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Sex Differences in Effects of Social Stress
One important feature of many mood disorders is that women are almost twice as likely as men to be affected. For a variety of reasons however, most animal models examining neurobiological mechanisms related to depression focus on males. Indeed, there is an urgent need for the development of model systems in which behaviors related to depression and anxiety can be studied in both sexes. The social stress (subordination) paradigm induces pronounced behavioral changes including anhedonia and a marked increase in social avoidance (or withdrawal). However, the overwhelming majority of studies using social stress have focused on males. This is because in most species of rodents, female aggression is minimal, so it is difficult to create social stress using intra-female aggression. In contrast, female California mice (Peromyscus californicus) are aggressive, as males and females defend joint territories. In addition, females have larger corticosterone responses than males during resident-intruder aggression tests. We are using the unique biology of the California mouse to examine sex differences in neurobiological mechanisms that mediate the effects of social stress on affective behaviors...
Estrogens and Aggression
In Peromyscus, it appears that photoperiod determines whether estrogens act via genomic or nongenomic pathways in the brain. In the bed nucleus of the stria terminalis, a brain nucleus that influences aggressive behavior, genes that are estrogen-dependent are upregulated in long days compared to short days. The increased estrogen-dependent gene expression in long days suggests that estrogens may decrease aggression by changing gene expression. In contrast, we demonstrated that an injection of estradiol increases aggressive behavior within 15 minutes when mice are housed in short days. The same estradiol injection has no effect on behavior when mice are housed in long days. Most researchers agree that 15 minutes is not enough time frame for changes in gene expression (and protein) to occur, so this suggests that the effects of estradiol on aggression in short days is occurring though nongenomic pathways. We will be testing this hypothesis by using an estrogen agonist that can not enter the nucleus (thereby preventing changes in gene expression).
Trainor, B. C., Takahashi, E. Y., Silva, A. L., Crean, K. K., and Hostetler, C. 2010. Sex differences in hormonal responses to social conflict in the monogamous California mouse. Hormones and Behavior, in press.
Silva, A. L, Fry, W. H. D., Sweeney, C. and Trainor, B. C. 2010. Effects of photoperiod and experience on aggressive behavior in female California mice. Behavioural Brain
Trainor, B. C., Crean, K. K., Fry, W. H. D., and Sweeney, C. 2010. Activation of extracellular signal-regulated kinases in social behavior circuits during resident-intruder aggression tests. Neuroscience, 165, 325-336.
Nelson, R. J. & Trainor, B. C. 2007. Neural mechanisms of aggression. Nature Reviews Neuroscience, 8, 536-546.
Trainor, B. C., Rowland, M. R. & Nelson, R. J. 2007. Photoperiod affects estrogen receptor alpha, estrogen receptor beta, and aggressive behavior. European Journal of Neuroscience, 26, 207-218.
Trainor, B. C., Lin, S., Finy, M. S., Rowland, M. R. & Nelson, R. J. 2007. Photoperiod reverses the effects of estrogens on male aggression via genomic and nongenomic pathways. Proceedings of the National Academy of Sciences U.S.A., 104, 9840-9845.
Trainor, B. C., Greiwe, K. M. & Nelson, R. J. 2006. Individual differences in ERa in select brain nuclei are associated with individual differences in aggression. Hormones and Behavior, 50, 338-345.
Trainor, B. C., Kyomen, H. H. & Marler, C. A. 2006. Estrogenic encounters: How interactions between aromatase and the environment modulated aggression. Frontiers in Neuroendocrinology, 27, 170-179.
Trainor, B. C., Bird, I. M. & Marler, C. A. 2004. Opposing hormonal mechanisms of aggression revealed through short-lived testosterone manipulations and multiple winning experiences. Hormones and Behavior, 45, 115-121.
Trainor, B. C. & Marler, C. A. 2002. Testosterone promotes paternal behaviour in a monogamous mammal via conversion to oestrogen. Proceedings of the Royal Society of London Series B, 269, 823-829
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