Undirected Song Research Articles

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

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. 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. 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. 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.

Contribution of Endocannabinoids to Intrinsic Motivation for Undirected Singing in Adult Zebra Finches

Songbirds, such as zebra finches, spontaneously produce many song renditions for vocal practice even in the absence of apparent recipients throughout their lives. Such “undirected singing” is driven by intrinsic motivation, which arises within individuals for internal satisfaction without immediate external rewards. Intrinsic motivation for undirected singing in adult zebra finches was previously demonstrated to be critically regulated by dopamine through D2 receptors. Here, we further investigate the mechanisms of intrinsic motivation for undirected singing by focusing on endocannabinoids, which modulate dopamine signaling and contribute to motivation and reward in mammals. In songbirds, endocannabinoids have been shown to be involved in the production of undirected songs, but whether they are involved in the intrinsic motivation for undirected singing remains unknown. Using latencies of the first song production following temporary singing suppression as a measure of intrinsic motivation for undirected singing, we demonstrate that systemic administration of the direct cannabinoid agonist WIN55212-2 decreases intrinsic motivation for singing and that those effects are largely reversed by the cannabinoid antagonist SR141716A co-administered with WIN55212-2. Administration of SR141716A alone or that of two indirect cannabinoid agonists did not significantly affect intrinsic singing motivation. These results suggest that endocannabinoids are critically involved in regulating intrinsic motivation for undirected singing and provide new insights into the neural mechanisms of intrinsically motivated motor behaviors.

Durations of preparatory motor activity in the avian basal ganglia for songs and calls in a species of songbirds

Male songbirds are highly motivated to sing undirected song (US) as juveniles during song learning, and as adults. Given that singing US is a self-driven, elaborated behavior, we would expect to see preparatory activity in the striatal area prior to vocalization, and this preparatory activity could have different characteristics compared to activity driven by calls. In general, songs are longer, complex and influenced by learning while calls are shorter, simpler, and less influenced by experience. The present study recorded neural activity in Area X, a nucleus of the basal ganglia, in male Java sparrows (Lonchura oryzivora) in a sound-proof box and analyzed differences in activity change before US and trill-calls. Trill-calls were often emitted in social arousal, but occasionally emitted when alone. We saw a gradual increase in firing rate for about 2.3 s prior to the onset of US, and a shorter increase of about 1.3 s in firing rate prior to the onset of trill-calls. The results reveal that initiating US may be influenced by a prolonged and specific activity increase in the extent that is not seen with trill-calls. Results suggest that direct or indirect projections to Area X, which may reflect motivational state, could be the cause of this activity change.

Differences in dopamine and opioid receptor ratios in the nucleus accumbens relate to physical contact and undirected song in pair-bonded zebra finches.

Long-term social bonds are critical for survival and reproductive success in many species. Although courtship and pair-bond formation are relatively well studied, much less is known about the neural regulation of behaviors that occur after pair bonding that reinforce the bond and contribute to reproductive success. Dopamine and opioids in the nucleus accumbens (NAc) alter motivational state and reward by binding to receptor subtypes that engage distinct and opposing second messenger systems, and there is evidence that receptor ratios may influence social behavior. We used quantitative real-time PCR to explore relationships between messenger RNA ratios for dopamine D1 and D2 receptors (D1:D2) and mu and kappa opioid receptors (MOR:KOR) in NAc and behaviors implicated in reproductive investment and pair-bond maintenance in established male-female zebra finch pairs. In males, D1:D2 expression in NAc related negatively, whereas MOR:KOR related positively, to undirected song production. D1:D2 receptors also related positively to physical contact with a female. For females, D1:D2 expression was lower in females exposed to high compared to low rates of the partner's undirected song, and MOR:KOR expression in females related positively to undirected song exposure and allopreening. Analyses of single genes did not yield the same results. These findings suggest that the ratio of D1 to D2 and MOR to KOR receptor signaling in NAc causes differences in behavior or that behavior (or the partner's behavior) causes receptor ratio changes to modulate behaviors that maintain pair bonds and promote reproductive investment. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Supplemental Material for Differences in Dopamine and Opioid Receptor Ratios in the Nucleus Accumbens Relate to Physical Contact and Undirected Song in Pair-Bonded Zebra Finches

