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The place of animal models in gerontological research *

The ageing process must be regarded as a dynamic process which can be studied in the mammalian species by essentially two categories of investigations: crosssectional or longitudinal studies. In cross-sectional studies, groups of various ages are examined and age-related differences are sought. In longitudinal studies, serial prospective measurements are obtained in one group of subjects at predetermined intervals. There are advantages and disadvantages to each of the two types of investigations and these have been reviewed by Rowe [I] for man. One of the primary goals of ageing research is to gain an understanding of the underlying mechanisms of ageing in order to find means for preventing or ameliorating ailments of old age before functional decline becomes clinically apparent. The development of animal models of senescence is of great importance for ageing research because of the legal and ethical constraints for conducting research in man. In addition, longitudinal studies in man are often impractical to conduct due to the long lifespan, frequent mobility, the necessity to standardize the laboratory methods over a long period, as well as that the genetic and environmental factors may vary greatly from one person to another. One has to realize that animals used in biomedical research act as substitutes for man. In gerontological research, animal models are used to study the basic mechanisms underlying the ageing process, the relationship between ageing and disease, and the influence of environmental factors on the ageing process. In order to appreciate the value of an animal model for ageing one should carefully define the model. Presently, the definition most used is that provided by a Committee on Animal Models for Research on Aging of the Institute of Laboratory Animal Resources, U.S.A. [2]: ‘a living organism on which a normative biological or behavioural aspect of ageing can be studied, or on which a spontaneous or induced age-related pathological process can be investigated, and in which the phenomenon in one or more respects resembles the same phenomenon in man’. From this definition, a limitation of studies in animals already emerges, viz. that it will not always be feasible to observe or reproduce identical phenomena in animals as observed in man. However, it has to be realized that animal models are used to establish facts.