Topographic representation of visceral target organs within the dorsal motor nucleus of the vagus nerve of the pigeon Columba livia

Molecular cell types as functional units of the efferent vagus nerve

The vagus nerve vitally connects the brain and body to coordinate digestive, cardiorespiratory, and immune functions. Its efferent neurons, which project their axons from the brainstem to the viscera, are thought to comprise "functional units" - neuron populations dedicated to the control of specific vagal reflexes or organ functions. Previous research indicates that these functional units differ from one another anatomically, neurochemically, and physiologically but have yet to define their identity in an experimentally tractable way. However, recent work with genetic technology and single-cell genomics suggests that genetically distinct subtypes of neurons may be the functional units of the efferent vagus. Here we review how these approaches are revealing the organizational principles of the efferent vagus in unprecedented detail.

Choline-acetyltransferase (ChAT) and acetylcholinesterase (AChE) in the human infant dorsal motor nucleus of the Vagus (DMNV), and alterations according to sudden infant death syndrome (SIDS) category

Amongst other molecules, the cholinergic system consists of choline-acetyltransferase (ChAT, - synthesis enzyme), acetylcholinesterase (AChE - primary hydrolysis enzyme), and butyrylcholinesterase (BuChE - secondary hydrolysis enzyme). In the brainstem, the Dorsal Motor Nucleus of The Vagus (DMNV) has high cholinergic expression and is a region of interest in the neuropathology of sudden infant death syndrome (SIDS). SIDS is the unexpected death of a seemingly healthy infant, but postmortem brainstem abnormalities suggesting altered cholinergic regulation have been found. This study aimed to determine the percentage of positive ChAT and AChE neurons within the infant DMNV through immunohistochemistry at the three levels of the brainstem medulla (caudal, intermediate, and rostral), to investigate whether the proportion of neurons positive for these enzymes differs amongst the diagnostic subgroups of SIDS compared to those with an explained cause of Sudden unexpected death in infancy (eSUDI), and whether there were any associations with SIDS risk factors (male gender, cigarette smoke exposure, co-sleeping/bed sharing, and prone sleeping). Results showed that ChAT-positive neurons were lower in the rostral DMNV in the SIDS II cohort, and within the caudal and intermediate DMNV of infants who were exposed to cigarette smoke. These findings suggest altered cholinergic regulation in the brainstem of SIDS infants, with potential contribution of cigarette smoke exposure, presumably via the nicotinic acetylcholinergic receptor system.

An overview of the phylogeny of cardiorespiratory control in vertebrates with some reflections on the 'Polyvagal Theory'

Mammals show clear changes in heart rate linked to lung ventilation, characterized as respiratory sinus arrhythmia (RSA). These changes are controlled in part by variations in the level of inhibitory control exerted on the heart by the parasympathetic arm of the autonomic nervous system (PNS). This originates from preganglionic neurons in the nucleus ambiguous that supply phasic, respiration-related activity to the cardiac branch of the vagus nerve, via myelinated, efferent fibres with rapid conduction velocities. An elaboration of these central mechanisms, under the control of a 'vagal system' has been endowed by psychologists with multiple functions concerned with 'social engagement' in mammals and, in particular, humans. Long-term study of cardiorespiratory interactions (CRI) in other major groups of vertebrates has established that they all show both tonic and phasic control of heart rate, imposed by the PNS. This derives centrally from neurones located in variously distributed nuclei, supplying the heart via fast-conducting, myelinated, efferent fibres. Water-breathing vertebrates, which include fishes and larval amphibians, typically show direct, 1:1 CRI between heart beats and gill ventilation, controlled from the dorsal vagal motor nucleus. In air-breathing, ectothermic vertebrates, including reptiles, amphibians and lungfish, CRI mirroring RSA have been shown to improve oxygen uptake during phasic ventilation by changes in perfusion of their respiratory organs, due to shunting of blood over across their undivided hearts. This system may constitute the evolutionary basis of that generating RSA in mammals, which now lacks a major physiological role in respiratory gas exchange, due to their completely divided systemic and pulmonary circulations.

Vagal Nerve Stimulation: The Effect on the Brain Oscillatory Field Potential

More than thirty years of medical treatment with the use of vagal nerve stimulation (VNS) has shown that this therapeutic procedure works in a number of homeostatic disturbances. Although the clinical usage of VNS has a long history, our knowledge about the central mechanisms underlying this treatment is still limited. In the present paper we review the effects of VNS on brain oscillations as a possible electrophysiological bio-marker of VNS efficacy. The review was prepared mainly on the basis of data delivered from clinical observations and the outcomes of electrophysiological experiments conducted on laboratory animals that are available in PubMed. We consciously did not focus on epileptiform activity understood as a pathologic oscillatory activity, which was widely discussed in the numerous previously published reviews. The main conclusion of the present paper is that further, well-designed experiments on laboratory animals are absolutely necessary to address the electrophysiological issues. These will fill a number of gaps in our present knowledge of the central mechanisms underlying VNS therapy.

Novel localizations of TRPC5 channels suggest novel and unexplored roles: A study in the chick embryo brain

Mammalian TRPC5 channels are predominantly expressed in the brain, where they increase intracellular Ca²⁺ and induce depolarization. Because they augment presynaptic vesicle release, cause persistent neural activity, and show constitutive activity, TRPC5s could play a functional role in late developmental brain events. We used immunohistochemistry to examine TRPC5 in the chick embryo brain between 8 and 20 days of incubation, and provide the first detailed description of their distribution in birds and in the whole brain of any animal species. Stained areas substantially increased between E8 and E16, and staining intensity in many areas peaked at E16, a time when chick brains first show organized patterns of whole-brain metabolic activation like what is seen consistently after hatching. Areas showing cell soma staining match areas showing Trpc5 mRNA or protein in adult rodents (cerebral cortex, hippocampus, amygdala, cerebellar Purkinje cells). Chick embryos show protein staining in the optic tectum, cerebellar nuclei, and several brainstem nuclei; equivalent areas in the Allen Institute mouse maps express Trpc5 mRNA. The strongest cell soma staining was found in a dorsal hypothalamic area (matching a group of parvicellular arginine vasotocin neurons and a pallial amygdalohypothalamic cell corridor) and the vagal motor complex. Purkinje cells showed strong dendritic staining at E20. Unexpectedly, we also describe neurite staining in the septum, several hypothalamic nuclei, and a paramedian raphe area; the strongest neurite staining was in the median eminence. These novel localizations suggest new unexplored TRPC5 functions, and possible roles in late embryonic brain development.

The α3 and α4 nicotinic acetylcholine receptor (nAChR) subunits in the brainstem medulla of sudden infant death syndrome (SIDS)

SIDS occurs in early infancy and predominantly during a sleep period. Abnormalities in nicotine receptor binding and in the expression of the nicotinic acetylcholine receptor (nAChR) subunits α7 and β2 have been reported in the brainstem of SIDS infants. This study focuses on the α3 and α4 nAChR subunits as α3 is important for early postnatal survival while α4 is crucial for nicotine-elicited antinociception and sleep-wake cycle regulation. Tissue from the rostral medulla of infants who died with a known cause of death (eSUDI, n = 7), and from SIDS classified as SIDS I (n = 8) and SIDS II (n = 27), was immunohistochemically stained for the α3 and α4 nAChR subunits and quantified in 9 nuclei comparing amongst these groups. The association with risk factors of sex, cigarette smoke exposure, upper respiratory tract infection (URTI), prone sleeping and bedsharing was also evaluated. Results showed that only α4 changes (increase) were evident in SIDS, occurring in the hypoglossal and cuneate nuclei of SIDS II infants and the nucleus of the spinal trigeminal tract of SIDS I infants. Amongst the SIDS infants, cigarette smoke exposure was only associated with decreased α4 in cribriform fibre tracts, while sex and bedsharing were associated with increases in α3 in the dorsal motor nucleus of the vagus and solitary nucleus, respectively. Combined, these findings suggest that abnormalities in endogenous acetylcholine synthesis and regulation may underlie the altered α3 and α4 nAChR subunit expressions in the SIDS brainstem medulla since the changes were not related to cigarette smoke exposure.

