One of the best ways of determining the different functions of MAO A and MAO B is using experiments with knockout mice, where it is possible to study how these enzymes behave in a living system (in vivo).
Animals are useful models for scientists to study the biological basis of behavior and disease. There is a high degree of similarity between animal and human genes. Experimental conditions are more easily controlled in animals than in humans.
Dr. Shih decided to use mice because they are the least expensive animal that can be used for transgenic studies (when a foreign gene - a transgene - is incorporated into the genome of an organism). Fish are another alternative to mice, but mice are closer to the human genetic makeup than fish.
