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 estima ted 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 c ell changed significantly, attaining maximum values at 24 months of 1733 mu m(2)/1000 mu m(3) (0.06) and 64 mu m(2) (0.03), respectively, (coefficient s of variation in parentheses). The corresponding values at 2 months were 7 06 mu m2/1000 mu m(3) (0.20) and 26 mu m(2) (0.24). The mean absolute volum e of the euchromatin changed significantly, with a minimum value of 57 mu m (3) (0.05) occurring at 21 months. We postulate that the increase in RER ma y be part of a mechanism that compensates for an age-related decrease in eu chromatin. An increase in the RER network may improve intracellular transpo rt of proteins, production of which is apparently diminished with aging. Th e increase may also compensate for the reported decrease in calcium buffer capacity of smooth endoplasmic reticulum. (C) 2000 Elsevier Science Inc. Al l rights reserved.