The fast regulation of aromatase activity by phosphorylations is species and tissue-independent.
Charlier, Thierry ; ; et al
Poster (2009)Detailed reference viewed: 10 (1 ULg)
Species and tissue-independent rapid regulation of aromatase activity by phosphorylations.
Charlier, Thierry ; ; et al
in Acta Neurologica Belgica (2009)
Aromatase activity (AA) is rapidly inhibited in male quail brains, following expression of sexual behavior, activation of glutamatergic receptors or exposure to phosphorylating conditions. Questions ... [more ▼]
Aromatase activity (AA) is rapidly inhibited in male quail brains, following expression of sexual behavior, activation of glutamatergic receptors or exposure to phosphorylating conditions. Questions remain as to whether direct aromatase phosphorylation is the common key regulatory mechanism and whether these inhibitions are specific to quail hypothalamus. We now showed that AA is rapidly downregulated in quail ovary homogenates incubated in phosphorylating conditions, similarly to what is observed in hypothalamic homogenates. To understand the processes underlying this control, we expressed human aromatase in the human cell line HEK293 and 1) researched whether human aromatase can also be rapidly modulated by phosphorylations and 2) investigated more precisely the processes involved in this rapid control of activity. AA in HEK293 was rapidly inhibited following depolarization of intact cells with 100 mM KCl or in cell lysates exposed to phosphorylating conditions. Thus inhibition of AA in phosphorylating conditions is not unique to the quail hypothalamus neural environment but seems to be a general process. We are now defining the contribution of single residues of the aromatase protein to this enzymatic control. [less ▲]Detailed reference viewed: 14 (4 ULg)
Estradiol, a key endocrine signal in the sexual differentiation and activation of reproductive behavior in quail.
Balthazart, Jacques ; Cornil, Charlotte ; Charlier, Thierry et al
in Journal of Experimental Zoology. Part A, Ecological Genetics and Physiology (2009), 311(5), 323-45
In Japanese quail, estrogen's effects on sexual behavior can be divided into three classes based on the underlying mechanisms and time-course of action and release. During embryonic life, the embryonic ... [more ▼]
In Japanese quail, estrogen's effects on sexual behavior can be divided into three classes based on the underlying mechanisms and time-course of action and release. During embryonic life, the embryonic ovary secretes large amounts of estrogens. In contrast to what is observed in mammals where sexual differentiation essentially proceeds via masculinization of the males, in quail, females are demasculinized by their endogenous ovarian estrogens, an effect that can be blocked by injection of an aromatase inhibitor and mimicked in male embryos by an injection of estradiol. In adulthood, testosterone secreted by the testes is converted into estrogens by the preoptic aromatase. Locally produced estrogens activate male sexual behavior largely through the activation of estrogen receptors resulting in the transcription of a variety of genes, including brain aromatase (genomic effect). Both changes in estrogen production and action are observed within latencies ranging from a few hours to a few days, and are completely reversible. Additionally, brain aromatase activity can be modulated within minutes by calcium-dependent phosphorylations, triggered by variations in glutamatergic neurotransmission. These rapid changes in aromatase activity affect with relatively short latencies (10-15 min) the expression of male sexual behavior in quail and also in mice. Overall, the effects of estrogens on sexual behavior can thus be categorized into three classes: organizational (irreversible genomic action during ontogeny), activational (reversible genomic action during adulthood) and rapid nongenomic effects. Rapid and slower changes in brain aromatase activity match well with the two modes of estrogen action on behavior and provide temporal variations in the estrogens' bioavailability that should be able to support the entire range of established effects for this steroid. [less ▲]Detailed reference viewed: 17 (8 ULg)
Behavioral effects of brain-derived estrogens in birds.
