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See detailPartial Cloning and Distribution of Estrogen Receptor Beta in the Avian Brain
Lakaye, Bernard ULg; Foidart, Agnès ULg; Grisar, Thierry ULg et al

in Neuroreport (1998), 9(12), 2743-8

A partial estrogen receptor beta (ER-beta) cDNA was isolated from testicular quail RNA by RT-PCR with degenerate primers specific to the rat ER-beta sequence. A high expression of ER-beta was demonstrated ... [more ▼]

A partial estrogen receptor beta (ER-beta) cDNA was isolated from testicular quail RNA by RT-PCR with degenerate primers specific to the rat ER-beta sequence. A high expression of ER-beta was demonstrated by RT-PCR in the telencephalon, diencephalon, pituitary, testis and kidneys of male quail but little or no expression was detected in the cerebellum, pectoral muscle and adrenal gland. In situ hybridization with a 35S-labelled oligoprobe in sections through the preoptic area-rostral hypothalamus identified high expression in the medial preoptic nucleus, bed nucleus striae terminalis and nucleus taeniae. These data demonstrate the presence of an ER-beta in brain areas implicated in the control of reproduction in a non-mammalian species. [less ▲]

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See detailAppetitive and consummatory male sexual behavior in Japanese quail are differentially regulated by subregions of the preoptic medial nucleus
Balthazart, Jacques ULg; Absil, Philippe ULg; Gérard, Marie-Paule ULg et al

in Journal of Neuroscience (1998), 18(16), 6512-6527

Central testosterone aromatization is required for the activation of both appetitive (ASB) and consummatory (CSB) male sexual behavior in Japanese quail. There are two major clusters of aromatase ... [more ▼]

Central testosterone aromatization is required for the activation of both appetitive (ASB) and consummatory (CSB) male sexual behavior in Japanese quail. There are two major clusters of aromatase immunoreactive (ARO-ir) cells in the rostral forebrain; these outline the nucleus preopticus medialis (POM) and the nucleus striae terminalis (BST). We investigated the role of these nuclei in the regulation of ASB and CSB. Appetitive male sexual behavior was measured with the use of a learned social proximity procedure that quantified the time spent by a male in front of a window with a view of a female who was subsequently released into the cage, providing an opportunity for CSB. Males first acquired the response and then received bilateral electrolytic lesions aimed at the POM or BST, followed by retesting for ASB and CSB. Brain sections were stained for ARO-ir, and lesions to the two ARO-ir cell groups were quantitatively characterized. Lesions damaging the POM completely abolished CSB and also significantly decreased ASB. Lesions of the rostral BST had no effect on ASB, but moderately decreased CSB. Detailed anatomical analysis revealed that lesions of a subdivision of the POM just rostral to the anterior commissure specifically impair CSB, whereas lesions that are more rostral to this subdivision induce a severe deficit in ASB. These data indicate that different subregions of the POM regulate ASB and CSB in a somewhat independent manner, whereas the BST is only important in the regulation of CSB. [less ▲]

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See detailDistribution of Androgen Receptor-Immunoreactive Cells in the Quail Forebrain and Their Relationship with Aromatase Immunoreactivity
Balthazart, Jacques ULg; Foidart, Agnès ULg; Houbart, M. et al

in Journal of Neurobiology (1998), 35(3), 323-40

The distribution of androgen receptor-like immunoreactive (AR-ir) cells in the quail brain was analyzed by immunocytochemistry with the use of the affinity-purified antibody PG-21-19A raised against a ... [more ▼]

The distribution of androgen receptor-like immunoreactive (AR-ir) cells in the quail brain was analyzed by immunocytochemistry with the use of the affinity-purified antibody PG-21-19A raised against a synthetic peptide representing the first 21 N-terminal amino acids of the rat and human AR. This antibody is known to bind to the receptor in the absence as well as in the presence of endogenous ligands, and it was therefore expected that a more complete and accurate characterization of AR-ir cells would be obtained in comparison with previous studies using an antibody that preferentially recognizes the occupied receptor. Selected sections were double labeled for aromatase (ARO) by a technique that uses alkaline phosphatase as the reporter enzyme and Fast blue as the chromogen. AR-ir material was detected in the nucleus of cells located in a variety of brain areas in the preoptic region and the hypothalamus including the medial preoptic (POM), the supraoptic, the paraventricular (PVN), and the ventromedial (VMN) nuclei, but also in the tuberculum olfactorium, the nucleus accumbens/ventral striatum, the nucleus taeniae, the tuberal hypothalamus, the substantia grisea centralis (GCt), and the locus ceruleus. Cells exhibiting a dense AR-ir label were also detected in the nucleus intercollicularis. Preincubation of the primary antibody with an excess of the synthetic peptide used for immunization completely eliminated this nuclear staining. A significant number of AR-ir cells in the POM, VMN, PVN, and tuberal hypothalamus also contained ARO-ir material in their cytoplasm. These data confirm and extend previous studies localizing AR in the avian brain, and raise questions about the possible regulation by androgens of the metabolizing enzyme aromatase. [less ▲]

