Antinociception produced by electrical stimulation of vagal afferents: independence of cervical and subdiaphragmatic branches

Expt. 1 showed that electrical stimulation of either the main dorsal or ventral branch of the subdiaphragmatic vagus could produce inhibition of the nociceptive tail-flick reflex in lightly anesthetized rats. The antinociception produced by electrical stimulation of the dorsal subdiaphragmatic vagus was eliminated by resection of the right cervical vagus, but relatively unaffected by resection of the left cervical vagus. The opposite effects for cervical vagal resection were obtained with electrical stimulation of the ventral branch of the subdiaphragmatic vagus. These results indicate that the antinociceptive effects of subdiaphragmatic vagal stimulation are mediated via uncrossed afferents traveling in the cervical vagus to activate an inhibitory spinopetal system. These findings are consistent with the established anatomy of vagal afferents. Expt. 2 showed that degeneration of the dorsal subdiaphragmatic vagus did not alter the threshold intensity of right cervical vagal stimulation necessary to produce inhibition of the tail-flick reflex. These results demonstrate that the antinociceptive effects of cervical vagal stimulation are primarily due to activation of the cardiopulmonary component of the nerve, rather than the subdiaphragmatic component. The second experiment also demonstrated that the subdiaphragmatic branch of the vagus can be selectively degenerated with ricin while leaving the cervical branch intact, even though the cell bodies of both sets of afferents are located within the nodose ganglion. These data are discussed in terms of vagal afferents and their role in the modulation of nociceptive transmission.     

Electrophysiological study on the vagal innervation of the adrenal gland in the rat.

Action potentials evoked by stimulation of the ventral or dorsal subdiaphragmatic vagal nerve trunks were recorded from the adrenal branch of the splanchnic nerve in the urethane-anesthetized rat. Action potentials were clearly demonstrated after averaging over 50 times by a computer. In some experiments action potentials evoked by stimulation of the adrenal branch of the splanchnic nerve were observed in the celiac branch of the vagus nerve. The observations indicate the existence of a nervous pathway from the ventral and dorsal subdiaphragmatic vagus nerve to the adrenal gland, and the conduction velocities (0.32-0.91 m/s) suggest that the majority of the nerve fibers belong to the non-myelinated C-fiber group.     

Connections of a vagal communicating branch in the ferret I. Pathways and cell body location

In contrast to most other species, ferrets possess a single communicating branch connecting the dorsal and ventral vagal trunks immediately rostral to the diaphragm. This branch is being used in physiological studies of gastrointestinal function and emesis. However, the fibre routes which pass through this branch are not known. In this study, the afferent and efferent pathways within this supradiaphragmatic vagal communicating branch of the ferret were studied through the use of the horseradish peroxidase (HRP) tracing technique. The region of the branch was exposed using a thoracotomy and HRP crystals were applied to one of the following: (A) the ventral end of the communicating branch, (B) the dorsal end of the communicating branch, (C) the distal end of the dorsal vagal trunk rostral to the communicating branch or (D) the distal end of the ventral vagal trunk rostral to the communicating branch. Following a 72 hour survival period, the animals were reanaesthetized and perfused. The superior cervical and nodose ganglia and the brain stem were processed using the tetramethylbenzidine method. Following application of HRP to the cut ventral end of the communicating branch, labelled cell bodies were found in the left and right nodose ganglia and in the left dorsal motor nucleus of the vagus. After HRP application to the cut dorsal end of the communicating branch, labelled cells were found in the left and right nodose ganglia. No HRP containing cell bodies were found following HRP application to the cut distal end of either the dorsal or the ventral vagal trunk. These results indicate that several afferent pathways exist within the branch, although only one consistently labelled efferent pathway was found.     

