Croll R P
Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4H7.
Microsc Res Tech. 2000 Jun 15;49(6):570-8. doi: 10.1002/1097-0029(20000615)49:6<570::AID-JEMT7>3.0.CO;2-Q.
Pond snails have long been the subject of intense scrutiny by researchers interested in general principles of development and also cellular and molecular neurobiology. Recent work has exploited both these fields of study by examining the ontogeny of the nervous system in these animals. Much of this work has focussed upon the development of specific transmitter phenotypes to provide vignettes of neuronal subpopulations that can be traced from early embryonic life through to adulthood. While such studies have generally confirmed previous explanations of gangliogenesis in gastropods, they have also indicated the presence of several neurons that appear earlier and in positions inconsistent with classical views of gastropods neurogenesis. The earliest of these cells contain FMRFamide-related peptides and have anteriorly projections that mark the future locations of ganglia and interconnecting pathways that will comprise the postembryonic central nervous system. These posterior, peptidergic cells, as well as certain, apical, monoaminergic neurons, disappear and apparently die near the end of embryonic life. Finally, populations of what appear to be peripheral sensory neurons begin to express catecholamines by around midway through embryonic life. Like several of the neurons expressing a variety of transmitters in the developing central ganglia, the catecholaminergic peripheral cells persist into postembryonic life. Transmitter phenotypes, cell shapes and locations, and neuritic morphologies all suggest that many of the neurons observed in early embryonic pond snails have recognizable homologues across the molluscs. Such observations have profoundly altered our views of neurogenesis in gastropods over the last few years. They also suggest the promise for pond snails as fruitful models for studying the roles and mechanisms for pioneering fibres, cues triggering apoptosis, and contrasting origins and mechanisms employed for generating central vs. peripheral neurons within a single organism.
长期以来，池塘蜗牛一直是对发育的一般原理以及细胞和分子神经生物学感兴趣的研究人员密切关注的对象。最近的研究通过检查这些动物神经系统的个体发育，利用了这两个研究领域。这项工作的大部分都集中在特定递质表型的发育上，以提供神经元亚群的实例，这些亚群可以从胚胎早期一直追踪到成年期。虽然这些研究总体上证实了之前对腹足纲动物神经节形成的解释，但它们也表明存在一些神经元，这些神经元出现得更早，而且位置与腹足纲动物神经发生的经典观点不一致。这些最早的细胞含有与FMRF酰胺相关的肽，并且有向前的投射，这些投射标记了神经节的未来位置以及将构成胚胎后中枢神经系统的相互连接的通路。这些位于后部的肽能细胞，以及某些位于顶端的单胺能神经元，在胚胎生命接近尾声时消失并显然死亡。最后，在胚胎生命大约中期左右，一群看似外周感觉神经元开始表达儿茶酚胺。与发育中的中枢神经节中表达多种递质的一些神经元一样，儿茶酚胺能外周细胞持续到胚胎后生命期。递质表型、细胞形状和位置以及神经突形态都表明，在早期胚胎池塘蜗牛中观察到的许多神经元在整个软体动物中都有可识别的同源物。在过去几年里，这些观察结果深刻地改变了我们对腹足纲动物神经发生的看法。它们还表明，池塘蜗牛有望成为研究先驱纤维的作用和机制、触发细胞凋亡的线索以及在单个生物体内产生中枢神经元与外周神经元的不同起源和机制的有效模型。
