Rapamycin blocks the neuroprotective effects of sex steroids in the adult birdsong system

In adult songbirds, the telencephalic song nucleus HVC and its efferent target RA undergo pronounced seasonal changes in morphology. In breeding birds, there are increases in HVC volume and total neuron number, and RA neuronal soma area compared to nonbreeding birds. At the end of breeding, HVC neurons die through caspase‐dependent apoptosis and thus, RA neuron size decreases. Changes in HVC and RA are driven by seasonal changes in circulating testosterone (T) levels. Infusing T, or its metabolites 5α‐dihydrotestosterone (DHT) and 17 β‐estradiol (E2), intracerebrally into HVC (but not RA) protects HVC neurons from death, and RA neuron size, in nonbreeding birds. The phosphoinositide 3‐kinase (PI3K)‐Akt (a serine/threonine kinase)‐mechanistic target of rapamycin (mTOR) signaling pathway is a point of convergence for neuroprotective effects of sex steroids and other trophic factors. We asked if mTOR activation is necessary for the protective effect of hormones in HVC and RA of adult male Gambel's white‐crowned sparrows (Zonotrichia leucophrys gambelii). We transferred sparrows from breeding to nonbreeding hormonal and photoperiod conditions to induce regression of HVC neurons by cell death and decrease of RA neuron size. We infused either DHT + E2, DHT + E2 plus the mTOR inhibitor rapamycin, or vehicle alone in HVC. Infusion of DHT + E2 protected both HVC and RA neurons. Coinfusion of rapamycin with DHT + E2, however, blocked the protective effect of hormones on HVC volume and neuron number, and RA neuron size. These results suggest that activation of mTOR is an essential downstream step in the neuroprotective cascade initiated by sex steroid hormones in the forebrain.     

Effects of testosterone on Reelin expression in the brain of male European starlings

Reelin, a large glycoprotein defective in reeler mice, is assumed to determine the final location of migrating neurons in the developing brain. We studied the expression of Reelin in the brain of adult male European starlings that had been treated or not with exogenous testosterone. Reelin-immunoreactive cells and fibers were widely distributed in the forebrain including areas in and around the song control nucleus, HVC. No labeling was detected in other song control nuclei with the exception of nucleus uvaeformis, which was delineated by a dense cluster of Reelin-immunoreactive perikarya. Reelin is thus expressed in areas incorporating new neurons in adulthood, such as HVC. Reelin expression was sharply decreased by testosterone in HVC, nucleus uvaeformis and dorsal thalamus but not in other brain regions. These results are consistent with the idea that seasonal changes in Reelin expression modulate the incorporation of neurons within HVC. The presence of Reelin in other brain areas that do not incorporate new neurons in adulthood indicates, however, that this protein must play other unrelated roles in the adult brain. Additional studies should now be carried out to determine the specific role played by this protein in the seasonal plasticity of the songbird brain.     

Seasonal changes in courtship song and the medial preoptic area in male European starlings (Sturnus vulgaris)

In male starlings (Sturnus vulgaris) courtship song plays a critical role in mate attraction. During the breeding season courtship song occurs prior to copulation and appears to reflect male sexual arousal. Outside the breeding season starlings sing, but song appears unrelated to reproduction. The aromatization of testosterone (T), likely within the medial preoptic nucleus (POM), is critical for the expression of male sexual arousal. The present study was performed to determine whether seasonal changes in the POM might relate to seasonal changes in courtship singing behavior in male starlings. T concentrations, the volume of the POM, and aromatase within the POM were examined both during and outside of the breeding season in male starlings. Song was also recorded at these times both with and without a female present. The POM was largest and contained dense aromatase immunostaining only during the spring breeding season, when T concentrations were highest and males responded to a female with an increase in courtship song. Outside the breeding season the volume of the POM was small, T concentrations were low, and males displayed no changes in song expression in response to female conspecifics. Song bout length was positively related to POM volume, and males sang longer songs in spring. Only males with nestboxes in spring responded to a female, and the POM tended to be larger in these males, suggesting that nestbox possession might influence neuroplasticity within the POM. Overall, the findings suggest that T-dependent plasticity and aromatase activity within the POM might regulate courtship singing in a wild songbird.     