Vagal innervation of the rat duodenum

Electrophysiologic and anterograde tract tracing studies have demonstrated that the vagus nerve innervates the duodenum. These studies, however, have provided little information regarding the finer anatomic topography within the vagal complex. In this study, the retrograde neuronal tracers WGA-HRP or DiI, applied to the duodenum, were used to characterize the vagal afferent and efferent innervation of this portion of the gastrointestinal tract. This approach labeled a substantial number of motor neurons in both the medial and lateral columns of the dorsal motor nucleus of the vagus (DMNV). Vagal motor neurons innervating the duodenum were seen across the medial-lateral extent of the DMNV and between 600 microm rostral to obex and 1600 microm caudal to obex. The three branches of the vagus nerve contained efferent fibers to the duodenum. The gastric branch of the vagus nerve was the pathway that connected the majority of DMNV neurons with the duodenum. These neurons were located in the medial and middle thirds of the DMNV. The celiac branch to the duodenum was composed of axons from the majority of lateral column neurons but also contained axons from neurons in the medial column. The hepatic branch of the vagus nerve contained only a small number of cell axons. Some neurons were located medially whereas others were in the lateral third of the duodenum. Although central terminations of vagal primary afferents from the duodenum were not found in previous tract tracing studies, we observed a large number of terminals in the subpostremal/commissural region of the nucleus of the solitary tract. Similar to the motor fibers, most afferent fibers from the duodenum were located in the gastric branch of the vagus nerve, although the hepatic and celiac branches also contained afferent neurons. These results demonstrate that the vagal innervation of the duodenum is unique, being an amalgam of what would be expected following labeling of more proximal and distal portions of the GI tract. The uniqueness of the sensory and motor innervation to the duodenum has implications for hypotheses regarding the organization of vagovagal reflexes controlling gastrointestinal function.     

Cells of origin of motor axons in the subdiaphragmatic vagus of the rat

The central cell groups that give rise to the motor axons that travel in the subdiaphragmatic vagus were re-examined in the rat by transecting the dorsal or ventral vagus near the stomach and incubating the nerve stump in crystalline horseradish peroxidase (HRP). An exceedingly large percentage of cells was labeled throughout the dorsal motor nucleus of the vagus (mX), with labeled cells extending even beyond the rostro-caudal limits of the nucleus usually assigned on the basis of cytoarchitecture alone. Different patterns of cell-labeling could be correlated with one or the other of the two vagal branches. Incubation of the ventral branch labeled cells only in the left mX, while incubation of the dorsal branch labeled cells on both sides, although more extensively on the right. HRP-positive somata were also observed bilaterally in the nucleus ambiguus (NA) after incubation of either branch of the subdiaphragmatic vagus; this finding is in contrast to previous accounts in which motor fibers from NA were considered to project only to cervical and thoracic structures. These results suggest that mX and NA are responsible for a substantial component of abdominal innervation in the rat.     

Medullary cells of origin of vagal cardioinhibitory fibers in the pigeon. I. Anatomical studies of peripheral vagus nerve and the dorsal motor nucleus

The organization to the dorsal motor nucleus of the vagus in the pigeon was studied in an attempt to localize the cells of origin of vagal cardioinhibitory fibers. The course of the peripheral vagus nerve is described form the intracranial rootlets to abdominal levels. Using combined microdissection and electrical stimulation techniques, the branches which mediate cardiodeceleration are found to arise from a localized segment of the vagal trunk below the thoracic ganglion, and above the level where the left and right vagi join. The dorsal motor nucleus, its cytoarchitectonic divisions, and other structures connected with vagal rootlets are described on the basis of normal material. Utilizing the above findings a series of retrograde degeneration experiments was undertaken. The distribution of chromatolytic neurons following cervical vagotomy was described to indicate the extent of the dorsal motor nucleus. Selective nerve sections (abdominal vagotomy, cardiac vagotomy, recurrent laryngeal neurotomy, or pneumonectomy) then indicated that there is an incompletely inverted topographic representation of the vagus nerve in the dorsal motor nucleus, including a representation of the recurrent laryngeal nerve; no evidence was found for the existence of a nucleus ambiguus. The vagal cardioinhibitory fibers appear to be represented throughout the rostral half of the nucleus, but they are most concentrated in the ventral portion of the nucleus, approximately three-quarters of a millimeter rostral to the obex.     

