Role of the midbrain dopaminergic system in modulation of vocal brain activation by social context

Sexually dimorphic activation of dopaminergic areas depends on affiliation during courtship and pair formation

For many species, dyadic interaction during courtship and pair bonding engage intense emotional states that control approach or avoidance behavior. Previous studies have shown that one component of a common social brain network (SBN), dopaminergic areas, are highly engaged during male songbird courtship of females. We tested whether the level of activity in dopaminergic systems of both females and males during courtship is related to their level of affiliation. In order to objectively quantify affiliative behaviors, we developed a system for tracking the position of both birds during free interaction sessions. During a third successive daily interaction session, there was a range of levels of affiliation among bird pairs, as quantified by several position and movement parameters. Because both positive and negative social interactions were present, we chose to characterize affiliation strength by pair valence. As a potential neural system involved in regulating pair valence, the level of activity of the dopaminergic group A11 (within the central gray) was selectively reduced in females of positive valence pairs. Further, activation of non-dopaminergic neurons in VTA was negatively related to valence, with this relationship strongest in ventral VTA of females. Together, these results suggest that inhibition of fear or avoidance networks may be associated with development of close affiliation, and highlight the importance of negative as well as positive emotional states in the process of courtship, and in development of long-lasting social bonds.

Emergence of context-dependent variability across a basal ganglia network

Context dependence is a key feature of cortical-basal ganglia circuit activity, and in songbirds the cortical outflow of a basal ganglia circuit specialized for song, LMAN, shows striking increases in trial-by-trial variability and bursting when birds sing alone rather than to females. To reveal where this variability and its social regulation emerge, we recorded stepwise from corticostriatal (HVC) neurons and their target spiny and pallidal neurons in Area X. We find that corticostriatal and spiny neurons both show precise singing-related firing across both social settings. Pallidal neurons, in contrast, exhibit markedly increased trial-by-trial variation when birds sing alone, created by highly variable pauses in firing. This variability persists even when recurrent inputs from LMAN are ablated. These data indicate that variability and its context sensitivity emerge within the basal ganglia network, suggest a network mechanism for this emergence, and highlight variability generation and regulation as basal ganglia functions.

Sexually-dimorphic expression of tyrosine hydroxylase immunoreactivity in the brain of a vocal teleost fish (Porichthys notatus)

Vocal communication has emerged as a powerful model for the study of neural mechanisms of social behavior. Modulatory neurochemicals postulated to play a central role in social behavior, related to motivation, arousal, incentive and reward, include the catecholamines, particularly dopamine and noradrenaline. Many questions remain regarding the functional mechanisms by which these modulators interact with sensory and motor systems. Here, we begin to address these questions in a model system for vocal and social behavior, the plainfin midshipman fish (Porichthys notatus). We mapped the distribution of immunoreactivity for the catecholamine-synthesizing enzyme tyrosine hydroxylase (TH) in the midshipman brain. The general pattern of TH(+) cell groups in midshipman appears to be highly conserved with other teleost fish, with a few exceptions, including the apparent absence of pretectal catecholamine cells. Many components of the midshipman vocal and auditory systems were innervated by TH(+) fibers and terminals, including portions of the subpallial area ventralis, the preoptic complex, and the anterior hypothalamus, the midbrain periaqueductal gray and torus semicircularis, several hindbrain auditory nuclei, and parts of the hindbrain vocal pattern generator. These areas thus represent potential sites for catecholamine modulation of vocal and/or auditory behavior. To begin to test functionally whether catecholamines modulate vocal social behaviors, we hypothesized that male and female midshipman, which are sexually dimorphic in both their vocal-motor repertoires and in their responses to hearing conspecific vocalizations, should exhibit sexually dimorphic expression of TH immunoreactivity in their vocal and/or auditory systems. We used quantitative immunohistochemical techniques to test this hypothesis across a number of brain areas. We found significantly higher levels of TH expression in male midshipman relative to females in the TH cell population in the paraventricular organ of the diencephalon and in the TH-innervated torus semicircularis, the main teleost midbrain auditory structure. The torus semicircularis has been implicated in sexually dimorphic behavioral responses to conspecific vocalizations. Our data thus support the general idea that catecholamines modulate vocal and auditory processing in midshipman, and the specific hypothesis that they shape sexually dimorphic auditory responses in the auditory midbrain.

Singing-related activity in anterior forebrain of male zebra finches reflects courtship motivation for target females

A critical function of singing by male songbirds is to attract a female mate. Previous studies have suggested that the anterior forebrain system is involved in this courtship behavior. Neural activity in this system, including the striatal Area X, is strikingly dependent on the function of male singing. When males sing to attract a female bird rather than while alone, less variable neural activity results in less variable song spectral features, which may be attractive to the female. These characteristics of neural activity and singing thus may reflect a male's motivation for courtship. Here, we compared the variability of neural activity and song features between courtship singing directed to a female with whom a male had previously formed a pair-bond or to other females. Surprisingly, across all units, there was no clear tendency for a difference in variability of neural activity or song features between courtship of paired females, nonpaired females, or dummy females. However, across the population of recordings, there was a significant relationship between the relative variability of syllable frequency and neural activity: when syllable frequency was less variable to paired than nonpaired females, neural activity was also less variable (and vice-versa). These results show that the lower variability of neural activity and syllable frequency during directed singing is not a binary distinction from undirected singing, but can vary in intensity, possibly related to the relative preference of a male for his singing target.

Dopamine modulates the excitability of projection neurons in the robust nucleus of the arcopallium in adult zebra finches

Background

The nervous system in songbirds is an accessible system for studying vocal learning and memory in vertebrates. In the song system, the anterior forebrain pathway (AFP) is essential for song learning and the vocal motor pathway (VMP) is necessary for song production. The premotor robust nucleus of the arcopallium (RA) located in the VMP receives input from the AFP. The RA receives dopaminergic innervations from the periaqueductal gray and ventral tegmental area–substantia nigra pars compacta, but the physiological functions of this projection remain unclear. In this study, we investigated the effects of dopamine (DA) on the excitability of projection neurons (PNs) in the RA.

