Role of vasoactive intestinal peptide and inflammatory mediators in enteric neuronal plasticity

Corticotropin releasing factor-distribution in rat intestine and role in neuroprotection

Aims of the present study were to describe the distribution of corticotropin releasing factor (CRF) immunoreactivity in rat small and large intestines, to quantify the percentage of CRF-immunoreactive (CRF-IR) enteric neurons, to reveal possible CRF immunoreactivity in cultured myenteric neurons from rat ileum and to examine if additions of CRF, urocortin 1 (Ucn1), CRF antagonist or vasoactive intestinal peptide (VIP) affect neuronal survival in vitro. Co-localization of CRF- and VIP-immunoreactivity was examined, as well as a possible interplay between CRF and VIP in neuroprotection. Further we wanted to elucidate if mast cells affect neuronal survival via CRF signaling. Networks of CRF-containing nerve cell bodies and fibers were detected in rat intestine. CRF-IR neurons contained to a high degree also VIP. A low number of cultured myenteric neurons was CRF-IR. CRF, Ucn1 or CRF-antagonist did not promote neuronal survival of cultured myenteric neurons, while VIP significantly enhanced neuronal survival. Simultaneous presence of CRF attenuated the VIP mediated increase in neuronal survival. Co-culturing neurons and mast cells resulted in a marked reduction in neuronal survival, not executed via CRF signaling pathways.

CONCLUSION

CRF is present in enteric neurons and counteracts the neuroprotective effect of VIP in vitro.

Quantitative and morphometric changes of subpopulations of myenteric neurons in swines with toxoplasmosis

The consequences of the infection caused by Toxoplasma gondii in myenteric neurons of the jejunum of swines reactive to NADH-diaphorase and NADPH-diaphorase were evaluated in this study. Ten 88-day-old mixed-breed swines (Pietrain and Wessex) were assigned into two groups: Control (n=5) and Experimental (n=5), which orally received 5000 sporulated oocysts from a genotype III T. gondii strain. After 30days, the animals were anesthetized, having part of their jejunum removed and stained with NADPH-diaphorase and NADH-diaphorase. NADPHd-p neurons (nitrergic) presented increase of the number of cells per ganglion and hypertrophy. The number of NADHd-p neurons (metabolic more active) and their nuclear area decreased.

Alterations of the myenteric plexus of the ileum and the descending colon caused by Toxoplasma gondii (genotype III)

Alterations caused by a genotype III strain of Toxoplasma gondii were assessed with respect to the number and the morphometry of the myenteric neurons in the terminal ileum and the descending colon. Eighteen rats were divided into four groups: Acute Control Group (ACG, n=4); Acute Experimental Group (AEG, n=4); Chronic Control Group (CCG, n=5) and Chronic Experimental Group (CEG, n=5). NaCl solution was administered through gavage to the animals in the ACG and CCG. Toxoplasma gondii tachyzoites (10(4)) from a genotype III strain were orally administered to the AEG and CEG. Acute Groups were died after 24 hours, and the Chronic Groups after 30 days. Neuronal loss was not observed in both organs. The neurons atrophied in the terminal ileum as the opposite occurred with the neurons at the descending colon during the chronic phase of infection. In the terminal ileum, the neurons atrophied during the chronic phase of the infection as no alteration was found during the acute phase. For the descending colon, the neurons became hypertrophic during the chronic infection in opposition to the atrophy found during the acute phase.

