Distribution and connections of inspiratory premotor neurons in the brainstem of the pigeon (Columba livia)

We have recorded extracellular, inspiratory-related (IR) unit activity in the medulla at locations corresponding to those of neurons retrogradely labeled by injections of retrograde tracers in the lower brachial and upper thoracic spinal cord, injections that covered cell bodies and dendrites of motoneurons innervating inspiratory muscles. Bulbospinal neurons were distributed throughout the dorsomedial and ventrolateral medulla, from the spinomedullary junction through about 0.8 mm rostral to the obex. Almost all of the 104 IR units recorded were located in corresponding parts of the ventrolateral medulla, rostral to nucleus retroambigualis, where expiratory related units are found. Injections of biotinylated dextran amine at the recording sites labeled projections both to the spinal cord and to the brainstem. In the lower brachial and upper thoracic spinal cord, bulbospinal axons traveled predominantly in the contralateral dorsolateral funiculus and terminated in close relation to the dendrites of inspiratory motoneurons retrogradely labeled with cholera toxin B-chain. In the brainstem, there were predominantly ipsilateral projections to the nucleus retroambigualis, tracheosyringeal motor nucleus (XIIts), ventrolateral nucleus of the rostral medulla, infraolivary superior nucleus, ventrolateral parabrachial nucleus, and dorsomedial nucleus of the intercollicular complex. In all these nuclei, except XIIts, retrogradely labeled neurons were also found, indicating reciprocity of the connections. These results suggest the possibility of monosynaptic connections between inspiratory premotor neurons and inspiratory motoneurons, which, together with connections of IR neurons with other brainstem respiratory-vocal nuclei, seem likely to mediate the close coordination that exists in birds between the vocal and respiratory systems. The distribution of IR neurons in birds is similar to that of the rostral ventral respiratory group (rVRG) in mammals.     

Localization of androgen receptor mRNA-containing cells in avian respiratory-vocal nuclei: an in situ hybridization study

Song development and song pattern formation in oscine songbirds are influenced by steroid hormones such as estrogens and androgens, and the control of vocal pattern generation is mediated via a network of interconnected vocal and respiratory nuclei. The main components of the respiratory part of the network are the expiratory and inspiratory premotor nuclei, known as retroambigualis (RAm) and the rostral ventral respiratory group (rVRG), respectively. These respiratory components play an integral role in song production either by providing the expiratory pulses of air required for each and every song syllable, or by controlling inspiration between syllables in the form of minibreaths, and between phrases for major replenishments of air. Here we analyze the distribution of androgen receptors (AR) and estrogen receptors (ER) in the midbrain and hindbrain of male and female zebra finches, and male canaries and green finches, using in situ hybridization with cRNA probes of the zebra finch AR and ER. ERmRNA was not expressed in any of the respiratory-vocal nuclei of the midbrain or hindbrain, but ARmRNA was expressed in the tracheosyringeal motor nucleus (nXIIts) and in RAm and rVRG. The size of the ARmRNA defined RAm and rVRG was similar in male and female zebra finches, but the size of ARmRNA defined nXIIts was slightly sexual dimorphic. Previously undescribed areas of ARmRNA expression outside the respiratory-vocal network in the brain stem were the nucleus semilunaris and layers 10-12 of the optic tectum. AR-mRNA expression in the respiratory-vocal nuclei of adult male songbirds, adult female zebra finches, and juvenile zebra finches suggests that the temporal pattern of learned and unlearned vocalizations is sensitive to androgen-dependent mechanisms mediated by RAm and rVRG.     

Anatomical organization of the limb premotor network in the turtle (Chrysemys picta) revealed by in vitro transport of biocytin and neurobiotin

