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Juli Wade - One of the best experts on this subject based on the ideXlab platform.
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Masculinized sexual partner preference in female zebra finches with sex-reversed gonads.
Hormones and behavior, 2001Co-Authors: Elizabeth Adkins-regan, Juli WadeAbstract:Previous research in the zebra finch, a socially monogamous pair-bonding species, suggests that the preference for opposite-sex partners may arise in part through the organizing actions of sex steroids. To further investigate this process, zebra finch eggs were injected with 20 μg Fadrozole, a potent estrogen synthesis inhibitor, or with the saline vehicle on embryonic day 5. As adults they were given two-choice sexual partner preference tests followed by group aviary tests. Fadrozole females had masculinized beak color and had testes or ovotestes instead of ovaries. Males were not affected by Fadrozole; they did not differ from controls on any measure. In contrast, sexual partner preference was substantially masculinized in Fadrozole females in the group aviary tests. Untreated males given a choice between Fadrozole and untreated females preferred the untreated females, but this was equally the case when they were given a choice between saline-treated and untreated females. These results suggest that males do not specifically avoid females with testes and that male avoidance is unlikely to explain why Fadrozole-treated females pair with other females. The present data add to the evidence that actions of gonadal steroids during development contribute to adult sex differences in partner preference in this pair-bonding species. Furthermore, because Fadrozole-treated females do not produce audible song, the mechanisms regulating partner preference and song system development are dissociated.
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Sexual differentiation of the zebra finch song system parallels genetic, not gonadal, sex.
Hormones and behavior, 1999Co-Authors: Juli Wade, David A. Swender, Teresa L. McelhinnyAbstract:Mechanisms regulating sexual differentiation of the zebra finch song system present an intriguing puzzle. Masculine development of brain regions and behavior can be induced in genetic females by posthatching estradiol treatment. That result is consistent with the hypothesis that estradiol, converted within the brain from testicular androgen via the aromatase enzyme, masculinizes neural structure and function. In contrast, treatment during specific stages of development with the aromatase inhibitor Fadrozole has not prevented masculine development, and the presence of testicular tissue in genetic females did not induce masculine organization of neuroanatomy or singing behavior. Fadrozole treatments in those previous studies were limited, however, and most genetic females had both ovarian and testicular tissue. The present experiments were designed to provide increased aromatase inhibition and to reliably produce genetic females with only testicular tissue. Eggs received a single injection at a later age or with higher doses of Fadrozole than had been used previously. Some embryos were exposed to Fadrozole more frequently by either injecting eggs on 2 days of development or dipping them for 10-12 days in Fadrozole. Finally, in some individuals from Fadrozole-treated eggs, the left gonad was removed, leaving each genetic male and female with a single right testis. None of these treatments significantly affected development of the song system compared to appropriate control groups. These results suggest that sexual differentiation of the zebra finch song system is not regulated by embryonic aromatase activity or by gonadal secretions and instead involves events that need not be mediated by steroid hormones.
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Fadrozole: a potent and specific inhibitor of aromatase in the zebra finch brain.
General and comparative endocrinology, 1994Co-Authors: Juli Wade, Barney A. Schlinger, Lynn Hodges, Arthur P. ArnoldAbstract:Aromatase and 5 beta-reductase activity are expressed at high levels in the zebra finch brain, especially in the telencephalon. Aromatization of androgens to estrogens is thought to be a critical step in the organization and activation of avian sexual behaviors. In contrast, 5 beta-reductase is thought to be an inactivating enzyme, one that catalyzes the conversion of androgens to biologically inactive metabolites. To address the importance of aromatase activity in this system, it is necessary to find an effective and selective aromatase inhibitor, one that has little or no effect on other androgen-metabolizing enzymes. The potency and specificity of Fadrozole hydrochloride as an aromatase inhibitor was tested in zebra finch telencephalon. The compound was tested in vitro in primary dissociated cell cultures made from hatching telencephalon and compared to a commonly used inhibitor, 1,4,6-androstatriene-3,17-dione (ATD). Untreated, these cultures express extremely high levels of aromatase and 5 beta-reductase activity and therefore allow sensitive measurement of the effectiveness of inhibitors. Aromatase activity was also measured in homogenates of adult telencephalon following in vivo Fadrozole injection. Finally, aromatase and 5 beta-reductase activity were quantified in zebra finch telencephalon following similar intramuscular injections in 4- to 6-day-old birds. In all three cases, Fadrozole was highly effective in reducing aromatase activity. Fadrozole increased 5 beta-reductase activity, presumably due to an increase in available substrate, but had no inhibitory effect on the enzyme. ATD was less effective in inhibiting aromatase, and it also inhibited 5 beta-reductase activity at high concentrations.
