Lactate utilization as an energy substrate in ischemic and thermal preconditoned rat brain slices

我们研究了利用乳酸作为能量底物在缺血或热预处理脑切片。取左侧大脑半球，于缺血前48 h阻断对侧大脑中动脉，制作缺血预处理脑片。从暴露于中暑的大鼠获得热预处理的切片（42-43）。在制备前48 h，用15 min的时间点。脑切片中高能磷酸盐的水平通过使用11 <31>P NMR在25 ° C下以8分钟的时间分辨率测量。C.碘乙酸预处理的脑片再用氟柠檬酸、胶质毒素处理2 h，（富含神经元的切片），在完整切片中，高K ^+刺激后含乳酸盐的人工脑脊液（ACSF）中磷酸肌酸（PCr）水平的恢复完全消失，而在缺血或热预处理切片中的PCr水平在与上述相似的其他条件下部分恢复（n=6）。这些结果表明，神经元，缺血或中暑预处理，获得利用乳酸作为能量底物的能力。在平行实验中，我们记录了群体兴奋性突触后电位和尖峰颗粒细胞在海马脑片。完整脑片在含乳酸的ACSF中的群体峰在30 min内完全消失，并且在完整脑片用标准ACSF再灌注后没有恢复，但缺血或热预处理的脑片在标准ACSF中能够恢复（n=6）。这些结果表明，缺血预处理和热预处理可引起神经元某些系统性变化，如乳酸转运蛋白的表达和/或乳酸脱氢酶的激活。

We examined the utilization of lactate as an energy substrate in ischemic or thermal preconditioned brain slices. The ischemic preconditioned slices were obtained from left hemisphere, of which the contralateral middle cerebral artery was occluded 48h before the slice preparation. The thermal preconditioned slices were obtained from the rat, which was exposed to heat stroke (42-43^。C for 15min) at 48h before the preparation. The levels of high-energy phosphates in brain slices were measured by using ^<31>P NMR with a time resolution of 8 min at 25^。C. When iodoacetic acid-pretreated brain slices were further treated with fluorocitrate, glial toxin, for 2h (neuron-rich slices), the recovery of the phosphocreatine (PCr) level in artificial cerebrospinal fluid (ACSF) containing lactate after high-K^+ stimulation was completely abolished in intact slices, whereas the PCr level in the ischemic or the thermal preconditioned slices partly recovered in otherwise similar conditions as above (n=6). These results indicated that neurons, which preconditioned with ischemia or the heat stroke, acquired the ability to utilize lactate as an energy substrate. In parallel experiments we recorded population excitatory postsynaptic potentials and spikes from granule cells in hippocampal slices. Population spikes of intact slices in ACSF containing lactate were completely abolished in 30 min and did not recover after intact slices were re-perfused with standard ACSF, but those of the ischemic or the thermal preconditioned slices were able to recover in standard ACSF (n=6). These results show that the ischemic and the thermal preconditioning may induce certain systematic changes in neurons, such as the expression of lactate transporters and/or the activation of lactate dehydrogenase.