Plasticity of vagal afferents at the site of an incision in the wall of the stomach

Clinical Feasibility of Large Gastrotomy Closure Using a Flexible Tissue Glue Based on N-Butyl-2-Cyanoacrylate: Experimental Study in Pigs

BACKGROUND

The use of synthetic adhesives such as cyanoacrylates has been established previously for a wide range of clinical indications. However, more research is necessary to evaluate their use in digestive closures or anastomosis. New chemical formulations developed to achieve more flexibility of synthetic adhesives (i.e., based on n-butyl-2-cyanoacrylate) could be an alternative to achieve this purpose. The aim of this study was to investigate the feasibility of using flexible cyanoacrylate adhesives for large gastric incision closure in an animal model.

METHODS

Twelve farm pigs were divided in two groups depending on the type of closure method applied. In all cases, extra-large seven centimeters gastrostomies were performed. Braided absorbable hand-sewn interrupted suture versus n-butyl-2-cyanoacrylate with softener closure were compared during a 3-week follow-up period. Histopathological aspects, hematologic and inflammatory biomarkers, and endoluminal pressure tolerated until leakage were assessed. The time spent on both closing procedures was compared.

RESULTS

No differences between the two groups were found in any of the histopathological and inflammatory variables evaluated. The glued group tolerated a significantly higher pressure than the manual suture group. A reduction of surgery time was also observed.

CONCLUSIONS

Our results suggest that flexible cyanoacrylates could be a feasible alternative to improve the clinical outcome of the closure of hollow viscera through more efficient sutureless procedures.

Introduction of Flexible Cyanoacrylates in Sutureless Gastric Closure

Background Clinical effectiveness and safety of biological and synthetic adhesives in digestive closures have been evaluated. Their use is becoming more prevalent, as rigidity and inflexibility are its more remarkable weaknesses. However, little is known about their role in gastric and anastomotic closures. Moreover, usefulness of novel flexible types of synthetic adhesives as n-butyl-cyanoacrylate has not been assessed yet. Materials and Methods One centimeter long gastrotomy was performed in 24 male Wistar rats, which were divided depending on the type of closure method employed: manual USP 5/0 silk interrupted suture versus sutureless closure with Histoacryl Flexible (n-butyl-cyanoacrylate with softener) or Histoacryl Double Component (n-butyl-cyanoacrylate with softener and hardener). Microscopic evaluation of the suture viability and integrity was performed, and adhesion formation during the cicatrization process were assessed. During an 8-week follow-up clinical and histopathological aspects as well as hematologic and inflammatory biomarkers were studied. Results No differences among groups where found in any of the clinical, analytical, or histopathological issues assessed except for a higher incidence rate of adhesions in the Histoacryl Double Component group when compared with hand-sewn suture group (P = .04). Our results support experimental studies in large mammals (pigs) for further study of sutureless hollow viscera closure.

Withdrawal and restoration of central vagal afferents within the dorsal vagal complex following subdiaphragmatic vagotomy

Vagotomy, a severing of the peripheral axons of the vagus nerve, has been extensively utilized to determine the role of vagal afferents in viscerosensory signaling. Vagotomy is also an unavoidable component of some bariatric surgeries. Although it is known that peripheral axons of the vagus nerve degenerate and then regenerate to a limited extent following vagotomy, very little is known about the response of central vagal afferents in the dorsal vagal complex to this type of damage. We tested the hypothesis that vagotomy results in the transient withdrawal of central vagal afferent terminals from their primary central target, the nucleus of the solitary tract (NTS). Sprague-Dawley rats underwent bilateral subdiaphragmatic vagotomy and were sacrificed 10, 30, or 60 days later. Plastic changes in vagal afferent fibers and synapses were investigated at the morphological and functional levels by using a combination of an anterograde tracer, synapse-specific markers, and patch-clamp electrophysiology in horizontal brain sections. Morphological data revealed that numbers of vagal afferent fibers and synapses in the NTS were significantly reduced 10 days following vagotomy and were restored to control levels by 30 days and 60 days, respectively. Electrophysiology revealed transient decreases in spontaneous glutamate release, glutamate release probability, and the number of primary afferent inputs. Our results demonstrate that subdiaphragmatic vagotomy triggers transient withdrawal and remodeling of central vagal afferent terminals in the NTS. The observed vagotomy-induced plasticity within this key feeding center of the brain may be partially responsible for the response of bariatric patients following gastric bypass surgery.

