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Acute and chronic effects of an aromatase inhibitor on territorial aggression in breeding and nonbreeding male song

K K Soma1, K A Sullivan, A D Tramontin

  • 1Department of Zoology, University of Washington, Seattle 98195, USA. ksoma@u.washington.edu

Journal of Comparative Physiology. A, Sensory, Neural, and Behavioral Physiology
|October 4, 2000
PubMed
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Estrogen, not testosterone, regulates male aggression in song sparrows during the nonbreeding season. Rapid estrogenic effects on territoriality were observed, with seasonal variations in endocrine mechanisms influencing male aggression.

Area of Science:

  • Neuroendocrinology
  • Behavioral Ecology

Background:

  • Male aggression is influenced by testosterone and its conversion to estradiol by brain aromatase.
  • Song sparrows exhibit territorial behavior year-round, even in the nonbreeding season when hormone levels are low.

Purpose of the Study:

  • To investigate the role of estrogens in regulating nonbreeding territorial aggression in male song sparrows.
  • To determine the seasonal differences in endocrine mechanisms controlling male aggression.

Main Methods:

  • Administered fadrozole, an aromatase inhibitor, acutely (1 day) and chronically (10 days) to male song sparrows.
  • Assessed territorial behavior and aggression levels in both breeding and nonbreeding seasons.
  • Measured brain aromatase activity and plasma hormone levels.

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Main Results:

  • Acute and chronic fadrozole treatment reduced nonbreeding aggression and territoriality, indicating a role for estrogens.
  • Fadrozole's effect on aggression was less pronounced in the spring breeding season.
  • Fadrozole treatment led to increased plasma testosterone in intact breeding males.

Conclusions:

  • Estrogens play a significant role in regulating nonbreeding male aggression in song sparrows.
  • The endocrine mechanisms underlying seasonal aggression differ, with estradiol being more critical in winter.
  • Sex steroids regulate male aggression seasonally, but the specific pathways vary between breeding and nonbreeding periods.