Comparative developmental neurobiology of molluscs and zebrafish

神经系统的发育和进化起源通常是不清楚的。例如，第一批神经元是在什么时候在不同动物的生命中发育出来的？这些细胞的功能是什么？单个神经元或神经回路能在不同的动物群体之间被识别吗？如果是这样的话，动物之间细胞和回路的哪些特征是一致的，哪些是不同的，从而允许进化变化？我们建议通过集中在3个不同的神经回路来回答这些问题，这些回路可以根据保守的神经递质内容和发育细节来识别。1)软体动物幼虫神经元与感觉功能有关。在软体动物幼虫体内发育的一些最早的细胞含有神经递质5-羟色胺。这些细胞似乎是感觉性的，并控制着与摄食和运动有关的纤毛。此外，在其他海洋无脊椎动物幼虫中也可以识别出相似的细胞，从而表明共同的进化起源(即同源性)。我们建议通过研究组胺、氨基丁酸(GABA)、乙酰胆碱和可能的谷氨酸的分布来扩大含有其他已知递质的幼虫细胞的目录，这些物质似乎都在成体软体动物的化学感觉和平衡感中发挥作用，但在软体动物或其他海洋幼虫的发育中尚未被研究。然而，我们假设，递质特异性标记将允许识别广泛存在于动物界的同源神经元，而这些同源神经元的识别将为神经系统的早期进化提供新的见解。2)斑马鱼的嗅觉通路。我们之前已经研究了感觉神经元轴突在进入嗅球时是如何组织的。接下来，我们将集中研究嗅球内含有GABA和多巴胺的中间神经元的发育，这种神经元在脊椎动物中随处可见。3)斑马鱼的心内神经系统。通过释放乙酰胆碱和去甲肾上腺素来控制心脏的自主神经通路的解剖学现在在鱼类中得到了很好的描述，并且与控制哺乳动物心脏的那些通路惊人地相似。接下来，我们将研究这些通路的个体发育，并深入了解它们何时开始发挥作用。

The developmental and evolutionary origins of the nervous system are generally unclear. When, for example, do the first neurons develop in the lives of different animals? What are the functions of these cells? Can individual neurons or neural circuits be recognized between different groups of animals? If so, which features of the cells and circuits are consistent between animals and which ones vary to permit evolutionary change? We proposed to answer such questions by focusing on 3 different neural circuits that can be recognized on the bases of conserved neurotransmitter contents and details of development. 1) Larval neurons related to sensory functions in molluscs. Some of the very first cells to develop in molluscan larvae contain the neurotransmitter serotonin. These cells appear to be sensory and to control cilia involved in feeding and locomotion. Furthermore, similar cells can be recognized in other marine invertebrate larvae, thus suggesting common evolutionary origins (i.e., homology). We propose to expand the catalogue of larval cells containing other known transmitters by examining the distributions of histamine, -amino butyric acid (GABA), acetylcholine and possibly glutamate which all appear to play roles in chemosensation and the sense of balance in adult molluscs but have not yet been studied in developing molluscs or other marine larvae. We hypothesize, however, that transmitter-specific labels will permit the identification of homologous neurons that are widespread in the animal kingdom, and identification of these homologues will provide new insights into the early evolution of nervous systems. 2) Olfactory pathways in zebrafish. We have previously studied the development of how axons of sensory neurons are organized as they enter the olfactory bulb. We will next concentrate on the development of interneurons within the olfactory bulb which contain on GABA and dopamine and are found throughout the vertebrates. 3) Intracardiac nervous system in zebrafish. The anatomy of autonomic pathways controlling the heart through the release of acetylcholine and norepinephrine are now well described in fish and are strikingly similar with those controlling the hearts of mammals. We will next seek to examine the ontogeny of those pathways and gain insights into when they first become functional.