Projections of the parabrachial nucleus in the pigeon (Columba livia)

Activation of the Nucleus Taeniae of the Amygdala by Umami Taste in Domestic Chicks (Gallus gallus)

In chickens, the sense of taste plays an important role in detecting nutrients and choosing feed. The molecular mechanisms underlying the taste-sensing system of chickens are well studied, but the neural mechanisms underlying taste reactivity have received less attention. Here we report the short-term taste behaviour of chickens towards umami and bitter (quinine) taste solutions and the associated neural activity in the nucleus taeniae of the amygdala, nucleus accumbens and lateral septum. We found that chickens had more contact with and drank greater volumes of umami than bitter or a water control, and that chicks displayed increased head shaking in response to bitter compared to the other tastes. We found that there was a higher neural activity, measured as c-Fos activation, in response to umami taste in the right hemisphere of the nucleus taeniae of the amygdala. In the left hemisphere, there was a higher c-Fos activation of the nucleus taeniae of the amygdala in response to bitter than in the right hemisphere. Our findings provide clear evidence that chickens respond differently to umami and bitter tastes, that there is a lateralised response to tastes at the neural level, and reveals a new function of the avian nucleus taeniae of the amygdala as a region processing reward information.

A neural circuit perspective on brain aromatase

This review explores the role of aromatase in the brain as illuminated by a set of conserved network-level connections identified in several vertebrate taxa. Aromatase-expressing neurons are neurochemically heterogeneous but the brain regions in which they are found are highly-conserved across the vertebrate lineage. During development, aromatase neurons have a prominent role in sexual differentiation of the brain and resultant sex differences in behavior and human brain diseases. Drawing on literature primarily from birds and rodents, we delineate brain regions that express aromatase and that are strongly interconnected, and suggest that, in many species, aromatase expression essentially defines the Social Behavior Network. Moreover, in several cases the inputs to and outputs from this core Social Behavior Network also express aromatase. Recent advances in molecular and genetic tools for neuroscience now enable in-depth and taxonomically diverse studies of the function of aromatase at the neural circuit level.

Inspiring song: The role of respiratory circuitry in the evolution of vertebrate vocal behavior

Vocalization is a common means of communication across vertebrates, but the evolutionary origins of the neural circuits controlling these behaviors are not clear. Peripheral mechanisms of sound production vary widely: fish produce sounds with a swimbladder or pectoral fins; amphibians, reptiles, and mammalians vocalize using a larynx; birds vocalize with a syrinx. Despite the diversity of vocal effectors across taxa, there are many similarities in the neural circuits underlying the control of these organs. Do similarities in vocal circuit structure and function indicate that vocal behaviors first arose in a single common ancestor, or have similar neural circuits arisen independently multiple times during evolution? In this review, we describe the hindbrain circuits that are involved in vocal production across vertebrates. Given that vocalization depends on respiration in most tetrapods, it is not surprising that vocal and respiratory hindbrain circuits across distantly related species are anatomically intermingled and functionally linked. Such vocal-respiratory circuit integration supports the hypothesis that vocal evolution involved the expansion and functional diversification of breathing circuits. Recent phylogenetic analyses, however, suggest vocal behaviors arose independently in all major tetrapod clades, indicating that similarities in vocal control circuits are the result of repeated co-options of respiratory circuits in each lineage. It is currently unknown whether vocal circuits across taxa are made up of homologous neurons, or whether vocal neurons in each lineage arose from developmentally and evolutionarily distinct progenitors. Integrative comparative studies of vocal neurons across brain regions and taxa will be required to distinguish between these two scenarios.

Neutral syndrome

Neutral models of evolution assume the absence of natural selection. Formerly confined to ecology and evolutionary biology, neutral models are spreading. In recent years they've been applied to explaining the diversity of baby names, scientific citations, cryptocurrencies, pot decorations, literary lexica, tumour variants and much more besides. Here, we survey important neutral models and highlight their similarities. We investigate the most widely used tests of neutrality, show that they are weak and suggest more powerful methods. We conclude by discussing the role of neutral models in the explanation of diversity. We suggest that the ability of neutral models to fit low-information distributions should not be taken as evidence for the absence of selection. Nevertheless, many studies, in increasingly diverse fields, make just such claims. We call this tendency 'neutral syndrome'.

Neural control of choroidal blood flow

The choroid is richly innervated by parasympathetic, sympathetic and trigeminal sensory nerve fibers that regulate choroidal blood flow in birds and mammals, and presumably other vertebrate classes as well. The parasympathetic innervation has been shown to vasodilate and increase choroidal blood flow, the sympathetic input has been shown to vasoconstrict and decrease choroidal blood flow, and the sensory input has been shown to both convey pain and thermal information centrally and act locally to vasodilate and increase choroidal blood flow. As the choroid lies behind the retina and cannot respond readily to retinal metabolic signals, its innervation is important for adjustments in flow required by either retinal activity, by fluctuations in the systemic blood pressure driving choroidal perfusion, and possibly by retinal temperature. The former two appear to be mediated by the sympathetic and parasympathetic nervous systems, via central circuits responsive to retinal activity and systemic blood pressure, but adjustments for ocular perfusion pressure also appear to be influenced by local autoregulatory myogenic mechanisms. Adaptive choroidal responses to temperature may be mediated by trigeminal sensory fibers. Impairments in the neural control of choroidal blood flow occur with aging, and various ocular or systemic diseases such as glaucoma, age-related macular degeneration (AMD), hypertension, and diabetes, and may contribute to retinal pathology and dysfunction in these conditions, or in the case of AMD be a precondition. The present manuscript reviews findings in birds and mammals that contribute to the above-summarized understanding of the roles of the autonomic and sensory innervation of the choroid in controlling choroidal blood flow, and in the importance of such regulation for maintaining retinal health.

Transmitter receptors reveal segregation of the arcopallium/amygdala complex in pigeons (Columba livia)

At the beginning of the 20th century it was suggested that a complex group of nuclei in the avian posterior ventral telencephalon is comparable to the mammalian amygdala. Subsequent findings, however, revealed that most of these structures share premotor characteristics, while some indeed constitute the avian amygdala. These developments resulted in 2004 in a change of nomenclature of these nuclei, which from then on were named arcopallial or amygdala nuclei and referred to as the arcopallium/amygdala complex. The structural basis for the similarities between avian and mammalian arcopallial and amygdala subregions is poorly understood. Therefore, we analyzed binding site densities for glutamatergic AMPA, NMDA and kainate, GABAergic GABA_A , muscarinic M₁ , M₂ and nicotinic acetylcholine (nACh; α₄ β₂ subtype), noradrenergic α₁ and α₂ , serotonergic 5-HT_1A and dopaminergic D_1/5 receptors using quantitative in vitro receptor autoradiography combined with a detailed analysis of the cyto- and myelo-architecture. Our approach supports a segregation of the pigeon's arcopallium/amygdala complex into the following subregions: the arcopallium anterius (AA), the arcopallium ventrale (AV), the arcopallium dorsale (AD), the arcopallium intermedium (AI), the arcopallium mediale (AM), the arcopallium posterius (AP), the nucleus posterioris amygdalopallii pars basalis (PoAb) and pars compacta (PoAc), the nucleus taeniae amgygdalae (TnA) and the area subpallialis amygdalae (SpA). Some of these subregions showed further subnuclei and each region of the arcopallium/amygdala complex are characterized by a distinct multi-receptor density expression. Here we provide a new detailed map of the pigeon's arcopallium/amygdala complex and compare the receptor architecture of the subregions to their possible mammalian counterparts.

