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

Three-dimensional spatial relationship of neuropeptides and receptors in the rat dorsal vagal complex

Retrograde tracing, multi-label fluorescence immunohistochemistry, confocal microscopy and three-dimensional (3-D) reconstruction techniques were combined to examine the spatial relationship of immunoreactive nerve terminals containing either calcitonin gene-related polypeptide (CGRP) or substance P (SP) to identified gastric efferent neurons in the dorsal motor nucleus of the vagus (DMV) in the brainstem of the rat. The availability of an antibody to the receptor for SP (NK-1r) permitted observation of the association between peptide and receptor. Although both SP-IR and CGRP-IR nerve fibres came in close spatial proximity to identified gastric efferent neurons, few discrete contacts between these fibres and the neuronal membrane were observed. In addition, NK-1r-IR was localized to the somatic and dendritic membranes of a subpopulation of neurons within the DMV, with the majority of receptor labelling not in close spatial proximity to SP-IR nerve fibres. The methodology described in this study permitted the simultaneous observation of the spatial relationship between neuropeptide and an identified neuron (and the corresponding receptor in the case of SP) in 3-D, which is something that cannot be achieved using conventional microscopic techniques

A 50-year perspective upon selective gastric vagotomy

BACKGROUND

The occurrence of postvagotomy complications was initially considered an unavoidable but acceptable consequence of duodenal ulcer surgery. Following the description of "selective" vagotomy procedures, however, it became apparent that effective ulcer surgery might be accomplished without unpleasant sequellae.

METHODS

In 1957 the experimental basis for "highly" selective vagotomy (HSV), which preserved antral innervation, was reported. HSV was performed in several European centers between 1960 and 1968, and was widely accepted there. Surgeons in the United States, in contrast, were largely reluctant to use HSV, an operation which had an excessive ulcer recurrence rate compared to vagotomy-antrectomy. More recently, HSV is recognized as a successful operation, due to more complete division of preganglionic gastric vagal nerves ("extended" HSV) and the liberal use of pyloric reconstruction in patients with juxtapyloric ulcers.

RESULTS

HSV is performed with minimal morbidity, with an incidence of recurrent ulcer which is less than 5%. Complications such as dumping, diarrhea, and gastric atony are quite rare.

CONCLUSIONS

HSV is an ideal procedure for most patients with duodenal ulcer. Because most operations for ulcer are performed for urgent or life-threatening problems, the most common operation performed in the United States today is truncal vagotomy combined with pyloroplasty or gastric resection. Earlier operation for chronic ulcer has many potential advantages.

Association of substance P and its receptor with efferent neurons projecting to the greater curvature of the rat stomach

Retrograde tracing and immunocytochemistry were used to identify and map the distribution of substance P (SP) and its receptor (NK-1r) associated with gastric motor neurons in the dorsal motor nucleus of the vagus (DMV) in the rat brain stem. The presence of peptide and receptor in surrounding regions within the dorsal vagal complex were also observed. Injection of the retrograde tracer Fluorogold (FG) into the greater curvature of the stomach produced bilateral labelling of neurons within the DMV. The majority of the NK-1r immunoreactivity appeared as an intricate lattice of fibres with a small number of immunoreactive cell bodies. The NK-1r-labelled fibres were detected within the DMV in close association with FG-labelled neurons and in the region between the DMV and nucleus of the solitary tract (NTS). A proportion of FG-labelled neuronal cell bodies were also labelled with NK-1r (7% of total). The greatest density of NK-1r-labelled fibres was observed at the rostral end of the FG-labelled neuron columns in the DMV (close to the IV ventricle) in the region where gastric vagal afferents terminate. Little NK-1r labelling was observed at the caudal end of the FG-labelled neuron tracts adjacent to the central canal. In the coronal plane, the NK-1r-labelled fibres were seen at the edges of the DMV extending into overlying NTS. Substance P was visualized as a dense network of fibres spanning the entire length of the DMV and in close association with FG-labelled neurons. Substance P staining was also detected in the NTS and in the ventral AP. Most of the association between SP/NK-1r immunoreactive fibres was observed within the DMV and at the border between the DMV and NTS. These findings suggest that SP directly regulates a subpopulation of efferent neurons in the DMV which project to the greater curvature of stomach.