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.     

The central distribution of the cervical vagus nerve and gastric afferent and efferent projections in the rat

The medullary distribution of afferent fibers and cells of origin of the cervical vagal trunk and of the vagal innervation of the stomach have been studied using the anterograde and retrograde transport of horseradish peroxidase (HRP). Injections of HRP were made into the cervical vagus nerve, the stomach wall, the proximal small intestine, or the peritoneal cavity. Two to four days following the injections, the rats were perfused and the medullae oblongatae and nodose ganglia were processed using the tetramethyl benzidine method. Cervical vagus nerve injections of HRP resulted in heavy anterograde labeling in the ipsilateral nucleus of the tractus solitarius (NTS) and the commissural nucleus. Lighter labeling was seen in these regions on the contralateral side, but did not extend as far rostrally in the NTS. Labeling was also seen in the area postrema. Retrogade labeling of somata was present in the ipsilateral side in the nodose ganglion, throughout the whole extent of the dorsal motor nucleus of the vagus, much of the nucleus ambiguus and in rostral levels of the cervical spinal cord. After stomach injections, labeling indicative of afferent fibers was observed bilaterally in the dorsomedial and medial portions of the NTS and in the commissural nucleus. Labeled efferent fibres arose from neurons in the dorsal motor nucleus of the vagus, nucleus ambiguus and the cervical spinal cord. Retrogradely labeled somata were found bilaterally, throughout the rostrocaudal length of the dorsal motor nucleus in all cases with stomach injections. In some, but not all cases, labeled somata were seen bilaterally in compact areas within the nucleus ambiguus, particularly rostrally. Control injections of HRP into the intestinal wall and peritoneal cavity indicated that the stomach was the primary source of afferent and efferent labeling in the medulla following subdiaphragmatic injections.     

Sources of anterior gastric vagal efferent discharge in rats: an electrophysiological study.

The source of vagal efferent discharge (VED) in the anterior branch of the gastric vagus was investigated in urethane-chloralose anesthetized rats using successive and selective vagal cuts. After cutting the right cervical vagus, the basal VEDs were increased in 15 out of 21 cases by 4-53% (median 18%). After both cervical vagi were cut, VEDs were reduced by 10-95% (median 90%) in 14 of 17 experiments and a subcervical basal VED was observed in all rats. Additional cut of the distal end of the anterior gastric branch did not induce a consistent effect. A small segment of subdiaphragmatic anterior gastric vagus (4-5 mm) was further isolated by a fourth cut at the proximal end of the anterior gastric vagus; abolition of the subcervical VED occurred in only 4 of 14 successful cuts whereas in the other 10 experiments, the VED was reduced by 38-94% (median 87%). Histological examination revealed the presence of neurons in a paraganglion lying within the isolated nerve segment. These findings indicate that the stomach not only receives VED descending directly from medullary vagal motor neurons (about 90%), but also (approximately 10%) from neural elements located between subcervical to upper abdomen levels (the 'subcervical VED') and/or between the bifurcation of the accessory celiac branch to the gastro-esophageal junction (the 'residual VED'). In rats there is little crossed gastric vagal innervation, in agreement with anatomical observations, although there is a robust inhibitory influence from contralateral vagal afferents on medullary vagal motor neurons.     

Antidromic activation of vagal and sympathetic afferents does not produce intestinal contractions in dogs.

The question has been asked whether vagal and sympathetic afferents activated antidromically play a role as motor nerves on the in vivo small intestine in dogs anesthetized with urethane. The vagus nerve of one side was cut above the nodose ganglion and the efferent fibers allowed to degenerate. Peripheral stimulation (5-50 Hz, 0.5-3 ms, 5-25 V) of an intact cervical vagus, being able to excite both efferent and afferent fibers, caused large contractions in the jejunum and stomach, whereas stimulation of the contralateral cut cervical vagus could not produce any response in the jejunum but small contractions in the stomach. Peripheral stimulation of the cut cervical vagus did not produce bradycardia and hypotension. Single- and multi-unit discharges to distension of the jejunal segments could be recorded from the peripheral cut end of the cut cervical vagus. Immunohistochemically, there were many substance P-containing cells in both nodose ganglia. Antidromic stimulation of the dorsal roots (T7-T10) did not induce any response in the jejunum but contractions in the stomach. The results may confirm that vagal and sympathetic afferents have no antidromic motor function at least in the in vivo canine small intestine.     