Balthazart, Jacques ; ; et al
in Annals of the New York Academy of Sciences (2009), 1163
In birds as in other vertebrates, estrogens produced in the brain by aromatization of testosterone have widespread effects on behavior. Research conducted with male Japanese quail demonstrates that ... [more ▼]
In birds as in other vertebrates, estrogens produced in the brain by aromatization of testosterone have widespread effects on behavior. Research conducted with male Japanese quail demonstrates that effects of brain estrogens on all aspects of sexual behavior, including appetitive and consummatory components as well as learned aspects, can be divided into two main classes based on their time course. First, estrogens via binding to estrogen receptors regulate the transcription of a variety of genes involved primarily in neurotransmission. These neurochemical effects ultimately result in the activation of male copulatory behavior after a latency of a few days. Correlatively, testosterone and its aromatized metabolites increase the transcription of the aromatase mRNA, resulting in an increased concentration and activity of the enzyme that actually precedes behavioral activation. Second, recent studies with quail demonstrate that brain aromatase activity can also be modulated within minutes by phosphorylation processes regulated by changes in intracellular calcium concentration, such as those associated with glutamatergic neurotransmission. The rapid upregulations or downregulations of brain estrogen concentration (presumably resulting from these changes in aromatase activity) affect, by nongenomic mechanisms with relatively short latencies (frequency increases or decreases respectively within 10-15 min), the expression of male sexual behavior in quail and also in rodents. Brain estrogens thus affect behavior on different time scales by genomic and nongenomic mechanisms similar to those of a hormone or a neurotransmitter. [less ▲]Detailed reference viewed: 16 (2 ULg)
Dopamine binds to alpha(2)-adrenergic receptors in the song control system of zebra finches (Taeniopygia guttata).
Cornil, Charlotte ; ;
in Journal of Chemical Neuroanatomy (2008), 35(2), 202-15
A commonly held view is that dopamine exerts its effects via binding to D1- and D2-dopaminergic receptors. However, recent data have emerged supporting the existence of a direct interaction of dopamine ... [more ▼]
A commonly held view is that dopamine exerts its effects via binding to D1- and D2-dopaminergic receptors. However, recent data have emerged supporting the existence of a direct interaction of dopamine with adrenergic but this interaction has been poorly investigated. In this study, the pharmacological basis of possible in vivo interactions between dopamine and alpha(2)-adrenergic receptors was investigated in zebra finches. A binding competition study showed that dopamine displaces the binding of the alpha(2)-adrenergic ligand, [(3)H]RX821002, in the brain. The affinity of dopamine for the adrenergic sites does not differ between the sexes and is 10- to 28-fold lower than that for norepinephrine. To assess the anatomical distribution of this interaction, binding competitions were performed on brain slices incubated in 5nM [(3)H]RX821002 in the absence of any competitor or in the presence of norepinephrine [0.1microM] or dopamine [1microM]. Both norepinephrine and dopamine displaced the binding of the radioligand though to a different extent in most of the regions studied (e.g., area X, the lateral part of the magnocellular nucleus of anterior nidopallium, HVC, arcopallium dorsale, ventral tegmental area and substantia grisea centralis) but not in the robust nucleus of the arcopallium. Together these data provide evidence for a direct interaction between dopamine and adrenergic receptors in songbird brains albeit with regional variation. [less ▲]Detailed reference viewed: 41 (3 ULg)
Interplay among catecholamine systems: dopamine binds to alpha2-adrenergic receptors in birds and mammals.
Cornil, Charlotte ;
in Journal of Comparative Neurology (The) (2008), 511(5), 610-27
Dopaminergic and adrenergic receptors are G-protein-coupled receptors considered to be different based on their pharmacology and signaling pathways. Some receptor subtypes that are members of one family ... [more ▼]
Dopaminergic and adrenergic receptors are G-protein-coupled receptors considered to be different based on their pharmacology and signaling pathways. Some receptor subtypes that are members of one family are actually closer in phylogenetic terms to some subtypes belonging to the other family, suggesting that the pharmacological specificity among these receptors from different families is not perfect. Indeed, evidence is accumulating that one amine can cross-talk with receptors belonging to the other system. However, most of these observations were collected in vitro using artificial cell models transfected with cloned receptors, so that the occurrence of this phenomenon in vivo as well as its distribution in the central nervous system is not known. In this study the pharmacological basis of possible in vivo interactions between dopamine and alpha(2)-adrenergic receptors was investigated in quail, zebra finches, and rats. Binding competitions showed that dopamine displaces the binding of the selective alpha(2)-adrenergic ligand, [(3)H]RX821002, in the brain of the three species with an affinity approximately 10-28-fold lower than that of norepinephrine. Dopamine also displaces with an affinity 3-fold lower than norepinephrine the binding of [(3)H]RX821002 to human alpha(h2A)-adrenergic receptors expressed in Sf9 cells. The anatomical distribution of this interaction was assessed in brain slices of quail and rat based on autoradiographic methods. Both norepinephrine and dopamine significantly displace [(3)H]RX821002 binding in all brain nuclei considered. Together, these data provide evidence for an interaction between the dopaminergic and noradrenergic systems in the vertebrate brain, albeit with species variations. [less ▲]Detailed reference viewed: 23 (1 ULg)
How useful is the appetitive and consummatory distinction for our understanding of the neuroendocrine control of sexual behavior?
