Sanabria E R, Su H, Yaari Y
Department of Physiology, Institute of Medical Sciences, Hebrew University-Hadassah Faculty of Medicine, Jerusalem 91120, Israel.
J Physiol. 2001 Apr 1;532(Pt 1):205-16. doi: 10.1111/j.1469-7793.2001.0205g.x.
Chronically epileptic rats, produced by prior injection of pilocarpine, were used to investigate whether changes in intrinsic neuronal excitability may contribute to the epileptogenicity of the hippocampus in experimental temporal lobe epilepsy (TLE). Paired extra-/intracellular electrophysiological recordings were made in the CA1 pyramidal layer in acute hippocampal slices prepared from control and epileptic rats and perfused with artificial cerebrospinal fluid (ACSF). Whereas orthodromic activation of CA1 neurons evoked only a single, stimulus-graded population spike in control slices, it produced an all-or-none burst of population spikes in epileptic slices. The intrinsic firing patterns of CA1 pyramidal cells were determined by intrasomatic positive current injection. In control slices, the vast majority (97%) of the neurons were regular firing cells. In epileptic slices, only 53% the pyramidal cells fired in a regular mode. The remaining 47% of the pyramidal cells were intrinsic bursters. These neurons generated high-frequency bursts of three to six spikes in response to threshold depolarizations. A subgroup of these neurons (10.1% of all cells) also burst fired spontaneously even after suppression of synaptic activity. In epileptic slices, burst firing in most cases (ca 70%) was completely blocked by adding the Ca2+ channel blocker Ni2+ (1 mM) to, or removing Ca2+ from, the ACSF, but not by intracellular application of the Ca2+ chelater 1,2-bis(o-aminophenoxy)ethane-N,N,N ',N '-tetra-acetic acid (BAPTA), suggesting it was driven by a Ca2+ current. Spontaneously recurring population bursts were observed in a subset of epileptic slices. They were abolished by adding 2 M 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX) to the ACSF, indicating that synaptic excitation is critical for the generation of these events. All sampled pyramidal cells fired repetitively during each population burst. The firing of spontaneously active bursters anteceded the population discharge, whereas most other pyramidal cells began to fire conjointly with the first population spike. Thus, spontaneous bursters are likely to be the initiators of spontaneous population bursts in epileptic slices. The dramatic up-regulation of intrinsic bursting in CA1 pyramidal cells, particularly the de novo appearance of Ca2+-dependent bursting, may contribute to the epileptogenicity of the hippocampus in the pilocarpine model of TLE. These findings have important implications for the pharmacological treatment of medically refractory human TLE.
通过预先注射毛果芸香碱制备的慢性癫痫大鼠，用于研究内在神经元兴奋性的变化是否可能导致实验性颞叶癫痫（TLE）中海马体的致痫性。在从对照大鼠和癫痫大鼠制备的急性海马切片的CA1锥体层中进行细胞外/细胞内配对电生理记录，并灌注人工脑脊液（ACSF）。在对照切片中，CA1神经元的顺向激活仅诱发单个刺激分级的群体峰电位，而在癫痫切片中则产生全或无的群体峰电位爆发。通过体细胞内向正电流注射确定CA1锥体细胞的内在放电模式。在对照切片中，绝大多数（97%）神经元为规则放电细胞。在癫痫切片中，只有53%的锥体细胞以规则模式放电。其余47%的锥体细胞为内在爆发性放电细胞。这些神经元在阈值去极化时产生三到六个峰电位的高频爆发。这些神经元的一个亚组（占所有细胞的10.1%）即使在突触活动被抑制后也会自发爆发放电。在癫痫切片中，大多数情况下（约70%）的爆发性放电通过向ACSF中添加Ca2+通道阻滞剂Ni2+（1 mM）或从ACSF中去除Ca2+而完全被阻断，但细胞内应用Ca2+螯合剂1,2-双（邻氨基苯氧基）乙烷-N,N,N',N'-四乙酸（BAPTA）则不能阻断，这表明它是由Ca2+电流驱动的。在一部分癫痫切片中观察到自发反复出现的群体爆发。通过向ACSF中添加2 μM 6-氰基-7-硝基喹喔啉-2,3-二酮（CNQX）可将其消除，这表明突触兴奋对于这些事件的发生至关重要。在每次群体爆发期间，所有采样的锥体细胞都重复放电。自发活跃的爆发性放电细胞的放电先于群体放电，而大多数其他锥体细胞则在第一个群体峰电位时开始联合放电。因此，自发爆发性放电细胞可能是癫痫切片中自发群体爆发的启动者。CA1锥体细胞内在爆发性放电的显著上调，特别是Ca2+依赖性爆发性放电的从头出现，可能导致TLE毛果芸香碱模型中海马体的致痫性。这些发现对难治性人类TLE的药物治疗具有重要意义。
