Abstract
Abstract: :
Purpose: To quantitate the inherent age-related loss of retinal ganglion cells (RGCs) in mice and rats. Methods: The entire population of RGCs was retrogradely labeled by bilateral Fluoro-Gold injection into the superior colliculi in mice and rats. RGC densities at equivalent retinal positions were compared in mice at 1, 4, 9 and 15 months of age and in rats at 2, 8, 16 and 24 months of age. Results: With age, mice lose approximately 2.3% RGCs/month and rats lose approximately 1.5% RGCs/ month. However, when normalized to an 18 months lifespan for mice and to a 24 months lifespan for rats, the inherent, age-related loss of RGCs is the same over the life of the two species. At the end of life, rats and mice have lost approximately 35-40% of their RGCs. Furthermore, this inherent loss of RGCs as these rodents age is similar, relative to lifespan, to that reported for monkeys and humans. Extrapolating linearly from published human data, if a human lives 76 years, at the end of life the human would have lost approximately 38% of their RGCs. Similarly from published rhesus monkey data, if the animal lives 26 years, at the end of life the monkey would have lost approximately 44% of their RGCs. To test the dependence of the rate of loss of RGCs on lifespan, we determined the densities of RGCs in mice and rats that were caloric restricted from an early age. Caloric restricted animals, which have a longer lifespan, had a slower rate of loss of RGCs than control ad lib fed animals. Conclusion: In humans, monkeys, rats and mice, the inherent, age-related losses of RGCs are quite similar when related to lifespan. The aging of this population of neurons does not follow "clock time" but is related to the biological factors that control lifespan of the species.
Keywords: 341 cell death/apoptosis • 309 aging • 415 ganglion cells