; Balthazart, Jacques
in Hormones and Behavior (2008), 53(2), 307-11315-8Detailed reference viewed: 19 (1 ULg)
Individual variation and the endocrine regulation of behaviour and physiology in birds: a cellular/molecular perspective.
; Balthazart, Jacques
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 ▲]Detailed reference viewed: 17 (0 ULg)
Rapid action on neuroplasticity precedes behavioral activation by testosterone.
Charlier, Thierry ; ; Balthazart, Jacques
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 ▲]Detailed reference viewed: 25 (3 ULg)
Site-specific effects of anosmia and cloacal gland anesthesia on Fos expression induced in male quail brain by sexual behavior.
; ; 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 ▲]Detailed reference viewed: 36 (0 ULg)
Topography in the preoptic region: Differential regulation of appetitive and consummatory male sexual behaviors
Balthazart, Jacques ;
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 ▲]Detailed reference viewed: 32 (1 ULg)
Down-regulation of the coactivator SRC-1 reveals different thresholds for testosterone-dependent regulation of male sexual behavior and brain aromatase
Charlier, Thierry ; ; Balthazart, Jacques
Poster (2006)Detailed reference viewed: 5 (1 ULg)
Steroid specificity and control by steroid receptor coactivator-1 (SRC-1) of male sexual behavior
Balthazart, Jacques ; Charlier, Thierry ;
Conference (2006)Detailed reference viewed: 3 (1 ULg)
Targeting steroid receptor coactivator-1 expression with locked nucleic acids antisense reveals different thresholds for the hormonal regulation of male sexual behavior in relation to aromatase activity and protein expression.
Charlier, Thierry ; ; et al
in Behavioural Brain Research (2006), 172(2), 333-43
Steroid receptors such as the androgen and estrogen receptors require the presence of several proteins, known as coactivators, to enhance the transcription of target genes. The first goal of the present ... [more ▼]
Steroid receptors such as the androgen and estrogen receptors require the presence of several proteins, known as coactivators, to enhance the transcription of target genes. The first goal of the present study was to define the role of SRC-1 on the steroid-dependent expression of the aromatase protein and its activity in male Japanese quail. The second goal was to analyze the rapid plasticity of the POM following antisense treatment interruption. We confirm here that the inhibition of SRC-1 expression by daily intracerebroventricular injections of locked nucleic acid antisense oligonucleotides in the third ventricle at the level of the preoptic area-hypothalamus (HPOA) significantly reduces testosterone-dependent male sexual behavior. In the first experiment, aromatase protein expression in HPOA was inhibited in SRC-1-depleted males but the enzymatic activity remained at the level measured in controls. We observed in the second experiment a recovery of the behavioral response to testosterone treatment after interruption of the antisense injection. However, several morphological characteristics of the POM were not different between the control group, the antisense-treated birds and antisense-treated birds in which treatment had been discontinued 3 days earlier. Antisense was also less effective in knocking-down SRC-1 in the present experiments as compared to our previous study. An analysis of this variation in the degree of knock-down of SRC-1 expression suggests dissociation among different aspects of steroid action on brain and behavior presumably resulting from the differential sensitivity of behavioral and neurochemical responses to the activation by testosterone and/or its estrogenic metabolites. [less ▲]Detailed reference viewed: 19 (8 ULg)
Coordinated and dissociated effects of testosterone on singing behavior and song control nuclei in canaries (Serinus canaria)
; Balthazart, Jacques ;
in Hormones & Behavior (2005), 47(4), 467-476
Temperate zone songbirds that breed seasonally exhibit pronounced differences in reproductive behaviors including song inside and outside the breeding season. Springlike long daylengths are associated ... [more ▼]
Temperate zone songbirds that breed seasonally exhibit pronounced differences in reproductive behaviors including song inside and outside the breeding season. Springlike long daylengths are associated with increases in plasma testosterone (T) concentrations, as well as with increases in singing and in the volume of several brain nuclei known to control this behavior. The mechanisms whereby T can induce changes in behavior and brain, and whether or not these effects are differentially regulated, have recently begun to be examined, as has the question of the relative contributions of T and its androgenic and estrogenic metabolites to the regulation of this seasonal behavioral and neural plasticity. In this experiment, we examined the effects of T, 5 alpha-dihydrotestosterone, or 17 beta-estradiol treatment on castrated male canaries housed on short days and compared neural and behavioral effects in these males to similarly-housed males given only blank implants. We observed that only T treatment was effective in eliciting significant increases in singing behavior after 11 days of hormone exposure. In addition, T alone was effective in increasing the volume of a key song production nucleus, HVC. However, at this time, none of the steroids had any effects on the volumes of two other song control nuclei, Area X of the medial striatum and the robust nucleus of the arcopallium (RA), that are efferent targets of HVC, known to be regulated by androgen in canaries and also to play a role in the control of adult song. T can thus enhance singing well before concomitant androgen-induced changes in the song control system are complete. (c) 2004 Elsevier Inc. All rights reserved. [less ▲]Detailed reference viewed: 15 (0 ULg)
Brain expression of the steroid receptor coactivator SRC-1 changes during the day.
