Plasticity in the myenteric plexus of the rat ileum after long-term sympathectomy

Upregulation of β1-adrenoceptors is involved in the formation of gastric dysmotility in the 6-hydroxydopamine rat model of Parkinson's disease

Gastrointestinal dysmotility is one of the nonmotor symptoms of Parkinson's disease (PD). Gastroparesis and upregulated β-adrenoceptors (β-ARs) have been reported in rats with bilateral microinjection of 6-hydroxydopamine (6-OHDA) in the substantia nigra, but the underlying mechanism is unclear. The aim of the current study is to investigate the role of β-ARs in gastroparesis in 6-OHDA rats. Gastric motility was studied through strain gauge measurement. Immunofluorescence, real-time reverse transcription-polymerase chain reaction and Western blotting were performed to examine the expression of β-ARs. Norepinephrine (NE) inhibited gastric motility in a dose-dependent fashion in both control and 6-OHDA rats, but much stronger adrenergic reactivity was observed in the 6-OHDA rats. The inhibition of gastric motility by NE in both control and 6-OHDA rats was not affected by tetrodotoxin, a neural sodium channel blocker. Blocking β1-AR or β2-AR did not affect the inhibition of strip contraction by NE in control rats, but β1-AR blockage obviously enhanced the half maximal inhibitory concentration value of NE in 6-OHDA rats. Selective inhibition of β3-AR blocked the effect of NE significantly in both control and 6-OHDA rats. The protein expression of β1-AR, but not β2-AR and β3-AR in gastric muscularis externa was increased significantly in 6-OHDA rats. In conclusion, β3-AR involves the regulation of gastric motility in control rats, whereas the upregulation of β1-AR is responsible for enhanced NE reactivity in 6-OHDA rats and therefore is involved in the formation of gastroparesis. The effect of both β1-AR and β3-AR on gastric motility is independent of the enteric nervous system.

Normalization of substance P levels in rectal mucosa of patients with faecal incontinence treated successfully by sacral nerve stimulation

Background

Sacral nerve stimulation (SNS) may improve faecal incontinence by modulating rectal sensation. This study measured changes in the peripheral expression of various neural epitopes in response to SNS.

Methods

Rectal mucosal biopsies were taken from 12 patients before and after temporary SNS, and from ten responders at 90 days after permanent stimulation. Sections were immunostained for substance P, transient receptor potential vanilloid (TRPV) 1, vasoactive intestinal peptide (VIP) and calcitonin gene-related peptide (CGRP). Levels were compared with those in nine continent controls.

Results

Baseline levels of percentage area immunoreactivities of substance P (median 0·51 (95 per cent confidence interval 0·31 to 0·73) versus 0·13 (0·07 to 0·27) per cent; P < 0·001) and TRPV1 (0·76 (0·41 to 1·11) versus 0·09 (0·04 to 0·14) per cent; P < 0·001), but not of VIP (1·26 (0·37 to 2·15) versus 1·28 (0·39 to 2·17); P = 0·943), were significantly greater than in controls. Successful SNS resulted in a significant decrease in substance P immunostaining after temporary (0·15 (0·06 to 0·51) per cent; P = 0·051) and permanent (0·17 (0 to 0·46) per cent; P = 0·051) stimulation. Immunoreactivity of TRPV1, VIP, CGRP and neural markers showed no qualitative change.

Conclusion

Patients with faecal incontinence demonstrate normalization of raised rectal mucosal substance P levels following successful SNS.

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

Our objectives were to determine whether the vagal afferent innervation of the stomach reorganizes after surgery and to observe how different wound closure techniques might influence such a process. The smooth muscle wall of the stomach served as a model because it is densely innervated by vagal axons and is frequently compromised by gastric surgery. Male Sprague-Dawley rats were assigned to one of six groups: three groups served as controls in which the stomach was exposed surgically and a) subjected to no further manipulation, b) traumatized with suture needle punctures of the muscle wall, or c) insulted by the placement of knotted suture thread in the stomach muscle; three surgical groups received a 1.0 cm incision through the ventral muscle wall of the stomach that was closed using either a) absorbable sutures, b) fibrin glue, or c) n-butyl cyanoacrylate. Rats were killed 4 to 7 months post-surgery. Prior to euthanasia, Micro-Ruby was injected into the left nodose ganglion of each rat to label vagal afferent axons and terminals. Twelve days post-injection, the stomachs were processed for microscopy. All groups recovered quickly from surgery, without differences in body weight. The presence of suture material in the muscle wall of the stomach was sufficient to produce reorganization of nearby vagal afferents. In addition, we observed that an incision of the smooth muscle wall of the stomach and the associated damage to vagal afferents provoked reorganization and regeneration of vagal afferents. Vagal remodeling at the incision was characteristic of axonal patterns found in neuromas (unlike the organized regeneration and differentiation that can occur after axotomy central to the target organ). Vagal afferent terminals located at the site of the incision were free nerve endings and growth cone profiles, and not the characteristically complex end organs normally found in the smooth muscle. Finally, the pattern of vagal plasticity was influenced by the wound closure technique used. Overall, the remodeling of afferents was aberrant in nature, and such neural pathology could contribute to the neuropathic symptoms and hyperalgesias associated with gastrointestinal trauma and bariatric surgery.