The dorsal motor nucleus of the vagus (DMNV) in sudden infant death syndrome (SIDS): pathways leading to apoptosis

Sudden infant death syndrome (SIDS) remains the commonest cause of death in the post-neonatal period in the developed world. A leading hypothesis is that an abnormality in the brainstem of infants who succumb to SIDS, either causes or predisposes to failure to respond appropriately to an exogenous stressor. Neuronal apoptosis can lead to loss of cardiorespiratory reflexes, compromise of the infant's ability to respond to stressors such as hypoxia, and ultimately a sleep-related death. The dorsal motor nucleus of the vagus (DMNV) is a medullary autonomic nucleus where abnormalities have regularly been identified in SIDS research. This review collates neurochemical findings documented over the last 30 years, including data from our laboratory focusing on neuronal apoptosis and the DMNV, and provides potential therapeutic interventions targeting neurotransmitters, growth factors and/or genes.

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.

Hox gene colinear expression in the avian medulla oblongata is correlated with pseudorhombomeric domains

The medulla oblongata (or caudal hindbrain) is not overtly segmented, since it lacks observable interrhombomeric boundaries. However, quail-chick fate maps showed that it is formed by 5 pseudorhombomeres (r7-r11) which were empirically found to be delimited consistently at planes crossing through adjacent somites (Cambronero and Puelles, 2000). We aimed to reexamine the possible segmentation or rostrocaudal regionalisation of this brain region attending to molecular criteria. To this end, we studied the expression of Hox genes from groups 3 to 7 correlative to the differentiating nuclei of the medulla oblongata. Our results show that these genes are differentially expressed in the mature medulla oblongata, displaying instances of typical antero-posterior (3' to 5') Hox colinearity. The different sensory and motor columns, as well as the reticular formation, appear rostrocaudally regionalised according to spaced steps in their Hox expression pattern. The anterior limits of the respective expression domains largely fit boundaries defined between the experimental pseudorhombomeres. Therefore the medulla oblongata shows a Hox-related rostrocaudal molecular regionalisation comparable to that found among rhombomeres, and numerically consistent with the pseudorhombomere list. This suggests that medullary pseudorhombomeres share some AP patterning mechanisms with the rhombomeres present in the rostral, overtly-segmented hindbrain, irrespective of variant boundary properties.

Effect of glucagon-like peptide-1 and -2 on regulation of food intake, body temperature and locomotor activity in the Japanese quail

To investigate the physiological roles of glucagon-like peptide-1 (GLP-1) and glucagon-like peptide-2 (GLP-2) in avian species, we elucidated the effect of intraperitoneal (i.p.) and intracerebroventricular (i.c.v.) administration of GLP-1 and GLP-2 on food intake, body temperature and gross locomotor activity in adult Japanese quail. Both i.p. and i.c.v. administration of GLP-1 suppressed food intake at 2, 4 and 12h after administration. Moreover, both i.p. and i.c.v. administration of GLP-1 significantly decreased both body temperature and gross locomotor activity 2h after administration. On the other hand, both i.p. and i.c.v. administration of GLP-2 had no effect on food intake, body temperature or gross locomotor activity. These results suggest that GLP-1 may have an important role in the regulation of food intake, body temperature and locomotor activity while GLP-2 may have no apparent effect on feeding regulation in adult Japanese quail.

Distribution of proglucagon mRNA and GLP-1 in the brainstem of chicks

Glucagon-like peptide-1 (GLP-1), structurally similar to glucagon, synthesized from the precursor proglucagon, is a well known anorexigenic peptide in the brain of several animal species. However, there are no previous reports concerning GLP-1-containing neurons in the chick brain. The aim of the present study was to investigate the distribution of proglucagon mRNA and GLP-1-immunoreactive (GLI) perikarya in various regions of the chick brain. We detected proglucagon mRNA in the brainstem, and to a lesser extent in the telencephalon. In the brainstem, a study using immunohistochemistry revealed that GLI perikarya were present in the nucleus motorius nervi facialis pars dosalis, nucleus motoris dorsalis nervi vagi and nucleus tractus solitarii. Furthermore, we found that proglucagon mRNA expression in the brainstem decreased after 24 h fasting. The present findings support the idea that endogenous GLP-1 is involved in feeding behavior of chicks.

Differential activation of medullary vagal nuclei during different phases of swallowing in the cat

The aim of this study was to identify the medullary vagal nuclei involved in the different phases of swallowing activated physiologically in a species with an esophagus similar to human. In decerebrate cats, the pharyngeal (0.5-1.0 ml water in pharynx (N=6)) or esophageal (1-3 ml air in esophagus (N=5)) phases of swallowing were stimulated separately once per minute for 3 h, and we compared the resulting c-fos immunoreactivity within neuronal cell nuclei of the dorsal motor nucleus (DMN), nucleus tractus solitarius (NTS) and nucleus ambiguus (NA) with a sham control group (N=5). We found that the pharyngeal phase was associated with an elevated number of c-fos positive neurons in the intermediate (NTSim), interstitial (NTSis), ventromedial (NTSvm) subnuclei of the NTS, caudal DMN, and dorsal NA; and the esophageal phase was associated with an elevated number of c-fos positive neurons in the central (NTSce), ventral, dorsolateral, ventrolateral subnuclei of the NTS, rostral DMN, and ventral NA. We concluded that the pharyngeal and esophageal phases of swallowing are associated with different sets of NTS subnuculei; and the DMN and NA may contain functionally different populations of motor neurons situated rostrocaudally and dorsoventrally associated with the different phases of swallowing. The central pattern generator (CPG) for swallowing probably receives significant peripheral feedback, and the NTSvm may participate in the transition of the pharyngeal to the esophageal phase of swallowing.