Acute Electrical Stimulation of Nucleus Ambiguus Enhances Immune Function in Rats

Background:

Up to now, many “immunoactive” brain areas have been identified, such a hypothalamic nuclei, brain reward system; but the nucleus ambiguous (Amb), a nucleus nervi vagis of medulla oblongata, was less well studied in neuroimmunomodulation.

Methods:

In order to obtain more profound comprehension and more knowledge on Amb, we studied the effect of acute electrical stimulation of Amb on thymus and spleen activity in rat. A stimulator was applied to stimulate the Amb of the anaesthetic rats using the parameter at 100μAx5ms x100 Hz every 1s for 1 min. The levels of TGF-β and thymosin-β4 mRNA in thymus, the release of IL-2 and IL-6 at splenocyte in vitro and splenic lymphocyte proliferation were measured at hour 0.5,1,2,3 following the electrical stimulation.

Results:

The results showed that concanavalin A (Con A)-induced splenic lymphocyte proliferation and the release of IL-2 and IL-6 were all significantly enhanced at 0.5, 1, and 2 h following effective Amb stimulation as compared to in the control group. However, as compared to in the control group, the levels of TGF-β and thymosin-β4 mRNA in the thymus were both remarkably reduced at 0.5, 1, and 2 h following effective Amb stimulation.

Conclusions:

These findings reveal that the Amb participates in the modulation of animal immune functions.

Genetic identification of the central nucleus and other components of the central extended amygdala in chicken during development

In mammals, the central extended amygdala shows a highly complex organization, and is essential for animal survival due to its implication in fear responses. However, many aspects of its evolution are still unknown, and this structure is especially poorly understood in birds. The aim of this study was to define the central extended amygdala in chicken, by means of a battery of region-specific transcription factors (Pax6, Islet1, Nkx2.1) and phenotypic markers that characterize these different subdivisions in mammals. Our results allowed the identification of at least six distinct subdivisions in the lateral part of the avian central extended amygdala: (1) capsular central subdivision; (2) a group of intercalated-like cell patches; (3) oval central nucleus; (4) peri-intrapeduncular (peri-INP) island field; (5) perioval zone; and (6) a rostral part of the subpallial extended amygdala. In addition, we identified three subdivisions of the laterodorsal bed nucleus of the stria terminalis (BSTLd) belonging to the medial region of the chicken central extended amygdala complex. Based on their genetic profile, cellular composition and apparent embryonic origin of the cells, we discuss the similarity of these different subdivisions of chicken with different parts of the mouse central amygdala and surrounding cell masses, including the intercalated amygdalar masses and the sublenticular part of the central extended amygdala. Most of the subdivisions include various subpopulations of cells that apparently originate in the dorsal striatal, ventral striatal, pallidal, and preoptic embryonic domains, reaching their final location by either radial or tangential migrations. Similarly to mammals, the central amygdala and BSTLd of chicken project to the hypothalamus, and include different neurons expressing proenkephalin, corticotropin-releasing factor, somatostatin or tyrosine hydroxylase, which may be involved in the control of different aspects of fear/anxiety-related behavior.

The respiratory-vocal system of songbirds: anatomy, physiology, and neural control

This wide-ranging review presents an overview of the respiratory-vocal system in songbirds, which are the only other vertebrate group known to display a degree of respiratory control during song rivalling that of humans during speech; this despite the fact that the peripheral components of both the respiratory and vocal systems differ substantially in the two groups. We first provide a brief description of these peripheral components in songbirds (lungs, air sacs and respiratory muscles, vocal organ (syrinx), upper vocal tract) and then proceed to a review of the organization of central respiratory-related neurons in the spinal cord and brainstem, the latter having an organization fundamentally similar to that of the ventral respiratory group of mammals. The second half of the review describes the nature of the motor commands generated in a specialized "cortical" song control circuit and how these might engage brainstem respiratory networks to shape the temporal structure of song. We also discuss a bilaterally projecting "respiratory-thalamic" pathway that links the respiratory system to "cortical" song control nuclei. This necessary pathway for song originates in the brainstem's primary inspiratory center and is hypothesized to play a vital role in synchronizing song motor commands both within and across hemispheres.

Afferents from vocal motor and respiratory effectors are recruited during vocal production in juvenile songbirds

Learned behaviors require coordination of diverse sensory inputs with motivational and motor systems. Although mechanisms underlying vocal learning in songbirds have focused primarily on auditory inputs, it is likely that sensory inputs from vocal effectors also provide essential feedback. We investigated the role of somatosensory and respiratory inputs from vocal effectors of juvenile zebra finches (Taeniopygia guttata) during the stage of sensorimotor integration when they are learning to imitate a previously memorized tutor song. We report that song production induced expression of the immediate early gene product Fos in trigeminal regions that receive hypoglossal afferents from the tongue and syrinx (the main vocal organ). Furthermore, unilateral lesion of hypoglossal afferents greatly diminished singing-induced Fos expression on the side ipsilateral to the lesion, but not on the intact control side. In addition, unilateral lesion of the vagus reduced Fos expression in the ipsilateral nucleus of the solitary tract in singing birds. Lesion of the hypoglossal nerve to the syrinx greatly disrupted vocal behavior, whereas lesion of the hypoglossal nerve to the tongue exerted no obvious disruption and lesions of the vagus caused some alterations to song behavior. These results provide the first functional evidence that somatosensory and respiratory feedback from peripheral effectors is activated during vocal production and conveyed to brainstem regions. Such feedback is likely to play an important role in vocal learning during sensorimotor integration in juvenile birds and in maintaining stereotyped vocal behavior in adults.

Characterization of the bed nucleus of the stria terminalis in the forebrain of anuran amphibians

Major common features have been reported for the organization of the basal telencephalon in amniotes, and most characteristics were thought to be acquired in the transition from anamniotes to amniotes. However, gene expression, neurochemical, and hodological data obtained for the basal ganglia and septal and amygdaloid complexes in amphibians (anamniotic tetrapods) have strengthened the idea of a conserved organization in tetrapods. A poorly characterized region in the forebrain of amniotes has been the bed nucleus of the stria terminalis (BST), but numerous recent investigations have characterized it as a member of the extended amygdala. Our study analyzes the main features of the BST in anuran amphibians to establish putative homologies with amniotes. Gene expression patterns during development identified the anuran BST as a subpallial, nonstriatal territory. The BST shows Nkx2.1 and Lhx7 expression and contains an Islet1-positive cell subpopulation derived from the lateral ganglionic eminence. Immunohistochemistry for diverse peptides and neurotransmitters revealed that the distinct chemoarchitecture of the BST is strongly conserved among tetrapods. In vitro tracing techniques with dextran amines revealed important connections between the BST and the central and medial amygdala, septal territories, medial pallium, preoptic area, lateral hypothalamus, thalamus, and prethalamus. The BST receives dopaminergic projections from the ventral tegmental area and is connected with the laterodorsal tegmental nucleus and the rostral raphe in the brainstem. All these data suggest that the anuran BST shares many features with its counterpart in amniotes and belongs to a basal continuum, likely controlling similar reflexes, reponses, and behaviors in tetrapods.