Central distribution of the cervical vagus nerve in Old and New World primates

The central distribution of the cervical vagus nerve was examined in Old and New World primates using anterograde transganglionic and retrograde horseradish peroxide (HRP) histochemistry. Crystals of HRP were applied to the cut central end of the cervical vagus nerve in two Old World (one bonnet, one cynomolgus) and two New World (squirrel) monkeys. Bright- and darkfield examination of coronal sections from the pons, medulla, and upper cervical spinal cord revealed two major concentrations of retrogradely labeled cells in the ipsilateral dorsal motor nucleus (DMX) and nucleus ambiguous (NA). DMX was heavily labeled, containing about 5 times as many labeled cells as NA. The anterograde distribution of reaction product did not extend as far in the rostrocaudal plane as did the retrograde distribution. Labeled afferent fibers entered the medulla at the level of the caudal dorsal cochlear nucleus, joined the solitary tract, and descended to the obex. Ipsilateral terminal label first appeared at the level where the nucleus of the solitary tract (NST) abuts the IVth ventricle. The terminal field grew in extent and density, until at the level of the area postrema (AP), the distribution extended throughout the medial NST, ventrolateral NST, and AP. Contralateral terminal label was sparse and restricted to the medial NST. In the commissural division of the solitary nucleus, sparse reaction product was present bilaterally, with the denser concentration ipsilateral to the treated nerve. Examination of peripheral ganglia revealed labeled somata in the nodose, jugular, and superior cervical ganglia.     

Localization and acetylcholinesterase content of vagal efferent neurons

The acetylcholinesterase (AChE) content of rat vagal efferent neurons was studied. Retrograde transport of horseradish peroxidase (HRP) by cut vagal axons provided a means for localizing efferent cell bodies; tissue sections were then processed for the simultaneous visualization of HRP and AChE. A dorsal vagal efferent column contained the dorsal motor nucleus of the vagus, as a primary component, and extended caudally into the upper cervical spinal cord. A ventral column contained neurons in the nucleus ambiguus and the surrounding reticular formation. Although most of the vagal efferent neurons stained with moderate to heave intensity for AChE there were some HRP-labeled cells that contained little AChE and a small percentage in which AChE was absent. In spite of the fact that AChE has been demonstrated in certain non-cholinergic neurons, it has also been found in all cholinergic neurons. Therefore, the presence of AChE has been regarded as a necessary (but not sufficient) component for identifying cholinergic neurons. The absence of AChE in a small percentage of the vagal efferent neurons indicates that some preganglionic parasympathetic fibers in the vagus nerve are not cholinergic.     

Longitudinal columnar organization within the dorsal motor nucleus represents separate branches of the abdominal vagus

To identify the distribution of central preganglionics associated with each branch of the subdiaphragmatic vagus, the fluorescent tracer True Blue (TB) was administered intraperitoneally to rats with 4 out of 5 branches cauterized, and then, after 72 h, the animals were sacrificed for histological analysis. Each vagal branch contained the axons of a topographically distinct column of cells within the dorsal motor nucleus of the vagus (DMN). The columns representing the 4 branches with the largest numbers of efferents are organized as paired, bilaterally symmetrical, longitudinal distributions on either side of the medulla. Each DMN side contains a column occupying the medial two-thirds or more of the nucleus and corresponding to one of the gastric branches (left DMN, anterior gastric; right DMN, posterior gastric). Also on each side, the lateral pole of the DMN consists of a coherent cell column corresponding to one of the celiac branches (left DMN, accessory celiac; right DMN, celiac). The fifth branch, the hepatic, is represented by a limited number of somata forming a diffuse column largely coextensive with that representing the anterior gastric branch. At some levels of the DMN, the columns overlap. Labeled cells observed in the reticular formation were correlated in number, left-right ratios and response to vagotomy with those in the DMN, which suggests that they are displaced cells of the nucleus. Distributions of labeled cells in the nucleus ambiguus and the retrofacial nucleus were not tightly correlated with those of the DMN. An analysis of cell counts obtained for each of the individual branches suggests that vagal axons do not generally send collaterals through more than one branch.     

