Brainstem projections of sensory and motor components of the vagus nerve in the rat

The sensory and motor connections of the cervical vagus nerves and of its inferior ganglion (nodose ganglion) have been traced in the medulla and upper cervical spinal cord of 16 male Wistar rats by using horseradish peroxidase (HRP) neurohistochemistry. The use of tetramethyl benzidine (TMB) as the substrate for HRP permitted the visualization of transganglionic and retrograde transport in sensory nerve terminals and perikarya, respectively. The vagus nerve in the rat enters the medulla in numerous fascicles with points of entry covering the entire lateral aspect of the medulla extending from level +4 to - 6 mm rostrocaudal to the obex. Fascicles of vagal sensory fibers enter the dorsolateral aspect of the medulla and travel to the tractus solitarius (TS) which was labeled for over 8.8 mm in the medulla. The caudal extent of the TS receiving vagal projections was found in lamina V of the cervical spinal cord (C1 to C2). Sensory terminal fields could be visualized bilaterally in the nucleus of the tractus solitarius (nTS), area postrema (ap) and dorsal motor nucleus of the vagus nerve (dmnX). The ipsilateral projection to the nTS and the dmnX was heavier than that found on the contralateral side. The area postrema was intensely labeled on both sides. Motor fibers from HRP-labeled perikarya in the dmnX travel ventromedially in a distinct fascicle and subsequently subdivide into a number of small fiber bundles that traverse the medullary reticular formation in the form of a fine network of HRP-labeled fibers. As these fibers from the dmnX approach the ventrolateral aspect of the medulla they are joined by axons from the nucleus ambiguus (nA), nucleus retroambigualis (nRA) and the retro facial nucleus (nRF). These latter fibers form hairpin loops in the middle of the reticular formation to accompany the axons from the dmnX exiting from the medulla in a ventrolateral location. HRP-labeled perikarya, in contrast to transganglionically transported HRP in sensory terminals in the nTS, were visualized on one side only, thus indicating that motor control via the vagus nerve is exerted only by motor neurons located ipsilaterally. Sensory information on the other hand, diverges to many nuclear subgroups located on both sides of the medulla.     

Corticotropin-releasing factor binding sites undergo axonal transport in the rat vagus nerve

Corticotropin-releasing factor (CRF) binding sites were found to be present in the rat vagus nerve and underwent axonal transport. Binding sites accumulated on both sides of ligatures placed on the nerve and at similar rates following ligation of right or left cervical vagal trunks of either male or female rats. CRF binding sites also accumulated proximal and distal to ligatures on subdiaphragmatic vagal trunks. Binding was specific, reversible and inhibited by the CRF receptor antagonist α-helical-CRF(9-41). [(125) l]Tyr(0) -ovine-CRF binding to rat vagus nerve was not guanine nucleotide-sensitive. CRF and cholecystokinin binding sites were transported at a similar rate in the cervical vagus, although turnover of CRF binding sites was more rapid. No differences in CRF binding site transport were observed between Zucker rats of lean or obese genotype.     

Contribution of the vagus nerve to angiotensin II binding sites in the canine medulla

Specific angiotensin II (Ang II) binding sites are present in the dorsal medulla of several species and dose-related cardiovascular effects are produced by microinjection of the peptide into this region. Because the anatomical location of Ang II binding sites in the area postrema (ap), nucleus tractus solitarii (nTS) and dorsal motor nucleus of the vagus (dmnX) coincides with the topography of vagal afferent fibers and efferent motor neurons, the effect of either nodose ganglionectomy or cervical vagotomy on Ang II binding sites in the dorsomedial medulla was investigated in dogs by in vitro receptor autoradiography. Two weeks after unilateral ganglionectomy, there was a marked reduction in the density of specific Ang II binding sites in the ipsilateral ap, nTS and dmnX and an absence of binding sites in the region where vagal afferent fibers course through the rostral medulla. Unilateral cervical vagotomy, which has been shown to spare central processes of afferent fibers, resulted in a loss of binding only in the ipsilateral dmnX. We also show that Ang II binding sites are present in the nodose ganglion and central and peripheral processes of the vagus nerve. The data indicate that medullary Ang II binding sites are associated with both vagal afferent fibers and efferent motor neurons.     