The in vitro turtle brainstem-cerebellum preparation has been a valuable tool in the study of central motor programs. In the present study, we investigate the anatomical organization of the turtle rubrocerebellar limb premotor network and its sensory connections in vitro by combining the rapid anterograde and retrograde transport of neurobiotin and biocytin with the extended viability of the isolated turtle brainstem-cerebellum. These compounds retrogradely labeled soma, dendrites, and axons, and orthogradely labeled axons and, to a lesser extent, terminals. The chelonian red nucleus receives a dense input from the contralateral lateral cerebellar nucleus and projects heavily to the contralateral spinal cord. Rubral axons sparsely innervate the lateral cerebellar nucleus and project heavily to the lateral reticular nucleus. Lateral reticular axons heavily innervate the lateral cerebellar nucleus before terminating in the pars lateralis of the cerebellar cortex as mossy fibers. These prominent, recurrent loops among the lateral cerebellar nucleus, red nucleus, and lateral reticular nucleus constitute the turtle rubrocerebellar limb premotor network. Sensory inputs to the red nucleus originate in the contralateral dorsal column nuclei, the principal trigeminal nucleus, and the spinothalamic system. These sites project bilaterally to the lateral reticular nucleus. The lateral cerebellar nucleus receives a contralateral input from the dorsal column nuclei. The red nucleus projects sparsely to the dorsal column nuclei. The red nucleus also receives an ipsilateral descending projection from the suprapeduncular nucleus, located in the diencephalon, and an ascending input from the rostral rhombencephalic reticular formation. An ipsilateral descending pathway originating in the red nucleus is likely to be the rubro-olivary tract.     

Projections of the dorsomedial nucleus of the intercollicular complex (DM) in relation to respiratory-vocal nuclei in the brainstem of pigeon (Columba livia) and zebra finch (Taeniopygia guttata)

Injections of neuronal tracers were made into the dorsomedial nucleus of the intercollicular complex (DM) of pigeons and zebra finches in order to investigate the projections of this nucleus which has long been implicated in respiratory-vocal control. Despite the fact that pigeons are nonsongbirds and zebra finches are songbirds, the projections were very similar in both species. Most descended throughout the brainstem, taking ventral and dorsal trajectories, which merged in the medulla. Those descending ventrally terminated upon the ventrolateral parabrachial nucleus (PBvl), the nucleus infraolivaris superior, a nucleus of the rostral ventrolateral medulla (RVL), and the nucleus retroambigualis (RAm). Those taking a dorsal trajectory via the occipitomesencephalic tract terminated in the tracheosyringeal part of the hypoglossal nucleus (XIIts), the suprahypoglossal region, and nucleus retroambigualis. There were also substantial projections throughout an arc extending between XIIts and RVL rostrally, and XIIts and RAm caudally. Neurons throughout this arc, which include inspiratory premotor neurons at levels straddling the obex and expiratory premotor neurons more caudally (in RAm), were retrogradely labeled from spinal injections. The DM projections were predominantly ipsilateral, but there were distinct contralateral projections to all the homologous nuclei in both species. All but the projections to PBvl and XIIts were reciprocal. In summary, the projections of DM suggest that it is able to influence all the key motor and premotor nuclei involved in patterned respiratory-vocal activity.     

Management of the patient with sickle cell disease

A discrete neural circuit mediates the production of learned vocalizations in oscine songbirds. Although this circuit includes some bilateral pathways at midbrain and medullary levels, the forebrain components of the song control network are not directly connected across the midline. There have been no previous reports of bilateral projections from medullary and midbrain vocal control nuclei back to the forebrain song system, but the existence of such bilateral corollary discharge pathways was strongly suggested by the recent observation that unilateral stimulation of a forebrain song nucleus during singing leads to a rapid readjustment of premotor activity in the contralateral forebrain. In the present study, we used neuroanatomical tracers to demonstrate bilateral projections from (a) the rostral ventrolateral medulla (RVL), which may control respiratory aspects of vocalization, to nucleus uvaeformis (Uva), and (b) the dorsomedial intercollicular nucleus (DM), a midbrain vocal control region, to Uva. Both RVL and DM receive descending projections from the forebrain song nucleus robustus archistriatalis, and Uva projects directly to the forebrain song nuclei interfacialis and high vocal center. We suggest that the bilateral feedback projections from DM and RVL to Uva function to coordinate the two hemispheres during singing in adult songbirds and to convey internal feedback of premotor signals to the forebrain in young birds that are learning to sing.     

