The air-breathing specialization has evolved idependently in vertebrates, as many different organs can perfom gas exchange. The largest obligate air-breathing fish from South America Arapaima gigas breathe air using its gas bladder, and its dependence on air breathing increases during its growth. During its development, gill morphology shows a dramatic change, remodeling with a gradual reduction of gill lamellae during the transition from water breathing to air breathing . It has been suggested that in this species the gills remain the main site of O2 and CO2 sensing. Consistent with this, we demonstrate for the first time the occurrence of the neuroepithelial cells (NECs) in the glottis, and in the gill filament epithelia and their distal halves. These cells contain a broader spectrum of neurotransmitters (5-HT, acetylcholine, nNOS), G-protein subunits and the muscarininic receptors that are coupled to G proteins (G-protein coupled receptors). We report also for the first time the presence of G alpha proteins coupled with muscarinic receptors on the NECs, that are thought as receptors that initiate the cardiorespiratory reflexes in aquatic vertebrates. Based on the specific orientation in the epithelia and their closest vicinity to efferent vasculatures, the gill and glottal NECs of A. gigas could be regarded as potential O2 and CO2 sensing receptors. However, future studies are needed to ascertain the neurophysiological characterization of these cells.

中文翻译：

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乙酰胆碱和 G 蛋白偶联毒蕈碱受体在必须呼吸空气的鱼的神经上皮细胞 (NEC) 中的表达，巨骨舌鱼 (巨骨舌鱼科: Teleostei)

呼吸空气的特化在脊椎动物中独立进化，因为许多不同的器官可以进行气体交换。南美洲最大的专性呼吸空气鱼类巨骨舌鱼使用其气囊呼吸空气，并且在其生长过程中对空气呼吸的依赖性增加。在其发育过程中，鳃的形态发生了巨大的变化，在从水呼吸到空气呼吸的过渡过程中，鳃片逐渐减少而重塑。有人提出，在这个物种中，鳃仍然是 O2 和 CO2 感应的主要部位。与此一致，我们首次证明了神经上皮细胞 (NEC) 在声门、鳃丝上皮及其远端半部的发生。这些细胞含有更广泛的神经递质（5-HT、乙酰胆碱、nNOS），G 蛋白亚基和与 G 蛋白偶联的毒蕈碱受体（G 蛋白偶联受体）。我们还首次报告了 NEC 上存在与毒蕈碱受体结合的 G α 蛋白，这些受体被认为是启动水生脊椎动物心肺反射的受体。基于上皮细胞的特定方向及其最靠近传出脉管系统，A. gigas 的鳃和声门 NEC 可被视为潜在的 O2 和 CO2 感应受体。然而，未来的研究需要确定这些细胞的神经生理学特征。它们被认为是在水生脊椎动物中启动心肺反射的受体。基于上皮细胞的特定方向及其最靠近传出脉管系统，A. gigas 的鳃和声门 NEC 可被视为潜在的 O2 和 CO2 感应受体。然而，未来的研究需要确定这些细胞的神经生理学特征。它们被认为是在水生脊椎动物中启动心肺反射的受体。基于上皮细胞的特定方向及其最靠近传出脉管系统，A. gigas 的鳃和声门 NEC 可被视为潜在的 O2 和 CO2 感应受体。然而，未来的研究需要确定这些细胞的神经生理学特征。