UBC Theses and Dissertations
Neuroendocrine modulation of aggressive behavior Jalabert, Cecilia
Aggression is an important social behavior that plays key roles in mediating access to limited resources. During the breeding season, aggression is stimulated by gonadal steroids. Interestingly, many species are highly aggressive during the non-breeding season, despite the gonads being regressed. Song sparrows, Melospiza melodia, are territorial year-round and therefore are an excellent animal model to study seasonal changes in the steroid modulation of aggression. Recent research has shown that the brain itself can produce steroids by metabolizing circulating precursors and even by de novo synthesis from cholesterol. Because steroids can be synthesized locally in the brain, steroid levels in the blood often do not reflect steroid levels in specific brain regions. Thus, it is critical to accurately measure steroid levels in discrete brain regions. Steroids are challenging to measure because they are present at very low levels and current techniques often lack the sensitivity required. In chapter 2, I developed and validated a liquid chromatography-tandem mass spectrometry assay for the measurement of steroids with a focus on androgens and their precursors. In chapter 3, I developed and validated a method to measure several estrogens with increased sensitivity. Both methods were validated in blood, plasma, and microdissected brain tissue of song sparrows and are broadly applicable to other species, allowing steroid profiling in circulation and microdissected brain. Further, we applied these methods and quantified steroids examining peripheral and neural synthesis of steroids across seasons and in response to an aggressive interaction in wild male song sparrows. Briefly, I report that 1) brain steroid levels can greatly differ from circulating steroid levels, 2) brain steroid levels show region-specific seasonal patterns that are not a simple reflection of circulating steroid levels, and 3) local steroid production rapidly increases in response to an aggressive interaction in the non-breeding season. Overall, steroid levels are regulated within the brain and local production is dependent on the season and behavioral context.
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