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See detailNew Insights into the Regulation and Function of Brain Estrogen Synthase (Aromatase)
Balthazart, Jacques ULg; Ball, G. F.

in Trends in Neurosciences (1998), 21(6), 243-9

In the brain, conversion of androgens into estrogens by the enzyme aromatase (estrogen synthase) is a key mechanism by which testosterone regulates many physiological and behavioral processes, including ... [more ▼]

In the brain, conversion of androgens into estrogens by the enzyme aromatase (estrogen synthase) is a key mechanism by which testosterone regulates many physiological and behavioral processes, including the activation of male sexual behavior, brain sexual differentiation and negative feedback effects of steroid hormones on gonadotropin secretion. Studies on the distribution and regulation of brain aromatase have led to a new perspective on the control and function of this enzyme. A growing body of evidence indicates that the estrogen regulation of aromatase is, at least in part, trans-synaptic. Afferent catecholamine pathways appear to regulate aromatase activity in some brain areas and thereby provide a way for environmental cues to modulate this enzyme.The localization of aromatase in pre-synaptic boutons suggests possible roles for estrogens at the synapse. [less ▲]

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See detailNeuroanatomical Distribution and Variations across the Reproductive Cycle of Aromatase Activity and Aromatase-Immunoreactive Cells in the Pied Flycatcher (Ficedula Hypoleuca)
Foidart, Agnès ULg; Silverin, B.; Baillien, M. et al

in Hormones & Behavior (1998), 33(3), 180-96

The anatomical distribution and seasonal variations in aromatase activity and in the number of aromatase-immunoreactive cells were studied in the brain of free-living male pied flycatchers (Ficedula ... [more ▼]

The anatomical distribution and seasonal variations in aromatase activity and in the number of aromatase-immunoreactive cells were studied in the brain of free-living male pied flycatchers (Ficedula hypoleuca). A high aromatase activity was detected in the telencephalon and diencephalon but low to negligible levels were present in the optic lobes, cerebellum, and brain stem. In the diencephalon, most aromatase-immunoreactive cells were confined to three nuclei implicated in the control of reproductive behaviors: the medial preoptic nucleus, the nucleus of the stria terminalis, and the ventromedial nucleus of the hypothalamus. In the telencephalon, the immunopositive cells were clustered in the medial part of the neostriatum and in the hippocampus as previously described in another songbird species, the zebra finch. No immunoreactive cells could be observed in the song control nuclei. A marked drop in aromatase activity was detected in the anterior and posterior diencephalon in the early summer when the behavior of the birds had switched from defending a territory to helping the female in feeding the nestlings. This enzymatic change is presumably controlled by the drop in plasma testosterone levels observed at that stage of the reproductive cycle. No change in enzyme activity, however, was seen at that time in other brain areas. The number of aromatase-immunoreactive cells also decreased at that time in the caudal part of the medial preoptic nucleus but not in the ventromedial nucleus of the hypothalamus (an increase was even observed), suggesting that differential mechanisms control the enzyme concentration and enzyme activity in the hypothalamus. Taken together, these data suggest that changes in diencephalic aromatase activity contribute to the control of seasonal variations in reproductive behavior of male pied flycatchers but the role of the telencephalic aromatase in the control of behavior remains unclear at present. [less ▲]

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See detailAnatomical Relationships between Aromatase and Tyrosine Hydroxylase in the Quail Brain: Double-Label Immunocytochemical Studies
Balthazart, Jacques ULg; Foidart, Agnès ULg; Baillien, M. et al

in Journal of Comparative Neurology (The) (1998), 391(2), 214-26

The activation of male sexual behavior in Japanese quail (Coturnix japonica) requires the transformation of testosterone to 17beta-estradiol by the enzyme aromatase (estrogen synthetase). There are ... [more ▼]

The activation of male sexual behavior in Japanese quail (Coturnix japonica) requires the transformation of testosterone to 17beta-estradiol by the enzyme aromatase (estrogen synthetase). There are prominent sex differences in aromatase activity that may be regulated in part by sex differences in catecholaminergic activity. In this study, we investigate, with double-label immunocytochemistry methods, the anatomical relationship between the catecholamine synthesizing enzyme, tyrosine hydroxylase (TH) and aromatase (ARO) in the quail brain. The immunoreactivity observed for each antigen generally matched the previously described distribution. One exception is the observation that cells weakly labeled for aromatase were found widely distributed throughout the telencephalon. The presence of telencephalic aromatase was confirmed independently by radioenzymatic assays. There was an extensive overlap between the distribution of the two antigens in many brain areas. In all densely labeled aromatase-immunoreactive (ARO-ir) cell groups, including the preoptic medial nucleus, nucleus of the stria terminalis, mediobasal hypothalamus, and paleostriatum ventrale, ARO-ir cells were found in close association with TH-ir fibers. These TH-ir fibers often converged on an ARO-ir cell, and one or more TH-ir punctate structure(s) were found in close contact with nearly every densely labeled ARO-ir cell. In the telencephalon (mostly the neostriatum), all TH-ir fibers were found to be part of fiber groups that surrounded weakly immunoreactive aromatase cells. The few cells exhibiting an intracellular colocalization were detected in the anteroventral periventricular nucleus. These results are consistent with the hypothesis that catecholaminergic inputs regulate brain aromatase. [less ▲]

