Kodama Naoki, Funahashi Makoto, Mitoh Yoshihiro, Minagi Shogo, Matsuo Ryuji
Department of Occlusal and Oral Functional Rehabilitation, Okayama University Graduate School of Medicine, Dentistry & Pharmaceutical Sciences, 2-5-1 Shikata-cho, Okayama 700-8525, Japan.
Brain Res. 2007 Aug 24;1165:50-9. doi: 10.1016/j.brainres.2007.06.003. Epub 2007 Jun 15.
ATP has been shown to excite neurons in various regions of the central nervous system. Whereas immunohistochemical studies show P2X receptors in the area postrema, the responsiveness of area postrema neurons to extracellular ATP has not been studied. To investigate the effects of purinoceptor activation on area postrema neuronal excitability, we performed whole-cell recordings from area postrema neurons in rat brain slices. Most area postrema neurons responded to ATP application, and most responses were excitatory. Voltage-clamp recordings showed three different types of response: (1) a postsynaptic or extrasynaptic excitatory response (inward currents; n=26/51 cells), (2) a presynaptic excitatory response (increased frequency of miniature excitatory postsynaptic currents with only a small direct postsynaptic current; n=24/51 cells, or (3) a postsynaptic inhibitory response (outward current; n=1/51). The excitatory responses were found in both of the two major electrophysiological cell classes, i.e. cells displaying I(h) and cells not displaying I(h), while the inhibitory responses were found in only cells not displaying I(h). Current-clamp recordings showed ATP-induced depolarization (n=13/15) or hyperpolarization (n=2/15) of membrane potential that modulated the frequency of action potentials. In the presence of CNQX, mEPSCs were abolished and bath-applied ATP did not generate mEPSCs, indicating that glutamate release was facilitated by the activation of presynaptically located ATP receptors. Our pharmacological results from studies with ATP, alphabetame-ATP, betame-ATP and PPADS indicate that the post- and/or extrasynaptic responses are most likely mediated by P2X(7) receptors and/or receptors composed of P2X(2) and P2X(5) subunits. We conclude that half of the presynaptic responses are most likely mediated by P2X(7) receptors and/or receptors composed of P2X(2) and P2X(5) subunits while the others also contain P2X(1) subunits. It is well known that P2X(7) subunit forms only homomultimeric P2X receptors. Finally, the present study suggests that purinoceptor activation may contribute to the control of several autonomic functions by area postrema neurons.
三磷酸腺苷（ATP）已被证明可兴奋中枢神经系统各区域的神经元。免疫组织化学研究显示最后区存在P2X受体，但最后区神经元对细胞外ATP的反应性尚未得到研究。为了研究嘌呤受体激活对最后区神经元兴奋性的影响，我们在大鼠脑片的最后区神经元上进行了全细胞膜片钳记录。大多数最后区神经元对施加的ATP有反应，且大多数反应是兴奋性的。电压钳记录显示出三种不同类型的反应：（1）突触后或突触外兴奋性反应（内向电流；n = 26/51个细胞），（2）突触前兴奋性反应（微小兴奋性突触后电流频率增加，仅有少量直接的突触后电流；n = 24/51个细胞），或（3）突触后抑制性反应（外向电流；n = 1/51）。在两种主要的电生理细胞类型中均发现了兴奋性反应，即显示I(h)的细胞和不显示I(h)的细胞，而抑制性反应仅在不显示I(h)的细胞中发现。电流钳记录显示ATP可诱导膜电位去极化（n = 13/15）或超极化（n = 2/15），进而调节动作电位频率。在存在CNQX时，微小兴奋性突触后电流被消除，且浴槽施加的ATP未产生微小兴奋性突触后电流，这表明突触前定位的ATP受体激活促进了谷氨酸释放。我们使用ATP、α,β-亚甲基ATP、β,γ-亚甲基ATP和PPADS进行研究的药理学结果表明，突触后和/或突触外反应很可能由P2X(7)受体和/或由P2X(2)和P2X(5)亚基组成的受体介导。我们得出结论，一半的突触前反应很可能由P2X(7)受体和/或由P2X(2)和P2X(5)亚基组成的受体介导，而其他反应还包含P2X(1)亚基。众所周知，P2X(7)亚基仅形成同多聚体P2X受体。最后，本研究表明嘌呤受体激活可能有助于最后区神经元对多种自主功能的控制。
