Zebrafish neurobiology: From development to circuit function and behaviour

This special issue of Developmental Neurobiology contains sixteen papers that will give readers a taste of some of the areas of neuroscience in which research using zebrafish is currently having a major impact. Since the early days of using zebrafish as an experimental model, nervous system development has been a major focus for research. The relative simplicity and stereotyped development of the nervous system attracted many of us to using the fish embryo in our research. Almost invariant patterns of reticulospinal neurons, motor neurons and various interneurons (e.g. Bernhardt et al., 1990; Metcalfe et al., 1986; Myers et al., 1986; Wilson and Easter, 1991) were highly reminiscent of invertebrates, but of course, the zebrafish is a vertebrate and its nervous system has essentially the same basic structure and organisation as in all other vertebrates. Coupled with this simplicity and stereotypy, the zebrafish proved itself to be an excellent genetic model system and various forward genetic screens provided the community with a wealth of mutant lines affecting nervous system development (Haffter et al., 1996; Driever et al., 1996). Until relatively recently, the community using zebrafish for neuroscience research was predominantly interested in questions relating to early neural development. A few labs recognized that, as for Xenopus tadpoles (e.g. Roberts et al., 1981), the zebrafish nervous system was well suited for studies of circuit function and behavior (e.g. O’Malley et al., 1996) but for many years, physiologists using zebrafish were in short supply. In recent years, the development of transgenic, optogenetic and imaging techniques and tools coupled with improved behavioural assays have seen a huge expansion in research probing circuit development, function and behavior in zebrafish. The fish is set to make much greater impact in these areas of neuroscience in the coming years than in the past. This special issue spans much of the spectrum of neuroscience research using zebrafish from early development to circuit building and function, behavior, stem cells and regeneration. Cavodeassi and Houart (2012) discuss early patterning of the neural plate, a topic for which the zebrafish is perhaps the model system most amenable to investigation of signaling and regionalization of the nervous system. Several other papers in this Special Issue cover development of specific regions or cell types. Schweitzer et al. (2012) discuss dopaminergic and noradrenergic circuitry; in humans disruptions to this circuitry is implicated in various neurological conditions and it is expected that zebrafish will provide good models for some of these conditions. There have been many studies of early regionalization and patterning at the midbrain/ hindbrain boundary using zebrafish but surprisingly few on the cerebellar structures that develops from this region; Hibi and Shimizu (2012) show how the developing and mature zebrafish cerebellum has excellent potential for the study of cerebellar circuitry and function. The zebrafish is currently the best model system for studying the genetic basis of brain asymmetry and Roussigné et al. (2012) provide an update on current studies addressing habenularand parapineal asymmetry. The habenular nuclei are gaining much attention in mammals as well as fish due to their role in various addictive and reward pathways and the reviews from Okamoto et al. (2012) and Jesuthasan (2012) discuss behaviours and emotional states that are influenced by habenular circuitry. Unlike the habenulae, there is no mammalian structure homologous to the lateral line, but this peripheral sensory organ has proved to be a beautiful model for studying cell migration, neuronal specification and morphogenesis. Chitnis et al. (2012) show why the lateral line is so favoured by the community for studies addressing these issues. Zebrafish have excellent vision and, not surprisingly, the visual system is well studied. Gestri et al. (2012) cover a broad spectrum of research on the zebrafish nervous system from early development to function and use for modeling human ocular diseases. Nikolaou and Meyer (2012) focus on imaging circuit formation, particularly retino-tectal connectivity, illustrating why the optical properties of the transparent fish brain are so well-suited to such analyses. ' 2011 Wiley Periodicals, Inc. Published online 5 November 2011 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/dneu.20997