Distribution and Dynamics in the Expression of Androgen and Estrogen Receptors in Vocal Control Systems of Songbirds

Gahr, Manfred; Metzdorf, Reinhold

doi:10.1016/s0361-9230(97)00233-5

Cited by 156 publications

(195 citation statements)

References 65 publications

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“…Therefore, it is plausible that in spotted antbirds the increased expression of ER in POM during the nonbreeding season is related to an involvement of E2 in the control of aggressive behavior. Interestingly, our data match previous findings of elevated ER expression during the nonbreeding season in song control nuclei of canaries (Serinus canaria), which might also function to increase estrogenic effects on song behavior at this time of year (Gahr and Metzdorf, 1997;Fusani et al, 2000).…”

Section: Ar Era and Arom Expression In Pomsupporting

confidence: 91%

“…Therefore, during the nonbreeding season estrogens may be primarily used to regulate territorial aggression. Different functions of E2 and T in the regulation of behavior have already been proposed not only with respect to aggressive behavior, but also song (Gahr and Metzdorf, 1997). The up-regulation of AR-mRNA expression in the POM fits with the observed increases in circulating T levels and testis sizes during the breeding season in male spotted antbirds.…”

Section: Ar Era and Arom Expression In Pomsupporting

confidence: 67%

“…Furthermore, we also found opposite seasonal changes of AR-and ER -mRNA within the same nucleus, the POM, indicating a possible dissociation between the endocrine control of sexual and aggressive behavior. When compared across sex, season, or species, increased expression of steroid receptors is often coupled to increased action of steroids on the brain (Gahr and Metzdorf, 1997;Soma et al, 1999b;Cushing et al, 2004;Shah et al, 2004;Tetel et al, 2004). We therefore propose that AR and ER are elevated in male spotted antbirds during the nonbreeding season to increase brain sensitivity to the actions of low concentrations of sex steroids.…”

Section: Resultsmentioning

confidence: 96%

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Low sex steroids, high steroid receptors: Increasing the sensitivity of the nonreproductive brain

Canoine

Fusani

Schlinger

et al. 2006

Developmental Neurobiology

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Male aggressive behavior is generally regulated by testosterone (T). In most temperate breeding males, aggressive behavior is only expressed during the reproductive period. At this time circulating T concentrations, brain steroid receptors, and steroid metabolic enzymes are elevated in many species relative to the nonreproductive period. Many tropical birds, however, display aggressive behavior both during the breeding and the nonbreeding season, but plasma levels of T can remain low throughout the year and show little seasonal fluctuation. Studies on the year-round territorial spotted antbird (Hylophylax n. naevioides) suggest that T nevertheless regulates aggressive behavior in both the breeding and nonbreeding season. We hypothesize that to regulate aggressive behaviors during the nonbreeding season, when T is at its minimum, male spotted antbirds increase brain sensitivity to steroids. This can be achieved by locally up-regulating androgen receptors (ARs), estrogen receptors (ERs), or the enzyme aromatase (AROM) that converts T into estradiol. We therefore compared mRNA expression of AR, ERa, and AROM in freeliving male spotted antbirds across reproductive and nonreproductive seasons in two brain regions known to regulate both reproductive and aggressive behaviors. mRNA expression of ER in the preoptic area and AR in the nucleus taeniae were elevated in male spotted antbirds during the nonbreeding season when circulating T concentrations were low. This unusual seasonal receptor regulation may represent a means for the year-round regulation of vertebrate aggressive behavior via steroids by increasing the brain's sensitivity to sex steroids during the nonbreeding season.

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Section: Ar Era and Arom Expression In Pomsupporting

confidence: 91%

Section: Ar Era and Arom Expression In Pomsupporting

confidence: 67%

Section: Resultsmentioning

confidence: 96%

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Low sex steroids, high steroid receptors: Increasing the sensitivity of the nonreproductive brain

Canoine

Fusani

Schlinger

et al. 2006

Developmental Neurobiology

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“…(ii) AR expression in RA neurons may be down-regulated in nonbreeding-condition birds (e.g., ref. 39) and require trophic input from HVc to be upregulated. Decreased AR levels would make RA less sensitive to the stimulatory effects of T. In addition, there is a somewhat lower proportion of T-accumulating cells in RA (Ϸ47%) than in HVc (57%) in canaries (40).…”

Section: )mentioning

confidence: 99%

Act locally and think globally: Intracerebral testosterone implants induce seasonal-like growth of adult avian song control circuits

Brenowitz

Lent

2002

Proc. Natl. Acad. Sci. U.S.A.