Supplemental Material for Differences in Dopamine and Opioid Receptor Ratios in the Nucleus Accumbens Relate to Physical Contact and Undirected Song in Pair-Bonded Zebra Finches

Experimental inhibition of a key cellular antioxidant affects vocal communication

Summary There is substantial interest of evolutionary ecologists in the proximate mechanisms that modulate vocal communication. In recent times, there has been growing interest in the role of oxidative stress as a mediator of avian song expression. Here, we tested whether the experimental inhibition of the synthesis of a key cellular antioxidant (glutathione) reduces song rate metrics of male European starlings (Sturnus vulgaris). We measured the effect of our treatment on total song rate and on its two components, undirected and nest‐box‐oriented song, outside the breeding season. Treated males that did not own a nest‐box (subordinate males likely to be of lower quality) suffered increased oxidative stress relative to untreated males, while treated males that owned a nest‐box (dominant males likely to be of higher quality) did not. Treated non‐owners also reduced their undirected song rate, whereas treated nest‐box owners did not suffer any reduction in song rate. Our results revealed that inhibition of a key cellular antioxidant results in decreased vocal communication in a social vertebrate, and that this effect is dependent on its social status (nest‐box owner vs. non‐owner). This work provides support for the hypothesis that acoustic signals may honestly convey information about the individual oxidative status and capacity to regulate the oxidative balance. Our findings raise the possibility of hitherto unexplored impacts of oxidative stress on fitness traits in social species. A lay summary is available for this article.

Song-associated reward correlates with endocannabinoid-related gene expression in male European starlings (Sturnus vulgaris)

Vocal communication is required for successful social interactions in numerous species. During the breeding season, songbirds produce songs that are reinforced by behavioral consequences (e.g., copulation). However, some songbirds also produce songs not obviously directed at other individuals. The consequences maintaining or reinforcing these songs are less obvious and the neural mechanisms associated with undirected communication are not well-understood. Previous studies indicate that undirected singing is intrinsically rewarding and mediated by opioid or dopaminergic systems; however, endocannabinoids are also involved in regulating reward and singing behavior. We used a conditioned place preference paradigm to examine song-associated reward in European starlings and quantitative real-time PCR to measure expression of endocannabinoid-related neural markers (CB1, FABP7, FABP5, FAAH, DAGLα), in brain regions involved in social behavior, reward and motivation (ventral tegmental area [VTA], periaqueductal gray [PAG], and medial preoptic nucleus [POM]), and a song control region (Area X). Our results indicate that starlings producing high rates of song developed a conditioned place preference, suggesting that undirected song is associated with a positive affective state. We found a significant positive relationship between song-associated reward and CB1 receptors in VTA and a significant negative relationship between song-associated reward and CB1 in PAG. There was a significant positive relationship between reward and the cannabinoid transporter FABP7 in POM and a significant negative relationship between reward and FABP7 in PAG. In Area X, FABP5 and DAGLα correlated positively with singing. These results suggest a role for endocannabinoid signaling in vocal production and reward associated with undirected communication.

Positive effect of dietary lutein and cholesterol on the undirected song activity of an opportunistic breeder.

Song is a sexually selected trait that is thought to be an honest signal of the health condition of an individual in many bird species. For species that breed opportunistically, the quantity of food may be a determinant of singing activity. However, it is not yet known whether the quality of food plays an important role in this respect. The aim of the present study was to experimentally investigate the role of two calorie-free nutrients (lutein and cholesterol) in determining the expression of a sexually selected behavior (song rate) and other behaviors (locomotor activity, self-maintenance activity, eating and resting) in male zebra finches (Taeniopygia guttata). We predicted that males supplemented with lutein and cholesterol would sing at higher rates than controls because both lutein and cholesterol have important health-related physiological functions in birds and birdsong mirrors individual condition. To control for testosterone secretion that may upregulate birdsong, birds were exposed to a decreasing photoperiod. Our results showed that control males down-regulated testosterone in response to a decreasing photoperiod, while birds treated with lutein or cholesterol maintained a constant singing activity. Both lutein- and cholesterol-supplemented groups sang more than control groups by the end of the experiment, indicating that the quality of food can affect undirected song irrespective of circulating testosterone concentrations. None of the other measured behaviors were affected by the treatment, suggesting that, when individuals have full availability of food, sexually selected song traits are more sensitive to the effect of food quality than other behavioral traits. Overall the results support our prediction that undirected song produced by male zebra finches signals access to high-quality food.