Redundant vagal mediation of the synergistic satiety effect of pancreatic glucagon and cholecystokinin in sham feeding rats

Simultaneous intraperitoneal injection of pancreatic glucagon (PG) and cholecystokinin (CCK) results in a functionally synergistic satiety effect in non-deprived sham feeding rats ("PG-CCK satiety"). That is, PG and CCK together inhibit feeding significantly more than the sum of their individual effects. Because the individual satiety effect of each peptide on normal feeding is dependent on the abdominal vagus nerve, we tested the vagal mediation of this synergistic effect of PG plus CCK. Vagotomies were verified anatomically and, in one experiment, histologically. Total abdominal vagotomy blocked PG-CCK satiety. Neither selective vagotomies of the hepatic, the gastric, the celiac, the gastric and celiac, nor the gastric and hepatic branches, however, affected PG-CCK satiety. This indicates that the vagal contribution to the synergistic satiety effect of PG plus CCK on sham feeding is redundant. Although some vagal fibers are necessary for PG-CCK satiety, no individual branch is required for the effect, and at least two branches, the hepatic and celiac, are each sufficient for mediating it.     

The motor nuclei and primary projections of the IXth,Xth, XIth,and XIIth cranial nerves in the monitor lizard,Varanus exanthematicus

The motor nuclei and sensory connections of the IXth, Xth, XIth, and XIIth cranial nerves of the reptile Varanus exanthematicus were studied with the methods of anterograde degeneration and anterograde and retrograde axonal transport. The motor nuclei of nerve IX are located ventrally in the rhombencephalon and are constituted medially by the large-celled glossopharyngeal part of the nucleus ambiguus and laterally by the small-celled nucleus salivatorius inferior. The motor nuclei of nerve X consist of the dorsomedially located dorsal motor nucleus of the vagus and the laterally located vagal part of the nucleus ambiguus. The rostral portion of the latter cell group contains smaller cells than its caudal portion and is rostrally continuous with the nucleus salivatorius inferior of nerve IX. The efferent axons of nerves IX and X arising from the ventrolateral medulla first course dorsomedially, form genua beneath the IVth ventricle, and then exit the brainstem. All primary afferent fibers of nerve IX and the majority of those of nerve X enter the solitary tract. Terminations of vagal fibers were observed in the postvagal portion of the nucleus of the solitary tract, the dorsal motor nucleus of the vagus, and the nucleus of the commissura infima. A small contingent of vagal fibers courses caudally just dorsolateral to the descending trigeminal tract. A separate spinal component of nerve XI could not be found. The bulbar component of this nerve forms part of nerve X and takes its main origin from a detached caudal element of the nucleus ambiguus. The motor nuclear complex of nerve XII consists of a large dorsal nucleus and a small ventral nucleus that extend from the medulla oblongata into the first segment of the cervical spinal cord.     

Vasopressin (VP) and neuropeptide FF (NPFF) systems in the normal and hypertensive human brainstem

