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See detailPhosphorylation processes mediate rapid changes of brain aromatase activity
Balthazart, Jacques ULg; Baillien, M.; Ball, G. F.

in Journal of Steroid Biochemistry & Molecular Biology (2001), 79(1-5), 261-277

The enzyme aromatase (also called estrogen synthase) that catalyzes the transformation of testosterone (T) into estradiol plays a key limiting role in the action of T on many aspects of reproduction. The ... [more ▼]

The enzyme aromatase (also called estrogen synthase) that catalyzes the transformation of testosterone (T) into estradiol plays a key limiting role in the action of T on many aspects of reproduction. The distribution and regulation of aromatase in the quail brain has been studied by radioenzyme assays on microdissected brain areas, immunocytochemistry, RT-PCR and in situ hybridization. High levels of aromatase activity (AA) characterize the sexually dimorphic, steroid-sensitive medial preoptic nucleus (PONI), a critical site of T action and aromatization for the activation of male sexual behavior. The boundaries of the POM are clearly outlined by a dense population of aromatase-containing cells as visualized by both immunocytochemistry and in situ hybridization histochemistry. Aromatase synthesis in the POM is controlled by T and its metabolite estradiol, but estradiol receptors alpha (ERalpha) are not normally co-localized with aromatase in this brain area. Estradiol receptor beta (ERbeta) has been recently cloned in quail and localized in POM but we do not yet know whether ERbeta occurs in aromatase cells. It is therefore not known whether estrogens regulate aromatase synthesis directly or by affecting different inputs to aromatase cells as is the case with the gonadotropin releasing hormone neurons. The presence of aromatase in presynaptic boutons suggests that locally formed estrogens may exert part of their effects by non-genomic mechanisms at the membrane level. Rapid effects of estrogens in the brain that presumably take place at the neuronal membrane level have been described in other species. If fast transduction mechanisms for estrogen are available at the membrane level, this will not necessarily result in rapid changes in brain function if the availability of the ligand does not also change rapidly. We demonstrate here that AA in hypothalamic homogenates is rapidly down-regulated by exposure to conditions that enhance protein phosphorylation (addition of Ca2+, Mg2+, ATP). This inhibition is blocked by kinase inhibitors which supports the notion that phosphorylation processes are involved. A rapid (within minutes) and reversible regulation of AA is also observed in hypothalamic explants incubated in vitro and exposed to high Ca2+ levels (K+-induced depolarization, treatment by thapsigargin, by kainate, AMPA or NMDA). The local production and availability of estrogens in the brain can therefore be rapidly changed by Ca2+ based on variation in neurotransmitter activity. Locally-produced estrogens are as a consequence available for non-genomic regulation of neuronal physiology in a manner more akin to the action of a neuropeptide/neurotransmitter than previously thought. (C) 2002 Elsevier Science Ltd. All rights reserved. [less ▲]

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See detailThe control of preoptic aromatase activity by afferent inputs in Japanese quail
Absil, Philippe ULg; Baillien, M.; Ball, G. F. et al

in Brain Research Reviews (2001), 37(1-mars Sp. Iss. SI), 38-58

This review summarizes current knowledge on the mechanisms that control aromatase activity in the quail preoptic area, a brain region that plays a key role in the control of reproduction. Aromatase and ... [more ▼]

This review summarizes current knowledge on the mechanisms that control aromatase activity in the quail preoptic area, a brain region that plays a key role in the control of reproduction. Aromatase and aromatase mRNA synthesis in the preoptic area are enhanced by testosterone and its metabolite estradiol, but estradiol receptors of the alpha subtype are not regularly colocalized with aromatase. Estradiol receptors of the beta subtype are present in the preoptic area but it is not yet known whether these receptors are colocalized with aromatase. The regulation by estrogen of aromatase activity may be, in part, trans-synaptically mediated, in a manner that is reminiscent of the ways in which steroids control the activity of gonadotropic hormone releasing hormone neurons, Aromatase-immunoreactive neurons are surrounded by dense networks of vasotocin-immunoreactive and tyrosine hydroxylase-immunoreactive fibers and punctate structures. These inputs are in part steroid-sensitive and could therefore mediate the effects of steroids on aromatase activity. In vivo pharmacological experiments indicate that catecholaminergic depletions significantly affect aromatase activity presumably by modulating aromatase transcription. In addition, in vitro studies on brain homogenates or on preoptic-hypothalamic explants show that aromatase activity can be rapidly modulated by a variety of dopaminergic compounds. These effects do not appear to be mediated by the membrane dopamine receptors and could involve changes in the phosphorylation state of the enzyme, Together, these results provide converging evidence for a direct control of aromatase activity by catecholamines consistent with the anatomical data indicating the presence of a catecholaminergic innervation of aromatase cells. These dopamine-induced changes in aromatase activity are observed after several hours or days and presumably result from changes in aromatase transcription but rapid non-genomic controls have also been identified. The potential significance of these processes for the physiology of reproduction is critically evaluated. (C) 2001 Elsevier Science BY. All rights reserved. [less ▲]

