Embryology and teratology

This chapter provides an update on rat (Rattus norvegicus) embryology, including the steps of preimplantation, implantation, and gastrulation. It also describes the process of organogenesis in the rat, with emphasis placed on neural tube formation, craniofacial development, and limb development. Teratology is the study of abnormalities of physiological development. Experimental teratology gained its current relevance after the thalidomide tragedy, which led to the development and revision of specific regulatory guidelines in drug safety. In studies to evaluate effects on embryo-fetal development, usually the rat is used as the primary species and rabbits as the secondary species. The International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use guidelines state that the rat is the most often used rodent species for reasons of practicality, general knowledge of pharmacology in this species, and the large amount of historical background data. This chapter describes in detail the various aspects of embryo-fetal developmental study design using the rat as the primary species.