Glutamate currents in morphologically identified human dentate granule cells in temporal lobe epilepsy
Glutamate currents in morphologically identified human dentate granule cells in temporal lobe epilepsy
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DOI：
10.1152/jn.1997.77.6.3355
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发表时间：
1997-06-01
影响因子：
2.5
通讯作者：
Engel, J
中科院分区：
文献类型：
--
作者：
Isokawa, M;Levesque, M;Engel, J
在形态学鉴定的海马齿状颗粒细胞 (DGC；n = 31) 中研究谷氨酸受体介导的突触传递，采用全细胞膜片钳记录，并在从手术切除的癫痫患者内侧颞叶标本（来自 14 名患者的 14 份标本）制备的切片中细胞内注射生物胞素或荧光黄。在电流钳记录中，穿通路径的低频刺激产生去极化突触后电位，该电位由兴奋性突触后电位和反相抑制性突触后电位组成，由γ-氨基丁酸-A (GABA(A)) 受体介导，静息膜电位为-62.7 +/- 2.0 (SE) mV。在电压钳记录中，两个谷氨酸电导，一个快速的α-氨基-3-羟基-5-甲基异恶唑-4-丙酸（AMPA）受体介导的兴奋性突触后电流（EPSC；AMPA EPSC）和缓慢发展的N-甲基-D-天冬氨酸（NMDA）受体介导的EPSC（NMDA） EPSC)，在 GABA(A) 受体拮抗剂存在下分离。 NMDA EPSC 通过呈现 N 形电流-电压关系，显示出电压依赖性电导随着去极化而增加。在 31 个 DGC 中，NMDA EPSC 的斜率电导范围为 1.1 至 9.4 nS，达到 AMPA 电导大小的两倍。 NMDA 电导的这种大小差异很大，导致双峰 EPSC 的生成，并且斜率电导非线性增加高达 37.5 nS，并具有正膜电位，类似于神经元亚群中的“阵发性电流”。相比之下，在 NMDA 受体拮抗剂（2-氨基-5-磷酸戊酸）存在下分离的 AMPA EPSC，在电流-电压关系中表现出与电压无关的线性变化，并被 6-氰基-7-硝基喹喔啉-2,3-二酮阻断。无论给定神经元的 NMDA 电导有多大，AMPA 电导几乎没有变化。 31 个人类 DGC 的平均 AMPA 斜率电导为 5.28 +/- 0.65 (SE) nS。该值与正常大鼠 DGC 中的 AMPA EPSC 电导相似（5.35 +/- 0.52 nS，平均值 +/- SE；n = 55）。对单个 DGC 中的树突形态和脊柱密度进行量化，以评估癫痫病理学。树突棘密度与 NMDA 受体介导的兴奋性突触后电位的较慢的上升时间和较长的半宽度呈负相关 (r(2) = 0.705)。结论是 AMPA 和 NMDA EPSC 都有助于癫痫海马中的人类 DGC 突触传递。然而，NMDA EPSC 斜率电导的大范围变化表明 NMDA 受体介导的电导可能在人类癫痫 DGC 中发生改变。这些变化可能影响慢性阈下致癫痫突触活动的产生，并引起导致癫痫发作和树突状病理的病理兴奋。
Glutamate-receptor-mediated synaptic transmission was studied in morphologically identified hippocampal dentate granule cells (DGCs; n = 31) with the use of whole cell patch-clamp recording and intracellular injection of biocytin or Lucifer yellow in slices prepared from surgically removed medial temporal lobe specimens of epileptic patients (14 specimens from 14 patients). In the current-clamp recording, low-frequency stimulation of the perforant path generated depolarizing postsynaptic potentials that consisted of excitatory postsynaptic potentials and phase-inverted inhibitory postsynaptic potentials mediated by the gamma-aminobutyric acid-A (GABA(A)) receptor at a resting membrane potential of -62.7 +/- 2.0 (SE) mV. In the voltage-clamp recording, two glutamate conductances, a fast alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-receptor-mediated excitatory postsynaptic current (EPSC; AMPA EPSC) and a slowly developing N-methyl-D-aspartate (NMDA)-receptor-mediated EPSC (NMDA EPSC), were isolated in the presence of a GABA(A), receptor antagonist. NMDA EPSCs showed a voltage-dependent increase in conductance with depolarization by exhibiting an N-shaped current-voltage relationship. The slope conductance of the NMDA EPSC ranged from 1.1 to 9.4 nS in 31 DGCs, reaching up to twice the size of the AMPA conductance. This widely varying size of the NMDA conductance resulted in the generation of double-peaked EPSCs and a nonlinear increase of the slope conductance of up to 37.5 nS with positive membrane potentials, which resembled ''paroxysmal currents,'' in a subpopulation of the neurons. In contrast, AMPA EPSCs, which were isolated in the presence of an NMDA receptor antagonist (2-amino-5-phosphonovaleric acid), showed voltage-independent linear changes in the current-voltage relationship and were blocked by 6-cyano-7-nitroquinoxaline-2,3-dione. The AMPA conductance showed little variance, regardless of the size of the NMDA conductance of a given neuron. The average AMPA slope conductance was 5.28 +/- 0.65 (SE) nS in 31 human DGCs. This value was similar to AMPA EPSC conductances in normal rat DGCs (5.35 +/- 0.52 nS, mean +/- SE; n = 55). Dendritic morphology and spine density were quantified in the individual DGCs to assess epileptic pathology. Dendritic spine density showed an inverse correlation (r(2) = 0.705) with a slower rise time and a longer half-width of the excitatory postsynaptic potentials mediated by the NMDA receptor. It is concluded that both AMPA and NMDA EPSCs contribute to human DGC synaptic transmission in epileptic hippocampus. However, a wide range of changes in the slope conductance of the NMDA EPSCs suggests that the NMDA-receptor-mediated conductance could be altered in human epileptic DGCs. These changes may influence the generation of chronic subthreshold epileptogenic synaptic activity and give rise to pathological excitation leading to epileptic seizures and dendritic pathology.