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Walters BJ, Alexiades NG, Saldanha CJ. Intracerebral estrogen provision increases cytogenesis and neurogenesis in the injured zebra finch brain. Dev Neurobiol 2011; 71:170-81. [PMID: 20878945 DOI: 10.1002/dneu.20839] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
To determine whether or not local, injury-induced aromatization and/or estrogen 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 INJ. 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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Affiliation(s)
- Bradley J Walters
- Department of Biological Sciences, Lehigh University, Bethlehem, Pennsylvania, USA
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52
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Taves MD, Ma C, Heimovics SA, Saldanha CJ, Soma KK. Measurement of steroid concentrations in brain tissue: methodological considerations. Front Endocrinol (Lausanne) 2011; 2:39. [PMID: 22654806 PMCID: PMC3356067 DOI: 10.3389/fendo.2011.00039] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/10/2011] [Accepted: 09/06/2011] [Indexed: 12/17/2022] Open
Abstract
It is well recognized that steroids are synthesized de novo in the brain (neurosteroids). In addition, steroids circulating in the blood enter the brain. Steroids play numerous roles in the brain, such as influencing neural development, adult neuroplasticity, behavior, neuroinflammation, and neurodegenerative diseases such as Alzheimer's disease. In order to understand the regulation and functions of steroids in the brain, it is important to directly measure steroid concentrations in brain tissue. In this brief review, we discuss methods for the detection and quantification of steroids in the brain. We concisely present the major advantages and disadvantages of different technical approaches at various experimental stages: euthanasia, tissue collection, steroid extraction, steroid separation, and steroid measurement. We discuss, among other topics, the potential effects of anesthesia and saline perfusion prior to tissue collection; microdissection via Palkovits punch; solid phase extraction; chromatographic separation of steroids; and immunoassays and mass spectrometry for steroid quantification, particularly the use of mass spectrometry for "steroid profiling." Finally, we discuss the interpretation of local steroid concentrations, such as comparing steroid levels in brain tissue with those in the circulation (plasma vs. whole blood samples; total vs. free steroid levels). We also present reference values for a variety of steroids in different brain regions of adult rats. This brief review highlights some of the major methodological considerations at multiple experimental stages and provides a broad framework for designing studies that examine local steroid levels in the brain as well as other steroidogenic tissues, such as thymus, breast, and prostate.
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Affiliation(s)
- Matthew D. Taves
- Department of Psychology, University of British ColumbiaVancouver, BC, Canada
- Department of Zoology, University of British ColumbiaVancouver, BC, Canada
- *Correspondence: Matthew D. Taves, Department of Psychology, University of British Columbia, 2136 West Mall, Vancouver, BC, Canada V6T 1Z4. e-mail:
| | - Chunqi Ma
- Department of Psychology, University of British ColumbiaVancouver, BC, Canada
| | - Sarah A. Heimovics
- Department of Psychology, University of British ColumbiaVancouver, BC, Canada
| | - Colin J. Saldanha
- Department of Biological Sciences, Lehigh UniversityBethlehem, PA, USA
- Program in Cognitive Science, Lehigh UniversityBethlehem, PA, USA
| | - Kiran K. Soma
- Department of Psychology, University of British ColumbiaVancouver, BC, Canada
- Department of Zoology, University of British ColumbiaVancouver, BC, Canada
- Graduate Program in Neuroscience, University of British ColumbiaVancouver, BC, Canada
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Gatson JW, Simpkins JW, Yi KD, Idris AH, Minei JP, Wigginton JG. Aromatase is increased in astrocytes in the presence of elevated pressure. Endocrinology 2011; 152:207-13. [PMID: 21047944 PMCID: PMC3033056 DOI: 10.1210/en.2010-0724] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/29/2010] [Accepted: 10/01/2010] [Indexed: 11/19/2022]
Abstract
After traumatic brain injury (TBI), a progressive injury and death of neurons and glia leads to decreased brain function. Endogenous and exogenous estrogens may protect these vulnerable cells. In this study, we hypothesized that increased pressure leads to an increase in aromatase expression and estrogen production in astrocytes. In this study, we subjected rat glioma (C6) cells and primary cortical astrocytes to increased pressure (25 mm Hg) for 1, 3, 6, 12, 24, 48, and 72 h. Total aromatase protein and RNA levels were measured using Western analysis and RT-PCR, respectively. In addition, we measured aromatase activity by assaying estrone levels after administration of its precursor, androstenedione. We found that increased pressure applied to the C6 cells and primary cortical astrocytes resulted in a significant increase in both aromatase RNA and protein. To extend these findings, we also analyzed aromatase activity in the primary astrocytes during increased pressure. We found that increased pressure resulted in a significant (P < 0.01) increase in the conversion of androstenedione to estrone. In conclusion, we propose that after TBI, astrocytes sense increased pressure, leading to an increase in aromatase production and activity in the brain. These results may suggest mechanisms of brain estrogen production after increases in pressure as seen in TBI patients.
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Affiliation(s)
- J W Gatson
- Department of Surgery, University of Texas Southern Medical Center Dallas, Texas 75390-8579, USA.
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54
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Le Page Y, Diotel N, Vaillant C, Pellegrini E, Anglade I, Mérot Y, Kah O. Aromatase, brain sexualization and plasticity: the fish paradigm. Eur J Neurosci 2010; 32:2105-15. [DOI: 10.1111/j.1460-9568.2010.07519.x] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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55
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Azcoitia I, Santos-Galindo M, Arevalo MA, Garcia-Segura LM. Role of astroglia in the neuroplastic and neuroprotective actions of estradiol. Eur J Neurosci 2010; 32:1995-2002. [DOI: 10.1111/j.1460-9568.2010.07516.x] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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56
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Mirzatoni A, Spence RD, Naranjo KC, Saldanha CJ, Schlinger BA. Injury-induced regulation of steroidogenic gene expression in the cerebellum. J Neurotrauma 2010; 27:1875-82. [PMID: 20925573 PMCID: PMC2953929 DOI: 10.1089/neu.2010.1330] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Sex steroids assist adult neural tissue in the protection from and repair of damage resulting from neural injury; some steroids may be synthesized in the brain. Songbirds are especially useful models to explore steroidal neuroprotection and repair. First, the full suite of cholesterol transporters and steroidogenic enzymes are expressed in the zebra finch (ZF) brain. Second, estrogens promote recovery of behavioral function after damage to the adult ZF cerebellum. Third, the estrogen synthetic enzyme aromatase is rapidly upregulated in reactive glia following neural injury, including in the ZF cerebellum. We hypothesized that cerebellar injury would locally upregulate steroidogenic factors upstream of aromatase, providing the requisite substrate for neuroestrogen synthesis. We tested this hypothesis by lesioning the cerebellum of adult songbirds using both males and females that peripherally synthesize steroids in different amounts. We then used quantitative PCR to examine expression of mRNAs for the neurosteroidogenic factors TSPO, StAR, SCC, 3β-HSD, CYP17, and aromatase, at 2 and 8 days post-lesion. Compared to sham lesions, cerebellar lesions significantly upregulated mRNA levels of TSPO and aromatase. Sex differences in response to the lesions were detected for TSPO, StAR, and aromatase. All birds responded to experimental conditions by showing time-dependent changes in the expression of TSPO, SCC, and aromatase, suggesting that acute trauma or stress may impact neurosteroidogensis for many days. These data suggest that the cerebellum is an active site of steroid synthesis in the brain, and each steroidogenic factor likely provides neuroprotection and promotes repair.
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Affiliation(s)
- Anahid Mirzatoni
- Department of Physiological Science (Integrative Biology and Physiology), and Laboratory of Neuroendocrinology, University of California–Los Angeles, Los Angeles, California
| | - Rory D. Spence
- Department of Neurology and Laboratory of Neuroendocrinology, Brain Research Institute, University of California–Los Angeles, Los Angeles, California
| | - Kevin C. Naranjo
- Department of Biological Sciences, Lehigh University, Bethlehem, Pennsylvania
| | - Colin J. Saldanha
- Department of Biological Sciences, Lehigh University, Bethlehem, Pennsylvania
| | - Barney A. Schlinger
- Department of Physiological Science (Integrative Biology and Physiology), and Laboratory of Neuroendocrinology, University of California–Los Angeles, Los Angeles, California
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57
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Charlier TD, Po KWL, Newman AEM, Shah AH, Saldanha CJ, Soma KK. 17beta-Estradiol levels in male zebra finch brain: combining Palkovits punch and an ultrasensitive radioimmunoassay. Gen Comp Endocrinol 2010; 167:18-26. [PMID: 20144613 PMCID: PMC2862860 DOI: 10.1016/j.ygcen.2010.02.002] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/02/2009] [Revised: 02/01/2010] [Accepted: 02/03/2010] [Indexed: 12/25/2022]
Abstract
Local aromatization of testosterone into 17beta-estradiol (E(2)) is often required for the physiological and behavioral actions of testosterone. In most vertebrates, aromatase is expressed in a few discrete brain regions. While many studies have measured brain aromatase mRNA or activity, very few studies have measured brain E(2) levels, particularly in discrete brain regions, because of technical challenges. Here, we used the Palkovits punch technique to isolate 13 discrete brain nuclei from adult male zebra finches. Steroids were extracted via solid phase extraction. E(2) was then measured with an ultrasensitive, specific and precise radioimmunoassay. Our protocol leads to high recovery of E(2) (84%) and effectively removes interfering brain lipids. E(2) levels were high in aromatase-rich regions such as caudal medial nidopallium and hippocampus. E(2) levels were intermediate in the medial preoptic area, ventromedial nucleus of the hypothalamus, lateral and medial magnocellular nuclei of anterior nidopallium, nucleus taeniae of the amygdala, and Area X. E(2) levels were largely non-detectable in the cerebellum, HVC, lateral nidopallium and optic lobes. Importantly, E(2) levels were significantly lower in plasma than in the caudal medial nidopallium. This protocol allows one to measure E(2) in discrete brain regions and potentially relate local E(2) concentrations to aromatase activity and behavior.