Social context differentially modulates activity of two interneuron populations in an avian basal ganglia nucleus.

Basal ganglia circuits are critical for the modulation of motor performance across behavioral states. In zebra finches, a cortical-basal ganglia circuit dedicated to singing is necessary for males to adjust their song performance and transition between spontaneous singing, when they are alone ("undirected" song), and a performance state, when they sing to a female ("female-directed" song). However, we know little about the role of different basal ganglia cell types in this behavioral transition or the degree to which behavioral context modulates the activity of different neuron classes. To investigate whether interneurons in the songbird basal ganglia encode information about behavioral state, I recorded from two interneuron types, fast-spiking interneurons (FSI) and external pallidal (GPe) neurons, in the songbird basal ganglia nucleus area X during both female-directed and undirected singing. Both cell types exhibited higher firing rates, more frequent bursting, and greater trial-by-trial variability in firing when male zebra finches produced undirected songs compared with when they produced female-directed songs. However, the magnitude and direction of changes to the firing rate, bursting, and variability of spiking between when birds sat silently and when they sang undirected and female-directed song varied between FSI and GPe neurons. These data indicate that social modulation of activity important for eliciting changes in behavioral state is present in multiple cell types within area X and suggests that social interactions may adjust circuit dynamics during singing at multiple points within the circuit.

Song in an Affiliative Context Relates to the Neural Expression of Dopamine- and Neurotensin-Related Genes in Male European Starlings

Some animals, including songbirds, vocalize at high rates when alone or in large groups. In songbirds, vocal behavior in these contexts is important for song learning and group cohesion. It is not obviously targeted at any particular individual and is described as ‘undirected'. Studies suggest a role for dopamine (DA) in undirected song. The neuropeptide neurotensin (NT) can enhance dopaminergic signaling upon binding to the NT receptor 1 (NTR1) and is found in regions where DA can influence song, including the ventral tegmental area (VTA), septum, and the song control nucleus Area X. To begin to test the hypothesis that NT and DA in these regions interact to influence undirected song, we used quantitative real-time PCR to relate undirected singing to mRNA expression of NT, NTR1, tyrosine hydroxylase (TH; a synthetic enzyme for DA) and D1 and D2 receptors in male European starlings. TH and NT expression in VTA, and NT and D1 expression in Area X, positively correlated with song. NT markers also correlated positively with DA markers in VTA. Given the role of VTA projections to Area X in song learning, these results suggest that interactions between NT and DA in these regions may contribute to vocal learning. In septum, NTR1 expression positively correlated with song and NT and DA markers were correlated, suggesting that NT in this region may influence dopaminergic transmission to facilitate undirected vocalizations. Overall, these findings implicate interactions between NT and DA in affiliative communication.

Relationship between the Sequencing and Timing of Vocal Motor Elements in Birdsong.

Accurate coordination of the sequencing and timing of motor gestures is important for the performance of complex and evolutionarily relevant behaviors. However, the degree to which motor sequencing and timing are related remains largely unknown. Birdsong is a communicative behavior that consists of discrete vocal motor elements (‘syllables’) that are sequenced and timed in a precise manner. To reveal the relationship between syllable sequencing and timing, we analyzed how variation in the probability of syllable transitions at branch points, nodes in song with variable sequencing across renditions, correlated with variation in the duration of silent gaps between syllable transitions (‘gap durations’) for adult Bengalese finch song. We observed a significant negative relationship between transition probability and gap duration: more prevalent transitions were produced with shorter gap durations. We then assessed the degree to which long-term age-dependent changes and acute context-dependent changes to syllable sequencing and timing followed this inverse relationship. Age- but not context-dependent changes to syllable sequencing and timing were inversely related. On average, gap durations at branch points decreased with age, and the magnitude of this decrease was greater for transitions that increased in prevalence than for transitions that decreased in prevalence. In contrast, there was no systematic relationship between acute context-dependent changes to syllable sequencing and timing. Gap durations at branch points decreased when birds produced female-directed courtship song compared to when they produced undirected song, and the magnitude of this decrease was not related to the direction and magnitude of changes to transition probabilities. These analyses suggest that neural mechanisms that regulate syllable sequencing could similarly control syllable timing but also highlight mechanisms that can independently regulate syllable sequencing and timing.

