【作者】 郭谊；

【导师】 丁美萍；

【作者基本信息】 浙江大学 ， 神经病学， 2009， 博士

【摘要】 重复经颅磁刺激（repetitive transcranial magnetic stimulation,rTMS）是一种无创的局部皮质刺激技术,它能够调节大脑皮质网络的兴奋性。磁刺激的一些特性如线圈形状、位置、刺激频率和强度都是rTMS对皮质兴奋性作用的影响因素。一般而言,低频rTMS（≤1Hz）降低皮质兴奋性,而高频rTMS（≥5Hz）增加皮质兴奋性。rTMS能阻断神经元功能,因而,能够干扰正在进行的癫痫发作。此外,低频rTMS可以持久地降低皮质兴奋性。临床癫痫研究显示rTMS对新皮质局灶性癫痫的作用要优于颞叶内侧面癫痫,这种现象可能是由于后者致痫灶位置在深部脑区,无法接受到有效刺激。低频rTMS对颞叶内侧面癫痫的作用仍然不清楚。动物研究显示低频rTMS能有效抑制颞叶癫痫大鼠的癫痫持续状态,但是,是否这种作用也能抑制癫痫形成尚不清楚。另一方面,低频rTMS预处理能抑制大鼠戊四氮致痫发作。然而,低频rTMS对戊四氮慢性点燃的作用尚未见报道。rTMS作用的具体机制仍然不清楚。大多数学者推测与类似长时程抑制和长时程增强的机制相关。但是,这种解释可能过于简单化,因为局灶刺激能激活远端脑区,甚至是在刺激点,也是不同特性神经元群体的同时激活。传统电生理或分子生物学的方法只能选择性地观察少数脑区的功能变化,而正电子发射断层显像（positron emission tomography,PET）技术却能够观察包括深部皮质下结构的整个大脑的代谢变化情况。脑的葡萄糖代谢水平与神经元的活动密切关联,利用PET技术能够全面地了解rTMS对脑葡萄糖代谢的影响,从而反映rTMS对神经元活动的作用。由于大鼠的大脑体积相对较小,rTMS对大鼠大脑的作用可能不同于人类,目前为止,尚未有关rTMS对大鼠葡萄糖脑代谢影响的报道。因此,本课题主要探讨重复经颅磁刺激对大鼠癫痫动物模型的作用,以及利用小动物PET（small animal PET,microPET）技术研究它对大鼠葡萄糖脑代谢的影响。第一部分:重复经颅磁刺激对大鼠癫痫动物模型的作用。低频中强度rTMS（1Hz、100%阈值强度、15分钟）的预处理能显著延长戊四氮致肌阵挛发作和脑电图痫样放电的潜伏期,降低癫痫发作级别;还可以显著抑制戊四氮点燃过程中癫痫发作级别的进展和肌阵挛发作潜伏期的缩短。低频低强度rTMS（1Hz、50%阈值强度、15分钟）的预处理对戊四氮致痫发作没有作用。低频高强度（1Hz、200%阈值强度、15分钟）的预处理能显著降低癫痫发作级别,而对肌阵挛发作和脑电图痫样放电的潜伏期没有作用。高频rTMS（20Hz、100%阈值强度、持续3秒、间隔57秒,共15个序列）预处理会显著缩短肌阵挛发作潜伏期并增高癫痫发作级别。低频中强度假刺激对戊四氮急性发作和慢性点燃都没有作用。低频和高频中强度刺激不会影响动脉血压、心率和呼吸频率,但高频易引起大鼠激惹。与对照组和假刺激组相比,低频中强度rTMS在匹罗卡品致癫痫持续状态发作48小时后给予每日15分钟刺激、连续5天干预后可能会延缓自发性发作的出现和降低平均发作级别。我们的结果表明rTMS预处理对戊四氮急性发作的作用具有频率和强度依赖性,低频中强度rTMS预处理能安全有效地抑制戊四氮慢性点燃过程,此外低频中强度rTMS的早期干预可能抑制匹罗卡品颞叶癫痫形成。第二部分:重复经颅磁刺激对大鼠葡萄糖脑代谢影响的microPET研究。为观察rTMS刺激中大鼠脑葡萄糖代谢率的变化,在大鼠¹⁸氟脱氧葡萄糖(2-[¹⁸F]fluoro-2-deoxy-D-glucose,FDG)摄取期同时给予低频（1Hz、100%阈值强度、15分钟）和高频（20Hz、100%阈值强度、持续3秒、间隔57秒,共15个序列）中强度的rTMS。我们发现无论是低频还是高频rTMS都显著降低了全脑平均葡萄糖代谢率,而且高频刺激引起的前脑区域（前额叶皮质、运动感觉皮质、海马、丘脑）的低代谢更明显。为观察rTMS刺激后大鼠脑葡萄糖代谢率的变化,在rTMS结束后立即给予注射FDG。与基础状态相比,我们发现低频和高频rTMS刺激后效应对脑葡萄糖代谢率有相反的作用,低频rTMS降低了前脑感兴趣区域（region ofinterest,ROI）的葡萄糖代谢率,高频rTMS却增加了前脑ROI的葡萄糖代谢率,两组的脑干葡萄糖代谢率都有升高,两组的全脑平均代谢率没有变化。1Hz的假刺激无论是在刺激中还是刺激后都没有显著改变葡萄糖代谢率。我们的结果提示rTMS对大鼠脑葡萄糖代谢率的作用是频率依赖的,rTMS能激活远端脑区。总之,本课题发现rTMS预处理对癫痫易感性的作用存在刺激频率和强度依赖性。低频中强度rTMS（1Hz、100%阈值强度、15分钟）预处理能降低癫痫易感性,并能安全有效抑制戊四氮点燃过程。我们还发现在匹罗卡品致癫痫持续状态后早期给予低频中强度rTMS的干预可能抑制后期颞叶癫痫的形成。此外,rTMS刺激中和刺激后对大鼠脑葡萄糖代谢的作用均是频率依赖的,rTMS能激活远端脑区。更多还原

【Abstract】 Repetitive transcranial magnetic stimulation(rTMS) is a method for noninvasive focal cortical stimulation that enables changes in the excitability of different cortical areas.Many characteristics of TMS such as coil form,position,frequency and intensity of the stimulus are important for the effect of rTMS on cortical excitability.In general, low-frequency rTMS(≤1 Hz) decreases cortical excitability,whereas frequencies above 5 Hz exert the inverse effect,causing its enhancement.rTMS can disrupt neuronal function and,thus,can interfere with ongoing seizures.Additionally, low-frequency rTMS can lead to lasting