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See detailSystemic and Intracerebroventricular Injections of Vasotocin Inhibit Appetitive and Consummatory Components of Male Sexual Behavior in Japanese Quail
Castagna, C.; Absil, Philippe ULg; Foidart, Agnès ULg et al

in Behavioral Neuroscience (1998), 112(1), 233-50

The authors investigated the behavioral actions of vasotocin (VT) in castrated testosterone-treated male Japanese quail. The appetitive and consummatory components of sexual behavior as well as the ... [more ▼]

The authors investigated the behavioral actions of vasotocin (VT) in castrated testosterone-treated male Japanese quail. The appetitive and consummatory components of sexual behavior as well as the occurrence frequency of crows were inhibited, in a dose-dependent manner, by injections of VT. The authors observed opposite effects after injection of the V1 receptor antagonist, dPTyr(Me)AVP. Lower doses of VT were more active after central than after systemic injection, and effects of systemic injections of VT were blocked by a central injection of dPTyr(Me)AVP. The behavioral inhibition was associated with a modified diuresis after systemic but not central injection. These results provide direct evidence that VT affects male sexual behavior in quail by a direct action on the brain independent of its peripheral action on diuresis. [less ▲]

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See detailEffects of Dopamine Agonists on Appetitive and Consummatory Male Sexual Behavior in Japanese Quail
Castagna, C.; Ball, G. F.; Balthazart, Jacques ULg

in Pharmacology, Biochemistry & Behavior (1997), 58(2), 403-14

The effects of pharmacological manipulations of dopaminergic transmission on appetitive and consummatory aspects of male sexual behavior were investigated in castrated male Japanese quail treated with ... [more ▼]

The effects of pharmacological manipulations of dopaminergic transmission on appetitive and consummatory aspects of male sexual behavior were investigated in castrated male Japanese quail treated with exogenous testosterone. Appetitive male sexual behavior was assessed by measuring a learned social proximity response and consummatory behavior was assessed by measuring copulatory behavior per se. The nonselective dopamine receptor agonist, apomorphine, inhibited in a dose-dependent manner both components of male sexual behavior. Two indirect dopamine agonists were also tested. Nomifensine, a dopamine re-uptake inhibitor, decreased appetitive sexual behavior but increased the frequency of mount attempts, a measure of consummatory sexual behavior. Amfonelic acid, a compound that enhances dopaminergic tone by a complex mechanism, increased aspects of both appetitive and consummatory behaviors. These data suggest that, in quail, as in rodents, increases in dopaminergic tone facilitate both appetitive and consummatory aspects of male sexual behavior. Apomorphine may be inhibitory in quail because it acts primarily on D2-like receptors, unlike in rats, where it stimulates sexual behavior and acts primarily on D1-like receptors at low doses but interacts with D2-like receptors at higher doses. This is supported by the observation that stereotyped pecking, a behavior stimulated selectively in quail by D2 agonists, was increased by apomorphine but not by the two indirect agonists. The observed partial dissociation between the effects of these dopaminergic agonists on appetitive and consummatory sexual behaviors suggests that these two components of male sexual behavior may be controlled by the action of dopamine through different neuronal systems. [less ▲]

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See detailDifferential Effects of D1 and D2 Dopamine-Receptor Agonists and Antagonists on Appetitive and Consummatory Aspects of Male Sexual Behavior in Japanese Quail
Balthazart, Jacques ULg; Castagna, C.; Ball, G. F.

in Physiology & Behavior (1997), 62(3), 571-80

Pharmacological studies in Japanese quail based on behavioral tests with a variety of dopaminergic compounds suggest that the activation of D2 dopamine receptors inhibits, and the activation of D1 ... [more ▼]

