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S W Bottjer

Publications and source records attributed to S W Bottjer.

At least 19 recordsLinked to original sources
PubMed2002

Neural strategies for learning during sensitive periods of development.

Precise patterns of neural connectivity and synaptic communication are modified by experience during restricted "sensitive" periods of development, and the circuitry and associated behaviors that emerge during such periods are frequently preserved throughout the lifespan. In many neural systems, the expression of various molecules that influence synaptic transmission and neuronal morphology are developmentally regulated and may serve to constrain the timing of enhanced sensitivity to experiential inputs. In this highly selective review I concentrate on recent findings from the visual system and the song system that provide novel insights into the mechanisms that regulate sensitive period plasticity, and that raise new questions concerning what makes sensitive periods so sensitive.

Animals↗
PubMed2001

Lesions of a telencephalic nucleus in male zebra finches: Influences on vocal behavior in juveniles and adults.

Male zebra finches learn to sing during a restricted phase of juvenile development. Song learning is characterized by the progressive modification of unstable song vocalizations by juvenile birds during development, a process that leads to the production of stereotyped vocal patterns as birds reach adulthood. The medial magnocellular nucleus of the anterior neostriatum (mMAN) is a small cortical region that has been implicated in song behavior based on its neuronal projection to the High Vocal Center (HVC), a nucleus that is critical for adult vocal production and presumably also plays a role in song learning. To assess the function of mMAN in song, ibotenic acid lesions of this brain region were made in juvenile male zebra finches during the period of vocal learning (40-50 days of age) and in adult males that were producing stable song (>90 days of age). Birds lesioned as juveniles produced highly abnormal, poor quality song as adults. Although the overall song quality of birds lesioned as adults was not highly disrupted or abnormal, the postoperative song behavior of these birds was discernibly different due to slight increases in variability of vocal production, particularly at the onset of singing. These results demonstrate that mMAN plays some important role in vocal production during the sensitive period for song learning, and is also important for consistent initiation and stereotyped production of adult song behavior.

Age Factors↗
PubMed2001

Birdsong: models and mechanisms.

Recent studies have provided important information concerning the neural signals that subserve vocal learning in songbirds: advanced signal processing techniques are beginning to clarify the behavioral trajectories followed by developing birds; single-unit physiology in behaving animals is providing important clues about sensory and motor representations during learning; in vitro whole-cell recordings are revealing patterns of synaptic communication; and experimental alterations in song behavior have advanced our understanding of specific structure-function relationships. The construction of theoretical and computational models will be crucial in integrating such disparate experimental results.

Animals↗
PubMed2000

Connections of a motor cortical region in zebra finches: relation to pathways for vocal learning.

The lateral magnocellular nucleus of the anterior neostriatum (lMAN) is necessary for both initial learning of vocal patterns in developing zebra finches, as well as for modification of adult song under some circumstances. Lateral MAN is composed of two subregions: a core of magnocellular neurons and a surrounding shell composed primarily of parvocellular neurons. Neurons in lMAN(core) project to a region of motor cortex known as robust nucleus of the archistriatum (RA), whereas neurons in lMAN(shell) project to a region adjacent to RA known as dorsal archistriatum (Ad). We studied the axonal connections of Ad in adult male zebra finches. In contrast to RA, Ad neurons make a large number of efferent projections, which do not include direct inputs to vocal or respiratory motor neurons. The major efferent projections of Ad are to: (1) the striatum of avian basal ganglia; (2) a dorsal thalamic zone (including the song-control nuclei dorsomedial nucleus of the posterior thalamus [DMP] and dorsolateral nucleus of the medial thalamus [DLM]); (3) restricted regions within the lateral hypothalamus (stratum cellulare externum [SCE]), which may also relay information to the same dorsal thalamic zone; (4) a nucleus in the caudal thalamus (medial spiriform nucleus [SpM]); (5) deep layers of the tectum, which project to the thalamic song-control nucleus Uva; (6) broad regions of pontine and midbrain reticular formation; and (7) areas within the ventral tegmental area and substantia nigra (ventral tegmental area [AVT], substantia nigra [SN]), which overlap with regions that project to Area X, a song-control nucleus of avian striatum. Inputs to Ad derive not only from lMAN(shell), but also from a large area of dorsolateral caudal neostriatum (dNCL), which also receives input from lMAN(shell). That is, lMAN(shell) neurons project directly to Ad, and also multisynaptically to Ad via dNCL. Double-labeling studies show that lMAN(shell) contains two different populations of projection neurons: one that projects to Ad and another to dNCL. These results are exciting for two main reasons. The first is that some of these projections represent potential closed-loop circuits that could relay information back to song-control nuclei of the telencephalon, possibly allowing diverse types of song-related information to be both integrated between loops and compared during the period of auditory-motor integration. Because both auditory experience with an adult (tutor) song pattern and auditory feedback are essential to vocal learning, closed-loop pathways could serve as comparator circuits in which efferent commands, auditory feedback, and the memory of the tutor song are compared in an iterative fashion to achieve a gradual refinement of vocal production until it matches the tutor song. In addition, these circuits seem to have a strong integrative and limbic flavor. That is, the axonal connections of Ad neurons clearly include regions that receive inputs not only from somatosensory, visual, and auditory areas of cortex, but also from limbic regions, suggesting that they may be involved in higher order sensory processing, arousal, and motivation.

