Aging of dendrites in the cerebral cortex of the mouse.

Quantitative analysis of the dendritic branchings of pyramidal cells in layers V and III of the visual cortex was performed in aging mice (540 and 720 days) and compared to adult mice (180 days). The number of spines on apical dendrites of the same cells was also counted. Between 180 and 720 days of age, the decrease in dendritic branchings around the perikaryon was dramatic (30-40%) and that in dendritic spines was even more so (about 50%). However, most of the decrease in both dendritic branchings and spines has already occurred at 540 days, and the difference between 540 and 720 days was not statistically significant. This suggests a real loss in cortical connections with aging, taking place prior to the final months of the lifespan of the mouse.