Seasonal Changes in Courtship Song and the Medial Preoptic Area in Male European Starlings (Sturnus vulgaris)

In male starlings (Sturnus vulgaris) courtship song plays a critical role in mate attraction. During the breeding season courtship song occurs prior to copulation and appears to reflect male sexual arousal. Outside the breeding season starlings sing, but song appears unrelated to reproduction. The aromatization of testosterone (T), likely within the medial preoptic nucleus (POM), is critical for the expression of male sexual arousal. The present study was performed to determine whether seasonal changes in the POM might relate to seasonal changes in courtship singing behavior in male starlings. T concentrations, the volume of the POM, and aromatase within the POM were examined both during and outside of the breeding season in male starlings. Song was also recorded at these times both with and without a female present. The POM was largest and contained dense aromatase immunostaining only during the spring breeding season, when T concentrations were highest and males responded to a female with an increase in courtship song. Outside the breeding season the volume of the POM was small, T concentrations were low, and males displayed no changes in song expression in response to female conspecifics. Song bout length was positively related to POM volume, and males sang longer songs in spring. Only males with nestboxes in spring responded to a female, and the POM tended to be larger in these males, suggesting that nestbox possession might influence neuroplasticity within the POM. Overall, the findings suggest that T-dependent plasticity and aromatase activity within the POM might regulate courtship singing in a wild songbird.     

Estrogen contributes to seasonal plasticity of the adult avian song control system

Songbirds show dramatic neural plasticity as adults, including large-scale anatomical changes in discrete brain regions ("song control nuclei") controlling the production of singing behavior. The volumes of several song control nuclei are much larger in the breeding season than in the nonbreeding season, and these seasonal neural changes are regulated by plasma testosterone (T) levels. In many cases, the effects of T on the central nervous system are mediated by neural conversion to estradiol (E(2)) by the enzyme aromatase. The forebrain of male songbirds expresses very high levels of aromatase, in some cases adjacent to song control nuclei. We examined the effects of aromatase inhibition and estrogen treatment on song nuclei size using wild male songbirds in both the breeding and nonbreeding seasons. In breeding males, aromatase inhibition caused the volume of a telencephalic song control nucleus (HVC) to decrease, and this effect was partially rescued by concurrent estrogen replacement. In nonbreeding males, estradiol treatment caused HVC to grow to maximal spring size within 2 weeks. Overall, these data suggest that aromatization of T is an important mediator of song control system plasticity, and that estradiol has neurotrophic effects in adult male songbirds. This study demonstrates that estrogen can affect adult neural plasticity on a gross anatomical scale and is the first examination of estrogen effects on the brain of a wild animal.     

Perineuronal nets and vocal plasticity in songbirds: A proposed mechanism to explain the difference between closed‐ended and open‐ended learning

Perineuronal nets (PNN) are aggregations of chondroitin sulfate proteoglycans surrounding the soma and proximal processes of neurons, mostly GABAergic interneurons expressing parvalbumin. They limit the plasticity of their afferent synaptic connections. In zebra finches PNN develop in an experience‐dependent manner in the song control nuclei HVC and RA (nucleus robustus arcopallialis) when young birds crystallize their song. Because songbird species that are open‐ended learners tend to recapitulate each year the different phases of song learning until their song crystallizes at the beginning of the breeding season, we tested whether seasonal changes in PNN expression would be found in the song control nuclei of a seasonally breeding species such as the European starling. Only minimal changes in PNN densities and total number of cells surrounded by PNN were detected. However, comparison of the density of PNN and of PNN surrounding parvalbumin‐positive cells revealed that these structures are far less numerous in starlings that show extensive adult vocal plasticity, including learning of new songs throughout the year, than in the closed‐ended learner zebra finches. Canaries that also display some vocal plasticity across season but were never formally shown to learn new songs in adulthood were intermediate in this respect. Together these data suggest that establishment of PNN around parvalbumin‐positive neurons in song control nuclei has diverged during evolution to control the different learning capacities observed in songbird species. This differential expression of PNN in different songbird species could represent a key cellular mechanism mediating species variation between closed‐ended and open‐ended learning strategies. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 975–994, 2017     