Noradrenergic system of the zebra finch brain: immunocytochemical study of dopamine-beta-hydroxylase

Oscine birds are among the few animal groups that have vocal learning, and their brains contain a specialized system for song learning and production. We describe here the immunocytochemical distribution of dopamine-beta-hydroxylase (DBH), a noradrenergic marker, in the brain of an oscine, the zebra finch (Taeniopygia guttata). DBH-positive cells were seen in the locus coeruleus, the nucleus subcoeruleus ventralis, the nucleus of the solitary tract, and the caudolateral medulla. Immunoreactive fibers and varicosities had a much wider brain distribution. They were particularly abundant in the hippocampus, septum, hypothalamus, area ventralis of Tsai, and substantia nigra, where they formed dense pericellular arrangements. Significant immunoreactivity was observed in auditory nuclei, including the nucleus mesencephalicus lateralis pars dorsalis, the thalamic nucleus ovoidalis, field L, the shelf of the high vocal center (HVC), and the cup of the nucleus robustus archistriatalis (RA), as well as in song control nuclei, including the HVC, RA, the lateral magnocellular nucleus of the anterior neostriatum, and the dorsomedial nucleus (DM) of the intercollicular complex. Except for the DM, DBH immunoreactivity within song nuclei was comparable to that of surrounding tissues. Conspicuously negative were the lobus paraolfactorius, including song nucleus area X, and the paleostriatum. Our results are in agreement with previous studies of the noradrenergic system performed in nonoscines. More importantly, they provide direct evidence for a noradrenergic innervation of auditory and song control nuclei involved in song perception and production, supporting the notion that noradrenaline is involved in vocal communication and learning in oscines.     

Sources of GABAergic input to the inferior colliculus of the rat

We have studied the GABAergic projections to the inferior colliculus (IC) of the rat by combining the retrograde transport of horseradish peroxidase (HRP) and immunohistochemistry for gamma-amino butyric acid (GABA). Medium-sized (0.06-0.14 microliter) HRP injections were made in the ventral part of the central nucleus (CNIC), in the dorsal part of the CNIC, in the dorsal cortex (DCIC), and in the external cortex (ECIC) of the IC. Single HRP-labeled and double (HRP-GABA)-labeled neurons were systematically counted in all brainstem auditory nuclei. Our results revealed that the IC receives GABAergic afferent connections from ipsi- and contralateral brainstem auditory nuclei. Most of the contralateral GABAergic input originates in the IC and the dorsal nucleus of the lateral lemniscus (DNLL). The dorsal region of the IC (DCIC and dorsal part of the CNIC) receives connections mostly from its homonimous contralateral region, and the ventral region from the contralateral DNLL. The commissural GABAergic projections originate in a morphologically heterogeneous neuronal population that includes small to medium-sized round and fusiform neurons as well as large and giant neurons. Quantitatively, the ipsilateral ventral nucleus of the lateral lemniscus is the most important source of GABAergic input to the CNIC. In the superior olivary complex, a smaller number of neurons, which lie mainly in the periolivary nuclei, display double labeling. In the contralateral cochlear nuclei, only a few of the retrogradely labeled neurons were GABA immunoreactive. These findings give us more information about the role of GABA in the auditory system, indicating that inhibitory inputs from different ipsi- and contralateral, mono- and binaural auditory brainstem centers converge in the IC.     

Premotor neurons for vertical eye movements in the rostral mesencephalon of monkey and human: histologic identification by parvalbumin immunostaining

In the monkey, premotor neurons for vertical gaze are located in the mesencephalic reticular formation: the rostral interstitial nucleus of the medial longitudinal fascicle (riMLF) contains medium-lead burst neurons, and the interstitial nucleus of Cajal (iC) acts as integrator for the eye-velocity signals to eye-position signals. Both nuclei lie adjacent to each other and are similar in appearance at the transition zone in Nissl-stained sections, which makes a delineation of the functionally different nuclei difficult in human. For a neuropathologic analysis of degenerative changes in saccadic disorders of patients, the histologic identification of the riMLF and the iC is important. The aim of this study is to identify both nuclei in human by using parvalbumin as a histologic marker. First, in monkeys the premotor neurons in riMLF and iC were identified by trans-synaptic labelling after injections of tetanus toxin fragment C into vertical-pulling eye muscles. Premotor neurons were found in the riMLF mainly ipsilateral to the corresponding eye muscle motoneurons and on both sides within the iC, but here the labelled cell populations differed: the contralateral side contained more medium-sized cells compared with the mainly small-sized cell population on the ipsilateral side. Double labelling showed that almost all premotor neurons in the iC and all premotor neurons in the riMLF were parvalbumin-immunoreactive. The immunocytochemical staining of human brainstem sections revealed the riMLF as a cluster of medium-sized, elongated parvalbumin-positive cells, with a similar appearance and at a similar location as that in monkey: a wing-shaped nucleus dorsomedial to the red nucleus, rostral to the traversing tractus retroflexus, dorsally bordered by the thalamo-subthalamic paramedian artery. The adjacent iC could be distinguished easily by its more densely packed, round parvalbumin-immunoreactive neurons. The exact identification of premotor neurons of the vertical system in the normal human brain provides a reference basis for the neuropathologic analysis of vertical gaze disorders at a cellular level.     

