Meeting Abstract
Dehydroepiandrosterone, or DHEA, is a testosterone/estradiol precursor, associated with avian aggression. Male song sparrows (Melospiza melodia morphna) show high aggression during breeding and non-breeding when circulating DHEA levels are also high, as compared to low aggression and low DHEA levels during molt. When artificially elevated, DHEA increases aggression in male song sparrows in the field and laboratory. We previously demonstrated that androgen receptor and aromatase mRNA expression are higher during breeding and/or non-breeding in brain regions associated with social behavior, but DHEA’s potential role in mediating these changes remained unclear. Here, non-breeding male song sparrows were captured and held in the laboratory on short days (8L:16D). Birds were implanted with subcutaneous DHEA-filled or empty (control) implants for 14 days. DHEA implants increased circulating DHEA and testosterone levels, and aggression, as assessed by a laboratory-based simulated territorial intrusion. Brains of DHEA-implanted birds showed higher aromatase mRNA expression in the preoptic area (POA) and higher androgen receptor mRNA expression in the periventricular nucleus of the medial striatum (pvMSt) and the ventromedial nucleus of the hypothalamus (VMH). These experimental increases in androgen receptor and aromatase mRNA expression are largely consistent with previously reported seasonal increases associated with naturally elevated DHEA levels. This suggests that DHEA may facilitate seasonal increases in aggression in male song sparrows by up-regulating steroid signaling/synthesis machinery in a brain region-specific fashion.
