Cronberg Tobias, Jensen Kimmo, Rytter Anna, Wieloch Tadeusz
Department of Clinical Neuroscience, Wallenberg Neuroscience Center, Laboratory for Experimental Brain Research, Lund University, BMC A13, S-221 84 Lund, Sweden.
Eur J Neurosci. 2005 Jul;22(2):310-6. doi: 10.1111/j.1460-9568.2005.04235.x.
A brief global ischemic insult to the brain leads to a selective degeneration of the pyramidal neurons in the hippocampal CA1 region while the neurons in the neighbouring CA3 region are spared. The reason for this difference is not known. The selective vulnerability of CA1 neurons to ischemia can be reproduced in vitro in murine organotypic slice cultures, if the ion concentrations in the medium during the anoxic/aglycemic insult are similar to that in the brain extracellular fluid during ischemia in vivo. As acidosis develops during ischemia, we studied the importance of extracellular pH for selective vulnerability. We found that cell death in the CA1 and CA3 regions was equally prevented by removal of calcium from the medium or following blockade of the N-methyl-D-aspartate (NMDA) receptor by D-2 amino-5-phosphonopentanoic-acid (D-APV). On the other hand, damage to the CA3 neurons markedly decreased with decreasing pH following in vitro ischemia, while the degeneration of CA1 neurons was less pH dependent. Patch-clamp recordings from pyramidal neurons in the CA1 and CA3 regions, respectively, revealed a pronounced inhibition of NMDA-receptor mediated excitatory postsynaptic currents (EPSCs) at pH 6.5 that was equally pronounced in the two regions. However, when changing pH from 6.5 to 7.4 the recovery of the EPSCs was significantly slower in the CA3 region. We conclude that acidosis selectively protects CA3 pyramidal neurons during in vitro ischemia, and differentially affects the kinetics of NMDA receptor activation, which may explain the difference in vulnerability between CA1 and CA3 pyramidal neurons to an ischemic insult.
对大脑进行短暂的全脑缺血性损伤会导致海马CA1区锥体细胞选择性退化，而相邻的CA3区神经元则不受影响。造成这种差异的原因尚不清楚。如果在缺氧/无糖损伤期间培养基中的离子浓度与体内缺血时脑细胞外液中的离子浓度相似，那么CA1神经元对缺血的选择性易损性可以在体外小鼠器官型脑片培养中重现。由于缺血期间会发生酸中毒，我们研究了细胞外pH值对选择性易损性的重要性。我们发现，通过从培养基中去除钙或用D-2-氨基-5-磷酸戊酸（D-APV）阻断N-甲基-D-天冬氨酸（NMDA）受体，CA1区和CA3区的细胞死亡均可得到同等程度的预防。另一方面，体外缺血后，随着pH值降低，CA3神经元的损伤明显减少，而CA1神经元的退化对pH值的依赖性较小。分别对CA1区和CA3区锥体细胞进行膜片钳记录发现，在pH值为6.5时，NMDA受体介导的兴奋性突触后电流（EPSC）受到明显抑制，且在两个区域中这种抑制作用同样明显。然而，当pH值从6.5变为7.4时，CA3区EPSC的恢复明显较慢。我们得出结论，酸中毒在体外缺血期间选择性地保护CA3锥体细胞，并对NMDA受体激活的动力学产生不同影响，这可能解释了CA1和CA3锥体细胞对缺血性损伤易损性的差异。
