Publications of Jacques Balthazart
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See detailThe underestimated role of olfaction in avian reproduction?
Balthazart, Jacques ULg; Taziaux, Mélanie ULg

in Behavioural Brain Research (2008)

Until the second half of the 20th century, it was broadly accepted that most birds are microsmatic if not anosmic and unable to detect and use olfactory information. Exceptions were eventually conceded ... [more ▼]

Until the second half of the 20th century, it was broadly accepted that most birds are microsmatic if not anosmic and unable to detect and use olfactory information. Exceptions were eventually conceded for species like procellariiforms, vultures or kiwis that detect their food at least in part based on olfactory signals. During the past 20-30 years, many publications have appeared indicating that this view is definitely erroneous. We briefly review here anatomical, electrophysiological and behavioral data demonstrating that birds in general possess a functional olfactory system and are able to use olfactory information in a variety of ethological contexts, including reproduction. Recent work also indicates that brain activation induced by sexual interactions with a female is significantly affected by olfactory deprivation in Japanese quail. Brain activation was measured via immunocytochemical detection of the protein product of the immediate early gene c-fos. Changes observed concerned two brain areas that play a key role in the control of male sexual behavior, the medial preoptic nucleus and the bed nucleus of the stria terminalis therefore suggesting a potential role of olfaction in the control of reproduction. The widespread idea that birds are anosmic or microsmatic is thus not supported by the available experimental data and presumably originates in our anthropomorphic view that leads us to think that birds do not smell because they have a rigid beak and nostrils and do not obviously sniff. Experimental analysis of this phenomenon is thus warranted and should lead to a significant change in our understanding of avian biology. [less ▲]

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See detaillocalized modulation of testosterone action: Function of steroid receptor coactivators in the brain
Charlier, Thierry ULg; Balthazart, Jacques ULg

in Ardis, L. I. (Ed.) New research on testosterone (2008)

Testosterone, through its activation of androgen and estrogen receptors, has been shown to play a critical role in brain development and physiology. Recent studies have shown that the activity of these ... [more ▼]

Testosterone, through its activation of androgen and estrogen receptors, has been shown to play a critical role in brain development and physiology. Recent studies have shown that the activity of these receptors can be modulated by the interaction with several proteins and, in particular, that coactivators are required to enhance their transcriptional activity. The steroid receptor coactivator-1, SRC-1 is the best-characterized coactivator and we review here the current knowledge on the distribution, regulation of expression and function of this protein in the brain, focusing mostly on our work in Japanese quail. As expected for a ubiquitous coactivator, SRC-1 is present throughout the brain in both mammalian and avian species but is found in particularly high concentrations in testosterone-sensitive areas such as the preoptic area in rat and Japanese quail and in the song control nuclei in songbirds. Further analysis demonstrates that the expression of SRC-1 is not constitutive but regulated in specific brain areas by the sex, acute stress and testosterone treatment. In addition, the protein concentration appears to fluctuate through the day in some brain regions. These modulations of SRC-1 expression by endogenous (sex) and exogenous (stress) factors could potentially exacerbate at specific times the competition or squelching between different nuclear receptors and therefore decrease the biological response induced by one or another hormonal system. Although the existence of such a phenomenon has not yet been demonstrated in a functionally intact biological system, the effects of SRC-1 antisense treatments clearly strengthen this hypothesis. Indeed, the decrease of SRC-1 expression in the hypothalamus induced by antisense oligonucleotide injections clearly inhibited both estrogen-dependent male sexual behavior and androgen-dependent pre- and post-copulatory displays (strut) in Japanese quail, therefore demonstrating a role of the coactivator in the transcriptional activation induced by both estrogen and androgen receptors. Interestingly, the inhibitory effect on sexual behavior of SRC-1 knock down was not systematically associated with modifications of several histological (definition of median preoptic nucleus [POM] using Nissl staining), immunohistochemical (aromatase and vasotocin cells and fibers in the POM) and biochemical (aromatase enzymatic activity) markers of testosterone action in the brain. This dissociation of the effects of SRC-1 on behavior on the one hand and on aromatase and POM neurochemistry on another hand suggests that other system(s) involved in the activation of male sexual behavior are likely more sensitive to a decrease of SRC-1 expression. In future research, it will be essential to determine the other cofactors involved in specific physiological responses and to define whether these coactivators act synergistically, in parallel or independently in the modulation of the activity of one or several nuclear receptors linked to a particular physiological event. In several biological models, the observed changes in concentration of the circulating hormone and /or its receptors are apparently not sufficient to explain the physiological and behavioral responses observed after testosterone treatment. The discovery of steroid receptor coactivators opens new perspectives in the study of the molecular basis of steroid action at the level of the organism and a complete understanding of the mechanisms of steroid action will not be achieved without a detailed characterization of nuclear receptor cofactors. [less ▲]