Testosterone-induced changes in adult canary brain are reversible

Brain nuclei that control song are larger in male canaries, which sing, than in females, which sing rarely or not at all. Treatment of adult female canaries with testosterone (T) induces song production and causes song-control nuclei to grow, approaching the volumes observed in males. For example, the higher vocal center (HVC) of adult females approximately doubles in size by 1 month following the onset of T treatment. Male HVC projects to a second telencephalic nucleus, RA (the robust nucleus of the archistriatum), which projects in turn to the vocal motor neurons. Whether HVC makes a similar connection in female canaries is not known, although HVC and RA are not functionally connected in female zebra finches, a species in which testosterone does not induce neural or behavioral changes in the adult song system. This experiment investigated whether HVC makes an efferent projection to RA in normal adult female canaries, or if T is necessary to induce the growth of this connection. In addition, we examined whether T-induced changes in adult female canary brain are reversible. Adult female canaries received systemic T implants that were removed after 4 weeks; these birds were killed 4 weeks after T removal (Testosterone-Removal, T-R). Separate groups of control birds received either (a) T implants for 4 weeks which were not removed (Testosterone-Control, T-C) or (b) empty implants (Untreated Control, øO-C). Crystals of the fluorescent tracer DiI were placed in the song-control nucleus HVC in order to anterogradely label both efferent targets of HVC, RA and Area X. Projections from HVC to RA and Area X were present in all treatment groups including untreated controls, and did not appear to differ either qualitatively or quantitatively. Thus, formation of efferent connections from HVC may be prerequisite to hormone-induced expression of song behavior in adult songbirds. The volumes of RA and Area X were measured using the distribution of anterograde label as well as their appearance in Nissl-stained tissue. RA was larger in T-treated control birds than in untreated controls. Experimental birds in which T was given and then removed (T-R) had RA volumes closer in size to untreated controls (ø-C). Because the volume of RA in T-treated controls (T-C) was larger than that of birds that did not receive T (ø-C), we conclude that the volume of RA increased in both T-C and T-R birds but regressed upon removal of T in T-R birds. Surprisingly, the volume of Area X did not increase in T-treated birds. Birds in this study were maintained on short days, suggesting that T-induced growth of Area X reported previously may have resulted from an interaction between T and another seasonal or photoperiodic factor induced by exposure to long daylengths. © 1993 John Wiley & Sons, Inc.     

Androgen control of vocal control region volumes in a wild migratory songbird (Junco hyemalis) is region and possibly age dependent

Previous laboratory studies have shown that photoperiodic adult songbirds experience seasonal variations in singing frequency that correlate with plasma androgen levels, as well as changes in the brain regions that control singing (vocal control regions). The present study investigates naturally occurring seasonal changes in the sizes of these regions in a wild migratory species (dark-eyed junco, Junco hyemalis), with samples from adolescence to post-breeding fall migration. In adult males, the volumes of the vocal control regions area X and the higher vocal center (HVC) were large during the breeding season when birds were singing and androgen levels were high, and decreased in size after the breeding season when singing had stopped and androgen levels were low. HVC volume in adolescent males caught in the fall (no singing), when plasma androgen levels were low, was smaller than in breeding adults, thereby following the seasonal pattern of change in plasma androgen levels. In adolescent males, however, area X volume was the same as in breeding adults. Thus, area X size in adolescent male juncos may be testosterone independent. The seasonal pattern of robust nucleus of the archistriatum volume was similar to that of the HVC. The volumes of neither the magnocellular nucleus of the anterior neostriatum nor the nucleus rotundus, a control region, differed seasonally. Castration of breeding adult males caused both area X and HVC volumes to decrease compared to castrated controls with testosterone replacement, indicating that maintenance of these two region volumes is testosterone dependent in adults. © 1997 John Wiley & Sons, Inc. J Neurobiol 32: 391–402, 1997.     

Early nutritional stress impairs development of a song-control brain region in both male and female juvenile song sparrows (Melospiza melodia) at the onset of song learning

Birdsong is a sexually selected trait and is often viewed as an indicator of male quality. The developmental stress hypothesis proposes a model by which song could be an indicator; the time during early development, when birds learn complex songs and/or local variants of song, is of rapid development and nutritional stress. Birds that cope best with this stress may better learn to produce the most effective songs. The developmental stress hypothesis predicts that early food restriction should impair development of song-control brain regions at the onset of song learning. We examined the effect of food restriction on song-control brain regions in fledgling (both sexes, 23-26 days old) song sparrows (Melospiza melodia). Food restriction selectively reduced HVC volume in both sexes. In addition, sex differences were evident in all three song-control regions. This study lends further support to a growing body of literature documenting a variety of behavioural, physiological and neural detriments in several songbird species resulting from early developmental stress.     

