IONIC CONTROL OF NERVE FIBER GROWTH AND SURVIVAL

局部用药控制神经纤维生长和存活的研究进展 提出了胞外钾的变化。一个被隔开的 将采用大鼠细胞体轴突的培养制剂 位于一个隔室中的神经元跨越硅胶润滑脂屏障生长 进入单独的隔间。以这种方式，流动的环境 远端轴突可以独立于流体环境进行控制 胞体和近端轴突。远端轴突可以在任何时候切除 时间和迅速再生。这允许相同的轴突再生 在不同条件下要连续观察的神经元数量 在实验条件下，随着神经元在体外的发育和老化。 轴突延伸的显微测量和显微照相 神经突起密度的比较将用于评估生长情况。另外， 隔室培养中的神经元可以在慢性电刺激下 刺激，允许有关实验的执行 电活动在生长发育中的作用。除了工作之外 对于分区培养，建议测量[K+]e的变化 通过K+选择性微电极在体内发生。 这项提案中涉及的问题是由于所作的观察而产生的 在这个实验室里使用了隔间培养。神经突起 交感神经元、背根神经节神经元和脊髓神经元 可被排除进入局部增加的胞外区域 钾([K+]e)。此外，[K+]e的近端-远端沿 神经突起对神经突起的生长有多种倒退作用， 再生和存活：伸长可以减慢，这是一个极端 神经突起可能随之回缩，并可能发生完全变性。 这些观察结果对神经纤维的机制有一定的启示。 伸长，而且它们也增加了自然的 体内正常发育过程中[K+]e的变化可能会很强烈 影响建立和/或维持相互之间的连接 神经元。例如，神经纤维在活动期间释放的K+可能 调节突触后部位的竞争性相互作用。它也是 [K+]e变化引起的倒退变化可能具有 对再生、衰老和癫痫发作活动问题的影响 在神经系统中。建议进行以下实验：(1)表征 局部K+升高对外周和中枢神经元的影响 特别强调随着发展和老龄化而发生的变化 体内和体外，(2)研究这些作用的机制，(3) 开始收集有关[K+]e变化幅度有多大的信息 发生在体内发育过程中，以及(4)建立体外系统以 研究活动对突触形成的长期影响和 维修。

Investigations into the control of nerve fiber growth and survival by local variations in extracellular potassium are proposed. A compartmentalized culture preparation will be employed in which axons from cell bodies of rat neurons located in one compartment grow across silicone grease barriers to enter separate compartments. In this way the fluid environment of the distal axons can be controlled independently of the fluid environment of the cell bodies and proximal axons. The distal axons can be removed at any time and promptly regenerate. This allows axonal regeneration of the same population of neurons to be observed sequentially under different experimental conditions and as the neurons develop and age in vitro. Micrometric measurements of neurite extension and photomicrographic comparisons of neurite density will be used to evaluate growth. Also, neurons in compartmentalized cultures can be chronically electrically stimulated, permitting the performance of experiments concerned with the role of electrical activity in growth and development. In addition to work with compartmentalized cultures, it is proposed to measure changes in [K+]e that occur in vivo by means of K+-selective microelectrodes. The questions addressed in this proposal arise because of observations made in this laboratory employing compartmentalized cultures. Neurites of sympathetic neurons, dorsal root ganglion neurons and spinal cord neurons can be excluded from entering a region of locally increased extracellular potassium ([K+]e). Also, a proximo-distal increase in [K+]e along the neurites has a variety of regressive effects on neurite growth, regeneration, and survival: elongation can be slowed, an extreme retraction of neurites can ensue, and complete degeneration can occur. These observations have implications for the mechanism of nerve fiber elongation, and they also raise the far-reaching possibility that natural variations in [K+]e in vivo during normal development may strongly influence the establishment and/or maintenance of connections between neurons. For example, K+ released by nerve fibers during activity may mediate competitive interactions for postsynaptic sites. It is also possible that regressive changes induced by variations in [K+]e may have implications for the problems of regeneration, aging, and seizure activity in the nervous system. Experiments are proposed to: (1) characterize the effects of locally elevated K+ on peripheral and central neurons with particular emphasis on changes that occur with development and aging in vivo and in vitro, (2) investigate the mechanisms of these effects, (3) begin to collect information about what magnitude of changes in [K+]e can occur during development in vivo, and (4) establish an in vitro system to study the long-term effects of activity on synapse formation and maintenance.