Animals↗
PubMed1999

Development of topography within song control circuitry of zebra finches during the sensitive period for song learning.

Refinement of topographic maps during sensitive periods of development is a characteristic feature of diverse sensory and motor circuits in the nervous system. Within the neural system that controls vocal learning and behavior in zebra finches, axonal connections of the cortical nucleus lMAN demonstrate striking functional and morphological changes during vocal development in juvenile males. These circuits are uniquely important for song production during the sensitive period for vocal learning, and the overall size of these brain regions and their patterns of axonal connectivity undergo dramatic growth and regression during this time. Axonal connections to and from lMAN are topographically organized in adult males that have already learned song. We wondered whether the large-scale changes seen in lMAN circuitry during the time that vocal behavior is being learned and refined could be accompanied by the emergence of topographic mapping. However, results presented herein demonstrate that most of these song-control circuits show the same broad patterns of axonal connectivity between subregions of individual nuclei at the onset of song learning as seen in adult birds. Thus, coarse topographic organization is not dependent on the types of experience that are crucial for vocal learning. Furthermore, this maintenance of topographic organization throughout the period of song learning is clearly not achieved by maintenance of static axonal arbors. In fact, because the volumes of song-control nuclei are growing (or regressing), topography must be maintained by active remodeling of axonal arbors to adapt to the changes in overall size of postsynaptic targets. A salient exception to this pattern of conserved topography is the projection from lMAN to the motor cortical region RA: this pathway is diffusely organized at the onset of song learning but undergoes substantial refinement during early stages of song learning, suggesting that remodeling of axonal connections within this projection during the period of vocal learning may signify the production of increasingly refined vocal utterances.

Aging↗
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↗
PubMed1998

Intrinsic and synaptic properties of neurons in the vocal-control nucleus IMAN from in vitro slice preparations of juvenile and adult zebra finches.

A common theme of diverse neural systems is that circuits that are important for initial acquisition of learning do not necessarily serve as a substrate for the long-term storage of that memory. The neural basis of vocal learning in songbirds provides an example of this phenomenon, since a circuit that is necessary for vocal production during initial stages of vocal development apparently plays no subsequent role in controlling learned vocalizations. This striking functional change suggests the possibility of marked physiological changes in synaptic transmission within this circuit. We therefore examined intrinsic and synaptic properties of neurons in the cortical nucleus IMAN (lateral magnocellular nucleus of the anterior neostriatum), which forms part of this developmentally regulated circuit, in an in vitro preparation of the zebra finch forebrain. Although both functional and morphological characteristics of these neurons change substantially during vocal development, we did not observe widespread, substantive changes in the electrophysiological characteristics of juvenile versus adult IMAN neurons examined in vitro. Overall, both the intrinsic properties and synaptic responses of IMAN neurons were similar in slices from juvenile birds (at ages when lesions of IMAN disrupt vocal production) and in slices from adult birds (when IMAN lesions have no effect on song production). However, one intrinsic property that did vary between juvenile and adult cells was spike duration, which was longer in juvenile cells, suggesting the potential for activation of second-messenger cascades and/or enhanced synaptic transmission onto target cells of IMAN neurons. The pattern of synaptic response observed in both juvenile and adult cells suggests that IMAN projection neurons receive direct excitatory afferent inputs, as well as disynaptic inhibitory inputs from interneurons within IMAN. Activation of inhibitory interneurons rapidly curtails the excitatory response seen in projection neurons. This inhibition was abolished by bicuculline, indicating that the inhibitory interneurons normally exert their postsynaptic response via GABA(A) receptors on projection neurons. The inhibitory response could also be blocked by CNQX (6-cyano-7-nitroquinoxaline-2,3-dione), suggesting that the activation of inhibitory interneurons within IMAN may be governed primarily by AMPA receptors.

