目的:研究慢性同型半胱氨酸对大鼠外周三叉神经血管系统兴奋性和N-甲基-D-天冬氨酸(NMDA)敏感性的影响。
背景:偏头痛是一种神经系统疾病,影响普通人群的15%-20%。流行病学观察表明,血浆中含硫氨基酸同型半胱氨酸的增加-称为高同型半胱氨酸血症-与偏头痛的高风险有关。尤其是有先兆的偏头痛.在动物研究中,高同型半胱氨酸血症大鼠表现出机械性异常疼痛,畏光,和焦虑,对皮质扩散抑制的敏感性更高。此外,高同型半胱氨酸血症的大鼠在硝酸甘油诱导的慢性偏头痛模型中更敏感,这表明外周伤害性机制的参与。本工作旨在分析产前高同型半胱氨酸血症大鼠三叉神经节分离的脑膜传入神经和神经元的兴奋性。
方法:实验是在怀孕前和怀孕期间饲喂富含蛋氨酸的饮食的雌性大鼠中进行的。脑膜传入的活性在离体半球制剂中在细胞外记录,并使用聚类分析表征动作电位。使用全细胞膜片钳记录技术和钙成像研究评估三叉神经节神经元的兴奋性。使用甲苯胺蓝对脑膜肥大细胞进行染色。
结果:在具有较大振幅动作电位的高同型半胱氨酸血症组中,三叉神经的基线细胞外记录电活动较高。较低浓度的KCl会导致大鼠半球离体制剂中记录的三叉神经传入的动作电位频率增加。在高同型半胱氨酸血症大鼠的三叉神经节神经元中,引起至少一个动作电位(流变酶)所需的电流较低,响应2×流变酶的刺激,诱导更多的动作电位。在控件中,短期应用同型半胱氨酸及其衍生物会增加三叉神经动作电位的频率,并诱导神经元中的Ca2瞬变,与NMDA受体的激活有关。同时,在高同型半胱氨酸血症的大鼠中,我们没有观察到三叉神经对NMDA的反应增加。同样,NMDA诱导的Ca2+瞬变参数,同型半胱氨酸,其衍生物在高同型半胱氨酸血症大鼠中没有变化。脑膜在高半胱氨酸和高半胱氨酸中的急性孵育并没有改变肥大细胞的状态,而在高同型半胱氨酸血症模型中,观察到脑膜中肥大细胞的脱颗粒增加。
结论:我们的结果表明高同型半胱氨酸血症大鼠三叉神经系统的兴奋性更高。结合我们先前关于高同型半胱氨酸血症大鼠皮质扩散抑制产生阈值较低的发现,目前的数据提供了证据表明,同型半胱氨酸是增加外周偏头痛机制敏感性的一个因素,控制同型半胱氨酸水平可能是降低偏头痛发作风险和/或严重程度的重要策略。
OBJECTIVE: Investigation of chronic homocysteine action on the excitability and N-methyl-D-aspartate (NMDA) sensitivity of the peripheral trigeminovascular system of rats.
BACKGROUND: Migraine is a neurological disease that affects 15%-20% of the general population. Epidemiological observations show that an increase of the sulfur-containing amino acid homocysteine in plasma-called hyperhomocysteinemia-is associated with a high risk of migraine, especially migraine with aura. In animal studies, rats with hyperhomocysteinemia demonstrated mechanical allodynia, photophobia, and anxiety, and higher sensitivity to cortical spreading depression. In addition, rats with hyperhomocysteinemia were more sensitive in a model of chronic migraine induced by nitroglycerin which indicated the involvement of peripheral nociceptive mechanisms. The present work aimed to analyze the excitability of meningeal afferents and neurons isolated from the trigeminal ganglion of rats with prenatal hyperhomocysteinemia.
METHODS: Experiments were performed on male rats born from females fed with a methionine-rich diet before and during pregnancy. The activity of meningeal afferents was recorded extracellularly in hemiskull preparations ex vivo and action potentials were characterized using cluster analysis. The excitability of trigeminal ganglion neurons was assessed using whole-cell patch clamp recording techniques and calcium imaging studies. Meningeal mast cells were stained using toluidine blue.
RESULTS: The baseline extracellular recorded electrical activity of the trigeminal nerve was higher in the hyperhomocysteinemia group with larger amplitude action potentials. Lower concentrations of KCl caused an increase in the frequency of action potentials of trigeminal afferents recorded in rat hemiskull ex vivo preparations. In trigeminal ganglion neurons of rats with hyperhomocysteinemia, the current required to elicit at least one action potential (rheobase) was lower, and more action potentials were induced in response to stimulus of 2 × rheobase. In controls, short-term application of homocysteine and its derivatives increased the frequency of action potentials of the trigeminal nerve and induced Ca2+ transients in neurons, which are associated with the activation of NMDA receptors. At the same time, in rats with hyperhomocysteinemia, we did not observe an increased response of the trigeminal nerve to NMDA. Similarly, the parameters of Ca2+ transients induced by NMDA, homocysteine, and its derivatives were not changed in rats with hyperhomocysteinemia. Acute incubation of the meninges in homocysteine and homocysteinic acid did not change the state of the mast cells, whereas in the model of hyperhomocysteinemia, an increased degranulation of mast cells in the meninges was observed.
CONCLUSIONS: Our results demonstrated higher excitability of the trigeminal system of rats with hyperhomocysteinemia. Together with our previous finding about the lower threshold of generation of cortical spreading depression in rats with hyperhomocysteinemia, the present data provide evidence of homocysteine as a factor that increases the sensitivity of the peripheral migraine mechanisms, and the control of homocysteine level may be an important strategy for reducing the risk and/or severity of migraine headache attacks.