Efferent connections of nucleus accumbens subdivisions of the domestic chicken (Gallus domesticus): an anterograde pathway tracing study

Envisaged as a limbic-motor interface, the mammalian nucleus accumbens (Ac) is responsible for motivation, emotionality, and reward mechanisms. As in mammals, Ac of the domestic chick has three subdivisions: the rostral pole (AcR) lying in the rostral part of basal telencephalon, the core (AcC), corresponding to the ventromedial medial striatum, and the shell (AcS), lying ventrally and ventrolaterally to the AcC. Less well known is the connectivity of subdivisions. Here we report on the efferents of Ac subregions, using biotinylated dextran amine as anterograde tracer, deposited into the AcR, AcS, and AcC. The projections of the accumbens subregions mainly overlap in the telencephalon and the diencephalon but differ in the brainstem. In the telencephalon, the main projection sites are the ventral pallidum, the basal nucleus (Meynert), and the nucleus of the diagonal band. The lateral hypothalamus and lateral preoptic area receive strong projections from the AcR and AcS, and weaker projections from the AcC. The AcR and AcC massively innervate the subthalamic nucleus. In the brainstem the bulk of accumbens fibers were found in the compact part of the substantia nigra. All subregions project to the parabrachial region, reticular formation, periaqueductal gray, and the raphe nuclei, with some differences in the weights and subregional distributions. AcR and AcS project extensively to the ventral tegmental area, while AcC sends massive innervation to the solitary and vagal motor nuclei. Overall, the results seem to support the previously suggested distribution of Ac subregions, emphasizing similarities and differences with mammals.

The avian subpallium: new insights into structural and functional subdivisions occupying the lateral subpallial wall and their embryological origins

The subpallial region of the avian telencephalon contains neural systems whose functions are critical to the survival of individual vertebrates and their species. The subpallial neural structures can be grouped into five major functional systems, namely the dorsal somatomotor basal ganglia; ventral viscerolimbic basal ganglia; subpallial extended amygdala including the central and medial extended amygdala and bed nuclei of the stria terminalis; basal telencephalic cholinergic and non-cholinergic corticopetal systems; and septum. The paper provides an overview of the major developmental, neuroanatomical and functional characteristics of the first four of these neural systems, all of which belong to the lateral telencephalic wall. The review particularly focuses on new findings that have emerged since the identity, extent and terminology for the regions were considered by the Avian Brain Nomenclature Forum. New terminology is introduced as appropriate based on the new findings. The paper also addresses regional similarities and differences between birds and mammals, and notes areas where gaps in knowledge occur for birds.

Localization of cerebellin-2 in late embryonic chicken brain: implications for a role in synapse formation and for brain evolution

Cerebellin-1 (Cbln1), the most studied member of the cerebellin family of secreted proteins, is necessary for the formation and maintenance of parallel fiber-Purkinje cell synapses. However, the roles of the other Cblns have received little attention. We previously identified the chicken homolog of Cbln2 and examined its expression in dorsal root ganglia and spinal cord (Yang et al. [2010] J Comp Neurol 518:2818-2840). Interestingly, Cbln2 is expressed by mechanoreceptive and proprioceptive neurons and in regions of the spinal cord where those afferents terminate, as well as by preganglionic sympathetic neurons and their sympathetic ganglia targets. These findings suggest that Cbln2 may demonstrate a tendency to be expressed by synaptically connected neuronal populations. To further assess this possibility, we examined Cbln2 expression in chick brain. We indeed found that Cbln2 is frequently expressed by synaptically connected neurons, although there are exceptions, and we discuss the implications of these findings for Cbln2 function. Cbln2 expression tends to be more common in primary sensory neurons and in second-order sensory regions than it is in motor areas of the brain. Moreover, we found that the level of Cbln2 expression for many regions of the chicken brain is very similar to that of the mammalian homologs, consistent with the view that the expression patterns of molecules playing fundamental roles in processes such as neuronal communication are evolutionarily conserved. There are, however, large differences in the pattern of Cbln2 expression in avian as compared to mammalian telencephalon and in other regions that show the most divergence between the two lineages.

Connections of the auditory brainstem in a songbird, Taeniopygia guttata. II. Projections of nucleus angularis and nucleus laminaris to the superior olive and lateral lemniscal nuclei

Three nuclei of the lateral lemniscus are present in the zebra finch, ventral (LLV), intermediate (LLI), and dorsal (LLD). LLV is separate from the superior olive (OS): it lies closer to the spinal lemniscus and extends much further rostrally around the pontine periphery. LLI extends from a caudal position ventrolateral to the principal sensory trigeminal nucleus (LLIc) to a rostral position medial to the ventrolateral parabrachial nucleus (LLIr). LLD consists of posterior (LLDp) and anterior (LLDa) parts, which are largely coextensive rostrocaudally, although LLDa lies medial to LLDp. All nuclei are identifiable on the basis of cytochrome oxidase activity. The cochlear nucleus angularis (NA) and the third-order nucleus laminaris (NL) project on OS predominantly ipsilaterally, on LLV and LLI predominantly contralaterally, and on LLD contralaterally only. The NA projections are heavier than those of NL and differ from them primarily in their terminations within LLD: NA projects to LLDp, whereas NL projects to LLDa. In this the projections are similar to those in the barn owl (Takahashi and Konishi [1988] J Comp Neurol 274:212-238), in which time and intensity pathways remain separate as far as the central nucleus of the inferior colliculus (MLd). In contrast, in the zebra finch, although NA and NL projections remain separate within LLD, the projections of LLDa and LLDp become intermixed within MLd (Wild et al., J Comp Neurol, this issue), consistent with the intermixing of the direct NA and NL projections to MLd (Krützfeldt et al., J Comp Neurol, this issue).

Patterns of fos-like immunoreactivity in the brains of parent ring doves (Streptopelia risoria) given tactile and nontactile exposure to their young

Neuronal activation was examined by fos immunohistochemistry in ring doves (Streptopelia risoria) reunited with their young after overnight separation. In an initial study, squab-exposed parents showed more fos immunoreactivity (ir) in the preoptic area (POA) and lateral hypothalamus (LH) than squab-deprived parents. In a 2nd study, parents allowed free access to young and those separated from young by a wire mesh partition showed more fos-ir in the POA, LH, and lateral septum than box-exposed controls. Contact with young also increased fos-ir in the medial preoptic nucleus and bed nucleus of the stria terminalis, but noncontact exposure did not. Conversely, nontactile squab exposure stimulated more fos-ir in the POA than did free access to young, which suggests POA involvement in appetitive aspects of parenting.

Avian nucleus retroambigualis: cell types and projections to other respiratory-vocal nuclei in the brain of the zebra finch (Taeniopygia guttata)

In songbirds song production requires the intricate coordination of vocal and respiratory muscles under the executive influence of the telencephalon, as for speech in humans. In songbirds the site of this coordination is suspected to be the nucleus retroambigualis (RAm), because it contains premotor neurons projecting upon both vocal motoneurons and spinal motoneurons innervating expiratory muscles, and because it receives descending inputs from the telencephalic vocal control nucleus robustus archopallialis (RA). Here we used tract-tracing techniques to provide a more comprehensive account of the projections of RAm and to identify the different populations of RAm neurons. We found that RAm comprises diverse projection neuron types, including: 1) bulbospinal neurons that project, primarily contralaterally, upon expiratory motoneurons; 2) a separate group of neurons that project, primarily ipsilaterally, upon vocal motoneurons in the tracheosyringeal part of the hypoglossal nucleus (XIIts); 3) neurons that project throughout the ipsilateral and contralateral RAm; 4) another group that sends reciprocal, ascending projections to all the brainstem sources of afferents to RAm, namely, nucleus parambigualis, the ventrolateral nucleus of the rostral medulla, nucleus infra-olivarus superior, ventrolateral parabrachial nucleus, and dorsomedial nucleus of the intercollicular complex; and 5) a group of relatively large neurons that project their axons into the vagus nerve. Three morphological classes of RAm cells were identified by intracellular labeling, the dendritic arbors of which were confined to RAm, as defined by the terminal field of RA axons. Together the ascending and descending projections of RAm confirm its pivotal role in the mediation of respiratory-vocal control.