Umbilical hernia repair increases the rate of functional gastrointestinal disorders in children

OBJECTIVES

To hypothesize that hernia repair would not change the incidence of functional gastrointestinal disorders (FGIDs) due to the benign and limited nature of the procedure.

STUDY DESIGN

This cohort study assessed a randomized selection of children aged 4-18 years who underwent hernia repair more than 4 years prior at Ann and Robert H. Lurie Children's Hospital of Chicago. Controls were siblings who had not undergone surgery previously. Parents completed the Questionnaire on Pediatric Gastrointestinal Symptoms-Rome III Version by telephone for subjects and controls. The primary outcome was the presence of FGIDs.

RESULTS

Fifty children with hernia repair and 43 sibling controls were identified. At the time of survey, subjects with hernia repair were average age 12.9 years (range 5-18 years, 60% male) and controls were average age 12.2 years (range 4-18 years, 49% male). Average age at surgical repair was 5.2 years (median 5.2 years, range 0.2-10.4 years) and average time since surgical repair was 7.8 years (range 4.8-13.7 years). FGIDs were diagnosed in 10/50 (20%) cases of hernia repair and 2/43 (5%) controls (P = .033, Fisher 2-tailed test).

CONCLUSIONS

Umbilical hernia repair increases the likelihood of FGIDs in childhood. Additional studies are needed to identify aspects of surgery that may be associated with development of FGIDs.

Molecular anatomy of the gut-brain axis revealed with transgenic technologies: implications in metabolic research

Neurons residing in the gut-brain axis remain understudied despite their important role in coordinating metabolic functions. This lack of knowledge is observed, in part, because labeling gut-brain axis neurons and their connections using conventional neuroanatomical methods is inherently challenging. This article summarizes genetic approaches that enable the labeling of distinct populations of gut-brain axis neurons in living laboratory rodents. In particular, we review the respective strengths and limitations of currently available genetic and viral approaches that permit the marking of gut-brain axis neurons without the need for antibodies or conventional neurotropic tracers. Finally, we discuss how these methodological advances are progressively transforming the study of the healthy and diseased gut-brain axis in the context of its role in chronic metabolic diseases, including diabetes and obesity.

Slit/Robo-mediated chemorepulsion of vagal sensory axons in the fetal gut

BACKGROUND

The vagus nerve descends from the brain to the gut during fetal life to reach specific targets in the bowel wall. Vagal sensory axons have been shown to respond to the axon guidance molecule netrin and to its receptor, deleted in colorectal cancer (DCC). As there are regions of the gut wall into which vagal axons do and do not extend, it is likely that a combination of attractive and repellent cues are involved in how vagal axons reach specific targets. We tested the hypothesis that Slit/Robo chemorepulsion can contribute to the restriction of vagal sensory axons to specific targets in the gut wall.

RESULTS

Transcripts encoding Robo1 and Robo2 were expressed in the nodose ganglia throughout development and mRNA encoding the Robo ligands Slit1, Slit2, and Slit3 were all found in the fetal and adult bowel. Slit2 protein was located in the outer gut mesenchyme in regions that partially overlap with the secretion of netrin-1. Neurites extending from explanted nodose ganglia were repelled by Slit2.

CONCLUSIONS

These observations suggest that vagal sensory axons are responsive to Slit proteins and are thus repelled by Slits secreted in the gut wall and prevented from reaching inappropriate targets.

Upper gastrointestinal dysmotility after spinal cord injury: is diminished vagal sensory processing one culprit?

