【作者】 罗乐；

【导师】 阮迪云；

【作者基本信息】 中国科学技术大学 ， 生物物理， 2008， 博士

【摘要】 胆碱能系统可以影响海马突触传递和突触可塑性,从而在海马的学习和记忆功能扮演着重要的角色。胆碱能调控作用主要通过毒蕈碱型胆碱受体（mAChR）。毒蕈碱型胆碱受体有M₁-M₅五种亚型,关于这五种亚型在胆碱的突触传递和突触可塑性调控中所起到的作用,目前仍不是十分清楚。铅是环境中的一种重金属污染物,具有神经毒性。铅暴露对多种递质系统以及神经系统功能都造成损伤。对于胆碱能调控是否也包括在铅的神经毒理内很少见报道。本文运用电生理学实验方法,研究海马中毒蕈碱型胆碱能系统对突触传递和突触可塑性的调控以及铅对这种胆碱能调控的影响。1.在海马齿状回区域（DG）内注射各种毒蕈碱型胆碱受体配体,在位记录兴奋性突触后电位,研究各种毒蕈碱型胆碱受体在突触传递和可塑性调控中的作用。结果表明,一种非选择性毒蕈碱型胆碱受体阻断剂阿托品可以压抑长时程增强（LTP）的诱导,证实了海马内毒蕈碱型胆碱系统参与了LTP的诱导。我们研究了M_2/4型胆碱受体拮抗剂和M_3/5AChR型胆碱受体拮抗剂对LTP的影响。发现向海马内注射M₁型胆碱受体拈抗剂和M_2/4型胆碱受体拮抗剂可以明显压抑LIP的诱导,而M_3/5AChR型胆碱受体拮抗剂则对LTP没有作用。结果表明毒蕈碱型胆碱能系统对突触传递和突触可塑性的调控是通过不同的受体亚型实现的。2.应用离体记录技术,研究了大鼠海马雪氏侧枝—CA1锥体神经元突触传递的毒蕈碱型胆碱能调控及铅对这种调控的作用。carbachol是胆碱能受体的激动剂。在本实验中,灌流5 M carbacbol使大鼠海马CA1锥体神经元的谷氨酸能EPSC幅度减小,这种抑制效应主要是由M型乙酰胆碱受体介导的。在使用美加明（mecamylamine,10M）阻断N型乙酰胆碱受体的作用后,carbacbol通过M型胆碱受体介导浓度依赖性地抑制EPSC;5M carbacbol增强了双脉冲易化效应和10Hz串刺激反应;并且降低了sEPSCs的频率,减小了sEPSCs的幅度和衰减时间。在相同条件下,10M铅离子灌流对于谷氨酸能EPSC的幅度没有显著性的影响,但是轻微地削弱了carbacbol对EPSC的压抑作用;铅抑制了carbachol对PPF和串刺激反应的增强作用;10 M铅降低了sEPSCs的频率和衰减,并且阻断了carbachol的进一步作用;10 M铅对sEPSCs的幅度没有显著性的作用,而且对carbachol的抑制作用也没有显著影响。胆碱能系统通过突触前和突触后的mAChRs对海马的突触传递和突触可塑性的调控作用,对学习和记忆功能有重要的意义。铅可能通过损伤谷氨酸能突触传递的胆碱能调控作用来影响突触传递效能和突触可塑性,可能是铅损伤学习记忆功能的机制之一。更多还原

【Abstract】 The roles of the muscarinic acetylcholine receptors(mAChRs)in synaptic transmission and Plasticity at many areas of the central nervous system including the hippocampus,have been extensively studied.However,not much is known about the modulation of LTP through individual subtypes of mAChR(M1-M5 subtype).Lead, known as a heavy metal pollutant,is a neurotoxicant.Lead exposure impairs many neurotransmitter systems and nerve system function.Few has been reported about whether lead can affect muscarinic modulation.In this study,using electrophysiological methods,we investigated muscarinic modulation on synaptic transmission and Plasticity and the effect of lead on it.1)we investigated the involvement of each individual subtypes of mAChR in LTP induction by intrahippocampal administration of cholinergic ligands at the dentate gyrus(DG)of anaesthetized rats.We found atropine,an antagonist of mAChRs,suppressed the induction of LTP.This observation confirmed that the muscarinic system is involved in LTP.We then examined the effects of M1AChR antagonists(pirenzepine and telenzepine),M2/4AChR antagonists(Methoctramine and{11-[[2-[(diethylamino)methyl]-1-piperidinyl]acetyl]-5,11 -dihydro-6H-pyrido[2, 3-b][1,4]benzodiazepin-6-one}(AFDX-116)),and M3/5AChR antagonist (4-diphenylacetoxy-N-methylpiperidine methiodide(4-DAMP))on LTP.Our results showed that both M1AChR and M2/4AChR antagonists but not M3/5AChR antagonist suppressed the amplitude of LTP.We also examined the effects of these cholinergic ligands on basal synaptic transmission and found that only pirenzepine augmented the amplitude of population spike(PS).This study suggests that individual mAChR subtypes play different modulation roles in LTP induction in the DG of rats.2)we investigated the the muscarinic modulation in the CA1 area of hippocampal slices and the effect of lead on it.Carbachol is an agonist of cholinergic receptors.In this study,application of 5 M carbacbol by perfusion inhibited the amplitude of glutamatergic EPSC in rat hippocampal CA1 pyramidal neurons.This inhibition was maily mediated by mAChRs.With the nAChRs blocked by perfusion of mecamylamine(10 M),carbachol inhibited EPSC concentration-dependently; 5 M carbachol enhanced paired-pulse facilitation(PPF)and responses to 10 Hz train of pulses;5 M carbachol also reduced sEPSCs frequency and decreased the amplitudes and decay time of sEPSCs.In the same conditions,10 M lead showed no slgnificant effect on the amplitude of EPSC,but slightly weakened the inhibition of carbachol on EPSC;lead inhibited the enhancement of PPF and responses to 10 Hz train of pulses;and lead reduced the frequency and decay of sEPSCs,and blocked the effect of carbachol while did not has significant effect on sEPSCs amplitudes and the inhibition by carbachol.Cholinergic system modulates synaptic transmission and plasticity in hippocampus through pre- and postsynaptic mAChRs, and plays an important role in learning and memory.The effects of lead on the cholinergic modulation of glutamatergic synaptic transmission and plasticity might be involved in the impairment of learning and memory by lead.更多还原