Generation of Metachronal Motor Patterns in Segmented Nervous Systems

脊椎动物和节肢动物的运动是一种复杂的行为，在运动过程中协调其肢体的神经机制还没有很好的理解。 淡水螯虾的腹泳节系统为研究体节间的运动协调提供了一个相对简单易行的系统。 在尾巴的每一节内，游泳桨显示出交替的动力冲程和回击，就像大多数运动附肢一样，相邻节的冲程显示出特定的时间关系。 每个节段内都有神经元（神经细胞）的小回路，这些神经元具有已知的可识别的单个细胞来驱动特定的运动，以及三种类型的中间神经元参与协调运动。 特别有用的是，螯虾腹神经索和游泳系统可以在体外分离，并且仍然显示出节间协调的游泳模式。 这个项目使用了一种结合生理和计算建模的方法来定义模式的动态电路。 神经细胞生理特性和网络连接的细胞模型被用来预测系统中相关神经元的神经脉冲活动的突发的相位模式。 这些预测进行了比较，在个别神经元的活动模式和连接生理记录在生活电路中，包括小电位在突触连接对单神经元之间，以及段之间的脉冲流量。 局部和intersegmented途径的相对重要性进行评估，刺激个人协调interneurons时，intersegmented途径是完整的，当他们被封锁。 细胞内染料填充在解剖学上证实了生理连接途径。 通过实验结果对模型进行改进，将对中间神经元的动力学如何有助于稳定的节间协调以及突触的特性如何有助于正常运动进行全面描述。 这项工作将产生超越甲壳类动物运动研究的影响，通过导致对神经机制的新见解，这些神经机制是更复杂的脊椎动物运动回路的基础。 计算建模与生理学的整合也将对神经科学和生理学领域的学生和博士后研究人员所需的多学科培训产生影响。

Locomotion in vertebrates and arthropods is a complex behavior, and the neural mechanisms that coordinate their limbs during locomotion are not well understood. The abdominal swimmeret system of the crayfish provides a relatively simple and accessible system to study the intersegmental coordination of movement. Within each segment of the tail, the swimmeret paddles show an alternating power stroke and a return stroke, as in most locomotor appendages, and the strokes of adjacent segments show specific timing relationships. There are small circuits of neurons (nerve cells) within each segment that have known identifiable single cells driving particular motor movements, and three types of interneurons that are involved in coordinating the movements. It is particularly useful that the crayfish ventral nerve cord and swimmeret system can be isolated in vitro and still show the intersegmentally coordinated swimming pattern. This project uses a combined physiological and computational modeling approach to define the dynamic circuitry for the pattern. A cellular model of the nerve cell physiological properties and network connections is used to predict the phase patterns of bursts of nerve impulse activity of the relevant neurons in the system. These predictions are compared with the activity patterns and connectivity in individual neurons recorded physiologically in the living circuit, including the small electrical potentials at synaptic connections between pairs of single neurons as well as the impulse traffic between segments. The relative importance of local and intersegmental pathways are assessed by stimulating individual coordinating interneurons when the intersegmental pathways are intact and when they are blocked. Intracellular dye fills anatomically confirm physiological connecting pathways. Refinements of the model by the experimental findings will yield a thorough description of how the dynamics of the interneurons contribute to stable intersegmental coordination, and how the properties of the synapses contribute to normal locomotion. This work will have an impact beyond crustacean locomotion research, by leading to new insights about neural mechanisms that underlie the much more complex vertebrate circuits for locomotion. The integration of computational modeling with physiology will also have an impact on needed multi-disciplinary training of students and postdoctoral researchers in neuroscience and physiology in general.