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There is pronounced seasonal plasticity in the morphology of the neural circuits that regulate song behavior in adult songbirds, primarily in response to changes in plasma testosterone (T) levels. Most song nuclei have androgen receptors. Afferent input from the telencephalic nucleus HVc (also known as the ''high vocal center'') is necessary for seasonal growth of the direct efferent target nuclei RA and area X. We asked here whether T-stimulated growth of HVc is sufficient to induce growth of its efferent nuclei. Intracerebral T implants were placed unilaterally near HVc or RA in photosensitive adult male white-crowned sparrows for one month. The T implant near HVc produced significant growth of the ipsilateral (but not contralateral) HVc, RA, and area X, and increased neuronal number in the ipsilateral HVc. The T implant near RA did not produce selective growth of ipsilateral RA, HVc, or area X. Intracerebral T implants did not elevate plasma T levels, nor did they stimulate growth of two peripheral androgen sensitive targets, the syrinx and the cloacal protuberance. These results suggest that seasonal growth of the adult song circuits results from T acting directly on HVc, which then stimulates the growth of RA and area X transynaptically.

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“…These data suggest that the brain is less sensitive to sex steroids in the nonbreeding season. Furthermore, hypothalamic aromatase and steroid receptors are often downregulated in the nonbreeding season (Hutchison et al 1986;Schlinger & Callard 1990;Gahr & Metzdorf 1997;Soma et al 1999b,c). Future studies will examine seasonal changes in aromatase and oestrogen receptors in song sparrows.…”

Section: (B) Possible Hypothesesmentioning

confidence: 99%

Oestrogen regulates male aggression in the non–breeding season

Soma

Tramontin

Wingfield

2000

Proc. R. Soc. Lond. B

190

107

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Extensive research has focused on territorial aggression during the breeding season and the roles of circulating testosterone (T) and its conversion to 17b -oestradiol (E 2 ) in the brain. However, many species also defend territories in the non-breeding season, when circulating T-levels are low. The endocrine control of non-breeding territoriality is poorly understood. The male song sparrow of Washington State is highly territorial year-round, but plasma T is basal in the non-breeding season (autumn and winter). Castration has no e¡ect on aggression in autumn, suggesting that autumnal territoriality is independent of gonadal hormones. However, non-gonadal sex steroids may regulate winter territoriality (e.g. oestrogen synthesis by brain aromatase). In this ¢eld experiment, we treated wild non-breeding male song sparrows with a speci¢c aromatase inhibitor (fadrozole, FAD) using micro-osmotic pumps. FAD greatly reduced several aggressive behaviours. The e¡ects of FAD were reversed by E 2 replacement. Treatment did not a¡ect body condition or plasma corticosterone, suggesting that all subjects were healthy. These data indicate that E 2 regulates male aggression in the non-breeding season and challenge the common belief that aggression in the non-breeding season is independent of sex steroids. More generally, these results raise fundamental questions about how sexual and/or aggressive behaviours are maintained in a variety of model vertebrate species despite low circulating levels of sex steroids or despite castration. Such nonclassical endocrine mechanisms may be common among vertebrates and play an important role in the regulation of behaviour.

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Distribution and Dynamics in the Expression of Androgen and Estrogen Receptors in Vocal Control Systems of Songbirds

Cited by 156 publications

References 65 publications

Low sex steroids, high steroid receptors: Increasing the sensitivity of the nonreproductive brain

Low sex steroids, high steroid receptors: Increasing the sensitivity of the nonreproductive brain

Act locally and think globally: Intracerebral testosterone implants induce seasonal-like growth of adult avian song control circuits

Oestrogen regulates male aggression in the non–breeding season

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