Date of Award


Degree Type


Degree Name

Master of Science




Dr. Scott MacDougall-Shackleton


The song-control system is a network of discrete nuclei in the songbird brain that controls the production and learning of birdsong, and exhibits some of the greatest neuroplasticity found in the adult brain. This plasticity is driven by the gonadal steroid testosterone. When acting on neural tissue, however, testosterone can be metabolized into 5a-dihydrotestosterone (DHT) or 17|3-estradiol (E2), which activate different hormonal signalling pathways. By treating adult starlings with both testosterone metabolites and metabolite antagonists, I isolated the effects of DHT and E2 treatment on neuroplasticity in the song-control system. E2 treatment induced some, but not all neuroplastic effects

reported with testosterone treatment. Conversely, DHT treatment induced no neuroplasticity. I documented the first evidence of sex-specific neuroplasticity in the songbird. These findings suggest that DHT and E2 signalling alone do not account for all songbird neuroplasticity and that future studies should account for species and sex differences in the brain.



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