Central connections of the sensory and motor nuclei of the vagus nerve

Recent morphological and immunohistochemical studies bearing on the central pathways involved in processing vagal afferent information and in modulating the activity of vagal preganglionic neurons are summarized. The nucleus of the solitary tract (NTS), the principal recipient of first order vagal afferent inputs, projects to preganglionic cell groups of both divisions of the autonomic nervous system, to motor nuclei of cranial nerves that supply the face and tongue, to a series of 'relay' nuclei in the brainstem, and to a number of cell groups in the hypothalamus and the limbic region of the telencephalon that integrate autonomic, neuroendocrine and regulatory behavioral responses. With the exception of the cranial nerve motor nuclei, each cell group in receipt of direct inputs from the NTS projects back to this region and/or to the vagal motor nuclei, and is thereby in a position to influence vagal motor outflow. This central vagal system is further characterized by the presence of neurons that contain an impressive diversity of neuropeptides and monoamines. Examples are cited to illustrate how biochemically specified projections within this system are organized, and how they provide potential substrates for encoding information transfer between its components.     

Characterization and autoradiographic distribution of neurotensin binding sites in the human brain

The characteristics and topographical distribution of monoiodo¹²⁵I-Tyr₃-neurotensin (NT) binding sites in normal human brain tissue were studied on brain sections and by quantitative autoradiography. Sections at the level of the substantia nigra show a dissociation constant and maximal binding capacity of4.8 ± 0.8nM and 70 ± 7fmol/mg protein, respectively. High density of¹²⁵I-NT binding sites were mainly found in dopaminergic (DA)-rich areas such as the substantia nigra, the ventral tegmental area, the striatum and the nucleus accumbens, further supporting an interaction between NT and DA neurons in human brain.     

Localization of specific neurotensin binding sites in the rat adrenal gland

Specific tritiated neurotensin binding sites were localized in the rat adrenal gland by receptor autoradiography and characterized using a tissue homogenate receptor binding assay. High levels of specific neurotensin binding sites were found in the inner layer of the adrenal cortex and lower amounts in the adrenal medulla with only background labeling in the outer cortical layers. The structure-activity profile of the specific neurotensin binding was consistent with binding to a physiological neurotensin receptor.     

Ultrastructural localization of phenylethanolamine N-methyltransferase in sensory and motor nuclei of the vagus nerve

The ultrastructural localization of phenylethanolamine N-methyltransferase (PNMT), the enzyme used in the final step in the synthesis of adrenaline, was examined in the medial nuclei of the solitary tracts (m-NTS) and in the dorsal motor nuclei of the vagus. Adult rats were anesthetized with Nembutal (50 mg/kg intraperitoneally), and the brains were fixed by vascular perfusion with a solution containing 3.75% acrolein and 2% paraformaldehyde in 0.1 M phosphate buffer. Coronal Vibratome sections were collected through the intermediate portions of the m-NTS at the level of the area postrema. These sections were immunocytochemically labeled employing a rabbit polyclonal antiserum against PNMT and the peroxidase-antiperoxidase method. Immunoreactivity was detected in perikarya, dendrites, and axon terminals in the intermediate portion of the m-NTS. The labeled perikarya were either small (10-15 microns diameter) and oval or large 20-30 microns) with two or more proximal processes. The PNMT-containing dendrites received synaptic input from unlabeled, small (0.5-1.0 microns) and large (2-3 microns) vagal-like afferents as well as from a few terminals, which also showed PNMT immunoreactivity. Axons and axon terminals containing immunoreactive PNMT were more frequently observed than the perikarya or dendrites in the m-NTS and were the only labeled profiles in the dorsal motor nuclei. In both regions the PNMT-labeled terminals formed principally symmetric synapses with unlabeled dendrites. However, a few asymmetric axodendritic and symmetric axosomatic synapses also were detected. These findings indicate that the adrenergic neurons may have multiple, but principally inhibitory, actions on other neurons within cardiovagal portions of baroreflex pathways.     

Opiate effects on rabbit vagus nerve: Electrophysiology and radioligand binding

Intracellular recordings were made from rabbit nodose ganglion cells in vitro. Morphine (up to 100 micro M), normorphine (up to 10 micro M) and D-Ala2, Leu5-enkephalin (DADLE) (up to 5 micro M) each had no detectable effect on the electrical properties of the cell membrane, except for local anesthetic-like actions at the highest concentrations which were not reversed by naloxone. Extracellular recordings were made from the infranodose vagus nerve in vitro using a sucrose gap method. No effects of morphine, normorphine or DADLE were detected on the resting potential, compound action potential or compound action potential enhanced by barium or tetraethylammonium. Moderate levels of stereospecific binding of tritiated dihydromorphine and DADLE were detected in both the nodose ganglion and vagus nerve. It is surmised that the radioligand binding sites on the nodose ganglion and vagus nerve are not functionally linked to detectable electrophysiological effects.     