reductions in cortical excitability.Focal epilepsies are ideal for the application of rTMS due to a epileptogenic zone of increased excitability.In human,different studies with rTMS have shown more marked effects on neocortical epilepsies on the convexity of the brain than on mesial temporal lobe epilepsies.The precise effects of low rTMS on mesial temporal lobe epilepsy remain unknown.Animal studies showed low rTMS could effectively suppress status epilepticus in rat models of temporal lobe epilepsy,however,whether this can also suppress epileptogenesis is unclear.In the other hand,preconditioning with low rTMS can suppress acute seizure induced by pentylenetetrazol(PTZ) in rats,nevertheless,the effects of low rTMS on seizure development of PTZ kindling have not been investigated yet.In spite of rTMS effectiveness,its precise mechanism of action has not yet been established.Long-term potentiation and long-term depression-like mechnasims have been mainly postulated as responsible for rTMS effects.However,the mechanism may be not so simple,since the effects of rTMS can spread to distant sites,even at the sites of stimulaton a mixture of neural populations are activated.Traditional technologies in neuroscience are used to investigate functional changes in a specific brain area,whereas PET technology provides the opportunity to monitor metabolism in the whole brain including deep subcortical areas.The level of glucose utilization correlates with the degree of neuronal activity.The impact of rTMS on cerebral glucose metabolim in rats, which reflect the effects for rTMS on neural activity,can be mapped by using microPET.The rat brain is much smaller than the human’s,so the effects for rTMS might be quite different between rats and human.So far,it has not been studied yet.Therefore,this study mainly focuses on the effects of rTMS on rat models of epilepsy and cerebral glucose metabolism.Part 1 Effects of rTMS on rat models of temporal lobe epilepsy and generalized epilepsy.Preconditioning with low rTMS(1Hz,100%motor threshold,15mins) significantly prolonged the latencies for myoclonic jerks induced by PTZ and epileptiform discharge on EEG,lowered the degree of seizure;and it also significant suppressed the development of PTZ kindling.Preconditioning with low-frequency low-intensity rTMS(1Hz,50%motor threshold,15mins) had no effect on seizure induced by PTZ.Precondition with low-frequency high-intensity rTMS(1Hz, 200%motor threshold,15mins) significantly lowered the degree of seizure,but had no effect on the latencies.Preconditioning with high-frequency rTMS(20Hz,100%motor threshold,3s,intertrains 57s,15 trains) not only significantly shortened the latency for myoclonic jerks,but also increased the degree of seizure.Sham stimulation(1Hz, 