Lnenicka 9511558 The development and regeneration of the nervous system is highly dependent upon the properties of the growing tip of the nerve cell, the growth cone. Growth cones control the extent and direction of nerve cell elongation and, thus, allow the formation of appropriate connections in the nervous system. The actions of growth cones are largely regulated by their level of intracellular calcium. Calcium enters the growth cone through calcium channels and is removed through a number of processes collectively referred to as calcium buffering. Nerve cells show differences in their properties of growth. Differences in the regulation of intracellular calcium and/or the sensitivity of growth cones to intracellular calcium play an important role in these differences in nerve cell growth. The purpose of this research is to define the role of calcium regulation and calcium sensitivity in these differences in nerve cell growth. In addition, the factors responsible for the development of these differences in growth cone properties will be examined. In particular, the hypothesis that the previous activity or "use" of nerve cells affects their properties of regeneration will be tested. These studies are possible by utilizing the relatively simple invertebrate nervous system, where large identified cells with differences in activity and growth cone properties can be directly examined. The studies will be performed using previously developed cell-culture techniques for studying the growth of regenerating axons of nerve cells. Axon growth will be followed using time-lapse video-microscopy of growth cones. Recently developed methods for measuring intracellular calcium concentration using imaging techniques will be used to determine the sensitivity of the growth cones to intracellular calcium, and their calcium buffering capacity. Calcium influx will also be directly measured in growth cones. These studies will contribute to our understanding of the basic mechanisms invo lved in the growth and regeneration of nerve cells.