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See detailSteroid-induced plasticity in the sexually dimorphic vasotocinergic innervation of the avian brain: behavioral implications
Panzica, G. C.; Aste, N.; Castagna, C. et al

in Brain Research Reviews (2001), 37(1-mars Sp. Iss. SI), 178-200

Vasotocin (VT, the antidiuretic hormone of birds) is synthesized by diencephalic magnocellular neurons projecting to the neurohypophysis. In addition, in male quail and in other oscine and non-oscine ... [more ▼]

Vasotocin (VT, the antidiuretic hormone of birds) is synthesized by diencephalic magnocellular neurons projecting to the neurohypophysis. In addition, in male quail and in other oscine and non-oscine birds, a sexually dimorphic group of VT-immunoreactive (ir) parvocellular neurons is located in a region homologous to the mammalian nucleus of the stria terminalis, pars medialis (BSTm) and in the medial preoptic nucleus (POM). These cells are not visible in females. VT-ir fibers are present in many diencephalic and extradiencephalic locations. Quantitative morphometric analyses demonstrate that, in quail, these elements are expressed in a sexually dimorphic manner (males>females) in regions involved in the control of different aspects of reproduction: i.e., the POM (copulatory behavior), the lateral septum (secretion of gonadotropin-releasing hormone [GnRH]), the nucleus intercollicularis (control of vocalizations), and the locus coeruleus (the main noradrenergic center of the avian brain). In many of these regions,VT-ir fibers are closely related to aromatase-ir, GnRH-ir, or estrogen receptor-expressing neurons. This dimorphism has an organizational nature: administration of estradiol-benzoate to quail embryos (a treatment that abolishes male sexual behavior) results in a dramatic decrease of the VT-immunoreactivity in all sexually dimorphic regions of the male quail brain. Conversely, the inhibition of estradiol (E,) synthesis during embryonic life (a treatment that stimulates the expression of male copulatory behavior in adult testosterone (T)-treated females) results in a male-like distribution of VT-ir cells and fibers. Castration markedly decreases the immunoreactivity in both the VT-immunopositive elements of the BSTm and the innervation of the SL and POM, whereas T-replacement therapy restores the VT immunoreactivity to a level typical of intact birds. These changes reflect modifications of VT mRNA concentrations (and probably synthesis) as demonstrated by in situ hybridization and they are paralleled by similar changes in male copulatory behavior (absent in castrated male quail, fully expressed in CX+T males). The aromatization of T into estradiol (E-2) also controls VT expression and, in parallel limits the activation of male sexual behavior by T. In castrated male quail, the restoration by T of the VT immunoreactivity in POM, BSTm and lateral septum could be fully mimicked by a treatment with E-2, but the androgen 5alpha-dihydrotestosterone (DHT) had absolutely no effect on the VT immunoreactivity in these conditions. At the doses used in this study, DHT also did not synergize with E, to enhance the density of VT immunoreactive structures. Systemic or i.c.v. injections of VT markedly inhibit the expression of all aspects of male sexual behavior. VT, presumably, does not simply represent one step in the biochemical cascade of events that is induced by T in the brain and leads to the expression of male sexual behavior. Androgens and estrogens presumably affect reproductive behavior both directly, by acting on steroid-sensitive neurons in the preoptic area, and indirectly, by modulating peptidergic (specifically vasotocinergic) inputs to this and other areas. The respective contribution of these two types of actions and their interaction deserves further analysis. (C) 2001 Elsevier Science BY All rights reserved. [less ▲]

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See detailPreoptic Aromatase Cells Project to the Mesencephalic Central Gray in the Male Japanese Quail (Coturnix Japonica)
Absil, Philippe ULg; Riters, L. V.; Balthazart, Jacques ULg

in Hormones & Behavior (2001), 40(3), 369-83

Previous tract-tracing studies demonstrated the existence of projections from the medial preoptic nucleus (POM) to the mesencephalic central gray (GCt) in quail. GCt contains a significant number of ... [more ▼]