Action Potentials↗
PubMed1997

Axonal connections of the medial magnocellular nucleus of the anterior neostriatum in zebra finches.

The medial magnocellular nucleus of the anterior neostriatum (mMAN) is a small cortical nucleus which was previously identified as a component of the neural circuitry controlling vocal behavior in songbirds based on its efferent connection to the High Vocal Center (HVC), a major song control nucleus (Nottebohm et al. [1982] J. Comp. Neurol. 207:344-357; Bottjer et al. [1989] J. Comp. Neurol. 279:312-326). We have conducted tract tracing experiments (using wheat-germ agglutinin-horseradish peroxidase (WGA-HRP), the carbocyanine dye DiI, and biocytin) to determine the complete pattern of afferent and efferent connections of mMAN in adult male zebra finches. We confirmed the existence of an efferent projection from mMAN to HVC and discovered a novel projection to the region medial to caudal HVC called paraHVC (pHVC). Injections of retrograde tracers into mMAN showed that afferent input to mMAN originates from the dorsomedial nucleus of the posterior thalamus (DMP). Injections of DiI into DMP produced anterograde label over mMAN, thus confirming the DMP-to-mMAN projection. Interestingly, this anterograde label extended beyond the region of mMAN defined by HVC-projecting neurons into the immediately surrounding cortex. This extended terminal field of DMP efferents indicates that mMAN encompasses a core population of projection neurons surrounded by a shell of non-HVC-projecting neurons, both of which receive input from the dorsal thalamus. Analysis of retrograde DiI label resulting from DMP injections revealed two major sources of afferent input to DMP originating in regions of the archistriatum and hypothalamus. Inputs to DMP were distributed throughout the dorsal archistriatum and included the area that receives a projection from the parvicellular shell region of the lateral magnocellular nucleus of the anterior neostriatum, a song control nucleus, as well as the dorsal portion of the robust nucleus of the archistriatum, the motor-cortical output of the song control system. The projections from song control regions of the archistriatum to DMP may feed information back into telencephalic song control circuitry via the DMP-->mMAN-->HVC/pHVC pathway. The other source of afferent input to DMP is located in the external cellular stratum of the lateral hypothalamus (SCE). This newly delineated SCE-->DMP-->mMAN-->HVC/pHVC pathway is the first report of a hypothalamic brain region neuroanatomically integrated with song control circuitry. Because hypothalamic brain regions are important for homeostasis and regulating behavior, the trans-synaptic circuitry of mMAN may help to integrate information about the bird's internal state, such as sexual maturation, with song learning and production.

Afferent Pathways↗
PubMed1997

Neurotrophins suppress apoptosis induced by deafferentation of an avian motor-cortical region.

Studies of the developing nervous system led to the general view that growth factors promote neuronal survival in a "retrograde" manner. For example, release of NGF from postsynaptic peripheral targets followed by uptake and retrograde transport by presynaptic neurons provided a widely accepted conceptual framework for the action of neurotrophins. In contrast, although presynaptic or "anterograde" influences on the survival of developing neurons have been recognized for some time, the mechanisms by which afferent input regulates the survival of postsynaptic cells have received considerably less attention. In the forebrain network for learned vocal behavior in zebra finches, lesions of a cortical region for song control, the lateral magnocellular nucleus of the anterior neostriatum (lMAN), remove presynaptic input to a motor-cortical song region, the robust nucleus of the archistriatum (RA), and cause massive RA neuron death in young birds that are entering the sensitive period for song learning. Here we report that lesions of lMAN followed by infusions of neurotrophins directly into RA completely suppress neuronal apoptosis in RA. Moreover, we show that lMAN neurons are able to transport neurotrophins in the anterograde direction to RA, that neurotrophin-like immunoreactivity is present in cells in lMAN and RA, and that neurotrophin receptor-like immunoreactivity is present in RA. Expression of neurotrophins in lMAN and RA suggests that lMAN presynaptic input could regulate RA neuron survival by synthesizing, transporting, and releasing neurotrophins anterogradely or by regulating the auto/paracrine release of neurotrophins within RA, or perhaps by both. These data provide the first in vivo demonstration that neurotrophins can prevent the death of deafferented cortical neurons, and they raise the possibility that nonretrograde signaling by neurotrophins may be a common means of promoting neuronal survival in the vertebrate telencephalon. Anterograde and auto/paracrine neurotrophin signaling, along with the more established view that neurotrophins regulate neuron survival via retrograde mechanisms, suggests multidirectional neurotrophin signaling in the vertebrate telencephalon.