Pharmacological studies in Japanese quail based on behavioral tests with a variety of dopaminergic compounds suggest that the activation of D2 dopamine receptors inhibits, and the activation of D1 dopamine receptors enhances, appetitive and consummatory components of male sexual behavior. This hypothesis was tested by studying the behavioral effects of specific D1 and D2 dopaminergic-receptor agonists and antagonists in castrated male Japanese quail chronically treated with exogenous testosterone (subcutaneous Silastic implants). The effects of 5 compounds were tested: 1 D1 (SKF38393) and 2 D2 (PPHT and quinpirole) agonists, and 1 D1 (SCH23390) and 1 D2 (Spiperone) antagonist. All compounds were tested at a low and a high dose (0.1 and 1 mg/kg, respectively, for all drugs, except spiperone where the doses were 2 and 10 mg/kg). A consistent effect of all drugs on consummatory sexual behavior was observed: it was stimulated by the D1 agonist and the D2 antagonist, but inhibited by the D1 antagonist and the D2 agonists. Far fewer effects of the treatments were detected on the measures of appetitive behavior. Measures of appetitive behavior were decreased by the 2 D2 agonists, but not affected by the other treatments. These data suggest that male copulatory behavior in quail is stimulated by dopamine acting on D1 receptors, but inhibited by activation of the D2 receptor subtype. The partial dissociation observed between the effects of the same treatments on appetitive and consummatory aspects of sexual behavior also suggests that these 2 behavioral systems may be controlled by the action of dopamine on different neuronal systems. [less ▲]

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See detailVasotocinergic Innervation of Areas Containing Aromatase-Immunoreactive Cells in the Quail Forebrain
Balthazart, Jacques ULg; Absil, Philippe ULg; Viglietti-Panzica, C. et al

in Journal of Neurobiology (1997), 33(1), 45-60

In the male quail forebrain, aromatase-immunoreactive (ARO-ir) elements are clustered within the sexually dimorphic medial preoptic nucleus (POM), nucleus striae terminalis (nST), nucleus accumbens (nAc ... [more ▼]

In the male quail forebrain, aromatase-immunoreactive (ARO-ir) elements are clustered within the sexually dimorphic medial preoptic nucleus (POM), nucleus striae terminalis (nST), nucleus accumbens (nAc), and ventromedial and tuberal hypothalamus. These ARO-ir cells are sensitive to testosterone and its metabolites: Their number and size increase after exposure to these steroids. The POM and lateral septum are also characterized by a dense vasotocinergic innervation that is also sensitive to testosterone. We analyzed here the anatomical relationships between ARO-ir elements and VT-ir fibers in the quail prosencephalon. Sequential staining for vasotocin, aromatase, or vasotocin plus aromatase was performed on adjacent 30-microm-thick cryostat sections. High concentrations of thin VT-ir fibers were observed within the POM, nST, lateral septum, periventricular mesencephalic central gray, and ventromedial and tuberal hypothalamus. There was a close correspondence between the extension of the ARO-ir cells and of VT-ir fibers. In double-labeled sections, all clusters of ARO-ir cells with the exception of those located in the nAc were embedded in a dense network of VT-ir fibers. Many of the VT-ir terminals appeared to end in the neuropile surrounding ARO-ir elements rather than directly on their cell bodies. This study supports the idea that the testosterone-dependent aromatase system is directly innervated by a testosterone-dependent peptidergic system. Aromatase-containing cells could therefore be modulated by steroids both directly and indirectly through the vasotocin system. Alternatively, this neuroanatomical arrangement may mediate the control of vasotocin synthesis or release by steroids. Functional studies demonstrate that both aromatase and vasotocin affect reproductive behavior in quail, and the present data provide anatomical support for the integration of these effects. [less ▲]

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See detailIdentification of Catecholaminergic Inputs to and Outputs from Aromatase-Containing Brain Areas of the Japanese Quail by Tract Tracing Combined with Tyrosine Hydroxylase Immunocytochemistry
Balthazart, Jacques ULg; Absil, Philippe ULg

in Journal of Comparative Neurology (The) (1997), 382(3), 401-28

In the quail brain, aromatase-immunoreactive (ARO-ir) neurons located in the medial preoptic nucleus (POM) and caudal paleostriatum ventrale/nucleus accumbens/nucleus striae terminalis complex (PVT/nAc ... [more ▼]

In the quail brain, aromatase-immunoreactive (ARO-ir) neurons located in the medial preoptic nucleus (POM) and caudal paleostriatum ventrale/nucleus accumbens/nucleus striae terminalis complex (PVT/nAc/nST) receive catecholaminergic inputs identified by the presence of tyrosine hydroxylase-immunoreactive (TH-ir) fibers and punctate structures. The origin of these inputs was analyzed by retrograde tracing with cholera toxin B subunit (CTB) or red latex fluospheres (RLF) combined with TH immunocytochemistry. CTB and RLF injected in the POM or PVT/nAc/nST were found in cells located in anatomically discrete areas in the telencephalon (hippocampus, septum, archistriatum), hypothalamus (many areas in periventricular position), thalamus, mesencephalon, and pons. In these last two regions, many retrogradely labeled cells were located in dopaminergic areas such as the retroruberal field (RRF), substantia nigra (SN), and area ventralis of Tsai (AVT) but also in noradrenergic cell groups such as the locus ceruleus and subceruleus. CTB tracing showed that most of these connections are bidirectional. Many retrogradely labeled cells contained TH-ir material. As a mean, 10-20% and 40-60% of the RLF-containing cells in the dopaminergic areas were TH-ir when RLF had been injected in the POM or PVT/nAc/nST, respectively. TH-ir cells projecting to the POM appeared to be mostly located in the periventricular hypothalamus and in AVT, whereas projections to the PVT/nAc/nST originated mainly in the SN (with significant contributions from the RRF and AVT). These data support the existence of functional relationships between aromatase and catecholamines. [less ▲]