Previous tract-tracing studies demonstrated the existence of projections from the medial preoptic nucleus (POM) to the mesencephalic central gray (GCt) in quail. GCt contains a significant number of aromatase-immunoreactive (ARO-ir) fibers and punctate structures, but no ARO-ir cells are present in this region. The origin of the ARO-ir fibers of the GCt was investigated here by retrograde tract-tracing combined with immunocytochemistry for aromatase. Following injection of fluorescent microspheres in GCt, retrogradely labeled cells were found in a large number of hypothalamic and mesencephalic areas and in particular within the three main groups of ARO-ir cells located in the POM, the ventromedial nucleus of the hypothalamus, and the bed nucleus striae terminalis. Labeling of these cells for aromatase by immunocytochemistry demonstrated, however, that aromatase-positive retrogradely labeled cells are observed almost exclusively within the POM. Double-labeled cells were abundant in both the rostral and caudal parts of the POM and their number was apparently not affected by the location of the injection site within GCt. At both rostro-caudal levels of the POM, ARO-ir retrogradely labeled cells were, however, more frequent in the lateral than in the medial POM. These data indicate that ARO-ir neurons located in the lateral part of the POM may control the premotor aspects of male copulatory behavior through their projection to GCt and suggest that GCt activity could be affected by estrogens released from the terminals of these ARO-ir neurons. [less ▲]

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See detailThe Distribution of Tyrosine Hydroxylase in the Canary Brain: Demonstration of a Specific and Sexually Dimorphic Catecholaminergic Innervation of the Telencephalic Song Control Nulcei
Appeltants, D.; Ball, G. F.; Balthazart, Jacques ULg

in Cell & Tissue Research (2001), 304(2), 237-59

Singing and the processing of auditory information related to song can be affected by experimental manipulations of catecholamine activity in the brain of zebra finches. We investigated, by ... [more ▼]

Singing and the processing of auditory information related to song can be affected by experimental manipulations of catecholamine activity in the brain of zebra finches. We investigated, by immunocytochemistry in the brain of male and female canaries, the distribution of tyrosine hydroxylase (TH), the rate-limiting step in the synthesis of catecholamines. Fibers immunoreactive for TH (TH-ir) were particularly abundant in the lobus parolfactorius, the paleostriatum primitivum, and the nucleus septalis lateralis. A high density of TH-ir basket-like structures was observed in the caudomedial neostriatum, an area involved in song perception and recognition. In most males, a high density of TH-ir fibers outlined the telencephalic song control nuclei including the high vocal center, the nucleus robustus archistriatalis, the nucleus interfascialis, the lateral and medial parts of the magnocellular nucleus of the anterior neostriatum, and area X of the lobus parolfactorius. The higher density of fibers immunoreactive for TH in these nuclei, compared with the surrounding telencephalon, supports the notion that the morphological evolution of the song control nuclei was accompanied by a neurochemical specialization. This specific innervation of the song control regions was, in general, not found in females. The specific presence of high densities of TH-ir fibers in the song system of male canaries and the sex difference of this innervation provide anatomical evidence in support of the claim that dopamine and/or norepinephrine play important roles in the modulation of song learning and production. [less ▲]

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See detailRapid and Reversible Inhibition of Brain Aromatase Activity
Balthazart, Jacques ULg; Baillien, M.; Ball, G. F.

in Journal of Neuroendocrinology (2001), 13(1), 63-73

Many actions of androgens require their conversion via the enzyme aromatase into oestrogens. Changes in brain aromatase activity are thought to take place via changes in enzyme concentration mediated by ... [more ▼]

Many actions of androgens require their conversion via the enzyme aromatase into oestrogens. Changes in brain aromatase activity are thought to take place via changes in enzyme concentration mediated by effects of sex steroids on aromatase transcription. These changes are relatively slow which fits in well with the fact that oestrogens are generally viewed as slow-acting messengers that act via changes in gene transcription. More recently, fast actions of oestrogens, presumably at the level of the cell membrane, have been described both in the female brain and in the male brain after the conversion of testosterone to oestradiol. It is difficult to reconcile the slow regulation of oestrogen synthesis (that occurs via changes in aromatase concentration) with a rapid action at the membrane level. Even if fast transduction mechanisms are available, this will not result in rapid changes in brain function if the availability of the ligand does not also change rapidly. Here, we report that aromatase activity in neural tissue of male Japanese quail (Coturnix japonica) is rapidly downregulated in the presence of Mg(2+), Ca(2+) and ATP in hypothalamic homogenates and in brain explants exposed to high Ca(2+) levels following a K(+)-induced depolarization or the stimulation of glutamate receptors. The K(+)-induced inhibition of aromatase activity is observed within minutes and reversible. Given that aromatase is present in presynaptic boutons, it is possible that rapidly changing levels of locally produced oestrogen are available for nongenomic regulation of neuronal physiology in a manner more akin to the action of a neuropeptide than previously hypothesized. [less ▲]