Lester R. Dragstedt and his role in the evolution of therapeutic vagotomy in the United States

The date October 22, 1993, marks the centenary of the birth of Lester R. Dragstedt. He emerged from humble roots of Swedish immigrant parents to become one of the pre-eminent surgical innovators of the twentieth century. Early in his scientific career, Dragstedt was profoundly influenced by another Swede, A. J. Carlson, who was initially employed as a Lutheran minister in Dragstedt's hometown of Anaconda, Montana. Carlson left the ministry for graduate school and later became chairman of The Department of Physiology at the University of Chicago. When Dragstedt finished his schooling, Carlson convinced him to attend the University of Chicago. In addition to Carlson, Dragstedt's research was influenced by many prominent physiologists and surgeons, including Pavlov and Latarjet. Their work, along with his own investigations, helped him both to formulate his hypotheses on the regulation of gastric acid secretion and to formalize the operation of truncal vagotomy. In 1943, Dragstedt initiated the clinical use of this procedure in North America. Although he studied his patients carefully and documented his results meticulously, the operation initially met with considerable resistance from both his medical and surgical colleagues. Over time, many other surgeons accepted vagotomy as a viable procedure and further modified his technique. The unique ability of Dragstedt to transfer his research studies to the development and implementation of rational surgical therapy remains an enduring example for the surgical profession.

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).

The vagus nerve and its vagaries

Without any further comments we advise the surgeon performing open or laparoscopic vagotomy to know the anatomy and the vagaries of the vagus nerve. In view of the demonstration that the nerves of the greater curvature, identified as a concern in achieving a "complete" PGV, are projected from up to 20% of the nerve cell bodies of the dorsal motor nucleus of the vagus nerve in the brain stem, we believe it is appropriate to adopt the technique of EHSV as a means of avoiding the high recurrence rates reported with conventional highly selective vagotomy or proximal gastric vagotomy. When pyloric stenosis or outlet obstruction is present, anterior hemipylorectomy provides a solution. If surgeons adopt a laparoscopic approach to EHSV, they must be cognizant of all sites of preganglionic innervation, and (ideally) attempt to verify the "completeness" of vagotomy by Congo red testing. We look forward, also, to the work of Andrus and Schneider, who are evaluating alternative methods of achieving complete vagotomy.

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.

Viscerotopic representation of preganglionic efferent vagus nerve in the brainstem of the rat: a Fluoro-Gold study

To investigate the viscerotopic distribution of the cells of origin of preganglionic vagus nerve in rats, Fluoro-Gold was injected into various visceral tissues. After injections into the gastroesophageal junction and the gastric corpus, labelled cells were localized in the medial half of the dorsal motor nucleus of the vagus (dmnX). Cells in the nucleus ambiguous (nA) were also labelled after injections into the gastroesophageal junction. After injections into the pancreatic head and the celiac plexus, labelled cells were located bilaterally in the lateral part of the caudal dmnX. In the rostral dmnX, however, the pancreatic head was represented in the medial segment. After injections into the lung, duodenum, liver and ascending colon, no labelling was observed in the brainstem.

Anatomical relationship between neuropeptide-containing fibers and efferent vagal neurons projecting to the rat corpus

Injections of the retrograde tracers into the posterior surface of the stomach at the greater curvature resulted in labelling of the right half of the dorsal motor nucleus of the vagus. Whereas injections into the anterior and posterior surfaces of the corpus resulted in bilateral labelling in the medulla. Immunocytochemical staining of the labelled sections using antisera to substance P was confined to a dense network of fibers within the dorsal motor nucleus of the vagus and the nucleus tractus solitarius with no cell bodies being detected. Calcitonin gene-related peptide-immunoreactivity was detected in nerve fibers in the nucleus tractus solitarius and cell bodies of the hypoglossal nucleus. Finally, neuropeptide Y-immunoreactivity was confined to nerve fibers within the vagal complex. Of the neurons labelled by the retrograde tracers injected into the corpus all were in close spatial contact with fibers containing substance P-immunoreactivity. A smaller number were associated with neuropeptide Y-containing fibers with a few adjacent to calcitonin gene-related peptide-immunoreactive fibers. These results indicate that substance P and neuropeptide Y may directly regulate efferent neurons controlling gastric motility and acid secretion. Calcitonin gene-related peptide, however, is unlikely to directly modulate the cell bodies of the neurons in the dorsal motor nucleus but may modulate the dendrites from these neurons in the nucleus tractus solitarius.

