Immediate early gene activity in song control nuclei and brain areas regulating motivation relates positively to singing behavior during, but not outside of, a breeding context

Brain Gene Regulatory Networks Coordinate Nest Construction in Birds

Nest building is a vital behavior exhibited during breeding in birds, and is possibly induced by environmental and social cues. Although such behavioral plasticity has been hypothesized to be controlled by adult neuronal plasticity, empirical evidence, especially at the neurogenomic level, remains limited. Here, we aim to uncover the gene regulatory networks that govern avian nest construction and examine whether they are associated with circuit rewiring. We designed an experiment to dissect this complex behavior into components in response to pair bonding and nest material acquisition by manipulating the presence of mates and nest materials in 30 pairs of zebra finches. Whole-transcriptome analysis of 300 samples from five brain regions linked to avian nesting behaviors revealed nesting-associated gene expression enriched with neural rewiring functions, including neurogenesis and neuron projection. The enriched expression was observed in the motor/sensorimotor and social behavior networks of female finches, and in the dopaminergic reward system of males. Female birds exhibited predominant neurotranscriptomic changes to initiate the nesting stage, while males showed major changes after entering this stage, underscoring sex-specific roles in nesting behavior. Notably, major neurotranscriptomic changes occurred during pair bonding, with minor changes during nest material acquisition, emphasizing social interactions in nest construction. We also revealed gene expression associated with reproductive behaviors and tactile sensing for nesting behavior. This study presents novel neurogenomic evidence supporting the hypothesis of adult neural plasticity underlying avian nest-construction behavior. By uncovering the genetic toolkits involved, we offer novel insights into the evolution of animals' innate ability to construct nests.

Distinct patterns of activity within columns of the periaqueductal gray are associated with functionally distinct birdsongs

Male songbirds produce female-directed songs in spring that convey a state of sexual motivation. Many songbirds also sing in fall flocks in affiliative/gregarious contexts in which song is linked to an intrinsic positive affective state. The periaqueductal gray (PAG) in mammals, which is organized into functional columns, integrates information from multiple brain regions and relays this information to vocal motor areas so that an animal emits a vocal signal reflective of its affective state. Here, we test the hypothesis that distinct columns in the songbird PAG play roles in the distinct affective states communicated by sexually motivated and gregarious song. We quantified the numbers of immediate early gene ZENK-positive cells in 16 PAG subregions in male European starlings (Sturnus vulgaris) after singing gregarious or sexually motivated song. Results suggest that distinct PAG columns in songbirds context-specifically regulate song, agonistic, and courtship behaviors. A second exploratory, functional tract-tracing study also demonstrated that inputs to the PAG from specific subregions of the medial preoptic nucleus may contribute to gregarious song and behaviors indicative of social dominance. Together, findings suggest that conserved PAG columns and inputs from the preoptic nucleus may play a role in context-specific vocal and other social behaviors.

Context-dependent activation of a social behavior brain network during learned vocal production

Neural activation in brain regions for vocal control is social context dependent. This context-dependent brain activation reflects social context-appropriate vocal behavior but has unresolved mechanisms. Studies of non-vocal social behaviors in multiple organisms suggest a functional role for several evolutionarily conserved and highly interconnected brain regions. Here, we use neural activity-dependent gene expression to evaluate the functional connectivity of this social behavior network within zebra finches in non-social and social singing contexts. We found that activity in one social behavior network region, the medial preoptic area (POM), was strongly associated with the amount of non-social undirected singing in zebra finches. In addition, in all regions of the social behavior network and the paraventricular nucleus (PVN), a higher percentage of EGR1 expression was observed during a social female-directed singing context compared to a non-social undirected singing context. Furthermore, we observed distinct patterns of significantly correlated activity between regions of the social behavior network during non-social undirected and social female-directed singing. Our results suggest that non-social vs. social contexts differentially activate this social behavior network and PVN. Moreover, neuronal activity within this social behavior network, PVN, and POM may alter context-appropriate vocal production.

Dehydroepiandrosterone (DHEA) increases undirected singing behavior and alters dopaminergic regulation of undirected song in non-breeding male European starlings (Sturnus vulgaris)

Introduction

It has been proposed that in species that defend territories across multiple life history stages, brain metabolism of adrenal dehydroepiandrosterone (DHEA) regulates aggressive behavior at times when gonadal androgen synthesis is low (i.e. the non-breeding season). To date, a role for DHEA in the regulation of other forms of social behavior that are expressed outside of the context of breeding remains unknown.

Methods

In this experiment, we used the European starling (Sturnus vulgaris) model system to investigate a role for DHEA in the neuroendocrine regulation of singing behavior by males in non-breeding condition. Starling song in a non-breeding context is spontaneous, not directed towards conspecifics, and functions to maintain cohesion of overwintering flocks.

Results

Using within-subjects design, we found that DHEA implants significantly increase undirected singing behavior by non-breeding condition male starlings. Given that DHEA is known to modulate multiple neurotransmitter systems including dopamine (DA) and DA regulates undirected song, we subsequently used immunohistochemistry for phosphorylated tyrosine hydroxylase (pTH, the active form of the rate-limiting enzyme in DA synthesis) to investigate the effect of DHEA on dopaminergic regulation of singing behavior in a non-breeding context. Pearson correlation analysis revealed a positive linear association between undirected singing behavior and pTH immunoreactivity in the ventral tegmental area and midbrain central gray of DHEA-implanted, but not control-implanted, males.

Discussion

Taken together, these data suggest that undirected singing behavior by non-breeding starlings is modulated by effects of DHEA on dopaminergic neurotransmission. More broadly, these data expand the social behavior functions of DHEA beyond territorial aggression to include undirected, affiliative social communication.

Context-dependent activation of a social behavior brain network associates with learned vocal production

In zebra finches, an avian brain network for vocal control undergoes context-dependent patterning of song-dependent activation. Previous studies in zebra finches also implicate the importance of dopaminergic input in producing context-appropriate singing behavior. In mice, it has been shown that oxytocinergic neurons originated in the paraventricular nucleus of the hypothalamus (PVN) synapse directly onto dopamine neurons in the ventral tegmental area (VTA), implicating the necessity of oxytocin signaling from the PVN for producing a context-appropriate song. Both avian and non-avian axonal tract-tracing studies indicate high levels of PVN innervation by the social behavior network. Here, we hypothesize that the motivation for PVN oxytocin neurons to trigger dopamine release originates in the social behavior network, a highly conserved and interconnected collection of six regions implicated in various social and homeostatic behaviors. We found that expression of the neuronal activity marker EGR1 was not strongly correlated with song production in any of the regions of the social behavior network. However, when EGR1 expression levels were normalized to the singing rate, we found significantly higher levels of expression in the social behavior network regions except the medial preoptic area during a social female-directed singing context compared to a non-social undirected singing context. Our results suggest neuronal activity within the male zebra finch social behavior network influences the synaptic release of oxytocin from PVN onto dopaminergic projection neurons in the VTA, which in turn signals to the vocal control network to allow for context-appropriate song production.

