Cardiotopic organization of the nucleus ambiguus? An anatomical and physiological analysis of neurons regulating atrioventricular conduction

Previous data indicate that there are anatomically segregated and physiologically independent parasympathetic postganglionic vagal motoneurons on the surface of the heart which are capable of selective control of sinoatrial rate, atrioventricular conduction and atrial contractility. We have injected a retrograde tracer into the cardiac ganglion which selectively regulates atrioventricular conduction (the AV ganglion). Medullary tissues were processed for the histochemical detection of retrogradely labeled neurons by light and electron microscopic methods. Negative dromotropic retrogradely labeled cells were found in a long column in the ventrolateral nucleus ambiguus (NA-VL), which enlarged somewhat at the level of the area postrema, but reached its largest size rostral to the area postrema in an area termed the rostral ventrolateral nucleus ambiguus (rNA-VL). Three times as many cells were observed in the left rNA-VL as compared to the right (P < 0.025). Retrogradely labeled cells were also consistantly observed in the dorsal motor nucleus of the vagus (DMV). The DMV contained one third as many cells as the NA-VL. The right DMV contained twice as many cells as the left (P < 0.05). These data are consistent with physiological evidence that suggests that the left vagus nerve is dominant in the regulation of AV conduction, but that the right vagus nerve is also influential. While recording the electrocardiogram in paced and non-paced hearts,l-glutamate (GLU) was microinjected into the rNA-VL. Microinjections of GLU caused a 76% decrease in the rate of atrioventricular (AV) conduction (P < 0.05) and occasional second degree heart block, without changing heart rate. The effects of GLU were abolished by ipsilateral cervical vagotomy. These physiological data therefore support the anatomical inference that CNS neurons that are retrogradely labeled from the AV ganglion selectively exhibit negative dromotropic properties. Retrogradely labeled negative dromotropic neurons displayed a round nucleus with ample cytoplasm, abundant rough endoplasmic reticulum and the presence of distinctive somatic and dendritic spines. These neurons received synapses from afferent terminals containing small pleomorphic vesicles and large dense core vesicles. These terminals made both asymmetric and symmetric contacts with negative dromotropic dendrites and perikarya, respectively. In conclusion, the data presented indicate that there is a cardiotopic organization of ultrastructurally distinctive negative dromotropic neurons in the NA-VL. This central organization of parasympathetic preganglionic vagal motoneurons mirrors the functional organization of cardioinhibitory postganglionic neurons of the peripheral vagus nerve. These data are further discussed in comparison to a recent report on the light microscopic distribution and ultrastructural characteristics of negative chronotropic neurons in the NA-VL⁴². The data support the hypothesis that anatomically separated and functionally selective parasympathetic preganglionic vagal motoneurons in the NA may independently control AV conduction and cardiac rate.     

Medullary cells of origin of physiologically identified cardiac nerves in the dog

Individual cardiac nerves from which stimulation elicited cardioinhibition (bradycardia and negative inotropism) were identified in 24 of 38 dogs. Subsequently, 3-25 microliters of 30% horseradish peroxidase (HRP) were injected into an identified cardiac nerve. After a 3-day survival period, the medulla oblongata was processed for HRP histochemistry. Retrograde labeling was observed to be concentrated primarily in the ipsilateral nucleus ambiguus (NA) and in medium-sized neurons located ventral and lateral to the larger neurons of the principal NA cell column. This latter location was so characteristic that it has been designated the ventrolateral nucleus ambiguus (VLNA). Labeled neurons were found at all levels of the NA and VLNA and their distribution was similar irrespective of the cardiac nerve injected. Relatively few labeled neurons were observed in the dorsal motor nucleus of the vagus nerve (DMV) except after injections into the left and right recurrent cardiac nerves and the left cranial vagal nerve. In some dogs labeled cells were present only in and ventrolateral to the NA and not in the DMV, even though stimulation of the injected nerve elicited both bradycardia and negative inotropism. These results demonstrate that ventrolateral regions of the NA represent the major site of cardioinhibitory motor neurons in the dog that they can regulate both rate and force.     

