HORMONAL CONTROL OF OLFACTORY LOBE DEVELOPMENT

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Hormonal control of neuronal development plays an important role in a wide variety of animals, including vertebrates. Among the best understood systems are the metamorphosing insects, where three identified hormones orchestrate the reshaping of the nervous system during metamorphosis. these hormones, most notably ecdysone (and its metabolite, 20- hydroxyecdysone), have been shown in the segmental body ganglia to have effects on neuronal proliferation, programmed cell death, and the growth and pruning of neuronal arbors. The study described in this proposal focusses on hormonal control of neural development within the insect brian. The olfactory (antennal) lobes of the brain of the moth Manduca sexta has been chosen in order to probe specific questions that have arisen from previous detailed studies of short-range intercellular interactions that guide development in that system. Many of these questions have not yet been asked in the segmental ganglia, and all are especially tractable in the olfactory lobes. Specifically, ecdysteroid levels will be manipulated experimentally during critical stages of metamorphosis to ask whether ecdysteroids affect timing and location of synaptogenesis, behavior of glial cells in the formation of glomeruli, development and neuritic arbors, development of neurotransmitter machinery, and onset of responsiveness of olfactory sensory neurons. These five developmental events were chosen because they span different cell types, different developmental stages, and different aspects of cellular behavior. The first four occur as ecdysteroid liters in the blood are rising; the last occurs as titers aspects of cellular behavior. The first four occur as ecdysteroid liters in the blood are rising; the last occurs as titers fall back toward baseline. All are significant events in the development of the olfactory lobe, and their timing and dependence upon afferent-axon ingrowth have been studied in detail. The proposed study will involve light and electron microscopy, intracellular dye-injection, immunocytochemistry and autoradiography, biochemical assays, and electrophysiology. Results of this study will extend knowledge of the processes underlying development of the olfactory lobe, and will shed light on hitherto unexplored aspects of development of the nervous system that may be under hormonal control. The studies will provide a better understanding of hormonal involvement in glial as well as neuronal development.