100%motor threshold,15mins) had no effect on acute seizures and kindling of PTZ. No significant changes in aterial blood pressure,heart rates and breath rates were found after rTMS.High-frequency stimulation caused irritability in some rats. Compared to control and sham stimulation,low rTMS(1Hz,100%motor threshold, 15mins,5days) which started 48h after status epilepticus induced by pilocarpine may postponed the occurrence of spontaneous recurrent seizures and lower the mean degree of seizure.Our results indicate the effects of rTMS on acute seizure induced by PTZ were dependent on frequency and intensity.Preconditioning with low rTMS(1Hz, 100%motor threshold,15mins) can safely and effectively suppress the development of PTZ kindling.In addition,the early treatment with low rTMS may inhibit epileptogenesis induced by pilocarpine.Part 2 Effects of rTMS on cerebral glucose metabolism in rats:a FDG-microPET study.Low-frequency rTMS(1Hz,100%motor threshold,15mins) and high-frequency rTMS(20Hz,100%motor threshold,3s,intertrains 57s,15 trains) were applied in rats during FDG uptake in order to observe glucose metabolic changes during stimulation. We found either low-frequency or high-frequency rTMS significantly reduced the mean glucose metabolism rate of whole brain.More obvious hypometabolism were found in forebrain areas(the prefrontal,sensorimotor cortices,the hippocampus, thalamus) during high-frequency stimulation than low-frequency stimulation.In order to observe glucose metabolic changes after rTMS,FDG were injected immediately after rTMS.We found that after effects of low-frequence rTMS reduced the regional normalized cerebral metabolic rate for glucose(nCMRglc) values in forebrain ROIs,whereas after effects of high -frequency rTMS increased the nCMRglc values in forebrain ROI.The nCMRglc values in brainstem was increased after either low-frequency or high-frequency rTMS.The mean glucose metabolism of whole brain didn’t change,comparing to baseline.No significant metabolic change was found in sham group.Our results indicate the impacts of rTMS on glucose metabolism in rat brain were dependent on frequency,and rTMS can activate the remote brain areas.In conclusion,we found the effects of preconditioning with rTMS on seizure susceptibility were dependent on frequency and intensity.Preconditioning with Low-frequency rTMS(1Hz,100%motor threshold,15mins) can decreases seizure susceptibility,safely and effectively suppress the development of PTZ kindling.We also observed the early delivery of low-frequency rTMS after status epilepticus induced by pilocarpine may suppress epileptogenesis.In addition,the impacts of rTMS on glucose metabolism in rat brain were dependent on frequency,and rTMS can activate the remote brain areas.更多还原