Scanning Electron Microscope Studies on the Development of the Nervous System in Vivo and in Vitro

Abstract

This chapter discusses the scanning electron microscope (SEM) studies on the development of the nervous system in vivo and in vitro . The interpretations of the observations, made by several light and electron microscope investigations, differ to such an extent that several different theories as to the mechanisms of migration have been proposed. These contradictory interpretations have their origin in the difficulties in obtaining a three-dimensional representation of the nervous structures imposed by conventional serial-sectioning techniques. The SEM allows approaching this problem in a new way. Particularly in the field of biology, the SEM has proved to be a valuable tool in the examination of free surfaces. The ventricular surface of the nervous system is a convenient subject for SEM observation, and in this case the preservation of topographical relationships is optimal. Three classes of differently shaped mitotic cells were recognized by investigators : (1) pyriform cells, with very long, fine, basal processes, probably in prophase or prometaphase, (2) conical cells with many microvilli, considered to be in prometaphase and early anaphase, and (3) globular cells without microvilli, representing cells in metaphase and late anaphase.