Charlier, Thierry ; ; Balthazart, Jacques
Poster (2005)Detailed reference viewed: 5 (1 ULg)
Steroid-induced plasticity in the medial preoptic nucleus, a key center for the activation of appetitive and consummatory sexual behavior in male quail
Balthazart, Jacques ; Charlier, Thierry ; et al
Conference (2005)Detailed reference viewed: 4 (2 ULg)
Rapid plasticity of the medial preoptic nucleus in male Japanese quail following testosterone treatment
Charlier, Thierry ; ; Balthazart, Jacques
Conference (2005)Detailed reference viewed: 4 (1 ULg)
Daily changes in the expression of the steroid receptor coactivator SRC-1.
Charlier, Thierry ; ; Balthazart, Jacques
in Hormones & Behavior (2005), 48
Steroid receptor coactivators such as SRC-1 significantly modulate the expression of steroid-dependent physiological and behavioral characteristics in birds and mammals. Changes in coactivator protein ... [more ▼]
Steroid receptor coactivators such as SRC-1 significantly modulate the expression of steroid-dependent physiological and behavioral characteristics in birds and mammals. Changes in coactivator protein expression are therefore likely to affect receptor-mediated transcriptional activity. We previously reported a tissue-dependent regulation of SRC-1 mRNA and protein levels by sex, stress and testosterone in the quail brain. In addition, SRC-1 expression has been shown to vary in mammals during development or in adulthood as a function of seasonal variation in photoperiod. We describe here tissue-specific changes of SRC-1 expression over the course of the day in quail. SRC-1 protein quantified by Western blots in the hindbrain gradually increased in the morning, reached a peak around midday and declined significantly in the afternoon. In contrast, SRC-1 protein levels in the optic lobes progressively decreased in the morning to reach their lowest values around midday before rising in the afternoon. The coactivator concentration in the hippocampus exhibited a progressive increase throughout the day. No change in the SRC-1 protein was detected during the day in the preoptic area and in the cerebellum. The functional significance and the mechanisms of regulation underlying such changes remain to be understood. An important unresolved question is whether this diurnal variation in SRC-1 expression is circadian in nature and if so if SRC-1 is an active player linked to clock genes in the generation of circadian rhythms or if the observed changes in SRC-1 expression are a consequence of the rhythms generated by these genes. [less ▲]Detailed reference viewed: 9 (5 ULg)
Modulation of steroid-dependent male sexual behavior and neural gene expression: A role for steroid receptor co-activators
Charlier, Thierry ; ; Balthazart, Jacques
in Trabajos del Instituto Cajal (2005), 80
One of the best-characterized actions of steroids is the regulation of brain areas involved in endocrine function and in the activation of reproductive behaviors in male and female vertebrates. Progress ... [more ▼]
One of the best-characterized actions of steroids is the regulation of brain areas involved in endocrine function and in the activation of reproductive behaviors in male and female vertebrates. Progress in the understanding of the mechanisms that control the expression of the eukaryotic genome by nuclear receptors has brought forward the importance of steroid receptor coactivators in mediating efficient gene transcription. However, little is know about the specific physiological requirements of these coactivators in vivo. In Japanese quail, testosterone treatment of castrated males restores the full copulatory behavior and increases the volume of the sexually dimorphic medial preoptic nucleus (POM) to the level observed in intact males . Testosterone also affects a number of sexually dimorphic neurochemical characteristics such as the vasotocineric innervation of the septum and meadial preoptic nucleus . The quail therefore provides an excellent model to study steroid-dependent sexual behavior and the associated neuroplasticity and should provide insights into the modulation of steroid action by steroid receptor coactivators. The present studies were focused on the steroid receptor co-activator-1 (SRC-1), which was already shown to be involved in the process of sexual differentiation of brain and behavior in rats . We first amplified by RT-PCR from quail brains a 3,411bp fragment highly homologous with the chicken (94.5%) and mammalian (70%) SRC-1 and