Birdsong and the Neural Regulation of Positive Emotion

Birds are not commonly admired for emotional expression, and when they are, the focus is typically on negative states; yet vocal behavior is considered a direct reflection of an individual's emotional state. Given that over 4000 species of songbird produce learned, complex, context-specific vocalizations, we make the case that songbirds are conspicuously broadcasting distinct positive emotional states and that hearing songs can also induce positive states in other birds. Studies are reviewed that demonstrate that that the production of sexually motivated song reflects an emotional state of anticipatory reward-seeking (i.e., mate-seeking), while outside the mating context song in gregarious flocks reflects a state of intrinsic reward. Studies are also reviewed that demonstrate that hearing song induces states of positive anticipation and reward. This review brings together numerous studies that highlight a potentially important role for the songbird nucleus accumbens, a region nearly synonymous with reward in mammals, in positive emotional states that underlie singing behavior and responses to song. It is proposed that the nucleus accumbens is part of an evolutionarily conserved circuitry that contributes context-dependently to positive emotional states that motivate and reward singing behavior and responses to song. Neural mechanisms that underlie basic emotions appear to be conserved and similar across vertebrates. Thus, these findings in songbirds have the potential to provide insights into interventions that can restore positive social interactions disrupted by mental health disorders in humans.

Using seasonality and birdsong to understand mechanisms underlying context-appropriate shifts in social motivation and reward

Social motivation and reward are dynamic and flexible, shifting adaptively across contexts to meet changing social demands. This is exceptionally apparent when seasonal contexts are considered in seasonally breeding songbirds as they cycle from periods of sexual motivation and reward during the breeding season to periods of extreme gregariousness outside the breeding season when non-sexual social interactions gain reward value, motivating birds to form flocks. Here we review evidence demonstrating a key integrative role for the medial preoptic area (mPOA) in the seasonally-appropriate adjustment of behaviors, with seasonal changes in dopamine activity in mPOA adjusting social motivation and changes in opioid activity modifying social reward. Experiments demonstrate that dramatic seasonal fluctuations in steroid hormone concentrations alter patterns of opioid- and dopamine-related protein and gene expression in mPOA to modify social motivation and reward to meet seasonal changes in social demands. These studies of birdsong and seasonality provide new insights into neural and endocrine mechanisms underlying adaptive changes in social motivation and reward and highlight an underappreciated, evolutionarily conserved role for the mPOA in important social behaviors in non-reproductive contexts.

Species-typical group size differentially influences social reward neural circuitry during nonreproductive social interactions

We investigated whether nonreproductive social interactions may be rewarding for colonial but not non-colonial species. We found that the colonial spiny mouse (Acomys cahirinus) is significantly more gregarious, more prosocial, and less aggressive than its non-colonial relative, the Mongolian gerbil (Meriones unguiculatus). In an immediate-early gene study, we examined oxytocin (OT) and tyrosine hydroxylase (TH) neural responses to interactions with a novel, same-sex conspecific or a novel object. The paraventricular nucleus of the hypothalamus (PVN) OT cell group was more responsive to interactions with a conspecific compared to a novel object in both species. However, the ventral tegmental area (VTA) TH cell group showed differential responses only in spiny mice. Further, PVN OT and VTA TH neural responses positively correlated in spiny mice, suggesting functional connectivity. These results suggest that colonial species may have evolved neural mechanisms associated with reward in novel, nonreproductive social contexts to promote large group-living.

Immunolabeling Provides Evidence for Subregions in the Songbird Nucleus Accumbens and Suggests a Context-Dependent Role in Song in Male European Starlings (Sturnus vulgaris)

Birdsong is well known for its role in mate attraction during the breeding season. However, many birds, including European starlings (Sturnus vulgaris), also sing outside the breeding season as part of large flocks. Song in a breeding context can be extrinsically rewarded by mate attraction; however, song in nonbreeding flocks, referred to here as gregarious song, results in no obvious extrinsic reward and is proposed to be intrinsically rewarded. The nucleus accumbens (NAC) is a brain region well known to mediate reward and motivation, which suggests it is an ideal candidate to regulate reward associated with gregarious song. The goal of this study was to provide new histochemical information on the songbird NAC and its subregions (rostral pole, core, and shell) and to begin to determine subregion-specific contributions to gregarious song in male starlings. We examined immunolabeling for tyrosine hydroxylase (TH), neurotensin, and enkephalin (ENK) in the NAC. We then examined the extent to which gregarious and sexually motivated song differentially correlated with immunolabeling for the immediate early genes FOS and ZENK in each subdivision of the NAC. We found that TH and ENK labeling within subregions of the starling NAC was generally similar to patterns seen in the core and shell of NACs in mammals and birds. Additionally, we found that gregarious song, but not sexually motivated song, positively correlated with FOS in all NAC subregions. Our observations provide further evidence for distinct subregions within the songbird NAC and suggest the NAC may play an important role in regulating gregarious song in songbirds.

Neural Circuits Underlying Nest Building in Male Zebra Finches

Nest building consists of a series of motor actions, which are concomitant with activity in regions of the anterior motor pathway, the social behavior network, and the reward circuity in nest building adult male zebra finches (Taeniopygia guttata). It is not clear, however, whether this activity is due to nest building, collection, and/or manipulation of nest material. To identify which areas of the brain are specifically involved, we used immunohistochemistry to quantify the immediate early gene c-Fos in male zebra finches that were nest building (Building), birds given a nest box but could interact only with tied down nest material (Fixed), and birds that were not given a nest box or nest material (Control). We investigated the following brain regions: the anterior motor pathway (anterior ventral mesopallium [AMV], AN, anterior striatum [ASt]), areas of the social behavior network (bed nucleus of the stria terminalis, dorsomedial subdivision [BSTmd], lateral septum [LS]), the dopaminergic reward circuitry (ventral tegmental area), and the cerebellum. We found that there was greater Fos immunoreactivity expression in the BSTmd, LS, and AMV with increased material deposition; in LS, AMV ASt, and Folium VI with increased material carrying; in LS, AMV, and ASt with increased nest material tucking; and in LS and all folia (except Folium VIII) with increased tugging at tied down material. These data confirm a functional role for areas of the anterior motor pathway, social behavior network, and the cerebellum in nest material collection and manipulation by birds.

Neuronal activation in zebra finch parents associated with reintroduction of nestlings

Recent studies of the brain mechanisms of parental behaviors have mainly focused on rodents. Using other vertebrate taxa, such as birds, can contribute to a more comprehensive, evolutionary view. In the present study, we investigated a passerine songbird, the zebra finch (Taeniopygia guttata), with a biparental caring system. Parenting-related neuronal activation was induced by first temporarily removing the nestlings, and then, either reuniting the focal male or female parent with the nestlings (parental group) or not (control group). To identify activated neurons, the immediate early gene product, Fos protein, was labeled. Both parents showed an increased level of parental behavior following reunion with the nestlings, and no sexual dimorphism occurred in the neuronal activation pattern. Offspring-induced parental behavior-related neuronal activation was found in the preoptic, ventromedial (VMH), paraventricular hypothalamic nuclei, and in the bed nucleus of the stria terminalis. In addition, the number of Fos-immunoreactive (Fos-ir) neurons in the nucleus accumbens predicted the frequency of the feeding of the nestlings. No difference was found in Fos expression when the effect of isolation or the presence of the mate was examined. Thus, our study identified a number of nuclei involved in parental care in birds and suggests similar regulatory mechanisms in caring females and males. The activated brain regions show similarities to rodents, while a generally lower number of brain regions were activated in the zebra finch. Furthermore, future studies are necessary to establish the role of the apparently avian-specific neuronal activation in the VMH of zebra finch parents.