Gastrointestinal projection maps of the vagus nerve are specified permanently in the perinatal period

The vagal innervation of the proximal gastrointestinal (GI) tract is lateralized. To determine whether this pattern is specified as early as the perinatal period, neonatal rat pups were given unilateral cervical vagotomies. Separate groups received (1) transections below the left nodose ganglion, (2) left cervical resections that included removal of the nodose ganglion, or (3) sham surgeries. At 4 months of age, each animal's vagal afferent projections from the unoperated side were mapped by injecting the nodose with WGA-HRP, preparing the stomach as wholemounts, and processing the tissue with tetramethyl benzidine. The two types of vagal afferent endings in GI smooth muscle, namely intraganglionic laminar endings and intramuscular arrays, were surveyed separately, and their regional distributions were mapped. Changes in the nucleus of the solitary tract (NST) and dorsal motor nucleus of the vagus (DMNX) were assessed with cell counts and area measurements. Neonatal loss of the vagus innervating one side of the GI tract, with or without ganglionectomy, did not cause the unoperated vagus to sprout to the denervated side. In addition, removal of the projections to the one side of the target organ did not produce a reorganization of the projection maps of the unoperated vagus within its normal or ipsilateral wall of the GI tract. Although the regional patterns of the unoperated ipsilateral vagus were not affected, the packing densities of both types of afferents supplied by this trunk were moderately reduced. The DMNX of the vagotomized side displayed extensive (approximately 83%) neuronal loss; the DMNX on the unoperated side as well as the NST on both sides exhibited limited (approximately 20--25%) losses. The lack of a peripheral projection field reorganization -- except for a moderate down-regulation -- after complete unilateral denervation suggests that both the laterality and the afferent terminal phenotypes (or target tissues) of the vagus in the proximal GI tract are specified by postnatal day one in the rat. The present results, taken together with other observations, also suggest that three different combinations of signals orchestrate the commitments of vagal afferents respectively to (1) the side of the organ, (2) the region within the organ wall, and (3) the accessory and innervated tissues that complex with the fully differentiated ending.

Nerve cells associated with the endocrine pancreas in young mice: an ultrastructural analysis of the neuroinsular complex type I

The neuroinsular complex type 1 is composed of pancreatic endocrine islet cells and nerve cell bodies intrinsic to the islet. The details of the relation between nerve cells and between endocrine cells and nerve cells in the complex are unknown. Pancreata from newborn and 18-day-old mice were analysed by electron microscopy to establish the ultrastructural morphology of the neuroinsular complex. Immunohistochemical staining for protein gene-product 9.5 was also performed. The study showed that nerve cell bodies were closely associated to each other in the periphery of the islets with no connective tissue separating the cells. The nerve cells were closely associated to both beta-cells and alpha-cells. Direct intercellular contacts were observed between nerve cells and endocrine cells and between Schwann cells and endocrine cells. Varicose nerve endings were frequently observed in the neuroinsular complex. In the peripheral parts the varicosities were mostly being associated to the nerve cell bodies. The varicosities contained small clear or small clear and larger dense cored vesicles, suggesting cholinergic and peptidergic contents. The varicosities made specialized synaptic connections with adjacently located nerve cells. The study shows that the neuronal part of the neuroinsular complex is closely associated to the endocrine islet cells and that it is richly innervated, indicating an important regulatory function of the nerve cell component in the neuroinsular complex.

Plasticity in the enteric nervous system

Enteric ganglia can maintain integrated functions, such as the peristaltic reflex, in the absence of input from the central nervous system, which has a modulatory role. Several clinical and experimental observations suggest that homeostatic control of gut function in a changing environment may be achieved through adaptive changes occurring in the enteric ganglia. A distinctive feature of enteric ganglia, which may be crucial during the development of adaptive responses, is the vicinity of the final effector cells, which are an important source of mediators regulating cell growth. The aim of this review is to focus on the possible mechanisms underlying neuronal plasticity in the enteric nervous system and to consider approaches to the study of plasticity in this model. These include investigations of neuronal connectivity during development, adaptive mechanisms that maintain function after suppression of a specific neural input, and the possible occurrence of activity-dependent modifications of synaptic efficacy, which are thought to be important in storage of information in the brain. One of the applied aspects of the study of plasticity in the enteric nervous system is that knowledge of the underlying mechanisms may eventually enable us to develop strategies to correct neuronal alterations described in several diseases.