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At least 19 recordsLinked to original sources

PubMed1998

Lucifer Yellow filling of area X-projecting neurons in the high vocal center of female canaries.

The avian high vocal center (HVC) is a complex forebrain nucleus that coordinates the sensorimotor integration necessary for song learning and production. It receives auditory and potentially somatosensory input, and sends major projections to vocal motor and anterior forebrain nuclei. The HVC has at least four morphological classes of neurons for which the connectivity remains uncertain. Previous studies have alluded to the functional identity of the cell classes, but none have provided the definitive evidence necessary for subsequent identification of behaviorally relevant changes within known neuronal populations. The cell filling technique we have adapted for use in the song system provides a method by which hodologically identified classes can be described with precision, and song related changes in their morphology can be readily identified. Neurons in female canaries (Serinus canarius) that project to Area X of the anterior forebrain pathway were retrogradely labeled, selectively filled with Lucifer Yellow in a fixed slice preparation, and converted to a Golgi-like stain through an immunocytochemical reaction. We have identified Area X-projecting neurons as belonging to the thick dendrite class of Nixdorf et al. [B.E. Nixdorf, S.S. Davis, T.J. DeVoogd, Morphology of golgi-impregnated neurons in hyperstriatum ventralis, pars caudalis in adult male and female canaries, J. Comp. Neurol. 284 (1989) 337-349] and have shown definitively that they are among the HVC neurons that can receive direct auditory input, as this cell class has short dendrites that extend into the shelf region ventral to HVC that is known to receive auditory inputs. Well-filled axons had collaterals that ramified and terminated within the nucleus, demonstrating a network through which Area X-projecting cells can contribute to intrinsic HVC communication.

Animals↗

PubMed2004

Neural correlates of song complexity in Bengalese finch high vocal center.

Auditory neurons in the songbird forebrain nucleus high vocal center HVC) show high selectivity to the temporal structure of bird's own song but the relationship between the degree of song complexity and neural selectivity is not known. We investigated the song temporal selectivity of HVC neurons by multi-unit recordings in seven male Bengalese finches with different song complexity. Results showed that HVC multi-units of the individuals with more complex songs responded strongly to each of the self-generated song elements but were relatively insensitive to the element order, while those with stereotyped songs responded only to the song elements ordered exactly as in the self-produced songs. Data suggest that the individually learned song syntax correlates with individualized temporal combination selectivity in HVC neurons.

Acoustic Stimulation↗

PubMed1994

Testosterone increases the recruitment and/or survival of new high vocal center neurons in adult female canaries.

New neurons are added to the high vocal center (HVC) of adult male and female canaries. Exogenous testosterone induces a marked increase in HVC size in adult female canaries, though the mechanisms responsible for this increase remain unknown. To understand the mechanisms, we analyzed the effects of testosterone on neuronal recruitment in the female HVC. Intact adult female canaries received Silastic implants that were empty or filled with testosterone. Birds in the short-survival group received the Silastic implant, followed by a single injection of [3H]thymidine 2 days later, and were killed on the following day. Birds in the long-survival group were injected once a day for 5 days with [3H]thymidine and received the Silastic implant 20 and 40 days later. These birds were killed 60 days after the first injection of [3H]thymidine. The number of 3H-labeled ventricular zone cells above, rostral, or caudal to HVC was not affected by the hormone treatment in the short-survival birds, suggesting that testosterone did not affect neuronal production. However, the number of 3H-labeled HVC neurons that projected to robust nucleus of the archistriatum (RA) in the long-survival birds was three times greater in the hormone-treated than in the control group, though the total number of RA-projecting cells did not change significantly. Testosterone also induced an increase in the size of the HVC cells that project to RA. Thus, these experiments suggest that testosterone affects the recruitment and/or survival of newly generated RA-projecting HVC neurons but does not affect their production.

Animals↗

PubMed1999

Fate of new neurons in adult canary high vocal center during the first 30 days after their formation.