Abdominal pathways and central origin of rat vagal fibers that stimulate gastric acid

The brainstem location and peripheral course of the vagal preganglionic fibers that stimulate gastric acid secretion were identified using electrical stimulation combined with retrograde (True Blue; Dr. K. G. Illing, Gross Umstadt, Germany) and anterograde (Dil; Molecular Probes) fluorescent neural tracers in rats with various selective vagotomies. Animals with only one or both gastric branch(es) spared had normal, large gastric acid responses to electrical stimulation of the ipsilateral cervical vagus and showed an abundance of Dil-labeled vagal fibers and terminals in the gastric myenteric plexus. Rats with only the unpaired hepatic branch spared had a much smaller but significant gastric acid response and a few labeled vagal profiles in the antral region of the stomach. In contrast, rats with only one or both celiac branch(es) intact had neither a gastric acid response, nor evidence for Dil transport to the stomach. Retrograde transport of True Blue through the spared vagal axons to the brainstem indicated that the cell bodies of the preganglionics that send their axons through the acid-positive gastric and hepatic branches occupy the medial longitudinal columnar subnuclei of the dorsal motor nucleus. It is concluded that besides the long-recognized gastric branches, which are the major access route to the parietal cells, the hepatic branch contains a small number of fibers that most likely reach the antrum through the right gastroepiploic artery along the greater curvature and/or the right gastric artery.

Indications for parietal cell vagotomy without drainage in gastrointestinal surgery

Parietal cell vagotomy (PCV) was used for a variety of gastrointestinal conditions in 658 patients. Operative and late related deaths after PCV were 1.1% (3/273) in patients with intractable duodenal ulcers, 1.1% (1/91) in perforated ulcers, 0% (0/43) in Type I gastric ulcers, 0% (0/45) in pyloric and prepyloric ulcers, 3.2% (6/188) when combined with fundoplication, 8.7% (2/23) when combined with vascular surgery, and 4.2% (1/24) in ulcer patients with acute bleeding. The recurrent ulcer rate after PCV was 8.4% in patients operated on for duodenal ulcer, 6.4% for perforated ulcer, 5.3% for bleeding ulcers, 10% for Type I gastric ulcers, and 31% for pyloric and prepyloric ulcers. PCV was preferred to total gastrectomy in four patients in whom a gastrinoma could not be located. PCV was used in 188 patients with reflux esophagitis and in 12 patients with achalasia to facilitate fundoplication and placement of the myotomy, respectively. Based on the results of the study, PCV is contraindicated in patients with pyloric and prepyloric ulcers. PCV is not recommended when traumatic dilatation of the pylorus is required to overcome obstruction. PCV may have limited application in patients with bleeding ulcers and Type I gastric ulcers. In our experience PCV is not contraindicated in patients with ulcers resistant to H2 receptor antagonists. PCV may be contraindicated when acid hypersecretion exceeds an as-yet undetermined level. PCV is an ideal procedure for intractable duodenal ulcers and perforated ulcers.

The neuroendocrine system of the gut

The digestive tract is the richest source of regulatory peptides outside the brain. Such peptides occur all along the gut in the neuroendocrine system which is composed of endocrine/paracrine cells disseminated in the epithelium and of intrinsic neurons that form continuous ganglionic chains in the submucosa and in the muscle layer. Some endocrine/paracrine cells, particularly in the stomach, still have not been associated with an identified regulatory peptide implying that our present knowledge is far from complete. The intracellular processing of regulatory peptide precursors involves multi-step proteolytic cleavage generating several fragments. In many instances more than one biologically active peptide is generated from one and the same precursor. In addition, certain endocrine/paracrine cells and neurons have been found to produce more than one peptide precursor and some are known to harbour 'classical' neurotransmitters, such as 5-hydroxytryptamine, histamine and GABA as well as regulatory peptides. Key questions for the future are the functional significance of the coexistence of multiple messengers within the same cells and the details of how the endocrine/paracrine cells and the neurons in the gut interact.