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58
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Diotel N, Le Page Y, Mouriec K, Tong SK, Pellegrini E, Vaillant C, Anglade I, Brion F, Pakdel F, Chung BC, Kah O. Aromatase in the brain of teleost fish: expression, regulation and putative functions. Front Neuroendocrinol 2010; 31:172-92. [PMID: 20116395 DOI: 10.1016/j.yfrne.2010.01.003] [Citation(s) in RCA: 230] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/20/2009] [Revised: 01/20/2010] [Accepted: 01/24/2010] [Indexed: 12/25/2022]
Abstract
Unlike that of mammals, the brain of teleost fish exhibits an intense aromatase activity due to the strong expression of one of two aromatase genes (aromatase A or cyp19a1a and aromatase B or cyp19a1b) that arose from a gene duplication event. In situ hybridization, immunohistochemistry and expression of GFP (green fluorescent protein) in transgenic tg(cyp19a1b-GFP) fish demonstrate that aromatase B is only expressed in radial glial cells (RGC) of adult fish. These cells persist throughout life and act as progenitors in the brain of both developing and adult fish. Although aromatase B-positive radial glial cells are most abundant in the preoptic area and the hypothalamus, they are observed throughout the entire central nervous system and spinal cord. In agreement with the fact that brain aromatase activity is correlated to sex steroid levels, the high expression of cyp19a1b is due to an auto-regulatory loop through which estrogens and aromatizable androgens up-regulate aromatase expression. This mechanism involves estrogen receptor binding on an estrogen response element located on the cyp19a1b promoter. Cell specificity is achieved by a mandatory cooperation between estrogen receptors and unidentified glial factors. Given the emerging roles of estrogens in neurogenesis, the unique feature of the adult fish brain suggests that, in addition to classical functions on brain sexual differentiation and sexual behaviour, aromatase expression in radial glial cells could be part of the mechanisms authorizing the maintenance of a high proliferative activity in the brain of fish.
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Affiliation(s)
- Nicolas Diotel
- Neurogenesis And OEstrogens, UMR CNRS 6026, IFR 140, Université de Rennes 1, Rennes, France
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59
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Hoyk Z, Csákvári E, Szájli A, Kóti J, Paragi G, Gyenes A, Wölfling J, Pfoh R, Rühl S, Párducz A. Computer-aided structure analysis of an epimerized dehydroepiandrosterone derivative and its biological effect in a model of reactive gliosis. Steroids 2010; 75:265-71. [PMID: 20064537 DOI: 10.1016/j.steroids.2010.01.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/06/2009] [Revised: 11/06/2009] [Accepted: 01/03/2010] [Indexed: 11/28/2022]
Abstract
The naturally occurring steroid dehydroepiandrosterone (DHEA) is reported to reduce glial fibrillary acidic protein (GFAP) overexpression in a model of reactive gliosis due to its conversion to estradiol by the enzyme aromatase. In the present study we examined the biological effect of a new epimerized derivative of DHEA, 16alpha-iodomethyl-13alpha-dehydroepiandrosterone derivative (16alpha-iodomethyl-13alpha-DHEAd, 16alpha-iodomethyl-13alpha-androst-5-en-3beta,17beta-diol), using the same model system, and compared the 3D structure of this molecule with that of DHEA and two steroidal type aromatase inhibitors, formestane and exemestane. The synthetic compound, in contrast to the reported effect of DHEA, was able to reduce GFAP overexpression only if the enzyme aromatase was inhibited. Data obtained from computational calculations fortified by X-ray crystallography revealed that contrary to the nearly planar sterane framework of DHEA, the synthetic derivative 16alpha-iodomethyl-13alpha-DHEAd has a bent sterane skeleton, resulting in a 3D structure that is similar to that of formestane or exemestane. Moreover, 16alpha-iodomethyl-13alpha-DHEAd resulted to be metabolically more stable than DHEA. The results suggest that epimerization of the sterane skeleton of DHEA inclines the plane of the D ring, leading to a significantly altered biological activity. The synthetic molecule has a DHEA-like effect on GFAP overexpression when the enzyme aromatase is inhibited and the naturally occurring DHEA is ineffective in this respect. On the other hand, based on their structural similarity it can be hypothesized that 16alpha-iodomethyl-13alpha-DHEAd applied alone might have a biological effect similar to that of formestane or exemestane.
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Affiliation(s)
- Zsófia Hoyk
- Institute of Biophysics, Biological Research Center, Szeged, Temesvári krt. 62, H-6726 Szeged, Hungary
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60
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Leães CGS, Meurer RT, Coutinho LB, Ferreira NP, Pereira-Lima JFS, da Costa Oliveira M. Immunohistochemical expression of aromatase and estrogen, androgen and progesterone receptors in normal and neoplastic human meningeal cells. Neuropathology 2010; 30:44-9. [DOI: 10.1111/j.1440-1789.2009.01047.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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61
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Azcoitia I, DonCarlos LL, Arevalo MA, Garcia-Segura LM. Therapeutic implications of brain steroidogenesis. Horm Mol Biol Clin Investig 2010; 1:21-6. [PMID: 25961968 DOI: 10.1515/hmbci.2010.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2009] [Accepted: 06/16/2009] [Indexed: 12/24/2022]
Abstract
The nervous system is a steroidogenic tissue and several steroids synthesized locally in the brain, such as pregnenolone, progesterone and estradiol, modulate neuronal and glial physiology and are neuroprotective. The brain upregulates steroidogenesis at sites of injury as part of a program triggered by neural tissue to cope with neurodegenerative insults. Pharmacological targets to increase brain steroidogenesis and promote neuroprotection include the molecules that transport cholesterol to the inner mitochondrial membrane, where the first enzyme for steroidogenesis is located. Furthermore, the human gene encoding aromatase, the enzyme that synthesizes estradiol, is under the control of different tissue-specific promoters, and it is therefore conceivable that selective aromatase modulators can be developed that will enhance the expression of the enzyme and the consequent increase in estrogen formation in the brain but not in other tissues.
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62
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Yague JG, Azcoitia I, DeFelipe J, Garcia-Segura LM, Muñoz A. Aromatase expression in the normal and epileptic human hippocampus. Brain Res 2009; 1315:41-52. [PMID: 19815003 DOI: 10.1016/j.brainres.2009.09.111] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2009] [Revised: 09/28/2009] [Accepted: 09/28/2009] [Indexed: 12/29/2022]
Abstract
Aromatase is a key enzyme in estrogen biosynthesis that is involved in neuronal plasticity in the rodent hippocampus. Although aromatase mRNA expression has been detected in the human hippocampus, its cellular distribution has yet to be determined. Here, we have examined the immunohistochemical distribution of aromatase in the normal and the epileptic and sclerotic human hippocampus. In both the normal and epileptic hippocampus, aromatase was detected in numerous CA1-CA3 pyramidal neurons, in granule cells of the dentate gyrus and in interneurons that co-expressed the calcium-binding proteins calbindin, calretinin or parvalbumin. However, only a small subpopulation of astrocytes was immunoreactive for aromatase in either the normal and epileptic hippocampus. The widespread expression of aromatase in a large population of neurons in the normal and damaged hippocampus suggests that local estrogen formation may play an important role in human hippocampal function.
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Affiliation(s)
- Josue G Yague
- Instituto Cajal, CSIC, Avenida Doctor Arce 37, E-28002 Madrid, Spain
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63
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Do Rego JL, Seong JY, Burel D, Leprince J, Luu-The V, Tsutsui K, Tonon MC, Pelletier G, Vaudry H. Neurosteroid biosynthesis: enzymatic pathways and neuroendocrine regulation by neurotransmitters and neuropeptides. Front Neuroendocrinol 2009; 30:259-301. [PMID: 19505496 DOI: 10.1016/j.yfrne.2009.05.006] [Citation(s) in RCA: 282] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/16/2009] [Revised: 05/12/2009] [Accepted: 05/21/2009] [Indexed: 01/09/2023]
Abstract
Neuroactive steroids synthesized in neuronal tissue, referred to as neurosteroids, are implicated in proliferation, differentiation, activity and survival of nerve cells. Neurosteroids are also involved in the control of a number of behavioral, neuroendocrine and metabolic processes such as regulation of food intake, locomotor activity, sexual activity, aggressiveness, anxiety, depression, body temperature and blood pressure. In this article, we summarize the current knowledge regarding the existence, neuroanatomical distribution and biological activity of the enzymes responsible for the biosynthesis of neurosteroids in the brain of vertebrates, and we review the neuronal mechanisms that control the activity of these enzymes. The observation that the activity of key steroidogenic enzymes is finely tuned by various neurotransmitters and neuropeptides strongly suggests that some of the central effects of these neuromodulators may be mediated via the regulation of neurosteroid production.
