Neuronal changes during development and evolution (an overview).

Abstract

This overview highlights the presentations made by several authors, with sidelights commentaries on the topics covered in this session. The Neurotropic hypothesis, formulated by Cajal more than one century ago, has been one of the fundamental tenets of modern Neuroscience. Research work is unveiling highly complex molecular mechanisms by means of which neuronal processes grow in the right direction leading to the formation of neural networks. Another interesting topic covered in this session pertains to the remarkably conserved similarity of most parts of the brain between reptiles, birds and mammals. The presence of the neocortex, which occurs in mammals, is discussed on the basis of different migratory behavior during development. The question of neuronal stability throughout the life cycle raises interesting aspects on the generation of new neurons. This is a particularly timely topic because recent evidence, denied by others, has shown the generation of new neocortical neurons in the adult. In another session, it was discussed the evidence showing that pyramidal cells and intrinsic cells of the neocortex have different developmental origins. Finally, several modern analyses show the role of different transcription factors in the formation of brain cortical maps before the arrival of their proper afferent connections.