Colin J. Saldanha - One of the best experts on this subject based on the ideXlab platform.
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Intracerebral estrogen provision increases cytogenesis and neurogenesis in the injured zebra finch brain
Developmental neurobiology, 2011Co-Authors: Bradley J. Walters, Nikita G. Alexiades, Colin J. SaldanhaAbstract:To determine whether or not local, injury-induced aromatization and/orestrogen provision can affect cyto-or neuro-genesis following mechanical brain damage, two groups of adult male zebra finches sustained bilateral penetrating brain injuries. The first received contralateral injections of vehicle or the aromatase inhibitor Fadrozole. The second group received contalateral injections of Fadrozole, or Fadrozole with 17β-estradiol. Subsequent to injury, birds were injected with the thymidine analog 5-Bromo-2′-deoxyuridine (BrdU). Two weeks following injury, the birds were perfused, and coronal sections were labeled using antibodies against BrdU and the neuronal proteins HuC/HuD. In a double blind fashion, BrdU positive cells and BrdU/Hu double-labeled cells in the subventricular zone (SVZ) and at the injury site (INJ) were imaged and sampled. The average numbers of cells per image were compared across brain regions and treatments using repeated measures ANOVAs and, where applicable, post-hoc, pairwise comparisons. Fadrozole administration had no detectable effect on cytogenesis or neurogenesis, however, Fadrozole coupled with estradiol significantly increased both measures. The dorsal SVZ had the greatest proportion of new cells that differentiated into neurons, though the highest numbers of BrdU labeled and BrdU, Hu double-labeled cells were detected at the injury site. In the adult zebra finch brain, local estradiol provision can increase cytogenesis and neurogenesis, however, whether or not endogenous glial aromatization is sufficient to similarly affect these processes remains to be seen.
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Inhibition of Injury-Induced Glial Aromatase Reveals a Wave of Secondary Degeneration in the Songbird Brain
Glia, 2008Co-Authors: Ryan D. Wynne, Bradley J. Walters, David J. Bailey, Colin J. SaldanhaAbstract:Mechanical or anoxic/ischemic brain insult results in reactive gliosis and a pronounced wave of apoptotic secondary degeneration (WSD). Reactive glia express aromatase (estrogen synthase) and glial estrogen synthesis decreases apoptosis and the volume of degeneration. Whether aromatization by glia affects gliosis itself or the initiation/maintenance of the WSD remains unknown. Adult male zebra finches (Taeniopygia guttata) were injured with a needle that contained the aromatase inhibitor Fadrozole or vehicle into contralateral hemispheres. Birds were killed at 0, 2, 6, 24, 72 h, 2 or 6 weeks postinjury. Gliosis and degeneration were measured with vimentin- and Fluoro-Jade B-expression, respectively. Reactive gliosis was detectable at 6 h, reached asymptote at 72 h, and continued until 6 weeks postinsult. Gliosis extended further around Fadrozole-injury than vehicle, an effect driven by a larger area of gliosis around Fadrozole- relative to vehicle-injury at 72 h postinsult. Glial aromatase was inhibited for about 2 weeks postinjury since aromatase relative optical density was higher around Fadrozole-injury relative to vehicle-injury until this time-point. Degeneration around vehicle-injury reached asymptote at 2 h postinsult, but that around Fadrozole-injury peaked 24– 72 h postinjury and decreased thereafter. Thus, the injuryinduced WSD as described in mammals is detectable in zebra finches only following glial aromatase inhibition. In the zebra finch, injury-induced estrogen provision may decrease reactive gliosis and severely dampen the WSD, suggesting that songbirds are powerful models for understanding the role of glial aromatization in secondary brain damage. V C 2007 Wiley-Liss, Inc.