Vasopressin (VP)-, neuropeptide FF (NPFF)-, and tyrosine hydroxylase (TH)-expressing neurons were studied by means of single and double immunocytochemistry in the human brainstem of controls who died suddenly due to trauma and of patients who suffered from essential hypertension and died due to acute myocardial infarction, while in one case there was brain hemorrhage. In the control and hypertensive groups VP fibers and NPFF neurons and fibers were the most abundantly present in the dorsal vagal complex, especially in the dorsal motor nucleus of the vagus. Numerous VP and NPFF fibers formed synaptic-like contacts with neuronal profiles in the dorsointermediate, centrointermediate, ventrointermediate, caudointermediate, and caudal parts of the dorsal motor nucleus of vagus as well as adjacent medial and intermediate subnuclei of the solitary nucleus. VP, but not NPFF, positive fibers were found to vastly contact TH-positive neuronal profiles in A2/C2, A2, and ambiguus nucleus (Amb). The density of VP fibers in the dorsal motor nucleus of the vagus and Amb did not differ between hypertensive patients and controls, whereas the density of NPFF fibers in hypertensives was 3.19 times lower in the dorsal motor nucleus of vagus and markedly decreased in the Amb. In both groups, VP and NPFF were scarcely present in the pain pathways, suggesting that these peptides are not crucially involved in nociceptive control in human. The reduction of NPFF release within the dorsal motor nucleus and Amb could serve as a possible cause of the impairment of cardiac vagal control in hypertensive patients.     

Involvement of glutamate in gastrointestinal vago-vagal reflexes initiated by gastrointestinal distention in the rat

Vago-vagal reflexes play an integral role in the regulation of gastrointestinal function. Although there have been a number of reports describing the effects of various stimuli on the firing rates of vagal afferent fibers and vagal motor neurons, little is known regarding the neurotransmitters that mediate the vago-vagal reflexes. In the present work, we investigated the role of glutamate in the vago-vagal reflex induced by gastrointestinal distention. Using single-cell recording techniques, we determined the effects of gastric and duodenal distention on the firing rates of gut-related neurons in the dorsal vagal complex, in the absence and presence of glutamate antagonists. Kynurenic acid, a competitive glutamate receptor antagonist, injected into the dorsal vagal complex, blocked the neuronal response of neurons in the dorsal motor nucleus of the vagus and the nucleus of the solitary tract to gastrointestinal distention. Injection of glutamate into the nucleus of the solitary tract produced inhibition of dorsal motor nucleus of the vagus neurons that were also inhibited by gastric and/or duodenal distention. Thus, the distention-induced inhibition of dorsal motor nucleus of the vagus neurons may be mediated by glutamate-induced excitation of gut-related nucleus of the solitary tract neurons. To investigate the role of the various glutamate receptor subtypes in the distention-induced events, we studied the effects of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a selective non-NMDA receptor antagonist, and DL-2-amino-5-phosphonopentanoic acid (DL-AP5), a selective NMDA receptor antagonist. CNQX injected into the dorsal vagal complex either blocked or attenuated the inhibitory response of the neurons in the dorsal motor nucleus of the vagus and nucleus of the solitary tract neurons to gastric and duodenal distention. In contrast, DL-AP5 had less effect, especially in the vago-vagal reflex elicited by gastric distention. The results suggest (1) distention activates vagal afferents in the gastrointestinal tract; (2) the central branches of the vagal afferents from the gut terminate in the nucleus of the solitary tract and release glutamate that mainly act on non-NMDA receptors; (3) glutamate activates the inhibitory neurons in the nucleus of the solitary tract that project to the dorsal motor nucleus of the vagus; and (4) the inhibitory neurotransmitter suppresses the activity of the dorsal motor nucleus of the vagus neurons. For the excitatory neuronal responses of the dorsal motor nucleus of the vagus neurons to gastrointestinal distention, the possible circuit is that the vagal afferents containing glutamate directly activate the receptors on the dendrites of the dorsal motor nucleus of the vagus.     

The origin of catecholaminergic nerve fibers in the subdiaphragmatic vagus nerve of rat.