Pairing Increases Activation of V1aR, but not OTR, in Auditory Regions of Zebra Finches: The Importance of Signal Modality in Nonapeptide-Social Behavior Relationships

Social relationships are complex, involving the production and comprehension of signals, individual recognition, and close coordination of behavior between two or more individuals. The nonapeptides oxytocin and vasopressin are widely believed to regulate social relationships. These findings come largely from prairie voles, in which nonapeptide receptors in olfactory neural circuits drive pair bonding. This research is assumed to apply to all species. Previous reviews have offered two competing hypotheses. The work of Sarah Newman has implicated a common neural network across species, the Social Behavior Network. In contrast, others have suggested that there are signal modality-specific networks that regulate social behavior. Our research focuses on evaluating these two competing hypotheses in the zebra finch, a species that relies heavily on vocal/auditory signals for communication, specifically the neural circuits underlying singing in males and song perception in females. We have demonstrated that the quality of vocal interactions is highly important for the formation of long-term monogamous bonds in zebra finches. Qualitative evidence at first suggests that nonapeptide receptor distributions are very different between monogamous rodents (olfactory species) and monogamous birds (vocal/auditory species). However, we have demonstrated that social bonding behaviors are not only correlated with activation of nonapeptide receptors in vocal and auditory circuits, but also involve regions of the common Social Behavior Network. Here, we show increased Vasopressin 1a receptor, but not oxytocin receptor, activation in two auditory regions following formation of a pair bond. To our knowledge, this is the first study to suggest a role of nonapeptides in the auditory circuit in pair bonding. Thus, we highlight converging mechanisms of social relationships and also point to the importance of studying multiple species to understand mechanisms of behavior.

Prodynorphin and kappa opioid receptor mRNA expression in the brain relates to social status and behavior in male European starlings

Numerous animal species display behavioral changes in response to changes in social status or territory possession. For example, in male European starlings only males that acquire nesting sites display high rates of sexual and agonistic behavior. Past studies show that mu and delta opioid receptors regulate behaviors associated with social ascension or defeat. Opioids also act at kappa receptors, with dynorphin binding with the highest affinity; however, the role of these opioids in social behavior has not been well studied. We observed flocks of male starlings during the breeding season and ran quantitative real-time polymerase chain reaction (qPCR) to measure expression of kappa opioid receptors (OPRK1) and prodynorphin (PDYN) in brain regions involved in social behavior and motivation (ventral tegmental area [VTA], medial preoptic nucleus [mPOA]) and vocal behavior (Area X). Males with nesting territories displayed more sexual/agonistic behavior than males without nesting territories. They also had lower OPRK1 expression in VTA and mPOA. OPRK1 expression in VTA correlated negatively with sexual/agonistic behaviors, consistent with past studies showing kappa receptors in VTA to inhibit sociosexual behaviors. PDYN in mPOA correlated negatively with a measure of nesting behavior that may also reflect sexual motivation. PDYN in Area X related positively to song. Distinct patterns of OPRK1 and PDYN expression in VTA, mPOA, and Area X related to gonad volume, suggesting that breeding condition may modify (or be modified by) OPRK1 and PDYN expression. Studies are now needed to further characterize the role of OPRK1 and PDYN in status-appropriate social behaviors.

Contributions of testosterone and territory ownership to sexually-motivated behaviors and mRNA expression in the medial preoptic area of male European starlings

Animals integrate social information with their internal endocrine state to control the timing of behavior, but how these signals are integrated in the brain is not understood. The medial preoptic area (mPOA) may play an integrative role in the control of courtship behavior, as it receives projections from multiple sensory systems, and is central to the hormonal control of courtship behavior across vertebrates. Additionally, data from many species implicate opioid and dopaminergic systems in the mPOA in the control of male courtship behavior. We used European starlings to test the hypothesis that testosterone (T) and social status (in the form of territory possession) interact to control the timing of courtship behavior by modulating steroid hormone-, opioid- and dopaminergic-related gene expression in the mPOA. We found that only males given both T and a nesting territory produced high rates of courtship behavior in response to a female. T treatment altered patterns of gene expression in the mPOA by increasing androgen receptor, aromatase, mu-opioid receptor and preproenkephalin mRNA and decreasing tyrosine hydroxylase mRNA expression. Territory possession did not alter mRNA expression in the mPOA, despite the finding that only birds with both T and a nesting territory produced courtship behavior. We propose that T prepares the mPOA to respond to the presence of a female with high rates of courtship song by altering gene expression, but that activity in the mPOA is under a continuous (i.e. tonic) inhibition until a male starling obtains a nesting territory.

Neural endocannabinoid CB1 receptor expression, social status, and behavior in male European starlings

Many species modify behavior in response to changes in resource availability or social status; however, the neural mechanisms underlying these modifications are not well understood. Prior work in male starlings demonstrates that status-appropriate changes in behavior involve brain regions that regulate social behavior and vocal production. Endocannabinoids are ubiquitously distributed neuromodulators that are proposed to play a role in adjusting behavior to match social status. As an initial step to provide insight into this hypothesis we observed flocks of male starlings in outdoor aviaries during the breeding season. We used quantitative real-time PCR to measure expression of endocannabinoid CB1 receptors in brain regions involved in social behavior and motivation (lateral septum [LS], ventral tegmental area [VTA], medial preoptic nucleus [POM]) and vocal behavior (Area X and robust nucleus of the arcopallium; RA). Males with nesting sites sang to females and displaced other males more than males without nesting sites. They also had higher levels of CB1 receptor expression in LS and RA. CB1 expression in LS correlated positively with agonistic behaviors. CB1 expression in RA correlated positively with singing behavior. CB1 in VTA also correlated positively with singing when only singing birds were considered. These correlations nicely map onto the well-established role of LS in agonistic behavior and the known role of RA in song production and VTA in motivation and song production. Studies are now needed to precisely characterize the role of CB1 receptors in these regions in the production of status-appropriate social behaviors.

Early Life Manipulations of the Nonapeptide System Alter Pair Maintenance Behaviors and Neural Activity in Adult Male Zebra Finches

Adult zebra finches (T. guttata) form socially monogamous pair bonds characterized by proximity, vocal communication, and contact behaviors. In this experiment, we tested whether manipulations of the nonapeptide hormone arginine vasotocin (AVT, avian homolog of vasopressin) and the V1a receptor (V1aR) early in life altered species-typical pairing behavior in adult zebra finches of both sexes. Although there was no effect of treatment on the tendency to pair in either sex, males in different treatments exhibited profoundly different profiles of pair maintenance behavior. Following a brief separation, AVT-treated males were highly affiliative with their female partner but sang very little compared to Controls. In contrast, males treated with a V1aR antagonist sang significantly less than Controls, but did not differ in affiliation. These effects on behavior in males were also reflected in changes in the expression of V1aR and immediate early gene activity in three brain regions known to be involved in pairing behavior in birds: the medial amygdala, medial bed nucleus of the stria terminalis, and the lateral septum. AVT males had higher V1aR expression in the medial amygdala than both Control and antagonist-treated males and immediate early gene activity of V1aR neurons in the medial amygdala was positively correlated with affiliation. Antagonist treated males showed decreased activity in the medial amygdala. In addition, there was a negative correlation between the activity of V1aR cells in the medial bed nucleus of the stria terminalis and singing. Treatment also affected the expression of V1aR and activity in the lateral septum, but this was not correlated with any behaviors measured. These results provide evidence that AVT and V1aR play developmental roles in specific pair maintenance behaviors and the neural substrate underlying these behaviors in a bird.