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See detailCloning and distribution of steroid receptor coactivator SRC-1 in quail.
Charlier, Thierry ULg; Lakaye, Bernard ULg; Ball, Gregory F. et al

Poster (2001)

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See detailEffects of lesions of the medial preoptic nucleus on the testosterone-induced metabolic changes in specific brain areas in male quail
Balthazart, Jacques ULg; Stamatakis, A.; Bacola, S. et al

in Neuroscience (2001), 108(3), 447-466

The effects of bilateral lesions of the medial preoptic nucleus in association with testosterone on the metabolic activity in discrete brain regions was studied quantitatively by the in vivo ... [more ▼]

The effects of bilateral lesions of the medial preoptic nucleus in association with testosterone on the metabolic activity in discrete brain regions was studied quantitatively by the in vivo autoradiographic 2-deoxyglucose method. Adult male quail were castrated and then left without hormone replacement therapy or treated with testosterone or treated with testosterone and submitted to a bilateral lesion of the medial preoptic nucleus, a brain region that plays a key role in the activation of male copulatory behavior by testosterone. Treatment for about 10 days with testosterone activated the expression of the full range of male sexual behaviors and these behaviors were completely suppressed by the medial preoptic nucleus lesions. Mapping of 2-deoxyglucose uptake revealed both increases and decreases of metabolic activity in discrete brain regions associated with the systemic treatment with testosterone as well as with the lesion of the medial preoptic nucleus. Testosterone affected the oxidative metabolism in brain areas that are known to contain sex steroid receptors (such as the nucleus taeniae and the paraventricular and ventromedial nuclei of the hypothalamus) but also in nuclei that are believed to be devoid of such receptors. Effects of testosterone in these nuclei may be indirect or reflect changes in terminals of axons originating in steroid-sensitive areas. Bilateral medial preoptic nucleus lesions affected 2-deoxyglucose uptake in a variety of brain regions. Some of these regions are known to be mono-synaptically connected to the medial preoptic nucleus. Metabolic depression in these areas may reflect retrograde changes in the neurons projecting to the damaged field. The metabolic changes identified in the present study confirm the prominent role of the preoptic area in the control of sexual behavior, show that changes in the physiology of the visual system represent one of the ways through which testosterone influences the occurrence of this behavior and demonstrate that the medial preoptic nucleus has marked effects on the metabolic activity in a variety of limbic and telencephalic structures. This study also indicates that the medial preoptic nucleus affects the activity of the area ventralis of Tsai, a dopaminergic area known to send projections to a variety of hypothalamic, thalamic and mesencephalic nuclei that are implicated in the control of male sexual behavior. These data therefore support the notion that the control of the dopaminergic activity in the area ventralis of Tsai by the medial preoptic nucleus represents one of the ways through which the medial preoptic area regulates male reproductive behavior. (C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved. [less ▲]

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See detailOntogeny of Aromatase and Tyrosine Hydroxylase Activity and of Aromatase-Immunoreactive Cells in the Preoptic Area of Male and Female Japanese Quail
Balthazart, Jacques ULg; Tlemcani, O.; Harada, N. et al

in Journal of Neuroendocrinology (2000), 12(9), 853-66

The aromatization of testosterone into oestrogens plays a key role in the control of many behavioural and physiological aspects of reproduction. In the quail preoptic area (POA), aromatase activity and ... [more ▼]

The aromatization of testosterone into oestrogens plays a key role in the control of many behavioural and physiological aspects of reproduction. In the quail preoptic area (POA), aromatase activity and the number of aromatase-immunoreactive (ARO-ir) cells are sexually differentiated (males > females). This sex difference is implicated in the control of the sexually dimorphic behavioural response of quail to testosterone. We analysed the ontogenetic development of this sex difference by measuring aromatase activity and counting ARO-ir cells in the POA of males and females from day 1 post hatch to sexual maturity. We investigated in parallel another enzyme: tyrosine hydroxylase, the rate limiting step in catecholamine synthesis. Between hatching and 4 weeks of age, aromatase activity levels were low and equal in males and females. Aromatase activity then markedly increased in both sexes when subjects initiated their sexual maturation but this increase was more pronounced in males so that a marked difference in aromatase activity was present in 6 and 8 week-old subjects. Tyrosine hydroxylase activity progressively increased with age starting immediately after hatching and there was no abrupt modification in the slope of this increase when birds became sexually mature. No sex difference was detected in the activity of this enzyme. The number of ARO-ir cells in the POA progressively increased with age starting at hatching. No sex difference in ARO-ir cell numbers could be detected before subjects reached full sexual maturity. The analysis of the three-dimensional organization of ARO-ir cells in the POA revealed that, with increasing ages, ARO-ir cells acquire a progressively more lateral position: they are largely periventricular in young birds but they are found at higher density in the lateral part of the medial preoptic nucleus in adults. These data indicate that aromatase activity differentiates sexually when birds reach sexual maturity presumably under the activating effects of the increased testosterone levels in males. The number of ARO-ir cells, however, begins to increase in a non sexually differentiated manner before the rise in plasma testosterone in parallel with the increased tyrosine hydroxylase activity. Whether this temporal coincidence results from a general ontogenetic pattern or from more direct causal links remains to be established. [less ▲]