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Affiliation(s)
- Jean Luc Do Rego
- Institut National de la Santé et de la Recherche Médicale (INSERM) Unité 413, 76821 Mont-Saint-Aignan, France
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64
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Saldanha CJ, Duncan KA, Walters BJ. Neuroprotective actions of brain aromatase. Front Neuroendocrinol 2009; 30:106-18. [PMID: 19450619 PMCID: PMC2700852 DOI: 10.1016/j.yfrne.2009.04.016] [Citation(s) in RCA: 135] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/18/2009] [Revised: 04/02/2009] [Accepted: 04/14/2009] [Indexed: 12/16/2022]
Abstract
The steroidal regulation of vertebrate neuroanatomy and neurophysiology includes a seemingly unending list of brain areas, cellular structures and behaviors modulated by these hormones. Estrogens, in particular have emerged as potent neuromodulators, exerting a range of effects including neuroprotection and perhaps neural repair. In songbirds and mammals, the brain itself appears to be the site of injury-induced estrogen synthesis via the rapid transcription and translation of aromatase (estrogen synthase) in astroglia. This induction seems to occur regardless of the nature and location of primary brain damage. The induced expression of aromatase apparently elevates local estrogen levels enough to interfere with apoptotic pathways, thereby decreasing secondary degeneration and ultimately lessening the extent of damage. There is even evidence suggesting that aromatization may affect injury-induced cytogenesis. Thus, aromatization in the brain appears to confer neuroprotection by an array of mechanisms that involve the deceleration and acceleration of degeneration and repair, respectively. We are only beginning to understand the factors responsible for the injury-induced transcription of aromatase in astroglia. In contrast, much of the manner in which local and circulating estrogens may achieve their neuroprotective effects has been elucidated. However, gaps in our knowledge include issues about the cell-specific regulation of aromatase expression, steroidal influences of aromatization distinct from estrogen formation, and questions about the role of constitutive aromatase in neuroprotection. Here we describe the considerable consensus and some interesting differences in knowledge gained from studies conducted on diverse animal models, experimental paradigms and preparations towards understanding the neuroprotective actions of brain aromatase.
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Affiliation(s)
- Colin J Saldanha
- Department of Biological Sciences, Lehigh University, Bethlehem, PA 18015, United States.
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65
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Spence RD, Zhen Y, White S, Schlinger BA, Day LB. Recovery of motor and cognitive function after cerebellar lesions in a songbird: role of estrogens. Eur J Neurosci 2009; 29:1225-34. [PMID: 19302157 DOI: 10.1111/j.1460-9568.2009.06685.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In addition to its key role in complex motor function, the cerebellum is increasingly recognized to have a role in cognition. Songbirds are particularly good models for the investigation of motor and cognitive processes but little is known about the role of the songbird cerebellum in these processes. To explore cerebellar function in a songbird, we lesioned the cerebellum of adult female zebra finches and examined the effects on a spatial working memory task and on motor function during this task. There is evidence for steroid synthesis in the songbird brain and neurosteroids may have an impact on some forms of neural plasticity in adult songbirds. We therefore hypothesized that neurosteroids would affect motor and cognitive function after a cerebellar injury. We found that cerebellar lesions produced deficits in motor and cognitive aspects of a spatial task. In line with our prediction, birds in which estrogen synthesis was blocked had impaired performance in our spatial task compared with those that had estrogen synthesis blocked but estrogen replaced. There was no clear effect of estrogen replacement on motor function. We also found that lesions induced expression of the estrogen synthetic enzyme aromatase in reactive astrocytes and Bergmann glia around a cerebellar lesion. These data suggest that the cerebellum of songbirds mediates both motor and cognitive function and that estrogens may improve the recovery of cognitive aspects of cerebellar function after injury.
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Affiliation(s)
- Rory D Spence
- Department of Physiological Science and Laboratory of Neuroendocrinology, Brain Research Institute, University of California, Los Angeles, CA, USA
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66
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Presence of aromatase and estrogen receptor alpha in the inner ear of zebra finches. Hear Res 2009; 252:49-55. [PMID: 19397967 DOI: 10.1016/j.heares.2009.04.012] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/17/2008] [Revised: 03/13/2009] [Accepted: 04/09/2009] [Indexed: 11/21/2022]
Abstract
Sex differences in song behavior and in the neural system controlling song in songbirds are well documented but relatively little is known about sex differences in hearing. We recently demonstrated the existence of sex differences in auditory brainstem responses in a songbird species, the zebra finch (Taeniopygia guttata). Many sex differences are regulated by sex steroid hormone action either during ontogeny or in adulthood. As a first step to test the possible implication of sex steroids in the control of sex differences in the zebra finch auditory system, we evaluated via immunocytochemistry whether estrogens are produced and act in the zebra finch inner ear. Specifically we examined the distribution of aromatase, the enzyme converting testosterone into an estrogen, and of estrogen receptors of the alpha subtype (ERalpha) in adult zebra finch inner ears. The anatomy of the basilar papillae was visualized by fluorescein-phalloidin, which delineated the actin structure of hair cells and supporting cells at their apical surface. Whole mount preparations of basilar papillae stained by immunocytochemistry revealed in both males and females an abundant aromatase distribution in the cytoplasm of hair cells, while ERalpha was identified in the nuclei of hair cells and of underlying supporting cells. Double-labeled preparations confirmed the extensive co-localization of aromatase and ERalpha in the vast majority of the hair cells. These results are consistent with studies on non-avian species, suggesting a role for estrogens in auditory function. These findings are also consistent with the notion that estrogens may contribute to a sex difference in hearing. To our knowledge, this is the first demonstration of the presence of aromatase and of the co-localization of aromatase and ERalpha in the sensory epithelium of the inner ear in any animal model.
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67
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Roselli CE, Liu M, Hurn PD. Brain aromatization: classic roles and new perspectives. Semin Reprod Med 2009; 27:207-17. [PMID: 19401952 DOI: 10.1055/s-0029-1216274] [Citation(s) in RCA: 135] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
Aromatization of testosterone to estradiol by neural tissue has classically been associated with the regulation of sexual differentiation, gonadotropin secretion, and copulatory behavior. However, new data indicate that the capacity for aromatization is not restricted to the endocrine brain and demonstrate roles for locally formed estrogens in neurogenesis and in responses of brain tissue to injury. This article summaries our current understanding of the distribution and regulation of aromatase in the brain and describes the classic and novel roles it plays. A better understanding of brain aromatization could shed new light on its physiologic and pathologic functions and someday lead to new, centrally acting drug therapies.
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Affiliation(s)
- Charles E Roselli
- Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, Oregon 97201-3098, USA.
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68
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Forebrain steroid levels fluctuate rapidly during social interactions. Nat Neurosci 2008; 11:1327-34. [PMID: 18820691 PMCID: PMC2577388 DOI: 10.1038/nn.2200] [Citation(s) in RCA: 268] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2008] [Accepted: 08/27/2008] [Indexed: 11/25/2022]
Abstract
Neurosteroids are powerful modulators of brain function and behavior, yet their dynamics within the brain have remained elusive. Using in vivo microdialysis in male zebra finches, we show that local estradiol levels increase rapidly within the forebrain during social interactions with females. Further, when males are exposed to other males’ song, local estradiol levels also increase and testosterone levels drop within a cortical/pallial auditory region that is analogous to mammalian auditory cortex. We also report that local estradiol and testosterone levels are differentially regulated in this same region by the conventional neurotransmitters glutamate and GABA, respectively. This study provides direct evidence that forebrain steroid levels are acutely and differentially regulated during social behavior, in a region-specific manner, and in a rapid time-course akin to that of traditional neuromodulators.
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69
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Caspase inhibitor infusion protects an avian song control circuit from seasonal-like neurodegeneration. J Neurosci 2008; 28:7130-6. [PMID: 18614682 DOI: 10.1523/jneurosci.0663-08.2008] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Sex steroids such as androgens and estrogens have trophic effects on the brain and can ameliorate neurodegeneration, and the withdrawal of circulating steroids induces neurodegeneration in several hormone-sensitive brain areas. Very little is known about the underlying molecular mechanisms that mediate neuronal regression caused by hormone-withdrawal, however. Here we show that reduction of programmed cell death by local infusion of caspase inhibitors rescues a telencephalic nucleus in the adult avian song control system from neurodegeneration that is induced by hormone withdrawal. This treatment also has trans-synaptic effects that provide some protection of an efferent target region. We found that unilateral infusion of caspase inhibitors in vivo in adult white-crowned sparrows rescued neurons within the hormone-sensitive song nucleus HVC (used as a proper name) from programmed cell death for as long as seven days after withdrawal of testosterone and a shift to short-day photoperiod and that the activation of caspase-3 was reduced by 59% on average in the ipsilateral HVC compared with the unmanipulated contralateral HVC. Caspase inhibitor infusion near HVC was sufficient to preserve neuron size ipsilaterally in a downstream nucleus, the robust nucleus of the arcopallium. This is the first report that sustained local application of caspase inhibitors can protect a telencephalic brain area from neurodegeneration in vivo and that a degenerating neural circuit rescued with caspase inhibitors produces sufficient trophic support to protect attributes of a downstream target that would otherwise degenerate. These results strengthen the case for the possible therapeutic use of caspase inhibitors under certain neurodegenerative conditions.
