Department of Neurobiology, University of Pittsburgh, Pittsburgh, PA 15261, USA.
Cerebellum. 2011 Sep;10(3):585-99. doi: 10.1007/s12311-011-0278-x.
Flavoprotein autofluorescence imaging, an intrinsic mitochondrial signal, has proven useful for monitoring neuronal activity. In the cerebellar cortex, parallel fiber stimulation evokes a beam-like response consisting of an initial, short-duration increase in fluorescence (on-beam light phase) followed by a longer duration decrease (on-beam dark phase). Also evoked are parasagittal bands of decreased fluorescence due to molecular layer inhibition. Previous work suggests that the on-beam light phase is due to oxidative metabolism in neurons. The present study further investigated the metabolic and cellular origins of the flavoprotein signal in vivo, testing the hypotheses that the dark phase is mediated by glia activation and the inhibitory bands reflect decreased flavoprotein oxidation and increased glycolysis in neurons. Blocking postsynaptic ionotropic and metabotropic glutamate receptors abolished the on-beam light phase and the parasagittal bands without altering the on-beam dark phase. Adding glutamate transporter blockers reduced the dark phase. Replacing glucose with lactate (or pyruvate) or adding lactate to the bathing media abolished the on-beam dark phase and reduced the inhibitory bands without affecting the light phase. Blocking monocarboxylate transporters eliminated the on-beam dark phase and increased the light phase. These results confirm that the on-beam light phase is due primarily to increased oxidative metabolism in neurons. They also show that the on-beam dark phase involves activation of glycolysis in glia resulting in the generation of lactate that is transferred to neurons. Oxidative savings in neurons contributes to the decrease in fluorescence characterizing the inhibitory bands. These findings provide strong in vivo support for the astrocyte-neuron lactate shuttle hypothesis.
黄素蛋白自发荧光成像作为一种内在的线粒体信号，已被证明可用于监测神经元活动。在小脑皮层中，平行纤维刺激会引起一束状反应，包括初始的短持续时间荧光增加（束上光相），随后是更长时间的减少（束上暗相）。此外，由于分子层抑制，还会引起平行纤维的荧光减少。以前的工作表明，束上光相是由于神经元中的氧化代谢。本研究进一步在体内研究了黄素蛋白信号的代谢和细胞起源，检验了以下假设：暗相是由胶质细胞激活介导的，抑制带反映了神经元中黄素蛋白氧化减少和糖酵解增加。阻断突触后离子型和代谢型谷氨酸受体可消除束上光相和平行纤维的带，而不改变束上暗相。添加谷氨酸转运体阻滞剂可减少暗相。用乳酸盐（或丙酮酸）代替葡萄糖或向灌流介质中添加乳酸盐可消除束上暗相并减少抑制带，而不影响光相。阻断单羧酸转运体可消除束上暗相并增加光相。这些结果证实，束上光相主要是由于神经元中氧化代谢的增加。它们还表明，束上暗相涉及胶质细胞中糖酵解的激活，导致产生的乳酸转移到神经元中。神经元中的氧化节约有助于荧光减少，这是特征性的抑制带。这些发现为星形胶质细胞-神经元乳酸穿梭假说提供了强有力的体内支持。