Mast cells reduce survival of myenteric neurons in culture

Mast cell-nerve interactions play a key role in intestinal inflammation and irritable bowel disease. Loss of enteric neurons has been reported in inflammatory conditions but the contribution of mast cells in this event is unknown. To study neuronal survival and plasticity of myenteric neurons in contact with mast cells a co-culture system using myenteric neurons from rat small intestine and peritoneal mast cells was set up. Dissociated myenteric neurons were cultured for 4 days before addition of mast cells isolated by peritoneal lavage. Neuronal survival and expression of vasoactive intestinal peptide (VIP) and nitric oxide synthase (NOS) were studied by immunocytochemistry and neuronal cell counting. Myenteric neurons cultured without mast cells were used to study the rate of neuronal survival after the addition of various mast cell mediators, proteinase-activated receptor(2) (PAR(2)) agonist, VIP or corticosteroid. A striking mast cell-induced neuronal cell death was found after co-culturing. It was counteracted by the addition of mast cell stabiliser doxantrazole, protease inhibitors, PAR(2) antagonist FSLLRY-amide, corticosteroid or VIP. In myenteric neurons cultured without mast cells the PAR(2) agonist SLIGRL-amide, prostaglandin D(2) and interleukin (IL) 6 reduced neuronal survival while histamine, serotonin, heparin, IL1beta and tumour necrosis factor alpha had no effect; corticosteroid and VIP enhanced neuronal survival. The relative numbers of VIP-, but not NOS-expressing myenteric neurons increased after co-culturing. Mast cell-induced neuronal cell death is suggested to be mediated via PAR(2) activation, IL6 and prostaglandin D(2). Corticosteroid and VIP are neuroprotective and able to prevent cell death of myenteric neurons in co-culture.

Immunohistochemical characterization and quantitative analysis of neurons in the myenteric plexus of the equine intestine

The present study was performed on whole-mount preparations to investigate the chemical neuroanatomy of the equine myenteric plexus throughout its distribution in the intestinal wall. The objective was to quantify neurons of the myenteric plexus, especially the predominant cholinergic and nitrergic subpopulations. Furthermore, we investigated the distribution of vasoactive intestinal polypeptide and the calcium-binding protein calretinin. Samples from different defined areas of the small intestine and the flexura pelvina were taken from 15 adult horses. After fixation and preparation of the tissue, immunofluorescence labeling was performed on free floating whole-mounts. Additionally, samples used for neuropeptide staining were incubated with colchicine to reveal the neuropeptide distribution within the neuronal soma. The evaluation was routinely accomplished using confocal laser-scanning microscopy. For quantitative and qualitative analysis, the pan-neuronal marker anti-HuC/D was applied in combination with the detection of the marker enzymes for cholinergic neurons and nitrergic nerve cells. Quantitative data revealed that the cholinergic subpopulation is larger than the nitrergic one in several different locations of the small intestine. On the contrary, the nitrergic neurons outnumber the cholinergic neurons in the flexura pelvina of the large colon. Furthermore, ganglia are more numerous in the small intestine compared with the large colon, but ganglion sizes are bigger in the large colon. However, comparison of the entire population of neurons in the different locations of the gut showed no difference. The present study adds further data on the chemoarchitecture of the myenteric plexus which might facilitate the understanding of several gastrointestinal disorders in the horse.

Postnatal and diet-dependent increases in enteric glial cells and VIP-containing neurones in preterm pigs

A mature enteric nervous system (ENS) is required to ensure a normal pattern of intestinal motility in order to regulate digestion after birth. We hypothesized that neuronal and glial components of the ENS would mature during the first postnatal days in preterm pigs that are a sensitive animal model of food intolerance and necrotizing enterocolitis (NEC). Stereological volume densities of the general neuronal population [assessed by betaIII-tubulin immunoreactivity (IR)] and subsets of neuronal (VIP-IR and nitrergic IR) and glial cells (GFAP-IR and S100-IR) were determined in the small intestine of newborn preterm piglets (93% gestation), after 3 days of receiving total parenteral nutrition (TPN) and after 3 days of TPN plus 2 days of enteral feeding with sow's colostrum or milk formula. Following TPN, VIP in the myenteric and inner submucous plexus and GFAP in the inner submucous plexus increased, while the relative volume of the total neuronal population remained constant. Introduction of enteral food induced variable degrees of food intolerance and NEC, especially after formula feeding, a diet that gave rise to a higher myenteric VIP and GFAP content in the inner submucous plexus than colostrum feeding. However, the ENS seemed unaffected by the presence of NEC-like intestinal lesions. Nevertheless, this study shows that the ENS is highly plastic during the first days after premature birth and adapts in an age- and diet-dependent manner. The observed postnatal adaptation in enteric VIP and GFAP may help to maintain intestinal homeostasis during suboptimal feeding regimens in preterm neonates.

Myenteric neurons of small intestine inhibit proliferation of smooth muscle cells cultured in vitro

AIM: To observe the inhibitory effect of myenteric neurons on the proliferation of cultured smooth muscle cells from rat colon.

