Medullary serotonin neurons are CO2 sensitive in situ
Medullary serotonin neurons are CO2 sensitive in situ
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DOI：
10.1152/jn.00288.2013
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发表时间：
2013-12-01
影响因子：
2.5
通讯作者：
Harris, Michael B.
中科院分区：
文献类型：
--
作者：
Iceman, Kimberly E.;Richerson, George B.;Harris, Michael B.
脑干中枢化学感受器对于高碳酸血症通气反应至关重要，但人们对它们的位置和身份知之甚少。在体外研究中，大鼠中缝内的血清素合成（5-HT）神经元本质上受到二氧化碳/酸中毒的刺激。然而，这些神经元对体内中枢化学敏感性的贡献存在争议。缺乏完整实验制剂中 CO2 敏感 5-HT 神经元的记录，也缺乏对其空间和比例分布的理解。在这里，我们检验了大鼠中缝中 5-HT 神经元对动脉高碳酸血症敏感的假设。我们在未麻醉的原位灌注去大脑脑干制剂中使用自发活动的髓缝神经元的细胞外记录和高碳酸血症挑战来评估单个细胞的化学敏感性。对记录的神经元子集进行细胞旁标记，然后对 5-HT 合成酶色氨酸羟化酶 (TPH) 进行免疫组织化学，可识别或排除电生理学特征的化学敏感和不敏感细胞中的这种神经递质表型。我们发现髓中缝拥有异质群体，包括化学敏感和不敏感的 5-HT 神经元。在 124 个记录的细胞中，16 个细胞被细胞旁填充、可视化，并根据 TPH 免疫反应性通过免疫组织化学鉴定为 5-HT 合成。 44% 的 5-HT 细胞受到 CO2 刺激（高碳酸血症导致放电率增加），而 56% 则未受到刺激。我们的结果表明，髓质中缝神经元是异质的，并且明显包括由动脉高碳酸血症兴奋的 5-HT 神经元子集。结合体外识别本质上 CO2 敏感的 5-HT 神经元的数据，这些结果支持此类细胞在完整系统中作为中央化学感受器的作用。
Brainstem central chemoreceptors are critical to the hypercapnic ventilatory response, but their location and identity are poorly understood. When studied in vitro, serotonin-synthesizing (5-HT) neurons within the rat medullary raphe are intrinsically stimulated by CO2/acidosis. The contributions of these neurons to central chemosensitivity in vivo, however, are controversial. Lacking is documentation of CO2-sensitive 5-HT neurons in intact experimental preparations and understanding of their spatial and proportional distribution. Here we test the hypothesis that 5-HT neurons in the rat medullary raphe are sensitive to arterial hypercapnia. We use extracellular recording and hypercapnic challenge of spontaneously active medullary raphe neurons in the unanesthetized in situ perfused decerebrate brainstem preparation to assess chemosensitivity of individual cells. Juxtacellular labeling of a subset of recorded neurons and subsequent immunohistochemistry for the 5-HT-synthesizing enzyme tryptophan hydroxylase (TPH) identify or exclude this neurotransmitter phenotype in electrophysiologically characterized chemosensitive and insensitive cells. We show that the medullary raphe houses a heterogeneous population, including chemosensitive and insensitive 5-HT neurons. Of 124 recorded cells, 16 cells were juxtacellularly filled, visualized, and immunohistochemically identified as 5-HT synthesizing, based on TPH-immunoreactivity. Forty-four percent of 5-HT cells were CO2 stimulated (increased firing rate with hypercapnia), while 56% were unstimulated. Our results demonstrate that medullary raphe neurons are heterogeneous and clearly include a subset of 5-HT neurons that are excited by arterial hypercapnia. Together with data identifying intrinsically CO2-sensitive 5-HT neurons in vitro, these results support a role for such cells as central chemoreceptors in the intact system.