Module 05 - Research Issues

Animal Models in Biomedical Research

Although the term "animal model" is commonly used, a definition may help clarify the context of the term. The American National Research Council Committee on Animal Models for Research and Aging drafted the following definition: "An animal model for biomedical research is one in which normative biology or behaviour can be studied, or in which a spontaneous or induced pathological process can be investigated, and in which the phenomenon in one or more respects resembles the same phenomenon in humans or other species of animals." Animal models used in biomedical research, particularly those used in the study of diseases and other conditions in humans, can be grouped as follows:

Spontaneous models - often called "natural" models. These include naturally occurring animal diseases or conditions that correspond to the same diseases or conditions in humans. Diabetes, hypertension, arthritis, immune deficiencies are just a few examples. Many hundreds of animal strains/stocks with inherited conditions have been characterized and conserved. The Jackson Laboratory holds one of the largest repository of these valuable animal models in mice ( http://www.jax.org/).

Experimental models. Experimental models are models in which a condition or disease is experimentally reproduced by the scientist. Examples include producing diabetes using the chemical streptozotocin to damage the insulin producing cells in the pancreas; using a chemical carcinogen to produce a certain type of cancer; producing a stroke model through surgery.

Genetically modified models are a special group of induced animal models, involving manipulation of the animal's genetic code to produce the condition that the scientist wants to study. Genetically modified animals may carry inserted foreign DNA in their genome, or have genes replaced or removed ("knock-out" models). These models can help scientists study the genetic basis of disease, susceptibility and resistance, etc.

Negative models. Some animals are resistant to a particular condition or disease. Examining why this is the case may provide answers to questions about disease resistance and its physiological basis.

Orphan models. Orphan models are conditions appearing naturally in an animal, for which there is no known human counterpart. Historically scrapie in sheep was such a model, but now is useful as a model for the human spongiform encephalopathies that are of so much concern (eg., BSE, "mad cow disease" and CWD, chronic Wasting Disease in deer).

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