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See detailSex differences in the rapid control of aromatase activity in the quail preoptic area.
Konkle, A. T. M.; Balthazart, Jacques ULg

in Journal of Neuroendocrinology (2011), 23(5), 424-34

Adult male quail show high levels of aromatase activity in the preoptic area-hypothalamus (POA-HYP), which parallels the high number of aromatase-immunoreactive cells and elevated mRNA concentrations ... [more ▼]

Adult male quail show high levels of aromatase activity in the preoptic area-hypothalamus (POA-HYP), which parallels the high number of aromatase-immunoreactive cells and elevated mRNA concentrations detected in this brain region by in situ hybridisation. Interestingly, females display considerably lower aromatase activity than males but have almost equal numbers of aromatase-immunoreactive cells and express similar levels of aromatase mRNA. Aromatase activity in the male POA-HYP can be rapidly regulated by calcium-dependent phosphorylations, in the absence of changes in enzyme concentration. In the present study, we investigated whether aromatase activity is differentially regulated by phosphorylations in males and females. A linear increase in accumulation of aromatisation products was observed in both sexes as a function of time but the rate of conversion was slower in females. Saturation analysis confirmed the lower maximum velocities (V(max) ) in females but indicated a similar affinity (K(m) ) in both sexes. Aromatase activity in females reacted differentially to manipulations of intracellular calcium. In particular, chelating calcium with ethylene glycol tetraacetic acid (EGTA) resulted in a larger increase of enzymatic activity in males than in females, especially in the presence of ATP. A differential reaction to kinase inhibitors was also observed between males and females (i.e. a larger increase in aromatase activity in females than in males after exposure to specific inhibitors). These findings suggest that the nature of aromatase is conserved between the sexes, although the control of its activity by calcium appears to be different. Additional characterizations of intracellular calcium in both sexes would therefore be appropriate to better understand aromatase regulation. [less ▲]

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See detailSexual differentiation of sexual behavior and its orientation.
Roselli, Charles; Balthazart, Jacques ULg

in Frontiers in Neuroendocrinology (2011), 32(2), 109

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See detailMinireview: Hormones and Human Sexual Orientation.
Balthazart, Jacques ULg

in Endocrinology (2011)

Many people believe that sexual orientation (homosexuality vs. heterosexuality) is determined by education and social constraints. There are, however, a large number of studies indicating that prenatal ... [more ▼]

Many people believe that sexual orientation (homosexuality vs. heterosexuality) is determined by education and social constraints. There are, however, a large number of studies indicating that prenatal factors have an important influence on this critical feature of human sexuality. Sexual orientation is a sexually differentiated trait (over 90% of men are attracted to women and vice versa). In animals and men, many sexually differentiated characteristics are organized during early life by sex steroids, and one can wonder whether the same mechanism also affects human sexual orientation. Two types of evidence support this notion. First, multiple sexually differentiated behavioral, physiological, or even morphological traits are significantly different in homosexual and heterosexual populations. Because some of these traits are known to be organized by prenatal steroids, including testosterone, these differences suggest that homosexual subjects were, on average, exposed to atypical endocrine conditions during development. Second, clinical conditions associated with significant endocrine changes during embryonic life often result in an increased incidence of homosexuality. It seems therefore that the prenatal endocrine environment has a significant influence on human sexual orientation but a large fraction of the variance in this behavioral characteristic remains unexplained to date. Genetic differences affecting behavior either in a direct manner or by changing embryonic hormone secretion or action may also be involved. How these biological prenatal factors interact with postnatal social factors to determine life-long sexual orientation remains to be determined. [less ▲]

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See detailOwn song selectivity in the songbird auditory pathway: Suppression by norepinephrine
Poirier, Colline; Boumans, Tiny; Vellema, Michiel et al

in PLoS ONE (2011), 6(5), 20131

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See detailAndrogens and estrogens synergistically regulate the expression of doublecortin and enhance neuronal recruitment in the song system of adult female canaries.
Yamamura, Takashi; Barker, Jennifer ULg; Balthazart, Jacques ULg et al

in Journal of Neuroscience (2011)