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See detailLocalization and Controls of Aromatase in the Quail Spinal Cord
Evrard, H.; Baillien, M.; Foidart, Agnès ULg et al

in Journal of Comparative Neurology (The) (2000), 423(4), 552-64

In adult male and female Japanese quail, aromatase-immunoreactive cells were identified in the spinal dorsal horns from the upper cervical segments to the lower caudal area. These immunoreactive cells are ... [more ▼]

In adult male and female Japanese quail, aromatase-immunoreactive cells were identified in the spinal dorsal horns from the upper cervical segments to the lower caudal area. These immunoreactive cells are located mostly in laminae I-III, with additional sparse cells being present in the medial part of lamina V and, at the cervical level exclusively, in lamina X around the central canal. Radioenzyme assays based on the measurement of tritiated water release confirmed the presence of substantial levels of aromatase activity throughout the rostrocaudal extent of the spinal cord. Contrary to what is observed in the brain, this enzyme activity and the number of aromatase-immunoreactive cells in five representative segments of the spinal cord are not different in sexually mature males or females and are not influenced in males by castration with or without testosterone treatment. The aromatase activity and the numbers of aromatase-immunoreactive cells per section are higher at the brachial and thoracic levels than in the cervical and lumbar segments. These experiments demonstrate for the first time the presence of local estrogen production in the spinal cord of a higher vertebrate. This production was localized in the sensory fields of the dorsal horn, where estrogen receptors have been identified previously in several avian and mammalian species, suggesting an implication of aromatase in the modulation of sensory (particularly nociceptive) processes. [less ▲]

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See detailFos Induction in the Japanese Quail Brain after Expression of Appetitive and Consummatory Aspects of Male Sexual Behavior
Tlemcani, O.; Ball, G. F.; D'Hondt, E. et al

in Brain Research Bulletin (2000), 52(4), 249-62

We investigated the expression of Fos, the protein product of the immediate early gene c-fos in the brain of male Japanese quail after they engaged in either appetitive or consummatory sexual behavior (i ... [more ▼]

We investigated the expression of Fos, the protein product of the immediate early gene c-fos in the brain of male Japanese quail after they engaged in either appetitive or consummatory sexual behavior (i. e., copulation). For 1 h, castrated males treated with testosterone were either allowed to copulate with a female or to exhibit a learned social proximity response indicative of appetitive sexual behavior. Control birds were either left in their home cage or placed in the experimental chamber but did not exhibit the appetitive sexual behavior because they had never learned it. Fos expression was studied with an immunocytochemical procedure in two sets of adjacent sections through the entire forebrain. These sections were immunolabelled with 2 different antibodies raised against a synthetic fragment corresponding to the 21 carboxy-terminal residues of the chicken Fos sequence. Contrary to the results of a previous study in which gonadally intact birds were used, Fos induction was observed neither in the medial preoptic nucleus nor in the nucleus intercollicularis in birds that had interacted for 1 h with a female. This may be related to a lower frequency of copulation in the testosterone-implanted birds than in intact birds, or to differences in the time the brains were collected after the birds engaged in sexual behavior between the two studies (60 min in this study, 120 min in the previous study). The performance of copulation and/or appetitive sexual behavior increased the number of Fos-immunoreactive cells in the ventral hyperstriatum, medial archistriatum, and nucleus striae terminalis. These increases were observed using both antibodies, although each antibody produced minor differences in the number of Fos-immunoreactive cells observed. Using one of the antibodies, but not the other, increases in Fos immunoreactivity were also observed in the nucleus accumbens and hyperstriatum after either copulation or appetitive sexual behavior. These differences illustrate how minor technical variations in the Fos immunocytochemical procedure influence the results obtained. These differences also show that Fos induction in a number of brain regions is observed after performance of consummatory (copulation) as well as appetitive (looking at the female) sexual behavior. This induction is, therefore, not related solely to the control of copulatory acts but, presumably, also to the processing in a variety of telencephalic association areas of stimuli originating from the female. The observation that increased Fos immunoreactivity is present in birds that had learned the response indicative of appetitive sexual behavior, and not in those that had not learned the behavior, further indicates that it is not simply the sight of the female that results in this Fos induction, but the analysis of the relevant stimuli in a sexually explicit context. Conditioned neural activity resulting from a learned association between the stimulus female and the performance of copulatory behavior may also explain some aspects of the brain activation observed in birds viewing, but not allowed to interact with, the female. [less ▲]