Animals↗
PubMed1997

Circuits, hormones, and learning: vocal behavior in songbirds.

Species-typical vocal patterns subserve species identification and communication for individual organisms. Only a few groups of organisms learn the sounds used for vocal communication, including songbirds, humans, and cetaceans. Vocal learning in songbirds has come to serve as a model system for the study of brain-behavior relationships and neural mechanisms of learning and memory. Songbirds learn specific vocal patterns during a sensitive period of development via a complex assortment of neurobehavioral mechanisms. In many species of songbirds, the production of vocal behavior by adult males is used to defend territories and attract females, and both males and females must perceive vocal patterns and respond to them. In both juveniles and adults, specific types of auditory experience are necessary for initial song learning as well as the maintenance of stable song patterns. External sources of experience such as acoustic cues must be integrated with internal regulatory factors such as hormones, neurotransmitters, and cytokines for vocal patterns to be learned and produced. Thus, vocal behavior in songbirds is a culturally acquired trait that is regulated by multiple intrinsic as well as extrinsic factors. Here, we focus on functional relationships between circuitry and behavior in male songbirds. In that context, we consider in particular the influence of sex hormones on vocal behavior and its underlying circuitry, as well as the regulatory and functional mechanisms suggested by morphologic changes in the neural substrate for song control. We describe new data on the architecture of the song system that suggests strong similarities between the songbird vocal control system and neural circuits for memory, cognition, and use-dependent plasticity in the mammalian brain.

Animals↗
PubMed1997

Developmental plasticity in neural circuits for a learned behavior.

The neural substrate underlying learned vocal behavior in songbirds provides a textbook illustration of anatomical localization of function for a complex learned behavior in vertebrates. The song-control system has become an important model for studying neural systems related to learning, behavior, and development. The song system of zebra finches is characterized by a heightened capacity for both neural and behavioral change during development and has taught us valuable information regarding sensitive periods, rearrangement of synaptic connections, topographic specificity, cell death and neurogenesis, experience-dependent neural plasticity, and sexual differentiation. The song system differs in some interesting ways from some well-studied mammalian model systems and thus offers fresh perspectives on specific theoretical issues. In this highly selective review, we concentrate on two major questions: What are the developmental changes in the song system responsible for song learning and the restriction of learning to a sensitive period, and what factors explain the highly sexually dimorphic development of this system? We discuss the important role of sex steroid hormones and of neurotrophins in creating a male-typical neural song circuit (which can learn to produce complex vocalizations) instead of a reduced, female-typical song circuit that does not produce learned song.

Animals↗
PubMed1997

Sex differences in neuropeptide staining of song-control nuclei in zebra finch brains.

This study examined the distribution of the neuropeptides somatostatin (SS) and calcitonin gene-related peptide (CGRP) in forebrain and midbrain song-control nuclei of male versus female brains in adult zebra finches (Poephila guttata) using immunohistochemical techniques. Vocal learning in songbirds is controlled by an interconnected, highly-localized system of brain nuclei. Male zebra finches produce learned vocalizations, and females do not. This behavioral sexual dimorphism is reflected in a substantial difference in the size of these song-control nuclei: males have larger nuclei containing a greater number of neurons than do females. Interestingly, previous studies describing neurochemical aspects of the song-control system in other songbird species have not reported any obvious sex differences. However, the results of this study showed that the level of neuropeptide staining was substantially greater in telencephalic song-control nuclei of male brains compared to female brains in zebra finches. In some brain regions females lacked any apparent staining, whereas male brains were intensely labeled. In other cases the number of neurons and/or intensity of labeling were diminished in females relative to males. The telencephalic pattern of somatostatin labeling revealed a large number of SS-labeled somata in the magnocellular nucleus of the anterior neostriatum species that occupy habitats with different hydrodynamic conditions. (MAN), the high vocal center (HVC) and the robust nucleus of the archistriatum (RA) of males, whereas female song-control nuclei contained many fewer or no labeled cells in these regions. Area X of the striatum appeared to contain a slightly higher level of somatostatin immunoreactivity than surrounding striatum in males, but the region corresponding to Area X in females could not be distinguished from the rest of striatum. The telencephalic pattern of CGRP staining was less extensive than that seen for SS. In male brains the magnocellular core region of lateral MAN contained many darkly labeled neurons, and RA was stained by a dense field of anterograde terminal label. Well labeled somata were also seen in medial MAN of males, but HVC was devoid of immunoreactivity. Area X in male brains contained a light field of terminal immunoreactivity. The pattern of labeling seen in males indicates that CGRP acts selectively as a neuromodulator along the efferent projection from lateral MAN to RA and Area X but not in the HVC-to-RA pathway. No telencephalic song-control nuclei in female brains contained CGRP staining. Although some diencephalic and midbrain nuclei contained well-labeled somata or fibers with either or both neuropeptides, there was little or no evidence of a sex difference in neuropeptide expression in these regions. This latter finding suggests that the greater anatomical specialization seen in cortical regions of songbirds compared to those regions in non-oscine species is accompanied by a greater neurochemical differentiation, whereas thalamic and midbrain regions may be more conserved across sex as well as species. These findings indicate that male neurons produce high levels of somatostatin and calcitonin gene-related peptide in major telencephalic vocal-control regions in zebra finches, whereas female neurons produce less or none at all. These dramatic neurochemical sex differences may be directly related to production of learned vocalizations in males, as well as to other aspects of song behavior and courtship.

