Recent advances in cell and molecular biology suggest that a number of cell surface adhesion and extracellular matrix (ECM) molecules are important for neuronal growth and guidance. The actual role of these molecules, however, must ultimately be determined using in vivo studies. The proposed research will examine the role of these molecules in vivo, using the sympathetic preganglionic projections of the chick. this neural system is ideal for such studies because the anatomy is relatively simple, the development is well understood and the presumptive pathways of growing axons are predictable and accessible for perturbation. Proposed in vivo studies include: (1) the determination of the spatio- temporal expression of cell surface adhesion and ECM molecules that are known to promote neuronal growth in vitro. and (2) the use of functional blockers to examine the role of these molecules on axonal growth and guidance. Cell surface adhesion and ECM molecules will be revealed by immuno- and histochemical staining; their functions will be evaluated according to changes in patterns of preganglionic projections subsequent to local injection of functional blockers to the pathway of preganglionic axons. The role of these molecules on neuronal specificity, growth, and fasciculation will be examined further under less complex and more controlled conditions, by studying the effects of functional blockers on identified neurons grown on tissue explants or cryostat sections in vitro. Finally, as a first step towards identifying novel guidance molecules in sympathetic preganglionic outgrowth, the specificity of preganglionic projections on tissue explants or cryostat sections obtained from embryos of different developmental stages will be examined to provide information of where and when molecular cues are expressed. These systematic studies on the sympathetic nervous system of the chick should provide important insights on axonal guidance mechanisms, knowledge that is extremely difficult to obtain from the complex central nervous system.