Water metabolism in the eel acclimated to sea water: from mouth to intestine

Eels seem to be a suitable model system for analysing regulatory mechanisms of drinking behavior in vertebrates, since most dipsogens and antidipsogens in mammals influence the drinking rate in the seawater eels similarly. The drinking behavior in fishes consists of swallowing alone, since they live in water and water is constantly held in the mouth for respiration. Therefore, contraction of the upper esophageal sphincter (UES) muscle limits the drinking rate in fishes. The UES of the eel was innervated by the glossopharyngeal-vagal motor complex (GVC) in the medulla oblongata (MO). The GVC neurons were immunoreactive to an antibody raised against choline acetyltransferase (ChAT), an acetylcholine (ACh) synthesizing enzyme, indicating that the eel UES muscle is controlled cholinergically by the GVC. The neuronal activity of the GVC was inhibited by adrenaline or dopamine, suggesting catecholaminergic innervation to the GVC. The AP and the commissural nucleus of Cajal (NCC) in the MO projected to the GVC and were immunoreactive to an antibody raised against tyrosine hydroxylase (TH), rate limiting enzyme to produce catecholamines from tyrosine. Therefore, it is likely that activation in the AP or the NCC may inhibit the GVC and thus relaxes the UES muscle, which allows for water to enter into the esophagus. During passing through the esophagus, the imbibed sea water (SW) was desalted to approximately 1/2 SW, which was further diluted in the stomach and arrived at the intestine as approximately 1/3 SW, almost isotonic to the plasma. Finally, from the diluted SW, the eel intestine absorbed water following the Na(+)-K(+)-2Cl(-) cotransport (NKCC2) system. The NaCl and water absorption across the intestine was regulated by various factors, especially by peptides such as atrial natriuretic peptide (ANP) and somatostatin (SS-25 II). During desalination in the esophagus, however, excess salt enters into the blood circulation, which is liable to raise the plasma osmolarity. However, the eel heart was constricted powerfully by the hyperosmolarity, suggesting that the hyperosmolarity enhances the stroke volume to the gill, where excess salt was extruded powerfully via Na(+)-K(+)-2Cl(-) cotransport (NKCC1) system.

Distribution of a novel avian gonadotropin-inhibitory hormone in the quail brain

We recently identified a novel hypothalamic neuropeptide inhibiting gonadotropin release in the quail brain and termed it gonadotropin inhibitory hormone (GnIH). In this study, we investigated the localization and distribution of GnIH in both sexes of adult quails by immunohistochemistry with a specific antiserum against GnIH and in situ hybridization. Quantitative analysis demonstrated that the concentration of GnIH in the diencephalon was greater than that in the mesencephalon without sex difference. GnIH concentrations in the cerebrum and cerebellum were below the level of detectability. Clusters of GnIH-like immunoreactive (GnlH-ir) cell bodies were localized in the paraventricular nucleus (PVN) of the hypothalamus. There was no significant difference in the number of GnlH-ir cells in the PVN between males and females. By double immunostaining with antisera reacting with GnIH or avian posterior pituitary hormones (vasotocin and mesotocin), GnIH-ir cells were found to be parvocellular neurons in the ventral portion of PVN, which showed no immunoreaction with the antisera against vasotocin and mesotocin. In situ hybridization revealed the cellular localization of GnIH mRNA in the PVN. GnIH-ir nerve fibers were however widely distributed in the diencephalic and mesencephalic regions. Dense networks of immunoreactive fibers were found in the ventral paleostriatum, septal area, preoptic area, hypothalamus, and optic tectum. The most prominent fibers were seen in the median eminence of the hypothalamus and the dorsal motor nucleus of the vagus in the medulla oblongata. Thus, GnIH may participate not only in neuroendocrine functions, but also in behavioral and autonomic mechanisms.

Central, but not peripheral, glucagon-like peptide-1 inhibits crop emptying in chicks

We investigated the effect of central and peripheral glucagon-like peptide-1 (GLP-1) on crop emptying in growing chicks. Intracerebroventricular injection of two concentrations of GLP-1 (15 and 60 pmol) similarly suppressed crop emptying, compared with control chicks. The delay in crop emptying induced by GLP-1 (15 pmol) was partly attenuated by co-administration with exendin (5-39) (600 pmol), a GLP-1 receptor antagonist, although exendin (5-39) alone did not affect crop emptying. On the other hand, intraperitoneal administration of several doses of GLP-1 (120, 300 and 3000 pmol) did not alter crop emptying. The present study revealed that central, but not peripheral, GLP-1 inhibits crop emptying in chicks.

Cholinergic innervation to the upper esophageal sphincter muscle in the eel, with special reference to drinking behavior

To elucidate innervation in the upper esophageal sphincter (UES) muscle of the eel, a key muscle in swallowing, repetitive electrical field stimulation (EFS; 30 mA, 40 V, 300 micros, 10 Hz, 10 trains) was employed. Anatomically, the eel UES muscle consists of striated fibers. The EFS-induced contraction of the UES was completely blocked by tetrodotoxin and curare, and abolished in Ca2+ -free Ringer solution. These results suggest that the EFS stimulates nerve fibers specifically and releases acetylcholine as a neurotransmitter. In fact, acetylcholine and carbachol constricted the UES in a concentration-dependent manner. Even after blocking neuronal firing with tetrodotoxin, acetylcholine constricted the UES muscle, suggesting the existence of acetylcholine receptors on the UES muscle cells. Both EFS- and carbachol-evoked contractions of the UES were blocked by curare at a lower concentration than by atropine or hexamethonium, suggesting that the acetylcholine receptor is nicotinic. Even in Ca2+ -free Ringer solution, a direct current stimulus (2 s duration) constricted the UES muscle to an extent similar to that in the presence of Ca2+, indicating that the muscle contraction itself does not need extracellular Ca2+, i.e., the muscle can be constricted by a release of Ca2+ from the sarcoplasmic reticulum.

Monoaminergic and peptidergic axonal projections to the vagal motor cell column of a teleost, the filefish Stephanolepis cirrhifer

In an immunohistochemical study, the vagal motor nucleus of a teleost, the filefish Stephanolepis cirrhifer, could be divided into a rostral part and a caudal part, and the former into a dorsolateral group and a ventromedial group. The dorsolateral group consisted of neurons immunoreactive for calcitonin gene-related peptide, whereas the ventrolateral-caudal group was negative for calcitonin gene-related peptide. The latter group was retrogradely labeled after dextran amine injection to the visceral ramus of the vagus nerve, suggesting that it is a general visceral efferent column, made up of parasympathetic preganglionic neurons, whereas the dorsolateral rostral group is a special visceral efferent column. In the general visceral efferent column, a dense concentration of nerve fibers immunoreactive for serotonin, tyrosine hydroxylase, cholecystokinin-8, and substance P, and a small number of fibers immunoreactive for neuropeptide Y was observed. Perikarya in contact with varicose terminals immunoreactive for these substances were frequently seen. In contrast, in the special visceral efferent column, only a moderate concentration of neuropeptide Y-immunoreactive nerve fibers and a sparse distribution of fibers immunoreactive for tyrosine hydroxylase were observed. Perikarya in contact with varicose terminals immunoreactive for these substances were rare. These results suggest that the vagal parasympathetic preganglionic neurons might receive multiple inputs of monoaminergic and peptidergic fibers involved in the regulation of the visceral organs. On the other hand, monoaminergic and peptidergic afferent fibers might be of much less significance in the activity of the special visceral efferent component of the vagus nerve.