Development and adult organization of the lateral part of the bed nucleus of the stria terminalis in the chicken

The lateral part of the bed nucleus of the stria terminalis (BSTL) is a component of the subpallial amygdala located near the ventral sulcus of the lateral ventricle, but its limits have not been well defined in birds. In this study, we analyzed the expression patterns of a number of neurochemical markers: GABA, calbindin (CB), calretinin (CR), or neuronal nitric oxide synthase (nNOS), in the embryonic and adult chicken brain, to further characterize the organization of the avian BSTL. From embryonic day 16, it was possible to distinguish three different regions within BSTL on the basis of cytoarchitectonic and immunohistochemical features. A central region, referred to as lateral bed nucleus of the stria terminalis pars densocellularis (BSTLdc), is characterized by numerous tightly packed cell bodies, most of which are GABA-immunoreactive (ir), and two peripheral regions with lower cellular density displaying a moderate GABA expression, referred to as lateral bed nucleus of the stria terminalis, plexiform part 1 (BSTLp1) and plexiform part 2 (BSTLp2), respectively. In contrast to BSTLdc, both plexiform parts are characterized by the presence of many fibers and terminals immunoreactive for nNOS and CR, as well as some CR-ir scattered cells. A distinctive feature of BSTLp2 is a population of CB-ir cells embedded in a slightly CB-ir neuropil. Comparison of our immunohistochemical data with gene expression data suggests that BSTLdc and BSTLp1 are pallidal in nature, whereas BSTLp2 receives important contributions from the entopeduncular/preoptic area.

Sensory feedback control of mammalian vocalizations

Somatosensory and auditory feedback mechanisms are dynamic components of the vocal motor pattern generator in mammals. This review explores how sensory cues arising from central auditory and somatosensory pathways actively guide the production of both simple sounds and complex phrases in mammals. While human speech is a uniquely sophisticated example of mammalian vocal behavior, other mammals can serve as examples of how sensory feedback guides complex vocal patterns. Echolocating bats in particular are unique in their absolute dependence on voice control for survival: these animals must constantly adjust the acoustic and temporal patterns of their orientation sounds to efficiently navigate and forage for insects at high speeds under the cover of darkness. Many species of bats also utter a broad repertoire of communication sounds. The functional neuroanatomy of the bat vocal motor pathway is basically identical to other mammals, but the acute significance of sensory feedback in echolocation has made this a profitable model system for studying general principles of sensorimotor integration with regard to vocalizing. Bats and humans are similar in that they both maintain precise control of many different voice parameters, both exhibit a similar suite of responses to altered auditory feedback, and for both the efficacy of sensory feedback depends upon behavioral context. By comparing similarities and differences in the ways sensory feedback influences voice in humans and bats, we may shed light on the basic architecture of the mammalian vocal motor system and perhaps be able to better distinguish those features of human vocal control that evolved uniquely in support of speech and language.

A mechanism for vocal-respiratory coupling in the mammalian parabrachial nucleus

Mammalian vocalizations require the precise coordination of separate laryngeal and respiratory motor pathways. Precisely how and where in the brain vocal motor patterns interact with respiratory rhythm control is unknown. The parabrachial nucleus (PB) is known to mediate key respiratory reflexes and is also considered a principle component of the mammalian vocal motor pathway, making it a likely site for vocal-respiratory interactions, yet a specific role for the PB in vocalizing has yet to be demonstrated. To investigate the role of the PB in vocal-respiratory coordination, we pharmacologically manipulated synaptic activity in the PB while spontaneously vocalizing horseshoe bats were provoked to emit either short, single syllable or long, multisyllabic vocal motor patterns. Iontophoresis of the GABAA agonist muscimol (MUS) into the lateral PB extended expiratory durations surrounding all vocalizations and increased mean call durations. Alternatively, application of the GABAA antagonist bicuculline methiodide (BIC) shortened expirations and call durations. In addition, BIC eliminated the occurrence of multisyllabic vocalizations. BIC caused a mild increase in quiet breathing rates, whereas MUS tended to slow quiet breathing. The results indicate that GABAA receptor-mediated inhibition in the lateral PB modulates the time course of respiratory phase switching during vocalizing, and is needed for proper coordination of calling and breathing in mammals. We hypothesize that vocal-respiratory rhythm entrainment is achieved at least in part via mechanisms similar to other forms of locomotor-respiratory coupling, namely somatosensory feedback influences on respiratory phase-switching in the lateral PB.

Anatomy of the Avian Hippocampal Formation

Increasing knowledge of the avian hippocampal formation (hippocampus and parahippocampal area) suggests that it plays a role in a variety of behaviors, such as homing, cache retrieving, visual discrimination, imprinting, and sexual behavior. Knowledge of the neural circuits in the hippocampal formation and its related areas or nuclei is important for the understanding of these functions. This review therefore describes the functional neuroanatomy of the avian hippocampal formations, i.e., its subdivisions, cytoarchitecture, and afferent and efferent connections. Evidence obtained by a combination of Nissl staining and tract-tracing shows that the pigeon hippocampal formation can be divided into seven subdivisions: dorsolateral (DL), dorsomedial (DM), triangular (Tr), V-shaped (V), magnocellular (Ma), parvocellular, and cell-poor regions. DL and DM can be further divided into dorsal and ventral, and lateral and medial portions, respectively. In the hippocampal formation, reciprocal connections are found between DL-DM, DL-Tr, DL-Ma, DM-Ma, DM-V, and Tr-V. Neurons in the V-shaped layer appear to be intrinsic neurons. Sensory inputs from higher order visual and olfactory stations enter DL and DM, are modified or integrated by intrinsic hippocampal circuitry, and the outputs are sent, via DL and DM, to various telencephalic nuclei, septum, and hypothalamus. The neural pathways indicate that the hippocampal formation plays a central role in the limbic system, which also includes the dorsolateral corticoid area, nucleus taeniae of the amygdala, posterior pallial amygdala, septum, medial part of the anterior dorsolateral nucleus of the thalamus, and the lateral mammillary nucleus. Connectional and comparative studies, including the use of kainic acid excitotoxicity, suggest that the V-shaped layer is comparable to the dentate gyrus of the mammalian hippocampal formation and DM to Ammon's horn and subiculum.