Hormone-induced changes in identified cell populations of the higher vocal center in male canaries

Male canaries revise their vocal repertoire every year. Early work indicated that the volume and neuron number of the song-control nucleus HVC (Higher Vocal Center) declined in late-summer/fall as birds added and deleted syllables from their repertoire, and increased in spring as the set of song syllables stabilized to a fixed number. Seasonal variation in serum testosterone levels suggested that these changes in brain and behavior were regulated by testosterone (T). However, although initial studies describing growth and regression of HVC used Nissl-staining to define its borders, recent experiments that have measured the distribution of identified populations of HVC cells (projection neurons, hormone target cells) suggest that there are no seasonal changes in HVC volume or neuron number. In order to clarify the role of T in the regulation of HVC morphology, we castrated male canaries, maintained them on short (fall-like) days, and treated them with either T, antisteroid drugs, or nothing. After 1 month of treatment, we used a double-labeling technique to characterize HVC projection neurons and androgen target cells. The results showed that hormonal manipulation influenced HVC volume, the density and size of HVC cells, and the absolute number and percentage of androgen target cells in HVC. Hormonal manipulation did not influence the absolute number of cells in HVC. Moreover, the distribution of projection neurons, androgen target cells, and the Nissl-defined borders of HVC were closely aligned in all experimental groups, indicating that exposure to T and/or its metabolites (estradiol and dihydrotestosterone) regulates the overall size of HVC by affecting the distributions of both projection neurons and androgen target cells. Analysis of double-labeling results suggests that T specifically influences both cell size and the ability to accumulate androgen among HVC neurons that project to the robust nucleus of the archistriatum (RA). The results of this study show that steroid hormones exert potent effects on HVC morphology in male canaries, but differences between our results and studies of seasonal males suggest there may be additional factors that can regulate HVC morphology. © 1993 John Wiley & Sons, Inc.     

BDNF mediates the effects of testosterone on the survival of new neurons in an adult brain

New neurons are incorporated into the high vocal center (HVC), a nucleus of the adult canary (Serinus canaria) brain that plays a critical role in the acquisition and production of learned song. Recruitment of new neurons in the HVC is seasonally regulated and depends upon testosterone levels. We show here that brain-derived neurotrophic factor (BDNF) is present in the HVC of adult males but is not detectable in that of females, though the HVC of both sexes has BDNF receptors (TrkB). Testosterone treatment increases the levels of BDNF protein in the female HVC, and BDNF infused into the HVC of adult females triples the number of new neurons. Infusion of a neutralizing antibody to BDNF blocks the testosterone-induced increase in new neurons. Our results demonstrate that BDNF is involved in the regulation of neuronal replacement in the adult canary brain and suggest that the effects of testosterone are mediated through BDNF.     

Coordinated interaction of neurogenesis and angiogenesis in the adult songbird brain

Neurogenesis proceeds throughout life in the higher vocal center (HVC) of the adult songbird neostriatum. Testosterone induces neuronal addition and endothelial division in HVC. We asked if testosterone-induced angiogenesis might contribute importantly to HVC neuronal recruitment. Testosterone upregulated both VEGF and its endothelial receptor, VEGF-R2/Quek1/KDR, in HVC. This yielded a burst in local HVC angiogenesis. FACS-isolated HVC endothelial cells produced BDNF in a testosterone-dependent manner. In vivo, HVC BDNF rose by the third week after testosterone, lagging by over a week the rise in VEGF and VEGF-R2. In situ hybridization revealed that much of this induced BDNF mRNA was endothelial. In vivo, both angiogenesis and neuronal addition to HVC were substantially diminished by inhibition of VEGF-R2 tyrosine kinase. These findings suggest a causal interaction between testosterone-induced angiogenesis and neurogenesis in the adult forebrain.     

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

In some species, such as songbirds, much is known about how the brain regulates vocal learning, production, and perception. What remains a mystery is what regulates the motivation to communicate. European starlings (Sturnus vulgaris) sing throughout most of the year, but the social and environmental factors that motivate singing behavior differ seasonally. Male song is highly sexually motivated during, but not outside of, the breeding season. Brain areas outside the song control system, such as the medial preoptic nucleus (POM) and ventral tegmental area (VTA), have been implicated in regulating sexually motivated behaviors in birds, including song. The present study was designed to explore whether these regions, as well as three song control nuclei [area X, the high vocal center (HVC), and the robust nucleus of the arcopallium (RA)], might be involved differentially in song produced within compared to outside of a breeding context. We recorded the behavioral responses of breeding and nonbreeding condition male starlings to the introduction of a female conspecific. Males did not show context-dependent differences in the overall amount of song sung. However, immunocytochemistry for the protein product of the immediate early gene cFOS revealed a positive linear relationship between the total amount of songs sung and number of cFOS-labeled cells in POM, VTA, HVC, and RA for birds singing during, but not outside of, a breeding context. These results suggest that these regions differentially regulate male song production depending on reproductive context. Overall the data support the hypothesis that the POM and VTA interact with the song control system, specifically HVC and RA, to regulate sexually motivated vocal communication in songbirds.     