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70
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Walters BJ, Saldanha CJ. Glial aromatization increases the expression of bone morphogenetic protein-2 in the injured zebra finch brain. J Neurochem 2008; 106:216-23. [PMID: 18363824 DOI: 10.1111/j.1471-4159.2008.05352.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In songbirds, brain injury upregulates glial aromatase. The resulting local estrogen synthesis mitigates apoptosis and enhances cytogenesis by poorly understood mechanisms. Bone morphogenetic proteins (BMPs), long studied for their role in neural development, are also neuroprotective and cytogenic in the adult brain. BMPs remain uncharacterized in songbirds, as do the mechanisms regulating their post-injury expression. We first established the expression of BMPs 2, 4, 6, and 7 in the adult zebra finch brain using RT-PCR. Next, we determined the effect of neural insult on BMP expression, by comparing BMP transcripts between injured and uninjured telencephalic hemispheres using semi-quantitative PCR. The expression of BMPs 2 and 4, but not 6 and 7, increased 24 h post-injury. To determine the influence of aromatase on BMP expression, we compared BMP expression following delivery of the aromatase inhibitor Fadrozole or vehicle into contralateral hemispheres. Fadrozole decreased BMP2, but not BMP4, expression, suggesting that aromatization may induce BMP2 expression following injury. Since BMPs are gliogenic and neurotrophic, future studies will test if the neuroprotective and cytogenic effects of aromatase upregulation are mediated by BMP2. Songbirds may be excellent models towards understanding the role of local estrogen synthesis and its downstream mechanisms on neuroprotection and repair.
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Affiliation(s)
- Bradley J Walters
- Department of Biological Sciences, Lehigh University, Bethlehem, Pennsylvania 18015, USA
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71
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Abstract
Aromatase, the enzyme that synthesises oestrogens from androgen precursors, is expressed in the brain, where it has been classically associated with the regulation of neuroendocrine events and behaviours linked with reproduction. Recent findings, however, have revealed new unexpected roles for brain aromatase, indicating that the enzyme regulates synaptic activity, synaptic plasticity, neurogenesis and the response of neural tissue to injury, and may contribute to control nonreproductive behaviours, mood and cognition. Therefore, the function of brain aromatase is not restricted to the regulation of reproduction as previously thought.
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72
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Wynne RD, Maas S, Saldanha CJ. Molecular characterization of the injury-induced aromatase transcript in the adult zebra finch brain. J Neurochem 2008; 105:1613-24. [PMID: 18312309 DOI: 10.1111/j.1471-4159.2008.05256.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In the zebra finch (Taeniopygia guttata), the aromatase gene is transcribed from one of two promoters resulting in two transcripts constitutively expressed in brain or ovary. These transcripts differ only in Exon 1 which lies in the 5' un-translated region (UTR). An inducible form of aromatase is expressed following brain injury in glia. Towards characterizing this transcript, we (a) examined the up-regulation of amplicons within the aromatase transcript using quantitative PCR (qPCR), (b) performed 5' and 3' rapid amplification of cDNA ends (RACE) on injured brain RNA and (c) sequenced the injury-induced aromatase transcript. qPCR suggested that inducible aromatase may contain a novel 3'UTR. However, neither 3' nor 5' RACE revealed novel UTRs in the injured telencephalon. We then sequenced aromatase from injured entopallium, a region that lacks detectable constitutive aromatase. Inducible aromatase was identical in sequence to the known neural aromatase transcript. These data suggest that injury-induced aromatase differs from ovarian, but is indistinguishable from neuronal aromatase. We suggest that an injury-specific signal in glia may modulate aromatase transcription. Alternatively, injury-induced aromatase transcription may be silenced under constitutive conditions. To the best of our knowledge, this is the first report that documents the sequence of inducible aromatase in any vertebrate.
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Affiliation(s)
- Ryan D Wynne
- Department of Biological Sciences, Lehigh University, Bethlehem, Pennsylvania 18015, USA
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73
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Wynne RD, Walters BJ, Bailey DJ, Saldanha CJ. Inhibition of injury-induced glial aromatase reveals a wave of secondary degeneration in the songbird brain. Glia 2008; 56:97-105. [PMID: 17955551 DOI: 10.1002/glia.20594] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
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, 72h, 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 injury-induced 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.
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Affiliation(s)
- Ryan D Wynne
- Department of Biological Sciences, Lehigh University, Bethlehem, Pennsylvania 18015, USA
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74
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Synthesis of estrogens in progenitor cells of adult fish brain: evolutive novelty or exaggeration of a more general mechanism implicating estrogens in neurogenesis? Brain Res Bull 2007; 75:274-80. [PMID: 18331884 DOI: 10.1016/j.brainresbull.2007.10.030] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2007] [Accepted: 10/17/2007] [Indexed: 02/04/2023]
Abstract
In contrast to other vertebrates, in which the adult brain shows limited adult neurogenesis, teleost fishes exhibit an unparalleled capacity to generate new neurons as adults, suggesting that their brains present a highly permissive environment for the maintenance and proliferation of adult progenitors. Here, we examine the hypothesis that one of the factors permitting establishment of this favourable environment is estradiol. Indeed, recent data showed that radial glial cells strongly expressed one of two aromatase duplicated genes. Aromatase is the estrogen-synthesizing enzyme and this observation is of great interest, given that radial glial cells are progenitor cells capable of generating new neurons. Given the well-documented roles of estrogens on cell fate, and notably on cell proliferation, these data suggest that estradiol could be involved in maintaining and/or activating these progenitors. Examination of recent data in birds and mammals suggests that the situation in fish could well be an exaggeration of a more general mechanism implicating estrogens in neurogenesis. Indeed, there is accumulating evidence that estrogens are involved in embryonic, adult or reparative neurogenesis in other vertebrates, notably in mammals.
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75
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Thompson CK, Bentley GE, Brenowitz EA. Rapid seasonal-like regression of the adult avian song control system. Proc Natl Acad Sci U S A 2007; 104:15520-5. [PMID: 17875989 PMCID: PMC2000488 DOI: 10.1073/pnas.0707239104] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
We analyzed how rapidly avian song control nuclei regress after testosterone (T) withdrawal. Regression of neuronal attributes resulting from T withdrawal has been observed in several animal models. The time course over which regression occurs is not known, however. To address this issue, we castrated adult male white-crowned sparrows and rapidly shifted them to short-day photoperiods after being held under breeding conditions (long-day photoperiod and systemic T exposure) for 3 weeks. We found that the volume of one song nucleus, HVC, regressed 22% within 12 h after T withdrawal. Changes in HVC neuron density after T withdrawal were dynamic; density increased at 12 h and then decreased by 4 days. HVC neuron number was reduced by 26% by 4 days. The volumes of Area X and the robust nucleus of the arcopallium (RA) were significantly regressed by 7 and 20 days, respectively. RA somatic area and neuronal spacing were significantly reduced by 2 days. The rapidity of HVC regression is unprecedented among vertebrate models of hormone-sensitive neural circuits. These results reveal that the rapid regression of the song control system provides a model for the important role sex steroid hormones play in mediating adult neural plasticity and in neuroprotection.
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Affiliation(s)
- Christopher K Thompson
- Graduate Program in Neurobiology and Behavior, University of Washington, Box 351525, Seattle, WA 98195-1525, USA.
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76
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Barreto G, Veiga S, Azcoitia I, Garcia-Segura LM, Garcia-Ovejero D. Testosterone decreases reactive astroglia and reactive microglia after brain injury in male rats: role of its metabolites, oestradiol and dihydrotestosterone. Eur J Neurosci 2007; 25:3039-46. [PMID: 17561817 DOI: 10.1111/j.1460-9568.2007.05563.x] [Citation(s) in RCA: 136] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Previous studies have shown that the neuroprotective hormone, testosterone, administered immediately after neural injury, reduces reactive astrogliosis. In this study we have assessed the effect of early and late therapy with testosterone or its metabolites, oestradiol and dihydrotestosterone, on reactive astroglia and reactive microglia after a stab wound brain injury in orchidectomized Wistar rats. Animals received daily s.c. injections of testosterone, oestradiol or dihydrotestosterone on days 0-2 or on days 5-7 after injury. The number of vimentin immunoreactive astrocytes and the volume fraction of major histocompatibility complex-II (MHC-II) immunoreactive microglia were estimated in the hippocampus in the lateral border of the wound. Both early and delayed administration of testosterone or oestradiol, but not dihydrotestosterone, resulted in a significant decrease in the number of vimentin-immunoreactive astrocytes. The volume fraction of MHC-II immunoreactive microglia was significantly decreased in the animals that received testosterone or oestradiol in both early and delayed treatments and in animals that received early dihydrotestosterone administration. Thus, both early and delayed administration of testosterone reduces reactive astroglia and reactive microglia and these effects may be at least in part mediated by oestradiol, while dihydrotestosterone may mediate part of the early effects of testosterone on reactive microglia. In conclusion, testosterone controls reactive gliosis and its metabolites, oestradiol and dihydrotestosterone, may be involved in this hormonal effect. The regulation of gliosis may be part of the neuroprotective mechanism of testosterone.
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77
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Abstract
It is well established that aromatization constitutes an essential part of testosterone's signaling pathway in brain and that estrogen metabolites, often together with testosterone, organize and activate masculine neural circuits. This paper summarizes the current understanding regarding the distribution, regulation and function of brain aromatase in mammals. Data from our laboratory are presented that highlight the important function of aromatase in the regulation of androgen feedback sensitivity in non-human primates and the possible role that aromatase plays in determining the brain structure and sexual partner preferences of rams. In addition, new data is presented indicating that the capacity for aromatization in cortical astrocytes is associated with cell survival and may be important for neuroprotection. It is anticipated that a better appreciation of the physiological and pathophysiological functions of aromatase will lead to important clinical insights.
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Affiliation(s)
- Charles F Roselli
- Department of Physiology and Pharmacology, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239-3098, USA.
