Aggressive interactions rapidly increase androgen synthesis in the brain during the non-breeding season.
In male song sparrows (Melospiza melodia), territorial challenges during the breeding season can rapidly increase circulating levels of testosterone (T). During the non-breeding season, male song sparrows are highly aggressive, but the gonads are regressed and plasma T levels are non-detectable and unaffected by territorial challenges. The pro-hormone dehydroepiandrosterone (DHEA) is elevated in song sparrow plasma and brain during the non-breeding season and may be locally converted to sex steroids in the brain to regulate aggression. The enzyme 3beta-hydroxysteroid dehydrogenase/Delta5-Delta4 isomerase (3beta-HSD) converts DHEA to androstenedione (AE) using the cofactor NAD(+), and this is a critical rate-limiting step. We predicted that brain 3beta-HSD activity varies seasonally and is rapidly modulated by aggressive challenges. In the first study, brain 3beta-HSD activity was highest in the non-breeding season in specific regions. In the second study, a simulated territorial challenge rapidly increased aggressive behavior in non-breeding song sparrows. Brain 3beta-HSD activity, when measured without exogenous NAD(+), increased by approximately 250 to 500% in telencephalic regions of challenged subjects. When brain 3beta-HSD activity was measured with exogenous NAD(+), these effects of territorial challenges were not observed. These data suggest that territorial challenges rapidly increase endogenous NAD(+) levels or increase 3beta-HSD activity specifically within a NAD-rich subcellular compartment. Together, these two studies suggest a shift from systemic to local sex steroid signaling in the non-breeding season. Local steroid signaling produces high spatial and temporal specificity of steroid signals and avoids the costs of high systemic T levels during the non-breeding season.
Pradhan
Devaleena S
DS
Department of Zoology, University of British Columbia, Vancouver, BC, Canada V6T 1Z4. dpradhan1@student.gsu.edu
Newman
Amy E M
AE
Wacker
Douglas W
DW
Wingfield
John C
JC
Schlinger
Barney A
BA
Soma
Kiran K
KK
D015096:3-Hydroxysteroid Dehydrogenases / Q000096:biosynthesis / Q000235:genetics; D000374:Aggression / Q000502:physiology*; D000728:Androgens / Q000096:biosynthesis*; D000818:Animals; D001923:Brain Chemistry / Q000187:drug effects / Q000502:physiology*; D002851:Chromatography, High Pressure Liquid; D003687:Dehydroepiandrosterone / Q000097:blood; D008297:Male; D009243:NAD / Q000494:pharmacology; D012621:Seasons; D012726:Sexual Behavior, Animal / Q000502:physiology*; D012931:Social Environment; D046370:Sparrows / Q000502:physiology*; D013737:Testis / Q000378:metabolism; D013739:Testosterone / Q000097:blood
D000728:Androgens; D009243:NAD; D013739:Testosterone; D003687:Dehydroepiandrosterone; D015096:3-Hydroxysteroid Dehydrogenases