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Glial aromatization decreases neural injury in the zebra finch (Taeniopygia guttata): influence on apoptosis.
Journal of neuroendocrinology, 2004Co-Authors: Ryan D. Wynne, Colin J. SaldanhaAbstract:Emerging evidence suggests a neuroprotective role for oestrogens following damage to the vertebrate brain. Aromatase (oestrogen synthase) is rapidly transcribed and translated in glial cells around areas of neural damage in several vertebrates. However, the potential neuroprotection afforded by locally up-regulated glial aromatase immediately surrounding the injury remains to be tested. Towards this end, individual birds sustained penetrating mechanical injuries via a needle that contained either vehicle or the aromatase inhibitor Fadrozole into contralateral hemispheres. Seventy-two hours later, the size of neural injury (as assessed by the extent of necrotic tissue) and the number of apoptotic cells around the injuries were evaluated. The size of injury in the hemisphere injected with Fadrozole was significantly larger than the injury caused by vehicle injection. Furthermore, a greater number of apoptotic nuclei were found around the Fadrozole-associated lesion relative to vehicle. Finally, constitutively expressed, neuronal aromatase close to the injury site did not differ between hemispheres. We conclude that local inhibition of glial aromatase immediately around the site of injury plays a neuroprotective role in the songbird brain and this protection involves apoptotic pathways. Local up-regulation of glial aromatase may play a pivotal role in the limitation of secondary damage and/or the acceleration of restorative processes following injury to the vertebrate brain.
Gerald T. Ankley - One of the best experts on this subject based on the ideXlab platform.
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Adverse Outcome Pathway Network-Based Assessment of the Interactive Effects of an Androgen Receptor Agonist and an Aromatase Inhibitor on Fish Endocrine Function.
Environmental toxicology and chemistry, 2020Co-Authors: Gerald T. Ankley, Kathleen M Jensen, Michael D Kahl, Jenna E. Cavallin, Brett R. Blackwell, Jon A. Doering, David J. Feifarek, Carlie A. Lalone, Shane T. Poole, Eric C. RandolphAbstract:Predictive approaches to assessing the toxicity of contaminant mixtures have been largely limited to chemicals that exert effects through the same biological molecular initiating event. However, by understanding specific pathways through which chemicals exert effects, it may be possible to identify shared "downstream" nodes as the basis for forecasting interactive effects of chemicals with different molecular initiating events. Adverse outcome pathway (AOP) networks conceptually support this type of analysis. We assessed the utility of a simple AOP network for predicting the effects of mixtures of an aromatase inhibitor (Fadrozole) and an androgen receptor agonist (17β-trenbolone) on aspects of reproductive endocrine function in female fathead minnows. The fish were exposed to multiple concentrations of Fadrozole and 17β-trenbolone individually or in combination for 48 or 96 h. Effects on 2 shared nodes in the AOP network, plasma 17β-estradiol (E2) concentration and vitellogenin (VTG) production (measured as hepatic vtg transcripts) responded as anticipated to Fadrozole alone but were minimally impacted by 17β-trenbolone alone. Overall, there were indications that 17β-trenbolone enhanced decreases in E2 and vtg in Fadrozole-exposed fish, as anticipated, but the results often were not statistically significant. Failure to consistently observe hypothesized interactions between Fadrozole and 17β-trenbolone could be due to several factors, including lack of impact of 17β-trenbolone, inherent biological variability in the endpoints assessed, and/or an incomplete understanding of interactions (including feedback) between different pathways within the hypothalamic-pituitary-gonadal axis. Environ Toxicol Chem 2020;39:913-922. © 2020 SETAC.
