Glycogenosomes in the aging rat brain: their occurrence in the visual pathways.

The significance of glycogenosomes (glycogen bodies), frequently seen in peripheral neurites of aging rats, is unknown and their occurrence elsewhere in nervous tissue is poorly documented. During the course of another study these bodies were observed by light microscopy in the visual pathways of aging rats where they have not previously been noted, and this report documents their occurrence, localisation and changes in density with age. Using the periodic acid-Schiff stain, small brightly red-staining bodies, digested by diastase and containing beta-glycogen particles, were seen in increasing numbers in the neuropil of the superior colliculi in brain sections from animals of 5 months of age onwards. From 1 year until more than 2 years of age they steadily became more numerous in the outer one third of the superior colliculus, but remained small, rarely exceeding 4 microm. They were also found at later times in small numbers lying singly in the optic tract, the optic chiasm and optic nerves, although rarely in lateral geniculate nuclei. Similar bodies were also found to accumulate with age in the retinal photoreceptor cell layer. Changes in their densities and size with age in both regions have been documented and it is suggested that, while their occurrence in retinal photoreceptor cells may be due to sustained light damage leading to mitochondrial oxidative stress, it is difficult to implicate this mechanism for their occurrence in retino-tectal nerve fibres. The role of physical trauma, suggested for the presence of these bodies in aging peripheral axons, can be excluded and they appear not to be related to polyglucosan bodies.