Sex, estradiol, and spatial memory in a food-caching corvid

Estrogens significantly impact spatial memory function in mammalian species. Songbirds express the estrogen synthetic enzyme aromatase at relatively high levels in the hippocampus and there is evidence from zebra finches that estrogens facilitate performance on spatial learning and/or memory tasks. It is unknown, however, whether estrogens influence hippocampal function in songbirds that naturally exhibit memory-intensive behaviors, such as cache recovery observed in many corvid species. To address this question, we examined the impact of estradiol on spatial memory in non-breeding Western scrub-jays, a species that routinely participates in food caching and retrieval in nature and in captivity. We also asked if there were sex differences in performance or responses to estradiol. Utilizing a combination of an aromatase inhibitor, fadrozole, with estradiol implants, we found that while overall cache recovery rates were unaffected by estradiol, several other indices of spatial memory, including searching efficiency and efficiency to retrieve the first item, were impaired in the presence of estradiol. In addition, males and females differed in some performance measures, although these differences appeared to be a consequence of the nature of the task as neither sex consistently out-performed the other. Overall, our data suggest that a sustained estradiol elevation in a food-caching bird impairs some, but not all, aspects of spatial memory on an innate behavioral task, at times in a sex-specific manner.

Dopamine physiology in the basal ganglia of male zebra finches during social stimulation

Accumulating evidence suggests that dopamine (DA) is involved in altering neural activity and gene expression in a zebra finch cortical–basal ganglia circuit specialized for singing, upon the shift between solitary singing and singing as a part of courtship. Our objective here was to sample changes in the extracellular concentrations of DA in Area X of adult and juvenile birds, to test the hypothesis that DA levels would change similarly during presentation of a socially salient stimulus in both age groups. We used microdialysis to sample the extracellular milieu of Area X in awake, behaving adult and juvenile male zebra finches, and analysed the dialysate using high-performance liquid chromatography coupled with electrochemical detection. The extracellular levels of DA in Area X increased significantly during both female presentation to adult males and tutor presentation to juvenile males. DA levels were not correlated with the time spent singing. We also reverse-dialysed Area X with pharmacologic agents that act either on DA systems directly or on norepinephrine, and found that all of these agents significantly increased DA levels (3- to 10-fold) in Area X. These findings suggest that changes in extracellular DA levels can be stimulated similarly by very different social contexts (courtship and interaction with tutor), and influenced potently by dopaminergic and noradrenergic drugs. These results raise the possibility that the arousal level or attentional state of the subject (rather than singing behavior) is the common feature eliciting changes in extracellular DA concentration.

From neurons to nests: nest-building behaviour as a model in behavioural and comparative neuroscience

Despite centuries of observing the nest building of most extant bird species, we know surprisingly little about how birds build nests and, specifically, how the avian brain controls nest building. Here, we argue that nest building in birds may be a useful model behaviour in which to study how the brain controls behaviour. Specifically, we argue that nest building as a behavioural model provides a unique opportunity to study not only the mechanisms through which the brain controls behaviour within individuals of a single species but also how evolution may have shaped the brain to produce interspecific variation in nest-building behaviour. In this review, we outline the questions in both behavioural and comparative neuroscience that nest building could be used to address, summarize recent findings regarding the neurobiology of nest building in lab-reared zebra finches and across species building different nest structures, and suggest some future directions for the neurobiology of nest building.

Sexually-motivated song is predicted by androgen-and opioid-related gene expression in the medial preoptic nucleus of male European starlings (Sturnus vulgaris)

Across vertebrates, communication conveys information about an individual's motivational state, yet little is known about the neuroendocrine regulation of motivational aspects of communication. For seasonally breeding songbirds, increases in testosterone in spring stimulate high rates of sexually-motivated courtship song, though not all birds sing at high rates. It is generally assumed that testosterone or its metabolites act within the medial preoptic nucleus (POM) to stimulate the motivation to sing. In addition to androgen receptors (ARs) and testosterone, opioid neuropeptides in the POM influence sexually-motivated song production, and it has been proposed that testosterone may in part regulate song by modifying opioid systems. To gain insight into a possible role for androgen-opioid interactions in the regulation of communication we examined associations between sexually-motivated song and relative expression of ARs, mu opioid receptors (muORs), and preproenkephalin (PENK) in the POM (and other regions) of male European starlings using qPCR. Both AR and PENK expression in POM correlated positively with singing behavior, whereas muOR in POM correlated negatively with song. Furthermore, the ratio of PENK/muOR expression correlated negatively with AR expression in POM. Finally, in the ventral tegmental area (VTA), PENK expression correlated negatively with singing behavior. Results support the hypothesis that ARs may alter opioid gene expression in POM to fine-tune singing to reflect a male's motivational state. Data also suggest that bidirectional relationships may exist between opioids and ARs in POM and song, and additionally support a role for opioids in the VTA, independent of AR activity in this region.

Neurotensin immunolabeling relates to sexually-motivated song and other social behaviors in male European starlings (Sturnus vulgaris)

The brain regions involved in vocal communication are well described for some species, including songbirds, but less is known about the neural mechanisms underlying motivational aspects of communication. Mesolimbic dopaminergic projections from the ventral tegmental area (VTA) are central to mediating motivated behaviors. In songbirds, VTA provides dopaminergic innervation to brain regions associated with motivation and social behavior that are also involved in sexually-motivated song production. Neurotensin (NT) is a neuropeptide that strongly modulates dopamine activity, co-localizes with dopamine in VTA, and is found in regions where dopaminergic cells project from VTA. Yet, little is known about how NT contributes to vocal communication or other motivated behaviors. We examined the relationships between sexually-motivated song produced by male European starlings (Sturnus vulgaris) and NT immunolabeling in brain regions involved in social behavior and motivation. Additionally, we observed relationships between NT labeling, non-vocal courtship behaviors (another measure of sexual motivation), and agonistic behavior to begin to understand NT's role in socially-motivated behaviors. NT labeling in VTA, lateral septum, and bed nucleus of the stria terminalis correlated with sexually-motivated singing and non-vocal courtship behaviors. NT labeling in VTA, lateral septum, medial preoptic nucleus, and periaqueductal gray was associated with agonistic behavior. This study is the first to suggest NT's involvement in song, and one of the few to implicate NT in social behaviors more generally. Additionally, our results are consistent with the idea that distinct patterns of neuropeptide activity in brain areas involved in social behavior and motivation underlie differentially motivated behaviors.

Functional interactions of dopamine cell groups reflect personality, sex, and social context in highly social finches

Dopamine (DA) is well known for its involvement in novelty-seeking, learning, and goal-oriented behaviors such as social behavior. However, little is known about how DA modulates social processes differentially in relation to sex and behavioral phenotype (e.g., personality). Importantly, the major DA cell groups (A8-A15) are conserved across all amniote vertebrates, and thus broadly relevant insights may be obtained through investigations of avian species such as zebra finches (Taeniopygia guttata), which express a human-like social organization based on biparental nuclear families that are embedded within larger social groups. We here build upon a previous study that quantified multidimensional personality structures in male and female zebra finches using principal components analysis (PCA) of extensive behavioral measures in social and nonsocial contexts. These complex dimensions of behavioral phenotype can be characterized as Social competence/dominance, Gregariousness, and Anxiety. Here we analyze Fos protein expression in DA neuronal populations in response to social novelty and demonstrate that the Fos content of multiple dopamine cell groups is significantly predicted by sex, personality, social context, and their interactions. In order to further investigate coordinated neuromodulation of behavior across multiple DA cell groups, we also conducted a PCA of neural variables (DA cell numbers and their phasic Fos responses) and show that behavioral PCs are associated with unique suites of neural PCs. These findings demonstrate that personality and sex are reflected in DA neuron activity and coordinated patterns of neuromodulation arising from multiple DA cell groups.

