Rapid effects of estradiol on aggression depend on genotype in the white-throated sparrow, a species with an estrogen receptor polymorphism Open Access

Merritt, Jennifer Rose (2017)

Permanent URL: https://etd.library.emory.edu/concern/etds/xg94hq280?locale=en


The white-throated sparrow represents a powerful model in behavioral neuroendocrinology because it occurs in two plumage morphs that differ with respect to steroid-dependent social behaviors. Birds of the white-striped (WS) morph engage in more territorial aggression than birds of the tan-striped (TS) morph. This behavioral polymorphism is caused by a chromosomal inversion that has captured many genes, including estrogen receptor alpha (ERα). ERα expression depends on morph in a number of brain regions implicated in social behavior, including the rostral medial preoptic area (rPOM) and nucleus taeniae of the amygdala (TnA), suggesting that the behavioral polymorphism might be explained by differential sensitivity to sex steroids. In this study, we tested whether exogenous estradiol (E2) administration produces differential effects on behavior and the brain in the two morphs, as predicted by the ERa polymorphism. We administered a bolus dose of E2 and quantified aggression toward a conspecific 10 min later--a time point at which E2 is known to increase aggression in song sparrows (Experiment 1). E2 increased aggression in WS birds, but not TS birds. Thus, in this study we found that the rapid effects of E2 depended on morph. To map neural responses to E2, we administered an identical dose of E2 and quantified Egr-1 induction in regions with known differential expression of ERα (Experiment 2). E2 treatment decreased Egr-1 immunoreactivity (IR) in both rPOM and TnA, but this effect did not depend on morph. We then tested whether morph differences in Egr-1-IR emerge after birds are treated with E2 for much longer (7 days; Experiment 3). We found an interaction between morph and treatment; E2 treatment increased Egr-1 in the TnA of WS birds, but decreased it in TS birds. Overall, our results suggest that the ERα polymorphism may contribute to morph differences in aggression via both nongenomic and genomic mechanisms.

Table of Contents

Page 1. Introduction

Page 5. Methods

Page 5. Experimental Design

Page 5. Experiment 1

Page 5. Animals

Page 7. Prescreening for Social Dominance

Page 8. Hormone Manipulation

Page 9. Rapid Effects of E2 on Behavior

Page 10. Analysis of Behavior

Page 11. Experiment 2

Page 11. Hormone Treatment and Tissue Collection

Page 11. Histology

Page 12. Quantification of Egr-1 Expression

Page 13. Analysis of Egr-1 Expression

Page 13. Experiment 3

Page 13. Animals

Page 13. Hormone Manipulation

Page 14. Tissue Collection

Page 14. Histology

Page 14. Quantification of Egr-1 Expression

Page 15. Analysis of Egr-1 Expression

Page 15. Results

Page 15. Experiment 1

Page 15. Attacks

Page 15. Cage Position

Page 16. Experiment 2

Page 16. Egr-1 Immunoreactivity

Page 16. Experiment 3

Page 16. Egr-1 Immunoreactivity

Page 17. Discussion

Page 17. Rapid Effects of E2 on Aggression

Page 19. Rapid Effects of E2 on Egr-1 Expression

Page 23. Slow-Acting Effects of E2 on Egr-1 Expression

Page 25. Summary

Page 26. References

Page 38. Figures

Page 44. Supplementary Tables

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