Nonsynaptic Neurotransmitter Effects on Developing Spinal Cord Circuitry

在成人大脑中，神经细胞通过在称为突触的细胞之间的特殊连接处分泌神经递质进行交流，神经递质是一种小的化学信使。当神经递质被分泌时，它穿过突触并与对面的神经细胞相互作用，后者将这种化学信息转化为电子信息。通过这种方式，信息可以在我们大脑的1000亿个神经细胞之间迅速传播，这样我们就可以执行复杂的计算任务，允许我们接收、处理和反应来自我们周围世界的信息。传统上，人们认为在发育中的大脑中，在突触连接形成之前，神经细胞信号传递不需要神经递质。然而，我们现在知道情况并非如此。发育中的神经细胞在建立突触联系之前会分泌神经递质，一系列研究表明，神经递质对发育中的神经组织的生长和成熟具有深远的影响。虽然这项工作为未成熟的脑细胞如何交流提供了重要线索，但很少有人对整个生物体进行研究。我们将通过研究斑马鱼胚胎发育过程中的神经传递来解决这个问题。斑马鱼是一种小型淡水鲤科动物，非常适合进行发育研究，因为受精是在外部进行的，这样就可以很容易地研究胚胎发育的各个步骤。此外，斑马鱼胚胎是透明的，这意味着我们可以在视觉上识别和监控神经细胞在活胚胎中的发育。我们的工作有三大目标。首先，在突触连接形成之前，了解神经递质是否会影响发育中的神经细胞的兴奋性。我们将使用专门的技术来记录暴露于神经递质后未成熟神经细胞的电活动。这将使我们能够定义细胞何时开始对化学信号做出反应，以及这些反应涉及哪种神经递质。我们的第二个目标将是确定胚胎神经细胞是否在没有突触连接的情况下使用神经递质相互交谈。我们将应用化学物质来阻断对分泌的神经递质的反应，并测量这如何影响发育中的神经细胞的电活动。这将使我们能够确定发育中的神经系统的神经细胞何时开始通信。我们的最终目标是确定未成熟神经传递在斑马鱼胚胎中的作用。我们将使用分子遗传学方法从发育开始就扰乱神经递质信号，并确定这如何影响神经系统的组装。我们将重点放在产生游泳的神经细胞网络上，因为它可以用作行为研究的简单模型网络。通过这种方式，我们将能够研究递质信号的中断如何影响神经发育的许多方面，从单个细胞的生长和成熟，到神经细胞网络的活动和行为的产生。我们的工作将为胚胎神经传递的重要性提供新的认识，并可能为神经递质活动失衡如何导致发育性疾病提供重要线索。

In the adult brain, nerve cells communicate by secreting neurotransmitters, small chemical messengers, at specialized junctions between cells called synapses. When neurotransmitter is secreted, it crosses the synapse and interacts with the apposing nerve cell which converts this chemical message into electrical information. In this way, information can rapidly spread between the 100 billion nerve cells of our brain so that complex computational tasks can be performed that allow us to receive, process and react to information from the world around us. Traditionally, it was believed that in the developing brain, before synaptic junctions form, neurotransmitters were not required for nerve cell signalling. However, we now know that this is not the case. Developing nerve cells secrete neurotransmitter before they establish synaptic contacts and a range of studies show profound neurotransmitter effects on the growth and maturation of developing nervous tissue. Whilst this work has provided important clues about how immature brain cells communicate, few whole organism studies have been undertaken. We will address this problem by studying neurotransmission during development of the zebrafish embryo. The zebrafish, a small freshwater cyprinid, is ideal for developmental studies because fertilization occurs externally so that steps during embryonic development can be easily studied. In addition, zebrafish embryos are transparent which means that we can visually identify and monitor nerve cells as they develop within a living embryo. Our work has three broad aims. The first is to understand whether neurotransmitters affect the excitability of developing nerve cells before synaptic junctions form. We will use specialized techniques to record electrical activity in immature nerve cells following exposure to neurotransmitters. This will allow us to define when cells first become responsive to chemical signalling and what kind of neurotransmitters are involved in these responses. Our second aim will be to determine if embryonic nerve cells use neurotransmitter to talk to one another in the absence of synaptic junctions. We will apply chemicals to block responses to secreted neurotransmitters and measure how this affects electrical activity of developing nerve cells. This will allow us to determine when nerve cells of the developing nervous system begin to communicate. Our final aim is to determine the role for immature neurotransmission in the zebrafish embryo. We will use molecular genetic methods to disrupt neurotransmitter signalling from the onset of development and determine how this affects assembly of the nervous system. We will focus on the nerve cell network that generates swimming as it can be used as a simple model network for the study of behaviour. In this way we will be able to examine how disruptions in transmitter signalling impact on the many aspects of nervous development, from the growth and maturation of individual cells through to the activity of nerve cell networks and the generation of behaviour. Our work will cast new light on the importance of embryonic neurotransmission and may provide important clues about how imbalances in neurotransmitter activity cause developmental disease.