Distribution of neurotensin-immunoreactivity within baroreceptive portions of the nucleus of the tractus solitarius and the dorsal vagal nucleus of the rat

We have examined the distribution of neurotensin immunoreactivity within subnuclear regions of the nucleus of the tractus solitarius (NTS) and the dorsal motor nucleus of the vagus nerve (DVN) in the rat. In order to determine which regions of the NTS were involved in the regulation of baroreceptor reflexes, we mapped the central distribution of the aortic branch of the vagus nerve using transganglionic transport of horseradish peroxidase. Comparison of the pattern of aortic nerve innervation with that of the distribution of neurotensin-immunoreactive cells and fibers shows the dorsomedial nucleus of the NTS both to be the primary site of aortic baroreceptor termination and to contain the highest concentration of neurotensin-immunoreactive elements within the NTS. Neurotensin-immunoreactive fibers are also present in medial regions of the NTS adjacent to the area postrema where they may be involved in the modulation of vagal gastric afferents. Double-label experiments, in which, on the same tissue sections, neurotensin immunohistochemistry was combined with retrograde horseradish peroxidase labeling of DVN neurons, reveal a topographic innervation of vagal preganglionic motoneurons by neurotensin-immunoreactive fibers. The heaviest innervation is of lateral portions of the DVN and adjacent ventral portions of the NTS at the level of the obex, an area which may contain cardiac motoneurons. In this region neurotensin-immunoreactive fibers can be observed in close proximity to retrogradely labeled cells. The concentration of neurotensin elements in a region of the NTS which is involved in the control of baroreceptor reflexes provides a morphological basis for the cardiovascular effects produced by central administration of the peptide. Additional control may be exerted at the level of the motoneuron, as evidenced by apparent neurotensin fiber innervation of presumptive cardiac preganglionic neurons. Similarly, the distribution of neurotensin fibers suggests that the peptide may be acting in gastric regulatory areas of the NTS or on vagal secretomotor neurons to regulate gastric acid secretion.     

Brainstem cells of origin of physiologically identified cardiopulmonary nerves in the rhesus monkey (Macaca mulatta)

The distributions of brainstem cells of origin of the cervical vagus nerve, its cervical and thoracic branches, and of neurons projecting to the cricothyroid muscle and the stomach wall were identified and compared following injections of horseradish peroxidase (HRP) in 18 Rhesus monkeys. Physiologically and/or anatomically identified cardiopulmonary nerves were injected with 3–20 μl of HRP to identify the locations of vagal preganglionic cardioinhibitory neurons in 10 of these monkeys. After injections into cardiopulmonary nerves, retrogradely labelled cells were concentrated ipsilaterally in the most lateral parts of the dorsal motor nucleus of the vagus nerve (DMV) and in the ventrolateral nucleus ambiguus (NA). Fewer labelled neurons were identified close to or in the principal (dorsal) division of the NA and in the intermediate zone between the DMV and NA. The results indicate that monkey cardiopulmonary nerves have multiple origins; their somata are located primarily in the ventrolateral NA and to a lesser extent in the lateral DMV. In monkeys, there is a stronger representation in the lateral DMV than in cat, dog and pig. The viscerotopic organization of the cells of origin of primate vagal nerves is similar to that in other species. The cells of origin of vagal projections to the superior laryngeal nerve and cricothyroid muscle were located in the NA rostrally to those of the inferior laryngeal nerve. Injections into the superior laryngeal nerve also resulted in significant labelling in the DMV and intermediate zone (IZ). The cells of origin of projections to the anterior stomach wall were restricted to the DMV with a bilateral distribution of labelled cells, concentrated medially in the nucleus.     