Methodology

We recorded the electrophysiological changes from neurons in brain slices of male adult zebra finches using a whole-cell recording technique.

Conclusions/Significance

We found that DA significantly increased the excitability of RA PNs. Furthermore, a D1-like receptor agonist increased the excitability of RA PNs, and a D1-like receptor antagonist suppressed the excitability induced by DA. However, a D2-like receptor agonist had no effect on the excitability of RA PNs. Moreover, the D2-like receptor agonist did not change the excitability induced by the D1 receptor agonist. These findings suggest that DA can significantly increase the excitability of RA PNs and that D1 receptors play the main role in regulating the excitability of RA PNs in response to DA, thereby providing direct evidence toward understanding the mechanism of DA signal mediation by its receptors to modulate the excitability of RA PNs.

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.

Translating birdsong: songbirds as a model for basic and applied medical research

Songbirds, long of interest to basic neuroscience, have great potential as a model system for translational neuroscience. Songbirds learn their complex vocal behavior in a manner that exemplifies general processes of perceptual and motor skill learning and, more specifically, resembles human speech learning. Song is subserved by circuitry that is specialized for vocal learning and production but that has strong similarities to mammalian brain pathways. The combination of highly quantifiable behavior and discrete neural substrates facilitates understanding links between brain and behavior, both in normal states and in disease. Here we highlight (a) behavioral and mechanistic parallels between birdsong and aspects of speech and social communication, including insights into mirror neurons, the function of auditory feedback, and genes underlying social communication disorders, and (b) contributions of songbirds to understanding cortical-basal ganglia circuit function and dysfunction, including the possibility of harnessing adult neurogenesis for brain repair.

Investigation of musicality in birdsong

Songbirds spend much of their time learning, producing, and listening to complex vocal sequences we call songs. Songs are learned via cultural transmission, and singing, usually by males, has a strong impact on the behavioral state of the listeners, often promoting affiliation, pair bonding, or aggression. What is it in the acoustic structure of birdsong that makes it such a potent stimulus? We suggest that birdsong potency might be driven by principles similar to those that make music so effective in inducing emotional responses in humans: a combination of rhythms and pitches-and the transitions between acoustic states-affecting emotions through creating expectations, anticipations, tension, tension release, or surprise. Here we propose a framework for investigating how birdsong, like human music, employs the above "musical" features to affect the emotions of avian listeners. First we analyze songs of thrush nightingales (Luscinia luscinia) by examining their trajectories in terms of transitions in rhythm and pitch. These transitions show gradual escalations and graceful modifications, which are comparable to some aspects of human musicality. We then explore the feasibility of stripping such putative musical features from the songs and testing how this might affect patterns of auditory responses, focusing on fMRI data in songbirds that demonstrate the feasibility of such approaches. Finally, we explore ideas for investigating whether musical features of birdsong activate avian brains and affect avian behavior in manners comparable to music's effects on humans. In conclusion, we suggest that birdsong research would benefit from current advances in music theory by attempting to identify structures that are designed to elicit listeners' emotions and then testing for such effects experimentally. Birdsong research that takes into account the striking complexity of song structure in light of its more immediate function - to affect behavioral state in listeners - could provide a useful animal model for studying basic principles of music neuroscience in a system that is very accessible for investigation, and where developmental auditory and social experience can be tightly controlled.

Exposure to advertisement calls of reproductive competitors activates vocal-acoustic and catecholaminergic neurons in the plainfin midshipman fish, Porichthys notatus

While the neural circuitry and physiology of the auditory system is well studied among vertebrates, far less is known about how the auditory system interacts with other neural substrates to mediate behavioral responses to social acoustic signals. One species that has been the subject of intensive neuroethological investigation with regard to the production and perception of social acoustic signals is the plainfin midshipman fish, Porichthys notatus, in part because acoustic communication is essential to their reproductive behavior. Nesting male midshipman vocally court females by producing a long duration advertisement call. Females localize males by their advertisement call, spawn and deposit all their eggs in their mate’s nest. As multiple courting males establish nests in close proximity to one another, the perception of another male’s call may modulate individual calling behavior in competition for females. We tested the hypothesis that nesting males exposed to advertisement calls of other males would show elevated neural activity in auditory and vocal-acoustic brain centers as well as differential activation of catecholaminergic neurons compared to males exposed only to ambient noise. Experimental brains were then double labeled by immunofluorescence (-ir) for tyrosine hydroxylase (TH), an enzyme necessary for catecholamine synthesis, and cFos, an immediate-early gene product used as a marker for neural activation. Males exposed to other advertisement calls showed a significantly greater percentage of TH-ir cells colocalized with cFos-ir in the noradrenergic locus coeruleus and the dopaminergic periventricular posterior tuberculum, as well as increased numbers of cFos-ir neurons in several levels of the auditory and vocal-acoustic pathway. Increased activation of catecholaminergic neurons may serve to coordinate appropriate behavioral responses to male competitors. Additionally, these results implicate a role for specific catecholaminergic neuronal groups in auditory-driven social behavior in fishes, consistent with a conserved function in social acoustic behavior across vertebrates.

Brain and pineal 7α-hydroxypregnenolone stimulating locomotor activity: identification, mode of action and regulation of biosynthesis

Biologically active steroids synthesized in the central and peripheral nervous systems are termed neurosteroids. However, the biosynthetic pathways leading to the formation of neurosteroids are still incompletely elucidated. 7α-Hydroxypregnenolone, a novel bioactive neurosteroid stimulating locomotor activity, has been recently identified in the brain of newts and quail. Subsequently, the mode of action and regulation of biosynthesis of 7α-hydroxypregnenolone have been determined. Moreover, recent studies on birds have demonstrated that the pineal gland, an endocrine organ located close to the brain, is an important site of production of neurosteroids de novo from cholesterol. 7α-Hydroxypregnenolone is a major pineal neurosteroid that stimulates locomotor activity in juvenile chickens, connecting light-induced gene expression with locomotion. This review summarizes the advances in our understanding of the identification, mode of action and regulation of biosynthesis of brain and pineal 7α-hydroxypregnenolone, a potent stimulator of locomotor activity.