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See detailIndividual variation and the endocrine regulation of behaviour and physiology in birds: a cellular/molecular perspective.
Ball, Gregory F; Balthazart, Jacques ULg

in Philosophical Transactions : Biological Sciences (2008), 363(1497), 1699-710

Investigations of the cellular and molecular mechanisms of physiology and behaviour have generally avoided attempts to explain individual differences. The goal has rather been to discover general ... [more ▼]

Investigations of the cellular and molecular mechanisms of physiology and behaviour have generally avoided attempts to explain individual differences. The goal has rather been to discover general processes. However, understanding the causes of individual variation in many phenomena of interest to avian eco-physiologists will require a consideration of such mechanisms. For example, in birds, changes in plasma concentrations of steroid hormones are important in the activation of social behaviours related to reproduction and aggression. Attempts to explain individual variation in these behaviours as a function of variation in plasma hormone concentrations have generally failed. Cellular variables related to the effectiveness of steroid hormone have been useful in some cases. Steroid hormone target sensitivity can be affected by variables such as metabolizing enzyme activity, hormone receptor expression as well as receptor cofactor expression. At present, no general theory has emerged that might provide a clear guidance when trying to explain individual variability in birds or in any other group of vertebrates. One strategy is to learn from studies of large units of intraspecific variation such as population or sex differences to provide ideas about variables that might be important in explaining individual variation. This approach along with the use of newly developed molecular genetic tools represents a promising avenue for avian eco-physiologists to pursue. [less ▲]

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See detailHow useful is the appetitive and consummatory distinction for our understanding of the neuroendocrine control of sexual behavior?
Ball, Gregory F; Balthazart, Jacques ULg

in Hormones and Behavior (2008), 53(2), 307-11315-8

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See detailRapid action on neuroplasticity precedes behavioral activation by testosterone.
Charlier, Thierry ULg; Ball, Gregory F; Balthazart, Jacques ULg

in Hormones & Behavior (2008), 54(4), 488-95

Testosterone has been shown to increase the volume of steroid-sensitive brain nuclei in adulthood in several vertebrate species. In male Japanese quail the volume of the male-biased sexually dimorphic ... [more ▼]

Testosterone has been shown to increase the volume of steroid-sensitive brain nuclei in adulthood in several vertebrate species. In male Japanese quail the volume of the male-biased sexually dimorphic medial preoptic nucleus (POM), a key brain area for the control of male sexual behavior, is markedly increased by testosterone. Previous studies assessed this effect after a period of 8-14 days but the exact time course of these effects is unknown. We asked here whether testosterone-dependent POM plasticity could be observed at shorter latencies. Brains from castrated male quail were collected after 1, 2, 7 and 14 days of T treatment (CX+T) and compared to brains of untreated castrates (CX) collected after 1 or 14 days. POM volumes defined either by Nissl staining or by aromatase immunohistochemistry increased in a time-dependent fashion in CX+T subjects and almost doubled after 14 days of treatment with testosterone while no change was observed in CX birds. A significant increase in the average POM volume was detected after only one day of testosterone treatment. The optical density of Nissl and aromatase staining was also increased after one or two days of testosterone treatment. Activation of male copulatory behavior followed these morphological changes with a latency of approximately one day. This rapid neurochemical and neuroanatomical plasticity observed in the quail POM thus seems to limit the activation of male sexual behavior and offers an excellent model to analyze features of steroid-regulated brain structure and function that determine behavior expression. [less ▲]

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See detailSite-specific effects of anosmia and cloacal gland anesthesia on Fos expression induced in male quail brain by sexual behavior.
Taziaux, Mélanie ULg; Keller, Matthieu; Ball, Gregory F et al

in Behavioural Brain Research (2008), 194(1), 52-65

In rats, expression of the immediate early gene, c-fos observed in the brain following male copulatory behavior relates mostly to the detection of olfactory information originating from the female and to ... [more ▼]