METHODS: Circular smooth muscle cells from the colon of adult female Sprague-Dawley rats were cultured. When the cultured smooth muscle cells reached confluence, myenteric ganglia from the rat small intestine were dissociated and co-cultured with smooth muscle cells for 10 d. Immunofluorescent techniques were employed for double labeling of the preparations. The percentage of VIP-immunoreactive neurons was calculated based on the total neurons of Hu-immunoreactivity. Immunocytochemistry with anti-VIP and anti-smooth muscle a-actin was employed to reveal the relationship between the cultured myenteric neurons and smooth muscle cells.

RESULTS: After co-culture in vitro, the percentage of VIP-immunoreactive neurons was 27.3% ± 5.6%. The number of smooth muscle cells was markedly decreased within the innervation area of VIP-immunoreactive fibers.

CONCLUSION: VIP-ergic neurons modulate the proliferation of cultured smooth muscle cells.

Neurotrophic factors in autonomic nervous system plasticity and dysfunction

During development, neurotrophic factors are known to play important roles in regulating the survival of neurons in the autonomic nervous system (ANS) and the formation of their synaptic connectivity with their peripheral targets in the cardiovascular, digestive, and other organ systems. Emerging findings suggest that neurotrophic factors may also affect the functionality of the ANS during adult life and may, in part, mediate the effects of environmental factors such as exercise and dietary energy intake on ANS neurons and target cells. In this article, we describe the evidence that ANS neurons express receptors for multiple neurotrophic factors, and data suggesting that activation of those receptors can modify plasticity in the ANS. Neurotrophic factors that may regulate ANS function include brain-derived neurotrophic factor, nerve growth factor, insulin-like growth factors, and ciliary neurotrophic factor. The possibility that perturbed neurotrophic factor signaling is involved in the pathogenesis of ANS dysfunction in some neurological disorders is considered, together with implications for neurotrophic factor-based therapeutic interventions.

Decrease in binding for the neuropeptide VIP in response to marked inflammation of the mucosa in ulcerative colitis

The neuropeptide vasoactive intestinal peptide (VIP) is involved in the neuroimmunomodulation of the intestine. In the present study, specimens from the sigmoid colon of ulcerative colitis (UC) and non-UC patients were examined for immunohistochemistry and in vitro receptor autoradiography. Marked occurrence of VIP binding was observed in the mucosa. However, there were very low levels of binding in areas showing pronounced inflammation/derangement. The study shows that marked derangement of the mucosa leads to a distinct decrease in VIP binding. Thus, it is possible that a decrease in trophic and anti-inflammatory VIP effects occurs in areas exhibiting a very marked inflammation.

Vasoactive intestinal peptide rescues cultured rat myenteric neurons from lipopolysaccharide induced cell death

The role of the enteric nervous system in intestinal inflammation is not fully understood and the plethora of cellular activities concurrently ongoing in vivo renders intelligible studies difficult. In order to explore possible effects of bacterial lipopolysaccharide (LPS) on enteric neurons we utilised cultured myenteric neurons from rat small intestine. Exposure to LPS caused markedly reduced neuronal survival and increased neuronal expression of vasoactive intestinal peptide (VIP), while the expression of Toll-like receptor 4 (TLR4) was unchanged. TLR4 was expressed in approximately 35% of all myenteric neurons irrespective of if they were cultured in the presence or absence of LPS. In neurons cultured in medium, without LPS, 50% of all TLR4-immunoreactive neurons contained also VIP. Addition of LPS to the neuronal cultures markedly increased the proportion of TLR4-immunoreactive neurons also expressing VIP, while the proportion of TLR4 neurons devoid of VIP decreased. Simultaneous addition of LPS and VIP to the neuronal cultures resulted in a neuronal survival comparable to controls.

CONCLUSIONS

LPS recognition by myenteric neurons is mediated via TLR4 and causes neuronal cell death. Presence of VIP rescues the neurons from LPS-induced neurodegeneration.