It is known that the vagus nerve contains catecholaminergic fibers. However, the origin of these fibers has not been systematically examined. In this study, we addressed this issue using retrograde tracing from the subdiaphragmatic vagus nerve combined with immunocytochemistry. The cervical and thoracic sympathetic trunk ganglia, the nodose ganglia and the dorsal motor nucleus of the vagus nerve were examined following injection of Fluoro-Gold or cholera toxin horseradish peroxidase conjugate into the trunks of the subdiaphragmatic vagus nerve of rats. Numerous retrogradely labeled neurons were seen in the nodose ganglion and the dorsal motor nucleus of the vagus nerve. Very few labeled neurons were found in the sympathetic ganglia (less than 0.06% of the neurons in either superior cervical ganglion or cervicothoracic ganglion were retrogradely labeled). Double labeling with immunofluoresence for catecholamine synthesizing enzymes revealed that: (1) 92% of all Fluoro-Gold retrogradely labeled tyrosine hydroxylase immunoreactive neurons were found in parasympathetic sources (75% in the dorsal motor nucleus of the vagus nerve and 17% in the nodose ganglia), and only 8% in the cervicothoracic sympathetic ganglia; (2) 12% of the retrogradely labeled catecholaminergic neurons in the dorsal motor nucleus of the vagus nerve were also dopamine-beta-hydroxylase immunopositive neurons; (3) 70% of the retrogradely labeled neurons in the sympathetic ganglia were tyrosine hydroxylase immunopositive and 54% of these catecholaminergic neurons contained dopamine-beta-hydroxylase, while 30% of the retrogradely labeled neurons were non-catecholaminergic neurons. These results indicate that catecholaminergic fibers in the abdominal vagus nerve are primarily dopaminergic and of parasympathetic origin, and that only an extremely small number of these fibers, mostly noradrenergic in nature, arise from postganglionic sympathetic neurons.     

Medullary origin of vagal preganglionic axons to the heart of the cat

It is apparent from the literature that a controversy exists concerning the site of origin of cardiac vagal preganglionic axons. Physiological studies have suggested that the location of these neurons may be different in different species and there has been disagreement between physiological and anatomical findings in the same species. We now present anatomical and neurophysiological studies suggesting that in the cat cardiac vagal preganglionic neurons are located in two medullary regions: the areas of the dorsal motor nucleus of the vagus (DMV) and of the nucleus ambiguus (AMB). This suggestion is based on the following observations. Firstly, after application of horseradish peroxidase to the right cardiac branches of the vagus nerve, labeled neurons were found primarily in the regions of te DMV and AMB. Additional scattered neurons were found in the reticular formation between these two nuclei. Secondly, following injections of tritiated amino acids into either the DMV or AMB, labeled vagal fibers were found in the atrial myocardium. Finally, electrical stimulation of the right cardiac branches of the vagus nerve antidromically activated DMV or AMB, labeled vagal fibers were found in the atrial myocardium. Finally, neurons in the DMV and AMB regions with latencies corresponding to conduction velocities of B-fibers. In addition, these neurons were orthodromically excited by electrical stimulation of the carotid sinus and aortic depressor nerves.     

Medullary sites mediating some abdominal vagal reflexes in the ferret using [C]2-deoxyglucose

The central projections of some abdominal visceral afferents passing through the vagal communicating branch were studied in anesthetized ferrets using [¹⁴C]2-deoxyglucose autoradiography. The reflex effects of electrical stimulation of the vagal communicating branch were studied while measurements of jejunal motor activity and transmural potential difference, a marker of electrogenic epithelial transport were made concurrently. The aim of this study was to examine brainstem projections of some afferent fibers in the communicating branch of the thoracic vagus nerve that are necessary for the reflex regulation of small intestinal motor activity and epithelial transport. In urethane-anesthetized ferrets, electrical stimulation of the cur central end of the vagal communicating branch increased jejunal motor activity and electrogenic epithelial transport. In addition, glucose utilization in the left medial sub-nucleus of the nucleus tractus solitarius and the dorsal motor nucleus of the vagus was significantly increased as compared with sham-operated non-stimulated control animals. Identical areas on the contralateral side of the brain showed no change in glucose utilization as compared with sham-operated non-stimulated controls. This functional brain-mapping study strongly suggests that the left medial sub-nucleus tractus solitarius and the dorsal motor nucleus of the vagus, in the ferret, are involved in processing alimentary affrent activity from both the small intestinal musculature and epithelium as well as the reflex changes in efferent vagal nerve activity to the same regions of the alimentary tract.