In rats, expression of the immediate early gene, c-fos observed in the brain following male copulatory behavior relates mostly to the detection of olfactory information originating from the female and to somatosensory feedback from the penis. However, quail, like most birds, are generally considered to have a relatively poorly developed sense of smell. Furthermore, quail have no intromittent organ (e.g., penis). It is therefore intriguing that expression of male copulatory behavior induces in quail and rats a similar pattern of c-fos expression in the medial preoptic area (mPOA), bed nucleus of the stria terminalis (BSTM) and parts of the amygdala. We analyzed here by immunocytochemistry Fos expression in the mPOA/BSTM/amygdala of male quail that had been allowed to copulate with a female during standardized tests. Before these tests, some of the males had either their nostrils plugged, or their cloacal area anesthetized, or both. A control group was not exposed to females. These manipulations did not affect frequencies of male sexual behavior and all birds exposed to a female copulated normally. In the mPOA, the increased Fos expression induced by copulation was not affected by the cloacal gland anesthesia but was markedly reduced in subjects deprived of olfactory input. Both manipulations affected copulation-induced Fos expression in the BSTM. No change in Fos expression was observed in the amygdala. Thus immediate early gene expression in the mPOA and BSTM of quail is modulated at least in part by olfactory cues and/or somatosensory stimuli originating from the cloacal gland. Future work should specify the nature of these stimuli and their function in the expression of avian male sexual behavior. [less ▲]

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See detailExpression of reelin, its receptors and its intracellular signaling protein, Disabled1 in the canary brain: relationships with the song control system.
Balthazart, Jacques ULg; Voigt, C.; Boseret, Géraldine ULg et al

in Neuroscience (2008), 153(4), 944-62

Songbirds produce learned vocalizations that are controlled by a specialized network of neural structures, the song control system. Several nuclei in this song control system demonstrate a marked degree ... [more ▼]

Songbirds produce learned vocalizations that are controlled by a specialized network of neural structures, the song control system. Several nuclei in this song control system demonstrate a marked degree of adult seasonal plasticity. Nucleus volume varies seasonally based on changes in cell size or spacing, and in the case of nucleus HVC and area X on the incorporation of new neurons. Reelin, a large glycoprotein defective in reeler mice, is assumed to determine the final location of migrating neurons in the developing brain. In mammals, reelin is also expressed in the adult brain but its functions are less well characterized. We investigated the relationships between the expression of reelin and/or its receptors and the dramatic seasonal plasticity in the canary (Serinus canaria) brain. We detected a broad distribution of the reelin protein, its mRNA and the mRNAs encoding for the reelin receptors (VLDLR and ApoER2) as well as for its intracellular signaling protein, Disabled1. These different mRNAs and proteins did not display the same neuroanatomical distribution and were not clearly associated, in an exclusive manner, with telencephalic brain areas that incorporate new neurons in adulthood. Song control nuclei were associated with a particular specialized expression of reelin and its mRNA, with the reelin signal being either denser or lighter in the song nucleus than in the surrounding tissue. The density of reelin-immunoreactive structures did not seem to be affected by 4 weeks of treatment with exogenous testosterone. These observations do not provide conclusive evidence that reelin plays a prominent role in the positioning of new neurons in the adult canary brain but call for additional work on this protein analyzing its expression comparatively during development and in adulthood with a better temporal resolution at critical points in the reproductive cycle when brain plasticity is known to occur. [less ▲]

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See detailEnhanced neural activation in brain regions mediating sexual responses following exposure to a conditioned stimulus that predicts copulation.
Taziaux, Mélanie ULg; Kahn, A.; Moore, J. et al

in Neuroscience (2008), 151(3), 644-58

Stimuli associated with sexual behavior increase reproductive success if presented prior to copulation. In Japanese quail, inseminations that take place in a context that predicts the arrival of a female ... [more ▼]

Stimuli associated with sexual behavior increase reproductive success if presented prior to copulation. In Japanese quail, inseminations that take place in a context that predicts the arrival of a female are more likely to result in fertilized eggs. We demonstrate here that in male Japanese quail a sexual conditioned stimulus (CS) also enhances activity in two brain regions that mediate sexual behavior, the medial preoptic area and the medial part of the bed nucleus of the stria terminalis. C-fos expression, a marker of neural activation, was higher in these areas in subjects exposed sequentially to a sexual CS and copulation than in subjects exposed to copulation or the CS alone or in subjects exposed to no sexual stimulus, either an identical, untrained CS or an empty arena. These results suggest a link between a proximate result of sexual CS presentation, male brain activation, and a known ultimate outcome, increased fertilizations. [less ▲]