Predicting plasticity: acute context-dependent changes to vocal performance predict long-term age-dependent changes.

Understanding the factors that predict and guide variation in behavioral change can lend insight into mechanisms of motor plasticity and individual differences in behavior. The performance of adult birdsong changes with age in a manner that is similar to rapid context-dependent changes to song. To reveal mechanisms of vocal plasticity, we analyzed the degree to which variation in the direction and magnitude of age-dependent changes to Bengalese finch song could be predicted by variation in context-dependent changes. Using a repeated-measures design, we found that variation in age-dependent changes to the timing, sequencing, and structure of vocal elements ("syllables") was significantly predicted by variation in context-dependent changes. In particular, the degree to which the duration of intersyllable gaps, syllable sequencing at branch points, and fundamental frequency of syllables within spontaneous [undirected (UD)] songs changed over time was correlated with the degree to which these features changed from UD song to female-directed (FD) song in young-adult finches (FDyoung). As such, the structure of some temporal features of UD songs converged over time onto the structure of FDyoung songs. This convergence suggested that the FDyoung song could serve as a stable target for vocal motor plasticity. Consequently, we analyzed the stability of FD song and found that the temporal structure of FD song changed significantly over time in a manner similar to UD song. Because FD song is considered a state of heightened performance, these data suggest that age-dependent changes could reflect practice-related improvements in vocal motor performance.

Immunization reduces vocal communication but does not increase oxidative stress in a songbird species

Itishypothesizedthatvariation inimmunefunction between individuals is due to costs incurred to sustain it. Sup- port for this hypothesis mostly comes from short-term studies on the either costs of innate responses or a combination of innate and antibody responses. Key studies on the fitness and physiological costs of acquired immunity, in which the antibody response is specifically stimulated over a long peri- od, are lacking. We specifically stimulated the antibody re- sponse against a virus (Newcastle virus) in male European starlings (Sturnus vulgaris) for 2 months to test whether im- munization reduces a fitness-related trait (song rate) and in- creases oxidative stress. Immunization did not affect the total song rate, but it caused a reduction of the undirected song rate (produced away from the nest box and mostly used for estab- lishing dominance hierarchy). We also found that immunized birds had a lower nest-box-oriented song rate (mostly used to attract females) than control birds although the interaction between treatment and sampling period was not significant. Immunization did not cause any changes in the blood oxida- tive status. Starlings with a higher nest-box-oriented song rate had significantly lower levels of oxidative protein damage. Finally, starlings that skipped the antibody response had an oxidative status similar to that of starlings that produced anti- bodies, but they had overall a lower rate of undirected song. Our results suggest that (i) immunized starlings preserved the song used to attract mates but not that used in social interac- tions and (ii) the antibody response incurs costs that are reflected in the expression of song, but also that these costs are unlikely to be determined by oxidative stress. Our results also suggest that bird song might convey information about a male's oxidative status.