Vocal control nuclei in songbirds display seasonal changes in volume that are regulated by testosterone (T) and its androgenic (5α-dihydrotestosterone; DHT) or estrogenic metabolites (17β-estradiol; E2 ... [more ▼]

Vocal control nuclei in songbirds display seasonal changes in volume that are regulated by testosterone (T) and its androgenic (5α-dihydrotestosterone; DHT) or estrogenic metabolites (17β-estradiol; E2). In male canaries, T regulates expression of the microtubule-associated protein doublecortin (DCX), a marker of neurogenesis. We examined the effect of T and its two metabolites alone or in combination on DCX expression in adult female canaries. Treatment with T or with DHT+E2 increased HVC volume and neuron numbers as well as the total numbers of fusiform (migrating) and round (differentiating) DCX neurons in the nucleus but generally not in adjacent areas. DHT or E2 alone did not increase these measures but increased the density of fusiform DCX cells per section. Similar results were observed in Area X although some effects did not reach significance presumably because plasticity in X is mediated transynaptically and follows HVC changes with some delay. There was no effect of any treatment on the total number of neurons in Area X and no change in DCX cell densities was detected in other parts of the nidopallium nor in LMAN. DHT and E2 by themselves thus increase density of DCX cells migrating through HVC but are not sufficient in isolation to induce the recruitment of these newborn neurons in the nucleus. These effects are generally not observed in the rest of the nidopallium implying that steroids only act on the attraction and recruitment of new neurons in HVC without having any major effects on their production at the ventricle wall. [less ▲]

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See detailAuditory forebrain activation in the female canary is modulated by male song quality.
Barker, Jennifer ULg; Monbureau, Marie; Leboucher, Gerard et al

Poster (2010, November 17)

One of the chief functions of birdsong is to attract and stimulate females. In canaries (Serinus canaria), specific phrases (“A” phrases) sung by males have been identified as especially attractive for ... [more ▼]

One of the chief functions of birdsong is to attract and stimulate females. In canaries (Serinus canaria), specific phrases (“A” phrases) sung by males have been identified as especially attractive for females. These phrases unite a number of characteristics that are particularly difficult to combine, including large frequency bandwidth, high repetition rate and multiple-note syllables. Females exposed to “A” phrases produce more copulation displays and deposit more testosterone into their eggs. However, the neuroendocrine pathway underlying the translation of song audition to changes in testosterone deposition in yolks is not understood. Increased expression of several immediate early genes including c-fos and zenk (also called egr-1 in mammals) in other songbird species has been observed in the auditory forebrain of females hearing attractive song, and such differential activation may represent a first step in signal processing linking auditory input to egg testosterone deposition. Female canaries in breeding condition were exposed to 60 minutes of “sexy” song with a preponderance of “A” phrases, “non-sexy” song lacking “A” phrases, or white noise. Thirty minutes after the end of song playback, brains were collected, fixed in acrolein and sectioned and stained by immunohistochemistry for quantification of the Fos protein, an indicator of neuronal activity, in several regions involved in audition and auditory processing. The endocrine condition of each female was determined by measuring ovarian and oviduct weight at the time of autopsy. In the caudomedial mesopallium (CMM), Fos expression was higher in females that had heard sexy song than those that heard non-sexy song or white noise. Expression of Fos in the caudomedial nidopallium (NCM), the nucleus spiriformis medialis (SPM), the nucleus ovoidalis (OV), and the song nucleus HVC was unaffected by song quality. Thus differential auditory processing in the CMM may be an initial stage in the assessment by a female of song information to differential testosterone deposition in the egg. [less ▲]

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See detailSexually differentiated cell proliferation in the medial preoptic nucleus of Japanese quail
Mouriec, Karen ULg; Bardet, Sylvia; Balthazart, Jacques ULg

Poster (2010, November)

The androgen-depend sequence of male copulatory behaviors is sexually differentiated in Japanese quail like in many other vertebrates. This behavior disappears within a week after castration of males and ... [more ▼]