Fiber connections of the compact division of the posterior pallial amygdala and lateral part of the bed nucleus of the stria terminalis in the pigeon (Columba livia)

The compact division of the posterior pallial amygdala (PoAc) and lateral part of the bed nucleus of the stria terminalis (BSTL) are components of the limbic system in the pigeon brain. In this study, we examined the position and fiber connections of these two nuclei by using Nissl staining and tract-tracing methods. PoAc occupies a central division in the posterior pallial amygdala. BSTL faces the ventral horn of the lateral ventricle and extends between A 7.25 and A 10.50. PoAc and BSTL connect bidirectionally by the stria terminalis. PoAc connects reciprocally with two nuclear groups in the cerebrum: 1) a continuum consisting of the caudoventral nidopallium, lateral part of the caudoventral nidopallium (NCVl), subnidopallium beneath NCVl, and piriform cortex and 2) rostral areas of the hemisphere, including the frontolateral and frontomedial nidopallium and the densocellular part of the hyperpallium. Extratelencephalic projections of PoAc terminate in the dorsomedial thalamic nuclei and reach the lateral hypothalamic area via the hypothalamic part of the occipito-mesencephalic tract. BSTL also connects reciprocally with two main regions: 1) the same continuum as for PoAc projections, except the piriform cortex and 2) rostral areas of the hemisphere, including the olfactory tubercle and nucleus accumbens. Extratelencephalic reciprocal connections are with the substantia nigra, nucleus subceruleus dorsalis, parabrachial nucleus, locus coeruleus, and nucleus of the solitary tract. The dorsomedial subdivision of the hippocampal formation projects massively to PoAc and BSTL. These findings indicate that PoAc and BSTL are important components of an interconnected neural circuit involving widespread regions of the neuraxis and mediating limbic-visceral functions.

Subpallial amygdala and nucleus taeniae in birds resemble extended amygdala and medial amygdala in mammals in their expression of markers of regional identity

Two regions were recently recognized as subpallial amygdaloid nuclei in birds, the nucleus taeniae of the amygdala (TnA) and the newly identified subpallial amygdala (SpA). Here we further confirm these nuclei to be subpallial and amygdaloid and show similarity to specific mammalian subpallial amygdaloid nuclei. By its topological, connectional and neurochemical traits, avian TnA has been suggested to be comparable to mammalian medial amygdala (MeA) and SpA to be comparable to the sublenticular part of mammalian extended amygdala (ExA). We examined molecular traits of these areas using immunohistochemistry for limbic system-associated membrane protein (LAMP) and in situ hybridization for glutamic acid decarboxylase-65 (GAD65) and chicken ovalbumin upstream promoter-transcription factor II (COUP-TF II). Mammalian GAD65 is a subpallial marker and was enriched in ExA and MeA. Chick GAD65 was enriched in SpA and TnA, indicating that they are subpallial. LAMP, which is enriched in limbic regions such as mammalian ExA and MeA, was enriched in avian SpA and TnA. COUP-TF II was enriched in mammalian amygdala including MeA and ExA to a lesser extent. In birds, COUP-TF II was enriched in TnA and moderate in SpA. Overlap of these markers confirms avian TnA resembles mammalian MeA and SpA resembles ExA.

Afferent and efferent connections of the dorsolateral corticoid area and a comparison with connections of the temporo-parieto-occipital area in the pigeon (Columba livia)

The dorsolateral corticoid area (CDL) in the pigeon telencephalon is a thin, superficial part of the caudal pallium adjoining the medially situated hippocampal formation. To determine the connectivity of CDL, and to distinguish CDL from the rostrally adjacent temporo-parieto-occipital area (TPO), injections of neural tracers were made into the caudal superficial pallium at various rostrocaudal levels. The results showed that injections caudal to A 6.75 (Karten and Hodos [1967] Baltimore: Johns Hopkins University Press) gave rise to reciprocal connections with subdivisions of the hippocampal formation, TPO, piriform cortex, posterior pallial amygdala, caudoventral nidopallium, densocellular part of the hyperpallium, lateral hyperpallium, frontolateral nidopallium, and lateral intermediate nidopallium. Of these, the hippocampal formation showed very strong connectivity with CDL, and projection fibers from CDL clearly separated the dorsomedial region of the hippocampal formation into lateral and medial portions. CDL projected directly to the olfactory bulb, but did not receive projections from it. In the diencephalon, CDL received efferents from a dorsal region of the medial part of the anterior dorsolateral nucleus of the thalamus, subrotundal nucleus, and internal paramedian nucleus of the thalamus. These findings suggest that CDL in the pigeon belongs to the limbic pallium and that in some respects it may be comparable to the mammalian cingulate cortex. In contrast, injections of tracers into the pallial surface at or rostral to A 7.00 showed marked differences in the pattern of both anterograde and retrograde labeling from that resulting from injections caudal to A 6.50, thereby indicating the approximate level of transition from CDL to TPO.

Distribution of the limbic system-associated membrane protein (LAMP) in pigeon forebrain and midbrain

The limbic system-associated membrane protein (LAMP) is an adhesion molecule involved in specifying regional identity during development, and it is enriched in the neuropil of limbic brain regions in mammals but also found in some somatic structures. Although originally identified in rat, LAMP is present in diverse species, including avians. In this study, we used immunolabeling with a monoclonal antibody against rat LAMP to examine the distribution of LAMP in pigeon forebrain and midbrain. LAMP immunolabeling was prominent in many telencephalic regions previously noted as limbic in birds. These regions include the hippocampal complex, the medial nidopallium, and the ventromedial arcopallium. Subpallial targets of these pallial regions were also enriched in LAMP, such as the medial-most medial striatum. Whereas some telencephalic areas that have not been regarded as limbic were also LAMP-rich (e.g., the hyperpallium intercalatum and densocellulare of the Wulst, the mesopallium, and the intrapeduncular nucleus), most nonlimbic telencephalic areas were LAMP-poor (e.g., field L, the lateral nidopallium, and somatic basal ganglia). Similarly, in the diencephalon and midbrain, prominent LAMP labeling was observed in such limbic areas as the dorsomedial thalamus, the hypothalamus, the ventral tegmental area, and the central midbrain gray, as well as in a few nonlimbic areas such as nucleus rotundus, the shell of the nucleus pretectalis, the superficial tectum, and the parvocellular isthmic nucleus. Thus, as in mammals, LAMP in birds appears to be enriched in most known forebrain and midbrain limbic structures but is present as well in some somatic structures.

Amygdalostriatal projections in reptiles: A tract-tracing study in the lizardPodarcis hispanica

Whereas the lacertilian anterior dorsal ventricular ridge contains unimodal sensory areas, its posterior part (PDVR) is an associative center that projects to the hypothalamus, thus being comparable to the amygdaloid formation. To further understand the organization of the reptilian cerebral hemispheres, we have used anterograde and retrograde tracing techniques to study the projections from the PDVR and adjoining areas (dorsolateral amygdala, DLA; deep lateral cortex, dLC; nucleus sphericus, NS) to the striatum in the lizard Podarcis hispanica. This information is complemented with a detailed description of the organization of the basal telencephalon of Podarcis. The caudal aspect of the dorsal ventricular ridge projects nontopographically mainly (but not exclusively) to the ventral striatum. The NS projects bilaterally (with strong ipsilateral dominance) to the nucleus accumbens, thus recalling the posteromedial cortical amygdala of mammals. The PDVR (especially its lateral aspect) and the dLC project massively to a continuum of structures connecting the striatoamygdaloid transition area (SAT) and the nucleus accumbens (rostrally), the projection arising from the dLC being probably bilateral. Finally, the DLA projects massively and bilaterally to both the ventral and dorsal striatum, including the SAT. Our findings lend further support to the view that the PDVR and neighboring structures constitute the reptilian basolateral amygdala and indicate that an emotional brain was already present in the ancestral amniote. These results are important to understand the comparative significance of the caudal aspect of the amniote cerebral hemispheres, and specifically challenge current views on the nature of the avian caudal neostriatum.

