Extrinsic control of Gastrointestinal Motility

肠道机械感觉神经元保证了食物从肠道一端到另一端的相对稳定的运动。机械感觉神经元至少有三种：形成内反射传入肢体的机械感觉内初级传入神经元；机械感觉肠道神经元（ifn），其轴突在肠壁外投射到椎前神经节，在那里它们与交感神经元进行突触接触；机械感觉结肠脊髓传入神经元（SANs）与椎前神经节神经元的轴突侧支。这项赠款建议的工作重点是后两个群体。ifn和结肠SANs机械敏感性的基础尚不清楚。我们的第一部分工作集中在确定变性素/上皮Na+通道（DEG/ENaC）是否是这些神经中机械换能器的组成部分。我们将通过RT-PCR、免疫组织化学和共聚焦3D成像来确定DEG/ENaC亚基是否在这些神经中表达，并通过细胞内和膜片钳记录DEG/ENaC在IFN功能中的作用。在我们工作的第二部分，我们将测试我们的假设，即机械感觉结肠SANs轴突侧支是酸敏感的。DRASIC和香草受体（VR1）可以被质子直接激活。我们将通过RT-PCR确定DRASIC是否存在于具有轴突侧枝的结肠SANs中，并通过免疫组织化学确定DRASIC和VR1是否共定位于这些神经中。接下来，我们将研究结肠酸性溶液对椎前神经节P物质释放突触输入的影响，并确定DRASIC和VR1在酸诱发反应中的作用。我们工作的意义是双重的。首先，它将提供数据支持DEG/ENaC阳离子通道在肠传入神经结肠运动和机械敏感性之间架起桥梁的观点。其次，它将提供数据支持下述假设：DRASIC和VR1介导具有轴突侧支的机械敏感结肠SANs的酸敏感性，这些机械感觉神经可能在炎症期间致敏。从我们的研究中获得的基础知识有望提高对肠传入神经机械敏感性和化学敏感性的分子成分的功能意义的理解。

Intestinal mechanosensory neurons ensure relatively constant movement of content from one end of the gut to the other. There are at least three populations of mechanosensory neurons: mechanosensory intrinsic primary afferent neurons that form the afferent limb of intrinsic reflexes; mechanosensory intestinofugal neurons (IFNs) that project their axons outside the intestinal wall to prevertebral ganglia where they make synaptic contact with sympathetic neurons; and mechanosensory colon spinal afferent neurons (SANs) with axon collaterals to prevertebral ganglion neurons. The work proposed in this grant focuses on the latter two populations. The basis for mechanosensitivity in IFNs and colon SANs is not understood. We focus the first part of our work on determining whether the degenerin/epithelial Na+-channel (DEG/ENaC) is a component part of the mechanotransducer in these nerves. We will determine by RT-PCR, immunohistochemistry and confocal 3D imaging if DEG/ENaC subunits are expressed in these nerves and by intracellular and patch clamp recording the role of DEG/ENaC in IFN function. In the second part of our work, we will test our hypothesis that mechanosensory colon SANs with axon collaterals are acid sensitive. DRASIC and the vanilloid receptor (VR1) can be directly activated by protons. We will determine by RT-PCR if DRASIC is present in colon SANs with axon collaterals and by immunohistochemistry whether DRASIC and VR1 are colocalized in these nerves. Next, we will examine the effect of acidic solutions placed in the colon on synaptic input to the release of substance P in prevertebral ganglia, and determine the role DRASIC and VR1 play in acid-evoked responses. The significance of our work is two fold. Firstly, it wil provide data to support the notion that DEG/ENaC cation ion channel bridges the gap between colonic motility and mechanosensitivity in intestinal afferent nerves. Secondly, it will provide data to support the hypothesis that DRASIC and VR1 mediate acid sensitivity in mechanosensitive colon SANs with axon collaterals and that these mechanosensory nerves may be sensitized during inflammation. The basic knowledge derived from our studies is expected to improve the understanding of the functional significance of the molecular components of mechanosensitivity and chemosensitivity of intestinal afferent nerves.