Kirchgessner A L, Gershon M D
Department of Anatomy and Cell Biology, College of Physicians and Surgeons, Columbia University, New York, New York 10032.
J Comp Neurol. 1988 Nov 22;277(4):487-98. doi: 10.1002/cne.902770403.
The enteric nervous system (ENS) can mediate reflex activity without input from the brain or spinal cord. The ENS thus contains intrinsic primary afferent neurons that link mucosal sensory receptors with motor neurons in the myenteric plexus. The intrinsic primary afferent neurons of the gut have not yet been identified. Although the submucosal plexus is known to innervate the mucosa, where enteric sensory receptors are located, no submucosal to myenteric projections have previously been found. In order to determine whether such projections exist, the submucosal plexus was examined following the microinjection of a retrograde tracer (Fluoro-Gold or 4-acetoamido, 4'-isothiocyanostilbene-2,2'-disulphonic acid [SITS]) into single myenteric ganglia. In addition, the myenteric plexus was studied following the iontophoretic injection of an anterograde tracer (Phaseolus vulgaris leucoagglutinin; [PHA-L]) into single submucosal ganglia. Ganglia were visualized by use of differential interference contrast optics and were injected from the beveled tip of a glass micropipette; 2.5-3.0 hours were allotted for retrograde and 20-24 hours (under culture conditions) for anterograde transport. In the myenteric plexus, a small number of the neurons of each injected ganglion were fluorescent and additional neurons in distant myenteric ganglia (predominantly orad) were also retrogradely labeled. About five to six submucosal neurons deep to but not directly underneath the injected myenteric ganglion were labeled by Fluoro-Gold or SITS and only rarely was there more than one labeled neuron in a submucosal ganglion. When control injections of Fluoro-Gold were placed into the muscle instead of a ganglion, some myenteric neurons near the injection site became labeled indicating an innervation of the circular muscle by myenteric neurons; however, there was no labeling of neurons in the submucosal plexus. Similarly, if connections between the myenteric and submucosal plexuses were severed before injecting Fluoro-Gold, no submucosal neurons were labeled. Following injection of PHA-L into a single submucosal ganglion, small-diameter axons were labeled in approximately 2 myenteric ganglia as well as in several distant submucosal ganglia (mainly anal and circumferential to the injection site). Additional labeled fibers traveled with blood vessels or surrounded mucosal crypts. It is concluded that submucosal neurons project to the myenteric plexus as well as to the mucosa and to one another. These observations are consistent with the hypothesis that at least some intrinsic enteric primary afferent neurons reside in the submucosal plexus.
肠神经系统（ENS）无需大脑或脊髓输入即可介导反射活动。因此，ENS包含内在初级传入神经元，这些神经元将黏膜感觉受体与肌间神经丛中的运动神经元相连。肠道的内在初级传入神经元尚未被识别。虽然已知黏膜下神经丛支配着存在肠感觉受体的黏膜，但此前尚未发现从黏膜下到肌间的投射。为了确定此类投射是否存在，在向单个肌间神经节微量注射逆行示踪剂（荧光金或4-乙酰氨基-4'-异硫氰酸芪-2,2'-二磺酸[SITS]）后，对黏膜下神经丛进行了检查。此外，在向单个黏膜下神经节离子电渗注射顺行示踪剂（菜豆白细胞凝集素；[PHA-L]）后，对肌间神经丛进行了研究。通过微分干涉对比光学观察神经节，并从玻璃微吸管的斜面尖端进行注射；逆行运输分配2.5 - 3.0小时，顺行运输（在培养条件下）分配20 - 24小时。在肌间神经丛中，每个注射神经节的少数神经元呈荧光，远处肌间神经节（主要是口侧）的其他神经元也被逆行标记。在注射的肌间神经节下方但不直接在其正下方约五到六个黏膜下神经元被荧光金或SITS标记，并且在一个黏膜下神经节中很少有一个以上的标记神经元。当将荧光金对照注射到肌肉而非神经节中时，注射部位附近的一些肌间神经元被标记，表明肌间神经元支配环行肌；然而，黏膜下神经丛中的神经元没有被标记。同样，如果在注射荧光金之前切断肌间和黏膜下神经丛之间的连接，则没有黏膜下神经元被标记。在向单个黏膜下神经节注射PHA-L后，约2个肌间神经节以及几个远处的黏膜下神经节（主要是肛门侧和注射部位周围）中的小直径轴突被标记。另外的标记纤维与血管伴行或围绕黏膜隐窝。得出的结论是，黏膜下神经元投射到肌间神经丛、黏膜以及彼此之间。这些观察结果与以下假设一致，即至少一些内在肠初级传入神经元存在于黏膜下神经丛中。