Status-appropriate singing behavior, testosterone and androgen receptor immunolabeling in male European starlings (Sturnus vulgaris)

Vocalizations convey information about an individual's motivational, internal, and social status. As circumstances change, individuals respond by adjusting vocal behavior accordingly. In European starlings, a male that acquires a nest site socially dominates other males and dramatically increases courtship song. Although circulating testosterone is associated with social status and vocal production it is possible that steroid receptors fine-tune status-appropriate changes in behavior. Here we explored a possible role for androgen receptors. Male starlings that acquired nest sites produced high rates of courtship song. For a subset of males this occurred even in the absence of elevated circulating testosterone. Immunolabeling for androgen receptors (ARir) was highest in the medial preoptic nucleus (POM) in males with both a nest site and elevated testosterone. For HVC, ARir was higher in dominant males with high testosterone (males that sang longer songs) than dominant males with low testosterone (males that sang shorter songs). ARir in the dorsal medial portion of the nucleus intercollicularis (DM) was elevated in males with high testosterone irrespective of dominance status. Song bout length related positively to ARir in POM, HVC and DM, and testosterone concentrations related positively to ARir in POM and DM. Results suggest that the role of testosterone in vocal behavior differs across brain regions and support the hypothesis that testosterone in POM underlies motivation, testosterone in HVC relates to song quality, and testosterone in DM stimulates vocalizations. Our data also suggest that singing may influence AR independent of testosterone and that alternative androgen-independent pathways regulate status-appropriate singing behavior.

Neural correlates of nesting behavior in zebra finches (Taeniopygia guttata)

•

We compare markers of neural activity to nesting behavior in zebra finches.

•

We visualized immediate early gene (Fos) expression in nesting and control finches.

•

Fos production in motor, social, and reward neural circuits correlated with nesting.

•

Fos production correlated with material pick-up in male nesting finches.

•

Fos production correlated with time spent in the nest in female nesting finches.

Nest building in birds involves a behavioral sequence (nest material collection and deposition in the nest) that offers a unique model for addressing how the brain sequences motor actions. In this study, we identified brain regions involved in nesting behavior in male and female zebra finches (Taeniopygia guttata). We used Fos immunohistochemistry to quantify production of the immediate early gene protein product Fos (a molecular indicator of neuronal activity) in the brain correlated this expression with the variation in nesting behavior. Using this technique, we found that neural circuitry involved in motor sequencing, social behavior, reward and motivation were active during nesting. Within pairs of nesting birds, the number of times a male picked up or deposited nesting material and the amount of time a female spent in the nest explained the variation in Fos expression in the anterior motor pathway, social behavior network, and reward neural circuits. Identification of the brain regions that are involved in nesting enables us to begin studying the roles of motor sequencing, context, and reward in construction behavior at the neural level.

Inverted-U shaped effects of D1 dopamine receptor stimulation in the medial preoptic nucleus on sexually motivated song in male European starlings

Past studies in songbirds have highlighted a central role for the medial preoptic nucleus (mPOA) in context-appropriate vocal communication. During the breeding season, male songbirds sing primarily to attract females (sexually motivated song) and to repel competitors (agonistically motivated song). Past data have linked dopamine and D1 dopamine receptors in the mPOA to sexually motivated but not agonistically motivated song; however, direct effects of dopamine receptor manipulations in the mPOA on song have not been experimentally tested. Here, we tested the hypothesis that D1 receptor stimulation in the mPOA selectively influences sexually motivated male song, and the possibility that the effects of D1 receptor agonism differ at low and high doses. In a first study, breeding-condition male European starlings received infusions of saline or a single dose of the D1 receptor agonist SKF 38393 on separate test days into the mPOA or hypothalamic control areas. Stimulation of D1 receptors in the mPOA triggered sexually motivated but not agonistically motivated song. A second study showed inverted-U shaped dose-response effects of the agonist, such that low levels of sexually motivated song were observed at low and high levels of D1 receptor activation. A third study showed that the effects of the D1 receptor agonist were blocked by the D1 receptor antagonist SCH 23390. These findings suggest that an optimal level of D1 receptor stimulation in the mPOA is needed to facilitate sexually motivated vocal production. The results support a central, context-specific role for the mPOA in vocal communication, and more broadly demonstrate a complex, modulatory influence of D1 receptors in the mPOA on sexually motivated behavior.

Estradiol differentially affects auditory recognition and learning according to photoperiodic state in the adult male songbird, European starling (Sturnus vulgaris)

Changes in hormones can affect many types of learning in vertebrates. Adults experience fluctuations in a multitude of hormones over a temporal scale, from local, rapid action to more long-term, seasonal changes. Endocrine changes during development can affect behavioral outcomes in adulthood, but how learning is affected in adults by hormone fluctuations experienced during adulthood is less understood. Previous reports have implicated the sex steroid hormone estradiol (E2) in both male and female vertebrate cognitive functioning. Here, we examined the effects of E2 on auditory recognition and learning in male European starlings (Sturnus vulgaris). European starlings are photoperiodic, seasonally breeding songbirds that undergo different periods of reproductive activity according to annual changes in day length. We simulated these reproductive periods, specifically 1. photosensitivity, 2. photostimulation, and 3. photorefractoriness in captive birds by altering day length. During each period, we manipulated circulating E2 and examined multiple measures of learning. To manipulate circulating E2, we used subcutaneous implants containing either 17-β E2 and/or fadrozole (FAD), a highly specific aromatase inhibitor that suppresses E2 production in the body and the brain, and measured the latency for birds to learn and respond to short, male conspecific song segments (motifs). We report that photostimulated birds given E2 had higher response rates and responded with better accuracy than those given saline controls or FAD. Conversely, photosensitive, animals treated with E2 responded with less accuracy than those given FAD. These results demonstrate how circulating E2 and photoperiod can interact to shape auditory recognition and learning in adults, driving it in opposite directions in different states.

What's in a name? Considerations of homologies and nomenclature for vertebrate social behavior networks

Behavioral neuroendocrinology is an integrative discipline that spans a wide range of taxa and neural systems, and thus the appropriate designation of homology (sameness) across taxa is critical for clear communication and extrapolation of findings from one taxon to another. In the present review we address issues of homology that relate to neural circuits of social behavior and associated systems that mediate reward and aversion. We first address a variety of issues related to the so-called "social behavior network" (SBN), including homologies that are only partial (e.g., whereas the preoptic area of fish and amphibians contains the major vasopressin-oxytocin cell groups, these populations lie in the hypothalamus of other vertebrates). We also discuss recent evidence that clarifies anterior hypothalamus and periaqueductal gray homologies in birds. Finally, we discuss an expanded network model, the "social decision-making network" (SDM) which includes the mesolimbic dopamine system and other structures that provide an interface between the mesolimbic system and the SBN. This expanded model is strongly supported in mammals, based on a wide variety of evidence. However, it is not yet clear how readily the SDM can be applied as a pan-vertebrate model, given insufficient data on numerous proposed homologies and a lack of social behavior data for SDM components (beyond the SBN nodes) for amphibians, reptiles or fish. Functions of SDM components are also poorly known for birds. Nonetheless, we contend that the SDM model provides a very sound and important framework for the testing of many hypotheses in nonmammalian vertebrates.

