Tancredi V, Hwa G G, Zona C, Brancati A, Avoli M
Montreal Neurological Institute, McGill University, Que., Canada.
Brain Res. 1990 Mar 19;511(2):280-90. doi: 10.1016/0006-8993(90)90173-9.
Extra- and intracellular recording techniques were used to study the epileptiform activity generated by rat hippocampal slices perfused with Mg2(+)-free artificial cerebrospinal fluid (ACSF). This procedure induced in both CA1 and CA3 subfields the appearance of synchronous, spontaneously occurring epileptiform discharges which consisted of extracellularly recorded 100-800 ms long, positive shifts with superimposed negative going population spikes. Simultaneous, extracellular recordings from CA1 and CA3 subfields revealed that the epileptiform discharges in CA3 preceded those occurring in CA1 by 5-25 ms. Surgical separation of the two areas led to the disappearance of spontaneous events in the CA1 but not in the CA3 subfield. In this type of experiment CA1 pyramidal cells still generated epileptiform discharges following orthodromic stimuli. The intracellular counterpart of both spontaneous and stimulus-induced epileptiform discharges in CA1 and CA3 pyramidal cells was a large amplitude depolarization with high frequency discharge of action potentials which closely resembled the paroxysmal depolarizing shift recorded in the experimental epileptogenic focus. A hyperpolarizing potential triggered by alvear stimuli was recorded in CA1 cells perfused with Mg2(+)-free ACSF. This hyperpolarization was blocked by bicuculline methiodide (BMI) indicating that it represented a GABAergic inhibitory postsynaptic potential (IPSP). BMI also caused a prolongation of both spontaneous and stimulus-induced Mg(+)-free epileptiform discharges. Perfusion of the slices with the N-methyl-D-aspartate (NMDA) receptor antagonist DL-2-amino-5-phosphono-valerate (APV) reduced and eventually abolished the Mg(+)-free epileptiform discharges. These effects were more pronounced in the CA1 than in the CA3 subfield. APV also reduced the amplitude and the duration of the alveus-induced IPSP. These data demonstrate that Mg(+)-free epileptiform activity is present in the hippocampal slice at a time when inhibitory GABAergic potentials are operant as well as that in the CA1 subfield this type of epileptiform activity is dependent upon NMDA-activated conductances. Our experiments also indicate that NMDA receptors might be involved in the neuronal circuit responsible for the hyperpolarizing IPSP generated by CA1 pyramidal neurons.
采用细胞外和细胞内记录技术，研究用无镁人工脑脊液（ACSF）灌注的大鼠海马切片所产生的癫痫样活动。此操作在CA1和CA3亚区均诱发了同步的、自发出现的癫痫样放电，这些放电由细胞外记录到的100 - 800毫秒长的正向偏移以及叠加的负向群体峰电位组成。同时从CA1和CA3亚区进行细胞外记录显示，CA3中的癫痫样放电比CA1中的提前5 - 25毫秒出现。两个区域的手术分离导致CA1中自发事件消失，但CA3亚区未消失。在这类实验中，CA1锥体细胞在接受顺向刺激后仍会产生癫痫样放电。CA1和CA3锥体细胞中自发和刺激诱发的癫痫样放电的细胞内对应物是一个大幅度去极化，伴有动作电位的高频发放，这与在实验性癫痫病灶中记录到的阵发性去极化偏移非常相似。在用无镁ACSF灌注的CA1细胞中，记录到由肺泡刺激触发的超极化电位。这种超极化被甲基荷包牡丹碱（BMI）阻断，表明它代表一种GABA能抑制性突触后电位（IPSP）。BMI还导致自发和刺激诱发的无镁癫痫样放电时间延长。用N - 甲基 - D - 天冬氨酸（NMDA）受体拮抗剂DL - 2 - 氨基 - 5 - 膦酸 - 戊酸（APV）灌注切片可减少并最终消除无镁癫痫样放电。这些效应在CA1中比在CA3亚区更明显。APV还降低了肺泡诱发的IPSP的幅度和持续时间。这些数据表明，在海马切片中存在无镁癫痫样活动时，抑制性GABA能电位也在起作用，并且在CA1亚区，这种癫痫样活动依赖于NMDA激活的电导。我们的实验还表明，NMDA受体可能参与了负责CA1锥体细胞产生超极化IPSP的神经元回路。