Oxytocin-immunoreactive innervation of identified neurons in the rat dorsal vagal complex

Background Oxytocin (OXT) has been implicated in reproduction and social interactions and in the control of digestion and blood pressure. OXT‐immunoreactive axons occur in the dorsal vagal complex (DVC; nucleus tractus solitarius, NTS, dorsal motor nucleus of the vagus, DMV, and area postrema, AP), which contains neurons that regulate autonomic homeostasis. The aim of the present work is to provide a systematic investigation of the OXT‐immunoreactive innervation of dorsal motor nucleus of the vagus (DMV) neurons involved in the control of gastrointestinal (GI) function. Methods We studied DMV neurons identified by (i) prior injection of retrograde tracers in the stomach, ileum, or cervical vagus or (ii) induction of c‐fos expression by glucoprivation with 2‐deoxyglucose. Another subgroup of DMV neurons was identified electrophysiologically by stimulation of the cervical vagus and then juxtacellularly labeled with biotinamide. We used two‐ or three‐color immunoperoxidase labeling for studies at the light microscopic level. Key Results Close appositions from OXT‐immunoreactive varicosities were found on the cell bodies, dendrites, and axons of DMV neurons that projected to the GI tract and that responded to 2‐deoxyglucose and juxtacellularly labeled DMV neurons. Double staining for OXT and choline acetyltransferase revealed that OXT innervation was heavier in the caudal and lateral DMV than in other regions. OXT‐immunoreactive varicosities also closely apposed a small subset of tyrosine hydroxylase‐immunoreactive NTS and DMV neurons. Conclusions & Inferences Our results provide the first anatomical evidence for direct OXT‐immunoreactive innervation of GI‐related neurons in the DMV.     

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.     

Association of neurotensin binding sites with sensory and visceromotor components of the vagus nerve

Specific neurotensin (NT) binding sites were recently shown to be highly concentrated in the nucleus of the solitary tract (NTS), which receives primary vagal afferents, and in the dorsal motor nucleus of the vagus (DMN), which contains the cell bodies of origin of vagal preganglionic neurons. To investigate the relationship of these binding sites with sensory and visceromotor components of the vagus nerve, they were labeled here in vitro, using monoiodo[Tyr3]neurotensin (125I-NT) and visualized by light microscopic radioautography in the dorsomedial medulla of both intact and unilaterally vagotomized rats, in the nodose ganglia of intact animals, and in ligated vagus nerves. Unilateral vagotomy performed above the nodose ganglion resulted in a significant ipsilateral decrease in 125I-NT binding within both the NTS and the DMN, suggesting that NT binding sites were associated with both primary afferent fibers and preganglionic nerve cell bodies. The selective radioautographic labeling of a subpopulation (approximately 15%) of neuronal perikarya in the nodose ganglion confirmed that a proportion of vagal afferent neurons contained NT binding sites. Following vagus nerve ligation, a pile up of radiolabeled NT binding sites was observed on both sides of the nerve crush, indicating that NT receptor components were transported both anterogradely and retrogradely along fibers of the vagus nerve. We conclude that NT receptors are synthesized and transported within a subpopulation of afferent and efferent components of the vagus nerve and that NT may therefore act presynaptically upon vagal axon terminals in both central and peripheral nervous systems.     

Effect of portal infusion of hypertonic saline on neurons in the dorsal motor nucleus of the vagus in the rat

Effects of hepatoportal osmo-receptive (or sodium-receptive) afferents on neurons within the dorsal motor nucleus of the vagus (DMV) were investigated electrophysiologically in urethane-chloralose anesthetized rats. Responses of 56 spontaneously active neurons to antidromic stimulation of the ventral trunk of the subdiaphragmatic vagus were recorded in the left DMV. Among them, 35 neurons were inhibited by electrical stimulation of the hepatic branch of the vagus nerve (inhibitory neurons), except two neurons that were slightly excited. Effects of portal infusion of 3.6% NaCl were examined on 26 inhibitory neurons. Sixteen neurons increased their discharge rates and one neuron decreased its discharge rate in response to portal infusion of hypertonic saline. Thirty-five DMV neurons responded to electrical stimulation of the dorsal trunk of the subdiaphragmatic vagus were inhibited by electrical stimulation of the hepatic branch of the vagus. Four neurons were excited by this stimulation. Relatively smaller number of neurons (5 out of 22 inhibitory neurons) increased their discharge rates in response to portal infusion of hypertonic saline. In conclusion, the response of DMV neuron observed in this experiment was characterized by increasing the frequency of spike discharges in response to portal infusion of hypertonic saline. However, these neurons were inhibited by electrical stimulation of the hepatic branch of the vagus nerve. These results suggest that the hepatoportal osmoreceptive afferents may be conveyed to the DMV via inhibitory synapses.     