Associated and disassociated patterns in hormones, song, behavior and brain receptor expression between life-cycle stages in male black redstarts, Phoenicurus ochruros

Testosterone has been suggested to be involved in the regulation of male territorial behavior. For example, seasonal peaks in testosterone typically coincide with periods of intense competition between males for territories and mating partners. However, some species also express territorial behavior outside a breeding context when testosterone levels are low and, thus, the degree to which testosterone facilitates territorial behavior in these species is not well understood. We studied territorial behavior and its neuroendocrine correlates in male black redstarts. Black redstarts defend territories in spring during the breeding period, but also in the fall outside a reproductive context when testosterone levels are low. In the present study we assessed if song output and structure remain stable across life-cycle stages. Furthermore, we assessed if brain anatomy may give insight into the role of testosterone in the regulation of territorial behavior in black redstarts. We found that males sang spontaneously at a high rate during the nonbreeding period when testosterone levels were low; however the trill-like components of spontaneously produced song contained less repetitive elements during nonbreeding than during breeding. This higher number of repetitive elements in trills did not, however, correlate with a larger song control nucleus HVC during breeding. However, males expressed more aromatase mRNA in the preoptic area - a brain nucleus important for sexual and aggressive behavior - during breeding than during nonbreeding. In combination with our previous studies on black redstarts our results suggest that territorial behavior in this species only partly depends on sex steroids: spontaneous song output, seasonal variation in trills and non-vocal territorial behavior in response to a simulated territorial intruder seem to be independent of sex steroids. However, context-dependent song during breeding may be facilitated by testosterone - potentially by conversion of testosterone to estradiol in the preoptic area.

Patterns of phosphorylated tyrosine hydroxylase vary with song production in female starlings

Vocal signal production in male songbirds is well studied, but the neural correlates of female song production are poorly understood. In European starlings, females sing to defend nesting resources, and song can be considered agonistically motivated. Across vertebrates catecholamines strongly influence motivated, agonistic social behaviors. The present study was designed to provide insight into a possible role for catecholamine activity in territorial song in female starlings. We presented females that were defending nest-cavities with an unfamiliar female and assessed song production. We then measured immunolabeling for phosphorylated tyrosine hydroxylase (pTH-ir), the rate-limiting enzyme for catecholamine synthesis, in brain regions in which catecholamines stimulate agonistic behavior. Females that sang had higher pTH-ir in the caudomedial ventral tegmental area and the lateral septum than females that did not sing. Furthermore, the number of songs produced correlated positively with pTH-ir in the medial preoptic nucleus. Phosphorylation of TH is thought to occur after catecholamine release, so these results link increased catecholamine activity in several brain regions governing agonistic behavior to territorial song production in females.

Patterns of FOS protein induction in singing female starlings

Females of many songbird species produce song, but information about the neural correlates of singing behavior is limited in this sex. Although well studied in males, activity in premotor song control regions and social behavior regions has not been examined in females during song production. Here, we examined the immediate early gene protein product FOS in both song control and social behavior brain regions after female starlings defending nest boxes responded to an unfamiliar female in a naturalistic setting. We found that females that sang in response to the intruder had much higher numbers of fos-immunoreactive neurons (fos-ir) in the vocal control regions HVC, the robust nucleus of the arcopallium (RA), and the dorsomedial part of the nucleus intercollicularis (DM of the ICo). In HVC, fos-ir correlated positively with song length. In RA, DM and Area X, fos-ir correlated positively with number of songs produced. In social behavior regions, singers showed higher fos-ir in the nucleus taeniae of the amygdala, the dorsal part of the bed nucleus of the stria terminalis, and the ventromedial hypothalamus than non-singers. Overall, patterns of fos-ir in song control regions in females were similar to those reported for males, but differences in fos-ir were identified in social behavior regions. These differences may reflect a distinct role for brain regions involved in social behavior in female song, or they may reflect differences in the social function of female and male song.

The role of motivation and reward neural systems in vocal communication in songbirds

Many vertebrates are highly motivated to communicate, suggesting that the consequences of communication may be rewarding. Past studies show that dopamine and opioids in the medial preoptic nucleus (mPOA) and ventral tegmental area (VTA) play distinct roles in motivation and reward. In songbirds, multiple lines of recent evidence indicate that the roles of dopamine and opioid activity in mPOA and VTA in male birdsong differ depending upon whether song is used to attract females (sexually-motivated) or is produced spontaneously (undirected). Evidence is reviewed supporting the hypotheses that (1) mPOA and VTA interact to influence the context in which a male sings, (2) distinct patterns of dopamine activity underlie the motivation to produce sexually-motivated and undirected song, (3) sexually-motivated communication is externally reinforced by opioids released as part of social interactions, and (4) undirected communication is facilitated and rewarded by immediate opioid release linked to the act of singing.

The vertebrate mesolimbic reward system and social behavior network: a comparative synthesis

All animals evaluate the salience of external stimuli and integrate them with internal physiological information into adaptive behavior. Natural and sexual selection impinge on these processes, yet our understanding of behavioral decision-making mechanisms and their evolution is still very limited. Insights from mammals indicate that two neural circuits are of crucial importance in this context: the social behavior network and the mesolimbic reward system. Here we review evidence from neurochemical, tract-tracing, developmental, and functional lesion/stimulation studies that delineates homology relationships for most of the nodes of these two circuits across the five major vertebrate lineages: mammals, birds, reptiles, amphibians, and teleost fish. We provide for the first time a comprehensive comparative analysis of the two neural circuits and conclude that they were already present in early vertebrates. We also propose that these circuits form a larger social decision-making (SDM) network that regulates adaptive behavior. Our synthesis thus provides an important foundation for understanding the evolution of the neural mechanisms underlying reward processing and behavioral regulation.

Rapid and widespread effects of 17β-estradiol on intracellular signaling in the male songbird brain: a seasonal comparison

Across vertebrate species, 17β-estradiol (E(2)) acts on the brain via both genomic and nongenomic mechanisms to influence neuronal physiology and behavior. Nongenomic E(2) signaling is typically initiated by membrane-associated estrogen receptors that modulate intracellular signaling cascades, including rapid phosphorylation of ERK. Phosphorylated ERK (pERK) can, in turn, rapidly phosphorylate tyrosine hydroxylase (TH) and cAMP response element-binding protein (CREB). Recent data suggest that the rapid effects of E(2) on mouse aggressive behavior are more prominent during short photoperiods (winter) and that acute aromatase inhibition reduces songbird aggression in winter only. To date, seasonal plasticity in the rapid effects of E(2) on intracellular signaling has not been investigated. Here, we compared the effects of acute (15 min) E(2) treatment on pERK, pTH, and pCREB immunoreactivity in male song sparrows (Melospiza melodia) pretreated with the aromatase inhibitor fadrozole during the breeding and nonbreeding seasons. We examined immunoreactivity in 14 brain regions including portions of the song control system, social behavior network, and the hippocampus (Hp). In both seasons, E(2) significantly decreased pERK in nucleus taeniae of the amygdala, pTH in ventromedial hypothalamus, and pCREB in mesencephalic central gray, robust nucleus of the arcopallium, and caudomedial nidopallium. However, several effects were critically dependent upon season. E(2) decreased pERK in caudomedial nidopallium in the breeding season only and decreased pCREB in the medial preoptic nucleus in the nonbreeding season only. Remarkably, E(2) decreased pERK in Hp in the breeding season but increased pERK in Hp in the nonbreeding season. Together, these data demonstrate that E(2) has rapid effects on intracellular signaling in multiple regions of the male brain and also demonstrate that rapid effects of E(2) can be profoundly different across the seasons.