Genomics analysis of potassium channel genes in songbirds reveals molecular specializations of brain circuits for the maintenance and production of learned vocalizations

Background

A fundamental question in molecular neurobiology is how genes that determine basic neuronal properties shape the functional organization of brain circuits underlying complex learned behaviors. Given the growing availability of complete vertebrate genomes, comparative genomics represents a promising approach to address this question. Here we used genomics and molecular approaches to study how ion channel genes influence the properties of the brain circuitry that regulates birdsong, a learned vocal behavior with important similarities to human speech acquisition. We focused on potassium (K-)Channels, which are major determinants of neuronal cell excitability.

Starting with the human gene set of K-Channels, we used cross-species mRNA/protein alignments, and syntenic analysis to define the full complement of orthologs, paralogs, allelic variants, as well as novel loci not previously predicted in the genome of zebra finch (Taeniopygia guttata). We also compared protein coding domains in chicken and zebra finch orthologs to identify genes under positive selective pressure, and those that contained lineage-specific insertions/deletions in functional domains. Finally, we conducted comprehensive in situ hybridizations to determine the extent of brain expression, and identify K-Channel gene enrichments in nuclei of the avian song system.

Results

We identified 107 K-Channel finch genes, including 6 novel genes common to non-mammalian vertebrate lineages. Twenty human genes are absent in songbirds, birds, or sauropsids, or unique to mammals, suggesting K-Channel properties may be lineage-specific. We also identified specific family members with insertions/deletions and/or high dN/dS ratios compared to chicken, a non-vocal learner. In situ hybridization revealed that while most K-Channel genes are broadly expressed in the brain, a subset is selectively expressed in song nuclei, representing molecular specializations of the vocal circuitry.

Conclusions

Together, these findings shed new light on genes that may regulate biophysical and excitable properties of the song circuitry, identify potential targets for the manipulation of the song system, and reveal genomic specializations that may relate to the emergence of vocal learning and associated brain areas in birds.

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.

New biosynthesis and biological actions of avian neurosteroids

De novo neurosteroidogenesis from cholesterol occurs in the brain of various avian species. However, the biosynthetic pathways leading to the formation of neurosteroids are still not completely elucidated. We have recently found that the avian brain produces 7α-hydroxypregnenolone, a novel bioactive neurosteroid that stimulates locomotor activity. Until recently, it was believed that neurosteroids are produced in neurons and glial cells in the central and peripheral nervous systems. However, our recent studies on birds have demonstrated that the pineal gland, an endocrine organ located close to the brain, is an important site of production of neurosteroids de novo from cholesterol. 7α-Hydroxypregnenolone is a major pineal neurosteroid that stimulates locomotor activity of juvenile birds, connecting light-induced gene expression with locomotion. The other major pineal neurosteroid allopregnanolone is involved in Purkinje cell survival during development. This paper highlights new aspects of neurosteroid synthesis and actions in birds.

The incentive salience of courtship vocalizations: hormone-mediated 'wanting' in the auditory system

Conspecific vocalizations differ from many other sounds in that they have natural incentive salience. Our thinking about auditory responses to vocalizations may therefore benefit from models originally developed to understand reward. According to those models, the brain attributes incentive salience to rewarding stimuli via the activity of monoaminergic neuromodulators. These neuromodulators, in turn, mediate the effects of experience and internal state. Songbirds lend themselves well to this discussion because the natural incentive salience of song is clearly modulated by both factors. Their auditory responses have been well-studied, particularly the song-induced expression of plasticity-associated genes such as ZENK. Here I review evidence that ZENK responses to song are regulated by monoamine neuromodulators, and I interpret this evidence in the context of incentive salience. First, hearing conspecific song engages monoaminergic activity in the auditory system and elsewhere. Second, in females this activity may be regulated by the same hormones that regulate behavioral preferences for song. Finally, much of the evidence thought to implicate neuromodulators in song discrimination and memory suggests that they may affect incentive salience. Expanding the study of incentive salience beyond the mesolimbic reward system may reveal some new ways of thinking about its underlying neural basis. This article is part of a Special Issue entitled "Communication Sounds and the Brain: New Directions and Perspectives".

Song competition affects monoamine levels in sensory and motor forebrain regions of male Lincoln's sparrows (Melospiza lincolnii)

Male animals often change their behavior in response to the level of competition for mates. Male Lincoln's sparrows (Melospiza lincolnii) modulate their competitive singing over the period of a week as a function of the level of challenge associated with competitors' songs. Differences in song challenge and associated shifts in competitive state should be accompanied by neural changes, potentially in regions that regulate perception and song production. The monoamines mediate neural plasticity in response to environmental cues to achieve shifts in behavioral state. Therefore, using high pressure liquid chromatography with electrochemical detection, we compared levels of monoamines and their metabolites from male Lincoln's sparrows exposed to songs categorized as more or less challenging. We compared levels of norepinephrine and its principal metabolite in two perceptual regions of the auditory telencephalon, the caudomedial nidopallium and the caudomedial mesopallium (CMM), because this chemical is implicated in modulating auditory sensitivity to song. We also measured the levels of dopamine and its principal metabolite in two song control nuclei, area X and the robust nucleus of the arcopallium (RA), because dopamine is implicated in regulating song output. We measured the levels of serotonin and its principal metabolite in all four brain regions because this monoamine is implicated in perception and behavioral output and is found throughout the avian forebrain. After controlling for recent singing, we found that males exposed to more challenging song had higher levels of norepinephrine metabolite in the CMM and lower levels of serotonin in the RA. Collectively, these findings are consistent with norepinephrine in perceptual brain regions and serotonin in song control regions contributing to neuroplasticity that underlies socially-induced changes in behavioral state.

