Nitric Oxide as an Inter- and Intracellular Messenger in Growth Cones

Georgia State University Research Foundation, Inc., Atlanta GA

Investigators

Abstract

Nitric oxide (NO), a non-traditional neurotransmitter/ neuromodulator, has been proposed to play an important role during neuronal development in both vertebrates and invertebrates. The exact location and mode of action of NO, however, is often unknown. Because many of the effects of NO occur during a time in development when neurons are in the process of 'wiring' the nervous system, this proposal tests a series of hypotheses aimed at determining the roles by which NO may function as a signaling molecule at the neuronal growth cone. Growth cones are the motile tips of advancing neuronal processes and lead them to their targets by a process termed pathfinding. The ability of a growth cone to navigate correctly has been demonstrated to depend on its filopodia, which are actin rich protrusions emanating in a fan-like fashion from the leading edge of the growth cone, and which function as 'remote sensors' exploring the molecular environment ahead of the growth cone proper. Preliminary evidence suggests that NO causes a transient increase in filopodial length and a decrease in the speed with which a growth cone advances. The same morphological changes are typically seen in growth cones approaching a decision area in vivo, suggesting that NO may act as a guidance cue and thus could play an important role in the process by which the nervous system is being 'wired'. This proposal has two specific aims which will investigate novel mechanisms by which NO could act at the growth cone to influence the outcome of pathfinding decisions. Dr. Rehder's research will be performed on a well-established model system, identified neurons from the central nervous system of the pond snail Helisoma trivolvis, and will employ laser confocal microscopy, photolysis of caged compounds, Ca2+-imaging, electrophysiology, pharmacology, and immunohistochemistry. The advantage of this preparation is that the snail nervous system offers large and identified neurons that can be studied in isolation and under controlled conditions in vitro. The results from this research will serve as an important stepping stone towards our long-term goal: to identify the role of NO during neuronal pathfinding in developing and regenerating nervous systems. The proposed work also has strong educational and outreach components. It contains projects particularly suited for undergraduate students and will involve students and K-12 teachers in developing teaching modules for community outreach activities that serve all Georgians.