Rostrocaudal nuclear relationships in the avian medulla oblongata: a fate map with quail chick chimeras

We present a correlative fate map of the nonsegmented caudal hindbrain down to the medullospinal boundary (medulla oblongata), as a companion to a previous fate mapping study of the hindbrain rhombomeres r2-r6 in quail chick chimeras at stages HH10/11 [Marín and Puelles (1995) Eur J Neurosci 7:1714-1738]. For reproducibility and equivalent precision of analysis, successive portions of the medulla-called pseudorhombomeres "r7" to "r11"-were delimited by transverse planes through the center of adjacent somites at stages HH10/11. These units were each grafted homotopically and isochronically from quail donors into chick hosts. The chimeric specimens were fixed at stages HH35/36 and alternate Nissl-stained sagittal sections were compared to adjacent sections in which quail cells were detected immunocytochemically. This analysis in general showed that there is little intermixing between adjacent pseudorhombomeric domains, although some neuronal populations in the vestibular and trigeminal columns, as well as in the reticular formation and pontine nuclei, do migrate selectively into the host hindbrain. Contralateral migration was scarce up to the stages examined. Several motor nuclei, i.e., the vagal motor complex, or sensory nuclei, i.e., the medial vestibular nucleus, show cytoarchitectonic limits that coincide with pseudorhombomeric ones; however, most conventional grisea were found to originate across several pseudorhombomeres. The inferior olivary complex originated between "r8" and "r11" (between the centers of somites 1 and 5). The medullospinal boundary coincided precisely with the center of the fifth somite, slightly caudal to the obex and the end of the choroidal roof, and correlated with the end of many medullary cytoarchitectonic units. In contrast, the dorsal column nuclei and the caudal subnucleus of the descending trigeminal column fell within the spinal cord. On the whole, the patterns observed were very similar to those found before within the overtly segmented part of the hindbrain, suggesting that some underlying common mechanism may account for the transverse cytoarchitectonic boundaries.

Central control of the cardiovascular and respiratory systems and their interactions in vertebrates

This review explores the fundamental neuranatomical and functional bases for integration of the respiratory and cardiovascular systems in vertebrates and traces their evolution through the vertebrate groups, from primarily water-breathing fish and larval amphibians to facultative air-breathers such as lungfish and some adult amphibians and finally obligate air-breathers among the reptiles, birds, and mammals. A comparative account of respiratory rhythm generation leads to consideration of the changing roles in cardiorespiratory integration for central and peripheral chemoreceptors and mechanoreceptors and their central projections. We review evidence of a developing role in the control of cardiorespiratory interactions for the partial relocation from the dorsal motor nucleus of the vagus into the nucleus ambiguus of vagal preganglionic neurons, and in particular those innervating the heart, and for the existence of a functional topography of specific groups of sympathetic preganglionic neurons in the spinal cord. Finally, we consider the mechanisms generating temporal modulation of heart rate, vasomotor tone, and control of the airways in mammals; cardiorespiratory synchrony in fish; and integration of the cardiorespiratory system during intermittent breathing in amphibians, reptiles, and diving birds. Concluding comments suggest areas for further productive research.

BDNF is a target-derived survival factor for arterial baroreceptor and chemoafferent primary sensory neurons

Brain-derived neurotrophic factor (BDNF) supports survival of 50% of visceral afferent neurons in the nodose/petrosal sensory ganglion complex (NPG; Ernfors et al., 1994a; Jones et al., 1994; Conover et al., 1995; Liu et al., 1995; Erickson et al., 1996), including arterial chemoafferents that innervate the carotid body and are required for development of normal breathing (Erickson et al., 1996). However, the relationship between BDNF dependence of visceral afferents and the location and timing of BDNF expression in visceral tissues is unknown. The present study demonstrates that BDNF mRNA and protein are transiently expressed in NPG targets in the fetal cardiac outflow tract, including baroreceptor regions in the aortic arch, carotid sinus, and right subclavian artery, as well as in the carotid body. The period of BDNF expression corresponds to the onset of sensory innervation and to the time at which fetal NPG neurons are BDNF-dependent in vitro. Moreover, baroreceptor innervation is absent in newborn mice lacking BDNF. In addition to vascular targets, vascular afferents themselves express high levels of BDNF, both during and after the time they are BDNF-dependent. However, endogenous BDNF supports survival of fetal NPG neurons in vitro only under depolarizing conditions. Together, these data indicate two roles for BDNF during vascular afferent pathway development; initially, as a target-derived survival factor, and subsequently, as a signaling molecule produced by the afferents themselves. Furthermore, the fact that BDNF is required for survival of functionally distinct populations of vascular afferents demonstrates that trophic requirements of NPG neurons are not modality-specific but may instead be associated with innervation of particular organ systems.

Neural sites and pathways regulating food intake in birds: a comparative analysis to mammalian systems

The paper reviews hypotheses explaining the regulation of food intake in mammals that have addressed specific anatomical structures in the brain. An hypothesis, poikilostasis, is introduced to describe multiple, homeostatic states whereby the regulation of metabolism and feeding occur in birds. Examples are given for both wild and domestic avian species, illustrating dynamic shifts in homeostasis responsible for the changes in body weights that are seen during the course of an annual cycle or by a particular strain of bird. The following neural structures are reviewed as each has been shown to affect food intake in birds or in mammals: ventromedial hypothalamic nucleus (n.), lateral hypothalamic area, paraventricular hypothalamic n., n. tractus solitarius and area postrema, amygdala, parabrachial n., arcuate n. and bed n. of the stria terminalis. Two neural pathways are described which have been proposed to regulate feeding. The trigeminal sensorimotor pathway is the most complete neural pathway characterized for this behavior and encompasses the mechanics of pecking, grasping and mandibulating food particles from the tip of the bill to the back of the buccal cavity. A second pathway, the visceral forebrain system (VFS), affects feeding by regulating metabolism and the balance of the autonomic nervous system. Wild, migratory birds are shown to exhibit marked changes in body weight which are hypothesized to occur due to shifts in balance between the sympathetic and parasympathetic nervous systems. Domestic avian species, selected for a rapid growth rate, are shown to display a dominance of the parasympathetic nervous system. The VFS is the neural system proposed to effect poikilostasis by altering the steady state of the autonomic nervous system in aves and perhaps is applicable to other classes of vertebrates as well.

Distribution of neurotensin-containing neurons in the central nervous system of the pigeon and the chicken

Neurotensin is widely located in neurons of the central and peripheral nervous systems among mammalian species. To obtain a comparative evaluation, we examined the distribution of neurotensin-containing cell bodies and fibers in the central nervous system of the pigeon and the chicken. The pattern of localization of neurotensin immunoreactivity was similar in the two species. Abundant accumulations of neurotensin-containing cell bodies were found in the dorsolateral corticoid area, the piriform cortex, the parahippocampal area, the medial part of the frontal neostriatum, the lateral part of the caudal neostriatum, nucleus accumbens, the bed nucleus of the stria terminalis, ventral paleostriatum, the preoptic area, the ventromedial hypothalamic nucleus, the inferior hypothalamic nucleus, the infundibular hypothalamic nucleus, and the mammillary nuclei. Extremely dense networks of neurotensin-containing fibers were found in the pallial commissure, the lateral septal nucleus, the preoptic area, the periventricular gray around the third ventricle, the dorsalis hypothalamic area, the hypothalamic nuclei, the parabrachial nucleus, the locus ceruleus, and the dorsal vagal complex. Major differences of immunoreactivity between the two species were as follows. 1) The chicken neurohypophysis contained an extremely large accumulation of immunoreactive fibers, but there were few in the median eminence. The reverse was found in the pigeon. 2) The optic tectum in the pigeon contained immunoreactive cells and fibers in layers 2 and 4, but no immunoreactivity was seen in the chicken optic tectum. 3) The cerebellar cortex in the pigeon contained a small number of immunoreactive fibers, whereas that in the chicken did not. 4) The pigeon spinal cord contained immunoreactive neurons in the subependymal layer, but the chicken spinal cord did not. Our observations suggest the presence of a very wide network of neurotensin-containing neurons in the avian brain and spinal cord, which is also the case in mammals.

