep brain tissue in conscious, freely moving animal. Compared with electroencephalogram and cortical electroencephalogram, It has higher spatiotemporal resolution. In this paper, Using multi-channel in vivo recording technique to observe the effects of low-frequency r TMS on the LFPs of hippocampus in rats, and further insight the anti-epileptic electrophysiological mechanisms and stimulation times of low-frequency r TMS,trying to provide evidence for the application of low-frequency r TMS in the field of epilepsy.Objective: To observe the effects of low-frequency r TMS on the LFPs of hippocampus in rats, Trying to further insight the anti-epileptic electrophysiological mechanisms and stimulation times of the low-frequency r TMS.Method:(1) The rats were randomly divided into r TMS group,control group and sham group, respectively variously treating with r TMS of continuous 7d.Using multi-channel in vivo recording technique acquisition LFPs ofhippocampus 20 min in anesthetized rats, then make pilocarpine( PILO)model and acquisition LFPs of hippocampus to 1h after Status epilepticus(SE). Before PILO injection and in SE,LFPs was respectively partitioned using the common physiological frequency bands:δ(0.5-3.5Hz)、θ(4-7Hz)、γ(30-80Hz)and ripple(100-250Hz), Both was estimated with spectrum analysis and power spectral density.(2) The rats were randomly divided into A, B, C group,and respectively treating with r TMS of different times(5 d, 10 d,15d), While control group were conducted. Then make PILO model, using multi-channel in vivo recording technique acquisition LFPs of hippocampus to 1h after SE in conscious, freely active rats. And then calculated the latency of the first seizure, latency of SE and the main discharge frequency,amplitude,the power spectral density of ripple oscillation.Result:(1) Results of spectrum analysis and power spectrum density : The results of spectrum analysis showed that compared with control group and sham group,low-frequency r TMS can increased spectrum energy of δ, θ,γ-band and decreased the value of ripple oscillation, while no significant difference between control group and sham group; The results of power spectrum density showed that compared with control group and sham group,low- frequency r TMS can increased the power spectral density of δ, θ,γ-band(all P <0.05), and decreased the value of ripple oscillation(P <0.05);While in the control group and the sham group, All were not statistically significant(P> 0.05).(2) Results of different stimulating time: 5 consecutive days of stimulation, the change of above parameters were not statistically significant(All P> 0.05); 10 consecutive days of stimulation, the change of latency of the first seizure and SE was not statistically significant(All P> 0.05), but the main discharge frequency, the amplitude and power spectral density of ripple oscillation were statistically significant(All P <0.05); 15 consecutive days of stimulation, the change of above parameters were statistically significant(All P <0.05).Conclusion:(1) Low-frequency r TMS can reduce the excitability of hippocampal in normal rats;(2) Low-frequency r TMS may has an inhibitory effects on seizure onset zone;(3) The underlying antiepileptic mechanism of low-frequency r TMS may be associated with reduced excitability of hippocampal and(or) to Inhibition seizure onset zone.(4) 15 consecutive days of stimulation significantly longer the latency of epileptic discharges, reducing amplitude of ripple, suppress seizures;Anti-epileptic effect of low-frequency rTMS may have time-dependent.