Subterranean Fishes of the World

3222

2013

AIM 2013

While the general features of the olfactory system are well-conserved across vertebrates, olfactory capabilities have been known to evolve rapidly in response to changing environmental conditions. In cave-dwelling populations of Astyanax mexicanus, several morphological and behavioral shifts occurred in adaptation to cave life characterized by total and permanent darkness. Previous studies have shown that sensory systems such as the lateral line and taste buds are modified in cavefish. Increases in the size and/or number of these sensory structures have been shown to accompany the loss of vision in cave animals, and are thought to provide a sensory compensation for life in dark cave environments. Our comparison of the olfactory system in Astyanax surface fish and Pachón cavefish showed an increase in the overall size of the olfactory organ (nose) in cave-dwelling morphs at both embryonic and post-embryonic stages. Molecular and cellular analyses further revealed a higher number of olfactory sensory neurons (OSNs), as well as increased neurogenesis within the post-embryonic olfactory epithelium (OE) of cave-fish, when compared to surface-fish. Current research efforts are focused on investigating the functional/behavioral consequences of increased size and modified neurogenesis in the cavefish OE. Recent work in mice suggests that increased turnover of neurons in the OE might affect olfactory capabilities by providing a dynamic mechanism to adapt the olfactory neuronal repertoire to the environment. Could the observed increase in olfactory epithelial neurogenesis provide such mechanism for adaptation to cave environments? What effects would this modification have on the ability of an animal to smell in the dark? To address these questions, we have developed an assay protocol to test olfactory function in response to food-related odors (amino-acids) in the dark. By combining behavioral and molecular assays, we are able to not only test the behavioral responses of both populations to various odorants, but also to quantify neuronal activation in response to odorant exposure. These studies should provide new insights into the mechanisms underlying olfactory adaptations in cave animals specifically, as well as the functional role of olfactory neurogenesis in general. Work supported by ANR grant [ASTYCO]

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