The nuclear hormone estrogen is reported to increase aggressive behavior in most birds and domesticated mice but to reduce aggression in Bluebanded gobies, California mice, and humans. Trainor et al. present data showing that in their preferred model, male beach mice, estrogen can produce both effects, depending on the season (or, more precisely, the photoperiod to which the animal is exposed). Short, winterlike days cause testicular regression and aggressive behavior in these mice. In castrated mice (in which constant testosterone concentrations were provided by an implant) exposed to short days (8 hours of light and 16 hours of darkness), activation of estrogen receptors increased aggression (measured as the time elapsed before they attacked a male intruder in their home cage). But when the mice were maintained on long days (16 hours of light and 8 of darkness), estrogen treatment caused a decrease in aggression. Microarray analysis of gene expression in an area of the brain associated with aggression showed that the decrease in aggression produced in animals exposed to long days was associated with increased estrogen-dependent gene expression. The opposite effects of estrogen to increase aggression in animals exposed to short days could be detected within 15 minutes, a time frame likely to be too short for transcriptionally mediated effects. Thus, the authors propose that the increased aggression is influenced by nongenomic actions of estrogens. Together, the findings show that the effects of these nuclear receptors on aggressive behavior are highly dependent on environmental cues.
B. C. Trainor, S. Lin, M. S. Finy, M. R. Rowland, R. J. Nelson, Photoperiod reverses the effects of estrogens on male aggression via genomic and nongenomic pathways. Proc. Natl. Acad. Sci. U.S.A. 104, 9840-9845 (2007). [Abstract] [Full Text]