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See detailSeasonal rewiring of the songbird brain: an in vivo MRI study.
De Groof, Geert; Verhoye, Marleen; Van Meir, Vincent et al

in European Journal of Neuroscience (2008), 28(12), 2475-852474

The song control system (SCS) of songbirds displays a remarkable plasticity in species where song output changes seasonally. The mechanisms underlying this plasticity are barely understood and research ... [more ▼]

The song control system (SCS) of songbirds displays a remarkable plasticity in species where song output changes seasonally. The mechanisms underlying this plasticity are barely understood and research has primarily been focused on the song nuclei themselves, largely neglecting their interconnections and connections with other brain regions. We investigated seasonal changes in the entire brain, including the song nuclei and their connections, of nine male starlings (Sturnus vulgaris). At two times of the year, during the breeding (April) and nonbreeding (July) seasons, we measured in the same subjects cellular attributes of brain regions using in vivo high-resolution diffusion tensor imaging (DTI) at 7 T. An increased fractional anisotropy in the HVC-RA pathway that correlates with an increase in axonal density (and myelination) was found during the breeding season, confirming multiple previous histological reports. Other parts of the SCS, namely the occipitomesencephalic axonal pathway, which contains fiber tracts important for song production, showed increased fractional anisotropy due to myelination during the breeding season and the connection between HVC and Area X showed an increase in axonal connectivity. Beyond the SCS we discerned fractional anisotropy changes that correlate with myelination changes in the optic chiasm and axonal organization changes in an interhemispheric connection, the posterior commissure. These results demonstrate an unexpectedly broad plasticity in the connectivity of the avian brain that might be involved in preparing subjects for the competitive and demanding behavioral tasks that are associated with successful reproduction. [less ▲]

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See detailA three-dimensional MRI atlas of the zebra finch brain in stereotaxic coordinates.
Poirier, Colline; Vellema, Michiel; Verhoye, Marleen et al

in NeuroImage (2008), 41(1), 1-6

The neurobiology of birdsong, as a model for human speech, is a fast growing area of research in the neurosciences and involves electrophysiological, histological and more recently magnetic resonance ... [more ▼]

The neurobiology of birdsong, as a model for human speech, is a fast growing area of research in the neurosciences and involves electrophysiological, histological and more recently magnetic resonance imaging (MRI) approaches. Many of these studies require the identification and localization of different brain areas (nuclei) involved in the sensory and motor control of song. Until now, the only published atlases of songbird brains consisted in drawings based on histological slices of the canary and of the zebra finch brain. Taking advantage of high-magnetic field (7 Tesla) MRI technique, we present the first high-resolution (80 x 160 x 160 microm) 3-D digital atlas in stereotaxic coordinates of a male zebra finch brain, the most widely used species in the study of birdsong neurobiology. Image quality allowed us to discern most of the song control, auditory and visual nuclei. The atlas can be freely downloaded from our Web site and can be interactively explored with MRIcro. This zebra finch MRI atlas should become a very useful tool for neuroscientists working on birdsong, especially for co-registrating MRI data but also for determining accurately the optimal coordinates and angular approach for injections or electrophysiological recordings. [less ▲]

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See detailTopography in the preoptic region: Differential regulation of appetitive and consummatory male sexual behaviors
Balthazart, Jacques ULg; Ball, Gregory F.

in Frontiers in Neuroendocrinology (2007), 28(4), 161-178

Several studies have suggested dissociations between neural circuits underlying the expression of appetitive (e.g., courtship behavior) and consummatory components (i.e., copulatory behavior) of ... [more ▼]

