Neural pathways in invertebrate nervous systems

我的实验室率先研究了简单的无脊椎动物神经系统，特别是果蝇黑腹果蝇的视觉系统和脊椎动物近亲海鞘的蝌蚪幼虫的中枢神经系统。利用电子显微镜，我们已经在这些微小的大脑中生成了突触网络的综合图，或连接体，这是一种研究神经功能的方法，现在已经比迄今为止得到了更广泛的认可。我们将继续采用这些方法，利用生物多样性的先进方法。这个问题本身很简单。大脑是一个网络，是由已识别的神经元之间的突触接触形成的。这些完整的连接组构成了对任何大脑的正式定义，对于我们建立动物行为的电路基础至关重要，这是神经科学的终极目标。当然，这个想法并不新鲜，最近电子成像的发展，特别是快速的计算机三维重建方法，使这个想法成为可能。功能研究允许突触传递被禁用，然后揭示了已识别的神经元在特定行为中所起的作用，这是连接组的最终价值。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的12种已识别的神经元类的视觉回路，这些神经元类在每个柱或盒中，在视觉层中，它们之前已经定义了进化关系。这将揭示突触回路如何在同源神经元之间进化，以服务于相关物种的不同视觉行为。我们的工作还将探讨大脑的进化是如何从突触回路的进化中进行的，突触回路是由这些视觉行为所选择的。***2)我们将重建一种相关的基础脊索动物的部分中枢神经系统的连接体，这是一种在海洋食物链中非常重要的物种——Oikopleura dioica的幼虫。像Ciona一样，它的中枢神经系统有一个恒定的细胞数量，但这些形式的电路是未知的，可能是上皮传导途径的补充。我们将研究足够小的幼虫阶段，以便从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，我们将记录下侏儒乌贼（Idiosepius）中枢神经系统中臂神经节的连接体。这个微小的头足类动物足够小，可以在复合显微镜浸泡物镜下放置整个支架，我们将使用免疫标记来识别神经元和EM来检查它们在这个重要中继站中的突触回路，最初提供这些回路的单元结构，这些回路调节着这个微小头足类动物的单臂。

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.