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Rapid effects of the aromatase inhibitor Fadrozole on steroid production and gene expression in the ovary of female fathead minnows (Pimephales promelas)
General and comparative endocrinology, 2017Co-Authors: Anthony L. Schroeder, Kathleen M Jensen, Michael D Kahl, Elizabeth A Makynen, Gerald T. Ankley, Tanwir Habib, Natàlia Garcia-reyero, Barbara Lynn Escalon, Elizabeth J. Durhan, Jenna E. CavallinAbstract:Abstract Cytochrome P450 aromatase catalyzes conversion of C19 androgens to C18 estrogens and is critical for normal reproduction in female vertebrates. Fadrozole is a model aromatase inhibitor that has been shown to suppress estrogen production in the ovaries of fish. However, little is known about the early impacts of aromatase inhibition on steroid production and gene expression in fish. Adult female fathead minnows ( Pimephales promelas ) were exposed via water to 0, 5, or 50 µg Fadrozole/L for a time-course of 0.5, 1, 2, 4, and 6 h, or 0 or 50 µg Fadrozole/L for a time-course of 6, 12, and 24 h. We examined ex vivo ovarian 17β-estradiol (E2) and testosterone (T) production, and plasma E2 concentrations from each study. Expression profiles of genes known or hypothesized to be impacted by Fadrozole including aromatase (cytochrome P450 [ cyp ] 19a1a ), steriodogenic acute regulatory protein ( star ), cytochrome P450 side-chain cleavage ( cyp11a ), cytochrome P450 17 alpha hydroxylase/17,20 lyase ( cyp17 ), and follicle stimulating hormone receptor ( fshr ) were measured in the ovaries by quantitative real-time polymerase chain reaction (QPCR). In addition, broader ovarian gene expression was examined using a 15k fathead minnow microarray. The 5 µg/L exposure significantly reduced e x vivo E2 production by 6 h. In the 50 µg/L treatment, ex vivo E2 production was significantly reduced after just 2 h of exposure and remained depressed at all time-points examined through 24 h. Plasma E2 concentrations were significantly reduced as early as 4 h after initiation of exposure to either 5 or 50 µg Fadrozole/L and remained depressed throughout 24 h in the 50 µg/L exposure. Ex vivo T concentrations remained unchanged throughout the time-course. Expression of transcripts involved in steroidogenesis increased within the first 24 h suggesting rapid induction of a mechanism to compensate for Fadrozole inhibition of aromatase. Microarray results also showed Fadrozole exposure caused concentration- and time-dependent changes in gene expression profiles in many HPG-axis pathways as early as 4 h. This study provides insights into the very rapid effects of aromatase inhibition on steroidogenic processes in fish.