Several studies have suggested dissociations between neural circuits underlying the expression of appetitive (e.g., courtship behavior) and consummatory components (i.e., copulatory behavior) of vertebrate male sexual behavior. The medial preoptic area (mPOA) clearly controls the expression of male copulation but, according to a number of experiments, is not necessarily implicated in the expression of appetitive sexual behavior. In rats for example, lesions to the mPOA eliminate male-typical copulatory behavior but have more subtle or no obvious effects on measures of sexual motivation. Rats with such lesions still pursue and attempt to mount females. They also acquire and perform learned instrumental responses to gain access to females. However, recent lesions studies and measures of the expression of the immediate early gene c-fos demonstrate that, in quail, sub-regions of the mPOA, in particular of its sexually dimorphic component the medial preoptic nucleus, can be specifically linked with either the expression of appetitive or consummatory sexual behavior. In particular more rostral regions can be linked to appetitive components while more caudal regions are involved in consummatory behavior. This functional sub-region variation is associated with neurochemical and hodological specializations (i.e., differences in chemical phenotype of the cells or in their connectivity), especially those related to the actions of androgens in relation to the activation of male sexual behavior, that are also present in rodents and other species. It could thus reflect general principles about POA organization and function in the vertebrate brain. (C) 2007 Elsevier Inc. All rights reserved. [less ▲]

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See detailEstradiol, a key endocrine signal in the sexual differentiation and activation of reproductive behavior in quail
Balthazart, Jacques ULg

in Comparative Biochemistry & Physiology Part A : Molecular & Integrative Physiology (2007, August), 148(Suppl. 1), 27

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See detailSexual Behavior activity tracks rapid changes in brain estrogen concentrations
Taziaux, Mélanie ULg; Keller, Matthieu ULg; Bakker, Julie ULg et al

in Journal of Neuroscience (2007), 27(24), 6563-6572

Estrogens are classically viewed as hormones that bind to intracellular receptors, which then act as transcription factors to modulate gene expression; however, they also affect many aspects of neuronal ... [more ▼]

Estrogens are classically viewed as hormones that bind to intracellular receptors, which then act as transcription factors to modulate gene expression; however, they also affect many aspects of neuronal functioning by rapid nongenomic actions. Brain estrogen production can be regulated within minutes by changes in aromatase (estrogen synthase) activity as a result of calcium-dependent phosphorylations of the enzyme. To determine the effects of rapid changes in estrogen availability on male copulatory behavior, we mimicked in male mice the rapid upregulation and downregulation of brain estrogen concentration that should occur after inactivation or activation of aromatase activity. A single injection of different aromatase inhibitors [Vorozole, 1,4,6-androstatrien-3,17-dione (ATD), or its metabolite 17-OH-ATD (1,4,6-androstatrien-17beta-ol-3-one)] almost completely suppressed male sexual behavior (mounts and intromissions) expressed 10-20 min later by C57BL/6J mice but did not affect behavior in aromatase knock-out (ArKO) mice, activated by daily injections of estradiol benzoate, thereby confirming the specificity of the behavioral inhibition observed in wild-type mice. The rapid ATD-induced inhibition was reversed by the simultaneous injection of a large dose of estradiol. A single injection of estradiol to ArKO mice also activated male sexual behavior within 15 min. Thus, rapid increases or decreases in brain estrogen concentrations are followed within minutes by corresponding changes in male sexual behavior. Sexual behavior can thus be used to monitor changes in local estrogen concentrations and analyze the mechanisms mediating the rapid decline in estrogen signaling that takes place after inhibition of estrogen synthesis. [less ▲]

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See detailThe microtubule-associated protein doublecortin is broadly expressed in the telencephalon of adult canaries
Boseret, Géraldine ULg; Ball, G. F.; Balthazart, Jacques ULg

in Journal of Chemical Neuroanatomy (2007), 33(3), 140-154

The protein doublecortin (DCX) is expressed in post-mitotic migrating and differentiating neurons in the developing vertebrate brain and, as a part of the microtubule machinery, is required for neuronal ... [more ▼]