Speech-induced striatal dopamine release is left lateralized and coupled to functional striatal circuits in healthy humans: a combined PET, fMRI and DTI study

Considerable progress has been recently made in understanding the brain mechanisms underlying speech and language control. However, the neurochemical underpinnings of normal speech production remain largely unknown. We investigated the extent of striatal endogenous dopamine release and its influences on the organization of functional striatal speech networks during production of meaningful English sentences using a combination of positron emission tomography (PET) with the dopamine D(2)/D(3) receptor radioligand [(11)C]raclopride and functional MRI (fMRI). In addition, we used diffusion tensor tractography (DTI) to examine the extent of dopaminergic modulatory influences on striatal structural network organization. We found that, during sentence production, endogenous dopamine was released in the ventromedial portion of the dorsal striatum, in both its associative and sensorimotor functional divisions. In the associative striatum, speech-induced dopamine release established a significant relationship with neural activity and influenced the left-hemispheric lateralization of striatal functional networks. In contrast, there were no significant effects of endogenous dopamine release on the lateralization of striatal structural networks. Our data provide the first evidence for endogenous dopamine release in the dorsal striatum during normal speaking and point to the possible mechanisms behind the modulatory influences of dopamine on the organization of functional brain circuits controlling normal human speech.

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.

Natural changes in brain temperature underlie variations in song tempo during a mating behavior

The song of a male zebra finch is a stereotyped motor sequence whose tempo varies with social context--whether or not the song is directed at a female bird--as well as with the time of day. The neural mechanisms underlying these changes in tempo are unknown. Here we show that brain temperature recorded in freely behaving male finches exhibits a global increase in response to the presentation of a female bird. This increase strongly correlates with, and largely explains, the faster tempo of songs directed at a female compared to songs produced in social isolation. Furthermore, we find that the observed diurnal variations in song tempo are also explained by natural variations in brain temperature. Our findings suggest that brain temperature is an important variable that can influence the dynamics of activity in neural circuits, as well as the temporal features of behaviors that some of these circuits generate.

Dopamine regulation of human speech and bird song: a critical review

To understand the neural basis of human speech control, extensive research has been done using a variety of methodologies in a range of experimental models. Nevertheless, several critical questions about learned vocal motor control still remain open. One of them is the mechanism(s) by which neurotransmitters, such as dopamine, modulate speech and song production. In this review, we bring together the two fields of investigations of dopamine action on voice control in humans and songbirds, who share similar behavioral and neural mechanisms for speech and song production. While human studies investigating the role of dopamine in speech control are limited to reports in neurological patients, research on dopaminergic modulation of bird song control has recently expanded our views on how this system might be organized. We discuss the parallels between bird song and human speech from the perspective of dopaminergic control as well as outline important differences between these species.

Specialized motor-driven dusp1 expression in the song systems of multiple lineages of vocal learning birds

Mechanisms for the evolution of convergent behavioral traits are largely unknown. Vocal learning is one such trait that evolved multiple times and is necessary in humans for the acquisition of spoken language. Among birds, vocal learning is evolved in songbirds, parrots, and hummingbirds. Each time similar forebrain song nuclei specialized for vocal learning and production have evolved. This finding led to the hypothesis that the behavioral and neuroanatomical convergences for vocal learning could be associated with molecular convergence. We previously found that the neural activity-induced gene dual specificity phosphatase 1 (dusp1) was up-regulated in non-vocal circuits, specifically in sensory-input neurons of the thalamus and telencephalon; however, dusp1 was not up-regulated in higher order sensory neurons or motor circuits. Here we show that song motor nuclei are an exception to this pattern. The song nuclei of species from all known vocal learning avian lineages showed motor-driven up-regulation of dusp1 expression induced by singing. There was no detectable motor-driven dusp1 expression throughout the rest of the forebrain after non-vocal motor performance. This pattern contrasts with expression of the commonly studied activity-induced gene egr1, which shows motor-driven expression in song nuclei induced by singing, but also motor-driven expression in adjacent brain regions after non-vocal motor behaviors. In the vocal non-learning avian species, we found no detectable vocalizing-driven dusp1 expression in the forebrain. These findings suggest that independent evolutions of neural systems for vocal learning were accompanied by selection for specialized motor-driven expression of the dusp1 gene in those circuits. This specialized expression of dusp1 could potentially lead to differential regulation of dusp1-modulated molecular cascades in vocal learning circuits.

Thinking outside the cortex: social motivation in the evolution and development of language

Alteration of the organization of social and motivational neuroanatomical circuitry must have been an essential step in the evolution of human language. Development of vocal communication across species, particularly birdsong, and new research on the neural organization and evolution of social and motivational circuitry, together suggest that human language is the result of an obligatory link of a powerful cortico-striatal learning system, and subcortical socio-motivational circuitry.

Reward and vocal production: song-associated place preference in songbirds

Vocal production is crucial for successful social interactions in multiple species. Reward can strongly influence behavior; however, the extent to which reward systems influence vocal behavior is unknown. In songbirds, singing occurs in different contexts. It can be spontaneous and undirected (e.g., song produced alone or as part of a large flock) or directed towards a conspecific (e.g., song used to attract a mate or influence a competitor). In this study, we developed a conditioned place preference paradigm to measure reward associated with different types of singing behavior in two songbird species. Both male zebra finches and European starlings developed a preference for a chamber associated with production of undirected song, suggesting that the production of undirected song is tightly coupled to intrinsic reward. In contrast, neither starlings nor zebra finches developed a place preference in association with directed song; however, male starlings singing directed song that failed to attract a female developed a place aversion. Unsuccessful contact calling behavior was also associated with a place aversion. These findings suggest that directed vocal behavior is not tightly linked to intrinsic reward but may be externally reinforced by social interactions. Data across two species thus support the hypothesis that the production of undirected but not directed song is tightly coupled to intrinsic reward. This study is the first to identify song-associated reward and suggests that reward associated with vocal production differs depending upon the context in which communication occurs. The findings have implications for understanding what motivates animals to engage in social behaviors and ways in which distinct reward mechanisms function to direct socially appropriate behaviors.