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developing predictive approaches to characterize adaptive responses of the reproductive endocrine axis to aromatase inhibition i data generation in a small fish model
Toxicological Sciences, 2013Co-Authors: Daniel L Villeneuve, Kathleen M Jensen, Elizabeth A Makynen, Jenna E. Cavallin, David C Bencic, Miyuki Breen, Linnea M Thomas, Leah C Wehmas, Rory B Conolly, Gerald T. AnkleyAbstract:Adaptive or compensatory responses to chemical exposure can significantly influence in vivo concentration-duration-response relationships. This study provided data to support development of a computational dynamic model of the hypothalamic-pituitary-gonadal axis of a model vertebrate and its response to aromatase inhibitors as a class of endocrine active chemicals. Fathead minnows (Pimephales promelas) were either exposed to the aromatase inhibitor Fadrozole (0.5 or 30 μg/l) continuously for 1, 8, 12, 16, 20, 24, or 28 days or exposed for 8 days and then held in control water (no Fadrozole) for an additional 4, 8, 12, 16, or 20 days. The time course of effects on ovarian steroid production, circulating 17β-estradiol (E2) and vitellogenin (VTG) concentrations, and expression of steroidogenesis-related genes in the ovary was measured. Exposure to 30 μg Fadrozole/l significantly reduced plasma E2 and VTG concentrations after just 1 day and those effects persisted throughout 28 days of exposure. In contrast, ex vivo E2 production was similar to that of controls on day 8-28 of exposure, whereas transcripts coding for aromatase and follicle-stimulating hormone receptor were elevated, suggesting a compensatory response. Following cessation of Fadrozole exposure, ex vivo E2 and plasma E2 concentrations exceeded and then recovered to control levels, but plasma VTG concentrations did not, even after 20 days of depuration. Collectively these data provide several new insights into the nature and time course of adaptive responses to an aromatase inhibitor that support development of a computational model (see companion article).
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altered gene expression in the brain and ovaries of zebrafish danio rerio exposed to the aromatase inhibitor Fadrozole microarray analysis and hypothesis generation
Environmental Toxicology and Chemistry, 2009Co-Authors: Daniel L Villeneuve, Ronglin Wang, David C Bencic, Adam D Biales, Dalma Martinovic, James M Lazorchak, Gregory P Toth, Gerald T. AnkleyAbstract:As part of a research effort examining system-wide responses of the hypothalamic-pituitary-gonadal (HPG) axis in fish to endocrine-active chemicals (EACs) with different modes of action, zebrafish (Danio rerio) were exposed to 25 or 100 μg/L of the aromatase inhibitor Fadrozole for 24, 48, or 96 h. Global transcriptional response in brain and ovarian tissue of fish exposed to 25 μg/L of Fadrozole was compared to that in control fish using a commercially available, 22,000-gene oligonucleotide microarray. Transcripts altered in brain were functionally linked to differentiation, development, DNA replication, and cell cycle. Additionally, multiple genes associated with the one-carbon pool by folate pathway (KEGG 00670) were significantly up-regulated. Transcripts altered in ovary were functionally linked to cell-cell adhesion, extracellular matrix, vasculogenesis, and development. Promoter motif analysis identified GATA-binding factor 2, Ikaros 2, alcohol dehydrogenase gene regulator 1, myoblast-determining factor, and several heat shock factors as being associated with coexpressed gene clusters that were differentially expressed following exposure to Fadrozole. Based on the transcriptional changes observed, it was hypothesized that Fadrozole elicits neurodegenerative stress in brain tissue and that fish cope with this stress through proliferation of radial glial cells. Additionally, it was hypothesized that changes of gene expression in the ovary of Fadrozole-exposed zebrafish reflect disruption of oocyte maturation and ovulation because of impaired vitellogenesis. These hypotheses and others derived from the microarray results provide a foundation for future studies aimed at understanding responses of the HPG axis to EACs and other chemical stressors.
