Quantitative age-changes in endoplasmic reticulum and nucleus of cerebellar granule cells

A stereological study was performed on cerebellar granule cells from rats 2 to 24 months of age (eight different ages, five animals per age group) to quantify age-related alterations in the rough endoplasmic reticulum (RER). The mean surface density and the mean total surface area of the nucleus, as well as the mean absolute volume of euchromatin per cell, were also estimated to examine whether or not these had quantitative relationships with the RER. The mean surface density and the mean total surface area of RER per cell changed significantly, attaining maximum values at 24 months of 1733 microm(2)/1000 microm(3) (0.06) and 64 microm(2) (0.03), respectively, (coefficients of variation in parentheses). The corresponding values at 2 months were 706 microm(2)/1000 microm(3) (0.20) and 26 microm(2) (0.24). The mean absolute volume of the euchromatin changed significantly, with a minimum value of 57 microm(3) (0.05) occurring at 21 months. We postulate that the increase in RER may be part of a mechanism that compensates for an age-related decrease in euchromatin. An increase in the RER network may improve intracellular transport of proteins, production of which is apparently diminished with aging. The increase may also compensate for the reported decrease in calcium buffer capacity of smooth endoplasmic reticulum.