Rapid social regulation of 3β-HSD activity in the songbird brain

Rapid increases in plasma androgens are generally associated with short-term aggressive challenges in many breeding vertebrates. However, some animals such as song sparrows (Melospiza melodia) are aggressive year-round, even during the non-breeding season, when gonads are regressed and systemic testosterone (T) levels are non-detectable. In contrast, levels of the prohormone dehydroepiandrosterone (DHEA) are elevated year-round in the plasma and brain. The local conversion of brain DHEA to potent androgens may be critical in regulating non-breeding aggression. 3β-hydroxysteroid dehydrogenase/Δ4-Δ5 isomerase (3β-HSD) catalyzes DHEA conversion to androstenedione (AE) and the cofactor NAD⁺ assists in this transformation. In this thesis, I asked whether brain 3β-HSD activity is regulated by social encounters in seasonally breeding male songbirds. In Experiment 1, I looked at the long-term seasonal regulation of brain 3β-HSD activity. 3β-HSD activity was highest in the non-breeding season compared to the breeding season and molt. In Experiment 2, I hypothesized that brain 3β-HSD activity is rapidly regulated by short-term social encounters during the non-breeding season. A 30 min social challenge increased aggressive behavior. Without exogenous NAD⁺, there was ~355% increase in 3β-HSD activity in the caudal telencephalon and ~615% increase in the medial central telencephalon compared to controls (p<0.05). With exogenous NAD⁺, there was no effect of social challenge on 3β-HSD activity. These data suggest that endogenous cofactors play a critical role in the neuroendocrine response to social challenges. The increase in brain DHEA conversion to AE during social challenges may be a mechanism to rapidly increase local androgens in the non-breeding season, when there are many costs of systemic T.

Name thesis:degree_name

Master of Science - MSc

Level thesis:degree_level

master's

Discipline thesis:degree_discipline

Zoology

Grantor dc:publisher

University of British Columbia

Year dc:date

2008

Author dc:creator

• Pradhan, Devaleena S.

Statement dc:rights

• Attribution-NonCommercial-NoDerivatives 4.0 International

Licence

• http://creativecommons.org/licenses/by-nc-nd/4.0/

Language dc:language

eng

Handle dc:identifier

http://hdl.handle.net/2429/1500

OAI identifier oai:identifier

oai:circle.library.ubc.ca:2429/1500