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

我们研究了乳酸在缺血或热预处理脑切片中作为能量底物的利用。左半球缺血预处理切片，在切片制备前48小时闭塞对侧大脑中动脉。热预处理切片取自中暑大鼠（42-43^）。C 15min)，制备前48h。脑切片中高能磷酸盐的水平是用^<31>P核磁共振在25^ . c下以8分钟的时间分辨率测量的。当碘乙酸预处理的脑切片进一步用氟柠檬酸胶质毒素处理2h（富神经元切片）时，在完整切片中，高k ^+刺激后含乳酸的人工脑脊液（ACSF）中磷酸肌酸（PCr）水平的恢复完全消失，而在其他类似条件下，缺血或热预处理切片中的PCr水平部分恢复（n=6）。这些结果表明，经过缺血或中暑预处理的神经元获得了利用乳酸作为能量底物的能力。在平行实验中，我们记录了海马切片颗粒细胞的群体兴奋性突触后电位和尖峰。在含乳酸的ACSF中，完整切片的种群峰值在30min内完全消失，在标准ACSF中再灌注完整切片后没有恢复，而在标准ACSF中，缺血或热预处理切片的种群峰值能够恢复（n=6）。这些结果表明，缺血和热预处理可引起神经元乳酸转运蛋白的表达和乳酸脱氢酶的激活等系统性变化。

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.