Brain stem projections of sensory and motor components of the vagus complex in the cat: I. The cervical vagus and nodose ganglion

The motor and sensory connections of the cervical vagus nerve and of its inferior ganglion (nodose ganglion) have been traced in the medulla oblongata of 32 adult cats with the neuroanatomical methods of horseradish peroxidase (HRP) histochemistry and amino acid autoradiography (ARG). In 14 of these subjects, an aqueous solution of HRP was applied unilaterally to the central end of the severed cervical vagus nerve. In 13 other cases, HRP was injected directly into the nodose ganglion. Three of these 13 subjects had undergone infranodose vagotomy 6 weeks prior to the HRP injection. A mixture of tritiated amino acid was injected into the nodose ganglion in five additional cats. The retrograde transport of HRP yielded reaction product in nerve fibers and perikarya of parasympathetic and somatic motoneurons in the medulla oblongata. Furthermore, a tetramethyl benzidine (TMB) method for visualizing HRP enabled the demonstration of anterograde and transganglionic transport, so that central sensory connections of the nodose ganglion and of the vagus nerve could also be traced. The central distribution of silver grain following injections of tritiated amino acids in the nodose ganglion corresponded closely with the distribution of sensory projections demonstrated with HRP, thus confirming the validity of HRP histochemistry as a method for tracing these projections. The histochemical and autoradiographic experiments showed that the vagus nerve enters the medulla from its lateral aspect in multiple fascicles and that it contains three major components—axons of preganglionic parasympathetic neurones, axons of skeletal motoneurons, and central processes of the sensory neurons in the nodose ganglion. Retrogradely labeled neurons were seen in the dorsal motor nucleus of X(dmnX), the nucleus ambiguus (nA), the nucleus retroambigualis (nRA), the nucleus dorsomedialis (ndm) and the spinal nucleus of the accessory nerve (nspA). The axons arising from motoneurons in the nA did not traverse the medulla directly laterally; rather, all of these axons were initially directed dorsomedially toward the dmnX, where they formed a hairpin loop and then accompanied the axons of dmnX neurons to their points of exit. Afferent fibers in the vagus nerve reached most of the subnuclei of the nTS bilaterally, with the more intense labeling being found on the ipsilateral side. Labeling of sensory vagal projections was also found in the area postrema of both sides and around neurons of the dmnX. These direct sensory projections terminating within the dmnX may provide an anatomical substrate for vagally mediated monosynpatic reflexes. Following deefferentiation by infranodose vagotomy 6 weeks prior to HRP injections into the nodose ganglion, a number of neurons in the dmnX were still intensely labeled with the HRP reaction product. The axons of these HRP-labeled perikarya may constitute the bulbar component of the accessory nerve.     

Alpha-bungarotoxin binding sites on sensory neurones and their axonal transport in sensory afferents

The autoradiographic localization of [125I]alpha-bungarotoxin binding sites on primary sensory fibres was investigated. Nicotinic alpha-bungarotoxin binding sites were localized to a small sub-population of large dorsal root ganglion cells in the rat, monkey, cat and human dorsal root ganglia. Ligation of the sciatic nerve or dorsal root in the rat resulted in an anterograde accumulation of binding sites proximal to the dorsal root ganglion, and a small retrograde accumulation. Unilateral dorsal root section in the rat produced a loss of toxin binding sites mainly within lamina III of the dorsal horn. These results suggest that nicotinic alpha-bungarotoxin binding sites manufactured in large dorsal root ganglion cell bodies are transported both centrally to the spinal cord and also peripherally.     

Paraganglioma of the vagus nerve

Paragangliomas of the vagus nerve are uncommon vascular benign neoplasms of neuroectodermic origin. Initial clinical manifestation is usually as an asymptomatic cervical mass, although sometimes may cause lower cranial nerve palsies. These paragangliomas seldom associate to high levels of circulating catecholamines. Diagnosis is based on the clinics aided by imaging, where CT and MRI play an important role. Angiography is not only diagnostic, but it also allows preoperative embolization of the mass. Most accepted treatment is surgical removal, even though some paragangliomas are suitable for radiation therapy in very specific patients. In this paper we describe a new case of paraganglioma of the vagus nerve in a cervical location, with hypertensive episodes and high catecholamine-levels. The authors review the literature describing the clinical presentation, the diagnosis and the treatment of this rare lesion.     

