A golgi study of dendritic morphology in the occipital cortex of socially reared aged rats

The possible role of the environment in the morphology of the aged brain has been previously discussed in a number of studies. This study used rats which were aged in social rather than in isolated environments. The density of basal dendrites from superficial pyramidal cells from the occipital cortex was analyzed utilizing the concentric circle method and the specific ordering of the dendrites quantified with the centripetal ordering system. There were dramatic increases in the density of dendrites in three defined ranges from the soma (50 to 100, 100 to 150, and 150 to 200 μm) from 414 to 630 days of age. The only range that did not increase in density was the soma to 50-μm range. The increase in density was due to increases in both terminal and intermediate segments. These findings suggest that the living conditions of the animal during aging play a role in the appearance of the cortical structure. This study also introduces the separate quantification of branchless segments of dendrites, which were found on 75% of the neurons studied at both 414 and 444 days of age. On the other hand, in both the 90- and the 630-day-old groups, only 33% of the neurons had branchless segments. We suggest that branchless segments may be dying segments in a state of retraction.