The androgen-depend sequence of male copulatory behaviors is sexually differentiated in Japanese quail like in many other vertebrates. This behavior disappears within a week after castration of males and is rapidly restored following treatment with testosterone. In contrast, ovariectomized females treated with testosterone never show these behaviors. This sex-specific responsiveness to testosterone results from organizational effects of embryonic ovarian estrogens. The behavioral phenotype of male and female quail is completely reversed by treatment, before embryonic day 12 (E12), of male embryos with estrogens or of female embryos with an inhibitor of aromatase, the enzyme converting testosterone into estradiol. In the quail brain, the medial preoptic nucleus (POM) is a necessary and sufficient site for the activation of sexual behavior by testosterone. It can be identified by a dense population of aromatase-immunoreactive neurons and, importantly, aromatase activity in this region is sexually differentiated (males>females) and this difference is maintained even when birds are treated with a same dose of testosterone. Aromatase is thus, like sexual behavior, a sex-specific feature regulated by testosterone in adult quail and presumably organized in early life by steroid action. The cellular basis of these organizational processes have not been identified. We analyzed the ontogeny of POM cells by injecting 5-bromo-2-deoxyuridine (BrdU) in eggs at different embryonic (E) stages (E8, E10, E12, E14 and E16) and quantifying BrdU-labeled cells at postnatal (PN) day 56. Large numbers of BrdU-positive cells were observed throughout the POM of males and females injected on E8-E10 but most cells were post-mitotic in both sexes on E14-E16. E12 injections resulted in a larger number of BrdU cells in females than in males at PN56. However, male and female embryos injected on E12 and killed on E13, PN1 or PN15 had similar numbers of BrdU positive cells. Furthermore, BrdU injections on E14 labeled very few cells at PN 56 suggesting that the POM is essentially post-mitotic at that age. Together these data suggest that a sex-specific apoptosis must occur between PN15 and PN56. Double-label immunohistochemistry for BrdU and for the neuron-specific marker Hu indicated that BrdU-positive cells born between E8 and E16 are not neurons and are thus presumably glial cells. This sex-specific cell proliferation occurring around the end of the critical period of sexual differentiation may have an important impact on brain and behavior differentiation. The phenotype of these cells and the mechanisms mediating their differential development are currently under investigation. [less ▲]

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See detailOntogeny of sex differences in steroid-sensitive regions in the quail brain (Coturnix Japonica)
Mouriec, Karen ULg; Bardet, Sylvia; Balthazart, Jacques ULg

Poster (2010, May)

Sex differences affecting the expression of sexual behavior are observed in many species. In quail, expression of the male-typical copulatory pattern is androgen-dependent. This behavior disappears within ... [more ▼]

Sex differences affecting the expression of sexual behavior are observed in many species. In quail, expression of the male-typical copulatory pattern is androgen-dependent. This behavior disappears within a week after castration and is restored after a few days of treatment with exogenous testosterone. In contrast, ovariectomized females treated with testosterone never show the sequence of male-typical copulatory behavior. This sex difference in responsiveness to testosterone results from organizational effects of embryonic estrogens secreted by the female ovary. The behavioral phenotype can be completely reversed by treatment, before embryonic day 12, of male embryos with estrogens or of female embryos with an aromatase inhibitor. In the quail brain, the medial preoptic nucleus (POM) is a necessary and sufficient site for the activation by testosterone of sexual behavior. Aromatase, the enzyme converting testosterone into estradiol, is densely expressed in POM and its activity is sexually differentiated (males>females) even when birds are treated with a same dose of testosterone. Aromatase and other neuroendocrine systems are thus, like sexual behavior, differentially activated by testosterone in adult quail but the cellular basis of these sexually differentiated features presumably organized in early life by steroid action have not been identified. To analyze the ontogeny of steroid sensitive regions that control behavioral sex differences in the quail brain, we injected 5-bromo-2-deoxyuridine (BrdU) in eggs at different stages of the embryonic (E) development (E8, E10, E12, E14 and E16) and sacrificed the animals at postnatal (PN) day 56. Large numbers of BrdU-positive cells were observed throughout the POM of males and females injected on E8-E10 but most cells were post-mitotic in both sexes on E14-E16. E12 injections resulted in a larger number of BrdU cells in females than in males. This differential number of BrdU-positive cells seen at PN56 in birds injected on E12 could result from a) a difference in the age at which cells become post-mitotic (males before females or alternatively females before males, so that male cells labeled by BrdU on E12 dilute their label in subsequent divisions) or b) a differential apoptosis between E13 and PN56. However, no sex differences in the number of BrdU positive cells was observed in embryos injected with BrdU on E12 and killed on E13. Furthermore, BrdU injections on E14 labeled very few cells at PN 56 suggesting that the POM is essentially post-mitotic at that age. The sex difference observed in birds injected at E12 should result from a differential apoptosis after E13. Double-label immunohistochemistry for BrdU and the neuronal marker Hu (C/D) indicated that all BrdU-positive cells born between E8 and E16 are not neurons (no double label) suggesting that these are glial cells. This sex difference in (glial?) proliferation around the end of the critical period of sexual differentiation may play a key role in the differentiation of brain and behavior. The specific phenotype of these cells and the mechanisms mediating their differential development are currently under investigation. [less ▲]

