Brain testosterone metabolism during ontogeny in the zebra finch

Balthazart, Jacques; Schumacher, Michaël; Pröve, Ekkehard

doi:10.1016/0006-8993(86)90927-3

Cited by 19 publications

(12 citation statements)

References 33 publications

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“…The presence of aromatase activity (AA) in the fetal, neonate, and adult brain has been demonstrated in many vertebrate species [9][10][11][12][13]. We undertook a study to determine whether AA is present in the fetal guinea pig brain.…”

Section: Introductionmentioning

confidence: 97%

Aromatase Activity in Developing Guinea Pig Brain: Ontogeny and Effects of Exogenous Androgens1

Connolly

Roselli

Resko

1994

Biology of Reproduction

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The formation of estrogens from androgens by aromatase in the developing brain is an important step in the sexual differentiation of many species. We characterized aromatase activity (AA) in a high-speed pellet of brain tissue from fetal guinea pigs. The apparent substrate affinity (approximately 17 nM) was comparable to reported values in other species. Aromatase activity was highest in the amygdala (AMG) and preoptic area (POA), with lesser amounts in the septum (SEPT) and medial basal hypothalamus (MBH). Activity was low but measurable in parietal cortex (CTX). In the AMG, POA, SEPT, and MBH, AA was highest in early gestation (Days 35-40) and showed a steady decline through development. No sex difference in AA was apparent. We also determined the effects of administration of exogenous androgens to pregnant females on brain AA in the fetus. Testosterone propionate (5 mg/day on Days 30-39 followed by 1 mg/day on Days 40-50) caused a significant increase (p < 0.05) in AA found in the MBH and CTX. Administration of dihydrotestosterone propionate (2.5 mg/day on Days 30-39 followed by 1 mg/day on Days 40-50) significantly stimulated AA in SEPT, MBH, and CTX. These data demonstrate that the fetal guinea pig brain contains high levels of AA during the critical period of sexual differentiation. Treatment with high levels of exogenous androgens consistently induces AA in the MBH and CTX. These latter effects may be among the mechanisms through which exogenous androgens act on the developing brain.

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Section: Introductionmentioning

confidence: 97%

Aromatase Activity in Developing Guinea Pig Brain: Ontogeny and Effects of Exogenous Androgens1

Connolly

Roselli

Resko

1994

Biology of Reproduction

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“…The use of a mammalian model of sexual differentiation to account for this process in zebra finches faces several difficulties, however (Adkins-Regan, 1990). First, measures of peripheral circulating sex steroid levels during development have so far failed to reveal any significant and consistently replicable dimorphism during the period when exogenous estrogen treatment is capable of masculinizing the song system ( Adkins-Regan et al, 1990;Hutchison et al, 1984;Prove, 1983;Schlinger and Arnold, 1992), nor has any dimorphism been found thus far in the levels of aromatase (the enzyme system that produces estrogen) or other sex steroid metabolizing enzymes in the hypothalamus or telencephalic song nuclei of developing finches (Balthazart et al, 1986;Schlinger and Arnold, 1992;Vockel et al, 1988Vockel et al, , 1990. Second, attempts to prevent or reduce masculinization of the song system of males by reducing estrogen exposure during development by castration or antiestrogen treatment have thus far not succeeded (Adkins-Regan and Ascenzi, 1990;Arnold, 1975a;Mathews et al, 1988;Mathews and Arnold, 1990), although these negative results could be due to the failure of castration to lower estrogen levels and of the drugs used to function as antiestrogens in the young finch brain ( Mathews and Arnold, 1990).…”

Section: Introductionmentioning

confidence: 99%

Sexual differentiation of brain and behavior in the zebra finch: Critical periods for effects of early estrogen treatment

et al. 1994

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In order to determine the critical period(s) during which estrogen alters sexually dimorphic behavior and neuroanatomy in zebra finches (Poephila guttata), nestlings were injected daily with 20 micrograms estradiol benzoate (EB) during posthatching week 1, week 2, week 3, or weeks 1, 2, and 3. At 7 months of age, birds were implanted with testosterone propionate and tested with female partners for singing, dancing, and copulatory mounting. Brains were subsequently processed for morphometry, and the volumes of the song system nuclei HVC, area X, and RA and the soma sizes and densities of neurons in RA were determined. Males given EB during week 1 failed to mount. Females given EB during week 1 were fully masculinized with respect to dancing and RA neuron soma size and density, and were partially masculinized with respect to song nuclei volumes and singing. Treatment beginning after week 1 was ineffective or less effective for all measures. Only for RA neuron measures was treatment for all three weeks more effective than week 1 treatment. Thus the first post-hatching week is the most influential period of those tested for effects of exogenous estrogen on sexual differentiation in this species, and is a period during which both masculinization of females and demasculinization of males is possible.

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“…It is expressed in large amounts in the zebra finch brain (Balthazart et al, 1986: Vockel et al, 1990. Therefore, it could compete with aromatase for available androgens and indirectly limit estrogen production in one sex or brain region at an appropriate time in development.…”

Section: Introductionmentioning

confidence: 99%

“…A third possibility involves the 50-reductase enzyme, which is thought to catalyze the conversion of androgens to biologically inert substances [T to SP-dihydrotestosterone and AE to 5P-androstanedione (SP-A)] (Steimer and Hutchison,198 1). It is expressed in large amounts in the zebra finch brain (Balthazart et al, 1986: Vockel et al, 1990. Therefore, it could compete with aromatase for available androgens and indirectly limit estrogen production in one sex or brain region at an appropriate time in development.…”

Section: Introductionmentioning

confidence: 99%

Aromatase and 5β‐reductase activity in cultures of developing zebra finch brain: An investigation of sex and regional differences

1995

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Estrogen treatment of hatchling female zebra finches causes the masculine development of singing behavior and of the telencephalic brain regions involved in the control of song. However, early estrogen treatment of males also blocks masculine development of copulatory behavior, presumably controlled by diencephalic regions. In an effort to determine whether the differences in estrogen action are related to sex and regional differences in androgen metabolism (estrogen synthesis or androgen inactivation), we measured aromatase and 5 beta-reductase activity in dissociated-cell cultures made separately from the telencephalon, diencephalon, and also cerebellum of hatchling zebra finches under a variety of conditions. Cultures from all three brain regions express high levels of aromatase and 5 beta-reductase activity. Comparisons between telencephalic and diencephalic cultures of the activity and kinetics of aromatase suggest that the telencephalic cultures convert androgen to estrogen more efficiently than diencephalic cultures, which might be important in the differential action of estrogen in the two brain regions. However, the activity of neither aromatase nor 5 beta-reductase was significantly different between the sexes in either telencephalic or diencephalic cultures. Thus, comparisons between the sexes do not support the idea that differences in posthatching aromatase or 5 beta-reductase activity account for the pattern of sexual differentiation of the song and copulatory systems.

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Brain testosterone metabolism during ontogeny in the zebra finch

Cited by 19 publications

References 33 publications

Aromatase Activity in Developing Guinea Pig Brain: Ontogeny and Effects of Exogenous Androgens1

Aromatase Activity in Developing Guinea Pig Brain: Ontogeny and Effects of Exogenous Androgens1

Sexual differentiation of brain and behavior in the zebra finch: Critical periods for effects of early estrogen treatment

Aromatase and 5β‐reductase activity in cultures of developing zebra finch brain: An investigation of sex and regional differences

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