Lack of a synergistic effect between estradiol and dihydrotestosterone in the masculinization of the zebra finch song system

Previous studies have suggested that both major active metabolites of testosterone, estradiol (E₂) and dihydrotestosterone (DHT), are needed for complete masculinization of the brain regions that control song in passerine birds. However, DHT treatment of hatchling female zebra finches has only small masculinizing effects on the song system. To assess whether E₂ and DHT have a synergistic effect on the masculinization of the zebra finch song system, female zebra finches were given Silastic implants of E₂ on the day of hatching (day 1) either without any additional hormone treatment or in combination with DHT on days 1, 14, or 70. At 105 to 110 days of age, we measured the volumes of Area X, higher vocal center (HVC), robust nucleus of the archistriatum (RA), soma sizes in HVC, RA, and the lateral magnocellular nucleus of the neostriatum (lMAN), and neuron density and number in RA. E₂ masculinized all of the measures in the song system with the exception of the number of neurons in RA. DHT did not synergize with E₂ to produce any additional masculinization of the attributes measured. These data demonstrate that the combination of E₂ and DHT did not result in the complete masculinization of the song control nuclei and argue against the importance of androgen in sexual differentiation of the song system. © 1995 John Wiley & Sons, Inc.     

Testosterone and the incidence of hormone target cells in song-control nuclei of adult canaries.

Adult male canaries learn to produce high-amplitude complex courtship songs each breeding season, whereas females do not, and brain nuclei involved with the production of song behavior are much larger in breeding males than in nonbreeding males or females (Nottebohm, 1980, 1981). However, treatment of adult females with testosterone (T) causes them to produce male-like song and stimulates pronounced growth of some song-control brain nuclei such as the caudal nucleus of the ventral hyperstriatum (HVc). We reexamined the effects of T on song-control nuclei in deafened birds. In order to examine whether the pattern of hormone accumulation varies as a function of circulating testosterone levels we described the distribution of testosterone-concentrating cells in HVc and the magnocellular nucleus of the anterior neostriatum (MAN) in hearing adult male, female, and T-treated female canaries, as well as in deaf T-treated and untreated females. In contrast to our previous findings (Bottjer, Schoonmaker, and Arnold, 1986a), we observed no tendency in this study for testosterone-induced growth of HVc to be attenuated in deafened birds. There was no difference between deaf and hearing birds in the incidence of labeled cells within HVc. We also observed no sex or hormone-induced differences in the percentage of hormone-concentrating cells in HVc: normal females have approximately the same proportion of hormone target cells as do males and T-treated females. However, males normally have many more neurons in HVc than do control females, and systemic exposure to testosterone induces a pronounced increase in the number of HVc neurons of adult females. Therefore, the absolute number of hormone target cells in HVc is likely to be much greater in males and T-treated females than in normal females. As in HVc, there were no differences among groups in the proportion of labeled cells within lateral MAN (IMAN), a nucleus that has been implicated in song learning (Bottjer, Miesner and Arnold, 1984). In contrast, the incidence of hormone target cells in medial MAN (mMAN) did vary as a function of hormonal condition: although mMAN of normal females is rarely visible in Nissl-stained sections and cells in this region are not hormone labeled, mMAN is clearly visible in Nissl-stained sections of males and T-treated females and contains many hormone-labeled cells. This testosterone-induced change in the phenotype of mMAN cells suggests a possible role for mMAN in learned song behavior.     