The distribution and chemical coding of intramural neurons supplying the porcine stomach - the study on normal pigs and on animals suffering from swine dysentery

The present study was designed to investigate the expression of biologically active substances by intramural neurons supplying the stomach in normal (control) pigs and in pigs suffering from dysentery. Eight juvenile female pigs were used. Both dysenteric (n = 4; inoculated with Brachyspira hyodysenteriae) and control (n = 4) animals were deeply anaesthetized, transcardially perfused with buffered paraformalehyde, and tissue samples comprising all layers of the wall of the ventricular fundus were collected. The cryostat sections were processed for double-labelling immunofluorescence to study the distribution of the intramural nerve structures (visualized with antibodies against protein gene-product 9.5) and their chemical coding using antibodies against vesicular acetylcholine (ACh) transporter (VAChT), nitric oxide synthase (NOS), galanin (GAL), vasoactive intestinal polypeptide (VIP), somatostatin (SOM), Leu(5)-enkephalin (LENK), substance P (SP) and calcitonin gene-related peptide (CGRP). In both inner and outer submucosal plexuses of the control pigs, the majority of neurons were SP (55% and 58%, respectively)- or VAChT (54%)-positive. Many neurons stained also for CGRP (43 and 45%) or GAL (20% and 18%) and solitary perikarya were NOS-, SOM- or VIP-positive. The myenteric plexus neurons stained for NOS (20%), VAChT (15%), GAL (10%), VIP (7%), SP (6%) or CGRP (solitary neurons), but they were SOM-negative. No intramural neurons immunoreactive to LENK were found. The most remarkable difference in the chemical coding of enteric neurons between the control and dysenteric pigs was a very increased number of GAL- and VAChT-positive nerve cells (up to 61% and 85%, respectively) in submucosal plexuses of the infected animals. The present results suggest that GAL and ACh have a specific role in local neural circuits of the inflamed porcine stomach in the course of swine dysentery.

Enteric neural pathways mediate the anti-inflammatory actions of glucagon-like peptide 2

Glucagon-like peptide-2 (GLP-2) is an important regulator of nutritional absorptive capacity with anti-inflammatory actions. We hypothesized that GLP-2 reduces intestinal mucosal inflammation by activation of vasoactive intestinal polypeptide (VIP) neurons of the submucosal plexus. Ileitis or colitis was induced in rats by injection of trinitrobenzene sulfonic acid (TNBS), or colitis was induced by administration of dextran sodium sulfate (DSS) in drinking water. Subsets of animals received (1-33)-GLP-2 (50 mug/kg sc bid) either immediately or 2 days after the establishment of inflammation and were followed for 3-5 days. The involvement of VIP neurons was assessed by concomitant administration of GLP-2 and the VIP antagonist [Lys(1)-Pro(2,5)-Arg(3,4)-Tyr(6)]VIP and by immunohistochemical labeling of GLP-2-activated neurons. In all models, GLP-2 treatment, whether given immediately or delayed until inflammation was established, resulted in significant improvements in animal weights, mucosal inflammation indices (myeloperoxidase levels, histological mucosal scores), and reduced levels of inflammatory cytokines (IFN-gamma, TNF-alpha, IL-1beta) and inducible nitric oxide synthase, with increased levels of IL-10 in TNBS ileitis and DSS colitis. Reduced rates of crypt cell proliferation and of apoptosis within crypts in inflamed tissues were also noted with GLP-2 treatment. These effects were abolished with coadministration of GLP-2 and the VIP antagonist. GLP-2 was shown to activate neurons and to increase the number of cells expressing VIP in the submucosal plexus of the ileum. These findings suggest that GLP-2 acts as an anti-inflammatory agent through activation of enteric VIP neurons, independent of proliferative effects. They support further studies to examine the role of neural signaling in the regulation of intestinal inflammation.

Role of VIP and Substance P in NANC Innervation in the Longitudinal Smooth Muscle of the Rat Jejunum—Influence of Extrinsic Denervation

BACKGROUND

This study was designed to determine changes in nonadrenergic, noncholinergic (NANC) neurotransmission mediated by Vasoactive Intestinal Polypeptide (VIP) and Substance P after small bowel transplantation (SBT).

MATERIALS AND METHODS

Six groups of rats (n > or = 6 per group) were studied: naïve controls (NC); 1 wk after anesthesia/sham celiotomy (SC-1); 1 or 8 wk after jejunal and ileal transection/reanastomosis (TA-1, TA-8), or syngeneic, orthotopic SBT (SBT-1, SBT-8). Jejunal longitudinal muscle strips were studied under NANC-conditions for spontaneous contractile activity, response to exogenous VIP and Substance P, and electrical field stimulation (EFS).

