Jacques Balthazart

Jacques Balthazart
University of Liège | ulg · GIGA-Neurosciences Unit

PhD (Zoology)

About

576
Publications
34,774
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Introduction
My research concerns the neuroendocrine and neurobiological bases of complex behaviours, using steroid-dependent male sexual behaviors as a model system. It is bridging various disciplines ranging from animal behavior to neuroendocrinology and molecular biology.
Additional affiliations
January 2011 - present
Oregon Health and Science University
January 2010 - present
January 2009 - present

Publications

Publications (576)
Article
Temperate-zone birds display marked seasonal changes in reproductive behaviors and the underlying hormonal and neural mechanisms. These changes were extensively studied in canaries (Serinus canaria) but differ between strains. Fife fancy male canaries change their reproductive physiology in response to variations in day length but it remains unclea...
Article
Adult treatments with testosterone (T) do not activate singing behavior nor promote growth of song control nuclei to the same extent in male and female canaries (Serinus canaria). Because T acts in part via aromatization into an estrogen and brain aromatase activity is lower in females than in males in many vertebrates, we hypothesized that this en...
Article
The avian homologue of oxytocin (OT), formerly called mesotocin, influences social behaviors in songbirds and potentially song production. We sought to characterize the distribution of OT peptide in the brain of two songbird species: canaries (Serinus canaria) and zebra finches (Taeniopygia guttata). To visualize OT, we performed immunocytochemistr...
Article
In male Japanese quail, brain aromatase is crucial for the hormonal activation of sexual behavior, but the sites producing neuro‐estrogens critical for these behaviors have not been completely identified. This study examined the function of aromatase expressed in several nuclei of the social behavior network on a measure of sexual motivation known...
Chapter
This chapter presents in a synthetic manner, the wealth of information that has accumulated primarly in the past 50–60 years concerning the mechanisms through which hormones modulate behaviors. It provides an introduction on how hormones are able to affect brain activity in relation to the control of behaviour, and describes the major concepts that...
Article
Full-text available
Classically, estrogens regulate male sexual behavior through effects initiated in the nucleus. However, neuroestrogens, i.e., estrogens locally produced in the brain, can act within minutes via membrane-initiated events. In male quail, rapid changes in brain aromatase activity occur after exposure to sexual stimuli. We report here that local extrac...
Article
It was assumed for a long time that sex steroids are activating reproductive behaviors by the same mechanisms that produce their morphological and physiological effects in the periphery. However during the last few decades an increasing number of examples were identified where behavioral effects of steroids were just too fast to be mediated via cha...
Article
Full-text available
Songbirds learn their vocalizations during developmental sensitive periods of song memorization and sensorimotor learning. Some seasonal songbirds, called open-ended learners, recapitulate transitions from sensorimotor learning and song crystallization on a seasonal basis during adulthood. In adult male canaries, sensorimotor learning occurs each y...
Article
A new study employing viral targeting techniques has identified excitatory and inhibitory cell groups in the songbird auditory forebrain that exhibit properties remarkably similar to those in the mammalian cortex. This network contributes to the neural substrate mediating sophisticated cognition in birds.
Preprint
Full-text available
Songbirds learn their vocalizations during sensitive periods of song memorization and sensorimotor learning during development. Some seasonal songbirds, called open-ended learners, recapitulate transitions from sensorimotor learning and song crystallization on a seasonal basis during adulthood. In adult male canaries, sensorimotor learning occurs e...
Article
Numerous studies have evaluated changes in time of testicular development in birds by exploratory laparotomy or post-mortem autopsy. The invasive nature of these approaches has obviously limited the frequency at which these measures can be collected. We demonstrate here that accurate assessment of gonadal size can be reliably and repeatedly obtaine...
Article
Aromatase converts androgens into estrogens in the brain of vertebrates including humans. This enzyme is also expressed in other tissues where its action may result in negative effects on human health (e.g., promotion of tumor growth). To prevent these effects, aromatase inhibitors were developed and are currently used to block human estrogen-depen...
Article
Full-text available
Song learning in zebra finches ( Taeniopygia guttata ) is a prototypical example of a complex learned behavior, yet knowledge of the underlying molecular processes is limited. Therefore, we characterized transcriptomic (RNA-sequencing) and epigenomic (RRBS, reduced representation bisulfite sequencing; immunofluorescence) dynamics in matched zebra f...
Article
In latitudinal avian migrants, increasing photoperiods induce fat deposition and body mass increase, and subsequent nighttime migratory restlessness in captive birds, but the underlying mechanisms remain poorly understood. We hypothesized that an enhanced hypothalamic neuronal plasticity was associated with the photostimulated spring migration phen...
Article
Male canaries (Serinus canaria) display seasonal changes in the motivation to sing which have been found to be dependent on the action of testosterone (T). During the breeding season when T is high, males sing at a higher rate compared with males with low T. The effect of T on song rate is known to be mediated by the medial preoptic nucleus (POM);...