designed digoxigenin-labeled oligonucleotides for in situ hybridization. A broad distribution of SRC-1 transcripts was observed throughout the male quail brain. A particularly dense coactivator expression was observed in limbic (e.g. POM, nucleus striae terminalis) and mesencephalic (e.g. substantia grisea centralis) nuclei associated with the control of male sexual behavior . Because male and female quail exhibit a very pronounced sexual dimorphism in the steroid-dependent mechanisms that activate male-typical copulatory behavior, we investigated the potential role of SRC-1 in the sexually differentiated responses to steroids by quantifiying the SRC-1 mRNA by real time quantitative polymerase chain reaction (qPCR) and the corresponding protein by western blot (WB). Contrary to previous results, which had identified a higher SRC-1 mRNA expression in the POM of males compared to females , we found in two separate experiments that sexually mature females had higher concentrations of SRC-1 in the preoptic area-hypothalamus (HPOA) compared to males. Additional studies should be carried out to identify the origins of this discrepancy but seasonality and time of the day when brains were collected are potentially involved. We also quantified the SRC-1 mRNA and protein in the preoptic area-hypothalamus (HPOA) of castrated males treated or not with testosterone. SRC-1 mRNA was increased by testosterone in two independent experiments but not in a third one. This difference is likely due to the differential manipulations of the birds during these experiments. Birds had been repeatedly handled to test their sexual behavior in the first experiment and we showed that stress tends to decrease the coactivator expression in the male HPOA. This interpretation is strengthened by recent work in rats indicating that stress regulates SRC-1 expression in hypothalamus and hippocampus . More surprisingly, we found a significant correlation between the expression of SRC-1 and the time of the day when birds were killed in the optic lobes, hippocampus and hindbrain. The expression of SRC-1 in the optic lobes increased throughout the day, independently of sex, testosterone treatment or stress. In the hippocampus and hindbrain, the coactivator concentration varied in opposite directions during the morning and afternoon and reached respectively its lowest or highest concentration around the middle of the day, here again independently of sex, stress and hormonal treatment. Together, these data support the idea that SRC-1 is not constitutively expressed but regulated by steroids, stress and possibly other unidentified factors. Differential controls also appear to take place in specific brain nuclei and these differential controls should be further analyzed by immunohistochemistry and in situ hybridization. A second part of our work was dedicated to the study of the physiological significance of SRC-1 whith the use of daily intra-cerebroventricular injections of modified antisense (AS) oligonucleotides (Locked nucleic acid LNA) to disrupt SRC-1 expression in the POM. AS injections significantly reduced the expression of male copulatory behavior in response to exogenous testosterone compared to control animals (Ctrl group) that received the vehicle alone or scrambled (SC) oligonucleotides. Moreover, sexual behavior was restored and even enhanced within 48 hours after interruption of AS injection (ASSC group). Western blot analysis confirmed the decrease of SRC-1 expression in AS animals and demonstrated an over-expression of the coactivator in ASSC animals. The effects of SRC-1 knock down on behavior was related to a reduced POM volume defined by Nissl-staining and aromatase immunohistochemistry. The aromatase index, indicative of the relative amount of aromatase in the POM as well as the vasotocinergic innervation of this nucleus were higher in the Ctrl group. Taken together, these findings indicate that SRC-1 functions as a critical regulatory molecule in the brain to modulate steroid-dependent gene transcription and behavior. The study of the modulation of nuclear receptors activity by different co-regulatory proteins is still in its infancy. Abnormal co-activator expression or function is currently being linked to some endocrine/neurological disorders in humans and it is thus critical to understand how co-activator expression and function are controlled in the developing as well as in the adult brain. [less ▲]Detailed reference viewed: 34 (3 ULg)