Figure 33.2 A typical survival curve for rodents.
statistical power and allow for expected mortality during the experiment (reviewed in Miller and Nadon, 2000). Figure 33.2 illustrates the need for excess animals when an experiment will require the animals to be maintained for some time. If the age of the animals puts them near the top of the mortality phase of the survival curve (arrowhead), few will die during the experimental period. But if the age of the animals puts them in the middle of the mortality phase (arrow), significantly more animals are needed to allow for the anticipated mortality. It is also important when comparing two different strains to compare biological age instead of chronological age. F344 x BN F1 male rats have a median lifespan of 34 months while F344 male rats have a median lifespan of 24 months. Comparing 24-month-old rats of the two strains would have them in very different points in their biological age. These concerns are covered in more detail in Chapter 4 of this book.
Getting started in the use of animal models to study biogerontology can be challenging, but there are many resources available to assist in this endeavor. The NIA supports many resources designed to provide the raw materials for studies into the process of normal aging and the prevention, progression and treatment of age-related diseases. Table 33.6 provides web URLs for NIA resources relating to animal models, as well as three informational resources: the Mouse Genome Informatics site, the Mouse Phenome Database, and the Rat Genome Database. The latter resources are valuable repositories of information crucial to deciding on the optimal strain for experimental purposes.
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