Article
Estrogens play a key role in the sexual differentiation of the brain and behavior. While early estrogen actions exert masculinizing effects on the male brain of rodents, a diametrically opposite effect is observed in birds where estrogens demasculinize the female brain. Yet, the two vertebrate classes express similar sex differences in the brain an...
Article
In the 1970s, Nottebohm and Arnold reported marked male-biased sex differences in the volume of three song control nuclei in songbirds. Subsequently a series of studies on several songbird species suggested that there is a positive correlation between the degree to which there is a sex difference in the volume of these song control nuclei and in so...
Article
BALTHAZART J. Sex partner preference in animals and humans. NEUROSCI BIOBEHV REV XX (Y) ZZZ-KKK, 2020. aaaaaaaaaa Sex differences in brain and behavior of animals including humans result from an interaction between biological and environmental influences. This is also true for the differences between men and women concerning sexual orientation. Sex...
Article
Testosterone aromatization into estrogens in the preoptic area (POA) is critical for the activation of male sexual behavior in many vertebrates. Yet, cellular mechanisms mediating actions of neuroestrogens on sexual behavior remain largely unknown. We investigated in male and female Japanese quail by dual‐label fluorescent in situ hybridization (FI...
Article
Full-text available
Songbirds are a powerful model to study vocal learning given that aspects of the underlying behavioral and neurobiological mechanisms are analogous in many ways to mechanisms involved in speech learning. Perineuronal nets (PNNs) represent one of the mechanisms controlling the closing of sensitive periods for vocal learning in the songbird brain. In...
Article
Development of the songbird brain provides an excellent experimental model for understanding the regulation of sex differences in ontogeny. Considering the regulatory role of the hypothalamus in endocrine, in particular reproductive, physiology, we measured the structural (volume) and molecular correlates of hypothalamic development during ontogeny...
Article
The first issue of Hormones and Behavior was published 50 years ago in 1969, a time when most of the techniques we currently use in Behavioral Endocrinology were not available. Researchers have during the last 5 decades developed techniques that allow measuring hormones in small volumes of biological samples, identify the sites where steroids act i...
Article
Songbirds learn their song during a sensitive period of development associated with enhanced neural plasticity. In addition, in open-ended learners such as canaries, a sensitive period for sensorimotor vocal learning reopens each year in the fall and leads to song modifications between successive breeding seasons. The variability observed in song p...
Article
Perineuronal nets (PNN) of the extracellular matrix are dense aggregations of chondroitin-sulfate proteoglycans that usually surround fast-spiking parvalbumin-expressing inhibitory interneurons (PV). The development of PNN around PV appears specifically at the end of sensitive periods of visual learning and limits the synaptic plasticity in the vis...
Article
Brood parasitic songbirds are a natural system in which developing birds are isolated from species-typical song and therefore present a unique opportunity to compare neural plasticity in song learners raised with and without conspecific tutors. We compared perineuronal nets (PNN) and parvalbumin (PV) in song control nuclei in juveniles and adults o...
Article
Adult neuroplasticity in the song control system of seasonal songbirds is largely driven by photoperiod-induced increases in testosterone. Prior studies of the relationships between testosterone, song performance and neuroplasticity used invasive techniques, which prevent analyzing the dynamic changes over time and often focus on pre-defined region...
Article
In male songbirds, song functions to attract a mate or to defend a territory; it is therefore often produced in the context of reproduction. Testosterone of gonadal origin increases during the reproductive phase of the annual cycle and significantly enhances song production as well as song development via effects on song crystallization. The neural...
Article
The authors of the original challenge hypothesis proposed influential hypotheses concerning the relationship between testosterone concentrations in the blood and aggressive social behaviors. Many of the key observations were made in avian species studied in the wild and in captivity. In this review we evaluate some remaining questions about the ide...
Article
Since the beginning of this century, research methods in neuroendocrinology enjoyed extensive refinements and innovation. These advances allowed collection of huge amounts of new data and the development of new ideas but have not led to this point, with a few exceptions, to the development of new conceptual advances. Conceptual advances that took p...
Article
Full-text available
In male songbirds, the motivation to sing is largely regulated by testosterone (T) action in the medial preoptic area, whereas T acts on song control nuclei to modulate aspects of song quality. Stereotaxic implantation of T in the medial preoptic nucleus (POM) of castrated male canaries activates a high rate of singing activity, albeit with a longe...
Article
Aromatization within the medial preoptic nucleus (POM) is essential for the expression of male copulatory behavior in Japanese quail. However, several nuclei within the social behavior network (SBN) also express aromatase. Whether aromatase in these loci participates in the behavioral activation is not known. Castrated male Japanese quail were impl...