Parasympathetic and sympathetic control of the pancreas: a role for the suprachiasmatic nucleus and other hypothalamic centers that are involved in the regulation of food intake

To reveal brain regions and transmitter systems involved in control of pancreatic hormone secretion, specific vagal and sympathetic denervation were combined with injection of a retrograde transsynaptic tracer, pseudorabies virus (PRV), into the pancreas. After sympathetic or vagal transsection first-order neurons were revealed in the dorsal motor nucleus of the vagus (DMV) or in preganglionic spinal cord neurons (SPN), respectively. Careful timing of the survival of the animals allowed the detection of cell groups in immediate control of these DMV or SPN neurons. A far larger number of cell groups is involved in the control of DMV than of SPN neurons. Examples are given of a high level of interaction between the sympathetic and parasympathetic nervous system. Several cell groups project to both branches of the autonomic nervous system, sometimes even the same neurotransmitter is used, e.g., oxytocin neurons in the paraventricular nucleus and melanin-concentrating hormone and orexin neurons in the lateral hypothalamus project to both the DMV and SPN neurons. Moreover, the appearance of third-order neurons located in the sympathetic SPN after complete sympathectomy and in the DMV after complete vagotomy illustrates the possibility that motor neurons of the sympathetic and parasympathetic system may exchange information by means of interneurons. The presence of second-order neurons in prefrontal, gustatory, and piriform cortex may provide an anatomic basis for the involvement of these cortices in the cephalic insulin response. The observation that second-order neurons in both vagal and sympathetic control of the pancreas contain neuropeptides that are known to play a role in food intake indicates a direct association between behavioral and autonomic functions. Finally, the observation of third-order neurons in the suprachiasmatic nucleus and ventromedial hypothalamus shows the modulatory action of the time of the day and metabolic state, respectively.     

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.     

Immunohistochemical characterization of cardiac vagal preganglionic neurons in the rat

Cardiac vagal preganglionic neurons (CVN) control cardiac activity by negative chronotropic, dromotropic and inotropic effects. We attempted to characterize the distribution and neuronal properties of the CVN by using double labeling with the retrograde tracer cholera toxin B subunit (CTb) and immunohistochemistry for choline acetyltransferase (ChAT), tyrosine hydroxylase (TH), calcitonin gene-related peptide (CGRP) or nitric oxide synthase (NOS). Injection of CTb into the sinoatrial ganglia resulted in many retrogradely labeled of neurons in the dorsal motor nucleus of the vagus (DMV), the compact (AmC), semicompact (AmS), loose (AmL), external (AmE) formations of the nucleus ambiguus, and the intermediate zone (IZ) between DMV and the nucleus ambiguus. Almost all CTb-labeled neurons showed ChAT immunoreactivity in the DMV, AmC, AmS, AmL and IZ, but most of the CTb-labeled neurons showed no ChAT immunoreactivity in the AmE. Most of the CTb-labeled neurons were double-labeled with CGRP immunoreactivity in the AmC, AmS and AmL, but a few double-labeled neurons were found in the DMV, IZ and AmE. A few CTb-labeled neurons were double-labeled with NOS immunoreactivity only in the DMV. No TH-immunoreactive neurons were found among the CVN. These results indicate that there are four kinds of neurons among the CVN: non-cholinergic CVN in the AmE, cholinergic and CGRP-containing CVN in the AmC, AmS and AmL, and cholinergic or cholinergic and NOS-containing CVN in the DMV.     