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See detailSteroid Control and Sexual Differentiation of Brain Aromatase
Balthazart, Jacques ULg

in Journal of Steroid Biochemistry & Molecular Biology (1997), 61(3-6), 323-39

Brain aromatase (ARO) activity in the quail is markedly enhanced by testosterone (T). This effect only becomes detectable after several hours and reaches its maximum within a few days, which suggests ... [more ▼]

Brain aromatase (ARO) activity in the quail is markedly enhanced by testosterone (T). This effect only becomes detectable after several hours and reaches its maximum within a few days, which suggests enzymatic induction at the genomic level. This idea is reinforced by the fact that T also increases the ARO protein, as observed by immunocytochemistry (ICC) and the ARO mRNA, as measured by reverse transcriptase-polymerase chain reaction (RT-PCR). These changes can be mimicked by the administration of estrogens and therefore presumably require T aromatization. In our first test, injection of the non-steroidal ARO inhibitor, R76713 (racemic vorozole), unexpectedly revealed an increase in ARO immunoreactivity in the preoptic area (POA) of treated birds. This property of R76713 was shared by another non-steroidal inhibitor, fadrozole, but not by two steroidal inhibitors, androstatrienedione (ATD) and 4-hydroxy-androstenedione (OHA). These last two compounds markedly decreased the concentration of brain ARO as estimated by ICC. In parallel, ATD and OHA decreased ARO mRNA concentration measured by RT-PCR but vorozole and fadrozole had no effect on these concentrations in the POA, and only caused them to decrease slightly in the posterior hypothalamus. Together, these data indicate that the removal of estrogens caused by steroidal inhibitors decreases the synthesis of ARO, presumably at the transcriptional level. Additional regulatory mechanisms apparently take place after the injection of non-steroidal inhibitors and probably include increased half-life of the protein. The induction of ARO activity by steroids appears to be greater in males than in females, but this difference has been difficult to localize and confirm by assay methods. We therefore analysed by ICC the tridimensional distribution of ARO-ir neurons in the POA of males and females that were sexually mature or gonadectomized and treated with T-filled or control empty implants. Localized sex differences and effects of T were detected in this way. In particular, males had more ARO-ir cells than females in the lateral POA but a difference in the opposite direction was evident in the medial part of this area. These sex differences are largely activational (i.e. caused by the higher T levels in males) but they may also reflect organizational effects of neonatal steroids. Castration decreased ARO-ir cell numbers in the lateral POA, but increased it in the periventricular region. This anatomically specialized control by T may be mediated by three potential mechanisms that are discussed and comparatively evaluated: a migration of ARO neurons towards the ventricle after castration; a differential colocalization of ARO with estrogen receptors or a differential modulation of ARO neurons by catecholaminergic inputs. [less ▲]

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See detailAromatase Inhibition Blocks the Activation and Sexual Differentiation of Appetitive Male Sexual Behavior in Japanese Quail
Balthazart, Jacques ULg; Castagna, C.; Ball, G. F.

in Behavioral Neuroscience (1997), 111(2), 381-97

Two experiments investigated the role of estrogens in the activation and sexual differentiation of appetitive sexual behavior (ASB) in Japanese quail (Coturnix japonica) as measured by a learned social ... [more ▼]

Two experiments investigated the role of estrogens in the activation and sexual differentiation of appetitive sexual behavior (ASB) in Japanese quail (Coturnix japonica) as measured by a learned social proximity response. Injection of the aromatase inhibitor R767 13 in castrated, testosterone (T)-treated male quail completely suppressed ASB, confirming that, like consummatory sexual behavior, ASB is mediated by T aromatization. ASB is not observed in female quail, even if they are treated with T as adults. The role of embryonic estrogens in the sexual differentiation of ASB was tested by blocking estrogen synthesis in ovo. Control male and T-treated female quail deprived of estrogens during embryonic life learned the social proximity response used to assess ASB, whereas control female quail did not, despite the presence of high T. Thus, ASB is demasculinized by the action of embryonic estrogens during ontogeny as is consummatory behavior. [less ▲]

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See detailA Direct Dopaminergic Control of Aromatase Activity in the Quail Preoptic Area
Baillien, M.; Balthazart, Jacques ULg

in Journal of Steroid Biochemistry & Molecular Biology (1997), 63(1-3, Sep-Oct), 99-113