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See detailTestosterone increases cell turnover in song nucleus HVC and increases cell recruitment into Area X of adult female canaries.
Barker, Jennifer ULg; Yamamura, Takashi; Balthazart, Jacques ULg et al

Poster (2010, May)

In songbirds, song control nuclei such as HVC and Area X, show seasonal changes in volume that are regulated, at least in part, by the action of gonadal testosterone (T) and its metabolites. These changes ... [more ▼]

In songbirds, song control nuclei such as HVC and Area X, show seasonal changes in volume that are regulated, at least in part, by the action of gonadal testosterone (T) and its metabolites. These changes in volume are a result of changes in cell size, dendritic branching and, in HVC, the incorporation of newborn neurons. Doublecortin (DCX) is a microtubule-associated protein expressed during development and in adulthood in post-mitotic migrating and differentiating neurons in mammals. Our previous studies in male canaries demonstrated that DCX is expressed in BrdU-positive neurons consistent with DCX being a marker of neurogenesis in adult canaries. Testosterone induces marked increases in song nuclei volume in adult female canaries making these nuclei more male-like. Within the songbird brain, T can be metabolized to 5 alpha-dihydrotestosterone (DHT) and 17 beta-estradiol (E2). We found previously that both these metabolites are required to increase the volume of song nuclei in adult female canaries, but the cellular basis of this adult neuroplasticity is not well understood. Within HVC, the number of DCX-immunoreactive (ir) cells can be increased by photostimulation or treatment with T, but the effects of T and its metabolites on cell death in the songbird brain had not yet been elucidated. We therefore examined the effect of DHT and E2 on DCX expression and cell death in the song nuclei of adult female canaries. Intact female canaries were implanted with Silastic tubing containing crystalline T, DHT, E2, or a combination of DHT+E2. Control animals received empty implants. All birds were kept under early spring-like photoperiodic conditions (11L:13D) for 3 weeks. In HVC, the total number of DCX-ir cells was increased by treatment with T or DHT+E2 as compared to control birds, but was not affected by treatment with DHT or E2 alone. The number of pyknotic cells observed in the HVC was also increased by T but not by its metabolites. In Area X, the total number of DCX-ir cells was increased by treatment with T or DHT+E2, but the number of pyknotic cells was unaffected by hormone treatment. These results suggest that T enhances cellular turnover in the HVC (migration into, and cell death within, HVC), but affects only recruitment of new neurons into Area X. [less ▲]

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See detailJapanese quail as a model system for studying the neuroendocrine control of reproductive and social behaviors.
Ball, Gregory F; Balthazart, Jacques ULg

in ILAR Journal (2010), 51(4), 310-25

Japanese quail (Coturnix japonica; referred to simply as quail in this article) readily exhibit sexual behavior and related social behaviors in captive conditions and have therefore proven valuable for ... [more ▼]

