Use of rodents as models for the study of "normal aging": conceptual and practical issues.

Certain guidelines may exist for selecting and using rodent models for aging research. These are based, however, on only operational criteria because we presently lack good biomarkers for (or even a suitable definition of) normal aging. Longevity and disease characteristics of the experimental population are the most important of the operational criteria for choosing a particular rodent model. These factors, in turn, are influenced by genetics and by environmental factors, including diet, housing, and physical activity.