In the quail preoptic area (POA) anatomical and pharmacological data suggest that catecholamines may be implicated in the control of testosterone (T) aromatization into estrogens. The biochemical ... [more ▼]

In the quail preoptic area (POA) anatomical and pharmacological data suggest that catecholamines may be implicated in the control of testosterone (T) aromatization into estrogens. The biochemical mechanism(s) mediating this control of the enzyme activity is (are) however unexplored. The present studies were carried out to investigate whether the catecholamines, dopamine (DA) and norepinephrine (NE) are able to directly affect aromatase activity (AA) measured during in vitro incubations of POA homogenates. AA was quantified in the POA-hypothalamus of adult male Japanese quail by measuring the tritiated water production from [1beta-3H]-androstenedione. Enzyme activity was linear as a function of the incubation time and of the protein content of homogenates. It exhibited a typical Michaelis-Menten kinetics, with an apparent Km of 2.8 nM and a Vmax of 266.6 fmol h(-1) mg wet weight(-1). AA was then measured at a substrate concentration of 25 nM in the presence of catecholamines and some of their receptor agonists or antagonists, at two concentrations, 10(-3) and 10(-6) M. Norepinephrine and prazosin (alpha1-adrenergic antagonist) had no or very limited effects on AA at both concentrations. In contrast, DA and some D1 and/or D2 receptor agonists (apomorphine[D1/D2], SKF-38393 [D1] and RU-24213 [D2]) depressed AA by 40 to 70% at the 10(-3) M concentration. One D2 receptor antagonist also produced a major inhibition of AA (sulpiride) while other antagonists either had no significant effect or only produced moderate decreases in enzyme activity (SCH-23390 [D1], spiperone [D2], pimozide [D2]) as did two DA indirect agonists, amfonelic acid and nomifensine. The inhibitory effect of the agonists was not antagonized by the less active antagonists, SCH-23390 [D1] or spiperone [D2]. Taken together these results suggest that the inhibitory effects do not involve specific binding of DA or its agonists/antagonists to dopaminergic receptors mediating changes in cAMP concentration. This conclusion is also supported by the observation that addition of dibutyryl cAMP did not change brain AA. It appears more likely that DA and dopaminergic drugs inhibit AA by a direct effect on the enzyme, as suggested by the competitive nature of DA and SKF-38393 inhibition of AA (Ki's of 59 and 84 microM, respectively). The functional significance of this effect should still be demonstrated but this mechanism may represent an important physiological pathway through which neurotransmitters could rapidly affect steroid-dependent processes such as the neural synthesis of estrogens. This would provide a mean by which environmental stimuli could affect reproductive behavior and physiology. [less ▲]

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See detailDo Sex Differences in the Brain Explain Sex Differences in the Hormonal Induction of Reproductive Behavior? What 25 Years of Research on the Japanese Quail Tells Us
Balthazart, Jacques ULg; Tlemcani, O.; Ball, G. F.

in Hormones & Behavior (1996), 30(4), 627-61

Early workers interested in the mechanisms mediating sex differences in morphology and behavior assumed that differences in behavior that are commonly observed between males and females result from the ... [more ▼]

Early workers interested in the mechanisms mediating sex differences in morphology and behavior assumed that differences in behavior that are commonly observed between males and females result from the sex specificity of androgens and estrogens. [less ▲]

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See detailDistribution of Aromatase-Immunoreactive Cells in the Forebrain of Zebra Finches (Taeniopygia Guttata): Implications for the Neural Action of Steroids and Nuclear Definition in the Avian Hypothalamus
Balthazart, Jacques ULg; Absil, Philippe ULg; Foidart, Agnès ULg et al

in Journal of Neurobiology (1996), 31(2), 129-48

Cells immunoreactive for the enzyme aromatase were localized in the forebrain of male zebra finches with the use of an immunocytochemistry procedure. Two polyclonal antibodies, one directed against human ... [more ▼]

