Non-genomic effects of steroids on teleost fish olfaction: behavioral and anatomical approaches
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Thomas W. Small
Social behavior is necessary for reproduction and survival in many vertebrates and is regulated, in part, by sex steroids. Classically, steroids were believed to act in the body only through so-called genomic pathways, in which they can elicit behavioral changes within hours. However, in the last few decades, steroids have also been shown to act through faster non-genomic or “rapid” pathways. In these pathways, steroids can facilitate behaviors within seconds to minutes. In order to elicit such rapid behavioral change, sex steroids may act at various spatiotemporal points within the behavioral neural circuit, including on sensory processing mechanisms, motivational processes, motor output mechanisms or a combination of these. Relatively little research has explored the rapid modulation of sensory systems directly. I examined these effects using the zebrafish (Danio rerio) as a behavioral model for olfactory sensitivity in reproductive contexts. I specifically investigated how androgens rapidly affect behavioral responses of zebrafish to prostaglandin F2 (PGF2), a pheromone (olfactory cue) crucial for spawning in many teleosts. Using an adapted social preference paradigm, I confirmed that male zebrafish approach PGF2 and found that androgens reduced this approach response, supporting that androgens may rapidly modulate zebrafish olfactory processing. I also explored susceptibility of the teleost olfactory system to rapid effects of sex steroids with a testosterone binding assay in goldfish (Carassius auratus) brain. I visualized putative membranal testosterone receptors in the olfactory bulb, corroborating behavioral findings that testosterone rapidly modulates teleost olfactory processing.
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