Animals↗
PubMed1995

Topographic organization of a forebrain pathway involved with vocal learning in zebra finches.

A serial pathway from a thalamic nucleus (DLM; the medial portion of the dorsolateral nucleus of the anterior thalamus) to a cortical region (lMAN; the lateral magnocellular nucleus of the anterior neostriatum) to a motor-cortical region (RA; the robust nucleus of the archistriatum) is necessary for vocal production during song learning in juvenile zebra finches but not for the recitation of a song already learned by adults. To obtain new information about the possible function of the DLM-->lMAN-->RA pathway in vocal learning, we used anterograde and retrograde tract-tracing techniques (pressure injections of DiI and DiA) to map the pattern of axonal connections between these brain regions in adult male zebra finches. Results revealed two topographically organized pathways that traverse the songbird forebrain in parallel. An oval-shaped dorsal/lateral portion of DLM projects solely to the central core of lMAN (lMANcore), whereas a crescent-shaped region, including ventral and medial DLM, projects exclusively to a parvicellular shell that encircles lMANcore (lMANshell). In turn, lMANshell neurons project solely to an arc-shaped region of dorsal archistriatum just lateral to RA (Ad; archistriatum, pars dorsalis), whereas lMANcore neurons project exclusively to RA. We also identified crossed and reciprocal pathways between lMANcore/shell and the lateral portion of the ventral archistriatum, which may contribute to interhemispheric coordination of vocal behavior. A robust topographic organization was observed in the axonal projections from dorsal/lateral-DLM-->lMANcore-->RA and from ventral/medial-DLM-->lMANshell-->Ad, raising the question of what is being mapped within these two forebrain pathways. Because RA projection neurons are organized myotopically with respect to the major vocal (syringeal) muscles (D.S. Vicario, 1991, J. Comp. Neurol. 309:486-494), one possibility is that a mapping of vocal/expiratory musculature is preserved "upstream" within these pathways. Similarly, the presence of song-selective auditory neurons in DLM, lMAN, and RA (A.J. Doupe and M. Konishi, 1991, Soc. Neurosci. Abstr. 18:527) suggests that these pathways might subserve some form of auditory or auditory-motor mapping.

Aging↗
PubMed1995

Differential estrogen accumulation among populations of projection neurons in the higher vocal center of male canaries.

The higher vocal center (HVC) of adult male canaries undergoes a seasonal change in volume that corresponds to seasonal modifications of vocal behavior: HVC is large when birds produce stereotyped song (spring) and is small when birds produce plastic song and add new song syllables into their vocal repertoires (fall). We reported previously that systemic exposure to testosterone (T) produces an increase in the volume of HVC similar to that observed with long-day photoperiods. T-induced growth of HVC occurred regardless of whether the borders of HVC were defined by Nissl-staining, the distribution of androgen-concentrating cells, or the distribution of projection neurons [separate neuronal populations within HVC project to the robust nucleus of the archistriatum (RA) and to Area X of the avian striatum (X)]. In the present study we used steroid autoradiography to determine whether T can influence the distribution of HVC cells that bind estrogen, and we combined estrogen autoradiography with retrograde labeling to determine whether HVC neurons that project to RA versus X differ in their ability to accumulate estrogen. Results showed that T increased the volume of Nissl-defined HVC and although HVC contained a low density of estrogen-concentrating cells, T increased the spatial distribution of these cells to match the Nissl borders of HVC. We also identified a region containing a high density of estrogen-concentrating cells located medial to HVC [we call this region paraHVC (pHVC)], and T also increased the volume of pHVC. pHVC also contained numerous X-projecting neurons, but few if any RA-projecting neurons. Double-labeling analysis revealed that RA-projecting neurons did not accumulate estrogen, a small percentage of X-projecting neurons in HVC accumulated estrogen, and the majority of X-projecting neurons in pHVC showed heavy accumulation of estrogen. The data reported here and in our previous article suggest distinct roles for gonadal steroids within the HVC-pHVC complex: estrogens are concentrated by neurons that project to a striatal region that influences vocal production during song learning (X), whereas androgens are concentrated primarily by neurons that project to a motor region that is involved in vocal production during both song learning and the recitation of already-learned song (RA).