Despite the widely recognized prevalence of gastric, colonic, and anorectal dysfunction after spinal cord injury (SCI), significant knowledge gaps persist regarding the mechanisms leading to post-SCI gastrointestinal (GI) impairments. Briefly, the regulation of GI function is governed by a mix of parasympathetic, sympathetic, and enteric neurocircuitry. Unlike the intestines, the stomach is dominated by parasympathetic (vagal) control whereby gastric sensory information is transmitted via the afferent vagus nerve to neurons of the nucleus tractus solitarius (NTS). The NTS integrates this sensory information with signals from throughout the central nervous system. Glutamatergic and GABAergic NTS neurons project to other nuclei, including the preganglionic parasympathetic neurons of the dorsal motor nucleus of the vagus (DMV). Finally, axons from the DMV project to gastric myenteric neurons, again, through the efferent vagus nerve. SCI interrupts descending input to the lumbosacral spinal cord neurons that modulate colonic motility and evacuation reflexes. In contrast, vagal neurocircuitry remains anatomically intact after injury. This review presents evidence that unlike the post-SCI loss of supraspinal control which leads to colonic and anorectal dysfunction, gastric dysmotility occurs as an indirect or secondary pathology following SCI. Specifically, emerging data points toward diminished sensitivity of vagal afferents to GI neuroactive peptides, neurotransmitters and, possibly, macronutrients. The neurophysiological properties of rat vagal afferent neurons are highly plastic and can be altered by injury or energy balance. A reduction of vagal afferent signaling to NTS neurons may ultimately bias NTS output toward unregulated GABAergic transmission onto gastric-projecting DMV neurons. The resulting gastroinhibitory signal may be one mechanism leading to upper GI dysmotility following SCI.

Genetic tracing of Nav1.8-expressing vagal afferents in the mouse

Nav1.8 is a tetrodotoxin-resistant sodium channel present in large subsets of peripheral sensory neurons, including both spinal and vagal afferents. In spinal afferents, Nav1.8 plays a key role in signaling different types of pain. Little is known, however, about the exact identity and role of Nav1.8-expressing vagal neurons. Here we generated mice with restricted expression of tdTomato fluorescent protein in all Nav1.8-expressing afferent neurons. As a result, intense fluorescence was visible in the cell bodies, central relays, and sensory endings of these neurons, revealing the full extent of their innervation sites in thoracic and abdominal viscera. For instance, vagal and spinal Nav1.8-expressing endings were seen clearly within the gastrointestinal mucosa and myenteric plexus, respectively. In the gastrointestinal muscle wall, labeled endings included a small subset of vagal tension receptors but not any stretch receptors. We also examined the detailed innervation of key metabolic tissues such as liver and pancreas and evaluated the anatomical relationship of Nav1.8-expressing vagal afferents with select enteroendocrine cells (i.e., ghrelin, glucagon, GLP-1). Specifically, our data revealed the presence of Nav1.8-expressing vagal afferents in several metabolic tissues and varying degrees of proximity between Nav1.8-expressing mucosal afferents and enteroendocrine cells, including apparent neuroendocrine apposition. In summary, this study demonstrates the power and versatility of the Cre-LoxP technology to trace identified visceral afferents, and our data suggest a previously unrecognized role for Nav1.8-expressing vagal neurons in gastrointestinal functions.

Age-related changes in vagal afferents innervating the gastrointestinal tract

Recent progress in understanding visceral afferents, some of it reviewed in the present issue, serves to underscore how little is known about the aging of the visceral afferents in the gastrointestinal (GI) tract. In spite of the clinical importance of the issue-with age, GI function often becomes severely compromised-only a few initial observations on age-related structural changes of visceral afferents are available. Primary afferent cell bodies in both the nodose ganglia and dorsal root ganglia lose Nissl material and accumulate lipofucsin, inclusions, aggregates, and tangles. Additionally, in changes that we focus on in the present review, vagal visceral afferent terminals in both the muscle wall and the mucosa of the GI tract exhibit age-related structural changes. In aged animals, both of the vagal terminal types examined, namely intraganglionic laminar endings and villus afferents, exhibit dystrophic or regressive morphological changes. These neuropathies are associated with age-related changes in the structural integrity of the target organs of the affected afferents, suggesting that local changes in trophic environment may give rise to the aging of GI innervation. Given the clinical relevance of GI tract aging, a more complete understanding both of how aging alters the innervation of the gut and of how such changes might be mitigated should be made research priorities.