Article
Testosterone activates singing within days in castrated male songbirds but full song quality only develops after a few weeks. Lesions of the medial preoptic nucleus (POM) inhibit while stereotaxic testosterone implants into this nucleus increase singing rate suggesting that this site plays a key role in the regulation of singing motivation. Testost...
Article
Full-text available
Both systemic and local production contribute to the concentration of steroids measured in the brain. This idea was originally based on rodent studies and was later extended to other species including humans and birds. In quail, a widely used model in behavioral neuroendocrinology, it was demonstrated that all enzymes needed to produce sex steroids...
Article
This study was designed to determine whether changes in sexual motivation acutely regulate brain estrogen synthesis by aromatase. Five experiments (Exp.1–5) were first conducted to determine the effect of recent mating and of the presentation of a new female (Coolidge effect) on sexual motivation. Exp.1–2 showed that 10 min or overnight access to c...
Article
The appearance of perineuronal nets (PNNs) represents one of the mechanisms that contribute to the closing of sensitive periods for neural plasticity. This relationship has mostly been studied in the ocular dominance model in rodents. Previous studies also indicated that PNN might control neural plasticity in the song control system of songbirds. T...
Article
In seasonally breeding songbirds such as canaries, singing behavior is predominantly under the control of testosterone and its metabolites. Short daylenths in the fall that break photorefractoriness are followed by increasing daylengths in spring that activate singing via both photoperiodic and hormonal mechanisms. However, we observed in a group o...
Article
Sex steroid hormones act during early development to shape the circuitry upon which these same hormones act in adulthood to control behavioral responses to various stimuli. The "organizational" vs. "activational" distinction was proposed to explain this temporal difference in hormone action. In both of these cases steroids were thought to act genom...
Article
This review introduces functional MRI (fMRI) as an outstanding tool to assess rapid effects of sex steroids on auditory processing in seasonal songbirds. We emphasize specific advantages of this method as compared to other more conventional and invasive methods used for this purpose and summarize an exemplary auditory fMRI study performed on male s...
Article
Estrogens exert pleiotropic effects on multiple physiological and behavioral traits including sexual behavior. These effects are classically mediated via binding to nuclear receptors and subsequent regulation of target gene transcription. Estrogens also affect neuronal activity and cell-signaling pathways via faster, membrane-initiated events. Alth...
Article
This brief commentary reviews key steps in the history of endocrinology that have resulted in important conceptual shifts. Our understanding of the "Fast Effects of Steroids" has now made substantial progress, including the major concept that steroids act rapidly on a variety of physiological and behavioral responses, via mechanisms that are too fa...
Article
In male quail, estrogens produced in the brain (neuroestrogens) exert a dual action on male sexual behavior: they increase sexual motivation within minutes via mechanisms activated at the membrane but facilitate sexual performance by slower, presumably nuclear-initiated, mechanisms. Recent work indicates that neuroestrogens are also implicated in t...
Article
Full-text available
The neural basis of how learned vocalizations change during development and in adulthood represents a major challenge facing cognitive neuroscience. This plasticity in the degree to which learned vocalizations can change in both humans and songbirds is linked to the actions of sex steroid hormones during ontogeny but also in adulthood in the contex...
Article
Since Arnold Adolph Berthold established in 1849 the critical role of the testes in the activation of male sexual behavior, intensive research has identified many sophisticated neurochemical and molecular mechanisms mediating this action. Studies in Japanese quail demonstrated the critical role of testosterone action and of testosterone aromatizati...
Article
It is increasingly recognized that brain-derived estrogens (neuroestrogens) can regulate brain physiology and behavior much faster than what was previously known from the transcriptional action of estrogens on nuclear receptors. One of the best examples of such neuromodulation by neuroestrogens concerns the acute regulation of sensory coding by the...
Chapter
This chapter will focus on how brain and behavior can change with season. Given the breadth of the topic, we will focus on prominent examples discerned from studies of birds though other vertebrate species will be discussed. The chapter will begin with a general discussion of the environmental control of seasonal changes in brain and behavior. We w...
Article
Perineuronal nets (PNN) are aggregations of chondroitin sulfate proteoglycans surrounding the soma and proximal processes of neurons, mostly GABAergic interneurons expressing parvalbumin. They limit the plasticity of their afferent synaptic connections. In zebra finches PNN develop in an experience-dependent manner in the song control nuclei HVC an...
Article
Estrogens are known to act rapidly, probably via membrane estrogen receptors, to induce fast effects on physiological and behavioral processes. Engaging in some of these behaviors, such as sexual behavior, results in an acute modulation of the production of estrogens in the brain by regulating the efficiency of the estrogen synthase enzyme, aromata...
Article
Full-text available
In songbirds, neurogenesis in the song control nucleus HVC is sensitive to the hormonal and social environment but the dynamics of this process is difficult to assess with a single exogenous marker of new neurons. We simultaneously used three independent markers to investigate HVC neurogenesis in male and female canaries. Males were castrated, impl...
