Fournier S, Kinkead R
Department of Pediatrics, Université Laval, Centre de Recherche du Centre Hospitalier Universitaire de Québec, Québec City, QC, Canada.
Neuroscience. 2008 Aug 26;155(3):983-96. doi: 10.1016/j.neuroscience.2008.05.044. Epub 2008 Jun 10.
The present study used an in vitro brainstem preparation from pre-metamorphic tadpoles and adult bullfrogs (Lithobates catesbeiana) to understand the neural mechanisms associated with central O(2) chemosensitivity and its maturation. In this species, brainstem hypoxia increases fictive lung ventilation in tadpoles but decreases in adults. Previous studies have shown that alpha(1)-adrenoceptor inactivation prevents these responses, suggesting that noradrenergic neurons are involved. We first tested the hypothesis that the pons (which includes noradrenergic neurons from the locus coeruleus; LC) plays a role in the lung burst frequency response to central hypoxia by comparing the effects of brainstem transection at the LC level between pre-metamorphic tadpoles and adults. Data show that brainstem transection prevents the lung burst frequency response in both stage groups. During development, the progressive decrease in the Na(+)/K(+)/Cl(-) co-transporter NKCC1 contributes to the maturation of neural networks. Because NKCC1 becomes activated during hypoxia, we then tested the hypothesis that NKCC1 contributes to maturation of the central O(2) chemoreflex. Double labeling experiments showed that the proportion of tyrosine hydroxylase positive neurons expressing NKCC1 in the LC decreases during development. Inactivation of NKCC1 with bumetanide bath application reversed the lung burst response to hypoxia in tadpoles. Bumetanide inhibited the response in adults. These data indicate that a structure within the pons (potentially the LC) is necessary to the central hypoxic chemoreflex and demonstrate that NKCC1 plays a role in central O(2) chemosensitivity and its maturation in this species.
本研究采用来自变态前蝌蚪和成年牛蛙（美国牛蛙）的体外脑干制剂，以了解与中枢性氧化学敏感性及其成熟相关的神经机制。在该物种中，脑干缺氧会增加蝌蚪的虚拟肺通气，但会降低成年牛蛙的虚拟肺通气。先前的研究表明，α1 - 肾上腺素能受体失活可阻止这些反应，这表明去甲肾上腺素能神经元参与其中。我们首先通过比较变态前蝌蚪和成年牛蛙在蓝斑（LC）水平进行脑干横切的影响，来测试脑桥（其中包括来自蓝斑的去甲肾上腺素能神经元）在对中枢性缺氧的肺爆发频率反应中是否起作用的假设。数据表明，脑干横切可阻止两个阶段组的肺爆发频率反应。在发育过程中，Na(+)/K(+)/Cl(-)共转运体NKCC1的逐渐减少有助于神经网络的成熟。由于NKCC1在缺氧时被激活，我们随后测试了NKCC1有助于中枢性氧化学反射成熟的假设。双重标记实验表明，在发育过程中，蓝斑中表达NKCC1的酪氨酸羟化酶阳性神经元的比例会降低。用布美他尼浴应用使NKCC1失活可逆转蝌蚪对缺氧的肺爆发反应。布美他尼抑制成年牛蛙的反应。这些数据表明，脑桥内的一个结构（可能是蓝斑）对于中枢性低氧化学反射是必需的，并证明NKCC1在该物种的中枢性氧化学敏感性及其成熟中起作用。
