Guyenet Patrice G, Stornetta Ruth L, Bayliss Douglas A, Mulkey Daniel K
Department of Pharmacology, University of Virginia Health System, PO Box 800735, 1300 Jefferson Park Avenue, Charlottesville, VA 22908-0735, USA.
Exp Physiol. 2005 May;90(3):247-53; discussion 253-7. doi: 10.1113/expphysiol.2004.029637. Epub 2005 Feb 25.
Central chemoreception is the mechanism by which arterial blood P(CO2) is detected by the CNS to regulate breathing. Two main theories have been proposed to account for the phenomenon. The distributed chemosensitivity theory argues that pH sensitivity is a widespread attribute of brainstem neurones and that central chemoreception results from the cumulative effects of pH on countless neurones. The specialized chemoreceptor theory envisions the existence of small and specialized populations of CNS cells (chemoreceptors) that are unique in their ability to detect very small pH fluctuations and, via specific connections, regulate a respiratory network that is itself unresponsive to pH. The recently identified CO2-sensitive neurones of the retrotrapezoid nucleus (RTN) seem to possess most of the attributes that one would expect of such chemoreceptors. In this review we also suggest that many fewer medullary neurones are intrinsically responsive to CO2 in vivo than might have been anticipated from prior experimentation in vitro. The properties of RTN neurones provide renewed support for the specialized chemoreceptor theory of central chemoreception, proposed in the early 1960s. However, many uncertainties remain, especially as regards the molecular mechanisms of chemoreception, the type of cell that actually detects pH in vivo (neurone, glia or others) and the number and location of bona fide central chemoreceptors.
中枢化学感受是中枢神经系统检测动脉血二氧化碳分压以调节呼吸的机制。针对这一现象，人们提出了两种主要理论。分布式化学敏感性理论认为，pH敏感性是脑干神经元的普遍特性，中枢化学感受是pH对无数神经元累积作用的结果。专门化学感受器理论设想存在一小群专门的中枢神经系统细胞（化学感受器），它们具有独特的能力，能够检测非常微小的pH波动，并通过特定的连接调节本身对pH不敏感的呼吸网络。最近发现的延髓头端腹外侧网状核（RTN）中的二氧化碳敏感神经元似乎具备人们期望这类化学感受器所具有的大多数特性。在这篇综述中，我们还指出，与之前体外实验的预期相比，体内对二氧化碳有内在反应的延髓神经元数量要少得多。RTN神经元的特性为20世纪60年代初提出的中枢化学感受专门化学感受器理论提供了新的支持。然而，许多不确定性仍然存在，特别是在化学感受的分子机制、体内实际检测pH的细胞类型（神经元、神经胶质细胞或其他细胞）以及真正的中枢化学感受器的数量和位置方面。