Local and commissural neuropeptide-containing projections of the nucleus of the solitary tract to the dorsal vagal complex in the pigeon

The neuropeptide content of neurons of the nucleus of the solitary tract (NTS), which have local and commissural projections to the dorsal motor nucleus of the vagus (DMNX) and to NTS, were demonstrated in the pigeon (Columba livia) by using a combined fluorescein-bead retrograde-transport-immunofluorescence technique. The specific peptides studied were bombesin, cholecystokinin, enkephalin, galanin, neuropeptide Y, neurotensin, and substance P. Perikarya immunoreactive for bombesin were located in medial tier subnuclei of NTS and the caudal NTS. Most galanin- and substance P-immunoreactive cells were found in subnucleus medialis ventralis. Cells immunoreactive for neuropeptide Y were found in the medial tier of NTS and in the lateral tier, especially in subnucleus lateralis dorsalis intermedius. The majority of enkephalin- and neurotensin-immunoreactive cells were found centrally in subnuclei medialis dorsalis and medialis intermedius. Cells immunoreactive for cholecystokinin were located in subnuclei lateralis dorsalis pars anterior, medialis superficialis, and the caudal NTS. Based on the presence of retrogradely labeled cells, numerous neurons of the medial tier of NTS, but extremely few lateral tier NTS neurons, had projections to the ipsilateral and contralateral DMNX and NTS. The number of retrogradely labeled NTS cells was always greater ipsilaterally than contralaterally. The percentages of peptide-immunoreactive NTS cells that projected to the ipsilateral and contralateral DMNX were in the ranges of 29-61% and 10-48%, respectively. The percentages of peptide-immunoreactive NTS cells that projected to the contralateral NTS ranged from 13 to 60%. Peptide-immunoreactive NTS cells that have local and commissural projections to DMNX and NTS may act as interneurons in vagovagal reflex pathways and in the integration of visceral sensory and forebrain input to NTS and DMNX.

The central connections of the vagus nerve in the ferret

The vagus nerve mediates emesis due to gastric irritation. The central representation of the vagus in the ferret was studied to establish how the nerve is connected to areas important in the regulation of emesis. In a series of 10 ferrets, WGA-HRP injections (10 microliters) were made into the nodose ganglion. After 24-48 h, animals were reanesthetized and perfused transcardially. A block extending from the pons to upper cervical spinal cord was cut at 50 microns and sections reacted. Nodose ganglion injections of WGA-HRP produced labeling of vagal preterminal segments in the ipsilateral dorsal vagal complex including all subnuclei of the solitary complex where the medial and subgelatinous subnuclei received the densest input, the area postrema (AP), which contained a modest amount of terminal label, and the dorsal motor nucleus of the vagus (DMX). Contralateral terminal label, quantitatively much less, was similarly distributed except that within the solitary complex it was limited to the medial and subgelatinous subnuclei. Retrogradely labeled cells formed ipsilateral dorsomedial and ventrolateral columns, corresponding, respectively, to the DMX and the nucleus ambiguus (including retrofacial and retroambiguus).

Nucleus of the solitary tract and dorsal motor nucleus of the vagus nerve of the pigeon: localization of peptide and 5-hydroxytryptamine immunoreactive fibers

The distribution of peptide and serotonin fibers in the nucleus of the solitary tract (NTS) and the dorsal motor nucleus of the vagus nerve (DMNX) in the pigeon (Columba livia) was investigated immunocytochemically. This information was correlated with the viscerotopic organization of the nuclei and with central NTS circuitry to suggest the role of the neurochemical containing fibers in the regulation of organ function. The distribution of fibers containing cholecystokinin (CCK), calcitonin gene-related peptide (CGRP), enkephalin (ENK), neuropeptide Y (NPY), neurotensin (NT), substance P (SP), somatostatin (SS), vasoactive intestinal peptide (VIP), and 5-hydroxytryptamine (5-HT) was determined. Each substance had a distinct distribution within the subnuclei of NTS-DMNX, but certain generalities can be deduced. In the DMNX, fibers immunoreactive for ENK, NT, and SP were found in greatest concentration, while CGRP and 5-HT immunoreactive fibers were the least dense. This suggests that ENK, NT, and SP may have a significant modulatory effect on gastrointestinal functions. In the NTS overall, ENK, NT, SP, and VIP fibers were found in high density, CCK, NPY, SS, and 5-HT fibers were found in moderate density, and CGRP fibers were found in low density. However, some individual NTS subnuclei were found to contain moderate to high concentrations of each of the substances, including CGRP. Fibers containing CCK, ENK, NT, SP, SS, and VIP in the medial dorsal NTS subnuclei may regulate gastroesophageal functions. The caudal part of subnucleus lateralis parasolitarius did not contain most of the substances, which suggests that pulmonary function is not modulated by these neurochemicals. The boundaries of a subnucleus could sometimes be demarcated by a change in density of immunoreactive fibers between adjacent subnuclei. This was particularly evident in NTS subnuclei medialis dorsalis anterior centralis and lateralis parasolitarius, and in DMNX subnucleus posterior dorsalis magnocellularis. The selective distribution of peptide and serotonin immunoreactive fibers in various subnuclei of NTS-DMNX suggests that these substances may be differentially involved in neural circuits that mediate cardiovascular and gastrointestinal functions.

Dorsal motor nucleus of the vagus nerve: a cyto- and chemoarchitectonic study in the human

In order to investigate the topography and subdivisions of the human dorsal motor nucleus of the vagus nerve (10), studies were conducted using cyto- and chemoarchitectonic (acetylcholinesterase and substance P-like immunoreactivity) and computer reconstruction techniques. The six brainstems examined were obtained within 17 hours postmortem from adults with no known neurological disorders. Serial sections cut in transverse, sagittal, and coronal planes were stained with cresyl violet, or tested for acetylcholinesterase or substance P. The neurons of the 10 (16,826 +/- 967) displayed cyto- and chemoarchitectonic heterogeneity and could be classified into six types. Types I-V consist of presumed vagal motor neurons (13,802 +/- 844), while the remaining type (Type VI) consisted of presumed interneurons (3,024 +/- 769). The 10 was subdivided into nine subnuclei grouped regionally into rostral, intermediate, and caudal divisions on the basis of neuronal morphology, cell density, and differential AChE and substance P reactivities. The rostral division contains the dorsorostral (DoR) and the ventrorostral (VeR) subnuclei; the intermediate division contains the rostrointermediate (RoI), dorsointermediate (DoI), centrointermediate (CeI), ventrointermediate (VeI), and caudointermediate (CaI) subnuclei; the caudal division (Ca) is not subdivided. Morphologically, small round or oval cells populate the VeR and VeI. Medium-sized oval cells occur in the DoR, CeI, and Ca, while medium-sized fusiform and multipolar cells are the main features of CaI. Large triangular cells appear mainly in DoI. Glial cells show the highest predilection for CeI, lowest densities in DoI and medial fringe subnucleus (MeF), and intermediate densities in the remaining six subnuclei. VeI showed the strongest AChE reactivity. Although the cell bodies of VeR and DoI are AChE positive, the neuropil (background) is weakly stained. Densely distributed fine granular substance P-like immunoreactivity occurs throughout the entire nucleus, while the intermediate and caudal divisions contain substance P-like-immunoreactive neurons. Three-dimensional computer reconstructions afforded an appreciation of the distinctiveness of the intermediate division (a division that contains the majority of cells) and the caudal division, which displays the lowest density of presumed vagal motoneurons. It is possible that the subnuclei identified herein form functional units innervating specific organs.

