Martín Víctor, Vale Carmen, Rubiolo Juan A, Roel Maria, Hirama Masahiro, Yamashita Shuji, Vieytes Mercedes R, Botana Luís M
†Departamento de Farmacología, Facultad de Veterinaria, Universidad de Santiago de Compostela, 27002 Lugo, Spain.
‡Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan.
Chem Res Toxicol. 2015 Jun 15;28(6):1109-19. doi: 10.1021/tx500506q. Epub 2015 May 19.
Ciguatoxins are sodium channels activators that cause ciguatera, one of the most widespread nonbacterial forms of food poisoning, which presents with long-term neurological alterations. In central neurons, chronic perturbations in activity induce homeostatic synaptic mechanisms that adjust the strength of excitatory synapses and modulate glutamate receptor expression in order to stabilize the overall activity. Immediate early genes, such as Arc and Egr1, are induced in response to activity changes and underlie the trafficking of glutamate receptors during neuronal homeostasis. To better understand the long lasting neurological consequences of ciguatera, it is important to establish the role that chronic changes in activity produced by ciguatoxins represent to central neurons. Here, the effect of a 30 min exposure of 10-13 days in vitro (DIV) cortical neurons to the synthetic ciguatoxin CTX 3C on Arc and Egr1 expression was evaluated using real-time polymerase chain reaction approaches. Since the toxin increased the mRNA levels of both Arc and Egr1, the effect of CTX 3C in NaV channels, membrane potential, firing activity, miniature excitatory postsynaptic currents (mEPSCs), and glutamate receptors expression in cortical neurons after a 24 h exposure was evaluated using electrophysiological and western blot approaches. The data presented here show that CTX 3C induced an upregulation of Arc and Egr1 that was prevented by previous coincubation of the neurons with the NaV channel blocker tetrodotoxin. In addition, chronic CTX 3C caused a concentration-dependent shift in the activation voltage of NaV channels to more negative potentials and produced membrane potential depolarization. Moreover, 24 h treatment of cortical neurons with 5 nM CTX 3C decreased neuronal firing and induced synaptic scaling mechanisms, as evidenced by a decrease in the amplitude of mEPSCs and downregulation in the protein level of glutamate receptors that was also prevented by tetrodotoxin. These findings identify an unanticipated role for ciguatoxin in the regulation of homeostatic plasticity in central neurons involving NaV channels and raise the possibility that some of the neurological symptoms of ciguatera might be explained by these compensatory mechanisms.
雪卡毒素是钠通道激活剂，可导致雪卡中毒，这是最普遍的非细菌性食物中毒形式之一，会出现长期神经功能改变。在中枢神经元中，活动的慢性扰动会诱发稳态突触机制，该机制会调节兴奋性突触的强度并调节谷氨酸受体的表达，以稳定整体活动。即刻早期基因，如Arc和Egr1，会响应活动变化而被诱导，并在神经元稳态过程中成为谷氨酸受体运输的基础。为了更好地理解雪卡中毒的长期神经后果，确定雪卡毒素引起的活动慢性变化对中枢神经元的作用很重要。在此，使用实时聚合酶链反应方法评估了体外培养10 - 13天（DIV）的皮质神经元暴露于合成雪卡毒素CTX 3C 30分钟对Arc和Egr1表达的影响。由于该毒素增加了Arc和Egr1的mRNA水平，因此使用电生理和蛋白质印迹方法评估了CTX 3C在暴露24小时后对皮质神经元中NaV通道、膜电位、放电活动、微小兴奋性突触后电流（mEPSCs）和谷氨酸受体表达的影响。此处呈现的数据表明，CTX 3C诱导了Arc和Egr1的上调，而神经元先前与NaV通道阻滞剂河豚毒素共同孵育可阻止这种上调。此外，慢性CTX 3C导致NaV通道的激活电压向更负电位发生浓度依赖性偏移，并产生膜电位去极化。此外，用5 nM CTX 3C处理皮质神经元24小时会降低神经元放电并诱导突触缩放机制，mEPSCs幅度降低以及谷氨酸受体蛋白水平下调证明了这一点，而河豚毒素也可阻止这种下调。这些发现确定了雪卡毒素在涉及NaV通道的中枢神经元稳态可塑性调节中的意外作用，并增加了雪卡中毒的一些神经症状可能由这些补偿机制解释 的可能性。
