Contemporary Sensory Neurobiology

same chemical stimulus and thereby attain their characteristic morphologies. Also included are observations of growing neurons from a mouse cerebellar mutant, and two papers on the role of nerve growth factor and laminin in determining the direction of neural elongation. The last section deals with a relatively new subspecialty, the electrophysiological study of the growth cone. It has long been known that an external electric field can affect the direction of neurite growth, but the mechanisms underlying this effect are largely unknown. This section presents some exciting new data and techniques addressing that issue. Of particular interest is M.-M. Poo's demonstration that a growth cone will respond to an extremely small local current, on the order of that produced by embryonic muscle fibers. Such observations, paired with Freeman et al.'s method for measuring the tiny voltage gradients around a growth cone, can clarify what role, if any, electrical fields play in neural development. This last chapter especially confirms the volume's aim: to present state-of-the-art techniques in the study of growth cones, rather than to provide a comprehensive introduction to the basic issues of growth cone behavior. A more intensive review, instead of the brief preface, might make this volume appropriate for a newcomer to the field. In addition, the problem of embryonic cell motility might be addressed in greater depth. Clearly, one intent of the editors is to show that growth cone study can tell the cell biologist much about general rules of embryonic cell movement, and vice versa. This collection demonstrates that understanding of these highly dynamic structures is becoming essential to the study of neuronal development and plasticity proper, and that we are just beginning to lay the technical groundwork for such study.