Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908, USA.
J Neurosci. 2013 May 1;33(18):7756-61. doi: 10.1523/JNEUROSCI.5550-12.2013.
Central respiratory chemoreceptors sense changes in CO2/H(+) and initiate the adjustments to ventilation required to preserve brain and tissue pH. The cellular nature of the sensors (neurons and/or glia) and their CNS location are not conclusively established but the glutamatergic, Phox2b-expressing neurons located in the retrotrapezoid nucleus (RTN) are strong candidates. However, a direct demonstration that RTN neurons are intrinsically sensitive to CO2/H(+), required for designation as a chemosensor, has been lacking. To address this, we tested the pH sensitivity of RTN neurons that were acutely dissociated from two lines of Phox2b-GFP BAC transgenic mice. All GFP-labeled cells assayed by reverse transcriptase-PCR (n = 40) were Phox2b+, VGlut2+, TH-, and ChAT-, the neurochemical phenotype previously defined for chemosensitive RTN neurons in vivo. We found that most dissociated RTN neurons from both lines of mice were CO2/H(+)-sensitive (∼79%), with discharge increasing during acidification and decreasing during alkalization. The pH-sensitive cells could be grouped into two populations characterized by similar pH sensitivity but different basal firing rates, as previously observed in recordings from GFP-labeled RTN neurons in slice preparations. In conclusion, these data indicate that RTN neurons are inherently pH-sensitive, as expected for a respiratory chemoreceptor.
中枢呼吸化学感受器感知二氧化碳/氢离子（CO2/H(+)）的变化，并启动通气调整，以维持脑和组织的 pH 值。感受器的细胞特性（神经元和/或神经胶质细胞）及其中枢神经系统（CNS）位置尚未得到明确证实，但位于延髓横形核（RTN）中的谷氨酸能 Phox2b 表达神经元是强有力的候选者。然而，直接证明 RTN 神经元对 CO2/H(+)具有内在敏感性，是作为化学感受器所必需的，这一点一直缺乏证据。为了解决这个问题，我们测试了从两种 Phox2b-GFP BAC 转基因小鼠中急性分离的 RTN 神经元对 pH 的敏感性。通过逆转录酶聚合酶链反应（RT-PCR）检测到的所有 GFP 标记细胞（n = 40）均为 Phox2b+、VGlut2+、TH-和 ChAT-，这是体内先前定义的化学敏感性 RTN 神经元的神经化学表型。我们发现，来自两种小鼠的大多数分离的 RTN 神经元均对 CO2/H(+)敏感（约 79%），酸化时放电增加，碱化时放电减少。pH 敏感细胞可分为两个群体，其 pH 敏感性相似，但基础放电率不同，这与在切片制备中 GFP 标记的 RTN 神经元记录中观察到的情况一致。总之，这些数据表明 RTN 神经元具有内在的 pH 敏感性，这是呼吸化学感受器的预期特性。