The protein doublecortin (DCX) is expressed in post-mitotic migrating and differentiating neurons in the developing vertebrate brain and, as a part of the microtubule machinery, is required for neuronal migration. DCX expression is generally maximal during embryonic and early post-natal life but decreases markedly and almost disappears in older animals in parallel with the major decrease or cessation of neurogenesis. In several seasonally breeding songbird species such as canaries, the volume of several song control nuclei in the brain varies seasonally such that the largest nuclei are observed in the late spring and early summer. This variation is based on changes in cell size, dendritic branching, and, in nucleus HVC, on the incorporation of neurons newly born in adulthood. Because songbirds maintain an active neurogenesis and neuronal incorporation in their telencephalon throughout their lives, we investigated here the distribution of DCX-immunoreactive (ir) structures in the brain of adult male canaries. Densely stained DCX-ir cells were found exclusively in parts of the telencephalon that are known to incorporate new neurons in adulthood, in particular the nidopallium. Within this brain region, the boundaries of the song control nucleus HVC could be clearly distinguished from surrounding structures by a higher density of DCX-ir structures. In most telencephalic areas, about two thirds of these cells displayed a uni- or bipolar fusiform morphology suggesting they were migrating neurons. The rest of the DCX-ir cells in the telencephalon were larger and had a round multipolar morphology. No such staining was found in the rest of the brain. The broad expression of DCX specifically in adult brain structures that exhibit the characteristic of active incorporation of new neurons suggests that DCX plays a key role in the migration of new neurons in the brain of adult songbirds as it presumably does during ontogeny. (c) 2007 Elsevier B.V. All rights reserved. [less ▲]

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See detailDifferential c-fos expression in the brain of male Japanese quail following exposure to stimuli that predict or do not predict the arrival of a female
Taziaux, Mélanie ULg; Lopez, J.; Cornil, Charlotte ULg et al

in European Journal of Neuroscience (2007), 25(9), 2835-2846

We investigated the effects of presenting a sexual conditioned stimulus on the expression of c-fos in male Japanese quail. Eight brain sites were selected for analysis based on previous reports of c-fos ... [more ▼]

We investigated the effects of presenting a sexual conditioned stimulus on the expression of c-fos in male Japanese quail. Eight brain sites were selected for analysis based on previous reports of c-fos expression in these areas correlated with sexual behaviour or learning. Males received either paired or explicitly unpaired presentations of an arbitrary stimulus and visual access to a female. Nine conditioning trials were conducted, one per day, for each subject. On the day following the ninth trial, subjects were exposed to the conditional stimulus (CS) for 5 min. Conditioning was confirmed by analysis of rhythmic cloacal sphincter movements (RCSM), an appetitive sexual behaviour, made in response to the CS presentation. Subjects in the paired condition performed significantly more RCSM than subjects in the unpaired group. Brains were collected 90 min following the stimulus exposure and stained by immunolhistochemistry for the FOS protein. Significant group differences in the number of FOS-immunoreactive (FOS-ir) cells were found in two brain regions, the nucleus taeniae of the amygdala (TnA) and the hippocampus (Hp). Subjects in the paired condition had fewer FOS-ir cells in both areas than subjects in the unpaired condition. These data provide additional support to the hypothesis that TnA is implicated in the expression of appetitive sexual behaviours in male quail and corroborate numerous previous reports of the involvement of the hippocampus in conditioning. Further, these data suggest that conditioned and unconditioned sexual stimuli activate different brain regions but have similar behavioural consequences. [less ▲]

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See detailNon-photoperiodic factors and timing of breeding in blue tits: Impact of environmental and social influences in semi-natural conditions
Caro, S. P.; Lambrechts, M. M.; Balthazart, Jacques ULg et al

in Behavioural Processes (2007), 75(1), 1-7

The seasonal development of life-history traits is influenced by many environmental factors. The impact of photoperiodic and non-photoperiodic factors on nest building and egg laying has been rarely ... [more ▼]

The seasonal development of life-history traits is influenced by many environmental factors. The impact of photoperiodic and non-photoperiodic factors on nest building and egg laying has been rarely investigated in non-domesticated avian species for which long term field data sets are available. Former investigations showed that blue tits originating from geographically close populations in the Mediterranean region do not respond in the same way to photoperiodic factors in semi-natural outdoor conditions. Here we show experimentally that nest building and onset of egg laying in captive blue tits is also proximately influenced by non-photoperiodic factors, including aspects related to aviary characteristics and social interactions between birds of the two sexes originating from different local Mediterranean study populations. In two successive experiments, we show that (1) increasing the volume of the aviary advanced the egg laying period of one specific population by almost I month, and (2) crossing pairs of birds from different origins strongly reduced the nest building and egg laying behaviours. These results indicate that obtaining biologically relevant breeding results in captivity with wild birds requires the control and experimental manipulation of a wide array of complex environmental cues. (c) 2007 Elsevier B.V All rights reserved. [less ▲]

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See detailExposure to oestrogen prenatally does not interfere with the normal female-typical development of odour preferences
Bakker, Julie ULg; De Mees, C.; Szpirer, J. et al

in Journal of Neuroendocrinology (2007), 19(5), 329-334

The neural mechanisms controlling mate recognition and heterosexual partner preference are sexually differentiated by perinatal actions of sex steroid hormones. We previously showed that the most ... [more ▼]