Distribution, parabrachial region projection, and coexistence of neuropeptide and catecholamine cells of the nucleus of the solitary tract in the pigeon

The chemical nature of the cells of the nucleus of the solitary tract (NTS) that project to the parabrachial nucleus (PB) was investigated in the pigeon by the use of fluorescent bead retrograde tracer and immunofluorescence for the detection of substance P (SP), leucine-enkephalin (LENK), cholecystokinin (CCK), neurotensin (NT), somatostatin (SS), and tyrosine hydroxylase (TH). Cells immunoreactive for CCK were located in subnuclei lateralis dorsalis pars anterior (LDa) and medialis superficialis pars posterior, and caudal NTS (cNTS); 22-26.5% of these cells were double-labeled bilaterally. Immunoreactive SP cells were found in ventral NTS subnuclei; 24-25% of these cells were double-labeled bilaterally. Cells immunoreactive for LENK and NT were concentrated in the anterior NTS; 5.5-7.5% of the LENK cells were double-labeled bilaterally, while 11% (ipsilateral) and 21% (contralateral) of the NT immunoreactive cells were double-labeled. Many SS immunoreactive cells were found in peripherally located subnuclei; 5.5-6.5% of these cells were double-labeled bilaterally. Catecholamine cells were distributed in LDa, peripheral subnuclei, and cNTS; 23% of these cells were double-labeled ipsilaterally and 8.5% contralaterally. A two-color double-labeling immunofluorescence technique revealed many cells immunoreactive for both NT and LENK, only a rare cell immunoreactive for both SS and SP, and no cells immunoreactive for both TH and SP. Cells immunoreactive for SP, CCK, NT, and TH are major contributors to NTS projections to PB. The confinement of these substances to specific NTS subnuclei, which receive visceral sensory information from specific organs, may contribute to the chemical encoding of ascending visceral information.

Central projections and motor nuclei of the facial, glossopharyngeal, and vagus nerves in the mormyrid fish Gnathonemus petersii

Most of the information about the anatomy of the fish's cranial nerves was collected in the first two decades of this century. Experimental analysis of the VIIth, IXth, and Xth cranial nerves by modern tract tracing techniques started about 20 years ago. Several species have been investigated to date, including one species of Agnatha (Myxinoidea), two species of elasmobranchs, and species of some orders of Teleostei like Cyprinidae, Siluriformes, Perciformes, and Gadidae. The sensory and motor nuclei of the VIIth, IXth, and Xth cranial nerves of Gnathonemus petersii were studied by anterograde and retrograde axoplasmatic transport of horseradish peroxidase and cobaltous lysine complex. The sensory nuclei form a continuous column of cells in the brain stem extending caudal to the obex. The rostral one-fourth of this column is occupied by the overlapping terminals of the VIIth and IXth nerves. The vagus nerve has 5 roots. The first 4 of these innervate the gills and the fifth supplies viscera. Afferents from the gills terminate ipsilaterally rostral to the obex in topographic order and their terminal fields overlap. Viscerosensory fibers terminate ipsilaterally in the obex region and bilaterally in the commissural nucleus of Cajal. The facial motor nucleus is located rostral to the sensory nucleus. Facial motoneurons have pear-shaped and multipolar perikarya. Their axons form a rostrally directed knee before leaving the brain. The motoneurons of the IXth and Xth nerves have a common cell column. The vagal motoneurons form a periventricular, a medial, and an intermediate cell group rostral to the obex. In the obex region and also caudal to it, a lateral and a caudal group can be distinguished. Vagal motoneurons show a topographic arrangement that is similar to that of the sensory vagal projections. The majority of motoneurons have pear-shaped perikary and ventrolaterally oriented dendrites. In the caudal nucleus the dendrites extend dorsally and overlap the terminals of sensory fibers. The axons form a dorsolaterally directed arch before joining the sensory roots. Since G. petersii uses its electrosensory system primarily for detection of food, its gustatory system is less developed than in other fishes, which possess a large number of taste buds.

Functional organization of vagal reflex systems in the brain stem of the goldfish, Carassius auratus

The coordination of secretory and motor responses to food within the alimentary canal requires well organized brain stem reflex systems. In the goldfish, Carassius auratus, three vagal reflex systems control three phases of ingestion and digestion. The orobranchial system sorts food from substrate, the pharyngeal chewing organ prepares items deemed to be food for digestion and absorption, and the abdominal system regulates the digestion of food. Each system is represented in the central nervous system by separate sensory and motor nuclei. The aim of the present study was to determine whether the interrelationships among the vagal sensory and motor nuclei reflect the peripheral organization. The sensory nucleus of each vagal system was injected with the neuronal tracer horseradish peroxidase (HRP), in separate cases. HRP injections into the vagal lobe sensory layers (orobranchial system) labeled fibers projecting topographically to the vagal lobe motor layer, but not at all to the pharyngeal or abdominal motor nuclei. Similarly, injections of HRP into the pharyngeal and abdominal sensory nuclei selectively labeled nerve fibers projecting to the pharyngeal and abdominal motor nuclei, respectively. All injections resulted in labeled fibers and/or cells in the lateral reticular formation, and in fibers ascending in the secondary gustatory-visceral tract. Gustatory information from the pharynx is apparently processed in the same brain stem system as pharyngeal general visceral information, suggesting that functional or regional characteristics of visceral sensory information may be more important for brain stem processing than the traditional "special" (gustatory) versus "general" visceral dichotomy. These results indicate that anatomically and functionally separate reflex systems exist within the goldfish vagal visceral nuclei.

Afferent and efferent projections of the glossopharyngeal-vagal nerve in the hagfish

Anterograde and retrograde transport of horseradish peroxidase was used to examine the afferent and efferent projections of the glossopharyngeal-vagal nerve in the hagfish Eptatretus burgeri. Anterogradely labeled ganglion cells are scattered in the glossopharyngeal-vagal nerve trunk, in the saccular ganglion, and in the brainstem. Afferent fibers of the glossopharyngeal-vagal nerve terminate in both the vagal lobe and the fasciculus communis. Close observation showed no morphological differentiation between these two structures, indicating that they are not separate entities, but a single, continuous structure that is homologous with the nucleus and tractus solitarius of other vertebrates. The median part of this structure (the commissura infima) is displaced more rostrally than the same part of the solitary nucleus in many other vertebrates. Some of the afferent fibers invade the ventral portion of the trigeminal sensory nucleus, which receives the maxillo-mandibular nerve fibers, and terminate there. Our study showed that the hagfish has only one nucleus in the vagal motor system, i.e., the vagal motor nucleus, which contains both parasympathetic and branchiomotor neurons. The dendrites of the vagal motor neurons in the hagfish are more highly developed than those in other vertebrates. This suggests that the motor reflex arc of the glossopharyngeal-vagal nerve in hagfishes may be simpler than in other vertebrates.

Localization of cardiac parasympathetic preganglionic neurons in the medulla oblongata of pigeon, Columba livia: a study using fragment C of tetanus toxin

The binding fragment of tetanus toxin, fragment C, was injected into several different regions of the pigeon heart. Retrogradely and/or transneuronally labeled cardiomotor parasympathetic preganglionic neurons were found in two separate nuclei within the medulla oblongata. The majority of fragment C-immunolabeled cells was confined to the caudal division of the nucleus ambiguus. This nuclear region is likely to be homologous to the ventrolateral nucleus of the external formation of the nucleus ambiguus in mammals. A smaller fraction (10-30%) of fragment C-positive cardiomotor preganglionic neurons were localized within a restricted portion of the ventrolateral subnucleus of the dorsal motor nucleus of the vagus nerve. This dual cardiac representation in an avian is very similar to the organization established in several mammalian species, and suggests that the brainstem organisation of cardiac parasympathetic efferents is evolutionarily stable across avians and mammals.