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78
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Schlinger BA, Pradhan DS, Soma KK. 3beta-HSD activates DHEA in the songbird brain. Neurochem Int 2007; 52:611-20. [PMID: 17643555 PMCID: PMC2441539 DOI: 10.1016/j.neuint.2007.05.003] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2007] [Revised: 04/13/2007] [Accepted: 05/02/2007] [Indexed: 11/29/2022]
Abstract
Dehydroepiandrosterone (DHEA) is an abundant circulating prohormone in humans, with a variety of reported actions on central and peripheral tissues. Despite its abundance, the functions of DHEA are relatively unknown because common animal models (laboratory rats and mice) have very low DHEA levels in the blood. Over the past decade, we have obtained considerable evidence from avian studies demonstrating that (1) DHEA is an important circulating prohormone in songbirds and (2) the enzyme 3beta-hydroxysteroid dehydrogenase/isomerase (3beta-HSD), responsible for converting DHEA into a more active androgen, is expressed at high levels in the songbird brain. Here, we first review biochemical and molecular studies demonstrating the widespread activity and expression of 3beta-HSD in the adult and developing songbird brain. Studies examining neural 3beta-HSD activity show effects of sex, stress, and season that are region-specific. Second, we review studies showing seasonal and stress-related changes in circulating DHEA in captive and wild songbird species. Third, we describe evidence that DHEA treatment can stimulate song behavior and the growth of neural circuits controlling song behavior. Importantly, brain 3beta-HSD and aromatase can work in concert to locally metabolize DHEA into active androgens and estrogens, which are critical for controlling behavior and robust adult neuroplasticity in songbirds. DHEA is likely secreted by the avian gonads and/or adrenals, as is the case in humans, but DHEA may also be synthesized de novo in the songbird brain from cholesterol or other precursors. Irrespective of its source, DHEA seems to be an important prohormone in songbirds, and 3beta-HSD is a key enzyme in the songbird brain.
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Affiliation(s)
- Barney A Schlinger
- Department of Physiological Science, Laboratory of Neuroendocrinology of the Brain Research Institute, UCLA, Los Angeles, CA 90095, USA.
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79
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Peterson RS, Fernando G, Day L, Allen TA, Chapleau JD, Menjivar J, Schlinger BA, Lee DW. Aromatase expression and cell proliferation following injury of the adult zebra finch hippocampus. Dev Neurobiol 2007; 67:1867-78. [PMID: 17823932 DOI: 10.1002/dneu.20548] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Estrogens can be neuroprotective following traumatic brain injury. Immediately after trauma to the zebra finch hippocampus, the estrogen-synthetic enzyme aromatase is rapidly upregulated in astrocytes and radial glia around the lesion site. Brain injury also induces high levels of cell proliferation. Estrogens promote neuronal differentiation, migration, and survival naturally in the avian brain. We suspect that glia are a source of estrogens promoting cell proliferation after neural injury. To explore this hypothesis, we examined the spatial and temporal relationship between glial aromatase expression and cell proliferation after neural injury in adult female zebra finches. Birds were ovariectomized and given a blank implant or one filled with estradiol; some birds were also administered an aromatase inhibitor or vehicle. All birds received penetrating injuries to the right hippocampus. Twenty-four hours after lesioning, birds were injected once with BrdU to label mitotically active cells and euthanized 2 h, 24 h, or 7 days later. The brains were processed for double-label BrdU and aromatase immunocytochemistry. Injury-induced glial aromatase expression was unaffected by survival time and aromatase inhibition. BrdU labeling was significantly reduced at 24 h by ovariectomy and by aromatase inhibition; effects were partially reversed by E2 replacement. Irrespective of ovariectomy, the densities of aromatase immunoreactive astrocytes and BrdU-labeled cells at known distances from the lesion site were highly correlated. These data suggest that injury-induced glial aromatization may influence the reorganization of injured tissue by providing a rich estrogenic environment available to influence cellular incorporation.
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Affiliation(s)
- R Scott Peterson
- Department of Physiological Science, University of California, Los Angeles, CA 90095, USA
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80
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Cornil CA, Ball GF, Balthazart J. Functional significance of the rapid regulation of brain estrogen action: where do the estrogens come from? Brain Res 2006; 1126:2-26. [PMID: 16978590 PMCID: PMC3523229 DOI: 10.1016/j.brainres.2006.07.098] [Citation(s) in RCA: 182] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2006] [Revised: 07/26/2006] [Accepted: 07/27/2006] [Indexed: 12/20/2022]
Abstract
Estrogens exert a wide variety of actions on reproductive and non-reproductive functions. These effects are mediated by slow and long lasting genomic as well as rapid and transient non-genomic mechanisms. Besides the host of studies demonstrating the role of genomic actions at the physiological and behavioral level, mounting evidence highlights the functional significance of non-genomic effects. However, the source of the rapid changes in estrogen availability that are necessary to sustain their fast actions is rarely questioned. For example, the rise of plasma estrogens at pro-estrus that represents one of the fastest documented changes in plasma estrogen concentration appears too slow to explain these actions. Alternatively, estrogen can be synthesized in the brain by the enzyme aromatase providing a source of locally high concentrations of the steroid. Furthermore, recent studies demonstrate that brain aromatase can be rapidly modulated by afferent inputs, including glutamatergic afferents. A role for rapid changes in estrogen production in the central nervous system is supported by experiments showing that acute aromatase inhibition affects nociception as well as male sexual behavior and that preoptic aromatase activity is rapidly (within min) modulated following mating. Such mechanisms thus fulfill the gap existing between the fast actions of estrogen and their mode of production and open new avenues for the understanding of estrogenic effects on the brain.
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Affiliation(s)
- Charlotte A Cornil
- Department of Psychological and Brain Sciences, Johns Hopkins University, 108 Ames Hall, 3400 North Charles Street, Baltimore, MD 21218-2686, USA.
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81
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Abstract
Starting from fetal life, estrogens are crucial in determining central gender dimorphism, and an estrogen-induced synaptic plasticity is well evident during puberty and seasonal changes as well as during the ovarian cycle. Estrogens act on the central nervous system (CNS) both through genomic mechanisms, modulating synthesis, release and metabolism of neurotransmitters, neuropeptides and neurosteroids, and through non-genomic mechanisms, influencing electrical excitability, synaptic function and morphological features. Therefore, estrogen's neuroactive effects are multifaceted and encompass a system that ranges from the chemical to the biochemical to the genomic mechanisms, protecting against a wide range of neurotoxic insults. Clinical evidences show that, during the climacteric period, estrogen withdrawal in the limbic system gives rise to modifications in mood, behaviour and cognition and that estrogen administration is able to improve mood and cognitive efficiency in post-menopause. Many biological mechanisms support the hypothesis that estrogens might protect against Alzheimer's disease (AD) by influencing neurotransmission, increasing cerebral blood flow, modulating growth proteins associated with axonal elongation and blunting the neurotoxic effects of beta-amyloid. On the contrary, clinical studies of estrogen replacement therapy (ERT) and cognitive function have reported controversial results, indicating a lack of efficacy of estrogens on cognition in post-menopausal women aged >or=65 years. These findings suggest the presence of a critical period for HRT-related neuroprotection and underlie the potential importance of early initiation of therapy for cognitive benefit. In this review, we shall first describe the multiple effects of steroids in the nervous system, which may be significant in the ageing process. A critical update of HRT use in women and a discussion of possible prospectives for steroid use are subsequently proposed.
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Affiliation(s)
- Andrea Riccardo Genazzani
- Department of Reproductive Medicine and Child Development, Division of Obstetrics and Gynecology, University of Pisa, Pisa, Italy.
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82
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Abstract
Hormonal and locally produced steroids act in the nervous system as neuroendocrine regulators, as trophic factors and as neuromodulators and have a major impact on neural development and function. Glial cells play a prominent role in the local production of steroids and in the mediation of steroid effects on neurons and other glial cells. In this review, we examine the role of glia in the synthesis and metabolism of steroids and the functional implications of glial steroidogenesis. We analyze the mechanisms of steroid signaling on glia, including the role of nuclear receptors and the mechanisms of membrane and cytoplasmic signaling mediated by changes in intracellular calcium levels and activation of signaling kinases. Effects of steroids on functional parameters of glia, such as proliferation, myelin formation, metabolism, cytoskeletal reorganization, and gliosis are also reviewed, as well as the implications of steroid actions on glia for the regulation of synaptic function and connectivity, the regulation of neuroendocrine events, and the response of neural tissue to injury.
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83
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Forlano PM, Schlinger BA, Bass AH. Brain aromatase: new lessons from non-mammalian model systems. Front Neuroendocrinol 2006; 27:247-74. [PMID: 16828853 DOI: 10.1016/j.yfrne.2006.05.002] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/04/2006] [Revised: 05/11/2006] [Accepted: 05/16/2006] [Indexed: 01/29/2023]
Abstract
This review highlights recent studies of the anatomical and functional implications of brain aromatase (estrogen synthase) expression in two vertebrate lineages, teleost fishes and songbirds, that show remarkably high levels of adult brain aromatase activity, protein and gene expression compared to other vertebrate groups. Teleosts and birds have proven to be important neuroethological models for investigating how local estrogen synthesis leads to changes in neural phenotypes that translate into behavior. Region-specific patterns of aromatase expression, and thus estrogen synthesis, include the vocal and auditory circuits that figure prominently into the life history adaptations of vocalizing teleosts and songbirds. Thus, by targeting, for example, vocal motor circuits without inappropriate steroid exposure to other steroid-dependent circuits, such as those involved in either copulatory or spawning behaviors, the neuroendocrine system can achieve temporal and spatial specificity in its modulation of neural circuits that lead to the performance of any one behavior.