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.

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.

A hypothesis for basal ganglia-dependent reinforcement learning in the songbird

Most of our motor skills are not innately programmed, but are learned by a combination of motor exploration and performance evaluation, suggesting that they proceed through a reinforcement learning (RL) mechanism. Songbirds have emerged as a model system to study how a complex behavioral sequence can be learned through an RL-like strategy. Interestingly, like motor sequence learning in mammals, song learning in birds requires a basal ganglia (BG)-thalamocortical loop, suggesting common neural mechanisms. Here, we outline a specific working hypothesis for how BG-forebrain circuits could utilize an internally computed reinforcement signal to direct song learning. Our model includes a number of general concepts borrowed from the mammalian BG literature, including a dopaminergic reward prediction error and dopamine-mediated plasticity at corticostriatal synapses. We also invoke a number of conceptual advances arising from recent observations in the songbird. Specifically, there is evidence for a specialized cortical circuit that adds trial-to-trial variability to stereotyped cortical motor programs, and a role for the BG in "biasing" this variability to improve behavioral performance. This BG-dependent "premotor bias" may in turn guide plasticity in downstream cortical synapses to consolidate recently learned song changes. Given the similarity between mammalian and songbird BG-thalamocortical circuits, our model for the role of the BG in this process may have broader relevance to mammalian BG function.

Genes, hormones, and circuits: an integrative approach to study the evolution of social behavior

Tremendous progress has been made in our understanding of the ultimate and proximate mechanisms underlying social behavior, yet an integrative evolutionary analysis of its underpinnings has been difficult. In this review, we propose that modern genomic approaches can facilitate such studies by integrating four approaches to brain and behavior studies: (1) animals face many challenges and opportunities that are ecologically and socially equivalent across species; (2) they respond with species-specific, yet quantifiable and comparable approach and avoidance behaviors; (3) these behaviors in turn are regulated by gene modules and neurochemical codes; and (4) these behaviors are governed by brain circuits such as the mesolimbic reward system and the social behavior network. For each approach, we discuss genomic and other studies that have shed light on various aspects of social behavior and its underpinnings and suggest promising avenues for future research into the evolution of neuroethological systems.

Food for song: expression of c-Fos and ZENK in the zebra finch song nuclei during food aversion learning

BACKGROUND

Specialized neural pathways, the song system, are required for acquiring, producing, and perceiving learned avian vocalizations. Birds that do not learn to produce their vocalizations lack telencephalic song system components. It is not known whether the song system forebrain regions are exclusively evolved for song or whether they also process information not related to song that might reflect their 'evolutionary history'.

METHODOLOGY/PRINCIPAL FINDINGS

To address this question we monitored the induction of two immediate-early genes (IEGs) c-Fos and ZENK in various regions of the song system in zebra finches (Taeniopygia guttata) in response to an aversive food learning paradigm; this involves the association of a food item with a noxious stimulus that affects the oropharyngeal-esophageal cavity and tongue, causing subsequent avoidance of that food item. The motor response results in beak and head movements but not vocalizations. IEGs have been extensively used to map neuro-molecular correlates of song motor production and auditory processing. As previously reported, neurons in two pallial vocal motor regions, HVC and RA, expressed IEGs after singing. Surprisingly, c-Fos was induced equivalently also after food aversion learning in the absence of singing. The density of c-Fos positive neurons was significantly higher than that of birds in control conditions. This was not the case in two other pallial song nuclei important for vocal plasticity, LMAN and Area X, although singing did induce IEGs in these structures, as reported previously.

CONCLUSIONS/SIGNIFICANCE

Our results are consistent with the possibility that some of the song nuclei may participate in non-vocal learning and the populations of neurons involved in the two tasks show partial overlap. These findings underscore the previously advanced notion that the specialized forebrain pre-motor nuclei controlling song evolved from circuits involved in behaviors related to feeding.

Social affiliation relates to tyrosine hydroxylase immunolabeling in male and female zebra finches (Taeniopygia guttata)

The catecholamines dopamine and norepinephrine are implicated in affiliative behaviors, yet few studies have addressed the extent to which affiliative behaviors within distinct social settings rely upon similar or distinct catecholaminergic mechanisms. To explore the role of catecholamines in affiliative behavior within distinct long-term social contexts, we examined the density of the catecholamine synthetic enzyme tyrosine hydroxylase (TH) in brain regions within both the mesolimbic dopaminergic system and "social behavior network" in male and female zebra finches (Taeniopygia guttata) paired for 21 days with either a same- or opposite-sex conspecific. On days 16-21 after pairing, members of both same- and mixed-sex pairs produced similar rates of affiliative behaviors. Measures of affiliation related to TH labeling in the ventral tegmental area (VTA), nucleus accumbens (Ac), medial preoptic nucleus (POM), and ventromedial nucleus of the hypothalamus (VMH). Relationships between TH labeling density and specific measures of affiliative behavior differed in rostral compared to caudal subregions of Ac and VTA, suggesting distinct roles for these subregions in the regulation of affiliative behavior. Finally, TH labeling density in the VMH and rostral VTA were positively related to the amount of courtship received from the partner and TH labeling in Ac was denser in opposite-sex pairs compared to same-sex pairs, indicative of socially induced brain plasticity. Overall, results highlight a complex region- and behavior-specific role for catecholamines in vertebrate affiliation.

