Over the course of the last 100 years, amphibian and fish embryos have been used to investigate the early development of vertebrates. Professor Harris and colleagues use these embryos, at pre-feeding stages, to find out how the nervous system forms, how nerve cells differentiate and how the correct synapses and circuits are made in the brain during the earliest stages of its development. While it is possible to explore issues of brain development at later stages using other animal models, these early stages of brain development are best addressed in animals where the embryonic stages are easily accessible to manipulation. Both frogs and fish, being aquatic vertebrates with external development, are among the best to use in such studies.
Early embryos of different vertebrate species are more alike than the more developed forms. Thus, the lessons learned from studies of the earliest phases of neural development in these animals are likely to be strongly pertinent to human brain development at similar embryonic stages. Zebrafish have excellent genetics and have the advantage of optical clarity, making it possible to use genetically-modified fish in combination with high-resolution microscopy to get the richest and hardest data with the least amount of invasive procedures in any vertebrate species. Almost all of the procedures used are mild, and involve mating of animals or assisted reproduction of adults in order to get the embryonic material on which to do studies.