The effects of naloxone on courtship and pairing behaviour in male and female zebra finches: the importance of testing mechanisms using multiple paradigms

Opioids are implicated in social attachments, but their role in avian pair bonds is not well understood. The present study tested the effects of naloxone, an opioid antagonist, on pairing using both a forced-choice and a mixed-sex aviary paradigm. First, three doses of naloxone were systemically administered in males using a repeated measures forced-choice design, partner preference formation was tested on the second day. Males treated with 20 mg/kg sang less undirected song. Males treated with 10 mg/kg of naloxone sang less to the familiar partner than when treated with saline and were less likely to form a partner preference than were other treatments. In females, 10 mg/kg of naloxone in a forced-choice paradigm increased preference for the unfamiliar over the familiar male. Finally, males and females were administered either naloxone (10 mg/kg) or saline in a mixed-sex aviary. In females, naloxone increased pairing behaviours, but had no other effects in either sex. Our findings suggest that the effects of naloxone on pairing-related behaviours are context-dependent; male–male competition may decrease the effects of naloxone on male song and a choice of mates may increase affiliation in females in a semi-naturalistic paradigm, and increase preferences for an unfamiliar partner in a forced-choice paradigm. Our findings highlight the importance of using multiple paradigms to test mechanisms of behaviour. These findings contribute to our understanding of the mechanisms of monogamous relationships and suggest that opioids play a role in male courtship, female affiliation and partner preferences in both sexes of zebra finches, but that context is important.

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.

Mate Choice in Adult Female Bengalese Finches: Females Express Consistent Preferences for Individual Males and Prefer Female-Directed Song Performances

In the process of mate selection by female songbirds, male suitors advertise their quality through reproductive displays in which song plays an important role. Females evaluate the quality of each signal and the associated male, and the results of that evaluation guide expression of selective courtship displays. Some studies reveal broad agreement among females in their preferences for specific signal characteristics, indicating that those features are especially salient in female mate choice. Other studies reveal that females differ in their preference for specific characteristics, indicating that in those cases female evaluation of signal quality is influenced by factors other than simply the physical properties of the signal. Thus, both the physical properties of male signals and specific traits of female signal evaluation can impact female mate choice. Here, we characterized the mate preferences of female Bengalese finches. We found that calls and copulation solicitation displays are equally reliable indicators of female preference. In response to songs from an array of males, each female expressed an individual-specific song preference, and those preferences were consistent across tests spanning many months. Across a population of females, songs of some males were more commonly preferred than others, and females preferred female-directed songs more than undirected songs, suggesting that some song features are broadly attractive. Preferences were indistinguishable for females that did or did not have social experience with the singers, indicating that female preference is strongly directed by song features rather than experiences associated with the singer. Analysis of song properties revealed several candidate parameters that may influence female evaluation. In an initial investigation of those parameters, females could be very selective for one song feature yet not selective for another. Therefore, multiple song parameters are evaluated independently. Together these findings reveal the nature of signal evaluation and mate choice in this species.

MiR-9 and miR-140-5p TargetFoxP2and Are Regulated as a Function of the Social Context of Singing Behavior in Zebra Finches

Mutations in the FOXP2 gene cause speech and language impairments, accompanied by structural and functional abnormalities in brain regions underlying speech-related sensory-motor processing, including the striatum and cerebellum. The sequence and expression patterns of FOXP2 are highly conserved among higher vertebrates. In the zebra finch brain, FoxP2 is expressed in Area X, a striatal nucleus required for vocal learning, and reduced FoxP2 expression impairs dendritic development and vocal learning. The FoxP2 gene encodes a transcription factor that controls the expression of many downstream genes. However, how FOXP2 gene expression is regulated is not clearly understood. miRNAs regulate gene expression post-transcriptionally by targeting the 3'-untranslated regions (UTRs) of mRNAs, leading to translational suppression or mRNA degradation. In this study, we identified miR-9 and miR-140-5p as potential regulators of the FoxP2 gene. We show that both miR-9 and miR-140-5p target specific sequences in the FoxP2 3'-UTR and downregulate FoxP2 protein and mRNA expression in vitro. We also show that the expression of miR-9 and miR-140-5p in Area X of the zebra finch brain is regulated during song development in juvenile zebra finches. We further show that in adult zebra finches the expression of miR-9 and miR-140-5p in Area X is regulated as a function of the social context of song behavior in males singing undirected songs. Our findings reveal a post-transcriptional mechanism that regulates FoxP2 expression and suggest that social vocal behavior can influence the basal ganglia circuit controlling vocal learning via a miRNA-FoxP2 gene regulatory network.