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See detailIdentification of the Origin of Catecholaminergic Inputs to Hvc in Canaries by Retrograde Tract Tracing Combined with Tyrosine Hydroxylase Immunocytochemistry
Appeltants, D.; Absil, Philippe ULg; Balthazart, Jacques ULg et al

in Journal of Chemical Neuroanatomy (2000), 18(3), 117-33

The telencephalic nucleus HVc (sometimes referred to as the high vocal center) plays a key role in the production and perception of birdsong. Although many afferent and efferent connections to this ... [more ▼]

The telencephalic nucleus HVc (sometimes referred to as the high vocal center) plays a key role in the production and perception of birdsong. Although many afferent and efferent connections to this nucleus have been described, it has been clear for many years, based on chemical neuroanatomical criteria, that there are projections to this nucleus that remain undescribed. A variety of methods including high performance liquid chromatography, immunohistochemistry and receptor autoradiography have identified high levels of catecholamine transmitters, the presence of enzymes involved in the synthesis of catecholamines such as tyrosine hydroxylase and a variety of catecholamine receptor sub-types in the HVc of several songbird species. However, no definitive projections to HVc have been described from cells groups known to synthesize catecholamines. These projections were analyzed in the present study by retrograde tract tracing combined with immunocytochemistry for tyrosine hydroxylase. The origin of the catecholaminergic inputs to HVc were determined based exclusively on birds in which injections of the retrograde tracer (latex fluospheres) were confined within the cytoarchitectonic boundaries of the nucleus. Retrogradely transported latex fluospheres were found mainly in cells of two dopaminergic nuclei, the mesencephalic central gray (A11) and, to a lesser extend, the area ventralis of Tsai (A10; homologous to the ventral tegmental area of mammals). A few retrogradely-labelled cells were also found in the noradrenergic nucleus subceruleus (A6). Most of these retrogradely-labelled cells were also tyrosine hydroxylase-positive. Other catecholaminergic nuclei were devoid of retrograde label. These data converge with others studies to indicate that HVc receives discrete dopaminergic and noradrenergic inputs. These inputs may influence the steroid regulation of HVc, attentional processes related to song and modulate sensory inputs to the song system. [less ▲]

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See detailImmunocytochemical localization of ionotropic glutamate receptors subunits in the adult quail forebrain
Cornil, Charlotte ULg; Foidart, Agnès ULg; Minet, Arlette ULg et al

in Journal of Comparative Neurology (The) (2000), 428

The excitatory amino acid glutamate is implicated in the central control of many neuroendocrine and behavioral processes. The ionotropic glutamate receptors are usually divided into the N-methyl-D ... [more ▼]

The excitatory amino acid glutamate is implicated in the central control of many neuroendocrine and behavioral processes. The ionotropic glutamate receptors are usually divided into the N-methyl-D-aspartate (NMDA) and non-NMDA (kainate and AMPA) subtypes. Subunits of these receptors have been cloned in a few mammalian species. Information available in birds is more limited. In quail, we recently demonstrated that glutamate agonists (kainate, AMPA, and NMDA) rapidly (within minutes) and reversibly decrease in vitro aromatase activity like several other manipulations affecting intracellular HCa21 pools. Aromatase catalyzes the conversion of androgens into estrogens which is a limiting step in the control by testosterone of many behavioral and physiologic processes. Therefore, glutamate could control estrogen production in the brain, but the anatomic substrate supporting this effect is poorly understood. In quail, aromatase is mainly localized in the preoptic-hypothalamic-limbic system. We visualized here the distribution of the major ionotropic glutamate receptors in quail by immunocytochemical methods by using commercial primary antibodies raised against rat glutamate receptor 1 and receptors 2-3 (GluR1, GluR2/3: AMPA subtype, Chemicon, CA), rat glutamate receptors 5-7 (GluR5-7: kainate subtype, Pharmingen, CA), and rat NMDA receptors (NMDAR1, Pharmingen, CA). Dense and specific signals were obtained with all antibodies. The four types of receptors are broadly distributed in the brain, and, in particular, immunoreactive cells are identified within the major aromatase cell groups located in the medial preoptic nucleus, ventromedial hypothalamus, nucleus striae terminalis, and nucleus taeniae. Dense specific populations of glutamate receptor immunoreactive cells are also present with a receptor subtype-specific distribution in broad areas of the telencephalon. The distribution of glutamate receptors, therefore, is consistent with the idea that these receptors could be located at the surface of aromatase-containing cells and mediate the rapid regulation of aromatase activity in a direct manner. [less ▲]