RESULTS

Spontaneous activity did not differ between the six groups. VIP inhibited contractile activity in all groups 1 wk postoperatively (P < 0.05), which was prevented by the NO synthase inhibitor L-N(G)-nitro arginine (L-NNA). In contrast, VIP had no effect in the other groups. Precontraction with Substance P exposed an inhibitory effect of VIP in all groups (P < 0.05 each). Substance P increased contractile activity in all groups, but to a lesser extent in SBT-8 compared with NC, TA-8, and SBT-1 (P < 0.05). The inhibitory effect of EFS at 6 Hz was prevented by L-NNA in NC and TA-8; addition of the VIP antagonist ([D-p-Cl-Phe(6), Leu(17)]-VIP) increased contractile activity in NC, but not in TA-8 and SBT-8. The Substance P antagonist ([D-Pro(2), D-Trp(7,9)]-Substance P) decreased contractile activity during EFS at 50 Hz in NC and SBT-8.

CONCLUSIONS

SBT decreased response to exogenous Substance P, although release of endogenous Substance P (EFS) is preserved. Changes in VIP signaling are acute and reversible and not caused by effects of SBT.

Unmyelinated visceral afferents exhibit frequency dependent action potential broadening while myelinated visceral afferents do not

Sensory information arising from visceral organ systems is encoded into action potential trains that propagate along afferent fibers to target nuclei in the central nervous system. These information streams range from tight patterns of action potentials that are well synchronized with the sensory transduction event to irregular, patternless discharge with no clear correlation to the sensory input. In general terms these afferent pathways can be divided into unmyelinated and myelinated fiber types. Our laboratory has a long standing interest in the functional differences between these two types of afferents in terms of the preprocessing of sensory information into action potential trains (synchrony, frequency, duration, etc.), the reflexogenic consequences of this sensory input to the central nervous system and the ionic channels that give rise to the electrophysiological properties of these unique cell types. The aim of this study was to determine whether there were any functional differences in the somatic action potential characteristics of unmyelinated and myelinated vagal afferents in response to different rates of sensory nerve stimulation. Our results showed that activity and frequency-dependent widening of the somatic action potential was quite prominent in unmyelinated but not myelinated vagal afferents. Spike broadening often leads to increased influx of Ca(2+) ions that has been associated with a diverse range of modulatory mechanisms both at the cell body and central synaptic terminations (e.g. increased neurotransmitter release.) We conclude that our observations are indicative of fundamentally different mechanisms for neural integration of sensory information arising from unmyelinated and myelinated vagal afferents.

Alterations of neuropeptides in the human gut during peritonitis

BACKGROUND AND AIMS

Gastrointestinal motility is reduced during sepsis but the pathomechanism involved is poorly understood. We investigated the expression of substance P (SP) and vasoactive intestinal peptide (VIP) in the myenteric plexus during peritonitis in human small bowel.

MATERIALS AND METHODS

Tissue samples of the small bowel were gathered from healthy patients and from patients with peritonitis. Immunohistochemistry for myeloperoxidase (MPO), SP, and VIP was performed in whole mount sections. To determine the level of inflammation, MPO-positive cells were counted in the circular muscle layer. SP and VIP immunoreactivity was analyzed in myenteric plexus neurons. The area of positive immunoreactivity for either neuropeptide within the plexus was analyzed and set in relation to the total area of the plexus and consecutively expressed as percentage.

RESULTS

During peritonitis, MPO-positive cells significantly increased by approximately fourfold as compared to healthy tissue. The immunoreactivity for SP was significantly reduced by approximately 80% in myenteric plexus neurons during peritonitis. In contrast, the immunoreactivity for VIP significantly increased by nearly twofold during peritonitis.

CONCLUSIONS

During peritonitis, the inflammatory reaction within the gut is increased. The neuropeptide expression in myenteric plexus neurons was observed as shifting towards increased expression of VIP, known to inhibit intestinal motility, and towards decreased expression of the prokinetic neuropeptide SP.

