Neuronal death in the development and aging of the cerebral cortex of the mouse.

The numbers of neurons and glial cells in the cerebral cortex of the mouse have been estimated during its whole life-span (5 to 720 days), taking into account both the cellular densities of several areas and the cortical volumes. The results clearly demonstrate that there is a massive neuronal loss in the cerebral cortex during early postnatal development, greater in layers II-IV than in layers V-VI. In contrast, aging is characterized by a discrete neuronal loss in the cerebral cortex, purely restricted to layers II-IV. The number of glial cells increases continuously from 5 to 720 days. We emphasize here the need to obtain volumetric measure together with cellular densities in order to get interpretable quantitative data on cellular death and proliferation.