Brain expression and song regulation of the cholecystokinin gene in the zebra finch (Taeniopygia guttata)

The gene encoding cholecystokinin (Cck) is abundantly expressed in the mammalian brain and has been associated with such functions as feeding termination and satiety, locomotion and self-stimulation, the modulation of anxiety-like behaviors, and learning and memory. Here we describe the brain expression and song regulation of Cck in the brain of the adult male zebra finch (Taeniopygia guttata), a songbird species. Using in situ hybridization we demonstrate that Cck is highly expressed in several discrete brain regions, most prominently the caudalmost portion of the hippocampal formation, the caudodorsal nidopallial shelf and the caudomedial nidopallium (NCM), the core or shell regions of dorsal thalamic nuclei, dopaminergic cell groups in the mesencephalon and pons, the principal nucleus of the trigeminal nerve, and the dorsal raphe. Cck was largely absent in song control system, a group of nuclei required for vocal learning and song production in songbirds, although sparse labeling was detected throughout the striatum, including song nucleus area X. We also show that levels of Cck mRNA and the number of labeled cells increase in the NCM of males and females following auditory stimulation with conspecific song. Double labeling further reveals that the majority of Cck cells, excluding those in the reticular nucleus of the thalamus, are non-GABAergic. Together, these data provide the first comprehensive characterization of Cck expression in a songbird, and suggest a possible involvement of Cck regulation in important aspects of birdsong biology, such as perceptual processing, auditory memorization, and/or vocal-motor control of song production.

Singing under the influence: examining the effects of nutrition and addiction on a learned vocal behavior

The songbird model is widely established in a number of laboratories for the investigation of the neurobiology and development of vocal learning. While vocal learning is rare in the animal kingdom, it is a trait that songbirds share with humans. The neuroanatomical and physiological organization of the brain circuitry that controls learned vocalizations has been extensively characterized, particularly in zebra finches (Taeniopygia guttata). Recently, several powerful molecular and genomic tools have become available in this organism, making it an attractive choice for neurobiologists interested in the neural and genetic basis of a complex learned behavior. Here, we briefly review some of the main features of vocal learning and associated brain structures in zebra finches and comment on some examples that illustrate how themes related to nutrition and addiction can be explored using this model organism.

Ultrasonic vocalizations in mouse models for speech and socio-cognitive disorders: insights into the evolution of vocal communication

Comparative analyses used to reconstruct the evolution of traits associated with the human language faculty, including its socio-cognitive underpinnings, highlight the importance of evolutionary constraints limiting vocal learning in non-human primates. After a brief overview of this field of research and the neural basis of primate vocalizations, we review studies that have addressed the genetic basis of usage and structure of ultrasonic communication in mice, with a focus on the gene FOXP2 involved in specific language impairments and neuroligin genes (NL-3 and NL-4) involved in autism spectrum disorders. Knockout of FoxP2 leads to reduced vocal behavior and eventually premature death. Introducing the human variant of FoxP2 protein into mice, in contrast, results in shifts in frequency and modulation of pup ultrasonic vocalizations. Knockout of NL-3 and NL-4 in mice diminishes social behavior and vocalizations. Although such studies may provide insights into the molecular and neural basis of social and communicative behavior, the structure of mouse vocalizations is largely innate, limiting the suitability of the mouse model to study human speech, a learned mode of production. Although knockout or replacement of single genes has perceptible effects on behavior, these genes are part of larger networks whose functions remain poorly understood. In humans, for instance, deficiencies in NL-4 can lead to a broad spectrum of disorders, suggesting that further factors (experiential and/or genetic) contribute to the variation in clinical symptoms. The precise nature as well as the interaction of these factors is yet to be determined.

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.

Mode of action and functional significance of 7α-hydroxypregnenolone stimulating locomotor activity

Previous studies over the past two decades have demonstrated that the brain and other nervous systems possess key steroidogenic enzymes and produces pregnenolone and other various neurosteroids in vertebrates in general. Recently, 7α-hydroxypregnenolone, a novel bioactive neurosteroid, was identified in the brain of newts and quail. Importantly, this novel neurosteroid is produced from pregnenolone through the enzymatic activity of cytochrome P450(7α) and acts on brain tissue as a neuronal modulator to stimulate locomotor activity in these vertebrates. Subsequently, the mode of action of 7α-hydroxypregnenolone was demonstrated. 7α-Hydroxypregnenolone stimulates locomotor activity through activation of the dopaminergic system. To understand the functional significance of 7α-hydroxypregnenolone in the regulation of locomotor activity, diurnal, and seasonal changes in 7α-hydroxypregnenolone synthesis were further characterized. Melatonin derived from the pineal gland and eyes regulates 7α-hydroxypregnenolone synthesis in the brain, thus inducing diurnal locomotor changes. Prolactin, an adenohypophyseal hormone, regulates 7α-hydroxypregnenolone synthesis in the brain, and also induces seasonal locomotor changes. In addition, 7α-hydroxypregnenolone mediates corticosterone action to modulate locomotor activity under stress. This review summarizes the current knowledge regarding the mode of action and functional significance of 7α-hydroxypregnenolone, a newly identified bioactive neurosteroid stimulating locomotor activity.

