Brain aromatase, 5α‐reductase, and 5β‐reductase change seasonally in wild male song sparrows: Relationship to aggressive and sexual behavior

Wiley - Tập 56 Số 3 - Trang 209-221 - 2003
Kiran K. Soma1, Barney A. Schlinger1, John C. Wingfield2, Colin J. Saldanha3
1Department of Physiological Science and Laboratory of Neuroendocrinology of the Brain Research Institute, University of California at Los Angeles, Los Angeles, California 90095
2Department of Zoology, University of Washington, Seattle, Washington, 98195
3Department of Biological Sciences, Lehigh University, Bethlehem, Pennsylvania, 18015

Tóm tắt

Abstract

In many species, territoriality is expressed only during the breeding season, when plasma testosterone (T) is elevated. In contrast, in song sparrows (Melospiza melodia morphna), males are highly territorial during the breeding (spring) and nonbreeding (autumn) seasons, but not during molt (late summer). In autumn, plasma sex steroids are basal, and castration has no effect on aggression. However, inhibition of aromatase reduces nonbreeding aggression, suggesting that neural steroid metabolism may regulate aggressive behavior. In wild male song sparrows, we examined the neural distribution of aromatase mRNA and seasonal changes in the activities of aromatase, 5α‐, and 5β‐reductase, enzymes that convert T to 17β‐estradiol, 5α‐dihydrotestosterone (5α‐DHT, a potent androgen), or 5β‐DHT (an inactive metabolite), respectively. Enzyme activities were measured in the diencephalon, ventromedial telencephalon (vmTEL, which includes avian amygdala), caudomedial neostriatum (NCM), and the hippocampus of birds captured during spring, molt, or autumn. Aromatase and 5β‐reductase changed seasonally in a region‐specific manner. Aromatase in the diencephalon was higher in spring than in molt and autumn, similar to seasonal changes in male sexual behavior. Aromatase activity in the vmTEL was high in both spring and autumn but significantly reduced at molt, similar to seasonal changes in aggression. 5β‐Reductase was not elevated during molt, suggesting that low aggression during molt is not a result of increased inactivation of androgens. These data highlight the relevance of neural steroid metabolism to the expression of natural behaviors by free‐living animals. © 2003 Wiley Periodicals, Inc. J Neurobiol 56: 209–221, 2003

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Wiley

Tập 56 Số 3

209-221

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