Projection neurons are added to the high vocal center (HVC) of adult songbirds. Here we report on events associated with their initial arrival in HVC. Neurons formed in adult canaries were labeled with [(3)H]-thymidine and examined 8, 15, 22, and 31 days later. By 8 days, some [(3)H]-labeled cells with the nuclear profile of postmigratory neurons were already present in HVC but could not be retrogradely labeled by Fluoro-Gold injections in the robust nucleus of the archistriatum (RA); 7 days later, a few such cells could be backfilled from RA. Thus, new neurons may arrive in HVC as much as 1 week prior to establishing connections with RA. By 31 days, 43% of the [(3)H]-labeled neurons could be backfilled from RA. In no case were new neurons backfilled by tracer injections into Area X, suggesting that newly formed HVC cells do not establish a transient connection with this region. At all survival times, the somata of new neurons were often clustered tightly together with other HVC neurons that differed in age and projection. Between days 15 and 25 after their birth, half of the new HVC neurons disappeared. We conclude: (1) that neurons arrive in HVC earlier than previously thought, (2) that soon after their arrival they become part of cell clusters in HVC, and (3) that in addition to the previously described death of new neurons that occurs over a period of months, there is an early wave of death that occurs soon after new neurons adopt a postmigratory phenotype.

Animals↗

PubMed1998

Axonal connections of the high vocal center and surrounding cortical regions in juvenile and adult male zebra finches.

Neuronal connections of the High Vocal Center (HVC), a cortical nucleus of songbirds necessary for learned vocal behavior, and the region adjacent to HVC called paraHVC (pHVC), were studied in adult and juvenile male zebra finches. Extremely small injections of fluorescent dextran amines or biocytin were made within subregions of HVC and pHVC to define the precise nature and development of these pathways. In adults, all HVC injections produced an even, nontopographic distribution of retrograde label throughout the medial magnocellular nucleus of the anterior neostriatum (mMAN), the interfacial nucleus (NIf), and the uvaeform nucleus of the thalamus (Uva) and an even distribution of anterograde label within area X of the striatum and the robust nucleus of the archistriatum (RA). These same patterns of projections were present in juvenile birds 20-23 days of age, including the projection from HVC to RA, which has previously been reported to develop only after 25-30 days of age. Results also establish a novel efferent projection from HVC to pHVC in both juvenile and adult birds. Injections into pHVC indicate that this region receives afferent input from song control areas HVC, mMAN, medial regions of the parvicellular shell of lateral MAN, NIf, and Uva and projects to Area X, caudomedial regions of striatum, and regions of the caudomedial neostriatum (NCM). Thus, neuronal connections of pHVC are highly integrated with circuitry important for vocal behavior and are distinct from those of HVC. Such differences establish HVC and pHVC as separate brain areas and suggest that each may serve a different function in vocal behavior. Control injections in both juveniles and adults produced specific patterns of projections from areas outside of HVC to areas outside of RA, illustrating an overall spatial organization of projections from HVC and neighboring cortical areas. Further, although neuronal connections of HVC are not topographic, projections of HVC, pHVC, and surrounding areas demonstrate a broad spatial organization of efferents to striatum and regions surrounding RA, thus defining a level of organization beyond that of individual song control nuclei.

Afferent Pathways↗

PubMed1994

Cell death and neuronal recruitment in the high vocal center of adult male canaries are temporally related to changes in song.

Adult male canaries modify their song every year. Most of these changes occur during late summer and early fall, after the end of the breeding season, and in late winter, immediately before the onset of the next breeding season. The high vocal center (HVC) is an important nucleus in the brain pathway that controls this learned behavior. New neurons continue to be added to the HVC of adult male canaries, where they replace older neurons that have died. The present report describes the monthly incidence of cell death and neuronal addition in the HVC of such birds. Different groups of 1- to 2-year-old male canaries were treated with [3H]thymidine, a marker of cell birth, during each month of the year and killed 27 days later. The ratio of 3H-labeled neurons to all neurons in the HVC showed seasonal peaks and troughs. This ratio was highest in October and March. Peaks in the ratio of pycnotic (dying) HVC cells to all neurons in HVC preceded the peaks in the ratio of 3H-labeled neurons. We suggest that seasonal peaks in cell loss and neuronal recruitment in HVC are related to endocrine changes and that all three play a role in the seasonality of song modification.

