Diversity and Convergence in Fish Olfactory Subsystems

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Fish utilize olfaction for feeding, alarm response, spawning migration, mate attraction and kin recognition. The neurons that respond to specific odorants project into separate glomerular clusters in the olfactory bulb of the brain. These glomeruli are the functional units of odorant discrimination, and the study of glomerular patterning is a valuable tool to assess the responsiveness to specific odorants. Knowledge of glomerular connections to specific higher brain structures is an indicator of the animal's response to an odorant. Recent studies have revealed much about glomerular mapping and functionality in zebrafish, however considerably less is known regarding the functional organization of the olfactory system in non-model fish. The goal of this research program is to map out glomerular function of the olfactory system in three fish: the sea lamprey, salmon and round goby. Olfaction has a dominant role in guiding behaviour in sea lamprey, a basal vertebrate. Both salmon and gobies are teleost fish. Salmon utilize olfactory signals during spawning migration and gobies use olfactory cues to attract mates. There are distinct main and accessory olfactory subsystems in lampreys, but a single olfactory system with different types of olfactory sensory neurons intermingling in the olfactory epithelium of teleost fish. There are three objectives.  Objective 1 focuses on medial glomeruli. In lampreys, these contain input from the accessory olfactory organ and neural output to a neural relay that controls movement. Objective 1a is to investigate chemoreceptive properties of individual cells in the lamprey accessory olfactory organ. The findings will determine if these neurons are generalists that stimulate movement in response to many odorants. Objective 1b is to probe for the bulbar glomeruli of olfactory sensory neuron crypt cells in salmon and goby, as these may project to medial glomeruli that input olfactory information during reproduction and kin recognition. Objective 2 is to compare odorant responses and neural projections for four non-medial glomeruli. For example, lateral glomeruli appear to be dedicated to amino acid chemoreception, from lampreys to salmon. Objective 3 is to produce a synthesis of bulbar organization in fish by mapping the glomeruli in these three fish. These maps will include olfactory sensory neuron input, glomerular organization, odorant mapping and output projections. This knowledge is important for understanding the neurobiology behind the organization of the olfactory system in species that survive under natural selection pressure. Knowledge of olfactory function is also valuable to the management of fish populations for conservation and habitat restoration. For example, the neurobiology of olfaction is particularly well described in insects and resulting concepts have driven novel approaches to pest control.