Curvilinear relationships between mu-opioid receptor labeling and undirected song in male European starlings (Sturnus vulgaris)

Female-directed communication in male songbirds has been reasonably well studied; yet, relatively little is known about communication in other social contexts. Songbirds also produce song that is not clearly directed towards another individual (undirected song) when alone or in flocks. Although the precise functions of undirected song may differ across species, this type of song is considered important for flock maintenance, song learning or practice. Past studies show that undirected song is tightly coupled to analgesia and positive affective state, which are both mediated by opioid activity. Furthermore, labeling for the opioid met-enkephalin in the medial preoptic nucleus (POM) correlates positively with undirected song production. We propose that undirected song is facilitated and maintained by opioid receptor activity in the POM and other brain regions involved in affective state, analgesia, and social behavior. To provide insight into this hypothesis, we used immunohistochemistry to examine relationships between undirected song and mu-opioid receptors in male starlings. Polynomial regression analyses revealed significant inverted-U shaped relationships between measures of undirected song and mu-opioid receptor labeling in the POM, medial bed nucleus of the stria terminalis (BSTm), and periaqueductal gray (PAG). These results suggest that low rates of undirected song may stimulate and/or be maintained by mu-opioid receptor activity; however, it may be that sustained levels of mu-opioid receptor activity associated with high rates of undirected song cause mu-opioid receptor down-regulation. The results indicate that mu-opioid receptor activity in POM, BSTm, and PAG may underlie previous links identified between undirected song, analgesia, and affective state.

Pairing context determines condition-dependence of song rate in a monogamous passerine bird

Condition-dependence of male ornaments is thought to provide honest signals on which females can base their sexual choice for genetic quality. Recent studies show that condition-dependence patterns can vary within populations. Although long-term association is thought to promote honest signalling, no study has explored the influence of pairing context on the condition-dependence of male ornaments. In this study, we assessed the influence of natural variation in body condition on song rate in zebra finches (Taeniopygia guttata) in three different situations: during short and long encounters with an unfamiliar female, and within heterosexual mated pairs. We found consistent individual differences in male directed and undirected song rate. Moreover, body condition had a positive effect on song rate in paired males. However, male song rate was not influenced by body condition during short or long encounters with unfamiliar females. Song rate appears to be an unreliable signal of condition to prospective females as even poor-condition birds can cheat and sing at a high rate. By contrast, paired females can reliably use song rate to assess their mate's body condition, and possibly the genetic quality. We propose that species' characteristics, such as mating system, should be systematically taken into account to generate relevant hypotheses about the evolution of condition-dependent male ornaments.

Context-Dependent Links between Song Production and Opioid-Mediated Analgesia in Male European Starlings (Sturnus vulgaris)

Little is known about the neural mechanisms that ensure appropriate vocal behaviors within specific social contexts. Male songbirds produce spontaneous (undirected) songs as well as female-directed courtship songs. Opioid neuropeptide activity in specific brain regions is rewarding, at least in mammals, and past studies suggest that the opioid met-enkephalin in such areas is more tightly linked to undirected than female-directed song. Recent data using a song-associated place preference paradigm further suggest that production of undirected but not directed song is tightly linked to intrinsic reward. Opioids have analgesic properties. Therefore, if production of undirected song is closely linked to opioid-mediated reward, the production of undirected but not directed song should be associated with analgesia. Consistent with this prediction, in male starlings we identified a positive correlation between analgesia (decreased reactivity to a hot water bath) and undirected song (in non-breeding season condition males in affiliative flocks) but not female-directed song (in breeding season condition males presented with females). When breeding condition males were divided according to social status, a negative correlation was found in subordinate males (i.e. males that failed to acquire a nest box). These data are consistent with the hypotheses 1) that the production of undirected song is facilitated or maintained by opioids (and/or other neuromodulators that also induce analgesia) and 2) that production of female-directed song is not linked in the same way to release of the same neuromodulators. Results also demonstrate a link between analgesia and song in subordinate individuals lacking a nesting territory within the breeding season. Overall, the findings indicate that distinct neural mechanisms regulate communication in different social contexts and support the working hypothesis that undirected but not directed song is tightly linked to opioid release.