Functional Neuroanatomy of the Sensorimotor Control of Singing

Reviews of the songbird vocal control system frequently begin by describing the forebrain nuclei and pathways that form anterior and posterior circuits involved in song learning and song production, respectively. They then describe extratelencephalic projections upon the brainstem respiratory-vocal system in a manner suggesting, quite erroneously, that this system is itself well understood. One aim of this chapter is to demonstrate how limited is our understanding of that system. I begin with an overview of the neural network for the motor control of song production, with a particular emphasis on brainstem structures, including the tracheosyringeal motor nucleus (XIIts), which innervates the syrinx, and nucleus retroambigualis (RAm), which projects upon XIIts and upon spinal motor neurons innervating expiratory muscles. I describe the sources of afferent projections to XIIts and RAm and discuss their probable role in coordinating the bilateral activity of respiratory and syringeal muscles during singing. I then consider the routes by which sensory feedback, which could arise from numerous structures involved in singing, might access the song system to guide song learning, maintain accurate song production, and inform the song system of the requirements for air. I describe possible routes of access of auditory feedback, which is known to be necessary for song learning and maintenance, and identify potential sites of interaction with somatosensory and visceral feedback that could arise from the syrinx, the lungs and air sacs, and the upper vocal tract, including the jaw. I conclude that the incorporation of brainstem-based respiratory-vocal variables is likely to be a necessary next step in the construction of more sophisticated models of the control of vocalization.

Revised nomenclature for avian telencephalon and some related brainstem nuclei

The standard nomenclature that has been used for many telencephalic and related brainstem structures in birds is based on flawed assumptions of homology to mammals. In particular, the outdated terminology implies that most of the avian telencephalon is a hypertrophied basal ganglia, when it is now clear that most of the avian telencephalon is neurochemically, hodologically, and functionally comparable to the mammalian neocortex, claustrum, and pallial amygdala (all of which derive from the pallial sector of the developing telencephalon). Recognizing that this promotes misunderstanding of the functional organization of avian brains and their evolutionary relationship to mammalian brains, avian brain specialists began discussions to rectify this problem, culminating in the Avian Brain Nomenclature Forum held at Duke University in July 2002, which approved a new terminology for avian telencephalon and some allied brainstem cell groups. Details of this new terminology are presented here, as is a rationale for each name change and evidence for any homologies implied by the new names. Revisions for the brainstem focused on vocal control, catecholaminergic, cholinergic, and basal ganglia-related nuclei. For example, the Forum recognized that the hypoglossal nucleus had been incorrectly identified as the nucleus intermedius in the Karten and Hodos (1967) pigeon brain atlas, and what was identified as the hypoglossal nucleus in that atlas should instead be called the supraspinal nucleus. The locus ceruleus of this and other avian atlases was noted to consist of a caudal noradrenergic part homologous to the mammalian locus coeruleus and a rostral region corresponding to the mammalian A8 dopaminergic cell group. The midbrain dopaminergic cell group in birds known as the nucleus tegmenti pedunculopontinus pars compacta was recognized as homologous to the mammalian substantia nigra pars compacta and was renamed accordingly; a group of gamma-aminobutyric acid (GABA)ergic neurons at the lateral edge of this region was identified as homologous to the mammalian substantia nigra pars reticulata and was also renamed accordingly. A field of cholinergic neurons in the rostral avian hindbrain was named the nucleus pedunculopontinus tegmenti, whereas the anterior nucleus of the ansa lenticularis in the avian diencephalon was renamed the subthalamic nucleus, both for their evident mammalian homologues. For the basal (i.e., subpallial) telencephalon, the actual parts of the basal ganglia were given names reflecting their now evident homologues. For example, the lobus parolfactorius and paleostriatum augmentatum were acknowledged to make up the dorsal subdivision of the striatal part of the basal ganglia and were renamed as the medial and lateral striatum. The paleostriatum primitivum was recognized as homologous to the mammalian globus pallidus and renamed as such. Additionally, the rostroventral part of what was called the lobus parolfactorius was acknowledged as comparable to the mammalian nucleus accumbens, which, together with the olfactory tubercle, was noted to be part of the ventral striatum in birds. A ventral pallidum, a basal cholinergic cell group, and medial and lateral bed nuclei of the stria terminalis were also recognized. The dorsal (i.e., pallial) telencephalic regions that had been erroneously named to reflect presumed homology to striatal parts of mammalian basal ganglia were renamed as part of the pallium, using prefixes that retain most established abbreviations, to maintain continuity with the outdated nomenclature. We concluded, however, that one-to-one (i.e., discrete) homologies with mammals are still uncertain for most of the telencephalic pallium in birds and thus the new pallial terminology is largely devoid of assumptions of one-to-one homologies with mammals. The sectors of the hyperstriatum composing the Wulst (i.e., the hyperstriatum accessorium intermedium, and dorsale), the hyperstriatum ventrale, the neostriatum, and the archistriatum have been renamed (respectively) the hyperpallium (hypertrophied pallium), the mesopallium (middle pallium), the nidopallium (nest pallium), and the arcopallium (arched pallium). The posterior part of the archistriatum has been renamed the posterior pallial amygdala, the nucleus taeniae recognized as part of the avian amygdala, and a region inferior to the posterior paleostriatum primitivum included as a subpallial part of the avian amygdala. The names of some of the laminae and fiber tracts were also changed to reflect current understanding of the location of pallial and subpallial sectors of the avian telencephalon. Notably, the lamina medularis dorsalis has been renamed the pallial-subpallial lamina. We urge all to use this new terminology, because we believe it will promote better communication among neuroscientists. Further information is available at http://avianbrain.org

Distribution of corticotropin-releasing factor-immunoreactive neurons in the central nervous system of the domestic chicken and Japanese quail

In birds, as in mammals, corticotropin-releasing factor (CRF) is present in a number of extrahypothalamic brain regions, indicating that CRF may play a role in physiological and behavioral responses other than the control of adrenocorticotropin hormone release by the pituitary. To provide a foundation for investigation of the roles of CRF in the control of avian behavior, the distribution of CRF immunoreactivity was determined throughout the central nervous system of the domestic chicken (Gallus domesticus) and Japanese quail (Coturnix japonica). The distribution of CRF-immunoreactive (-ir) perikarya and fibers in the chicken and quail brain was found to be more extensive than previously reported, notably in the telencephalon. Numerous CRF-ir perikarya and fibers were present in the hyperstriatum, hippocampus, neostriatum, lobus parolfactorius, and archistriatum, as well as in the nucleus taeniae, nucleus accumbens, and bed nucleus of the stria terminalis, which exhibited the strongest immunolabeling in the telencephalon. The presence of dense populations of CRF-ir perikarya in the medial lobus parolfactorius, nucleus of the stria terminalis, and paleostriatum ventrale, apparently giving rise to CRF-ir projections to the mesencephalic reticular formation, the parabrachial/pericerulear region, and the dorsal vagal complex, suggests that these telencephalic areas may constitute part of the avian "central extended amygdala." These results have important implications for understanding the role of extrahypothalamic CRF systems in emotional responses in birds.