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altered gene expression in the brain and liver of female fathead minnows pimephales promelas rafinesque exposed to Fadrozole
Journal of Fish Biology, 2008Co-Authors: Daniel L Villeneuve, Iris Knoebl, Patrick Larkin, Ann L. Miracle, Barbara J. Carter, Nancy D. Denslow, Gerald T. AnkleyAbstract:The fathead minnow (Pimephales promelas) is a small fish species widely used for ecotoxicology research and regulatory testing in North America. This study used a novel 2000 gene oligonucleotide microarray to evaluate the effects of the aromatase inhibitor, Fadrozole, on gene expression in the liver and brain tissue of exposed females. Exposure to 60 μg 1-1 Fadrozole/L for 7 d, resulted in the significant (p<0.05; high-moderate agreement among multiple probes spotted on the array) up-regulation of approximately 47 genes in brain and 188 in liver, and the significant down-regulation of 61 genes in brain and 162 in liver. In particular, Fadrozole exposure elicited significant up-regulation of five genes in brain involved in the cholesterol synthesis pathway and altered the expression of over a dozen cytoskeleton-related genes. In the liver, there was notable down-regulation of genes coding for vitellogenin precursors, vigillin, and fibroin-like ovulatory proteins which were consistent with an expected reduction in plasma estradiol concentrations as a result of Fadrozole exposure and an associated reduction in measured plasma vitellogenin concentrations. These changes coincided with a general down-regulation of genes coding for non-mitochondrial ribosomal proteins and proteins that play a role in translation. With the exception of the fibroin-like ovulatory proteins,more » real-time PCR results largely corroborated the microarray responses. Overall, results of this study demonstrate the utility of high density oligonucleotide microarrays for unsupervised, discovery-driven, ecotoxicogenomics research with the fathead minnow and helped inform the subsequent development of a 22,000 gene microarray for the species.« less
Ryan D. Wynne - One of the best experts on this subject based on the ideXlab platform.
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Glial Aromatization Decreases Neural Injury in the Zebra Finch (Taeniopygia guttata): Influence on Apoptosis
2013Co-Authors: Ryan D. Wynne, C J SaldanhaAbstract:Emerging evidence suggests a neuroprotective role for oestrogens following damage to the vertebrate brain. Aromatase (oestrogen synthase) is rapidly transcribed and translated in glial cells around areas of neural damage in several vertebrates. However, the potential neuroprotection afforded by locally upregulated glial aromatase immediately surrounding the injury remains to be tested. Towards this end, individual birds sustained penetrating mechanical injuries via a needle that contained either vehicle or the aromatase inhibitor Fadrozole into contralateral hemispheres. Seventy-two hours later, the size of neural injury (as assessed by the extent of necrotic tissue) and the number of apoptotic cells around the injuries were evaluated. The size of injury in the hemisphere injected with Fadrozole was significantly larger than the injury caused by vehicle injection. Furthermore, a greater number of apoptotic nuclei were found around the Fadrozole-associated lesion relative to vehicle. Finally, constitutively expressed, neuronal aromatase close to the injury site did not differ between hemispheres. We conclude that local inhibition of glial aromatase immediately around the site of injury plays a neuroprotective role in the songbird brain and this protection involves apoptotic pathways. Local up-regulation of glial aromatase may play a pivotal role in the limitation of secondary damage and/or the acceleration of restorative processes following injury to th
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Inhibition of Injury-Induced Glial Aromatase Reveals a Wave of Secondary Degeneration in the Songbird Brain
Glia, 2008Co-Authors: Ryan D. Wynne, Bradley J. Walters, David J. Bailey, Colin J. SaldanhaAbstract:Mechanical or anoxic/ischemic brain insult results in reactive gliosis and a pronounced wave of apoptotic secondary degeneration (WSD). Reactive glia express aromatase (estrogen synthase) and glial estrogen synthesis decreases apoptosis and the volume of degeneration. Whether aromatization by glia affects gliosis itself or the initiation/maintenance of the WSD remains unknown. Adult male zebra finches (Taeniopygia guttata) were injured with a needle that contained the aromatase inhibitor Fadrozole or vehicle into contralateral hemispheres. Birds were killed at 0, 2, 6, 24, 72 h, 2 or 6 weeks postinjury. Gliosis and degeneration were measured with vimentin- and Fluoro-Jade B-expression, respectively. Reactive gliosis was detectable at 6 h, reached asymptote at 72 h, and continued until 6 weeks postinsult. Gliosis extended further around Fadrozole-injury than vehicle, an effect driven by a larger area of gliosis around Fadrozole- relative to vehicle-injury at 72 h postinsult. Glial aromatase was inhibited for about 2 weeks postinjury since aromatase relative optical density was higher around Fadrozole-injury relative to vehicle-injury until this time-point. Degeneration around vehicle-injury reached asymptote at 2 h postinsult, but that around Fadrozole-injury peaked 24– 72 h postinjury and decreased thereafter. Thus, the injuryinduced WSD as described in mammals is detectable in zebra finches only following glial aromatase inhibition. In the zebra finch, injury-induced estrogen provision may decrease reactive gliosis and severely dampen the WSD, suggesting that songbirds are powerful models for understanding the role of glial aromatization in secondary brain damage. V C 2007 Wiley-Liss, Inc.
