Hauer Brandon E, Negash Biruk, Chan Kingsley, Vuong Wesley, Colbourne Frederick, Pagliardini Silvia, Dickson Clayton T
Neuroscience and Mental Health Institute, University of Alberta , Edmonton, Alberta , Canada.
Department of Psychology, University of Alberta , Edmonton, Alberta , Canada.
J Neurophysiol. 2018 Oct 1;120(4):1505-1515. doi: 10.1152/jn.00373.2018. Epub 2018 Jun 27.
Oxygen (O) is a crucial element for physiological functioning in mammals. In particular, brain function is critically dependent on a minimum amount of circulating blood levels of O and both immediate and lasting neural dysfunction can result following anoxic or hypoxic episodes. Although the effects of deficiencies in O levels on the brain have been reasonably well studied, less is known about the influence of elevated levels of O (hyperoxia) in inspired gas under atmospheric pressure. This is of importance due to its typical use in surgical anesthesia, in the treatment of stroke and traumatic brain injury, and even in its recreational or alternative therapeutic use. Using local field potential (EEG) recordings in spontaneously breathing urethane-anesthetized and naturally sleeping rats, we characterized the influence of different levels of O in inspired gases on brain states. While rats were under urethane anesthesia, administration of 100% O elicited a significant and reversible increase in time spent in the deactivated (i.e., slow-wave) state, with concomitant decreases in both heartbeat and respiration rates. Increasing the concentration of carbon dioxide (to 5%) in inspired gas produced the opposite result on EEG states, mainly a decrease in the time spent in the deactivated state. Consistent with this, decreasing concentrations of O (to 15%) in inspired gases decreased time spent in the deactivated state. Further confirmation of the hyperoxic effect was found in naturally sleeping animals where it similarly increased time spent in slow-wave (nonrapid eye movement) states. Thus alterations of O in inspired air appear to directly affect forebrain EEG states, which has implications for brain function, as well as for the regulation of brain states and levels of forebrain arousal during sleep in both normal and pathological conditions. NEW & NOTEWORTHY We show that alterations of oxygen concentration in inspired air biases forebrain EEG state. Hyperoxia increases the prevalence of slow-wave states. Hypoxia and hypercapnia appear to do the opposite. This suggests that oxidative metabolism is an important stimulant for brain state.
氧气（O）是哺乳动物生理功能的关键元素。特别是，脑功能严重依赖于最低限度的循环血液中氧气水平，缺氧或低氧发作后可能会导致即时和持久的神经功能障碍。尽管氧气水平不足对大脑的影响已得到较为充分的研究，但对于常压下吸入气体中氧气水平升高（高氧）的影响却知之甚少。鉴于其在手术麻醉、中风和创伤性脑损伤治疗中的典型应用，甚至在娱乐或替代治疗中的应用，这一点很重要。通过在自发呼吸的氨基甲酸乙酯麻醉和自然睡眠的大鼠中进行局部场电位（脑电图）记录，我们表征了吸入气体中不同氧气水平对脑状态的影响。在大鼠处于氨基甲酸乙酯麻醉状态下时，给予100%氧气会使失活（即慢波）状态下的时间显著且可逆地增加，同时心率和呼吸频率均降低。在吸入气体中增加二氧化碳浓度（至5%）对脑电图状态产生相反的结果，主要是失活状态下的时间减少。与此一致的是，吸入气体中氧气浓度降低（至15%）会减少失活状态下的时间。在自然睡眠的动物中也发现了高氧效应的进一步证实，即它同样增加了慢波（非快速眼动）状态下的时间。因此，吸入空气中氧气的改变似乎直接影响前脑脑电图状态，这对脑功能以及正常和病理条件下睡眠期间脑状态和前脑觉醒水平的调节都有影响。新发现与值得注意的点我们表明，吸入空气中氧气浓度的改变会使前脑脑电图状态产生偏差。高氧增加慢波状态的发生率。低氧和高碳酸血症似乎有相反作用。这表明氧化代谢是脑状态的重要刺激因素。
