Endocrine and social regulation of adult neurogenesis in songbirds.
Balthazart, Jacques ;
in Frontiers in neuroendocrinology (2016)
The identification of pronounced seasonal changes in the volume of avian song control nuclei stimulated the discovery of adult neurogenesis in songbirds as well as renewed studies in mammals including ... [more ▼]
The identification of pronounced seasonal changes in the volume of avian song control nuclei stimulated the discovery of adult neurogenesis in songbirds as well as renewed studies in mammals including humans. Neurogenesis in songbirds is modulated by testosterone and other factors such as photoperiod, singing activity and social environment. Adult neurogenesis has been widely studied by labeling, with tritiated thymidine or its analog BrdU, cells duplicating their DNA in anticipation of their last mitotic division and following their fate as new neurons. New methods based on endogenous markers of cell cycling or of various stages of neuronal life have allowed for additional progress. In particular immunocytochemical visualization of the microtubule-associated protein doublecortin has provided an integrated view of neuronal replacement in the song control nucleus HVC. Multiple questions remain however concerning the specific steps in the neuronal life cycle that are modulated by various factors and the underlying cellular mechanisms. [less ▲]Detailed reference viewed: 36 (5 ULg)
Seasonal changes in the neuroendocrine system: Introduction to the special issue.
; Balthazart, Jacques
in Frontiers in neuroendocrinology (2015), 37Detailed reference viewed: 21 (2 ULg)
Developmental variations in environmental influences including endocrine disruptors on pubertal timing and neuroendocrine control: Revision of human observations and mechanistic insight from rodents
Parent, Anne-Simone ; Franssen, Delphine ; FUDVOYE, Julie et al
in Frontiers in Neuroendocrinology (2015)Detailed reference viewed: 154 (19 ULg)
Policy decisions on endocrine disruptors should be based on science across disciplines: A response to Dietrich, et al.
; Balthazart, Jacques ; et al
in Frontiers in neuroendocrinology (2014), 35(1), 2-5Detailed reference viewed: 61 (7 ULg)
Endocrine disruptors: A relevant issue for neuroendocrinology also!
Balthazart, Jacques ;
in Frontiers in neuroendocrinology (2014), 35(1), 1Detailed reference viewed: 15 (3 ULg)
Roles of sex and gonadal steroids in mammalian pheromonal communication.
; Bakker, Julie
in Frontiers in neuroendocrinology (2013), 34(4), 268-84
A brain circuit (the accessory olfactory system) that originates in the vomeronasal organ (VNO) and includes the accessory olfactory bulb (AOB) plus additional forebrain regions mediates many of the ... [more ▼]
A brain circuit (the accessory olfactory system) that originates in the vomeronasal organ (VNO) and includes the accessory olfactory bulb (AOB) plus additional forebrain regions mediates many of the effects of pheromones, typically comprised of a variety of non-volatile and volatile compounds, on aspects of social behavior. A second, parallel circuit (the main olfactory system) that originates in the main olfactory epithelium (MOE) and includes the main olfactory bulb (MOB) has also been shown to detect volatile pheromones from conspecifics. Studies are reviewed that point to specific roles of several different steroids and their water-soluble metabolites as putative pheromones. Other studies are reviewed that establish an adult, 'activational' role of circulating sex hormones along with sex differences in the detection and/or processing of non-steroidal pheromones by these two olfactory circuits. Persisting questions about the role of sex steroids in pheromonal processing are posed for future investigation. [less ▲]Detailed reference viewed: 22 (0 ULg)
Rapid control of male typical behaviors by brain-derived estrogens
Cornil, Charlotte ; ; Balthazart, Jacques
in Frontiers in Neuroendocrinology (2012)
Beside their genomic mode of action, estrogens also activate a variety of cellular signaling pathways through non-genomic mechanisms. Until recently, little was known regarding the functional significance ... [more ▼]
Beside their genomic mode of action, estrogens also activate a variety of cellular signaling pathways through non-genomic mechanisms. Until recently, little was known regarding the functional significance of such actions in males and the mechanism that control local estrogen concentration with a spatial and time resolution compatible with these non-genomic actions had rarely been examined. Here, we review evidence that estrogens rapidly modulate a variety of behaviors in male vertebrates. Then, we present in vitro work supporting the existence of a control mechanism of local brain estrogen synthesis by aromatase along with in vivo evidence that rapid changes in aromatase activity also occur in a region-specific manner in response to changes in the social or environmental context. Finally, we suggest that the brain estrogen provision may also play a significant role in females. Together these data bolster the hypothesis that brain-derived estrogens should be considered as neuromodulators. [less ▲]Detailed reference viewed: 49 (7 ULg)
Sexual differentiation of sexual behavior and its orientation.
; Balthazart, Jacques
in Frontiers in Neuroendocrinology (2011), 32(2), 109Detailed reference viewed: 54 (10 ULg)
Steroids and neuroprotection: New advances.
