Transgenic technology exists for many organisms, including mice, rats, fish, flies, and worms. Modeling in invertebrates such as Drosophila and Caenorhabditis elegans offers advantages in terms of the high degree of experimental control and the relatively short life span of the organisms. They, however, suffer the disadvantage of being far removed phylo-genetically from mammals. Although efforts to model AD in these systems continue, they have had less impact than models in mammalian systems and are not discussed further. The interested reader is, however, referred to 2 recent reviews of transgenic modeling of AD in Drosophila and C. elegans.1,2 Among vertebrates, mice are by far the species most used. Transgenic modeling in mice is relatively inexpensive. Mice also have a relatively short life span, and the techniques for performing genetic modifications in them are well developed. Transgenic technology exists for rats but is not as widely available as that for mice, although some transgenic AD rat lines have recently been described.3–6