Vocal parameters that indicate threat level correlate with FOS immunolabeling in social and vocal control brain regions

Transmitting information via communicative signals is integral to interacting with conspecifics, and some species achieve this task by varying vocalizations to reflect context. Although signal variation is critical to social interactions, the underlying neural control has not been studied. In response to a predator, black-capped chickadees (Poecile atricapilla) produce mobbing calls (chick-a-dee calls) with various parameters, some of which convey information about the threat stimulus. We predicted that vocal parameters indicative of threat would be associated with distinct patterns of neuronal activity within brain areas involved in social behavior and those involved in the sensorimotor control of vocal production. To test this prediction, we measured the syntax and structural aspects of chick-a-dee call production in response to a hawk model and assessed the protein product of the immediate early gene FOS in brain regions implicated in context-specific vocal and social behavior. These regions include the medial preoptic area (POM) and lateral septum (LS), as well as regions involved in vocal motor control, including the dorsomedial nucleus of the intercollicular complex and the HVC. We found correlations linking call rate (previously demonstrated to reflect threat) to labeling in the POM and LS. Labeling in the HVC correlated with the number of D notes per call, which may also signal threat level. Labeling in the call control region dorsomedial nucleus was associated with the structure of D notes and the overall number of notes, but not call rate or type of notes produced. These results suggest that the POM and LS may influence attributes of vocalizations produced in response to predators and that the brain region implicated in song control, the HVC, also influences call production. Because variation in chick-a-dee call rate indicates predator threat, we speculate that these areas could integrate with motor control regions to imbue mobbing signals with additional information about threat level.

Individual differences in the motivation to communicate relate to levels of midbrain and striatal catecholamine markers in male European starlings

Individuals display dramatic differences in social communication even within similar social contexts. Across vertebrates dopaminergic projections from the ventral tegmental area (VTA) and midbrain central gray (GCt) strongly influence motivated, reward-directed behaviors. Norepinephrine is also rich in these areas and may alter dopamine neuronal activity. The present study was designed to provide insight into the roles of dopamine and norepinephrine in VTA and GCt and their efferent striatal target, song control region area X, in the regulation of individual differences in the motivation to sing. We used high pressure liquid chromatography with electrochemical detection to measure dopamine, norepinephrine and their metabolites in micropunched samples from VTA, GCt, and area X in male European starlings (Sturnus vulgaris). We categorized males as sexually motivated or non-sexually motivated based on individual differences in song produced in response to a female. Dopamine markers and norepinephrine in VTA and dopamine in area X correlated positively with sexually-motivated song. Norepinephrine in area X correlated negatively with non-sexually-motivated song. Dopamine in GCt correlated negatively with sexually-motivated song, and the metabolite DOPAC correlated positively with non-sexually-motivated song. Results highlight a role for evolutionarily conserved dopaminergic projections from VTA to striatum in the motivation to communicate and highlight novel patterns of catecholamine activity in area X, VTA, and GCt associated with individual differences in sexually-motivated and non-sexually-motivated communication. Correlations between dopamine and norepinephrine markers also suggest that norepinephrine may contribute to individual differences in communication by modifying dopamine neuronal activity in VTA and GCt.

Seasonal and individual variation in singing behavior correlates with α2-noradrenergic receptor density in brain regions implicated in song, sexual, and social behavior

In seasonally breeding male songbirds, both the function of song and the stimuli that elicit singing behavior change seasonally. The catecholamine norepinephrine (NE) modulates attention and arousal across behavioral states, yet the role of NE in seasonally-appropriate vocal communication has not been well-studied. The present study explored the possibility that seasonal changes in alpha 2-noradrenergic receptors (α(2)-R) within song control regions and brain regions implicated in sexual arousal and social behavior contribute to seasonal changes in song behavior in male European starlings (Sturnus vulgaris). We quantified singing behavior in aviary housed males under spring breeding season conditions and fall conditions. α(2)-R were identified with the selective ligand [(3)H]RX821002 using autoradiographic methods. The densities of α(2)-R in song control regions (HVC and the robust nucleus of the arcopallium [RA]) and the lateral septum (LS) were lower in Spring Condition males. α(2)-R densities in the caudal portion of the medial preoptic nucleus (POM) related negatively to singing behavior. Testosterone concentrations were highest in Spring Condition males and correlated with α(2)-R in LS and POM. Results link persistent seasonal alterations in the structure or function of male song to seasonal changes in NE α(2)-Rs in HVC, RA, and LS. Individual differences in α(2)-R in the POM may in part explain individual differences in song production irrespective of the context in which a male is singing, perhaps through NE modification of male sexual arousal.

Pleasure seeking and birdsong

Songbirds sing at high rates within multiple contexts, suggesting that they are highly motivated to communicate and that the act of singing itself may be rewarding. Little is known about the neural regulation of the motivation to communicate. Dopamine and opioid neuropeptides play a primary role in reward seeking and sensory pleasure. In songbirds, these neurochemicals are found within brain regions implicated in both motivation and reward, including the medial preoptic nucleus (mPOA) and ventral tegmental area (VTA). Several lines of research indicate that dopamine and opioids in these regions play a role in birdsong that differs depending upon whether song is used to attract females (female-directed song) or is not directed towards other individuals (undirected song). Evidence is reviewed supporting the hypotheses: (1) that distinct patterns of dopamine activity influence the motivation to produce undirected and female-directed song, (2) that undirected communication is intrinsically reinforced by immediate release of opioids induced by the act of singing, and (3) that directed communication is socially reinforced by opioids released as part of social interactions.

Mu-opioid receptor densities are depleted in regions implicated in agonistic and sexual behavior in male European starlings (Sturnus vulgaris) defending nest sites and courting females

Social status and resource availability can strongly influence individual behavioral responses to conspecifics. In European starlings, males that acquire nest sites sing in response to females and dominate other males. Males without nest sites sing, but not to females, and they do not interact agonistically with other males. Little is known about the neural regulation of status- or resource-appropriate behavioral responses to conspecifics. Opioid neuropeptides are implicated in birdsong and agonistic behavior, suggesting that opioids may underlie differences in the production of these behaviors in males with and without nest sites. Here, we examined densities of immunolabeled mu-opioid receptors in groups of male starlings. Males that defended nest boxes dominated other males and sang at higher rates when presented with a female than males without nest boxes, independent of testosterone concentrations. Multiple regression analyses showed nest box ownership (not agonistic behavior or singing) predicted the optical density of receptor labeling in the medial bed nucleus of stria terminalis, paraventricular nucleus, ventral tegmental area and the medial preoptic nucleus. Compared to males without nest boxes, males with nest boxes had lower densities of immunolabeled mu-opioid receptors in these regions. Singing additionally predicted the area covered by labeling in the ventral tegmental area. The results suggest that elevated opioid activity in these regions suppresses courtship and agonistic behavioral responses to conspecifics in males without nest boxes. The findings are consistent with a dynamic role for opioid receptors in adjusting social behavior so that it is appropriate given the resources available to an individual.