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See detailEstrogen Receptor-Beta in Quail: Cloning, Tissue Expression and Neuroanatomical Distribution
Foidart, Agnès ULg; Lakaye, Bernard ULg; Grisar, Thierry ULg et al

in Journal of Neurobiology (1999), 40(3), 327-42

A partial estrogen receptor-beta (ERbeta) cDNA had been previously cloned and sequenced in Japanese quail. The 3'- and 5'-rapid amplification of cDNA ends techniques were used here to identify a cDNA ... [more ▼]

A partial estrogen receptor-beta (ERbeta) cDNA had been previously cloned and sequenced in Japanese quail. The 3'- and 5'-rapid amplification of cDNA ends techniques were used here to identify a cDNA sequence of the quail ERbeta that contains a complete open reading frame. For the first time in an avian species, this cDNA sequence and the corresponding amino acid sequence are described. They are compared with the known ERbeta sequences previously described in mammals and with the ERalpha sequences identified in a selection of mammalian and avian species. The analysis by Northern blotting of the ERbeta mRNA expression in the brain and kidneys revealed the presence of several transcripts. The presence of ERbeta identified by reverse transcriptase-polymerase chain reaction demonstrated a widespread distribution quite different from the distribution of ERalpha. The complete neuroanatomical distribution of ERbeta mRNA as determined by in situ hybridization with 35S- and 33P-labeled oligoprobes is also presented. Transcripts are present in many nuclei implicated in the control of reproduction such as the medial preoptic nucleus, the nucleus striae terminalis, and the nucleus taeniae, the avian homologue of the amygdala. These data demonstrate the presence of ERbeta in a nonmammalian species and indicate that the (neuro)-anatomical distribution of this receptor type has been conserved in these two classes of vertebrates. The role of this receptor in the control of reproduction and other physiological processes should now be investigated. [less ▲]

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See detailMating-Induced Fos and Aromatase Are Not Co-Localized in the Preoptic Area
Foidart, Agnès ULg; Meddle, S. L.; Balthazart, Jacques ULg

in Neuroreport (1999), 10(5), 907-12

Male sexual behavior is determined by the interaction of endocrine and environmental stimuli originating from the female, yet it is unknown how and where these stimuli are integrated within the brain ... [more ▼]

Male sexual behavior is determined by the interaction of endocrine and environmental stimuli originating from the female, yet it is unknown how and where these stimuli are integrated within the brain. Activation of copulatory behavior by testosterone is limited by its central aromatization into an estrogen in the preoptic area. We investigated whether mating-induced neuronal activation as identified by the expression of the immediate early gene Fos occurs in aromatase-immunoreactive (ARO-ir) cells of the male quail preoptic area. Fos-immunoreactive (ir) cells were observed within and lateral to these ARO-ir cells groups but few ARO-ir cells contained Fos-ir indicating that mating-related stimuli do not directly affect estrogen-synthesizing cells. [less ▲]

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See detailRegional Distribution and Control of Tyrosine Hydroxylase Activity in the Quail Brain
Baillien, M.; Foidart, Agnès ULg; Balthazart, Jacques ULg

in Brain Research Bulletin (1999), 48(1), 3-17

Tyrosine hydroxylase (TH) activity, the rate-limiting step in the synthesis of catecholamines, was quantified in the preoptic area-hypothalamus of adult male Japanese quail by a new assay measuring the ... [more ▼]

Tyrosine hydroxylase (TH) activity, the rate-limiting step in the synthesis of catecholamines, was quantified in the preoptic area-hypothalamus of adult male Japanese quail by a new assay measuring the tritiated water production from 3,5-[3H]-L-tyrosine. Maximal levels of activity were observed at a 20-25 microM concentration of substrate, with more than 50% inhibition of the activity being recorded at a 100 microM concentration. TH activity was linear as a function of the incubation time during the first 20 min and maximal at a pH of 6.0. TH was heterogeneously distributed in the quail brain with highest levels of activity being found (in decreasing order) in the mesencephalon, diencephalon, and telencephalon. Given the large size of the telencephalon, this is the brain area that contains, as a whole, the highest level of enzyme activity. TH inhibitors that have been well-characterized in mammals, such as 3-iodo-L-tyrosine and L-alpha-methyl-p-tyrosine (AMPT) completely inhibited the enzyme activity at a 100 microM concentration. In mammals, the accumulation of catecholamines exerts a negative feedback control on TH activity. Similar controls were observed in the quail brain. Two inhibitors of the DOPA decarboxylase that should lead to accumulation of DOPA depressed TH activity by 60% or more, and the inhibitor of the dopamine beta-hydroxylase, fusaric acid that should cause an accumulation of dopamine, suppressed 90% of the TH activity. The addition of exogenous DOPA, dopamine, or norepinephrine to the brain homogenates also strongly inhibited TH activity, independently confirming the feedback effects of the enzyme products on the enzyme activity. These data demonstrate that TH activity in the quail brain is heterogeneously distributed and acutely regulated, as it is in mammals, by the accumulation of its products and of the derived catecholamines. [less ▲]