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Affiliation(s)
- Paul M Forlano
- Vollum Institute, Oregon Health and Science University, Portland, OR 97239, USA.
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84
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Peterson RS, Yarram L, Schlinger BA, Saldanha CJ. Aromatase is pre-synaptic and sexually dimorphic in the adult zebra finch brain. Proc Biol Sci 2006; 272:2089-96. [PMID: 16191621 PMCID: PMC1559905 DOI: 10.1098/rspb.2005.3181] [Citation(s) in RCA: 134] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Oestrogens organize and activate circuits within the vertebrate central nervous system. Oestrogen synthesis occurs via the expression of aromatase, a P450 enzyme detected in microsomes and more recently in pre-synaptic boutons. Synaptic aromatase has only been described in brain regions that express aromatase in many subcellular compartments, so its function remains poorly understood. To more thoroughly study the role of oestrogen synthesis at synaptic terminals, we examined the ultrastructural compartmentalization of aromatase in the zebra finch; a species in which high aromatase activity can be measured in brain areas that do not contain somal aromatase. Here, we report the presence of aromatase in pre-synaptic boutons in the hippocampus and the high vocal centre brain areas with low and undetectable somal aromatase, respectively, in addition to areas with abundant somal aromatase such as the preoptic area and caudomedial nidopallium. At these brain areas, males had more total synapses, more aromatase pre-synaptic boutons and importantly, the proportion of total synaptic profiles that expressed aromatase was significantly higher in males relative to females. Aromatase-positive pre-synaptic boutons were always observed innervating aromatase-negative post-synaptic elements. We conclude that oestrogen may be provided to discrete oestrogen-sensitive targets by synaptic aromatization. Further, some targets may be exposed to more oestrogen in males. The expression of aromatase in individual synapses of projection neurons represents a unique mechanism of neuroendocrine action. Neurons with steroidogenic capability may modulate distant targets with the specificity of axonal innervation.
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Affiliation(s)
- R. Scott Peterson
- Physiological SciencesUCLA, Los Angeles, CA 90095, USA
- The Laboratory for Neuroendocrinology BRIUCLA, Los Angeles, CA 90095, USA
| | - Lakshmi Yarram
- Department of Biological Sciences, Lehigh University111 Research Drive, Bethlehem, PA 18015, USA
| | - Barney A Schlinger
- Physiological SciencesUCLA, Los Angeles, CA 90095, USA
- The Laboratory for Neuroendocrinology BRIUCLA, Los Angeles, CA 90095, USA
| | - Colin J Saldanha
- Department of Biological Sciences, Lehigh University111 Research Drive, Bethlehem, PA 18015, USA
- The Program in Cognitive Science, Lehigh University111 Research Drive, Bethlehem, PA 18015, USA
- Author for correspondence ()
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85
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Lavaque E, Mayen A, Azcoitia I, Tena-Sempere M, Garcia-Segura LM. Sex differences, developmental changes, response to injury and cAMP regulation of the mRNA levels of steroidogenic acute regulatory protein, cytochrome p450scc, and aromatase in the olivocerebellar system. ACTA ACUST UNITED AC 2006; 66:308-18. [PMID: 16329132 DOI: 10.1002/neu.20221] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Compelling evidence has now demonstrated direct biological actions of sex steroids at the cerebellum. Likewise, the expression of key steroidogenic factors, such as the steroidogenic acute regulatory protein (StAR), cytochrome P450 side chain cleavage (P450scc), and aromatase, at this neural site has been reported. Little is known, however, about the regulation of their genes in the cerebellum. Assessment of StAR, P450scc, and aromatase mRNAs in the cerebellum of male and female rats revealed that the expression of these genes is developmentally regulated, with the highest levels at early postnatal ages in both sexes and with significantly higher mRNA levels in postnatal males. Expression of these genes in the female remained unaltered after perinatal androgenization and along the estrous cycle. In contrast, damage of cerebellar afferent neurons of the inferior olivary nucleus evoked a significant increase in StAR, P450scc, and aromatase mRNA levels at this site, as well as a transient elevation in StAR mRNA at the cerebellum. Finally, enhancement of cAMP levels in cultured cerebellar neurons induced a significant increase in StAR and aromatase mRNA levels. In summary, we present herein novel evidence for the developmentally regulated and partially sexually dimorphic pattern of expression of StAR, P450scc, and aromatase genes in the rat cerebellum. These observations, together with the finding that the mRNA levels of these steroidogenic molecules are sensitive to injury and are regulated by intracellular cAMP, strongly suggest that local steroidogenesis is likely to play an important role during development and adaptation to neurodegenerative processes in the olivocerebellar system.
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86
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Yague JG, Muñoz A, de Monasterio-Schrader P, Defelipe J, Garcia-Segura LM, Azcoitia I. Aromatase expression in the human temporal cortex. Neuroscience 2006; 138:389-401. [PMID: 16426763 DOI: 10.1016/j.neuroscience.2005.11.054] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2005] [Revised: 11/03/2005] [Accepted: 11/20/2005] [Indexed: 10/25/2022]
Abstract
The expression of the human cyp19 gene, encoding P450 aromatase, the key enzyme for estrogen biosynthesis, involves alternative splicing of multiple forms of exon I regulated by different promoters. Aromatase expression has been detected in the human cerebral cortex, although the precise cellular distribution and promoter regulation are not fully characterized. We examined the variants of exon I of cyp19 by PCR analysis and the cellular distribution of the enzyme using immunohistochemistry in the human temporal cortex. We detected four different variants of exon I, suggesting a complex regulation of cyp19 in the cerebral cortex. In addition, the enzyme was localized mainly in a large subpopulation of pyramidal neurons and in a subpopulation of astrocytes. However, the majority of GABAergic interneurons identified by their expression of the calcium-binding proteins calbindin, calretinin and parvalbumin, did not display aromatase immunoreactivity. The broad range of potential modulators of the cyp19 gene in the cortex and the widespread expression of the protein in specific neuronal and glial subpopulations suggest that local estrogen formation may play an important role in human cortical function.
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Affiliation(s)
- J G Yague
- Instituto Cajal, Consejo Superior de Investigaciones Cientificas, E-28002 Madrid, Spain
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87
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Sortino MA, Platania P, Chisari M, Merlo S, Copani A, Catania MV. A major role for astrocytes in the neuroprotective effect of estrogen. Drug Dev Res 2006. [DOI: 10.1002/ddr.20051] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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88
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Veiga S, Azcoitia I, Garcia-Segura LM. Extragonadal synthesis of estradiol is protective against kainic acid excitotoxic damage to the hippocampus. Neuroreport 2005; 16:1599-603. [PMID: 16148753 DOI: 10.1097/01.wnr.0000179081.39659.7d] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Gonadal or exogenous estradiol is neuroprotective in multiple experimental paradigms. The role exerted by endogenous extragonadal estradiol synthesis in neuroprotection, however, is poorly understood. Here we show that a dose of kainic acid (3 mg/kg body weight) that does not produce detectable neuronal damage in control male and female gonadectomized rats induces a significant loss of hippocampal hilar neurons after the systemic inhibition of aromatase, the enzyme involved in estradiol biosynthesis from androgens. Extragonadal aromatase inhibition exerts a similar neuronal loss in both male and female rats (26% and 30% reduction in the number of hilar neurons, respectively). These findings indicate that extragonadal estradiol exerts a neuroprotective effect in both sexes, which prevents neuronal loss as a consequence of mild neurodegenerative signals.
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Affiliation(s)
- Sergio Veiga
- Instituto Cajal, Consejo Superior de Investigaciones Científicas, Spain
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89
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Schlinger BA, Saldanha CJ. Songbirds: A novel perspective on estrogens and the aging brain. AGE (DORDRECHT, NETHERLANDS) 2005; 27:287-296. [PMID: 23598662 PMCID: PMC3455882 DOI: 10.1007/s11357-005-4555-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2005] [Accepted: 08/28/2005] [Indexed: 06/02/2023]
Abstract
Songbirds perform some remarkable feats of memory, including forming memories for songs and for complex spatial features of their environments. Research into the neural and hormonal control of these behaviors reveals discrete circuits that can retain considerable plasticity in adulthood. The songbird brain is also a prominent site of estrogen synthesis and a target of estrogen action. Estrogens contribute to the plasticity of the adult songbird brain and contribute to the bird's capacity to form and retrieve some memories. We describe the brain, behavior and endocrinology of songbirds and discuss these findings within the context of the neurology of the aging brain.
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Affiliation(s)
- Barney A. Schlinger
- Department of Physiological Science and Laboratory of Neuroendocrinology, Brain Research Institute, UCLA, Los Angeles, CA USA
- Physiological Science, UCLA, 621 Charles E. Young Drive South, Los Angeles, CA 90095 USA
| | - Colin J. Saldanha
- Department of Biological Sciences, Lehigh University, Bethlehem, PA USA
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90
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Goodson JL, Saldanha CJ, Hahn TP, Soma KK. Recent advances in behavioral neuroendocrinology: insights from studies on birds. Horm Behav 2005; 48:461-73. [PMID: 15896792 PMCID: PMC2570788 DOI: 10.1016/j.yhbeh.2005.04.005] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/02/2005] [Revised: 04/05/2005] [Accepted: 04/07/2005] [Indexed: 01/16/2023]
Abstract
Ever since investigations in the field of behavioral endocrinology were hatched with experiments on roosters, birds have provided original insights into issues of fundamental importance for all vertebrate groups. Here we focus on more recent advances that continue this tradition, including (1) environmental regulation of neuroendocrine and behavioral systems, (2) steroidogenic enzyme functions that are related to intracrine processes and de novo production of neurosteroids, and (3) hormonal regulation of neuroplasticity. We also review recent findings on the anatomical and functional organization of steroid-sensitive circuits in the basal forebrain and midbrain. A burgeoning body of data now demonstrates that these circuits comprise an evolutionarily conserved network, thus numerous novel insights obtained from birds can be used (in a relatively straightforward manner) to generate predictions for other taxa as well. We close by using birdsong as an example that links these areas together, thereby highlighting the exceptional opportunities that birds offer for integrative studies of behavioral neuroendocrinology and behavioral biology in general.
