Animal models of human disorders - General aspects

Animal models serve to imitate (patho)physiological states known to occur i n target species (usually man but sometimes other species as well). The use of animal models has had and may continue to have a tremendous impact on m edical progress. Laboratory animals are now used in the study of basic (pat ho)physiological mechanisms, in the development, production and evaluation of therapeutic and diagnostic agents, in safety studies to assess carcenoge nic, teratogenic or reproductive toxicity of investigational agents, and in education and training. The quality or utility of a model often depends up on its validity, which is highest in so-called homologous models where the symptoms displayed as well as the cause of the condition in the animal are identical to those of the human condition. Isomorphic models display simila r symptoms, but the condition is not provoked by the same events as the hum an condition. Partial models do not attempt to model the entire condition, but focus only on limited aspects. Models can be further classified into sp ontaneous, induced, negative and "orphan" models. Uncritical extrapolation of animal findings to the human condition may lead to unreliable or even da ngerous conclusions. Extrapolation tends to be most reliable when a plurisp ecies approach is taken, and when differences in metabolic patterns and spe ed as well as several other confounding variables are taken into account. A nimal models have been crucial to neurological and psychiatric research, ev en though the search for valid models has been difficult in these fields be cause of the differences in brain structure and function between humans and other species.