Neuron atrophy during aging: programmed or sporadic?

Atrophy of neurons is a common change during aging in laboratory rodents and humans. However, cholinergic neurons of the same type have been found to atrophy, hypertrophy or not change at all, according to various reports on different species and genotypes. Possible factors responsible for these diverse outcomes include species- and genotype-specific aging changes and age-related diseases. An open question is whether slowly evolving changes in neuronal size share any mechanisms with the rapid programmed death of neurons that occurs during development. Progress in the study of neuronal atrophy with aging may be furthered by using fewer rodent genotypes.