Molecular Control of Neural Development

Abstract

There are probably more different cell types in the mature nervous system than in all of the other tissues of the body combined. Estimates of the number of different kinds of neurons vary, depending upon the criteria used to distinguish them, from as low as 1000 to as high as 100,000. Broad classes of neurons can be recognized by their distinctive morphologies, as revealed by the brilliant work of the Spanish neurobiologist Ramón y Cajal. Further divisions can be made on the basis of the neurotransmitters and peptides that neurons secrete, and of the receptors and ion channels they contain. More recently, the advent of monoclonal antibodies and cloned DNA probes has revealed that even neurons that appear morphologically identical can be molecularly distinct. The many classes of neurons in the brain are not mixed randomly but are highly organized in three-dimensional patterns. In the cerebral cortex, for example, different types of neurons are arranged in both layers and columns. How are we to begin to understand the molecular mechanisms that generate a structure of such fantastic diversity and complex architecture?