Functional neuroanatomy of auditory pathways in the sound-producing fish Pollimyrus

We have described the acoustic pathway from the ear to the diencephalon in a sound-producing fish (Pollimyrus) based on simultaneous neurophysiological recordings from single neurons and injections of biotin pathway tracers at the recording sites. Fundamental transformations of auditory information from highly phase-locked and entrained responses in primary eighth nerve afferents and first-order medullary neurons to more weakly phase-locked responses in the auditory midbrain were revealed by physiological recordings. Anatomical pathway tracing uncovered a bilateral array of both first- and second-order medullary nuclei and a perilemniscal nucleus. Interconnections within the medullary auditory areas were extensive. Medullary nuclei projected to the auditory midbrain by means of the lateral lemniscus. Midbrain auditory areas projected to both ipsilateral and contralateral optic tecta and to an array of three nuclei in the auditory thalamus. The significance of these findings to the elucidation of mechanisms for the analysis of communication sounds and spatial hearing in this vertebrate animal is discussed.     

Interhemispheric coordination of premotor neural activity during singing in adult zebra finches

The song system, a neural network that mediates the learning and production of song by oscine songbirds, is investigated extensively as a model system for understanding the neural basis of complex skill learning. Part of the complexity of birdsong arises from the coordinated recruitment of multiple groups of muscles on both sides of the body. Although the song system is bilaterally organized, little is known about how premotor activities on the two sides are coordinated during singing. We investigated this by unilaterally recording neural activity in the forebrain song nucleus HVc (also known as the high vocal center) during singing and by forcing the premotor activities in the two hemispheres out of synchrony by perturbing neural activity in the contralateral HVc with electrical stimulation. Perturbing the activity in one HVc at any time during a song led to a short-latency readjustment of activity in the contralateral HVc. This readjustment consisted of a true resetting of the temporal pattern of activity in the contralateral HVc rather than merely a transient activity suppression overlaid on an unaltered pattern of premotor activity. These results strongly suggest that the output of song premotor areas in the forebrain is continuously monitored and that an active mechanism exists for resynchronizing the outputs from the two hemispheres whenever their gross temporal patterns differ significantly. The possible anatomical substrates for these coordinating mechanisms and their potential roles in song learning are discussed.     

Recovery of hearing and vocal behavior after hair-cell regeneration

Postmitotic hair-cell regeneration in the inner ear of birds provides an opportunity to study the effect of renewed auditory input on auditory perception, vocal production, and vocal learning in a vertebrate. We used behavioral conditioning to test both perception and vocal production in a small Australian parrot, the budgerigar. Results show that both auditory perception and vocal production are disrupted when hair cells are damaged or lost but that these behaviors return to near normal over time. Precision in vocal production completely recovers well before recovery of full auditory function. These results may have particular relevance for understanding the relation between hearing loss and human speech production especially where there is consideration of an auditory prosthetic device. The present results show, at least for a bird, that even limited recovery of auditory input soon after deafening can support full recovery of vocal precision.     

Medial auditory thalamic nuclei are necessary for eyeblink conditioning.

