Obaid A L, Nelson M E, Lindstrom J, Salzberg B M
Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6074, USA.
J Exp Biol. 2005 Aug;208(Pt 15):2981-3001. doi: 10.1242/jeb.01732.
Nicotinic transmission in the enteric nervous system (ENS) is extensive, but the role of individual nicotinic acetylcholine receptor (nAChR) subtypes in the functional connectivity of its plexuses has been elusive. Using monoclonal antibodies (mAbs) against neuronal alpha3-, alpha4-, alpha3/alpha5-, beta2-, beta4- and alpha7-subunits, combined with radioimmunoassays and immunocytochemistry, we demonstrate that guinea-pig enteric ganglia contain all of these nAChR-subunits with the exception of alpha4, and so, differ from mammalian brain. This information alone, however, is insufficient to establish the functional role of the identified nAChR-subtypes within the enteric networks and, ultimately, their specific contributions to gastrointestinal physiology. We have used voltage-sensitive dyes and a high-speed CCD camera, in conjunction with specific antagonists to various nAChRs, to elucidate some of the distinct contributions of the individual subtypes to the behaviour of enteric networks. In the guinea-pig, the submucous plexus has the extraordinary advantage that it is virtually two-dimensional, permitting optical recording, with single cell resolution, of the electrical activity of all of its neurones. In this plexus, the block of alpha3beta2-, alpha3beta4- and/or alpha7-nAChRs always results in a decrease in the magnitude of the synaptic response. However, the magnitude of the fast excitatory post-synaptic potentials (epsps) evoked by electrical stimulation of a neighbouring ganglion varies from cell to cell, reflecting the differential expression of subunits already observed using mAbs, as well as the strengths of the activated synaptic inputs. At the same time, we observe that submucous neurones have a substantial mecamylamine (Mec)-insensitive (non-nicotinic) component to their fast epsps, which may point to the presence of purinergic or serotonergic fast epsps in this system. In the myenteric plexus, on the other hand, the antagonist-induced changes in the evoked synaptic response vary depending upon the location of the stimulating electrode with respect to the ganglion under study. The range of activity patterns that follows sequential pharmacological elimination of individual subtypes suggests that nAChRs may be capable of regulating the activity of both excitatory and inhibitory pathways, in a manner similar to that described in the central nervous system.
肠神经系统（ENS）中的烟碱传递广泛存在，但单个烟碱型乙酰胆碱受体（nAChR）亚型在其神经丛功能连接中的作用一直难以捉摸。我们使用针对神经元α3、α4、α3/α5、β2、β4和α7亚基的单克隆抗体（mAb），结合放射免疫分析和免疫细胞化学方法，证明豚鼠肠神经节中除α4外含有所有这些nAChR亚基，因此与哺乳动物脑不同。然而，仅凭这一信息不足以确定已鉴定的nAChR亚型在肠神经网络中的功能作用，以及它们最终对胃肠生理学的具体贡献。我们使用电压敏感染料和高速CCD相机，结合针对各种nAChR的特异性拮抗剂，来阐明各个亚型对肠神经网络行为的一些独特贡献。在豚鼠中，黏膜下神经丛具有特别的优势，即它几乎是二维的，允许以单细胞分辨率光学记录其所有神经元的电活动。在这个神经丛中，阻断α3β2、α3β4和/或α7 - nAChR总是导致突触反应幅度降低。然而，通过电刺激相邻神经节诱发的快速兴奋性突触后电位（epsp）的幅度在细胞间存在差异，这反映了使用mAb已经观察到的亚基差异表达，以及激活的突触输入强度。同时，我们观察到黏膜下神经元的快速epsp有很大一部分对美加明（Mec）不敏感（非烟碱型）成分，这可能表明该系统中存在嘌呤能或5 - 羟色胺能快速epsp。另一方面，在肌间神经丛中，拮抗剂诱导的诱发突触反应变化取决于刺激电极相对于所研究神经节的位置。依次药理学消除各个亚型后出现的一系列活动模式表明，nAChR可能能够以类似于中枢神经系统中所描述的方式调节兴奋性和抑制性通路的活动。
