Atkinson L, Batten T F, Deuchars J
School of Biomedical Sciences, University of Leeds, LS2 9NQ, Leeds, UK.
Neuroscience. 2000;99(4):683-96. doi: 10.1016/s0306-4522(00)00233-5.
Adenosine 5'-triphosphate (ATP) can function as a fast synaptic transmitter through its actions on ionotropic (P2X) and metabotropic (P2Y) receptors in neuronal tissue. The ionotropic receptors have been classified into seven subtypes (P2X(1)-P2X(7)) by molecular cloning. However, they are difficult to distinguish pharmacologically owing to an absence of specific agonists and antagonists. In this study we used neuroanatomical methods to determine the origin and neurochemical phenotype of the P2X(2) subtype of purinoceptor in the dorsal medulla of the rat. Using immunohistochemistry we observed dense networks of P2X(2) receptor immunoreactive labelled fibres and terminals in the dorsal vagal complex and area postrema, as well as labelled cell bodies in the dorsal vagal nucleus and the area postrema. The P2X(2) receptor was localized presynaptically in vagal afferent fibres and terminals in the nucleus tractus solitarius at the ultrastructural level by combining injections of an anterograde tracer (biotin dextran amine) into the nodose ganglion with pre-embedding immunogold visualization of P2X(2) immunoreactivity. Terminals immunoreactive for the P2X(2) receptor in the nucleus tractus solitarius were found to contain glutamate, but not GABA immunoreactivity by post-embedding immunogold-labelling techniques. In cell bodies in the area postrema, dual immunofluorescence also indicated that P2X(2) receptor immunoreactive cells are glutamatergic but not GABAergic. The P2X(2) receptor was localized to vagal preganglionic neurons in the dorsal vagal nucleus that were identified by prior intraperitoneal injections of the retrograde tracer FluoroGold. No cells immunoreactive for the P2X(2) receptor were observed in the nucleus tractus solitarius. The localization of P2X(2) receptor immunoreactivity presynaptically in vagal afferent terminals indicates that the receptor may be involved in modulating transmitter release from vagal afferent fibres. Furthermore, the presence of the P2X(2) receptor in vagal preganglionic cells and in glutamatergic cells of the area postrema implies that it may, respectively, play a role in regulation of vagal efferent cell activity and modulation of excitatory outputs from the area postrema to other brain regions.
5'-三磷酸腺苷（ATP）可通过作用于神经组织中的离子型（P2X）和代谢型（P2Y）受体，作为一种快速突触递质发挥作用。通过分子克隆，离子型受体已被分为七个亚型（P2X(1)-P2X(7)）。然而，由于缺乏特异性激动剂和拮抗剂，它们在药理学上难以区分。在本研究中，我们使用神经解剖学方法来确定大鼠延髓背侧嘌呤受体P2X(2)亚型的起源和神经化学表型。通过免疫组织化学，我们在迷走神经背侧复合体和最后区观察到P2X(2)受体免疫反应性标记纤维和终末的密集网络，以及迷走神经背核和最后区的标记细胞体。通过将顺行示踪剂（生物素葡聚糖胺）注射到结状神经节中，并结合P2X(2)免疫反应性的预包埋免疫金可视化，在超微结构水平上，P2X(2)受体定位于孤束核中的迷走传入纤维和终末的突触前部位。通过包埋后免疫金标记技术发现，孤束核中对P2X(2)受体免疫反应的终末含有谷氨酸，但不含有GABA免疫反应性。在最后区的细胞体中，双重免疫荧光也表明，P2X(2)受体免疫反应性细胞是谷氨酸能的，而不是GABA能的。通过先前腹腔注射逆行示踪剂FluoroGold鉴定，P2X(2)受体定位于迷走神经背核中的迷走神经节前神经元。在孤束核中未观察到对P2X(2)受体免疫反应的细胞。P2X(2)受体免疫反应性在迷走传入终末的突触前定位表明，该受体可能参与调节迷走传入纤维的递质释放。此外，P2X(2)受体在迷走神经节前细胞和最后区的谷氨酸能细胞中的存在意味着，它可能分别在调节迷走传出细胞活性和调节最后区向其他脑区的兴奋性输出中发挥作用。