Animals↗

PubMed1992

High vocal center growth and its relation to neurogenesis, neuronal replacement and song acquisition in juvenile canaries.

It is generally thought that most circuits of the adult central nervous system (CNS) are sculpted, in part at least, by selective elimination of some of the neurons present in an initial overabundant set. In this scenario, the birth of neurons precedes the period when brain functions, such as learning, first occur. In contrast to this form of brain assembly, we describe here the delayed development of the high vocal center (HVC) and one of its efferent pathways in canaries. The retrograde tracer Fluoro-Gold (FG) was injected into one of HVC's two efferent targets, the nucleus robustus archistriatalis (RA), to define the boundaries of HVC. The HVC grows markedly between 1 and 4 months, invading neighboring territories of the caudal telencephalon. During this same period, 0.43%-0.64% of the HVC neurons present at 1 year of age are labeled per day of [3H]-thymidine injection. [3H]-Thymidine labeling is a marker of cell birth, and during the first 4 months HVC neuron number increases, probably accounting for part of the HVC growth observed. Thereafter, the number of HVC neurons remains constant, but neuronal birth persists. We infer from this that neuronal replacement starts as early as 4 months after hatching and perhaps before then. About half of the neurons born after posthatching day 10 grow an axon to RA to form the main efferent pathway exiting from HVC. HVC growth, neurogenesis, axogenesis, and the observed replacement of neurons happen during the period of juvenile vocal learning. However, the recruitment of neurons that are still present at 1 year shows no particular inflections corresponding to the various stages in song learning, and continues at essentially the same rate after the more stereotyped adult song has been acquired. We suggest that a combination of neurogenesis and neuronal replacement provides unique advantages for learning.

Animals↗

PubMed1995

Two histological markers reveal a similar photoperiodic difference in the volume of the high vocal center in male European starlings.

Most studies of seasonal changes in the avian song control system have used Nissl stains to characterize the nuclei. More recent work has indicated that changes in nucleus volume evident in Nissl-stained tissue are not always apparent when investigated with other histochemical criteria. In this experiment, we used two different markers (Nissl stain and alpha 2-adrenergic receptor autoradiography) to characterize changes in the song system of European starlings (Sturnus vulgaris). Fluctuating levels of circulating testosterone (T) appear to be causally related to seasonal changes in the song system. Therefore, we used photoperiod manipulations to place male starlings into different physiological conditions. Photosensitive male starlings were placed on 11L:13D or 16L:8D photoperiods for at least 5 months. Birds on 11L:13D have enlarged gonads and circulating T. In contrast, starlings maintained on 16L:8D initially show marked gonadal growth. However, after about 6-8 weeks the birds are photorefractory (i.e., the gonads are regressed and T falls to undetectable levels). The volume of the high vocal center (HVC) was 44% larger in the 11L:13D than in 16L;8D birds in Nissl-stained tissue. The density of alpha 2-adrenergic receptors as determined by in vitro receptor autoradiography with [3H]p-amino-clonidine (PAC) is higher in HVC than in the surrounding neostriatum, clearly delineating the boundaries of the nucleus. We reconstructed the volume of HVC using PAC stained tissue. Thus, two histochemical markers indicate a photoperiodic difference in HVC volume of male starlings.

Animals↗

PubMed1996

Quantitative assessment of song-selectivity in the zebra finch "high vocal center".