The neural mechanisms controlling mate recognition and heterosexual partner preference are sexually differentiated by perinatal actions of sex steroid hormones. We previously showed that the most important action of oestrogen during prenatal development is to defeminise and, to some extent, masculinise brain and behaviour in mice. Female mice deficient in alpha-foetoprotein (AFP) due to a targeted mutation in the Afp gene (AFP-KO) do not show any female sexual behaviour when paired with an active male because they lack the protective action of AFP against maternal oestrogens. In the present study, we investigated whether odour preferences, another sexually differentiated trait in mice, are also defeminised and/or masculinised in AFP-KO females due to their prenatal exposure to oestrogens. AFP-KO females of two background strains (CD1 and C57Bl/6j) preferred to investigate male over female odours when given the choice between these two odour stimuli in a Y-maze, and thus remained very female-like in this regard. Thus, the absence of lordosis behaviour in these females cannot be explained by a reduced motivation of AFP-KO females to investigate male-derived odours. Furthermore, the presence of a strong male-directed odour preference in AFP-KO females suggests a postnatal contribution of oestrogens to the development of preferences to investigate opposite-sex odours. [less ▲]

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See detailSexual versus individual differentiation: the controversial role of avian maternal hormones
Carere, C.; Balthazart, Jacques ULg

in Trends in Endocrinology and Metabolism (2007), 18(2), 73-80

Avian embryos are exposed not only to endogenous sex steroids, which are produced by their gonads and have a key role in sexual differentiation, but also to maternal steroids transferred into the egg yolk ... [more ▼]

Avian embryos are exposed not only to endogenous sex steroids, which are produced by their gonads and have a key role in sexual differentiation, but also to maternal steroids transferred into the egg yolk, which can modulate the development of individual differences in behavior. Studies of maternal hormones have primarily focused on ultimate questions (evolutionary trade-offs, functional significance), whereas proximate mechanistic questions have been largely ignored. A central problem that must be addressed is how exposure to maternal hormones affects the individual phenotype without interfering with sexual differentiation. Separate effects could result from the action of different hormones, at different doses or at different times, on different targets. [less ▲]

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See detailNeuroanatomical specificity of sex differences in expression of aromatase mRNA in the quail brain
Voigt, C.; Ball, G. F.; Balthazart, Jacques ULg

in Journal of Chemical Neuroanatomy (2007), 33(2), 75-86

In birds and mammals, aromatase activity in the preoptic-hypothalamic region (HPOA) is usually higher in males than in females. It is, however, not known whether the enzymatic sex difference reflects the ... [more ▼]

In birds and mammals, aromatase activity in the preoptic-hypothalamic region (HPOA) is usually higher in males than in females. It is, however, not known whether the enzymatic sex difference reflects the differential activation of aromatase transcription or some other control mechanism. Although sex differences in aromatase activity are clearly documented in the HPOA of Japanese quail (Coturnix japonica), only minimal or even no differences at all were observed in the number of aromatase-immunoreactive (ARO-ir) cells in the medial preoptic nucleus (POM) and in the medial part of the bed nucleus striae terminalis (BSTM). We investigated by in situ hybridization the distribution and possible sex differences in aromatase mRNA expression in the brain of sexually active adult quail. The distribution of aromatase mRNA matched very closely the results of previous immunocytochemical studies with the densest signal being observed in the POM, BSTM and in the mediobasal hypothalamus (MBH). Additional weaker signals were detected in the rostral forebrain, arcopallium and mesencephalic regions. No sex difference in the optical density of the hybridization signal could be found in the POM and MBH but the area covered by mRNA was larger in males than in females, indicating a higher overall expression in males. In contrast, in the BSTM, similar areas were covered by the aromatase expression in both sexes but the density of the signal was higher in females than in males. The physiological control of aromatase is thus neuroanatomically specific and with regard to sex differences, these controls are at least partially different if one compares the level of transcription, translation and activity of the enzyme. These results also indirectly suggest that the sex difference in aromatase enzyme activity that is present in the quail HPOA largely results from differentiated controls of enzymatic activity rather than differences in enzyme concentration. (c) 2007 Elsevier B.V. All rights reserved. [less ▲]

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