Survival and neurotransmitter plasticity in cultured rat colonic myenteric neurons

The enteric nervous system is of great importance for maintenance and proper function of the gastrointestinal tract. The aim of this study was to quantify myenteric neuronal subpopulations expressing calcitonin gene-related peptide (CGRP), galanin, neuropeptide Y (NPY), somatostatin, vasoactive intestinal peptide (VIP) and nitric oxide synthase (NOS) in rat colon in vivo and after culturing. Further we investigated if culturing in the presence of CGRP, galanin, VIP, S-nitroso-N-acetyl-D,L-penicillamine (SNAP, a NO donor) or N-nitro-L-arginine methyl ester (L-NAME, a NOS inhibitor) affect neuronal survival. After 4 days of culturing the proportions of neurons expressing CGRP, NPY, somatostatin or VIP increased as compared to in vivo, while the proportions of neurons expressing galanin or NOS did not change. Neuronal survival was unaffected after culturing in media enriched with CGRP, galanin, VIP, SNAP or L-NAME. Neither did addition of CGRP, galanin nor VIP to the cultures affect the relative numbers of neurons expressing CGRP, galanin or VIP respectively. Addition of SNAP or L-NAME did not change the percentage of neurons expressing NOS. In conclusion, cultured rat colonic myenteric neurons increase their expression of CGRP, NPY, somatostatin and VIP, suggesting that these neuropeptides are of importance for neuronal survival.

CART in the enteric nervous system

The expression, distribution, origin, projections, chemical coding and functions of cocaine and amphetamine-regulated transcript (CART) in the gastro-intestinal tract are reviewed. CART is extensively expressed in the enteric nervous system. Except from being a possible modulator of NO induced intestinal relaxation CART does not seem to play any pivotal role in intestinal motility. Accumulating evidence suggest CART to be neuroprotective, involved in survival and maintenance of enteric neurons. CART expression increases in atrophic intestine thus suggesting a role of CART in intestinal adaptation. In rat antral mucosa CART is expressed in gastrin cells indicating a hormonal role of gastric CART.

Enteric neuroplasticity evoked by inflammation

Neuroplastic changes in the enteric nervous system (ENS) may be observed in physiological states, such as development and aging, or occur as a consequence of different pathological conditions, ranging from enteric neuropathies (e.g., Hirschsprung's disease) to intestinal (e.g., inflammatory bowel disease) or extra-intestinal diseases (e.g., Parkinson's disease). Studying ENS plasticity may help to elucidate the pathophysiology of several diseases and have a bearing on the development of new pharmacological interventions. In the present review, we would like to focus on neuronal plasticity evoked by gastrointestinal inflammation occurring in inflammatory bowel disease and in a subset of patients with severe derangement of gut motility due to an enteric neuropathy characterized by an inflammatory infiltrate of the enteric plexuses. Major features of neuroplasticity within the enteric microenvironment encompass structural abnormalities ranging from nerve re-arrangement (e.g., hypertrophy and hyperplasia) to degeneration and loss of enteric ganglion cells; altered synthesis, content and release of neurotransmitters as well as up- or down-regulation of receptor systems; gastrointestinal dysfunction characterized by sensory-motor and secretory impairment of the gut. Interestingly, neuronal changes may also occur in segments of the gastrointestinal tract remote from the site of the original inflammation, e.g. the ileum may show neuroplastic changes during colitis. Sometimes, the inflamed site may even be outside the gut. Among potential mechanisms underlying ENS plasticity, neurotrophins and enteric glia deserve special attention. A better comprehension of ENS plasticity during inflammation could be instrumental to develop new therapeutic options for patients with IBD and inflammatory enteric neuropathies.

Three-dimensional slice cultures from murine fetal gut for investigations of the enteric nervous system

Three-dimensional intestinal cultures offer new possibilities for the examination of growth potential, analysis of time specific gene expression, and spatial cellular arrangement of enteric nervous system in an organotypical environment. We present an easy to produce in vitro model of the enteric nervous system for analysis and manipulation of cellular differentiation processes. Slice cultures of murine fetal colon were cultured on membrane inserts for up to 2 weeks without loss of autonomous contractility. After slice preparation, cultured tissue reorganized within the first days in vitro. Afterward, the culture possessed more than 35 cell layers, including high prismatic epithelial cells, smooth muscle cells, glial cells, and neurons analyzed by immunohistochemistry. The contraction frequency of intestinal slice culture could be modulated by the neurotransmitter serotonin and the sodium channel blocker tetrodotoxin. Coculture experiments with cultured neurospheres isolated from enhanced green fluorescent protein (eGFP) transgenic mice demonstrated that differentiating eGFP-positive neurons were integrated into the intestinal tissue culture. This slice culture model of enteric nervous system proved to be useful for studying cell-cell interactions, cellular signaling, and cell differentiation processes in a three-dimensional cell arrangement.