Cells immunoreactive for the enzyme aromatase were localized in the forebrain of male zebra finches with the use of an immunocytochemistry procedure. Two polyclonal antibodies, one directed against human placental aromatase and the other directed against quail recombinant aromatase, revealed a heterogeneous distribution of the enzyme in the telencephalon, diencephalon, and mesencephalon. Staining was enhanced in some birds by the administration of the nonsteroidal aromatase inhibitor, R76713 racemic Vorozole) prior to the perfusion of the birds as previously described in Japanese quail. Large numbers of cells immunoreactive for aromatase were found in nuclei in the preoptic region and in the tuberal hypothalamus. A nucleus was identified in the preoptic region based on the high density of aromatase immunoreactive cells within its boundaries that appears to be homologous to the preoptic medial nucleus (POM) described previously in Japanese quail. In several birds alternate sections were stained for immunoreactive vasotocin, a marker of the paraventricular nucleus (PVN). This information facilitated the clear separation of the POM in zebra finches from nuclei that are adjacent to the POM in the preoptic area-hypothalamus, such as the PVN and the ventromedial nucleus of the hypothalamus. Positively staining cells were also detected widely throughout the telencephalon. Cells were discerned in the medial parts of the ventral hyperstriatum and neostriatum near the lateral ventricle and in dorsal and medial parts of the hippocampus. They were most abundant in the caudal neostriatum where they clustered in the dorsomedial neostriatum, and as a band of cells coursing along the dorsal edge of the lamina archistriatalis dorsalis. They were also present in high numbers in the ventrolateral aspect of the neostriatum and in the nucleus taeniae. None of the telencephalic vocal control nuclei had appreciable numbers of cells immunoreactive for aromatase within their boundaries, with the possible exception of a group of cells that may correspond to the medial part of the magnocellular nucleus of the neostriatum. The distribution of immunoreactive aromatase cells in the zebra finch brain is in excellent agreement with the distribution of cells expressing the mRNA for aromatase recently described in the finch telencephalon. This widespread telencephalic distribution of cells immunoreactive for aromatase has not been described in non-songbird species such as the Japanese quail, the ring dove, and the domestic fowl. [less ▲]

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See detailLocalization of Testosterone-Sensitive and Sexually Dimorphic Aromatase-Immunoreactive Cells in the Quail Preoptic Area
Balthazart, Jacques ULg; Tlemcani, O.; Harada, N.

in Journal of Chemical Neuroanatomy (1996), 11(3), 147-71

The distribution of aromatase-immunoreactive cells was studied in the medial preoptic nucleus of male and female quail that were sexually mature and gonadally intact, or gonadectomized, or gonadectomized ... [more ▼]

The distribution of aromatase-immunoreactive cells was studied in the medial preoptic nucleus of male and female quail that were sexually mature and gonadally intact, or gonadectomized, or gonadectomized and treated with testosterone. The study first confirmed the existence of a significant difference in the number of aromatase-immunoreactive cells between males and females (males > females) and the marked effect of castration and testosterone treatment which, respectively, decrease and restore the number of these cells. An analysis of the distribution in space of this neurochemically defined cell population was also carried out. This study revealed that castration does not uniformly decrease the density of aromatase-immunoreactive cells, but local increases are observed in an area directly adjacent to the third ventricle. A number of new sex differences in the organization of the medial preoptic nucleus and its population of aromatase cells have, in addition, been identified. The density of aromatase-immunoreactive cells is not higher in males than in females throughout the nucleus, but a higher density of immunoreactive cells is present in the ventromedial part of the nucleus in females as compared to males. In addition, the cross-sectional area of the nucleus as defined by the population of aromatase-immunoreactive cells is larger in males than in females in its rostral part and its shape is more elongated in the dorso-ventral direction in females than in males. Some of these differences (e.g. higher density of ARC-ir cells in the ventromedial part of the female POM, shape of the nucleus) appear to be organizational in nature, because they are still present in birds exposed to the same endocrine conditions during adult life (e.g. gonadectomized and treated with a same dose of testosterone). This conclusion should now be tested by experiments manipulating the endocrine environment of quail embryos. The anatomical heterogeneity of the medial preoptic nucleus revealed by this study also suggests a functional heterogeneity and the specific roles of the medial and lateral parts of the nucleus should also be investigated. [less ▲]

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See detailEffects of Testosterone and Its Metabolites on Aromatase-Immunoreactive Cells in the Quail Brain: Relationship with the Activation of Male Reproductive Behavior
Balthazart, Jacques ULg; Foidart, Agnès ULg; Absil, Philippe ULg et al

in Journal of Steroid Biochemistry & Molecular Biology (1996), 56(1-6 Spec No), 185-200

The enzyme aromatase converts testosterone (T) into 17 beta-estradiol and plays a pivotal role in the control of reproduction. In particular, the aromatase activity (AA) located in the preoptic area (POA ... [more ▼]