Article
Testosterone plays a key role in the control of seasonal changes in singing behavior and its underlying neural circuitry. After administration of exogenous testosterone, song quality and song control nuclei volumes change over the course of weeks, but song rate increases within days. The medial preoptic nucleus (POM) controls sexual motivation and...
Article
The zebra finch (Taeniopygia guttata) song control system consists of several series of interconnected brain nuclei that undergo marked changes during ontogeny and sexual development, making it an excellent model to study developmental neuroplasticity. Despite the demonstrated influence of hormones such as sex steroids on this phenomenon, thyroid h...
Chapter
The brains of some birds contain the most striking structural sex differences yet observed in any vertebrates. Birds are also famous for sex differences in behavior, including sexual behavior and singing. Some of these result from differential activation by sex steroids in adulthood. Others are due to long-lasting (permanent) organizational effects...
Chapter
This chapter reviews the neural and endocrine bases of reproductive behaviors in birds with a particular focus on the role played by gonadal sex steroid hormones in the regulation of sexual behaviors. Studies of birds continue to be valuable for the elucidation of the neuroendocrine control of behavior. The avian brain also exhibits a remarkable de...
Article
Full-text available
During sociosexual encounters, different brain mechanisms interact to orchestrate information about the salience of external stimuli along with the current physiological and environmental conditions in order to process these in an optimal manner. One candidate neural system involves the potential interplay between the medial preoptic nucleus (POM)...
Article
The functions of birdsong include attracting a mate and repelling competitors. It is therefore not surprising that, in males in the temperate zone especially, birdsong is often produced in the context of reproduction. Testosterone of gonadal origin increases during the reproductive phase of the annual cycle and can significantly influence song prod...
Article
Full-text available
Recent evidence has implicated steroid hormones, specifically estrogens, in the rapid modulation of cognitive processes. Songbirds have been a useful model system in the study of complex cognitive processes including birdsong, a naturally learned vocal behavior regulated by a discrete steroid sensitive telencephalic circuitry. Singing behavior is k...
Article
Although aromatase is expressed in both male and female brains, its functional significance in females remains poorly understood. In female quail, sexual receptivity is activated by estrogens. However it is not known whether sexual motivation is similarly estrogen-dependent and whether estrogens locally produced in the brain contribute to these beh...
Article
Full-text available
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...
Article
A large number of morphological, physiological and behavioural traits are differentially expressed by males and females in all vertebrates including humans. These sex differences, sometimes, reflect the different hormonal environment of the adults, but they often remain present after subjects of both sexes are placed in the same endocrine condition...
Article
Full-text available
Steroid hormones coordinate multiple aspects of behavior and physiology. The same hormone often regulates different aspects of a single behavior and its underlying neuroplasticity. This pleiotropic regulation of behavior and physiology is not well understood. Here, we investigated the orchestration by testosterone (T) of birdsong and its neural sub...
Chapter
Full-text available
We summarize here the current knowledge on the biological and neurophysiological mechanisms that control the selection of a suitable sexual partner, and the formation and maintenance of a more or less long-lasting pair bond with this partner in socially monogamous species. These aspects of sexual reproduction have always been of great interest to t...
Article
Estradiol (E2) can act in the brain in a relatively fast manner (i.e., seconds to minutes) usually through signaling initiated at the cell membrane. Brain-derived E2 has thus been considered as another type of neurotransmitter. Recent work found that behaviors indicative of male sexual motivation are activated by estrogenic metabolites of testoster...
Article
Full-text available
Large morphological sex differences in the vertebrate brain were initially identified in song control nuclei of oscines. Besides gross differences between volumes of nuclei in males and females, sex differences also concern the size and dendritic arborization of neurons and various neurochemical markers, such as the calcium-binding protein parvalbu...
Article
Full-text available
In canaries, specific phrases of male song (sexy songs, SS) that are difficult to produce are especially attractive for females. Females exposed to SS produce more copulation displays and deposit more testosterone into their eggs than females exposed to non-sexy songs (NS). Increased expression of the immediate early genes c-Fos or zenk (a.k.a. egr...
Article
Full-text available
Estrogens can induce rapid, short-lived physiological and behavioral responses, in addition to their slow, but long-term, effects at the transcriptional level. To be functionally relevant, these effects should be associated with rapid modulations of estrogens concentrations. 17β-estradiol is synthesized by the enzyme aromatase, using testosterone a...
Article
Although the existence of newborn neurons had originally been suggested, but not broadly accepted, based on studies in adult rodent brains, the presence of an active neurogenesis process in adult homoeothermic vertebrates was first firmly established in songbirds. Adult neurogenesis was initially studied with the tritiated thymidine technique, late...