; Balthazart, Jacques
in Frontiers in Neuroendocrinology (2009), 30(2), -
Gonadal hormones exert neuroprotective actions. In addition, it has become evident that the local synthesis of these molecules in the central nervous system may prevent or reduce neurodegeneration.The ... [more ▼]
Gonadal hormones exert neuroprotective actions. In addition, it has become evident that the local synthesis of these molecules in the central nervous system may prevent or reduce neurodegeneration.The neuroprotective actions of steroids involve neurons, glial cells and blood vessels, are exerted via steroid receptor signaling initiated at the nuclear or membrane level and steroid receptor independent mechanisms. They include the regulation of phosphatases and kinases and the regulation of the expression of molecules controlling inflammation and apoptosis. In addition, mitochondria have emerged as new central targets for neuroprotective actions of steroids. These neuroprotective actions have been documented in different experimental models of neurological alterations, including motoneuron injury, Parkinson's disease, traumatic brain injury, multiple sclerosis, stroke and Alzheimer's disease. In addition, steroids promote serotonergic neuronal function and protect against affective disorders. This special issue of Frontiers in Neuroendocrinology contains a collection of reviews of the most recent ideas and findings on these various aspects of sex steroid-dependent neuroprotection [less ▲]Detailed reference viewed: 153 (2 ULg)
Who's in charge? Nuclear receptor coactivator and corepressor function in brain and behavior.
; ; Charlier, Thierry
in Frontiers in Neuroendocrinology (2009), 30
Steroid hormones act in brain and throughout the body to regulate a variety of functions, including development, reproduction, stress and behavior. Many of these effects of steroid hormones are mediated ... [more ▼]
Steroid hormones act in brain and throughout the body to regulate a variety of functions, including development, reproduction, stress and behavior. Many of these effects of steroid hormones are mediated by their respective receptors, which are members of the steroid/nuclear receptor superfamily of transcriptional activators. A variety of studies in cell lines reveal that nuclear receptor coregulators are critical in modulating steroid receptor-dependent transcription. Thus, in addition to the availability of the hormone and the expression of its receptor, nuclear receptor coregulators are essential for efficient steroid-dependent transactivation of genes. This review will highlight the importance of nuclear receptor coregulators in modulating steroid-dependent gene expression in brain and the regulation of behavior. [less ▲]Detailed reference viewed: 37 (3 ULg)
Role for Estradiol in Female-Typical Brain and Behavioral Sexual Differentiation
Bakker, Julie ;
in Frontiers in Neuroendocrinology (2008), 29(1), 1-16
The importance of estrogens in controlling brain and behavioral sexual differentiation in female rodents is an unresolved issue in the field of behavioral neuroendocrinology. Whereas, the current dogma ... [more ▼]
The importance of estrogens in controlling brain and behavioral sexual differentiation in female rodents is an unresolved issue in the field of behavioral neuroendocrinology. Whereas, the current dogma states that the female brain develops independently of estradiol, many studies have hinted at possible roles of estrogen in female sexual differentiation. Accordingly, it has been proposed that alpha-fetoprotein, a fetal plasma protein that binds estrogens with high affinity, has more than a neuroprotective role and specifically delivers estrogens to target brain cells to ensure female differentiation. Here, we review new results obtained in aromatase and alpha-fetoprotein knockout mice showing that estrogens can have both feminizing and defeminizing effects on the developing neural mechanisms that control sexual behavior. We propose that the defeminizing action of estradiol normally occurs prenatally in males and is avoided in fetal females because of the protective actions of alpha-fetoprotein, whereas the feminizing action of estradiol normally occurs postnatally in genetic females. [less ▲]Detailed reference viewed: 31 (0 ULg)
Novel mechanisms for neuroendocrine regulation of aggression.