Fiber connections of the hippocampal formation and septum and subdivisions of the hippocampal formation in the pigeon as revealed by tract tracing and kainic acid lesions

The organization of the pigeon hippocampal formation was examined by tract tracing by using biotinylated dextran amine (BDA) and cholera toxin B subunit (CTB) and by injections of kainic acid to produce excitotoxic lesions. The hippocampal formation was divided into seven subdivisions based on Nissl staining and intrinsic and septal connections: dorsomedial (DM), dorsolateral (DL), triangular (Tr), V-shaped layer, magnocellular (Ma), parvocellular, and cell-poor regions. DL was composed of dorsal and ventral portions and sent associational fibers to DM, the V-shaped layer, and Tr. DL had strong reciprocal connections with the densocellular part of the hyperpallium (HD) and projected to the dorsolateral corticoid area. DM had reciprocal fiber connections with the V-shaped layer, Ma, and DL as well as with several subdivisions of the arcopallium. DL and DM, but not the V-shaped layer, projected fibers to the septum where those from DM exceeded in number those from DL. These projections further extended to the hypothalamus, particularly the lateral hypothalamic area. The lateral and medial septal nuclei projected back a very small number of ascending fibers to the hippocampal formation. Intraventricular injections of kainic acid induced neuronal loss widely in the hippocampal formation and subsequently produced gliosis in DM. These results indicate that DL receives its main afferents from HD and in turn sends inputs to an intrinsic circuit composed of hippocampal subdivisions DM, Ma, Tr, and the V-shaped layer; and also that DM is the main exit to the septum and hypothalamus. It is suggested that neurons in the V-shaped layer are intrinsic. Together, the results suggest that the V-shaped layer is comparable to the dentate gyrus of the mammalian hippocampal formation and that DM incorporates components comparable to both Ammon's horn and the subiculum.

Efferent connections of the dorsomedial thalamic nuclei of the domestic chick (Gallus domesticus)

Small iontophoretic injections of the anterograde tracer Phaseolus vulgaris leucoagglutinin were placed in the thalamic anterior dorsomedial nucleus (DMA) of domestic chicks. The projections of the DMA covered the rostrobasal forebrain, ventral paleostriatum, nucleus accumbens, septal nuclei, Wulst, hyperstriatum ventrale, neostriatal areas, archistriatal subdivisions, dorsolateral corticoid area, numerous hypothalamic nuclei, and dorsal thalamic nuclei. The rostral DMA projects preferentially on the hypothalamus, whereas the caudal part is connected mainly to the dorsal thalamus. The DMA is also connected to the periaqueductal gray, deep tectum opticum, intercollicular nucleus, ventral tegmental area, substantia nigra, locus coeruleus, dorsal lateral mesencephalic nucleus, lateral reticular formation, nucleus papillioformis, and vestibular and cranial nerve nuclei. This pattern of connectivity is likely to reflect an important role of the avian DMA in the regulation of attention and arousal, memory formation, fear responses, affective components of pain, and hormonally mediated behaviors.

Feeding induced by microinjections of NMDA and AMPA-kainate receptor antagonists into ventral striatal and ventral pallidal areas of the pigeon

The participation of glutamatergic circuits of the ventral basal ganglia in feeding-related regulatory mechanisms has been extensively indicated in primate and rodent species. In avian species, it has been shown that ICV injections of MK-801 or of CNQX increase food intake and reduce the latency of feeding initiation in free-feeding pigeons. In the present study, the effects of local injections of MK-801 (6 nmol), CNQX (160 nmol) or vehicle (0.2 microl) into a number of ventral striatopallidal nuclei on feeding, drinking and non-ingestive (sleep, preening) spontaneous behaviors were investigated in free-feeding pigeons (Columba livia). Intense feeding responses associated with an increased duration of feeding behavior were consistently recorded after injections of MK-801 or CNQX into the medial two-thirds of the tuberculum olfactorium (TO), the ventral aspect of lobus parolfactorium (LPOv), or the ventral pallidum (VP). In contrast, the latency of feeding initiation was unaffected by these treatments. No changes in drinking, preening or sleep responses were observed after drug injections into the TO/LPOv/VP area. These data indicate that glutamate-mediated circuits in the TO/LPOv/VP area can play an inhibitory role in feeding behavior in this species, contributing to the conclusion of a feeding bout, thus delaying satiation processes, and that these effects may be mediated by AMPA and NMDA receptors. Additionally, our data support the notion that a region functionally and anatomically comparable to the mammalian accumbens shell may be present in the TO/LPOv/VP region of the pigeon, and that the existence of a glutamatergic circuit in the ventral striatum controlling feeding-related phenomena may represent a highly conserved attribute throughout the amniote's evolution.

Respiratory and telencephalic modulation of vocal motor neurons in the zebra finch

Birdsong, like speech, involves coordinated vocal and respiratory activity achieved under telencephalic control. The avian vocal organ, or syrinx, is innervated by motor neurons (MNs) in the tracheosyringeal part of the hypoglossal nucleus (XIIts) that receive their synaptic input from medullary respiratory areas and telencephalic song control areas. Despite the importance of XIIts MNs to learned vocalizations, little is known about their intrinsic electrical properties or their synaptic inputs. Therefore, we made in vitro and in vivo intracellular recordings from XIIts MNs in adult male zebra finches to characterize their intrinsic properties and their synaptic modulation by respiratory and telencephalic areas. In vitro, electrical stimulation of ipsilateral or contralateral medullary respiratory areas (RAm) routinely evoked glycine receptor-mediated inhibition in XIIts. With inhibition blocked, similar stimulation evoked excitatory synaptic responses capable of driving sustained MN firing that was mediated partly by NMDA receptors. These inhibitory and excitatory inputs likely arise from RAm neurons, because chemical or electrical stimulation of RAm evoked similar responses in XIIts. In vivo, XIIts MNs displayed rhythmical, expiratory-related activity. EPSPs were pronounced at expiratory onset, but IPSPs were not apparent during inspiration, although XIIts MN firing was suppressed. However, hyperpolarizations as well as excitation were evoked by playback of the bird's own song, a stimulus that potently excites the telencephalic song nucleus that innervates XIIts. These findings illuminate functional properties of the songbird's brainstem circuitry and its specific activation by telencephalic inputs, which could coordinate vocal and respiratory activity during singing.

Organization of the avian basal forebrain: chemical anatomy in the parrot (Melopsittacus undulatus)

Hodological, electrophysiological, and ablation studies indicate a role for the basal forebrain in telencephalic vocal control; however, to date the organization of the basal forebrain has not been extensively studied in any nonmammal or nonhuman vocal learning species. To this end the chemical anatomy of the avian basal forebrain was investigated in a vocal learning parrot, the budgerigar (Melopsittacus undulatus). Immunological and histological stains, including choline acetyltransferase, acetylcholinesterase, tyrosine hydroxylase, dopamine and cAMP-regulated phosphoprotein (DARPP)-32, the calcium binding proteins calbindin D-28k and parvalbumin, calcitonin gene-related peptide, iron, substance P, methionine enkephalin, nicotinamide adenine dinucleotide phosphotase diaphorase, and arginine vasotocin were used in the present study. We conclude that the ventral paleostriatum (cf. Kitt and Brauth [1981] Neuroscience 6:1551-1566) and adjacent archistriatal regions can be subdivided into several distinct subareas that are chemically comparable to mammalian basal forebrain structures. The nucleus accumbens is histochemically separable into core and shell regions. The nucleus taeniae (TN) is theorized to be homologous to the medial amygdaloid nucleus. The archistriatum pars ventrolateralis (Avl; comparable to the pigeon archistriatum pars dorsalis) is theorized to be a possible homologue of the central amygdaloid nucleus. The TN and Avl are histochemically continuous with the medial aspects of the bed nucleus of the stria terminalis and the ventromedial striatum, forming an avian analogue of the extended amygdala. The apparent counterpart in budgerigars of the mammalian nucleus basalis of Meynert consists of a field of cholinergic neurons spanning the basal forebrain. The budgerigar septal region is theorized to be homologous as a field to the mammalian septum. Our results are discussed with regard to both the evolution of the basal forebrain and its role in vocal learning processes.

