DEVELOPMENT OF NEURONAL CIRCUITS FOR SIMPLE BEHAVIORS

这项研究的目的是了解发育中的神经元 在特定的神经元上形成突触， 电路.这些机制将在一个相对简单的神经网络中进行研究。 因为它的许多神经元可以被 甚至在他们开始成长之前就已经确定了 突触的位置。此外，我们还知道很多关于 这些可识别的神经元的形态和生理特性， 包括它们中的许多在产生行为中所起的作用。 实验将集中在两个井的连接的发展- 定义的神经回路：一对已识别的 运动神经元，两者都支配体壁中的相同肌肉， 并且以反射路径的方式连接， 受体、效应神经元和少量的中间层 的中间神经元。 特异性的生成将使用以下方法进行处理 技术：详细的空间形态学检查 神经元分支之间的关系作为接触是第一 建立;从突触连接的生理记录， 它们形成;单个神经元的消融，神经元分支的消融，或 来扰乱神经元活动的环境 正在发展。这些实验将确定哪些机制 在这个明确的系统中运行。例如，我们将测试 神经元与它们所连接的任何其他神经元形成突触， 在特定的时间足够接近;潜在的突触是否 目标对环境信号的反应方式 尽管这两个神经元的行为 相互独立;竞争是否发生突触 神经元之间的空间，可能有资格形成突触到 同一个神经元;神经元的外围目标如何控制 它将接受的突触;以及电活动是否对 建立或维持突触联系。其他实验 物种，包括高等哺乳动物，已经表明，这些相同的 控制人类突触特异性的机制。实验 胚胎期水蛭神经系统的可塑性使得 研究这些机制如何相互作用以形成功能性神经元回路 在一个物种中的许多已识别的神经元中， 揭示了功能性神经元回路是如何在我们的大脑中建立的， 自己的神经系统。

The objective of this research is to understand how developing neurons form synapses onto particular neurons to form a functional neuronal circuit. These mechanisms will be studied in a relatively simple nervous system--that of the medicinal leech--because many of its neurons can be identified even before they start to grow the processes that will be the sites of synapses. In addition, a great deal is known about the morphological and physiological properties of these identifiable neurons, including the role that many of them play in generating behavior. Experiments will focus on the development of connections in two well- defined neural circuits: the connection between a pair of identified motor neurons, both of which innervate the same muscles in the body wall, and the connections in a reflex path way that includes a sensory receptor, an effector neuron, and an intervening layer of a small number of interneurons. The generation of specificity will be approached using the following techniques: detailed morphological examinations of the spatial relationship between neuronal branches as the contacts are first established; physiological recordings from the synaptic connections as they form; and ablations of single neurons, of branches of neurons, or of peripheral targets, to perturb the environment in which the neurons are developing. These experiments will determine which mechanisms are operating in this well-defined system. For example, we will test whether neurons form synapses with any other neurons to which they are sufficiently close at a particular time; whether potential synaptic targets respond to environmental signals in a way that puts their branches in close proximity, even though the two neurons are behaving independently of one another; whether competition occurs for synaptic space between neurons that might he eligible to form synapses onto the same neuron; how the peripheral target of a neuron can control which synapses it will accept; and whether electrical activity is important for establishing or maintaining synaptic contacts. Experiments on other species, including higher mammals, have suggested that these same mechanisms control synaptic specificity in humans. The experimental tractability of the embryonic leech nervous system makes it possible to examine how the mechanisms interact to form a functional neuronal circuit among a number of identified neurons in a single species, thereby shedding light on how functional neuronal circuits are established in our own nervous system.