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See detailSteroid sensitive sites in the avian brain: does the distribution of the estrogen receptor alpha and beta types provide insight into their function?
Ball, G. F.; Bernard, D. J.; Foidart, Agnès ULg et al

in Brain, Behavior & Evolution (1999), 54

Studies in avian species have often been useful in elucidating basic concepts relevant to the regulation of reproductive behaviors by sex steroid hormones. Once a link between a steroid hormone and a ... [more ▼]

Studies in avian species have often been useful in elucidating basic concepts relevant to the regulation of reproductive behaviors by sex steroid hormones. Once a link between a steroid hormone and a behavioral response has been established, one can use the localization of steroid hormone receptors in the brain to facilitate the identification of neural circuits that control behavior. The recent identification of a second type of estrogen receptor called estrogen receptor beta or ERbeta has raised new issues about the action of steroid hormones in the brain. A hypothesis has been proposed by Kuiper et al. [1998] based on studies in mammalian species suggesting that ERalpha (the name given to the ER that was previously described) is important for reproduction while ERbeta is more important for non-reproductive functions. In this paper we apply this hypothesis more generally by examining possible functions of ERbeta in avian species. We have initiated studies of the ERbeta in the brain of two avian species, the Japanese quail (Coturnix japonica) and the European starling (Sturnus vulgaris). ERbeta was cloned in both species and the mRNA for this receptor type was localized in the brain employing in situ hybridization histochemistry methods. In both species ERbeta was found to be diffusely present in telencephalic areas consistent with a role for this receptor subtype in cognitive functions. However, ERbeta mRNA was also found in many brain areas that are traditionally thought to be important in the regulation of reproductive functions such as the preoptic region, the bed nucleus of the stria terminalis and the nucleus taeniae. Of the two receptor types, only mRNA for ERalpha was observed in the telencephalic vocal control nucleus HVc of male starlings. Steroid receptors in this nucleus are thought to be an example of an evolutionary specialization that has evolved to coordinate the production of courtship vocalizations with other aspects of reproduction. The lack of ERbeta mRNA expression in HVc is consistent with the hypothesis that ERalpha is preferentially involved in reproductive behaviors while ERbeta is involved in the steroid regulation of other neural functions. However, the widespread occurrence of ERbeta in other nuclei involved in reproductive function suggests that one must be cautious about the general applicability of the above hypothesis until more is known about ERbeta function in these other nuclei [less ▲]

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See detailEffects of Brain Testosterone Implants on Appetitive and Consummatory Components of Male Sexual Behavior in Japanese Quail
Riters, L. V.; Absil, Philippe ULg; Balthazart, Jacques ULg

in Brain Research Bulletin (1998), 47(1), 69-79

Aromatization of testosterone (T) into an estrogen is necessary for the activation of consummatory and appetitive sexual behavior in male Japanese quail. T action within the medial preoptic nucleus (POM ... [more ▼]

Aromatization of testosterone (T) into an estrogen is necessary for the activation of consummatory and appetitive sexual behavior in male Japanese quail. T action within the medial preoptic nucleus (POM) is necessary and sufficient to activate consummatory behavior, and some evidence suggests that POM might be involved in the control of appetitive behavior, but other brain regions, such as the bed nucleus of the stria terminalis (BST), an area that contains a dense population of aromatase-immunoreactive neurons, are also likely to be involved. This study was performed to assess the effects of stereotaxic T implants targeting either the POM or the BST on the activation of both components of sexual behavior in castrated male quail. Appetitive sexual behavior was measured by an acquired social proximity response in which a male will approach a window providing visual access to a female after the window has been repeatedly paired with physical access to a female and the possibility to freely interact with her. Rhythmic cloacal sphincter movements that are produced by the male when given visual access to a female were used as another measure of appetitive sexual behavior that does not appear to depend on sexual learning. The experiments confirmed that copulation is necessary for males to develop the social proximity response that is used to measure the appetitive sexual behavior. T implants in the POM activated both components of sexual behavior, suggesting that these components cannot be completely dissociated. In contrast, T implants located within the BST did not affect either component, but because implants in the BST did not activate copulatory behavior, these results do not preclude a role for BST in the expression of a previously acquired appetitive sexual behavior. [less ▲]

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