Testosterone and the incidence of hormone target cells in song-control nuclei of adult canaries

Adult male canaries learn to produce high-amplitude complex courtship songs each breeding season, whereas females do not, and brain nuclei involved with the production of song behavior are much larger in breeding males than in nonbreeding males or females (Nottebohm, 1980, 1981). However, treatment of adult females with testosterone (T) causes them to produce male-like song and stimulates pronounced growth of some song-control brain nuclei such as the caudal nucleus of the ventral hyperstriatum (HVc). We reexamined the effects of T on song-control nuclei in deafened birds. In order to examine whether the pattern of hormone accumulation varies as a function of circulating testosterone levels we described the distribution of testosterone-concentrating cells in HVc and the magnocellular nucleus of the anterior neostriatum (MAN) in hearing adult male, female, and T-treated female canaries, as well as in deaf T-treated and untreated females. In contrast to our previous findings (Bottjer, Schoonmaker, and Arnold, 1986a), we observed no tendency in this study for testosterone-induced growth of HVc to be attenuated in deafened birds. There was no difference between deaf and hearing birds in the incidence of labeled cells within HVc. We also observed no sex or hormone-induced differences in the percentage of hormone-concentrating cells in HVc: normal females have approximately the same proportion of hormone target cells as do males and T-treated females. However, males normally have many more neurons in HVc than do control females, and systemic exposure to testosterone induces a pronounced increase in the number of HVc neurons of adult females. Therefore, the absolute number of hormone target cells in HVc is likely to be much greater in males and T-treated females than in normal females. As in HVc, there were no differences among groups in the proportion of labeled cells within lateral MAN (IMAN), a nucleus that has been implicated in song learning (Bottjer, Miesner and Arnold, 1984). In contrast, the incidence of hormone target cells in medial MAN (mMAN) did vary as a function of hormonal condition: although mMAN of normal females is rarely visible in Nissl-stained sections and cells in this region are not hormone labeled, mMAN is clearly visible in Nisslstained sections of males and T-treated females and contains many hormone-labeled cells. This testosterone-induced change in the phenotype of mMAN cells suggests a possible role for mMAN in learned song behavior.     

Birth,migration, incorporation,and death of vocal control neurons in adult songbirds

Neurogenesis continues in the brain of adult birds. These cells are born in the ventricular zone of the lateral ventricles. Young neurons then migrate long distances guided, in part, by radial cell processes and become incorporated throughout most of the telencephalon. In songbirds, the high vocal center (HVC), which is important for the production of learned song, receives many of its neurons after hatching. HVC neurons which project to the robust nucleus of the archistriatum to form part of the efferent pathway for song production, and HVC interneurons continue to be added throughout life. In contrast, Area X-projecting HVC cells, thought to be part of a circuit necessary for song learning but not essential for adult song production, are only born in the embryo. New neurons in HVC of juvenile and adult birds replace older cells that die. There is a correlation between seasonal cell turnover rates (addition and loss) and testosterone levels in adult male canaries. Available evidence suggests that steroid hormones control the recruitment and/or survival of new HVC neurons, but not their production. The functions of neuronal replacement in adult birds remain unclear. However, rates of HVC neuron turnover are highest at times of year when canaries modify their songs. Replaceable HVC neurons may participate in the modification of perceptual memories or motor programs for song production. In contrast, permanent HVC neurons could hold long-lasting song-related information. The unexpected large-scale production of neurons in the adult brain holds important clues about brain function and, in particular, about the neural control of a learned behavior—birdsong. © 1997 John Wiley & Sons, Inc. J Neurobiol 33: 585–601, 1997     

A species-specific view of song representation in a sensorimotor nucleus

Songbirds constitute a powerful model system for the investigation of how complex vocal communication sounds are represented and generated, offering a neural system in which the brain areas involved in auditory, motor and auditory–motor integration are well known. One brain area of considerable interest is the nucleus HVC. Neurons in the HVC respond vigorously to the presentation of the bird’s own song and display song-related motor activity. In the present paper, we present a synthesis of neurophysiological studies performed in the HVC of one songbird species, the canary (Serinus canaria). These studies, by taking advantage of the singing behavior and song characteristics of the canary, have examined the neuronal representation of the bird’s own song in the HVC. They suggest that breeding cues influence the degree of auditory selectivity of HVC neurons for the bird’s own song over its time-reversed version, without affecting the contribution of spike timing to the information carried by these two song stimuli. Also, while HVC neurons are collectively more responsive to forward playback of the bird’s own song than to its temporally or spectrally modified versions, some are more broadly tuned, with an auditory responsiveness that extends beyond the bird’s own song. Lastly, because the HVC is also involved in song production, we discuss the peripheral control of song production, and suggest that interspecific variations in song production mechanisms could be exploited to improve our understanding of the functional role of the HVC in respiratory–vocal coordination.