1. Auditory responses in the zebra finch (Taenopygia guttata) song-system nucleus HVc were assessed at 54 recording sites by 3 different methods: discriminated action potentials; excitatory summed responses; and excitatory minus inhibitory summed responses. Four standard stimuli were presented at each site: the bird's own song; this song reversed; a conspecific song; and a noise burst. Responses were quantified by calculating a relative response index that partitoned the response, to provide a response profile, across the stimuli. 2. Regardless of analysis method, the strongest response was most often to the bird's own song (78-82%, depending on method). The predominant rank order of response strength across the remaining three stimuli was conspecific song > reversed song > noise. 3. The distribution of relative response magnitude was sensitive to analysis method. Discriminated spikes captured the heterogeneity of HVc neurons, whereas the excitatory summed responses reflected. the overall trends more consistently. When inhibition was subtracted from excitation in the summed responses, the variance of the relative responses increased, but this method presented some problems for statistical analysis. 4. A small sample of neurons in other forebrain auditory areas was used for comparative analyses. At these recording sites, the bird's own song did not consistently elicit the best response and there were generally smaller differences in the relative responses to the four stimuli. The smaller degree of stimulus selectivity among these cells resulted in less sensitivity to differences in the assessment methods.

Acoustic Stimulation↗

PubMed1995

Assessment of volumetric sex differences in the song control nuclei HVC and RA in zebra finches by immunocytochemistry for methionine enkephalin and vasoactive intestinal polypeptide.

In this study we assessed sex differences in the volume of two vocal control nuclei, the high vocal center (HVC) and the robust nucleus of the archistriatum (RA) in zebra finches (Taeniopygia guttata) exposed to various endocrine treatments (neonatal treatment with an aromatase inhibitor and/or an adult treatment with testosterone). The boundaries of these nuclei were defined in sections stained for Nissl substance and compared to alternate sections stained with an immunocytochemical procedure for two neuropeptides, methionine enkephalin and vasoactive intestinal polypeptide. A high density of immunoreactive fibers for methionine enkephalin and vasoactive intestinal polypeptide completely covered the high vocal center in male and female zebra finches and these fibers were not observed in the surrounding neostriatum. With the use of these markers to define the boundary of the high vocal center, it became possible to reconstruct its volume. Positively staining perikarya were not apparent within the boundaries of this nucleus. Immunoreactive fibers for vasoactive intestinal polypeptide and enkephalin also allowed one to define the boundary of the robust nucleus of the archistriatum but they did not fill the entire area of the nucleus as is the case for the high vocal center. When the volumes of both nuclei were reconstructed based on enkephalin or vasoactive intestinal polypeptide immunoreactivity, the presence of a marked sex difference in the volume of these nuclei was confirmed. Neonatal and adult endocrine manipulations did not affect the volumes of these two nuclei measured in Nissl-stained material nor did they affect the volumes as defined based on the peptidergic innervations of the nuclei. Also, the volumetric estimates of these two nuclei derived from sections stained by immunocytochemistry were in good agreement in all groups of birds with the values obtained based on an analysis of the Nissl-stained material. These results illustrate the usefulness of employing a variety of histochemical markers to define a brain area when investigating brain variation and plasticity.

Animals↗

PubMed1996

Divergent and parallel development in volume sizes of telencephalic song nuclei in male and female zebra finches.

Song control regions in passerine birds are known to be sexually dimorphic in the adult brain in species like zebra finches in which most males sing whereas females do not. As a first step toward the analysis of the establishment of anatomical sex differences, volumetric changes of Nissl-defined song control regions in the forebrain of the zebra finch have been quantified in both sexes at 10-day intervals starting at day 10 posthatching. In males, the Nissl-defined volume of the high vocal center, the robust nucleus of the archistriatum, and area X of the lobus parolfactorius increased with age, reaching the adult value at 60, 50, and at 40 days posthatching, respectively. The lateral magnocellular nucleus of the anterior neostriatum increased in volume until 20 days and then gradually decreased to reach the adult value at about 40 days. Whereas area X is absent in females, the high vocal center, the robust nucleus of the archistriatum, and the lateral magnocellular nucleus of the anterior neostriatum were detectable throughout development and in adulthood. In contrast to the males, volumes of the high vocal center and of the robust nucleus of the archistriatum decreased in females between 10 and 40 days posthatching (58% and 61%, respectively), when adult values were reached. Contrary to the development of these two nuclei in females, the volumetric development of the lateral magnocellular nucleus of the anterior neostriatum was very similar in both sexes. Females began with a smaller lateral magnocellular nucleus of the anterior neostriatum at 10 days posthatch, which led to a sexual dimorphism in juvenile stages, but there was no sexual dimorphism of volume size in adult brains.