Seasonal changes in aromatase and androgen receptor, but not estrogen receptor mRNA expression in the brain of the free-living male song sparrow, Melospiza melodia morphna

Free-living male song sparrows experience three annually repeating life history stages associated with differential expression of sex steroid-dependent reproductive and aggressive behavior. In the breeding stage, they display reproductive and aggressive behavior and have elevated circulating testosterone levels. During molt, males show little or no aggression and no reproductive behavior, and have basal levels of circulating testosterone. In the non-breeding stage, they display high levels of aggression and no reproductive behavior, and have basal levels of circulating testosterone. In order to understand more fully the neural regulation of seasonal aggressive and reproductive behavior, birds were collected during all three life history stages, and levels of neural aromatase, androgen receptor (AR), and estrogen receptor alpha (ERalpha) and beta (ERbeta) mRNA expression were measured. Breeding males had the highest levels of aromatase expression in both the preoptic area (POA) and medial preoptic area/medial bed nucleus of the stria terminalis (mPOA/BSTm), and the highest AR expression levels in the POA, consistent with the well-established role these regions play in the regulation of male reproductive behavior. Aromatase expression in the ventromedial nucleus of the hypothalamus (VMH) was higher during breeding and non-breeding compared with molt, suggesting that the VMH may play a role in the estrogen-dependent regulation of aggression in this species. AR expression also varied in medial HVC and pvMSt, a newly described periventricular region in the medial striatum. ERalpha and ERbeta mRNA expression did not vary seasonally in any brain region examined, suggesting that estrogen-dependent changes in behavior are mediated by differences in neural estrogen synthesis.

Selective behavioral responses to male song are affected by the dopamine agonist GBR-12909 in female European starlings (Sturnus vulgaris)

Female songbirds use attributes of male song to select mates. Different types of male song differ in incentive value (or the ability to attract females). Dopamine plays a role in incentive value and reward; however, little is known about its role in selective female behavioral responses to male courtship signals. We examined the effects of the indirect dopamine agonist (dopamine reuptake inhibitor) GBR-12909 on female songbird responses to male song stimuli. Female European starlings were played recordings of long starling song (presumed high incentive value), short starling song (presumed lower incentive value), or purple martin song (lowest incentive value). Vehicle-treated females investigated nest boxes playing starling song more than purple martin song. However, GBR-12909 disrupted preferential responses to the starling song stimuli. GBR-12909 also increased cFOS immunolabeling in the ventromedial nucleus of the hypothalamus (VMH) at the same dose that disrupted female selective responses to male starling song. The results suggest that dopamine receptors play an important role in female selective responses to biologically meaningful stimuli and that the VMH may be influenced by dopamine to alter female responses to male song.

Plasticity in singing effort and its relationship with monoamine metabolism in the songbird telencephalon

Factors intrinsic or extrinsic to individuals, such as their quality or the quality of competition in their social environment, can influence their communication signaling effort. We hypothesized that telencephalic monoamine secretion mediates the effects of a male's own quality and quality of his social environment on his sexual signaling effort. The duration of a male European starling's (Sturnus vulgaris) principal sexual signal, his song, positively correlates with several aspects of his quality, including his reproductive success, immunocompetence, and ability to attract mates. Therefore, the length of songs to which he is exposed reflects, in part, the quality of competition in his social environment. We manipulated the quality of the competitive environment by exposing male starlings to long or short songs for 1 week. We measured the length of songs produced by experimental males to gauge their quality, counted the number of songs they produced to gauge singing effort, and quantified telencephalic monoamine metabolism using high-pressure liquid chromatography. Singing effort increased with the length of the males' own songs and with the length of songs to which we exposed them. Norepinephrine metabolism in area X of the song control system was negatively correlated with the subjects' mean song length and singing effort. Serotonin metabolism in the caudomedial mesopallium of the auditory telencephalon increased with the length of songs to which we exposed the subjects and with their singing effort. This raises the hypothesis that serotonin and norepinephrine secretion in the telencephalon help mediate the effects of extrinsic and intrinsic factors on signaling effort.

Integrating genomes, brain and behavior in the study of songbirds

Songbirds share some essential traits but are extraordinarily diverse, allowing comparative analyses aimed at identifying specific genotype-phenotype associations. This diversity encompasses traits like vocal communication and complex social behaviors that are of great interest to humans, but that are not well represented in other accessible research organisms. Many songbirds are readily observable in nature and thus afford unique insight into the links between environment and organism. The distinctive organization of the songbird brain will facilitate analysis of genomic links to brain and behavior. Access to the zebra finch genome sequence will, therefore, prompt new questions and provide the ability to answer those questions.

Structural changes between seasons in the songbird auditory forebrain

The song control system (SCS) of seasonal songbirds shows remarkable seasonal plasticity. Male starlings (Sturnus vulgaris) sing throughout the year, but in the breeding season, when concentrations of testosterone are elevated, the song is highly sexually motivated. The main goal of this study was to investigate structural seasonal changes in regions involved in auditory processing and in socio-sexual behavior. Using in vivo Diffusion Tensor Imaging (DTI), we measured in breeding and nonbreeding seasons volume and tissue characteristics of several brain regions of nine adult male starlings. We demonstrate that the songbird brain exhibits an extreme seasonal plasticity not merely limited to the SCS. Volumetric analysis showed seasonal telencephalon volume changes and more importantly also a volumetric change in the caudal region of the nidopallium (NCM), a region analogous to the mammalian secondary auditory cortex. Analysis of the DTI data allowed detection of seasonal changes in cellular attributes in NCM and regions involved in social behavior. This study extends our view on a seasonally dynamic avian brain which not only hones its song control system but also auditory and social systems to be prepared for the breeding season.

Dopaminergic system in birdsong learning and maintenance

Dopamine function in birdsong has been studied extensively in recent years. Several song and auditory nuclei are innervated by midbrain dopaminergic fibers and contain neurons with various dopamine receptors. During sexually motivated singing, activity of midbrain dopaminergic neurons in the ventral tegmental area and dopamine release in the striatal Area X, involved in song learning and maintenance, are higher. In this review we provide an overview of the dopaminergic system and neurotransmission in songbirds and the outline of possible involvement of dopamine in control of song learning, production, and maintenance. Based on both behavioral and computational biology data, we describe several models of song learning and the proposed role of dopamine in them. Special attention is given to possible role of dopamine in incentive salience (wanting) and reward prediction error signaling during song learning and maintenance, as well as the role of dopamine-mediated synaptic plasticity in reward processing. Finally, the role of dopamine in determination of personality traits in relation to birdsong is discussed.

Song competition changes the brain and behavior of a male songbird

Males should adjust their behavior and its neural substrates according to the quality of competition that they assess by eavesdropping on other males' courtship signals. In European starlings (Sturnus vulgaris), females base mate choice, in part, on aspects of male song associated with its length, which positively correlates with the males' reproductive success, immunocompetence, age and ability to repel competing males. To determine how variation in the quality of male courtship song affects the brain and behavior of incidental male receivers, we exposed adult male starlings to either long or short songs periodically over 7 days, followed by 1 day of no song. We found no difference between groups in the length (i.e. quality) of songs that subjects produced during the experiment. However, compared with males exposed to short songs, those exposed to long songs sang more songs, exhibited more non-singing activity and, by the end of the experiment, weighed less and had a 30% larger robust nucleus of the arcopallium (RA), a forebrain nucleus that translates pre-motor signals into the appropriate combination of respiratory and syringeal activity. The change in RA volume was not entirely due to variation in song output, suggesting, for the first time, the possibility of acoustically driven plasticity in this motor nucleus. We hypothesize that such neuroplasticity helps prepare the individual for future song output tailored to the prevailing competitive environment.