Morphology of VIP/nNOS-immunoreactive myenteric neurons in the human gut

In this study, we characterized human myenteric neurons co-immunoreactive for neuronal nitric oxide synthase (nNOS) and vasoactive intestinal peptide (VIP) by their morphology and their proportion as related to the putative entire myenteric neuronal population. Nine wholemounts (small and large intestinal samples) from nine patients were triple-stained for VIP, neurofilaments (NF) and nNOS. Most neurons immunoreactive for all three markers displayed radially emanating, partly branching dendrites with spiny endings. These neurons were called spiny neurons. The spiny character of their dendrites was more pronounced in the small intestinal specimens and differed markedly from enkephalinergic stubby neurons described earlier. Exclusively in the duodenum, some neurons displayed prominent main dendrites with spiny side branches. Of the axons which could be followed from the ganglion of origin within primary strands of the myenteric plexus beyond the next ganglion (70 out of 140 traced neurons), 94.3% run anally and 5.7% orally. Very few neurons reactive for both VIP and nNOS could not be morphologically classified due to weak or absent NF-immunoreactivity. Another six wholemounts were triple-stained for VIP, nNOS and Hu proteins (HU). The proportion of VIP/nNOS-coreactive neurons in relation to the number of HU-reactive neurons was between 5.8 and 11.5% in the small and between 10.6 and 17.5% in the large intestinal specimens. We conclude that human myenteric spiny neurons co-immunoreactive for VIP and nNOS represent either inhibitory motor or descending interneurons.

Lipopolysaccharide induces cell death in cultured porcine myenteric neurons

Enteric bacteria execute, via lipopolysaccharide (LPS), a pathogenic role in intestinal inflammation. The effects of LPS on survival and neurotransmitter expression in cultured porcine myenteric neurons were investigated. Myenteric neurons were isolated and cultured for 6 days in medium, in LPS (100 ng/ml) with or without alpha-ketoglutarate or the nitric oxide synthase (NOS) inhibitor L-NAME, in alpha-ketoglutarate or in the NO donor SNAP. Neuronal survival and expression of vasoactive intestinal peptide (VIP) and NOS were evaluated by immunocytochemistry. Addition of LPS significantly decreased neuronal survival; only 40% survived, compared to controls run in parallel. The LPS-induced neurotoxic effect was not counteracted by the simultaneous presence of alpha-ketoglutarate or L-NAME. Either SNAP or alpha-ketoglutarate influenced neuronal survival. Culturing, particularly in the presence of LPS, markedly increased the proportion of VIP-immunoreactive neurons; NOS-immunoreactive neurons were unchanged. The reported LPS-induced neurotoxicity indicates loss of enteric neurons as a consequence of intestinal inflammation.

Effects of vasoactive intestinal peptide and galanin on survival of cultured porcine myenteric neurons

Enteric neuronal plasticity is probably fundamental in order to withstand injury or changes in intestinal activity. The role of the neuropeptides in neuroprotection is still enigmatic. The expression of galanin and vasoactive intestinal peptide (VIP) and the effects of the two peptides on survival of small intestinal porcine myenteric neurons cultured for 6 days were studied. Immunocytochemistry and cell counting were used to evaluate the numbers of surviving neurons and their expression of galanin and VIP. To reflect the in vivo situation, cryostat sections of porcine mid-jejunum were used. A concentration-dependent and marked increase in neuronal survival was noted when neurons were grown in the presence of VIP (10(-8)-10(-6) M), whereas addition of galanin (10(-8)-10(-6) M) slightly decreased neuronal survival. A dramatic increase in the proportions of myenteric neurons containing VIP or galanin immunoreactivity occurred during culturing. The presence of VIP further increased the number of galanin-expressing neurons. A majority of the galanin-immunoreactive neurons lacked VIP, while all VIP-immunoreactive neurons contained galanin. In conclusion, culturing porcine myenteric neurons in the presence of VIP increases, while the presence of galanin reduces, survival. Culturing significantly increased the proportion of neurons expressing VIP and/or galanin; the presence of VIP further increased the number of galanin-expressing neurons.