ABSTRACT

Neurons exist within a complex milieu, in which they are exposed to many factors that affect their growth, survival, and function. These factors can be grouped into three general categories: chemical (growth factors, neurotransmitters, or adhesion molecules, which can be either soluble or substratum bound), physical (contours of the three-dimensional space surrounding the cell), and electrical (standing extracellular voltage gradients). During development and repair, neurons use these environmental factors to guide the tips of growing axons, called growth cones, to appropriate targets (e.g., another neuron or a

Introduction ....................................................................................................... 201 Endogenous DC Electric Fields in the Developing Amphibian Nervous System ............................................................................................................... 202 Endogenous DC Electric Fields in the Damaged Nervous System .................. 205 Neuronal Growth Cone Responses to Physiological DC EFs Applied In Vitro ... 208

Tissue Culture Caveats ................................................................................. 212 The Cellular Basis for Directed Growth Cone Guidance ..................................214