Brainstem origin of preganglionic cardiac motoneurons in the muskrat

The muskrat, an aquatic rodent with a brisk and reliable diving response, shows a remarkable bradycardia after nasal stimulation. However, the medullary origin of cardiac preganglionic motoneurons is unknown in this species. We injected fat pads near the base of the heart of muskrats with a WGA-HRP solution to label retrogradely preganglionic parasympathetic neurons that project to the cardiac plexi. Results showed that the preponderance of labeled neurons was in ventrolateral parts of the medulla from 1.5 mm caudal to the obex to 2.0 mm rostral. Eighty-nine percent of the labeled neurons were located bilaterally in the external formation of the nucleus ambiguus, 5.6% were in the lateral extreme of the dorsal motor nucleus of the vagus nerve and 5.3% were found in the intermediate area in between these two nuclei. Although controversy still exists concerning the medullary origin of preganglionic cardiac motoneurons, our results from muskrats agree with those from most other species where preganglionic cardiac motoneurons were located just ventral to the nucleus ambiguus.     

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.     

Excitatory and inhibitory local circuit input to the rat dorsal motor nucleus of the vagus originating from the nucleus tractus solitarius

The nucleus tractus solitarius (NTS) and dorsal motor nucleus of the vagus nerve (DMV) constitute sensory and motor nuclei of the dorsal vagal complex, respectively. We used whole-cell patch-clamp recordings from DMV neurons in rat brain slices and three methods of stimulation (electrical, glutamate microdrop, glutamate photostimulation) to test the hypothesis that convergent excitatory and inhibitory inputs to DMV neurons originate from intact neurons in multiple NTS areas. Electrical stimulation of the NTS resulted in evoked excitatory and inhibitory postsynaptic currents (eEPSCs and eIPSCs) in DMV neurons. Stimulation of the dorsal NTS with glutamate microdrops, which selectively stimulates the soma and dendrites of intact neurons, resulted in 31% of DMV neurons receiving eEPSCs, 44% receiving eIPSCs, and 6% receiving convergent excitatory and inhibitory inputs. Glutamate photostimulation allowed selective activation of intact neurons in multiple, discrete areas of the NTS and resulted in 36% of DMV neurons receiving eEPSCs, 65% receiving eIPSCs and 20% receiving both inputs. Data obtained by stimulation of multiple NTS areas support the hypothesis that there are anatomically convergent inputs to DMV neurons originating from intact neurons within the NTS. These data support the hypothesis that there is transfer of convergent information from the NTS to the DMV, implying that significant sensory-motor processing occurs within the brainstem.     

Influence of electric stimulation of the medulla oblongata on the smooth muscle tone of the airway in cats

Changes in the tracheal smooth muscle tone have been studied in 30 cats anaesthetized with a chloralose-urethane mixture and paralyzed with succinyl choline bromide during electrical stimulation of the medulla oblongata. Constrictor responses were evoked from the regions including the caudal portion of the dorsal motor nucleus of the vagus, nucleus ambiguous and neighbouring structures of the reticular formation. Dilatory responses of the tracheal smooth muscle were observed during stimulation of the reticular formation at the level from 1 mm caudally to 6 mm rostrally of the obex. It is supposed that structures responsible for contractile responses are vagal preganglionic neurons, located in the dorsal motor nucleus of the vagus, in the nucleus ambiguous and in neighbouring regions and axons of these cells, looping through the medial part of the medulla. It is also supposed that dilatory responses are associated with excitation of sympathotonic reticular neurons, inhibitory neurons activated by the input from pulmonary stretch receptors and, possibly, vagal efferent neurons belonging to the nonadrenergic nervous system of the bronchi.     