The avian oesophageal motor function and its nervous control: some physiological, pharmacological and comparative aspects

1. This paper deals with the avian oesophageal motor function and it attempts to draw some comparative aspects between neural regulation of the avian and mammalian oesophagus. 2. Different from the mammalian oesophagus, the avian oesophagus, presents at rest electrical activity associated to spontaneous contractions. 3. Swallowing elicits peristaltic contraction, characterized by an inhibitory and an excitatory component. 4. Non-adrenergic, non-cholinergic neurons are responsible for the inhibitory component. 5. Contrarily to what observed in mammals, where the peripheral mechanism are important for the peristaltic sequence, the primary peristaltism of birds seems to be entirely mediated by extrinsic nervous system.

Brain stem topography of vagus nerve to the greater curvature of the stomach

If preganglionic vagus nerve fibers enter the stomach via all of its neurovascular bundles, then proximal gastric vagotomy that divides only the bundles along the lesser curvature of the stomach neglects a potential source of innervation to the parietal cells. To determine whether or not these bundles contained preganglionic efferent vagal nerve fibers, horseradish peroxidase was applied to the central cut end of selected neurovascular bundles along the greater curvature of the stomach in rats and ferrets. Cells in the dorsal motor nucleus of the vagus (dmnX) of the rat were labeled after horseradish peroxidase applications to the right gastroepiploic, the splenic, and the short gastric bundles. The ferrets had horseradish peroxidase applied to the right gastroepiploic bundle and they also had cellular labeling of the dmnX. The labeling in cells of the dorsal motor nucleus of the vagus had a distinct topographic, rostrocaudal distribution in both species, and was maximal in the vicinity of the obex. Cells of the bilateral dmnX were labeled after horseradish peroxidase applications at all bundles. This study showed (1) that the bundles along the greater curvature of the stomach contained preganglionic efferent vagus nerve fibers, (2) that the cells of origin of these fibers were represented in the localized rostrocaudal position of the dmnX, and (3) that these fibers had their origins in the bilateral dmnX. Such nerve fibers may account for incomplete vagal denervation of the parietal cells after proximal gastric vagotomy.

False-positive artifacts of tracer strategies distort autonomic connectivity maps

The widespread use of new axonal transport tracing techniques in the ANS has resulted in substantially revised and amended descriptions of ANS organization. The present review suggests, however, that at least some of the results on which proposed revisions of ANS anatomy have been based have incorporated artifacts and therefore should be cautiously interpreted. The peripheral nervous system and viscera are composed in part of connective and endothelial tissues that are porous or 'leaky' to solutes with appropriate chemical characteristics, including the major tracer compounds. As a result, several extra-axonal routes for redistribution of label from the application site into other tissues are present. These include (1) diffusion through tissue membranes to enter directly adjacent tissues and (2) leakage into extracellular fluids within the body cavity, vasculature, lymphatics, exocrine ducts, or organ lumens to migrate to more distant tissues. As a consequence of the extreme sensitivity of the methods used, such redistribution of even minute amounts of label can produce false positives. Review of autonomic neuroanatomy suggests additional mechanisms, including tracer uptake by fibers of passage, can produce artifactual staining. Based on these surveys of tissue composition, tracer characteristics and sources of artifact, experimental controls and criteria for identifying and avoiding labeling artifacts are described. Since no single procedure is foolproof for ANS experimentation, the routine application of multiple controls, particularly ones which restrict or prevent tracer diffusion, are needed.

Projections of the nucleus of the tractus solitarius in the pigeon (Columba livia)

With the aid of autoradiographic and histochemical (WGA-HRP) tracing techniques, the projections of the nucleus of the tractus solitarius (nTS) in the pigeon have been delineated and related to the viscerotopic organization of the nucleus. As in mammals, nTS projects to both brainstem and forebrain structures. At medullary levels, projections were seen to nTS itself, to the dorsal motor nucleus of the vagus and to the subjacent and more ventral reticular formation. There is a substantial projection to the parabrachial nuclear complex with terminations in all its subnuclei and minor projections to locus coeruleus and several mesencephalic areas, including the ventral area of Tsai, the nucleus of the ascending brachium conjunctivum, and the compact portion of the tegmental pedunculopontine nucleus. At diencephalic levels, projections to the hypothalamus (magnocellular periventricular nucleus, stratum cellulare internum and externum) and dorsal thalamus were seen. Terminal fields within the basal telencephalon included the nucleus of the pallial commissure, the bed nucleus of the stria terminalis, and the nucleus accumbens. The organization of nTS projections in pigeons is correlated with the pattern of inputs to specific nTS subnuclei. Lateral tier subnuclei receiving cardiovascular and pulmonary inputs project upon the ventrolateral reticular formation and the ventrolateral parabrachial complex. Medial tier subnuclei receiving gustatory and gastrointestinal inputs project upon dorsal and medial parabrachial nuclei. Transparabrachial projections arise from nTS subnuclei receiving little or no primary input from the viscera.

Preganglionic vagus nerve fibers also enter the greater curvature of the stomach in rats and ferrets

The efferent gastric vagus nerve fibers appear to enter the stomach by several routes. For example, the rate of gastric acid secretion is directly affected by the nerves of the greater curvature of the stomach. Specifically, acid secretion decreases abruptly after division of the gastroepiploic nerve(s). To determine whether efferent vagus nerve fibers are contained in the gastroepiploic nerve(s), horseradish peroxidase, a protein that undergoes retrograde axonal transport, was applied to these nerves; the brainstem locus of the nuclei of the vagus nerves was examined 2 days later. Typical peroxidase labeling was observed in the dorsal motor nucleus of the vagus nerve in 5 of 6 rats and 3 of 3 ferrets; the hypothesis that efferent vagus nerves enter the greater curvature of the stomach was thus supported in two vertebrate species. These previously unrecognized nerves should be considered in the interpretation of experimental and clinical phenomena.

Central projections of the glossopharyngeal and vagal nerves in the channel catfish, Ictalurus punctatus: clues to differential processing of visceral inputs

Transganglionic transport of horseradish peroxidase was used to trace the pattern of medullary terminations of the glossopharyngeal and vagal nerve complex in the channel catfish, Ictalurus punctatus. The glossopharyngeal root terminates centrally in the anterior end of the vagal lobe except for two fascicles that terminate in separate regions of the nucleus intermedius of the facial lobe. Vagal nerve branches innervating regions of the oropharynx terminate in an overlapping, segmental fashion throughout the ipsilateral vagal lobe and the nucleus intermedius of the vagal lobe. The descending branch of the vagus, innervating the abdominal viscera, terminates in the general visceral nucleus and in the nucleus intermedius of the vagal lobe. In addition, abdominal visceral fibers decussate through the commissural nucleus of Cajal and terminate in the general visceral nucleus of the contralateral side. Efferents included in the oropharyngeal and abdominal branches of the vagus also originate from two morphologically separable populations of motor neurons.