Neurosteroid biosynthesis and function in the brain of domestic birds

It is now established that the brain and other nervous systems have the capability of forming steroids de novo, the so-called "neurosteroids." The pioneering discovery of Baulieu and his colleagues, using rodents, has opened the door to a new research field of "neurosteroids." In contrast to mammalian vertebrates, little has been known regarding de novo neurosteroidogenesis in the brain of birds. We therefore investigated neurosteroid formation and metabolism in the brain of quail, a domestic bird. Our studies over the past two decades demonstrated that the quail brain possesses cytochrome P450 side-chain cleavage enzyme (P450scc), 3β-hydroxysteroid dehydrogenase/Δ(5)-Δ(4)-isomerase (3β-HSD), 5β-reductase, cytochrome P450 17α-hydroxylase/c17,20-lyase (P450(17α,lyase)), 17β-HSD, etc., and produces pregnenolone, progesterone, 5β-dihydroprogesterone (5β-DHP), 3β, 5β-tetrahydroprogesterone (3β, 5β-THP), androstenedione, testosterone, and estradiol from cholesterol. Independently, Schlinger's laboratory demonstrated that the brain of zebra finch, a songbird, also produces various neurosteroids. Thus, the formation and metabolism of neurosteroids from cholesterol is now known to occur in the brain of birds. In addition, we recently found that the quail brain expresses cytochrome P450(7α) and produces 7α- and 7β-hydroxypregnenolone, previously undescribed avian neurosteroids, from pregnenolone. This paper summarizes the advances made in our understanding of neurosteroid formation and metabolism in the brain of domestic birds. This paper also describes what are currently known about physiological changes in neurosteroid formation and biological functions of neurosteroids in the brain of domestic and other birds.

Characterization of the dopamine system in the brain of the túngara frog, Physalaemus pustulosus

Dopamine is an evolutionarily ancient neurotransmitter that plays an essential role in mediating behavior. In vertebrates, dopamine is central to the mesolimbic reward system, a neural network concerned with the valuation of stimulus salience, and to the nigrostriatal motor system and hypothalamic nuclei involved in the regulation of locomotion and social behavior. In amphibians, dopaminergic neurons have been mapped out in several species, yet the distribution of dopaminoreceptive cells is unknown. The túngara frog, Physalaemus pustulosus, is an excellent model system for the study of neural mechanisms by which valuations of stimuli salience and social decisions are made, especially in the context of mate choice. In order to better understand where dopamine acts to regulate social decisions in this species, we have determined the distribution of putative dopaminergic cells (using tyrosine hydroxylase immunohistochemistry) and cells receptive to dopaminergic signaling (using DARPP-32 immunohistochemistry) throughout the brain of P. pustulosus. The distribution of dopaminergic cells was comparable to other anurans. DARPP-32 immunoreactivity was identified in key brain regions known to modulate social behavior in other vertebrates including the proposed anuran homologues of the mammalian amygdalar complex, nucleus accumbens, hippocampus, striatum, preoptic area, anterior hypothalamus, ventromedial hypothalamus, and ventral tegmental area/substantia nigra pars compacta. Due to its widespread distribution, DARPP-32 likely also plays many roles in non-limbic brain regions that mediate non-social information processing. These results significantly extend our understanding of the distribution of the dopaminergic system in the anuran brain and beyond.

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.

Neurobiology of vocal communication: mechanisms for sensorimotor integration and vocal patterning

This review will focus on recent developments in the sensorimotor integration of vocal communication. Two broad themes are emphasized: the evolution of vocal production and perception, and the role of social context. Advances include: a proposal for the emergence of vocal patterning during vertebrate evolution, the role of sensory mechanisms such as categorical perception in decoding communication signals, contributions of sensorimotor integration phenomena including mirror neurons and vocal learning, and mechanisms of hormone-dependent plasticity in both auditory and vocal systems. Transcriptional networks activated in humans but not in chimps by the FoxP2 gene suggest molecular mechanisms underlying vocal gestures and the emergence of human language.

Activity in a cortical-basal ganglia circuit for song is required for social context-dependent vocal variability

Variability in adult motor output is important for enabling animals to respond to changing external conditions. Songbirds are useful for studying variability because they alter the amount of variation in their song depending on social context. When an adult zebra finch male sings to a female ("directed"), his song is highly stereotyped, but when he sings alone ("undirected"), his song varies across renditions. Lesions of the lateral magnocellular nucleus of the anterior nidopallium (LMAN), the output nucleus of a cortical-basal ganglia circuit for song, reduce song variability to that of the stereotyped "performance" state. However, such lesions not only eliminate LMAN's synaptic input to its targets, but can also cause structural or physiological changes in connected brain regions, and thus cannot assess whether the acute activity of LMAN is important for social modulation of adult song variability. To evaluate the effects of ongoing LMAN activity, we reversibly silenced LMAN in singing zebra finches by bilateral reverse microdialysis of the GABA(A) receptor agonist muscimol. We found that LMAN inactivation acutely reduced undirected song variability, both across and even within syllable renditions, to the level of directed song variability in all birds examined. Song variability returned to pre-muscimol inactivation levels after drug washout. However, unlike LMAN lesions, LMAN inactivation did not eliminate social context effects on song tempo in adult birds. These results indicate that the activity of LMAN neurons acutely and actively generates social context-dependent increases in adult song variability but that social regulation of tempo is more complex.

The neuroendocrine action potential. Winner of the 2008 Frank Beach Award in Behavioral Neuroendocrinology

Animals are remarkably well equipped to respond to changes in their environment across different time scales and levels of biological organization. Here, I introduce a novel perspective that incorporates the three main processes the nervous system uses to integrate and process information: electrophysiological, genomic, and neuroendocrine action potentials. After discussing several examples of neuroendocrine action potentials, I lay out the commonalities of these temporally organized responses and how they might be interrelated with electrophysiological activity and genomic responses. This framework provides a novel outlook on longstanding questions in behavioral neuroendocrinology and suggests exciting new avenues for further research that will integrate across disciplines and levels of biological organization.