The nitric oxide synthase inhibitor NG-Nitro-L-arginine increases basal forebrain acetylcholine release during sleep and wakefulness

Cholinergic neurotransmission in the basal forebrain changes across the sleep/wake cycle, and considerable data show cortical activation by ACh originating from basal forebrain neurons. These findings have stimulated efforts to elucidate molecular modulators of ACh release within the basal forebrain. Basal forebrain cholinergic neurons contain nitric oxide synthase (NOS), the enzyme that produces the gaseous neuromodulator nitric oxide. This study tested the hypothesis that administration of an NOS inhibitor to the basal forebrain would alter basal forebrain ACh release, sleep, and respiratory rate. Seven cats were instrumented for recording sleep and wakefulness and for in vivo microdialysis and microinjection. Compared with Ringer's solution (control), microdialysis delivery of the NOS inhibitor N(G)-nitro-l-arginine (NLA; 10 mm) increased ACh release during wakefulness (33%), non-rapid eye movement (NREM) sleep (70%), and rapid eye movement (REM) sleep (16%). Mean +/- SEM ACh levels (pmol/10 min) during control and NLA dialysis, respectively, were 0.58 +/- 0.03 and 0.77 +/- 0.06 in wakefulness, 0.36 +/- 0.01 and 0.61 +/- 0.06 in NREM sleep, and 0.68 +/- 0.06 and 0.79 +/- 0.09 in REM sleep. Increases in ACh release were not evoked by dialysis delivery of the less active enantiomer N(G)-nitro-d-arginine. Dialysis administration of NLA did not alter respiratory rate. Sleep-dependent changes in basal forebrain ACh release were localized specifically to lateral basal forebrain regions and did not occur in medial basal forebrain sites. Microinjection of NLA into the lateral basal forebrain did not significantly alter the sleep/wake cycle. In contrast to NLA-induced depression of REM sleep and ACh release in the cat pons, the present results demonstrate that NLA increased ACh release in the cat basal forebrain and had no effect on sleep. The different effects of NLA on ACh release in the cat pons and cat basal forebrain may prove relevant for developing compounds that differentially alter cholinergic neurotransmission in specific brain regions.

Distribution of calcitonin gene-related peptide-like immunoreactivity in the brain of the lizard Podarcis hispanica

The present work studies the distribution of calcitonin gene-related peptide-immunoreactive (CGRP-li) neurons and fibers in the brain of a reptile, the lizard Podarcis hispanica. CGRP-li perikarya were not present in the telencephalon. In the thalamus, CGRP-li perikarya were restricted to the posteromedial and posterolateral nuclei. In the hypothalamus, CGRP-li cells were found mainly in the supramammillary and mammillary nuclei. In the midbrain and brainstem, CGRP-li cells appeared in the ventral tegmental area, the parabrachial nucleus, and the motor nuclei of the III-VII, IX, X, and XII cranial nerves. Motoneurons of the ventral horn of the spinal cord were also immunoreactive for CGRP. CGRP-li fibers were seen in the telencephalic hemispheres, where a dense plexus of reactive fibers appeared in the septum and in the lateral striatoamygdaloid transition area. From the latter, CGRP-li fibers entered the posterior dorsal ventricular ridge, the cell layer and deep stratum of the ventral lateral cortex, and various amygdaloid nuclei. Parts of the striatum (nucleus accumbens) and pallidum also displayed CGRP-li innervation. In the diencephalon, CGRP-li innervation was observed in parts of the dorsal thalamus and in the periventricular and medial hypothalamus. The pretectum and deep layers of the optic tectum also showed CGRP-li fibers, and numerous CGRP-li fibers were observed in the midbrain central gray, tegmentum, and pons. Some of the sensory fibers of the trigeminal, vagal, and spinal nerves were also CGRP-li. These results show that the distribution of CGRP-li structures in the reptilian brain is similar to that described for other vertebrates and suggest that the thalamotelencephalic CGRPergic projections appear to be conserved among amniote vertebrates.

Light and electron microscopic observations of a direct projection from mesencephalic trigeminal nucleus neurons to hypoglossal motoneurons in the rat

A direct projection from rat mesencephalic trigeminal nucleus (Vme) neurons to the hypoglossal nucleus (XII) motoneurons was studied using a double labeling method of anterogradely biotinylated dextran amine (BDA) tracing combined with retrogradely horseradish peroxidase (HRP) transport at both light and electron microscopic levels. BDA was iontophoresed unilaterally into the caudal Vme, and 7 days later HRP was injected into the ipsilateral tongue to label hypoglossal motoneurons. The BDA-labeled fibers were seen descended along Probst' tract and were traced to the caudal medulla. In this course, the fibers gave off axon collaterals bearing varicosities in the trigeminal motor nucleus (Vmo), the parvicellular reticular formation (PCRt), the dorsomedial portions of the subnuclei of oralis (Vodm) and interpolaris (Vidm) and in the XII ipsilaterally. The labeling of terminals was most dense in the PCRt at the levels of caudal pons and rostral medulla, which displayed a "dumbbell-shaped" form in the transverse planes. In the XII, labeled terminals were distributed mainly in the dorsal compartment of the nucleus. One hundred sixty-eight appositions made by BDA-labeled terminals on HRP-labeled motoneurons were seen in the dorsal compartment (71%) and in the lateral subcompartment (24%) of the ventral XII. Under electron microscopy BDA-labeled boutons containing clear, spherical synaptic vesicles were found to form synaptic contacts with the somata and dendrites of hypoglossal motoneurons with asymmetric specializations. The present study provides new evidence that the trigeminal proprioceptive afferent neurons terminate in the XII and make synaptic contacts with their motoneurons.

Gender-related changes in the avian vasotocin system during ontogeny

The arginine vasotocin (AVT) system of the avian brain includes a sexually dimorphic part that extends from the caudal part of preoptic region through the medial part of the bed nucleus of stria terminalis (BSTm) to the lateral septum. It is composed of the parvocellular neurons located in the BSTm and the dense innervation of the medial preoptic region and lateral septum. In this part of the brain, AVT expression is stronger in males than in females in a few bird species investigated to date. This review focuses on the ontogeny of sexual differences in the vasotocinergic system of two gallinaceous species, domestic chicken and Japanese quail, and on the role of gonadal hormones in organizing during development and maintaining in adulthood these differences. Parvocellular AVT neurons become discernible in the BSTm of males and females during the second half of embryonic development. These cells undergo a profound and irreversible sexual differentiation during ontogenetic development. Recent findings demonstrate a dual role of estrogens in the organization and activation of sex differences in the AVT system. During the embryonic period of ontogeny, estrogens differentiate the AVT system in a sexually dimorphic manner in parallel with the differentiation of sexual behavior, while in adulthood estrogens, locally produced from testosterone in the male brain, activate AVT synthesis in the BSTm. The sexually dimorphic part of the AVT system is sensitive to a number of abiotic factors such as light, temperature, and water availability. It is suggested that sex dimorphic vasotocinergic systems could be implicated in processes of social recognition in various behavioral contexts.