Neural pathways in invertebrate nervous systems

我的实验室对简单的无脊椎动物神经系统进行了开创性的研究，特别是果蝇的视觉系统和海鞘的蝌蚪幼虫的中枢神经系统(CNS)，后者是脊椎动物的近亲。使用电子显微镜，我们已经在这些微小的大脑中生成了突触网络的全面地图或连接，这是一种神经功能的方法，现在得到了比以往更广泛的认可。我们将使用利用生物多样性的先进方法，继续这些方法。这个问题本身很简单。大脑是一个网络，由识别出的神经元之间的突触接触形成的网络。这些形式的完整连接体构成了对任何大脑的正式定义，对于了解我们是否要为动物行为建立电路基础至关重要，这是神经科学的最终目标。当然，这种想法并不新鲜，电子成像的最新发展，特别是快速的计算机3D重建方法，现在已经使这种想法成为可能。功能研究允许禁止突触传递，然后揭示识别出的神经元在特定行为中所起的作用，这是连接体的最终价值。我们将把这些想法应用于下面描述的三个精心挑选的神经系统。 1)我们将比较夏威夷果蝇精选物种视板中每个柱或盒中12个已识别神经元类别的视觉回路，这些物种之前已确定了进化关系。这将揭示同源神经元之间的突触电路是如何进化的，以辅助相关物种的不同视觉行为。我们的工作还将解决大脑是如何从突触电路的进化中进化出来的，这些突触回路是由这些支持的视觉行为选择的。 2)补充我们发表的关于Ciona幼虫CNS的工作，我们将重建一种相关的基础脊索动物Oikopleura dioica的CNS的部分连接组，Oikopleura dioica是一种在海洋食物链中非常重要的物种。像Ciona一样，它的CNS有一个恒定的细胞数量，但这些形式的回路尚不清楚，可能还有上皮传导通路作为补充。我们将用足够小的幼虫阶段从EM系列中进行检查，并为未来的成像和其他功能研究提供足够的透明度。 3)在一个全新的神经系统选择中，也利用了Dalhousie在海洋资源方面的独特优势，我们将记录侏儒鱿鱼Idiosepius中枢神经系统中臂神经节的连接体。这种微小的头足类动物足够小，可以安装在一个复合显微镜浸泡物镜下，我们将使用免疫标记来识别神经元，并在这个重要的中继站使用EM来检查它们的突触电路，最初是为了提供那些调节这种微小头足类动物单臂的电路的单元结构。

My lab has pioneered studies on simple invertebrate nervous systems, in particular the visual system of the fruit fly Drosophila melanogaster and the central nervous system (CNS) of the tadpole larva in the ascidian Ciona intestinalis, a close sibling relative of vertebrates. Using electron microscopy, we have generated comprehensive maps, or connectomes, of synaptic networks in these tiny brains, an approach to neural function that has now become far more widely recognized than hitherto. We will continue these approaches, using advanced methods harnessed to biological diversity. The question itself is simple enough. The brain is a network, one formed by synaptic contacts between identified neurons. The complete connectome these form constitutes a formal definition of any brain, essential to know if we are ever to establish the circuit basis for animal behaviour, an ultimate objective in neuroscience. Certainly not new, this idea is now enabled by recent developments in electron imaging and especially by rapid computer 3D reconstruction methods. Functional studies that allow synaptic transmission to be disabled then reveal the role that identified neurons play in specific behaviours, the ultimate value of a connectome. We will apply these ideas to three carefully chosen nervous systems described below. 1) We will compare the visual circuits of 12 identified neuron classes in each column, or cartridge, in the optic lamina of select species of Hawaiian drosophilids, which have previously defined evolutionary relationships. This will reveal how synaptic circuits have evolved among homologous neurons to subserve different visual behaviours in related species. Our work will also address how the evolution of brains has proceeded from the evolution of their synaptic circuits, selected by the visual behaviours these support. 2) Complementing our published work on the larval CNS of Ciona we will reconstruct the connectome for parts of the CNS of a related basal chordate, the larvacean, Oikopleura dioica, a species immensely important in the sea's food chains. Like Ciona, its CNS has a constant cell number, but the circuits these form are not known and may be supplemented by epithelial conduction pathways. We will work with larval stages small enough to examine from EM series, and sufficiently transparent for future imaging and other functional studies. 3) In an entirely new choice of nervous system that also exploits Dalhousie's unique strength in marine resources, we will document the connectome of the brachial ganglion in the CNS of the pygmy squid, Idiosepius. This tiny cephalopod is small enough to fit in whole-mounts beneath a compound microscope immersion objective, and we will use immunolabelling to identify neurons and EM to examine their synaptic circuits in this important relay station, initially to provide the unit structure of those circuits that regulate a single arm of this tiny cephalopod.