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Glial aromatization decreases neural injury in the zebra finch (Taeniopygia guttata): influence on apoptosis.
Journal of neuroendocrinology, 2004Co-Authors: Ryan D. Wynne, Colin J. SaldanhaAbstract:Emerging evidence suggests a neuroprotective role for oestrogens following damage to the vertebrate brain. Aromatase (oestrogen synthase) is rapidly transcribed and translated in glial cells around areas of neural damage in several vertebrates. However, the potential neuroprotection afforded by locally up-regulated glial aromatase immediately surrounding the injury remains to be tested. Towards this end, individual birds sustained penetrating mechanical injuries via a needle that contained either vehicle or the aromatase inhibitor Fadrozole into contralateral hemispheres. Seventy-two hours later, the size of neural injury (as assessed by the extent of necrotic tissue) and the number of apoptotic cells around the injuries were evaluated. The size of injury in the hemisphere injected with Fadrozole was significantly larger than the injury caused by vehicle injection. Furthermore, a greater number of apoptotic nuclei were found around the Fadrozole-associated lesion relative to vehicle. Finally, constitutively expressed, neuronal aromatase close to the injury site did not differ between hemispheres. We conclude that local inhibition of glial aromatase immediately around the site of injury plays a neuroprotective role in the songbird brain and this protection involves apoptotic pathways. Local up-regulation of glial aromatase may play a pivotal role in the limitation of secondary damage and/or the acceleration of restorative processes following injury to the vertebrate brain.
Arthur P. Arnold - One of the best experts on this subject based on the ideXlab platform.
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Fadrozole: a potent and specific inhibitor of aromatase in the zebra finch brain.
General and comparative endocrinology, 1994Co-Authors: Juli Wade, Barney A. Schlinger, Lynn Hodges, Arthur P. ArnoldAbstract:Aromatase and 5 beta-reductase activity are expressed at high levels in the zebra finch brain, especially in the telencephalon. Aromatization of androgens to estrogens is thought to be a critical step in the organization and activation of avian sexual behaviors. In contrast, 5 beta-reductase is thought to be an inactivating enzyme, one that catalyzes the conversion of androgens to biologically inactive metabolites. To address the importance of aromatase activity in this system, it is necessary to find an effective and selective aromatase inhibitor, one that has little or no effect on other androgen-metabolizing enzymes. The potency and specificity of Fadrozole hydrochloride as an aromatase inhibitor was tested in zebra finch telencephalon. The compound was tested in vitro in primary dissociated cell cultures made from hatching telencephalon and compared to a commonly used inhibitor, 1,4,6-androstatriene-3,17-dione (ATD). Untreated, these cultures express extremely high levels of aromatase and 5 beta-reductase activity and therefore allow sensitive measurement of the effectiveness of inhibitors. Aromatase activity was also measured in homogenates of adult telencephalon following in vivo Fadrozole injection. Finally, aromatase and 5 beta-reductase activity were quantified in zebra finch telencephalon following similar intramuscular injections in 4- to 6-day-old birds. In all three cases, Fadrozole was highly effective in reducing aromatase activity. Fadrozole increased 5 beta-reductase activity, presumably due to an increase in available substrate, but had no inhibitory effect on the enzyme. ATD was less effective in inhibiting aromatase, and it also inhibited 5 beta-reductase activity at high concentrations.