Characterization of neurotensin binding sites on rat mesencephalic cells in primary culture.

Many studies have reported the presence of high amounts of neurotensin (NT) binding sites in the mesencephalon of adult rat, and their possible role in mediating the effects of the peptide on the activity of mesencephalic dopaminergic neurons. In the present study, we demonstrate the presence of NT sites in primary cultures of embryonic rat mesencephalic cells. On these cells, a single class of high affinity 125I-NT binding sites was observed. The value of the apparent affinity constant (0.3 nM) did not show any significant change throughout time, from 3 to 14 days in culture. The number of sites, however, increased until day 11 and decreased thereafter. Acetylneurotensin (8-13), NT and neuromedin N were potent competitors of 125I-NT binding, while NT (1-10), NT (1-11) and levocabastine were uneffective. These results indicate that the sites detected in the mesencephalic cultures share common binding properties with the high-affinity NT sites already described in adult rat brain. The neuronal localization of the NT sites was suggested by their presence in neuron-enriched serum-free cultures and their absence in glial cultures. Autoradiographic studies confirmed the cellular localization of NT sites and indicated that, under our experimental conditions, cells labeled by 125I-NT represented 0.14% of the initially plated cell number. Taken together, these results show that the development of mesencephalic neurons in primary culture is associated with an increased expression of NT binding sites. Since such cultures have been shown previously to contain functional dopaminergic neurons, we suggest that they could provide a good model to investigate the modulation of the activity of these neurons by NT.     

Effect of neonatal capsaicin treatment on cholecystokinin-(CCK8) satiety and axonal transport of CCK binding sites in the rat vagus nerve

Cholecystokinin (CCK) binding sites which accumulate at ligatures placed on the rat vagus nerve may mediate the satiety actions of CCK. Treatment of neonatal rats with capsaicin attenuated the satiety effect of injected CCK in adult life. Capsaicin pretreatment also reduced, but did not eliminate, the accumulation of CCK binding sites proximal and distal to ligatures on either cervical trunk. A similar effect was observed following ligation of subdiaphragmatic vagal trunks. The CCK receptor antagonists, MK-329 and L-365,260, inhibited binding to capsaicin- and vehicle-treated nerves to a similar degree. Densities of CCK binding sites in the nucleus tractus solitarius and area postrema were also markedly affected by neonatal capsaicin treatment.     

EEG changes with vagus nerve stimulation.

Vagus nerve stimulation (VNS) has been shown to induce EEG changes in animals, but human studies have not shown any significant acute EEG changes. This study is to determine the long-term effect of VNS on EEG. Twenty-one patients aged 4 to 31 years (mean: 14.1 +/- 7.0 years) were studied for a mean duration of 16.8 months with serial EEGs performed at baseline and at 3 months, 6 months, and 12 months after receiving a VNS implant. Five patients who showed active spikes/spike and wave activity on baseline EEGs were found to have synchronization of epileptiform activity, progressive increase in duration of spike-free intervals (P < 0.05), and progressive decrease in duration and frequency of spikes/spike and wave activity (P < 0.01) with time. The remaining 16 patients with less active baseline EEGs did not show obvious synchronization or clustering of spikes but also showed a statistically significant progressive decrease in the number of spikes on EEG with time (P < 0.004 at 3 months, P < 0.008 at 6 months, and P < 0.004 at 1 year). Vagus nerve stimulation induces progressive EEG changes in the form of clustering of epileptiform activity followed by progressively increased periods of spike-free intervals. This may reflect the mechanism of action of VNS in achieving seizure control: alternating synchronization and desynchronization of EEG, with the latter being progressively the dominant feature.     

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.     

Rapid axonal transport of labeled proteins in regenerating sensory and motor fibers of rabbit vagus nerve.

The axonal transport [³H]leucine-labeled proteins in sensory fibers of rabbit vagus nerve was studied at various times after the nerves had been crushed in vivo. Up to 8 weeks after the crush, proteins transported from the nodose ganglion accumulated at the site of the crush under in vitro incubation conditions. This was in contrast to transport in sensory vagal fibers in vivo, which continued distal to the crush zone into the newly-regenerated fibers. Motor fibers in the vagus nerve behaved similarly; in vitro incubation conditions which support transport in mature nerves were unable to support it in newly-grown fibers. Four or five months after the crush some transport occurred in the regenerated axons in vitro, but accumulation still occurred at the crush zone.