Contributions of the neocortical SVZ to human brain development

Abstract

One of the main characteristics of the developing CNS is that all neurons and a majority of the macroglia originate in the proliferative layer situated near the lumen of the cerebral ventricles and the central canal in the brain and spinal cord, respectively, and then migrate to their final destinations. In the developing forebrain, this proliferative layer can be subdivided into the ventricular (VZ) and subventricular (SVZ) zones. The SVZ reaches a very large size in the human fetal forebrain where it was originally discovered. This transient zone can be considered a secondary proliferative compartment, which has been mitotically active in the human for several gestational months, serving as a major source of cortical interneurons and glial cells. Besides the SVZ of the dorsal forebrain, two additional secondary proliferative zones in the brain are the ganglionic eminence (GE) at the floor of the lateral ventricle, and the rhombic lip (RL) in the lateral recess of the IVth ventricle. The GE-SVZ produces interneurons and glial cells that migrate tangentially to become incorporated into the structures already containing neurons that have arrived radially from the cortical VZ/SVZs. The enlargements of the secondary proliferative zones in humans can be considered as an evolutionary adaptation to increase selective areas of the central nervous system, and thus have great importance for the expansion and cellular organization of the human cerebral cortex. This chapter focuses on the human fetal neocortical SVZ, which will be referred to as the SVZ or neocortical SVZ throughout the text.