The Regulation of Neuronal Production during Retinal Neurogenesis

Abstract

The vertebrate central nervous system is composed of a large number of different types of neurons that can be distinguished on the basis of morphology, biochemistry, and electrophysiology. During the development of the nervous system, these various kinds of neurons are produced in precise ratios with respect to one another, resulting in the appropriate numbers of the different cell types necessary for the functioning of the adult nervous system. How these different cell types are generated in the correct numbers and ratios is a central problem of developmental neurobiology. While there is some information concerning the factors involved in the origin of cellular diversity in the peripheral nervous system (Patterson, 1978; Le Douarin, 1986; Rohrer et al, 1986) and work in neural crest has shown that a variety of environmental factors can influence the particular phenotype the neural crest cell ultimately achieves, little is known about the mechanisms that give rise to the even greater cellular diversity in the central nervous system. The question of how the precise ratios of neurons found in the adult CNS arise during development is the subject of this chapter. While cell death is likely to play a very important role in regulating final neuronal numbers in many areas of the CNS (Cowan, 1973), this aspect of neural development is reviewed in other chapters in this volume (Chapters 7, 9, and 10) and therefore will only be considered briefly in this chapter.