A Golgi study of the superficial pyramidal cells in the somatosensory cortex of socially reared old adult rats

Abstract

Following a series of investigations into the appearance of the basal dendritic skirt of pyramidal cells in the supragranular layers of the occipital cortex of the aged rat, we now extend our findings to the somatosensory cortex of these same animals. Specifically, the total number of dendritic branches increased from 414 to 630 days of age due primarily to an increase in third and sixth order branches. The total number of branchless segments which we have suggested may be a vestige of a portion of the dendritic tree was greater in the 414-day-old group than in the 630-day-old group. The dendritic density was also measured in four specific ranges from the soma (0 to 50 μm, 50 to 100 μm, 100 to 150 μm, 150 to 200 μm). Only the 50 to 100-μm range did not show an increase in density with age. By utilizing an orientation factor in the concentric circle analysis, the increase in dendritic density for the range nearest the soma was found to be only in the upper sector of the dendritic domain. This suggests a shift in the dendritic tree away from the region of primary input in layer IV toward the pial surface. We consider that the increases in dendritic parameters measured are a compensatory-type growth as we earlier suggested in the occipital cortex. The functional meaning of this growth remains undetermined.