Mechanisms of hypothalamic neuronal circuit development in zebrafish

About This Grant

PROJECT SUMMARY The development of functional connections between neurons that comprise the nervous system is among the most astonishing feats of animal development. Work in the last few decades has revealed some general principles of neuronal circuit formation, including the concept that targets can play an active role in attracting neuronal projections. However, this work has mostly focused on the development of sensory and motor systems, and it is unclear whether these or other principles apply to the development of neuronal circuits within the brain. We will address this question using the zebrafish, a model organism that is well-suited for neurodevelopmental studies due to its conserved yet simple vertebrate brain, transparency, accessibility for live imaging, and amenability to optogenetic and chemogenetic manipulations. We will focus on hypothalamic nuclei that regulate arousal because arousal plays a critical role in many aspects of physiology and behavior, and is clinically significant for disorders such as narcolepsy, Parkinson’s disease and Alzheimer’s disease, but we have only limited knowledge of how hypothalamic neuronal circuits form and are maintained. Zebrafish are a useful model to study hypothalamic nuclei that regulate arousal because several of these nuclei in zebrafish are anatomically, molecularly, and functionally conserved with those of mammals. In particular, we will study the 10-15 larval zebrafish hypothalamic neurons that express the neuropeptide hypocretin (Hcrt), which promote arousal in both zebrafish and mammals. In Specific Aim 1, we will use the Brainbow technique to label each Hcrt neuron with a different color and use these animals to generate anatomical maps of neuronal projections at the single neuron level. These maps will allow us to ask questions about the architecture of the Hcrt neuronal circuit at a level of detail that is unprecedented for a vertebrate animal. In Specific Aim 2, we will investigate the role of hypothalamic neuron targets in the development and maintenance of hypothalamic neuronal circuits. Specifically, we will test whether the targets of Hcrt neuron projections in the brain are necessary and/or sufficient to guide and maintain these projections. We will also test whether neuromodulators produced by these targets and/or the activity of target neurons are important for the development and maintenance of Hcrt neuron projections. We will also evaluate the effects of the perturbations in Aims 1 and 2 on behavior. Results from these experiments will shed light on the development and maintenance of projections between small but critical nuclei in the brain. If we find that development and maintenance of these projections follow principles similar to those described for sensory and motor systems, we will have laid the foundation for more extensive investigations of neuronal circuit development in the brain. If we find this is not the case, we will have established that at least some neuronal circuits in the brain develop according to principles distinct from those observed in sensory and motor systems, which will lead to new hypotheses regarding brain-specific mechanisms of neuronal circuit development.