Japanese quail (Coturnix japonica; referred to simply as quail in this article) readily exhibit sexual behavior and related social behaviors in captive conditions and have therefore proven valuable for studies of how early social experience can shape adult mate preference and sexual behavior. Quail have also been used in sexual conditioning studies illustrating that natural stimuli predict successful reproduction via Pavlovian processes. In addition, they have proven to be a good model to study how variation in photoperiod regulates reproduction and how variation in gonadal steroid hormones controls sexual behavior. For example, studies have shown that testosterone activates male-typical behaviors after being metabolized into estrogenic and androgenic metabolites. A critical site of action for these metabolites is the medial preoptic nucleus (POM), which is larger in males than in females. The enzyme aromatase converts testosterone to estradiol and is enriched in the POM in a male-biased fashion. Quail studies were the first to show that this enzyme is regulated both relatively slowly via genomic actions of steroids and more quickly via phosphorylation. With this base of knowledge and the recent cloning of the entire genome of the closely related chicken, quail will be valuable for future studies connecting gene expression to sexual and social behaviors. [less ▲]

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See detailDiversity of mechanisms involved in aromatase regulation and estrogen action in the brain
Charlier, Thierry ULg; Cornil, Charlotte ULg; Ball, Gregory et al

in Biochimica et Biophysica Acta - General Subjects (2010)

Background In recent years, the mechanisms through which estrogens modulate neuronal physiology, brain morphology, and behavior have proven to be far more complex than previously thought. For example, a ... [more ▼]

Background In recent years, the mechanisms through which estrogens modulate neuronal physiology, brain morphology, and behavior have proven to be far more complex than previously thought. For example, a second nuclear estrogen receptor has been identified, a new family of coregulatory proteins regulating steroid-dependent gene transcriptions was discovered and, finally, it has become clear that estrogens have surprisingly rapid effects based on their actions on cell membranes, which in turn result in the modulation of intracellular signaling cascades. Scope of review This paper presents a selective review of new findings in this area related to work in our laboratories, focusing on the role of estrogens in the activation of male sexual behavior. Two separate topics are considered. We first discuss functions of the steroid receptor coactivator-1 (SRC-1) that has emerged as a key limiting factor for behavioral effects of estradiol. Knocking-down its expression by antisense oligonucleotides drastically inhibits male-typical sexual behaviors. Secondly, we describe rapid regulations of brain estradiol production by calcium-dependent phosphorylations of the aromatase enzyme, themselves under the control of neurotransmitter activity. These rapid changes in estrogen bioavailability have clear behavioral consequences. Increases or decreases in estradiol concentrations respectively obtained by an acute injection of estradiol itself or of an aromatase inhibitor lead within 15–30 min to parallel changes in sexual behavior frequencies. These new controls of estrogen action offer a vast array of possibilities for discrete local controls of estrogen action. They also represent a formidable challenge for neuroendocrinologists trying to obtain an integrated view of brain function in relation to behavior. [less ▲]

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See detailPheromones in birds: myth or reality?
Caro, Samuel P; Balthazart, Jacques ULg

in Journal of Comparative Physiology. A, Neuroethology, Sensory, Neural and Behavioral Physiology (2010), 196(10), 751-66

Birds are anosmic or at best microsmatic... This misbelief persisted until very recently and has strongly influenced the outcome of communication studies in birds, with olfaction remaining neglected as ... [more ▼]

Birds are anosmic or at best microsmatic... This misbelief persisted until very recently and has strongly influenced the outcome of communication studies in birds, with olfaction remaining neglected as compared to acoustic and visual channels. However, there is now clear empirical evidence showing that olfaction is perfectly functional in birds and birds use olfactory information in a variety of ethological contexts. Although the existence of pheromones has never been formally demonstrated in this vertebrate class, different groups of birds, such as petrels, auklets and ducks have been shown to produce specific scents that could play a significant role in within-species social interactions. Behavioral experiments have indeed demonstrated that these odors influence the behavior of conspecifics. Additionally, in quail, deprivation of olfactory inputs decreases neuronal activation induced by sexual interactions with a female. It seems therefore well established that birds enjoy a functional sense of smell and a fast growing body of experimental evidence suggests that they use this channel of olfactory communication to control their social life. The unequivocal identification of an avian pheromone is, however, still ahead of us but there are now many exciting opportunities to unravel the behavioral and physiological particularities of chemical communication in birds. [less ▲]

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See detailOwn song selectivity in the songbird auditory pathway: suppression by norepinephrine
Poirier, Colline; Boumans, Tiny; Vellema, Michiel et al

Poster (2010)

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