Analysis of Variance↗

PubMed1999

Seasonal neuroplasticity in the songbird telencephalon: a role for melatonin.

Neuroplasticity in the vocal control system of songbirds is strongly influenced by seasonal fluctuations in circulating testosterone. These seasonally plastic telencephalic structures are implicated in the learning and production of song in songbirds. The role of the indoleamine melatonin in seasonal adaptations in birds has remained unclear. In this experiment, European starlings were castrated to remove the neuromodulating activity of gonadal steroids and were exposed to different photoperiods to induce reproductive states characteristic of different seasonal conditions. Long days increased the volume of the song-control nucleus high vocal center compared with its volume on short days. Exogenous melatonin attenuated the long-day-induced volumetric increase in high vocal center and also decreased the volume of another song-control nucleus, area X. This effect was observed regardless of reproductive state. To our knowledge, this is the first direct evidence of a role for melatonin in functional plasticity within the central nervous system of vertebrates.

Animals↗

PubMed2000

TrkB-like immunoreactivity in the song system of developing zebra finches.

The neural song system in zebra finches develops for approximately the first 2 months after hatching. During that time, male-biased sexual dimorphisms emerge in the volume of song control nuclei as well as in the number and size of neurons within them. Brain derived neurotrophic factor (BDNF) has been documented in song control nuclei at various stages of development. Its high affinity receptor (tyrosine kinase B; trkB) is also in the song system, at least at around I month of age. The present study was designed to more completely describe the timing and potential location of BDNF action by investigating trkB expression during sexual differentiation of the song control nuclei. The pattern of immunoreactivity to a trkB antibody was examined in male and female zebra finches at post-hatching days 3-60. Labeling in somata and neuropil appeared to define the telencephalic components of the motor pathway (high vocal center and robust nucleus of the archistriatum) for song production in males from days 30 to 60, and in females on days 45 and 60 (high vocal center). These results are consistent with the hypothesis that the receptor, and its ligand BDNF, play a role in processes related to song learning in both sexes, including perhaps the motor component exhibited by developing males.

Animals↗

PubMed1997

Motor-driven gene expression.

There is increased neuronal firing in the high vocal center (a motor nucleus) and other song nuclei of canaries, Serinus canaria, and zebra finches, Taeniopygia guttata, whenever these songbirds sing or hear song. These observations suggested that song perception involved sensory and motor pathways. We now show that the act of singing, but not hearing song, induces a rapid and striking increase (up to 60-fold) in expression of the transcriptional regulator ZENK in the high vocal center and other song nuclei. This motor-driven gene expression is independent of auditory feedback, since it occurs in deafened birds when they sing and in muted birds when they produce silent song. Conversely, hearing song, but not the act of singing, induces ZENK expression in parts of the auditory forebrain. Our observations show that even though the same auditory stimulus activates sensory and motor pathways, perception and production of song are accompanied by anatomically distinct patterns of gene expression.

Animals↗

PubMed2004

Neural response to bird's own song and tutor song in the zebra finch field L and caudal mesopallium.

Neurons in the song system nuclei of songbirds exhibit a strong preference for the sound of the bird's own song relative to that of conspecific songs. This selectivity is observed in the high vocal center and the nucleus interface of the nidopallium, two song nuclei that receive input from the bird's auditory system. To investigate the role of the auditory system in generating the selective responses observed in the song system, we recorded auditory responses in the zebra finch primary auditory forebrain, field L, and in a secondary auditory area, the caudal mesopallium. Field L and caudal mesopallium project directly or indirectly to the high vocal center and nucleus interface of the nidopallium and are presumed to provide substantial auditory input to the song system. We found that, on average, neurons in field L and caudal mesopallium did not show positive selective responses for the bird's own song or tutor song relative to conspecific song. Moreover, there were no particular sub-areas in the auditory telencephalon that were relatively more selective than the average. The selectivity for the bird's own song would therefore be restricted to song nuclei and would arise in one processing step, potentially found at the interface between the auditory and the song systems.

