Adult Neurogenesis in the Spiny Lobster, Panulirus Argus: Molecular, Cellular, and Physiological Changes of Olfactory Receptor Neurons

Adult neurogenesis of olfactory receptor neurons (ORNs) occurs in diverse organisms including in decapod crustaceans. This dissertation describes the molecular, cellular, and physiological changes that occur during adult neurogenesis of ORNs in the antennular lateral flagellum (LF) of the spiny lobster Panulirus argus. Examination of the role of splash (spiny lobster achaete scute homolog) in adult neurogenesis and regeneration using in situ hybridization showed splash was not closely associated with the formation of sensory neurons under normal physiological conditions. Damage to the LF, which induces regeneration, enhanced splash expression, suggesting an association between splash with regeneration and repair. This study suggests that splash plays multiple roles in the olfactory organ of adult spiny lobsters. Examination of extracellular and intracellular Ca in mediating spontaneous and odorinduced responses of ORNs, using calcium imaging showed that odor-induced Ca transient responses and spontaneous Ca oscillations in ORN somata are primarily mediated by an influx of extracellular Ca through Co -sensitive Ca channels, but that intracellular Castores also have some contribution. These responses are independent of TTX-sensitive Na channels, suggesting that these Ca responses may reflect receptor potentials. Examination of changes in odor specificity, sensitivity, and temporal responses in adult-born ORNs showed an increase in the percentage of odorant-responsive ORNs as they age from newly-born cells to mature, and a decrease in odorant-responsive ORNs as they senesce. As adult-born ORNs age, there was a decrease in the percentage of ORNs that undergo spontaneous Ca oscillations and an increase in the amplitude of oscillation. ORNs became more broadly tuned as they senesce, and their response profile, defined by the most effective odorant, changed. Odor sensitivity changed with age. This study demonstrated that the physiological response properties of adult-born ORNs changed with functional maturation. Taken together, this dissertation reveals molecular, cellular and physiological changes in adult born ORNs and elucidates mechanisms of adult neurogenesis. INDEX WORDS: Sensory neuron, Olfactory system, Neurogenesis, Regeneration, In situ hybridization, Calcium imaging, Odorant, Chemical senses, Panulirus argus ADULT NEUROGENESIS IN THE SPINY LOBSTER, PANULIRUS ARGUS: MOLECULAR, CELLULAR, AND PHYSIOLOGICAL CHANGES OF OLFACTORY RECEPTOR NEURONS