Mittmann T, Qü M, Zilles K, Luhmann H J
Institute of Neurophysiology, University of Düsseldorf, Germany.
Neuroscience. 1998 Jul;85(1):15-27. doi: 10.1016/s0306-4522(97)00638-6.
The long-term (< or = six months) functional consequences of permanent middle cerebral artery occlusion were studied with in vitro extra- and intracellular recording techniques in adult mouse neocortical slices. After survival times of one to three days, 28 days and six months, intracellular recordings from layers II/III pyramidal cells in the vicinity of the infarct did not reveal any statistically significant changes in the intrinsic membrane properties when compared to age-matched control animals. However, a pronounced hyperexcitability could be observed upon orthodromic synaptic stimulation in neocortical slices obtained from mice 28 days after induction of ischemia. Low-intensity electrical stimulation of the afferents elicited particularly in this group epileptiform extracellular field potential responses and intracellular excitatory postsynaptic potentials, that were longer in duration as compared to the controls. When the N-methyl-D-aspartate receptor-mediated excitatory postsynaptic potential was pharmacologically isolated in a bathing solution containing 0.1 mM Mg2+ and 10 microM 6-cyano-7-nitroquinoxaline-2,3-dione, the synaptic responses were longer and larger in the ischemic cortex as compared to the controls. Higher stimulus intensities evoked in normal medium a biphasic inhibitory postsynaptic potential, that contained in the 28 days post-ischemia group a prominent amino-phosphonovaleric acid-sensitive component, indicating a strong concurrent activation of a N-methyl-D-aspartate receptor-mediated excitatory postsynaptic potential. This pronounced co-activation could only be observed in the 28 days ischemic group, and neither after one to three days or six months post-ischemia nor in the controls. The quantitative analysis of the efficiency of stimulus- evoked inhibitory postsynaptic potentials recorded in amino-phosphono-valeric acid revealed a reduction of GABA-mediated inhibition in ischemic cortex. Although this reduction in intracortical inhibition may already contribute to an augmentation of N-methyl-D-aspartate receptor-mediated excitation, our results do also indicate that the function of N-methyl-D-aspartate receptors is transiently enhanced in the ischemic cortex. This transient hyperexcitability does not only cause cellular dysfunction in the vicinity of the infarct, but may also contribute to neuronal damage due to excitotoxicity.
采用体外细胞外和细胞内记录技术，在成年小鼠新皮质切片中研究大脑中动脉永久性闭塞的长期（≤6个月）功能后果。在存活1至3天、28天和6个月后，与年龄匹配的对照动物相比，梗死灶附近II/III层锥体细胞的细胞内记录未显示内在膜特性有任何统计学上的显著变化。然而，在缺血诱导后28天的小鼠获得的新皮质切片中，经正相突触刺激可观察到明显的过度兴奋性。传入神经的低强度电刺激在该组中尤其引发癫痫样细胞外场电位反应和细胞内兴奋性突触后电位，与对照组相比，其持续时间更长。当在含有0.1 mM Mg2+和10 μM 6-氰基-7-硝基喹喔啉-2,3-二酮的浴液中从药理学上分离N-甲基-D-天冬氨酸受体介导的兴奋性突触后电位时，与对照组相比，缺血皮质中的突触反应更长且更大。在正常培养基中，较高的刺激强度诱发双相抑制性突触后电位，在缺血后28天组中，该电位包含一个突出的对氨基膦酸戊酸敏感的成分，表明N-甲基-D-天冬氨酸受体介导的兴奋性突触后电位同时强烈激活。这种明显的共同激活仅在缺血28天组中观察到，在缺血后1至3天或6个月后以及对照组中均未观察到。对在氨基膦酸戊酸中记录的刺激诱发抑制性突触后电位效率的定量分析显示，缺血皮质中GABA介导的抑制作用降低。虽然皮质内抑制的这种降低可能已经导致N-甲基-D-天冬氨酸受体介导的兴奋增强，但我们的结果也表明，缺血皮质中N-甲基-D-天冬氨酸受体的功能短暂增强。这种短暂的过度兴奋性不仅会导致梗死灶附近的细胞功能障碍，还可能因兴奋性毒性导致神经元损伤。