Animals↗
PubMed1995

Localization of met-enkephalin and vasoactive intestinal polypeptide in the brains of male zebra finches.

An interconnected series of brain nuclei controls song learning and behavior in male zebra finches (Poephila guttata). This study examined the distribution of fibers, terminals, and somata immunoreactive for two neuropeptides, methionine-enkephalin (ENK) and vasoactive intestinal polypeptide (VIP), in song-control nuclei of adult males. In addition, the broad pattern of major regions of labeling throughout the forebrain and midbrain was determined. The telencephalic song-control nuclei MAN (magnocellular nucleus of the anterior neostriatum), Area X of the striatum, HVC (higher vocal center), and RA (robust nucleus of the archistriatum) contained abundant ENK immunoreactivity, including labeled fibers and somata. In addition, intensely labeled fibers and terminals were seen in the thalamic nucleus DLM (medial portion of the dorsolateral nucleus of the anterior thalamus). High levels of VIP immunoreactivity were also seen in MAN, HVC, and RA, but this label consisted of fiber and terminals only. Area X and surrounding striatum contained extremely sparsely distributed VIP-labeled processes. Somata positive for VIP were not seen throughout cortical regions such as the neostriatum and hyperstriatum but were abundant in the lateral striatum (paleostriatum augmentatum, PA) and may contribute to a dense field of terminal labeling seen in the globus pallidus. The apparent presence of a robust VIP-positive striato-pallidal projection is not typical of major basal ganglia pathways in vertebrates, raising the possibility that passerine birds have diverged from the typical amniote pattern.

Animals↗
PubMed1993

The distribution of tyrosine hydroxylase immunoreactivity in the brains of male and female zebra finches.

A system of brain nuclei controls song learning and behavior in zebra finches (Poephila guttata). The size of song-control nuclei are much larger in males, which sing, than in females, which do not sing. This study examined the distribution of fibers, terminals, and cell bodies that are immunoreactive for tyrosine hydroxylase (TH) (the rate-limiting enzyme in the synthesis of catecholamines) in song-control nuclei of adult males and females and juvenile males. In addition, the broad pattern of TH staining throughout the brain was described. There was a sex difference in TH immunoreactivity within song-control nuclei: males had light to moderate staining in all three cortical nuclei examined, whereas females had little or no label in corresponding areas [lateral magnocellular nucleus of the anterior neostriatum (IMAN), higher vocal center (HVC), and robust nucleus of the archistriatum (RA)]. The song-control nucleus area X (X), located in the striatum of avian basal ganglia, was more darkly stained than the surrounding striatum only in males; X was not defined by more intense immunoreactivity in females and hence could not be visualized. There were no apparent differences in TH staining in males ranging in age from 50 days to adulthood (> 90 days). Outside of the song-control system there were no substantive differences as a function of sex or age in the pattern or intensity of TH labeling. Major areas of telencephalic staining included the striatal region of basal ganglia, which was covered with dense, fine-grained label, and the septum, where cell bodies were encircled by extremely well-labeled thick processes. In the diencephalon, the preoptic area and hypothalamus included a complex pattern of darkly stained somata and fiber and terminal labeling. Darkly stained somata surrounded the pretectal nucleus, and labeled processes ramified throughout the superficial layers of the optic tectum. The midbrain and hindbrain contained a dense plexus of extremely dark cell bodies corresponding to mammalian substantia nigra, adjacent tegmental areas, and locus ceruleus. Labeled hindbrain cells were also seen in the pontine region, around nucleus solitarius, and in the ventrolateral medulla.

Animals↗
PubMed1993

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.

Animals↗