Song environment affects singing effort and vasotocin immunoreactivity in the forebrain of male Lincoln's sparrows

Male songbirds often establish territories and attract mates by singing, and some song features can reflect the singer's condition or quality. The quality of the song environment can change, so male songbirds should benefit from assessing the competitiveness of the song environment and appropriately adjusting their own singing behavior and the neural substrates by which song is controlled. In a wide range of taxa, social modulation of behavior is partly mediated by the arginine vasopressin or vasotocin (AVP/AVT) systems. To examine the modulation of singing behavior in response to the quality of the song environment, we compared the song output of laboratory-housed male Lincoln's sparrows (Melospiza lincolnii) exposed to 1 week of chronic playback of songs categorized as either high or low quality, based on song length, complexity, and trill performance. To explore the neural basis of any facultative shifts in behavior, we also quantified the subjects' AVT immunoreactivity (AVT-IR) in three forebrain regions that regulate sociosexual behavior: the medial bed nucleus of the stria terminalis (BSTm), the lateral septum (LS), and the preoptic area. We found that high-quality songs increased singing effort and reduced AVT-IR in the BSTm and LS, relative to low-quality songs. The effect of the quality of the song environment on both singing effort and forebrain AVT-IR raises the hypothesis that AVT within these brain regions plays a role in the modulation of behavior in response to competition that individual males may assess from the prevailing song environment.

Identification of gonadotropin-inhibitory hormone in the zebra finch (Taeniopygia guttata): Peptide isolation, cDNA cloning and brain distribution

Two novel RFamide peptides, kisspeptins and gonadotropin-inhibitory hormone (GnIH) are neuropeptides that appear critical in the regulation of the reproductive neuroendocrine axis. GnIH was first identified in avian brain, however, kisspeptins have not been identified in birds. To determine biochemically the presence of kisspeptins and GnIH in the zebra finch, a study was conducted to isolate these two peptides from zebra finch brain. Peptides were isolated by immunoaffinity purification and only one peptide was characterized by mass spectrometry. This peptide was confirmed to be a 12-amino acid sequence with RFamide at its C-terminus; its sequence is SIKPFSNLPLRFamide (zebra finch GnIH). By this approach, however, identification of kisspeptin from zebra finch brain was not achieved. Cloned zebra finch GnIH precursor cDNA encoded three peptides that possess characteristic LPXRFamide (X=L or Q) motifs at the C-termini. In situ hybridization and immunohistochemical analysis revealed the cellular localization of zebra finch GnIH mRNA and peptide in the paraventricular nucleus and the dorsomedial nucleus of the hypothalamus. Fluorescent immunohistochemistry with confocal microscopy indicated that GnIH-immunoreactive (ir) fibers are very close appositions with gonadotropin-releasing hormone-I (GnRH-I) cells. Furthermore GnIH-ir nerve fibers were widely distributed in the multiple brain regions including the septum, preoptic area, median eminence, optic tectum and median eminence. The prominent fibers were seen in the ventral tegmental area, midbrain central gray and dorsal motor nucleus of the vagus in the medulla. Thus, GnIH may participate in not only neuroendocrine functions but also regulation of motivation for social behavior and autonomic mechanisms.

Dopamine receptors in a songbird brain

Dopamine is a key neuromodulatory transmitter in the brain. It acts through dopamine receptors to affect changes in neural activity, gene expression, and behavior. In songbirds, dopamine is released into the striatal song nucleus Area X, and the levels depend on social contexts of undirected and directed singing. This differential release is associated with differential expression of activity-dependent genes, such as egr1 (avian zenk), which in mammalian brain are modulated by dopamine receptors. Here we cloned from zebra finch brain cDNAs of all avian dopamine receptors: the D1 (D1A, D1B, D1D) and D2 (D2, D3, D4) families. Comparative sequence analyses of predicted proteins revealed expected phylogenetic relationships, in which the D1 family exists as single exon and the D2 family exists as spliced exon genes. In both zebra finch and chicken, the D1A, D1B, and D2 receptors were highly expressed in the striatum, the D1D and D3 throughout the pallium and within the mesopallium, respectively, and the D4 mainly in the cerebellum. Furthermore, within the zebra finch, all receptors, except for D4, showed differential expression in song nuclei relative to the surrounding regions and developmentally regulated expression that decreased for most receptors during the sensory acquisition and sensorimotor phases of song learning. Within Area X, half of the cells expressed both D1A and D2 receptors, and a higher proportion of the D1A-only-containing neurons expressed egr1 during undirected but not during directed singing. Our findings are consistent with hypotheses that dopamine receptors may be involved in song development and social context-dependent behaviors. J. Comp. Neurol. 518:741–769, 2010. © 2009 Wiley-Liss, Inc.

7α-hydroxypregnenolone, a new key regulator of locomotor activity of vertebrates: identification, mode of action, and functional significance

Steroids synthesized de novo by the central and peripheral nervous systems are called neurosteroids. The formation of neurosteroids from cholesterol in the brain was originally demonstrated in mammals by Baulieu and colleagues. Our studies over the past two decades have also shown that, in birds and amphibians as in mammals, the brain expresses several kinds of steroidogenic enzymes and produces a variety of neurosteroids. Thus, de novo neurosteroidogenesis from cholesterol is a conserved property that occurs throughout vertebrates. However, the biosynthetic pathways of neurosteroids in the brain of vertebrates was considered to be still incompletely elucidated. Recently, 7α-hydroxypregnenolone was identified as a novel bioactive neurosteroid stimulating locomotor activity in the brain of newts and quail through activation of the dopaminergic system. Subsequently, diurnal and seasonal changes in synthesis of 7α-hydroxypregnenolone in the brain were demonstrated. Interestingly, melatonin derived from the pineal gland and eyes regulates 7α-hydroxypregnenolone synthesis in the brain, thus inducing diurnal locomotor changes. Prolactin, an adenohypophyseal hormone, regulates 7α-hydroxypregnenolone synthesis in the brain, and may also induce seasonal locomotor changes. This review highlights the identification, mode of action, and functional significance of 7α-hydroxypregnenolone, a new key regulator of locomotor activity of vertebrates, in terms of diurnal and seasonal changes in 7α-hydroxypregnenolone synthesis, and describes some of their regulatory mechanisms.