Dehydroepiandrosterone (DHEA) is a testosterone/oestrogen precursor and known modulator ofvertebrate aggression. Male song sparrows ( Melospiza melodia morphna) show high aggressionduring breeding and nonbreeding life-history stages when circulating DHEA levels are high, andlow aggression during molt when DHEA levels are low. We previously showed that androgenreceptor and aromatase mRNA expression are higher during breeding and/or nonbreeding inbrain regions associated with reproductive and aggressive behaviour, although the potential roleof DHEA in mediating these seasonal changes remained unclear. In the present study, nonbreed-ing male song sparrows were captured and held in the laboratory under short days (8 : 16 hlight/dark cycle) and implanted with s.c. DHEA-ﬁlled or empty (control) implants for 14 days.DHEA implants increased aggression in a laboratory-based simulated territorial intrusion. Brainsof 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 medialstriatum (pvMSt) and ventromedial nucleus of the hypothalamus. The DHEA-induced increasesin aromatase expression in the POA and androgen receptor expression in the pvMSt are consis-tent with previously reported seasonal increases in these markers associated with naturally ele-vated DHEA levels. This suggests that DHEA facilitates seasonal increases in aggression innonbreeding male song sparrows by up-regulating steroid signalling/synthesis machinery in abrain region-speciﬁc fashion.
- androgen receptor