Meeting Abstract

P3.136  Jan. 6  Brain and Plasma Steroid Levels in a Developing Free-Living Songbird CHIN, E.H.*; SCHMIDT, K.L.; SHELDON, L.D.; SHAH, A.H.; LOVE, O.P.; SOMA, K.K.; University of British Columbia, Vancouver, B.C., Canada; University of British Columbia, Vancouver, B.C., Canada; University of British Columbia, Vancouver, B.C., Canada; University of British Columbia, Vancouver, B.C., Canada; Simon Fraser University, Vancouver, B.C., Canada; University of British Columbia, Vancouver, B.C., Canada ehchin@zoology.ubc.ca

In passerine birds, the nestling phase contains a critical period during which the telencephalic song nuclei are sexually differentiated. Traditionally, this sexual differentiation has been thought to be determined by gonadal steroids, but recent studies suggest that non-gonadal steroids are important. Dehydroepiandrosterone (DHEA), a precursor to androgens and estrogens, can be synthesized in the adrenal glands and/or brain, and DHEA may play a role in sex differentiation. Here, we examined DHEA and 17β-estradiol (E₂) levels in plasma and brain tissue in developing European starling (Sturnus vulgaris). We collected blood from chicks on post-hatching day 0 (P0) to P20. Blood was collected from either the brachial or jugular vein. Brain tissue was collected on P0, P6 and P8. Steroids were extracted using solid phase extraction (C18 columns), and DHEA and E₂ levels were measured. For brachial DHEA, levels were approximately 1.5 times higher in males than females on P4. In contrast, for jugular DHEA, the sex difference was reversed, and females had higher levels on P0 and P10. For brachial E₂, levels were highest from P4 to P8 in both sexes. For jugular E₂, levels were highest from P2 to P6 in both sexes. Current studies are examining steroid levels in brain tissue. These data suggest that circulating DHEA from a peripheral organ plays a role in songbird sexual differentiation.