Neurohistological Studies of Developing Mouse Brain

Publisher Summary Systematic studies of the developing brain have been made in many species of vertebrates but not on that of the mouse. This chapter is concerned with the part of the multidisciplinary study in which the development of the mouse brain was examined in terms of behavioral observations, alterations of the electrocorticogram, and neurohistological changes of the cerebral cortex. This chapter shows that histological maturation of the mouse cerebral cortex parallels developmental changes in its electrocorticogram and behavior. While Nissl substance is almost invariably present in cortical neurons at birth, they are otherwise quite immature. Only 4 relatively undifferentiated layers may be distinguished in the cortex of the newborn animal. A 5th layer is formed, at 6 days of age, by the separation of small and medium sized pyramidal cells. By this time, also, there is considerable branching of the dendrites of all types of pyramidal cells, and horizontal cells have appeared in the molecular layer. By 15 to 17 days of age, when the ECoG and behavior appear to be mature, the cortical differentiation is likewise complete.