The auditory conditioned stimulus (CS) pathway that is necessary for delay eyeblink conditioning was investigated with induced lesions of the medial auditory thalamus contralateral to the trained eye in rats. Rats were given unilateral lesions of the medial auditory thalamus or a control surgery followed by twenty 100-trial sessions of delay eyeblink conditioning with a tone CS and then five sessions of delay conditioning with a light CS. Rats that had complete lesions of the contralateral medial auditory thalamic nuclei, including the medial division of the medial geniculate, suprageniculate, and posterior intralaminar nucleus, showed a severe deficit in conditioning with the tone CS. Rats with complete lesions also showed no cross-modal facilitation (savings) when switched to the light CS. The medial auditory thalamic nuclei may modulate activity in a short-latency auditory CS pathway or serve as part of a longer latency auditory CS pathway that is necessary for eyeblink conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of species identification in ducklings: III. Maturational rectification of perceptual deficit caused by auditory deprivation.

In 3 experiments, mute Peking ducklings, devocalized as embryos and manipulated in auditory isolation, manifested a selective high-frequency perceptual deficit vis-a-vis the maternal cal of their species at 24 hrs after hatching. Since it takes a rather specific auditory experiential input to rectify this high-frequency insensitivity at 24 hrs, it was predicted that, in the absence of auditory experience, devocal-isolated Ss would fail to show sufficient endogenously mediated improvement to bring them up to the level of perceptual competence of vocal-communal Ss at any age. This hypothesis proved wrong in that the proportion of devocalized Ss showing a preference for the normal maternal call over the >825-Hz attenuated one, became equivalent to the vocal Ss at 48 hrs after hatching, as did their ability to discriminate the normal maternal call from >1,800-Hz attenuated maternal call. At 65 hrs, however, the devocalized Ss' performance deteriorated back to the level observed at 24 hrs. It is concluded that embryonic exposure to the (sibling) contact-contentment call prevents the perceptual deficit at 24 hrs and the deterioration at 65 hrs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Connections of the torus semicircularis and oliva superior in the frog, Rana esculenta: a Phaseolus vulgaris leucoagglutinin labeling study

The afferent and efferent connections of the frog principal nucleus (TP) of torus semicircularis (TOS) and superior olive (SO) were examined by employing the anterograde and retrograde transport patterns of Phaseolus vulgaris leucoagglutinin (PHA-L). After injecting the tracer into these nuclei it was found that the TP projected to the ipsilateral posterior and central thalamic nuclei, all subdivisions of the bilateral TDS and the ipsilateral nucleus isthmi (NI). In the rhombencephalon the projection was restricted mainly to the contralateral SO and the cochlear nucleus (CN). Retrogradely labeled cells were found in most of the areas that contained anterogradely labeled terminals. The termination areas of the SO fibers were similar to the projections of fibers of TP origin in the diencephalic and in the mesencephalic auditory centers. A strong projection was followed into the contralateral SO; the CNs received fibers at both sides. Caudally to the SO the reticular formation, the spinal nucleus of the trigeminal nerve, the solitary nucleus and the dorsal column nuclei were supplied by the fibers of the SO origin. Retrogradely labeled cells were found in the TOS, tegmental nuclei, solitary nucleus, dorsal column nuclei and in the spinal nucleus of the trigeminal nerve. Our results indicate that the frog auditory pathway is more complex at the level of the secondary and tertiary fiber projections than has been previously recognized.     

Soldiers, surgeons and the campaigns to combat sexually transmitted diseases in colonial India, 1805-1860

Here, we examine the connectivity of two previously identified telencephalic stations of the auditory system of adult zebra finches, the neostriatal "shelf" that underlies the high vocal center (HVC) and the archistriatal "cup" adjacent to the robust nucleus of the archistriatum (RA). We used different kinds of neuroanatomical tracers to visualize the projections from the shelf to the HVC. In addition, we show that the shelf projects to the cup and that the cup projects to thalamic, midbrain, and pontine nuclei of the ascending auditory pathway. Our observations extend to songbirds anatomical features that are found in the auditory pathways of a nonoscine bird, the pigeon (Wild et al. [1993] J. Comp. Neurol. 337:32-62), and we suggest that the descending auditory projections found in mammals may also be a general property of the avian brain. Finally, we show that the oscine song control system is closely apposed to auditory pathways at many levels. Our observations may help in understanding the evolution and organization of networks for vocal communication and vocal learning in songbirds.     