Tyrosine hydroxylase-immunoreactive fibers in the human vagus nerve

Sympathetic catecholaminergic fibers in the vagus nerve were immunohistochemically examined in formalin-fixed human cadavers using an antibody against the noradrenalin-synthetic enzyme tyrosine hydroxylase (TH). TH-positive fibers were extensively distributed in the vagal nerve components, including the superior and inferior ganglia, the main trunk and the branches (superior and recurrent laryngeal, superior and inferior cardiac, and pulmonary branches). The inferior ganglion and its continuous cervical main trunk contained numerous TH-positive fibers with focal or diffuse distribution patterns in each nerve bundle. From these findings, we conclude that sympathetic fibers are consistently included in the human vagus nerve, a main source of parasympathetic preganglionic fibers to the cervical, thoracic and abdominal visceral organs.     

The location of extrinsic efferent and afferent nerve cell bodies of the normal canine stomach

The location of the extrinsic efferent and afferent nerve cell bodies to the mucosa, submucosa, and tunica muscularis of the cardiac, gastric, and pyloric gland regions of the ventral stomach and to the mucosa-submucosa alone of these 3 glandular gastric regions was determined using the horseradish peroxidase technique. All animals of the study demonstrated labeling bilaterally in the rostrocaudal extent of the dorsal motor nucleus of the vagus nerve (DMV) although mucosa-submucosa injections resulted in fewer labeled cells in the DMV. There was no evidence of viscerotopic organization within the DMV for the different gastric regions. However, the left nucleus generally contained a greater number of labeled cells than the right nucleus. Injection of the mucosa, submucosa, and tunica muscularis of the cardiac gland region also resulted in labeling in the nucleus ambiguus in 4 of 5 animals. The vast majority of labeled postganglionic sympathetic neurons were found in the celiacomesenteric ganglion. Labeled cells were also located variously in the stellate ganglion, middle cervical ganglion, and sympathetic trunk ganglia for the different groups. There was no discernible pattern of localization of labeled cells within a sympathetic ganglion. For the stomach, afferent labeled cells were located in the range of the first thoracic to fourth lumbar spinal ganglia and the nodose ganglia, bilaterally. As with sympathetic neurons, there was no discernible pattern of localization of labeled cells within a sensory ganglion.     

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.     

Horseradish peroxidase localization of cardiac vagal preganglionic somata

Cardiac vagal preganglionic somata were labeled in cats by the horseradish peroxidase (HRP) technique. The anatomical characteristics of cell bodies with axons in the left and right cervicl vagi were compared. HRP was injected subepicardially in three groups of pentobarbital anesthetized animals. In two test groups, injections were made after a left and right cervical vagotomy, respectively. In a control group, peripheral cardiac parasympathectomies were performed prior to HRP injection. The controls served to determine the number of somata labeled by HRP uptake via vagal fibers innervating viscera closely approximating the myocardium. After a 48 h survival period the cats were reanesthetized, perfused and fixed. Brain stems were removed, cut in the transverse or sagittal plane and developed with 3,3′-diaminobenzidine.Control cats had 6.8% the number of labeled cell bodies identified in animals with an intact vagus. Thus, few labeled somata in test cats were associated with noncardia ti tissue.The number, distribution and sizes of labeled cell bodies in test cats were similar. Somata were located ipsilateral to the intact vagus in three regions: the nucleus ambiguus (NA), the dorsal motor nucleus of the vagus (DMN) and an intermediate zone (IZ) between the NA and DMN. The NA contained the maximum number of cell bodies while successively fewer somata were located in the DMN and IZ. Somata of the NA were heterogeneously distributed along the longitudinal neuraxis. The region of maximal cell body concentration was between 1.0 and 1.8 mm rostral to the obex. Somata of the DMN and IZ were homogeneously and sparsely distributed along the neuraxis. The long and short axes of NA somata were larger than corresponding dimensions of cell bodies in the DMN or IZ. However, the dimensions of somata in the DMN and IZ were similar. The identification of labeled cell bodies in three medullary regions and the size differences of the somata in these regions may reflect a central physiological organization of cardia vagal somata.