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Affiliation(s)
- James L Goodson
- Psychology Department, University of California, 5212 McGill Hall, San Diego, La Jolla, CA 92093-0109, USA.
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91
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Saldanha CJ, Rohmann KN, Coomaralingam L, Wynne RD. Estrogen provision by reactive glia decreases apoptosis in the zebra finch (Taeniopygia guttata). ACTA ACUST UNITED AC 2005; 64:192-201. [PMID: 15818556 DOI: 10.1002/neu.20147] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Upregulation of aromatase (estrogen synthase) in glia around the site of neural injury may limit neural degeneration. Systemic administration of estrogen limits neural damage, but the specific role of local estrogen provision in this effect is unclear. In male zebra finches, we tested the effect of local aromatase inhibition and estrogen replacement on type of cellular degeneration and the distance of this degeneration from the source of insult. Subjects received injections of the aromatase inhibitor fadrozole into one telencephalic lobe and fadrozole and estradiol into the contralateral lobe. Seventy-two hours later, we used Fluoro-Jade B and TUNEL to label dying and apoptotic cells, respectively. Since each subject was its own control, we were able to assess the influence of local estrogen replacement in relative distinction from circulating steroids and constitutive aromatization. Cellular degeneration around the lesion was measured with Fluoro-Jade B, TUNEL, and indirectly with aromatase expression. Additionally, the glial nature of aromatase-positive cells around the injury was queried by co-localization with vimentin. The estrogen replaced injury had fewer apoptotic cells clustered more closely around the injury compared to the hemisphere injected with fadrozole alone. Since Fluoro-Jade B and TUNEL labeled similar numbers of cells, and the distance of these cells from the injection was identical, we suggest that estrogen replacement functions primarily to restrict apoptosis in the current paradigm. Lastly, aromatase-positive cells around injuries co-localize vimentin, establishing their glial nature. Thus, glial estrogen provision at sites of neural insult may be critical in limiting the cellular degeneration caused by injury via an inhibition of apoptosis.
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Affiliation(s)
- Colin J Saldanha
- Department of Biological Sciences, Lehigh University, 111 Research Drive, Bethlehem, Pennsylvania 18015, USA.
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92
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Carswell HVO, Dominiczak AF, Garcia-Segura LM, Harada N, Hutchison JB, Macrae IM. Brain aromatase expression after experimental stroke: topography and time course. J Steroid Biochem Mol Biol 2005; 96:89-91. [PMID: 15896953 DOI: 10.1016/j.jsbmb.2005.02.016] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/01/2004] [Accepted: 02/04/2005] [Indexed: 11/25/2022]
Abstract
Brain aromatase has been shown to be increased in expression after neurotoxic damage and to exert neuroprotection via generation of local oestrogens. The present study investigates the topography and time course of brain aromatase expression after experimental stroke (middle cerebral artery occlusion (MCAO)). Ovariectomised stroke prone spontaneously hypertensive rats underwent distal MCAO by electrocoagulation. Immunohistochemistry revealed increased brain aromatase expression at 24h and 8 days in the cortical penumbra/peri-infarct zones with no increase evident at 2h or 30 days post-MCAO. Double label studies indicate that some of the increased aromatase expression is associated with astrocytic processes. Thus, this is the first evidence that aromatase protein is increased after MCAO and the location (peri-infarct), time course (within 24h) and cellular localisation (astrocytic) indicate the potential for aromatase to promote the survival of cells in the penumbra after experimental stroke by local synthesis of oestrogens.
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Affiliation(s)
- H V O Carswell
- Wellcome Surgical Institute, Division of Clinical Neuroscience, University of Glasgow, Glasgow G61 1QH, Scotland, UK.
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93
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Pellegrini E, Menuet A, Lethimonier C, Adrio F, Gueguen MM, Tascon C, Anglade I, Pakdel F, Kah O. Relationships between aromatase and estrogen receptors in the brain of teleost fish. Gen Comp Endocrinol 2005; 142:60-6. [PMID: 15862549 DOI: 10.1016/j.ygcen.2004.12.003] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/24/2004] [Revised: 12/08/2004] [Accepted: 12/13/2004] [Indexed: 11/18/2022]
Abstract
Teleost fish are known for exhibiting a high aromatase activity mainly due to the expression of the cyp19b gene, encoding aromatase B (AroB). Recent studies based on both in situ hybridization and immunohistochemistry have demonstrated in three different species that this activity is restricted to radial glial cells. In agreement with measurements of aromatase activity, such aromatase-expressing cells are more abundant in the telencephalon, preoptic area, and mediobasal hypothalamus, although positive cells are also found in the midbrain and hindbrain. Comparative distribution of AroB and estrogen receptor (ERalpha, ERbeta1, and ERbeta2) expression indicates that the preoptic region and hypothalamus are major target for locally produced estradiol (E2) which is likely involved in controlling expression of genes implicated in neuroendocrine regulations. However, AroB and ER have never been reported to be co-expressed in the same cells which is intriguing given that, at least in some species, AroB is strongly up-regulated by E2 itself in agreement with the presence of an estrogen-responsive element (ERE) in the proximal promoter of the cyp19b gene. In vivo data in zebrafish have shown that E2 up-regulates AroB only in radial glial cells. This is in agreement with in vitro transfection experiments indicating that this ERE is functional, but not sufficient, as the E2 regulation of AroB only occurs in glial cell contexts, suggesting a cooperation between ER and so far unidentified glial-specific factors. These data also suggest that radial glial cells may express low amounts of ER that escaped detection until now. The expression of AroB in radial cells, well known for their roles in neurogenesis and now considered as progenitor cells, suggests that local E2 production within these cells could influence the well-documented capacity of the brain of teleosts to grow during adulthood.
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Affiliation(s)
- Elisabeth Pellegrini
- Endocrinologie Moléculaire de la Reproduction, UMR CNRS 6026, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes cedex, France
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94
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Veiga S, Melcangi RC, Doncarlos LL, Garcia-Segura LM, Azcoitia I. Sex hormones and brain aging. Exp Gerontol 2005; 39:1623-31. [PMID: 15582278 DOI: 10.1016/j.exger.2004.05.008] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2004] [Accepted: 05/17/2004] [Indexed: 02/07/2023]
Abstract
Sex steroids exert pleiotropic effects in the nervous system, preserving neural function and promoting neuronal survival. Therefore, the age-related decrease in sex steroids may have a negative impact on neural function. Progesterone, testosterone and estradiol prevent neuronal loss in the central nervous system in different experimental animal models of neurodegeneration. Furthermore, progesterone and its reduced derivatives dihydroprogesterone and tetrahydroprogesterone reduce aging-associated morphological abnormalities of myelin and aging-associated myelin fiber loss in rat peripheral nerves. However, the results from hormone replacement studies in humans are thus far inconclusive. A possible alternative to hormonal replacement therapy is to increase local steroidogenesis by neural tissues, which express enzymes for steroid synthesis and metabolism. Proteins involved in the intramitochondrial trafficking of cholesterol, the first step in steroidogenesis, such as the peripheral-type benzodiazepine receptor and the steroidogenic acute regulatory protein, are up-regulated in the nervous system after injury. Furthermore, steroidogenic acute regulatory protein expression is increased in the brain of 24-month-old rats compared with young adult rats. This suggests that brain steroidogenesis may be modified in adaptation to neurodegenerative conditions and to the brain aging process. Furthermore, recent studies have shown that local formation of estradiol in the brain, by the enzyme aromatase, is neuroprotective. Therefore, steroidogenic acute regulatory protein, peripheral-type benzodiazepine receptor and aromatase are attractive pharmacological targets to promote neuroprotection in the aged brain.
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Affiliation(s)
- Sergio Veiga
- Instituto Cajal, CSIC, Avenida Doctor Arce 37, 28002 Madrid, Spain
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95
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Balthazart J, Baillien M, Cornil CA, Ball GF. Preoptic aromatase modulates male sexual behavior: slow and fast mechanisms of action. Physiol Behav 2005; 83:247-70. [PMID: 15488543 DOI: 10.1016/j.physbeh.2004.08.025] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
In many species, copulatory behavior and appetitive (anticipatory/motivational) aspects of male sexual behavior are activated by the action in the preoptic area of estrogens locally produced by testosterone aromatization. Estrogens bind to intracellular receptors, which then act as transcription factors to activate the behavior. Accordingly, changes in aromatase activity (AA) result from slow steroid-induced modifications of enzyme transcription. More recently, rapid nongenomic effects of estrogens have been described and evidence has accumulated indicating that AA can be modulated by rapid (minutes to hour) nongenomic mechanisms in addition to the slower transcriptional changes. Hypothalamic AA is rapidly down-regulated in conditions that enhance protein phosphorylation, in particular, increases in the intracellular calcium concentration, such as those triggered by neurotransmitter (e.g., glutamate) activity. Fast changes in brain estrogens can thus be caused by aromatase phosphorylation as a result of changes in neurotransmission. In parallel, recent studies demonstrate that the pharmacological blockade of AA by specific inhibitors rapidly (within 15-45 min) down-regulates motivational and consummatory aspects of male sexual behavior in quail while injections of estradiol can rapidly increase the expression of copulatory behavior. These data collectively support an emerging concept in neuroendocrinology, namely that estrogen, locally produced in the brain, regulates male sexual behavior via a combination of genomic and nongenomic mechanisms. Rapid and slower changes of brain AA match well with these two modes of estrogen action and provide temporal variations in the estrogen's bioavailability that can support the entire range of established effects for this steroid.
