9808919 LNENICKA The electrical activity, or "use" of the nervous system plays an important role in its development, maintenance, and modification. In particular, electrical activity can influence the development of mechanisms involved in regulating the internal calcium concentration ( Ca++ i) of nerve cells. The regulation of Ca++ i is very important since internal calcium regulates a broad spectrum of events ranging from neuronal growth during development, to communication between neurons in the adult, to cell death in the aging nervous system. Recent findings show that activity-dependent changes in calcium regulation influence the growth and degeneration of axons (the elongated portion of the nerve cell that forms connections with other cells). The growing tip of the axon, the growth cone, controls the extent and direction of axon elongation and, thus, allow the formation of appropriate connections during development and nerve regeneration. The actions of growth cones are regulated by changes in Ca++ i resulting from calcium entry through channels and calcium removal through its binding to calcium-buffering proteins, uptake into organelles, and extrusion across the outer cell membrane. Moderate changes in Ca++ i can influence the rate of growth, and large increases in Ca++ i can produce axon retraction and degeneration. Increased electrical activity strengthens calcium removal, influencing the response of the growing axon to environmental cues as well making it more resistant to degeneration. Dr. Lnenicka has planned experiments to identify the calcium-removal processes that are strengthened by increased electrical activity, and to determine whether altered activity produces changes in the sensitivity of the growth cone to Ca++ i. He will also examine the effect of increased electrical activity upon the structure of growing axons. Finally, the mechanisms through which electrical activity produces these neuronal changes will be explored. These st udies are possible by utilizing the relatively simple nervous system of the crayfish, where large identified cells with differences in activity and growth cone properties can be directly examined. Dr. Lnenicka has previously developed a cell-culture system of identified crayfish neurons, and in these studies, he will use time-lapse video-microscopy to follow the developing growth cones in the cultures under various treatment conditions. Calcium removal processes will be examined by measuring the changes in Ca++ i in growth cones with the fluorescent calcium indicator, fura-2. Axon and growth cone structure will be examined with light and electron microscopy. These studies will advance our knowledge of the basic mechanisms of nerve regeneration and the influence of experience on the formation and plasticity of the nervous system.
