Three-dimensional analysis and molecular Mechanism of the autonomic nervous system in chronically hypoxic carotid body

颈动脉小体是感知动脉血气和氢离子浓度变化的主要感觉器官，在慢性低、等和高二氧化碳低氧条件下，颈动脉小体增大。在低氧和等颅压缺氧时，VIP纤维密度显著增加，NPY纤维密度不变。在高碳酸血症中，NPY纤维密度显著增加，而VIP纤维密度无明显变化。由于这些神经肽在本质上是血管活性的，颈动脉体循环的改变可能有助于慢性缺氧对化学感觉机制的调节。三维分析表明，这些肽能纤维主要与扩张的血管有关。此外，缺氧性颈动脉小体中的Calbindin D-28k纤维明显减少。慢性缺氧结束后1个月，颈动脉小体体积变小，NPY纤维密度增加。低氧可引起血管球体细胞[Ca^&lt；2+&gt；]i升高或降低。ACh和NaCN主要增加血管球体细胞[Ca^&lt；2+&gt；]i的ACh和NaCN，并在去除Ca^&lt；2+&gt；的情况下维持这种[Ca^&lt；2+&gt；]i反应幅度的50%。在这些结果的基础上，我们提出了细胞内和细胞间化学转导对化学刺激的反应模型。相对较多的球状细胞代表超极化，较少的细胞代表去极化。缝隙连接和相互突触被描述为球体细胞和传入终末之间相互作用的重要结构。有些传入神经纤维不产生放电，因为它们的终末相对的球体细胞不是去极化，而是超极化。需要进一步的研究来阐明是什么触发了化学转导机制。

The carotid bodies, which are the primary sensory organs for sensing changes in arterial blood gases and hydrogen ion concentration, were enlarged in the rat exposed to chronic hypo-, iso-, and hypercapnic hypoxia. In the hypo- and isocapnic hypoxia, the density of VIP fibers increased significantly, and the density of NPY fibers were unchanged. In the hypercapnic hypoxia, the density of NPY fibers was significantly increased, and that of VIP was unchanged. Because these neuropeptides are vasoactive in nature, altered carotid body circulation may contribute to modulation of the chemosensory mechanisms by chronic hypoxia. Three-dimensional analysis showed that these peptidergic fibers are mainly associated with expanded vasculatures. In addition, calbindin D-28k fibers in the hypoxic carotid bodies was significantly decreased. The carotid body one month after the termination of chronic hypoxia was diminished in size, and the density of NPY fibers was increased.The hypoxia induced either an increase or a decrease in [Ca^<2+>] i in glomus cells. ACh and NaCN mostly increased in [Ca^<2+>] i in glomus cells, and maintained 50% of the amplitude of this [Ca^<2+>] response under the removal of Ca^<2+>. On the basis of these results, we proposed a model of intracellular and cell-to-fiber chemo-transduction in response to chemical stimuli. Relatively large number of glomus cells represent hyperpolarization, while a small number of cells represent depolarization. Gap junction and reciprocal synapses are depicted as important structures for interaction among glomus cells and afferent terminals. Some afferent nerve fibers produced no discharge, since the glomus cells apposed by their terminals do not depolarize, but rather hyperpolarize. A further study is necessary to elucidate what triggers chemo-transduction mechanism.