Analysis of the functional and biological roles of the hyperpolarization-activated cation current in the central nervous system,

本研究采用全细胞膜片钳技术记录最后区神经元的超极化激活阳离子电流（Ih），探讨其功能和生物学作用。1）形态学特征根据电生理学标准，将AP神经元分为三组：1）同时显示超极化激活阳离子电流（Ih）和快速瞬时外向电流（fast <to>I_0）的细胞; 2）仅显示快速I_0的细胞<to>; 3）仅显示慢I_0的细胞。所有AP神经元都有一个明显比细胞树突细的轴突。没有系统的差异，各组，在树突或轴突的方向进行了鉴定。第3组神经元的细胞大小和电容的平均值显著大于其他组。有趣的是，第1组和第3组中的一些细胞，而不是第2组，发现它们的树突延伸到孤束核（NTS），这表明AP神经元可以在孤束核内表达。 ...更多信息 d在NTS内的树突末端接受迷走神经传入输入。虽然AP已经暗示包含均匀形状的神经元，本研究表明AP神经元的显著不同的亚群的存在，其特征不仅在于电生理学，而且形态学。2）ATP敏感性大多数最后区神经元响应ATP的应用，大多数反应是兴奋性的。电压钳记录显示了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，只有一个小的直接突触后电流; 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（显示I_h的细胞和不显示I_h的细胞）中都发现了兴奋性反应，而仅在不显示I_h的细胞中发现了抑制性反应。电流钳记录显示ATP诱导的去极化（n=13/15）或超极化（n=2/15）的膜电位调制的动作电位的频率。在CNQX存在下，mEPSC被消除，并且浴施加的ATP不产生mEPSC，表明谷氨酸释放通过激活位于突触前的ATP受体而促进。我们用ATP、α βme-ATP、βyme-ATP和PPADS研究的药理学结果表明，P2X_2、P2X_5和P2X_7可能是突触后和/或突触外区P2 X受体的组成亚基。结果表明，突触前P2 X受体中有一半可能是由P2X_2、P2X_5和P2X_7亚基组成，而另一半可能还含有P2X_1亚基。众所周知，P2X_7亚基仅形成同源多聚体P2 X受体。最后，本研究表明，嘌呤受体激活可能有助于控制几个自主神经功能的最后区神经元。少

We performed whole-cell patch-clamp recordings from area postrema neurons to investigate the functional and biological roles of the hyperpolarization-activated cation current (Ih).1) Morphological propertiesUsing electrophysiological criteria, AP neurons were subdivided into three groups : 1) cells displaying both the hyperpolarization-activated cation current (I_h) and the fast transient outward current (fast I_<to>) ; 2) cells displaying only the fast I_<to> ; and 3) cells displaying only the slow Ito. All AP neurons had a single axon that was distinctly thinner than the cells' dendrites. No systematic differences, across groups, in the orientation of dendrites or axons were identified. Mean values of cell size and capacitance of neurons from group 3 were significantly larger than those of the other groups. Interestingly, a number of cells from group 1 and 3 but not group 2 were found to extend their dendrites into the nucleus tractus solitarius (NTS), suggesting that AP neurons coul … More d receive vagal afferent inputs at their dendritic termini within the NTS. Although the AP have been implicated to contain uniformly shaped neurons, this study indicates the presence of significantly different subpopulations of AP neurons, which were characterized not only electrophysiologically but also morphologically.2) Sensitivity to ATPMost 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, aβme-ATP, βyme-ATP and PPADS indicate that P2X_2, P2X_5 and P2X_7 are the most likely subunits which compose the P2X receptor in the post-and/or extrasynaptic regions. We conclude that half of the presynaptic P2X receptors are most likely composed of P2X_2, P2X_5 and P2X_7 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. Less