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Affiliation(s)
- Jacques Balthazart
- Center for Cellular and Molecular Neurobiology, Research Group in Behavioral Neuroendocrinology, University of Liège, 17 place Delcour (Bat. L1), B-4020 Liège, Belgium.
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96
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Hoyk Z, Párducz A, Garcia-Segura LM. Dehydroepiandrosterone regulates astroglia reaction to denervation of olfactory glomeruli. Glia 2005; 48:207-16. [PMID: 15390121 DOI: 10.1002/glia.20070] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Effects of dehydroepiandrosterone (DHEA) on glial reactions of the peripherally denervated olfactory bulb were studied in adult male rats. Denervation was achieved by destroying the olfactory mucosa with ZnSO(4) (0.17 M) irrigation of the nasal cavities. In one series of experiments, chronic DHEA treatment was applied (daily injections for 7 days, i.p., 10 mg/kg b.w. and 25 mg/kg b.w.); in the other series of experiments, animals received a single injection of DHEA (i.p., 10 mg/kg b.w., 25 mg/kg b.w. and 50 mg/kg b.w.) 2 h following ZnSO(4) treatment. To determine whether DHEA conversion to estradiol was involved in the mechanism of DHEA action on glia, a third series of experiments was carried out in which the aromatase inhibitor fadrozole (4.16 mg/ml) was administered using subcutaneously implanted osmotic minipumps. Rats were killed on day 7 after chemical denervation, and the reaction of glial cells was monitored within the olfactory bulb, using GFAP and vimentin immunohistochemistry. Qualitative changes in GFAP expression were analyzed by Western blot. Chronic DHEA treatment with both doses (10 mg/kg b.w. and 25 mg/kg b.w.) and acute DHEA treatment with the highest dose applied (50 mg/kg b.w.), inhibited the increase in GFAP expression induced by the denervation of the olfactory bulb. Furthermore, GFAP and vimentin immunostaining in the glomerular layer of the olfactory bulb were diminished in the denervated and DHEA treated groups. However, when DHEA treatment was combined with fadrozole administration, such a decrease in GFAP expression could not be detected in the chemically denervated olfactory bulb. These findings indicate that DHEA, depending on the dose applied and the mode of administration, attenuates glial reaction to denervation and may regulate glial plasticity in the olfactory glomeruli. These effects are likely to be mediated at least in part by the conversion of DHEA to estradiol.
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Affiliation(s)
- Zsófia Hoyk
- Institute of Biophysics, Biological Research Center, Szeged, Hungary
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97
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Garcia-Ovejero D, Azcoitia I, Doncarlos LL, Melcangi RC, Garcia-Segura LM. Glia-neuron crosstalk in the neuroprotective mechanisms of sex steroid hormones. ACTA ACUST UNITED AC 2005; 48:273-86. [PMID: 15850667 DOI: 10.1016/j.brainresrev.2004.12.018] [Citation(s) in RCA: 170] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2004] [Accepted: 12/09/2004] [Indexed: 11/22/2022]
Abstract
Proteins involved in the intramitochondrial trafficking of cholesterol, the first step in steroidogenesis, such as the steroidogenic acute regulatory protein (StAR) and the peripheral-type benzodiazepine receptor (PBR), are upregulated in the nervous system after injury. Accordingly, a local increase in the levels of steroids, such as pregnenolone and progesterone, is observed following traumatic injury in the brain and spinal cord. The expression and activity of aromatase, the enzyme that synthesizes estradiol, is also increased in injured brain areas and its inhibition results in an increased neurodegeneration. These findings suggest that an increase in steroidogenesis is part of an overall mechanism used by the nervous tissue to cope with neurodegenerative conditions. Neural steroidogenesis is the result of a coordinated interaction of neurons and glia. For example, after neural injury, there is an upregulation of StAR in neurons and of PBR in microglia and astroglia. Aromatase is expressed in neurons under basal conditions and is upregulated in reactive astrocytes after injury. Some of the steroids produced by glia are neuroprotective. Progesterone and progesterone derivatives produced by Schwann cells, promote myelin formation and the remyelination and regeneration of injured nerves. In the central nervous system, the steroids produced by glia regulate synaptic function, affect anxiety, cognition, sleep and behavior, and exert neuroprotective and reparative roles. In addition, glial cells are targets for steroids and mediate some of the effects of these molecules on neurons, including the regulation of survival and regeneration.
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98
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Menuet A, Pellegrini E, Brion F, Gueguen MM, Anglade I, Pakdel F, Kah O. Expression and estrogen-dependent regulation of the zebrafish brain aromatase gene. J Comp Neurol 2005; 485:304-20. [PMID: 15803511 DOI: 10.1002/cne.20497] [Citation(s) in RCA: 197] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Compared with adult mammals, the brain of teleost fish is characterized by an extremely high capacity to aromatize androgens into estrogens, and this metabolic activity results from the expression of a specific brain aromatase (AroB) generated by the cyp19b gene. In this study, we first generated antibodies to zebrafish AroB and used them to map AroB-positive structures in the brain of adult zebrafish. We show that AroB is exclusively expressed in radial glial cells, mainly in the olfactory bulbs, telencephalon, preoptic area, and hypothalamus. Second, we investigated in vivo and in vitro the mechanisms involved in the estradiol (E2) regulation of the cyp19b gene. By means of whole-mount hybridization and immunohistochemistry on zebrafish embryos and larvae, we confirmed the E2-dependent upregulation of the cyp19b gene, and we show that E2 triggers AroB expression in radial glial cells mainly in the preoptic area and mediobasal hypothalamus of 48 hpf (hours post fertilization) and 108 hpf larvae. In addition, an in vitro analysis of 0.5 kb of the promoter region of the cyp19b gene demonstrated that this E2-dependent regulation involves a direct transcriptional action of estrogen receptors requiring estrogen-responsive elements. However, the data obtained on different cell lines demonstrate that a glial cell context is necessary for full E2 induction. The correlation between our in vivo and in vitro data suggests that the E2-dependent upregulation of AroB is favored by a glial cell context.
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Affiliation(s)
- Arnaud Menuet
- Endocrinologie Moléculaire de la Reproduction, Unité Mixte de Recherche 6026 Centre National de la Recherche Scientifique, Université de Rennes 1, 35042 Rennes, France
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99
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Kretz O, Fester L, Wehrenberg U, Zhou L, Brauckmann S, Zhao S, Prange-Kiel J, Naumann T, Jarry H, Frotscher M, Rune GM. Hippocampal synapses depend on hippocampal estrogen synthesis. J Neurosci 2004; 24:5913-21. [PMID: 15229239 PMCID: PMC6729232 DOI: 10.1523/jneurosci.5186-03.2004] [Citation(s) in RCA: 333] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Estrogens have been described to induce synaptogenesis in principal neurons of the hippocampus and have been shown to be synthesized and released by exactly these neurons. Here, we have focused on the significance of local estrogen synthesis on spine synapse formation and the synthesis of synaptic proteins. To this end, we reduced hippocampal estrogen synthesis in vitro with letrozole, a reversible nonsteroidal aromatase inhibitor. In hippocampal slice cultures, letrozole treatment resulted in a dose-dependent decrease of 17beta-estradiol as quantified by RIA. This was accompanied by a significant decrease in the density of spine synapses and in the number of presynaptic boutons. Quantitative immunohistochemistry revealed a downregulation of spinophilin, a marker of dendritic spines, and synaptophysin, a protein of presynaptic vesicles, in response to letrozole. Surprisingly, no increase in the density of spines, boutons, and synapses and in spinophilin expression was seen after application of estradiol to the medium of cultures that had not been treated with letrozole. However, synaptophysin expression was upregulated under these conditions. Our results point to an essential role of endogenous hippocampal estrogen synthesis in the maintenance of hippocampal spine synapses.
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Affiliation(s)
- Oliver Kretz
- Institute of Anatomy and Cell Biology, Albert-Ludwigs-Universität Freiburg, D-79104 Freiburg, Germany
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100
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Abstract
The song system of zebra finches (Taeniopygia gutatta) is highly sexually dimorphic. Only males sing, and the brain regions and muscles controlling song are much larger in males than in females. Development of the song system is highly sensitive to steroid hormones. However, unlike similar sexually dimorphic systems in other animal models, masculinization of song system structure and function is most likely not induced by testosterone secreted from the testes. Instead, sex-specific development of the neural song system appears to be regulated by factors intrinsic to the brain, probably by the expression of sex chromosome gene(s) that influence the levels of estradiol synthesized in the brain and/or the responses of brain tissue to estradiol. However, the existing data are complex and in some cases contradictory. More work is required to identify the critical genes and their relationships with steroid hormones.
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Affiliation(s)
- Juli Wade
- Department of Psychology, Michigan State University, Neuroscience Program, 108 Giltner Hall, East Lansing, MI 48824-1101, USA.
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