Altered mechanosensitive properties of vagal afferent fibers innervating the stomach following gastric surgery in rats

BACKGROUND AND AIMS

Several types of gastric surgeries have been associated with early satiety, dyspepsia and food intolerances. We aimed to examine alterations in gastric vagal afferents following gastric surgery-fundus ligation.

METHODS

Six week old, male Sprague-Dawley rats underwent chronic ligation (CL) of the fundus. Sham rats underwent abdominal surgery, but without ligation. Another group of rats underwent acute ligation (AL) of the fundus immediately prior to experiments. CL and sham rats were allowed to grow to age 3-4 months. Food intake and weights were recorded post-operatively. Gastric compliance and gastric wall thickness was measured at baseline and during gastric distension (GD). Extracellular recordings were made to examine response characteristics of vagal afferent fibers to GD and to map the stomach receptive field (RF). The morphological structures of afferent terminals in the stomach were examined with retrograde tracings from the nodose ganglion.

RESULTS

The CL group consumed significantly less food and weighed less than sham control. The mean compliance of the CL group was significantly less than control, but higher than the AL group. The spontaneous firing and responses to GD of afferent fibers from the CL rats were significantly higher than AL rats. There was a marked expansion of the gastric RF in the CL rats with significant reorganization and regeneration of intramuscular array (IMA) terminals. There was no difference in total wall or muscle thickness among the groups.

CONCLUSION

CL results in aberrant remodeling of IMAs with expansion of the gastric RF and alters the mechanotransduction properties of vagal afferent fibers. These changes could contribute to altered sensitivity following gastric surgery.

The nervous system and gastrointestinal function

The enteric nervous system is an integrative brain with collection of neurons in the gastrointestinal tract which is capable of functioning independently of the central nervous system (CNS). The enteric nervous system modulates motility, secretions, microcirculation, immune and inflammatory responses of the gastrointestinal tract. Dysphagia, feeding intolerance, gastroesophageal reflux, abdominal pain, and constipation are few of the medical problems frequently encountered in children with developmental disabilities. Alteration in bowel motility have been described in most of these disorders and can results from a primary defect in the enteric neurons or central modulation. The development and physiology of the enteric nervous system is discussed along with the basic mechanisms involved in controlling various functions of the gastrointestinal tract. The intestinal motility, neurogastric reflexes, and brain perception of visceral hyperalgesia are also discussed. This will help better understand the pathophysiology of these disorders in children with developmental disabilities.

Characterization of weight loss and weight regain mechanisms after Roux-en-Y gastric bypass in rats

Roux-en-Y gastric bypass (RYGB) is the most effective therapy for morbid obesity, but it has a ∼20% failure rate. To test our hypothesis that outcome depends on differential modifications of several energy-related systems, we used our established RYGB model in Sprague-Dawley diet-induced obese (DIO) rats to determine mechanisms contributing to successful (RGYB-S) or failed (RYGB-F) RYGB. DIO rats were randomized to RYGB, sham-operated Obese, and sham-operated obese pair-fed linked to RYGB (PF) groups. Body weight (BW), caloric intake (CI), and fecal output (FO) were recorded daily for 90 days, food efficiency (FE) was calculated, and morphological changes were determined. d-Xylose and fat absorption were studied. Glucose-stimulated vagal efferent nerve firing rates of stomach were recorded. Gut, adipose, and thyroid hormones were measured in plasma. Mitochondrial respiratory complexes in skeletal muscle and expression of energy-related hypothalamic and fat peptides, receptors, and enzymes were quantified. A 25% failure rate occurred. RYGB-S, RYGB-F, and PF rats showed rapid BW decrease vs. Obese rats, followed by sustained BW loss in RYGB-S rats. RYGB-F and PF rats gradually increased BW. BW loss in RYGB-S rats is achieved not only by RYGB-induced decreased CI and increased FO, but also via sympathetic nervous system activation, driven by increased peptide YY, CRF, and orexin signaling, decreasing FE and energy storage, demonstrated by reduced fat mass associated with the upregulation of mitochondrial uncoupling protein-2 in fat. These events override the compensatory response to the drop in leptin levels aimed at conserving energy.

