Tortora Maria, Corsini Silvia, Nistri Andrea
Department of Neuroscience, International School for Advanced Studies (SISSA), Trieste, Italy.
Department of Neuroscience, International School for Advanced Studies (SISSA), Trieste, Italy.
Neurosci Lett. 2017 Feb 3;639:43-48. doi: 10.1016/j.neulet.2016.12.021. Epub 2016 Dec 19.
In several neurodegenerative diseases, glutamate-mediated excitotoxicity is considered to be a major process to initiate cell degeneration. Indeed, subsequent to excessive glutamate receptor stimulation, reactive oxygen species (ROS) generation and mitochondrial dysfunction are regarded as two major gateways leading to neuron death. These processes are mimicked in an in vitro model of rat brainstem slice when excitotoxicity is induced by DL-threo-β-benzyloxyaspartate (TBOA), a specific glutamate-uptake blocker that increases extracellular glutamate. Our recent study has demonstrated that brainstem hypoglossal motoneurons, which are very vulnerable to this damage, were neuroprotected from excitotoxicity with nicotine application through the activation of nicotinic acetylcholine receptors (nAChRs) and subsequent inhibition of ROS and mitochondrial dysfunction. The present study examined if endogenous cholinergic activity exerted any protective effect in this pathophysiological model and how ROS production (estimated with rhodamine fluorescence) and mitochondrial dysfunction (measured as methyltetrazolium reduction) were time-related during the early phase of excitotoxicity (0-4h). nAChR antagonists did not modify TBOA-evoked ROS production (that was nearly doubled over control) or mitochondrial impairment (25% decline), suggesting that intrinsic nAChR activity was insufficient to contrast excitotoxicity and needed further stimulation with nicotine to become effective. ROS production always preceded mitochondrial dysfunction by about 2h. Nicotine prevented both ROS production and mitochondrial metabolic depression with a delayed action that alluded to a complex chain of events targeting these two lesional processes. The present data indicate a relatively wide time frame during which strong nAChR activation can arrest a runaway neurotoxic process leading to cell death.
在几种神经退行性疾病中，谷氨酸介导的兴奋性毒性被认为是引发细胞退变的主要过程。确实，在谷氨酸受体受到过度刺激后，活性氧（ROS）生成和线粒体功能障碍被视为导致神经元死亡的两个主要途径。当用DL-苏式-β-苄氧基天冬氨酸（TBOA，一种增加细胞外谷氨酸的特异性谷氨酸摄取阻滞剂）诱导兴奋性毒性时，大鼠脑干切片的体外模型中会出现这些过程。我们最近的研究表明，极易受到这种损伤的脑干舌下运动神经元，通过激活烟碱型乙酰胆碱受体（nAChRs）以及随后抑制ROS和线粒体功能障碍，可因应用尼古丁而免受兴奋性毒性的影响。本研究探讨了内源性胆碱能活性在该病理生理模型中是否发挥任何保护作用，以及在兴奋性毒性早期阶段（0 - 4小时）ROS生成（用罗丹明荧光估计）和线粒体功能障碍（以甲基四氮唑还原测量）如何与时间相关。nAChR拮抗剂并未改变TBOA诱发的ROS生成（比对照增加近一倍）或线粒体损伤（下降25%），这表明内在的nAChR活性不足以对抗兴奋性毒性，需要用尼古丁进一步刺激才能生效。ROS生成总是比线粒体功能障碍提前约2小时出现。尼古丁可预防ROS生成和线粒体代谢抑制，其作用延迟，这暗示了针对这两个损伤过程的一系列复杂事件。目前的数据表明，在一个相对较宽的时间范围内，强烈的nAChR激活可以阻止导致细胞死亡的失控神经毒性过程。