Topographic representation of the sensory and motor roots of the vagus nerve in the medulla of goldfish, Carassius auratus

The coelomic root of the vagus nerve in goldfish is connected with sensory and motor nuclei of the medulla that are distinct from those serving the orobranchial roots of the same nerve. The primary sensory nucleus for coelomic sensation is itself divisible into medial and lateral subnuclei on the basis of afferent input and immunocytochemistry. The lateral subnucleus receives sensory input from the specialized chewing organ in the posterior pharynx and is poor in both substance P-like and tyrosine-hydroxylase-like immunoreactivities. The medial subnucleus receives input from the subdiaphragmatic gastrointestinal tract and is rich in substance P-like and tyrosine-hydroxylase-like immunoreactivities. The primary sensory fibers that innervate the gastrointestinal tract also project directly to the area postrema and to the vicinity of subdiaphragmatic visceral motor neurons. The vagal motor neuronal pool is divisible into three columns: paramedian (cardiac), medial, and lateral. The paramedian group innervates the heart and is situated in a loosely aggregated column at the boundary zone between the ventricular ependyma and the underlying brainstem. The medial vagal motor neurons innervate the subdiaphragmatic viscera, while the lateral column motor neurons innervate the posterior pharynx and muscles of the chewing organ. The motor neurons in this motor column are arranged in a topographic rostrocaudal order within the motor column according to the muscle of innervation. Thus both the general visceral sensory and general visceral motor nuclei of the medulla are organized into functional domains. Furthermore, in the goldfish, the special visceral (gustatory) and general visceral sensory nuclei form a continuous series in the medulla with the external and oral systems represented anteriorly and the pharyngeal and digestive systems represented posteriorly.

Projections of the lateral hypothalamus and bed nucleus of the stria terminalis to the dorsal vagal complex in the pigeon

The dorsal vagal complex is composed of the nucleus tractus solitarii (Nts) and the dorsal motor nucleus of the vagus (DMN X). In the pigeon, these nuclei are composed of cytoarchitectonically well-defined subnuclear groups, which have connections that are partially segregated to specific organs (Katz and Karten: J. Comp. Neurol. 218:42-73, '83b, J. Comp. Neurol. 242:397-414, '85). The present study sought to determine whether forebrain afferents to Nts-DMN X are differentially distributed to specific subnuclei and thereby modulate the functions of specific organs. Forebrain afferents to the dorsal vagal complex were determined by retrograde tracing techniques. Labeled perikarya were found in the bed nucleus of the stria terminalis (BNST), ventral paleostriatum, and stratum cellulare externum (SCE) of the lateral hypothalamus, and in the medial hypothalamus, nucleus periventricularis magnocellularis (PVM), which is the avian homologue to a portion of the mammalian paraventricular nucleus. The pattern of axonal distribution to Nts-DMN X subnuclei from the BNST-ventral paleostriatum and SCE were investigated by anterograde tracing techniques. These experiments revealed axonal projections distributed to specific Nts-DMN X subnuclei. However, there is a high degree of overlap of the axonal projections to Nts-DMN X subnuclei from BNST-ventral paleostriatum and SCE, as well as from PVM (Berk and Finkelstein: J. Comp. Neurol. 220:127-136, '83). Labeled fibers from BNST-ventral paleostriatum and SCE project heavily to Nts subnuclei medialis superficialis, lateralis dorsalis, and medialis ventralis and to DMN X subnucleus ventralis parvicellularis. Fewer labeled fibers were found in Nts subnucleus medialis intermedius and extremely sparse labeling was found in Nts subnucleus medialis dorsalis. The Nts and DMN X subnuclei that receive forebrain projections also have peripheral connections with the aortic nerve, crop, esophagus, glandular stomach, and caudal abdominal organs. Thus, the forebrain could modulate the functions of these segments of the cardiovascular and digestive systems.

Cobaltic lysine study of the morphology and distribution of the cranial nerve efferent neurons (motoneurons and preganglionic parasympathetic neurons) and rostral spinal motoneurons in the Japanese toad

The morphology and distribution of the cranial nerve motoneurons (except III, IV, and VI) and rostral spinal motoneurons were systematically studied in the Japanese toad (Bufo japonicus) by retrograde labelling with cobaltic lysine complex. The cobaltic lysine clearly labelled whole neurons, i.e., cell bodies, proximal and distal dendrites, and axons. The branchial motoneurons (V, VII, IX, and X) had similar morphological characteristics and formed a more-or-less continuous cell column through the brainstem. The dendrites could be grouped mainly into the dorsomedial and the ventrolateral dendritic arrays. The dorsomedial dendrites formed a dendritic plexus in the subependymal gray matter, which extended as far peripherally as beneath the ependymal layer. The ventrolateral dendrites formed a broom-like dendritic plexus in the lateral to ventrolateral white matter. They usually extended as far peripherally as the pial surface. The rostrocaudal extent of the dendritic field was also wide and usually exceeded the motor nuclear boundaries. The hypoglossal motoneurons were grouped into the dorsomedial and ventrolateral cell groups, and the latter was considered to be part of the rostral spinal motoneuron column, from their morphology and distribution. The former had well-differentiated dendrites and occupied a more medial position than the branchial motoneurons. Besides the equivalent of the dorsomedial and ventrolateral dendritic arrays of the branchial motoneurons, they had dorsal and commissural dendrites. The accessory motoneurons had morphological characteristics and a distribution pattern similar to those of the rostral spinal motoneurons rather than the branchial motoneurons. The rostral spinal motoneurons had morphological characteristics somewhat different from the branchial motoneurons and the hypoglossal motoneurons (dorsomedial group). Functional implications of the motoneuron morphology are discussed, mainly based on the present results and earlier anatomical and physiological studies of the spinal motoneurons. The present study also revealed the anatomical features of the preganglionic parasympathetic neurons supplying some cranial nerves. These neurons had small somata with less elaborate dendrites and formed an almost continuous cell column that occupied a more dorsal position than the motoneurons of the corresponding nerve. They are thought to be homologous to the salivatory nucleus and the dorsal motor nucleus of the vagus. The basic anatomical organization of the general visceral efferent column seems to be similar throughout vertebrates.

Axotomy increases NADPH-diaphorase staining in rat vagal motor neurons

Left cervical vagotomy increased NADPH-diaphorase (NADPH-d) histochemical staining in neuronal perikarya of the ipsilateral dorsal motor nucleus of the vagus (dmnX) and the rostral part of the nucleus ambiguus (nAmb). This effect appeared by 2 days, was maximal around 10 days, and declined by 30 days after vagotomy. Light and dark stained perikarya occurred in dmn X ipsilateral to the vagotomy which could not be explained on the basis of the biochemical or transmitter content of these neurons. It is unlikely that the increases of NADPH-d activity resulted from changes in cholinergic transmission since vagotomy is known to decrease cholinergic enzyme function. Since vagotomy increased both the glucose metabolic rate and NADPH-d staining of dmnX and nAmb in these experiments, it is more likely that these effects represent regenerative metabolic responses to axotomy.

Morphology and distribution of the preganglionic parasympathetic neurons of the facial, glossopharyngeal and vagus nerves in the Japanese toad: a cobaltic lysine study

We labelled the preganglionic parasympathetic neurons of the facial, glossopharyngeal and vagus nerves of the Japanese toad by applying the cobaltic lysine to the cut end of the respective nerve, and examined their morphology and distribution. These neurons form an almost continuous cell column consisting of small neurons with less elaborate dendrites, and occupy a more dorsal position than the motoneurons of the corresponding nerves. The results suggest the presence of the amphibian homologues of the salivatory nucleus and the dorsal motor nucleus of the vagus.