; ; et al
in Frontiers in Neuroendocrinology (2008), 29(4), 476-89
In 1849, Berthold demonstrated that testicular secretions are necessary for aggressive behavior in roosters. Since then, research on the neuroendocrinology of aggression has been dominated by the paradigm ... [more ▼]
In 1849, Berthold demonstrated that testicular secretions are necessary for aggressive behavior in roosters. Since then, research on the neuroendocrinology of aggression has been dominated by the paradigm that the brain receives gonadal hormones, primarily testosterone, which modulate relevant neural circuits. While this paradigm has been extremely useful, recent studies reveal important alternatives. For example, most vertebrate species are seasonal breeders, and many species show aggression outside of the breeding season, when gonads are regressed and circulating testosterone levels are typically low. Studies in birds and mammals suggest that an adrenal androgen precursor-dehydroepiandrosterone (DHEA)-may be important for the expression of aggression when gonadal testosterone synthesis is low. Circulating DHEA can be metabolized into active sex steroids within the brain. Another possibility is that the brain can autonomously synthesize sex steroids de novo from cholesterol, thereby uncoupling brain steroid levels from circulating steroid levels. These alternative neuroendocrine mechanisms to provide sex steroids to specific neural circuits may have evolved to avoid the "costs" of high circulating testosterone during particular seasons. Physiological indicators of season (e.g., melatonin) may allow animals to switch from one neuroendocrine mechanism to another across the year. Such mechanisms may be important for the control of aggression in many vertebrate species, including humans. [less ▲]Detailed reference viewed: 59 (2 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: 68 (1 ULg)
Neuroendocrinology of song behavior and avian brain plasticity: Multiple sites of action of sex steroid hormones
; ; Balthazart, Jacques
in Frontiers in Neuroendocrinology (2002), 23(2), 137-178
Seasonal changes in the brain of songbirds are one of the most dramatic examples of naturally occuring neuroplasticity that have been described in any vertebrate species. In males of temperate-zone ... [more ▼]
Seasonal changes in the brain of songbirds are one of the most dramatic examples of naturally occuring neuroplasticity that have been described in any vertebrate species. In males of temperate-zone songbird species, the volumes of several telencephalic nuclei that control song behavior are significantly larger in the spring than in the fall. These increases in volume are correlated with high rates of singing and high concentrations of testosterone in the plasma. Several song nuclei express either androgen receptors or estrogen receptors, therefore it is possible that testosterone acting via estrogenic or androgenic metabolites regulates song behavior by seasonally modulating the morphology of these song control nuclei. However, the causal links among these variables have not been established. Dissociations among high concentrations of testosterone, enlarged song nuclei, and high rates of singing behavior have been observed. Singing behavior itself can promote cellular changes associated with increases in the volume of the song control nuclei. Also, testosterone may stimulate song behavior by acting in brain regions outside of the song control system such as in the preoptic area or in catecholamine cell groups in the brainstem. Thus testosterone effects on neuroplasticity in the song system may be indirect in that behavioral activity stimulated by testosterone acting in sites that promote male sexual behavior could in turn promote morphological changes in the song system. (C) 2002 Elsevier Science (USA). [less ▲]Detailed reference viewed: 27 (0 ULg)
Neuroendocrine regulation of GnRH release in induced ovulators.
Bakker, Julie ;
in Frontiers in Neuroendocrinology (2000), 21(3), 220-62
GnRH is the key neuropeptide controlling reproductive function in all vertebrate species. Two different neuroendocrine mechanisms have evolved among female mammals to regulate the mediobasal hypothalamic ... [more ▼]
GnRH is the key neuropeptide controlling reproductive function in all vertebrate species. Two different neuroendocrine mechanisms have evolved among female mammals to regulate the mediobasal hypothalamic (MBH) release of GnRH leading to the preovulatory secretion of LH by the anterior pituitary gland. In females of spontaneously ovulating species, including rats, mice, guinea pigs, sheep, monkeys, and women, ovarian steroids secreted by maturing ovarian follicles induce a pulsatile pattern of GnRH release in the median eminence that, in turn, stimulates a preovulatory LH surge. In females of induced ovulating species, including rabbits, ferrets, cats, and camels, the preovulatory release of GnRH, and the resultant preovulatory LH surge, is induced by the receipt of genital somatosensory stimuli during mating. Induced ovulators generally do not show "spontaneous" steroid-induced LH surges during their reproductive cycles, suggesting that the positive feedback actions of steroid hormones on GnRH release are reduced or absent in these species. By contrast, mating-induced preovulatory surges occasionally occur in some spontaneously ovulating species. Most research in the field of GnRH neurobiology has been performed using spontaneous ovulators including rat, guinea pig, sheep, and rhesus monkey. This review summarizes the literature concerning the neuroendocrine mechanisms controlling GnRH biosynthesis and release in females of several induced ovulating species, and whenever possible it contrasts the results with those obtained for spontaneously ovulating species. It also considers the adaptive, evolutionary benefits and disadvantages of each type of ovulatory control mechanism. In females of induced ovulating species estradiol acts in the brain to induce aspects of proceptive and receptive sexual behavior. The primary mechanism involved in the preovulatory release of GnRH among induced ovulators involves the activation of midbrain and brainstem noradrenergic neurons in response to genital-somatosensory signals generated by receipt of an intromission from a male during mating. These noradrenergic neurons project to the MBH and, when activated, promote the release of GnRH from nerve terminals in the median eminence. In contrast to spontaneous ovulators, there is little evidence that endogenous opioid peptides normally inhibit MBH GnRH release among induced ovulators. Instead, the neural signals that induce a preovulatory LH surge in these species seem to be primarily excitatory. A complete understanding of the neuroendocrine control of ovulation will only be achieved in the future by comparative studies of several animal model systems in which mating-induced as well as spontaneous, hormonally stimulated activation of GnRH neurons drives the preovulatory LH surge. [less ▲]Detailed reference viewed: 23 (4 ULg)