Division of Neurobiology, Faculty of Biology, Ludwig-Maximillians-Universität (LMU), Munich, Germany.
Graduate School of Systemic Neurosciences (GSN), Ludwig-Maximillians-Universität (LMU), Munich, Germany.
J Neurochem. 2024 May;168(5):663-676. doi: 10.1111/jnc.16091. Epub 2024 Mar 4.
Neurons exhibit a high energetic need, and the question arises as how they metabolically adapt to changing activity states. This is relevant for interpreting functional neuroimaging in different brain areas. Particularly, neurons with a broad firing range might exhibit metabolic adaptations. Therefore, we studied MNTB (medial nucleus of the trapezoid body) principal neurons, which generate action potentials (APs) at frequencies up to several hundred hertz. We performed the experiments in acute brainstem slices of the Mongolian gerbil (Meriones unguiculatus) at 22.5-24.5°C. Upon electrical stimulation of afferent MNTB fibres with 400 stimuli at varying frequencies, we monitored autofluorescence levels of NAD(P)H and FAD and determined the extremum amplitudes of their biphasic response. Additionally, we compared these data with alterations in O concentrations measured with an electrochemical sensor. These O changes are prominent since MNTB neurons rely on oxidative phosphorylation as shown by our pharmacological experiments. We calculated the O consumption rate as change in O concentration divided by stimulus durations, because these periods varied inversely with stimulus frequency as a result of the constant number of 400 stimuli applied. The O consumption rate increased with stimulation frequency up to a constant value at 600 Hz; that is, energy demand depends on temporal characteristics of activity despite the same number of stimuli. The rates showed no correlation with peak amplitudes of NAD(P)H or FAD, whilst the values of the two molecules were linearly correlated. This points at the complexity of analysing autofluorescence imaging for quantitative metabolic studies, because these values report only relative net changes of many superimposed oxidative and reductive processes. Monitoring O concentration rates is, thus, an important tool to improve the interpretation of NAD(P)H/FAD autofluorescence data, as they do not under all conditions and in all systems appropriately reflect the metabolic activity or energy demand.
神经元表现出高度的能量需求，因此出现了一个问题，即它们如何在代谢上适应不断变化的活动状态。这对于解释不同脑区的功能神经影像学非常重要。特别是，具有较宽的放电范围的神经元可能表现出代谢适应。因此，我们研究了 MNTB（梯形体的内侧核）主要神经元，这些神经元在高达几百赫兹的频率下产生动作电位（AP）。我们在 22.5-24.5°C 的蒙古沙鼠（Meriones unguiculatus）急性脑干切片上进行了实验。通过对传入 MNTB 纤维进行 400 次不同频率的电刺激，我们监测了 NAD（P）H 和 FAD 的自发荧光水平，并确定了它们双相反应的极值幅度。此外，我们将这些数据与通过电化学传感器测量的 O 浓度变化进行了比较。由于 MNTB 神经元如我们的药理学实验所示依赖于氧化磷酸化，因此这些 O 变化非常显著。我们通过将 O 浓度变化除以刺激持续时间来计算 O 消耗率，因为这些时间段由于施加的 400 个刺激的数量不变而与刺激频率成反比。O 消耗率随着刺激频率的增加而增加，直到在 600 Hz 时达到恒定值；也就是说，尽管刺激的数量相同，但能量需求取决于活动的时间特征。这些速率与 NAD（P）H 或 FAD 的峰值幅度没有相关性，而这两个分子的值呈线性相关。这表明分析自发荧光成像进行定量代谢研究的复杂性，因为这些值仅报告许多重叠的氧化和还原过程的相对净变化。因此，监测 O 浓度速率是改进 NAD（P）H/FAD 自发荧光数据解释的重要工具，因为它们在所有条件下和所有系统中都不能适当地反映代谢活性或能量需求。