The enzyme aromatase converts testosterone (T) into 17 beta-estradiol and plays a pivotal role in the control of reproduction. In particular, the aromatase activity (AA) located in the preoptic area (POA) of male Japanese quail is a limiting step in the activation by T of copulatory behavior. Aromatase-immunoreactive (ARO-ir) cells of the POA are specifically localized within the cytoarchitectonic boundaries of the medial preoptic nucleus(POM), a sexually dimorphic and steroid-sensitive structure that is a necessary and sufficient site of steroid action in the activation of behavior. Stereotaxic implantation of aromatase inhibitors in but not around the POM strongly decreases the behavioral effects of a systemic treatment with T of castrated males. AA is decreased by castration and increased by aromatizable androgens and by estrogens. These changes have been independently documented at three levels of analysis: the enzymatic activity measured by radioenzymatic assays in vitro, the enzyme concentration evaluated semi-quantitatively by immunocytochemistry and the concentration of its messenger RNA quantified by reverse transcription-polymerase chain reaction (RT-PCR). These studies demonstrate that T acting mostly through its estrogenic metabolites regulates brain aromatase by acting essentially at the transcriptional level. Estrogens produced by central aromatization of T therefore have two independent roles: they activate male copulatory behavior and they regulate the synthesis of aromatase. Double label immunocytochemical studies demonstrate that estrogen receptors(ER) are found in all brain areas containing ARO-ir cells but the extent to which these markers are colocalized varies from one brain region to the other. More than 70% of ARO-ir cells contain detectable ER in the tuberal hypothalamus but less than 20% of the cells display this colocalization in the POA. This absence of ER in ARO-ir cells is also observed in the POA of the rat brain. This suggests that locally formed estrogens cannot control the behavior and the aromatase synthesis in an autocrine fashion in the cells where they were formed. Multi-neuronal networks need therefore to be considered. The behavioral activation could result from the action of estrogens in ER-positive cells located in the vicinity of the ARO-ir cells where they were produced (paracrine action). Alternatively, actions that do not involve the nuclear ER could be important. Immunocytochemical studies at the electron microscope level and biochemical assays of AA in purified synaptosomes indicate the presence of aromatase in presynaptic boutons. Estrogens formed at this level could directly affect the pre-and post-synaptic membrane or could directly modulate neurotransmission namely through their metabolization into catecholestrogens (CE) which are known to be powerful inhibitors of the catechol- omicron - methyl transferase (COMT). The inhibition of COMT should increase the catecholaminergic transmission. It is significant to note, in this respect, that high levels of 2-hydroxylase activity, the enzyme that catalyzes the transformation of estrogens in CE, are found in all brain areas that contain aromatase. On the other hand, the synthesis of aromatase should also be controlled by estrogens in an indirect, transynaptic manner very reminiscent of the way in which steroids indirectly control the production of LHRH. Fibers that are immunoreactive for tyrosine hydroxylase (synthesis of dopamine), dopamine beta-hydroxylase (synthesis of norepinephrine) or vasotocine have been identified in the close vicinity of ARO-ir cells in the POM and retrograde tracing has identified the origin of the dopaminergic and noradrenergic innervation of these areas. A few preliminary physiological experiments suggest that these catecholaminergic inputs regulate AA and presumably synthesis. [less ▲]

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See detailPre- and Post-Translational Regulation of Aromatase by Steroidal and Non-Steroidal Aromatase Inhibitors
Foidart, Agnès ULg; Tlemcani, O.; Harada, N. et al

in Brain Research (1995), 701(1-2), 267-78

Treatment of castrated quail with testosterone (T) reliably activates male copulatory behavior and, at the same time, increases the aromatase activity (AA), the number of aromatase-immunoreactive (ARO-ir ... [more ▼]

Treatment of castrated quail with testosterone (T) reliably activates male copulatory behavior and, at the same time, increases the aromatase activity (AA), the number of aromatase-immunoreactive (ARO-ir) cells and the concentration of aromatase mRNA as measured by RT-PCR in the brain. All these effects can be mimicked by estrogens. The behavioral effects of T can be blocked by a variety of aromatase inhibitors and, in parallel, the AA is strongly inhibited in the preoptic area (POA). We showed recently that the steroidal inhibitor, 4-OH-androstenedione (OHA) markedly decreases the immunostaining density of brain ARO-ir cells while the non-steroidal inhibitor, R76713 (racemic Vorozole; VOR) unexpectedly increased the density of this staining, despite the fact that the enzyme activity was completely inhibited. To generalize these findings and try to identify the underlying mechanism, we compared here the effects of two steroidal (OHA and androstatrienedione [ATD]) and two non-steroidal (VOR and Fadrozole [FAD]) aromatase inhibitors on the aromatase immunostaining and aromatase mRNA concentration in the brain of castrated quail concurrently treated with T. The 4 inhibitors significantly blocked the activation by T of male copulation. The two steroidal inhibitors decreased the immunostaining of brain ARO-ir cells but both VOR and FAD markedly enhanced the density of this staining. In parallel, OHA and ATD completely blocked the T-induced increase in aromatase mRNA concentration, while VOR and FAD had no effect on these RNA concentrations in the POA-anterior hypothalamus and they decreased them only slightly in the posterior hypothalamus. Taken together these results suggest that the inhibition of AA by ATD or OHA and the subsequent removal of locally produced estrogens blocks the synthesis of aromatase presumably at the transcriptional level. By contrast, the two non-steroidal inhibitors tested here block AA but in parallel increase the aromatase immunostaining. This effect does not result from an enhanced transcription and it is therefore speculated that these compounds increase either the translation of the aromatase mRNA or the half-life of the protein itself. [less ▲]

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