Morphology and topography of nucleus ambiguus projections to cardiac ganglia in rats and mice

Vagal efferent axons from the nucleus ambiguus (NA) innervate ganglionated plexuses in the dorsal surface of cardiac atria, which in turn, may have different functional roles in cardiac regulation. However, the morphology and topography of vagal efferent projections to these ganglionated plexuses in rats and mice have not been well delineated. In the present study, we injected the tracer 1,1'-dioctadecyl-3,3,3',3' tetramethylindocarbocyanine methanesulfonate (DiI) into the left NA to label vagal efferent axons and terminals in cardiac ganglia and administered Fluoro-Gold (FG) i.p. to stain cardiac ganglia. Then, we used confocal microscopy and a Neurolucida 3-D Digitization System to qualitatively and quantitatively examine the distribution and structure of cardiac ganglia, and NA efferent projections to cardiac ganglia in the whole-mounts of Sprague-Dawley (SD) rats and FVB mice. Our observations were: 1) Cardiac ganglia of different shapes and sizes were distributed in the sinoatrial (SA) node, atrioventricular (AV) node, and lower pulmonary vein (LPV) regions on the dorsal surface of the atria. In each region, several ganglia formed a ganglionated plexus. The plexuses at different locations were interconnected by nerves. 2) Vagal efferent fibers ramified within cardiac ganglia, formed a complex network of axons, and innervated cardiac ganglia with very dense basket endings around individual cardiac principal neurons (PNs). 3) The percent of the PNs in cardiac ganglia which were innervated by DiI-labeled axons was 54.3+/-3.2% in mice vs. 53.2+/-3.2% in rats (P>0.10). 4) The density of axonal putative-synaptic varicosities on the surface of PNs was 0.15+/-0.02/microm(2) in mice vs. 0.16+/-0.02/microm(2) in rats (P>0.10). Thus, the distributions of cardiac ganglia and vagal efferent projections to cardiac ganglia in mice and rats were quite similar both qualitatively and quantitatively. Our study provides the structural foundation for future investigation of functional differentiation of ganglionated plexuses and the brain-heart circuitry in rodent models of human disease.

Direct synaptic contacts on the myenteric ganglia of the rat stomach from the dorsal motor nucleus of the vagus

The myenteric ganglia regulate not only gastric motility but also secretion, because a submucous plexus is sparsely developed in the rodent stomach. We have examined whether the neurons of the dorsal motor nucleus of the vagus (DMV) have direct synaptic contacts on the myenteric ganglia and the ultrastructure of the vagal efferent terminals by using wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). The myenteric ganglia of the rat were composed of four types of neurons, i.e., small, medium-sized, large, and elongated neurons. The average numbers of axosomatic terminals per profile were 2.0 on the small neurons, 3.1 on the medium-sized neurons, 1.2 on the large neurons, and 4.2 on the elongated neuron. More than half of the axosomatic terminals contained round vesicles and formed asymmetric synaptic contacts on the small, medium-sized, and large neurons. About 80% of the axosomatic terminals on the elongated neurons contained pleomorphic vesicles and formed asymmetric synaptic contacts. When WGA-HRP was injected into the DMV, many anterogradely labeled terminals were found around the myenteric neurons. The labeled terminals were large (3.16 +/- 0.10 microm) and contacted exclusively the somata. Most of them (about 90%) contained round vesicles and formed asymmetric synaptic contacts. Serial ultrathin sections revealed that almost all neurons in a ganglion received projections from the DMV. The vagal axon terminals generally contacted the medium-sized or the elongated neurons, whereas a few labeled terminals contacted the small and the large neurons. The present results indicate that the DMV projects to all types of neurons and that their axon terminals contain mostly round synaptic vesicles and form asymmetric synaptic contacts.