Short interpregnancy intervals and the risk of adverse birth outcomes among five racial/ethnic groups in the United States

Unilateral microinjections of acetylcholine into the rat solitary tract nucleus evoked inhibitory effects in electrical activity of symmetrical portions of the diaphragm and external intercostal muscles. Administration of propranolol exerted excitatory respiratory responses. The findings suggest participation of cholin- and noradrenergic systems in inhibitory mechanisms of respiratory control. Different roles of the right and left solitary tract nuclei in their involvement in formation of efferent impulses to bilateral inspiratory muscles, are discussed.     

Prognostic value of bcl-2 expression in patients with operable carcinoma of the uterine cervix

The nucleus retroambiguus (NRA) is a group of premotor neurons at the transition between brainstem and spinal cord. It projects to certain motoneuronal cell groups, among which is a distinct set of motoneurons in the lumbar enlargement innervating muscles including iliopsoas, adductor longus, and hamstrings. To find out whether these NRA-motoneuronal projections are monosynaptic, injections of wheat germ-agglutinin horseradish peroxidase (WGA-HRP) into the NRA were combined with injections of cholera toxin subunit b (CTb) into the hamstring muscles. Electron microscopical examination revealed that the NRA terminal profiles make monosynaptic contacts with dendrites of motoneurons innervating these muscles. The NRA terminal profiles formed asymmetrical synapses, and contained spherical and a few dense core vesicles. These findings provide evidence of monosynaptic NRA-hindlimb motoneuronal projections which are likely to be excitatory.     

Development of species identification in ducklings: XII. Ineffectiveness of auditory self-stimulation in wood ducklings (Aix sponsa).

Examined the actual vocalizations of 24 auditory self-stimulated and 21 unstimulated wood ducklings to explore the possibility that there is a difference in the kind and/or amount of auditory self-stimulation in the 2 groups. Previous research shows that wood ducklings vocalized copiously when in auditory isolation; however, such self-stimulation was ineffective in maintaining their preference for descending frequency-modulated (FM) notes of the maternal call. Only isolated ducklings that had been exposed to recorded descending sib calls exhibited the normal preference for descending maternal notes in a choice test with ascending and descending maternal calls. Results of the present study with a similar choice test show that although stimulated Ss produced more ascending notes than unstimulted Ss, no differences were found in the overall vocal behavior, vocal reactivity, or specific kinds of frequency modulation produced by Ss that preferred the descending maternal call and other Ss that responded in the choice test. This absence of a difference in vocal production supports the previous conclusion that self-stimulation plays no role in the development or maintenance of the species-typical perceptual preference for descending FM notes. (14 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parvalbumin, calbindin D-28k, and calretinin immunoreactivity in the ascending auditory pathway of horseshoe bats

In the subcortical auditory system of Rhinolophus rouxi, antibodies directed against the calcium-binding proteins parvalbumin, calbindin D-28k, and calretinin yield partly overlapping and partly complementary labeling patterns which are described in detail for each nucleus. The most general features of the labeling patterns are that: 1) Parvalbumin is a potent marker for large and heterogeneous populations of cells and puncta (presumed axon terminals) throughout the auditory pathway. 2) Immunostaining with the monoclonal calbindin-antiserum was typically absent or sparse in most auditory brainstem centers, but prominent in auditory nerve fibers and in cells of the medial geniculate body (MGB). 3) Calretinin label is abundant but more restricted to subsets of auditory nuclei or subpopulations of cells than parvalbumin. 4) Calcium-binding proteins are useful markers to define particular subregions or cell types in auditory nuclei: for example, i) different labeling patterns are obtained within the nuclei of the lateral lemniscus and adjacent tegmental zones; ii) in the inferior colliculus both calbindin- and calretinin-antisera yield similar regional specific staining patterns, but label different cell types; iii) subregions of the medial geniculate body have characteristic profiles of calcium-binding proteins; and iv) analyses of different nuclei showed that there is no simple common denominator for cells characterized by the expression of particular calcium-binding proteins, nor does labeling correspond in a straightforward way with specific functional systems. 5) there are profound differences between the calbindin labeling patterns seen in Rhinolophus and those in other mammals.