COUPLING OF METABOLIC PROCESSES AND FUNCTIONAL ACTIVITY IN BRAIN

一段时间以来，人们普遍认为存在一种动态 耗氧量和葡萄糖的平衡和化学计量 利用来满足大脑的能量需求，以支持其功能 活动。这一概念最近因为研究而受到了挑战 报告说葡萄糖的利用在化学计量上超过了 在认知或感觉挑战期间和之后的耗氧量 刺激。现在有一种普遍的猜测，即 大脑是由糖酵解产生的能量支持的，如果在 全部，来自氧化新陈代谢。在氧气有限的条件下 供应，这是意料之中的，但如果这种情况发生在 充足的氧气违背了传统的能源观念 新陈代谢。因此，我们已经在体内检查了 [14C][14C]在葡萄糖消耗量为 通过功能激活而增加。我们发现大脑的标签 在K+刺激的代谢过程中，乳酸库增加了3倍 活动。大脑吸收的葡萄糖中约有20%损失给了 作为乳酸盐的血液，以及类似数量的血液必须从 激活的组织转移到其他脑区。因此，贩运 大脑中的中间代谢物可以是广泛的，一种新的， 出乎意料的发现。另一方面，在感官过程中和之后 刺激后乳酸在脑内积聚和血液流失。 小得多，即使氧/葡萄糖摄取率降低， 表明葡萄糖的利用率超过了化学计量比 相当于耗氧量。然而，我们发现，糖原， 主要定位于神经胶质细胞，被感觉耗尽 功能激活，表明部分，如果不是全部，过剩的 在功能激活后持续的葡萄糖利用 可以用葡萄糖碳转移到补给中来解释 代谢池被功能性和非功能性的能量需求耗尽 新陈代谢激活。

It has been generally believed for some time that there is a dynamic balance and stoichiometry between oxygen consumption and glucose utilization to meet the brain's energy demands to support its functional activity. This concept has recently been challenged because of studies reporting that glucose utilization is stoichiometrically in excess of oxygen consumption during and following cognitive challenges or sensory stimulation. It is now a common speculation that functional activity in brain is supported by energy derived from glycolysis and little, if at all, from oxidative metabolism. Under conditions of limited oxygen supply, this would be expected, but for this to happen in the presence of adequate oxygen violates traditional concepts about energy metabolism. We have, therefore, examined in vivo the metabolism of [14C]glucose in rat brain in conditions in which glucose consumption was increased by functional activation. We found that labeling of the brain lactate pool was increased 3-fold during K+- stimulated metabolic activity. About 20% of the glucose taken up by brain was lost to the blood as lactate, and similar quantities must have been transported from activated tissue to other brain regions. Thus, trafficking of intermediary metabolites within the brain can be extensive, a new, unexpected finding. On the other hand, during and following sensory stimulation lactate accumulation in the brain and loss to the blood were much smaller even though the oxygen/glucose uptake ratio was reduced, indicating that glucose utilization exceeded the stoichiometric equivalent of the oxygen consumption. We found, however, that glycogen, which is localized mainly in glial cells, is depleted by sensory functional activation, indicating that some, if not all, of the excess glucose utilization that persists following the functional activation can be explained by the diversion of glucose carbon to the replenishment of metabolic pools depleted by the energy demands of the functional and metabolic activation's.