Acoustic Stimulation↗

PubMed1991

Production and survival of projection neurons in a forebrain vocal center of adult male canaries.

Neurons are produced in the adult canary telencephalon. Many of these cells are incorporated into the high vocal center (nucleus HVC), which participates in the control of learned song. In the present work, 3H-thymidine and fluorogold were employed to follow the differentiation and survival of HVC neurons born in adulthood. We found that many HVC neurons born in September grow long axons to the robust nucleus of the archistriatum (nucleus RA) and thus become part of the efferent pathway for song control. Many of these new neurons have already established their connections with RA by 30 d after their birth. By 240 d, 75-80% of the September-born HVC neurons project to RA. Most of these new projection neurons survive at least 8 months. The longevity of HVC neurons born in September suggests that these cells remain part of the vocal control circuit long enough to participate in the yearly renewal of the song repertoire.

Animals↗

PubMed2006

Singing-related activity of identified HVC neurons in the zebra finch.

High vocal center (HVC) is part of the premotor pathway necessary for song production and is also a primary source of input to the anterior forebrain pathway (AFP), a basal ganglia-related circuit essential for vocal learning. We have examined the activity of identified HVC neurons of zebra finches during singing. Antidromic activation was used to identify three classes of HVC cells: neurons projecting to the premotor nucleus RA, neurons projecting to area X in the AFP, and putative HVC interneurons. HVC interneurons are active throughout the song and display tonic patterns of activity. Projection neurons exhibit highly phasic stereotyped firing patterns. X-projecting (HVC((X))) neurons burst zero to four times per motif, whereas RA-projecting neurons burst extremely sparsely--at most once per motif. The bursts of HVC projection neurons are tightly locked to the song and typically have a jitter of <1 ms. Population activity of interneurons, but not projection neurons, was significantly correlated with syllable patterns. Consistent with the idea that HVC codes for the temporal order in the song rather than for sound, the vocal dynamics and neural dynamics in HVC occur on different and uncorrelated time scales. We test whether HVC((X)) neurons are auditory sensitive during singing. We recorded the activity of these neurons in juvenile birds during singing and found that firing patterns of these neurons are not altered by distorted auditory feedback, which is known to disrupt learning or to cause degradation of song already learned.

Acoustic Stimulation↗

PubMed2006

Sleep-related spike bursts in HVC are driven by the nucleus interface of the nidopallium.

The function and the origin of replay of motor activity during sleep are currently unknown. Spontaneous activity patterns in the nucleus robustus of the arcopallium (RA) and in HVC (high vocal center) of the sleeping songbird resemble premotor patterns in these areas observed during singing. We test the hypothesis that the nucleus interface of the nidopallium (NIf) has an important role for initiating and shaping these sleep-related activity patterns. In head-fixed, sleeping zebra finches we find that injections of the GABA(A)-agonist muscimol into NIf lead to transient abolishment of premotor-like bursting activity in HVC neurons. Using antidromic activation of NIf neurons by electrical stimulation in HVC, we are able to distinguish a class of HVC-projecting NIf neurons from a second class of NIf neurons. Paired extracellular recordings in NIf and HVC show that NIf neurons provide a strong bursting drive to HVC. In contrast to HVC neurons, whose bursting activity waxes and wanes in burst epochs, individual NIf projection neurons are nearly continuously bursting and tend to burst only once on the timescale of song syllables. Two types of HVC projection neurons-premotor and striatal projecting-respond differently to the NIf drive, in agreement with notions of HVC relaying premotor signals to RA and an anticipatory copy thereof to areas of a basal ganglia pathway.

Action Potentials↗