HIPPOCAMPAL INHIBITORY NEURON ACTIVITY IN THE ELEVATED POTASSIUM MODEL OF EPILEPSY
HIPPOCAMPAL INHIBITORY NEURON ACTIVITY IN THE ELEVATED POTASSIUM MODEL OF EPILEPSY
复制标题
DOI：
10.1152/jn.1994.72.6.2853
复制
发表时间：
1994-12-01
影响因子：
2.5
通讯作者：
MCBAIN, CJ
中科院分区：
文献类型：
--
作者：
MCBAIN, CJ
1. 对体外培养的大鼠海马CA1东向层抑制神经元进行全细胞膜片钳记录，以确定细胞外钾离子浓度（[K+](o)）从3.5 mm升高至8.5 mm时，CA1东向层抑制神经元对癫痫样活动的影响。在电流箝位条件下，抑制性神经元的自发动作电位活动通常以非突触的内在机制为节奏的持续重复放电模式发生。当[K+](o)升高到8.5 mm时，活动模式发生改变，使得动作电位簇被静默期打断，而没有明显的后超极化（AHP）。此外，[K+](o)的升高导致AHP动作电位幅度和持续时间的大幅减少，并导致AHP逆转电位的20 mv移位。在电压钳中，在所有被研究的中间神经元中，在引入升高的钾后，观察到一个小的持续向内电流，同时自发兴奋性突触后电流（EPSCs）的频率增加。在短时间（类似于1分钟）后，同步发生的EPSCs的时间总和贡献了一个周期性的内向电流（PIC; 10-40 pA, 0.8 Hz），该电流在[K+](o)升高期间持续存在。与PIC相关的电荷转移分析表明，它们由类似于35个EPSCs的时间总和组成。该PIC与CA1锥体神经元层记录的细胞外场电位同步。由于α -氨基-3-羟基-5-甲基-4-异恶唑烯丙酸（AMPA）受体拮抗剂6,7-二硝基喹啉-2,3-二酮（DNQX）阻断EPSC活性，尽管继续施用8.5 mm [K+](o)，但PIC可消除PICs并使动作电位活性恢复到单次持续放电(o)。n -甲基- d -天冬氨酸受体拮抗剂对PICs和动作电位活性均无影响。添加代谢性谷氨酸受体（mGluR）拮抗剂(+)-2-甲基-4-羧基苯基甘氨酸（MCPG）可可逆地消除PIC，而不影响EPSC频率的增加。8.5 mm [K+](o) CA3锥体神经元的记录表明，间隔活动发生的频率与中间神经元中观察到的PICs相同。MCPG使CA3锥体神经元间期活性减弱，但未完全消除，提示mGluR受体在维持CA3.7区间期活性中发挥作用。[K+] 0升高时，在少量CA1锥体神经元上观察到同步抑制性突触后电流（IPSCs），这与这些神经元是取向层/泡间神经元的突触靶点一致。出乎意料的是，在向CA1锥体神经元癫痫样活动过渡的过程中，观察到IPSC活性的下降。在CA1锥体神经元中，在对γ -氨基丁酸（GABA）的峰值响应时测量的电流-电压关系在正常或升高的[K+]中是相同的(0)。然而，在GABA响应消退期间确定的随后的电流-电压关系显示，在控制和8.5 mm [K+](o)条件下，逆转电位都出现了正偏移。这种逆转电位正向转移的机制目前尚不清楚，但可能是由于持续的GABA受体激活后细胞内Cl-的积累。这些实验表明，在[K+](o)升高引起的电活动期间，CA1中间神经元群持续的内在动作电位活动被“覆盖”。由此产生的活动是由CA3锥体神经元群中发生的间隔事件来决定的。mGluRs在CA3锥体神经元群间期活动中的作用也被描述。在癫痫样活动建立后，对CA1锥体神经元的突触抑制严重减弱。这不是由[K+](o)升高本身引起的，而可能是由持续IPSC活动后CA1锥体神经元中活动依赖的Cl-再分布引起的。
1. Whole cell patch-clamp recordings were made from CA1 stratum oriens inhibitory neurons of rat hippocampal slices in vitro to determine their contribution to the epileptiform activity elicited by elevating the extracellular potassium ion concentration ([K+](o)) from 3.5 to 8.5 mm.2. Under current-clamp conditions, spontaneous action potential activity in inhibitory neurons normally occurs in a sustained repetitive firing mode paced by nonsynaptic, intrinsic mechanisms. On elevation of [K+](o) to 8.5 mm the pattern of activity is altered such that clusters of action potentials occur interrupted by periods of silence without an appreciable afterhyperpolarization (AHP). In addition, elevation of [K+](o) caused a large reduction in the action potential AHP amplitude and duration concomitant with a 20-mV shift in the reversal potential of the AHP.3. In voltage clamp a small persistent inward current was observed after the introduction of elevated potassium concomitant with an increase in the frequency of spontaneous excitatory postsynaptic currents (EPSCs) in all interneurons studied. After a short period of time (similar to 1 min) temporal summation of synchronously occurring EPSCs contributed a periodic inward current (PIC; 10-40 pA, 0.8 Hz) that persisted for the duration of the [K+](o) elevation. Analysis of the charge transfer associated with the PIC suggests that they comprise the temporal summation of similar to 35 EPSCs. This PIC was synchronous with the extracellular field potential recorded from the CA1 pyramidal neuron layer.4. The PIC was responsible for the clustering of action potential activity because blockade of EPSC activity by the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX) abolished PICs and reverted action potential activity to single sustained firing, despite the continued application of 8.5 mm [K+](o). Antagonists of N-methyl-D-aspartate receptors were without effect on either the PICs or the action potential activity.5. Addition of the metabotropic glutamate receptor (mGluR) antagonist (+)-2-methyl-4-carboxyphenylglycine (MCPG) reversibly abolished the PIC without affecting the increase in EPSC frequency.6. Recordings from CA3 pyramidal neurons in 8.5 mm [K+](o) demonstrated that interictal activity occurred at a frequency identical to the PICs observed in interneurons. Interictal activity in CA3 pyramidal neurons was attenuated but never abolished by MCPG, suggesting a role for mGluR receptors in the maintenance of interictal activity in area CA3.7. Flurries of synchronous inhibitory postsynaptic currents (IPSCs) were observed on a small number of CA1 pyramidal neurons on elevation of [K+]o, consistent with these neurons being the synaptic target of stratum oriens/alveus interneurons. Unexpectedly, a rundown of this IPSC activity was observed during the transition to CA1 pyramidal neuron epileptiform activity.8. In CA1 pyramidal neurons, current-voltage relationships measured at the peak response to gamma-aminobutyric acid (GABA) were identical in both normal or elevated [K+](o). However, subsequent current-voltage relationships determined during the fade of the GABA response revealed a positive shift in the reversal potential in both control and 8.5 mm [K+](o) conditions. The mechanism for this positive shift in reversal potential is at present un known but may occur due to the intracellular accumulation of Cl- after sustained GABA receptor activation.9. These experiments suggest that the ongoing intrinsic action potential activity of the CA1 interneuron population is ''overridden'' during electrographic activity resulting from [K+](o) elevation. The resulting activity is paced by interictal events occurring in the CA3 pyramidal neuron population. A role for mGluRs in the interictal activity of the CA3 pyramidal neuron population is also described. After the establishment of epileptiform activity, synaptic inhibition onto CA1 pyramidal neurons is severly attenuated. This results not from the [K+](o) elevation per se but possibly from an activity-dependent Cl- redistribution across the CA1 pyramidal neurons after sustained IPSC activity.