Extrinsic Denervation Research Articles

Role of Alpha-2 Adrenoceptors in Regulation of Giant Migrating Contractions and Defecation in Conscious Dogs

The aim was to investigate the effects of alpha(2)-adrenoceptor antagonist yohimbine on colonic motility and defecation. The effects of yohimbine (0.5, 1.0, and 3.0 mg/kg) on colonic motility and defecation were studied in neurally intact dogs (N=6), dogs with extrinsic denervation of the ileocolon (N=4), and dogs with enterically isolated ileocolnic loops (N=5) equipped with strain gauge force transducers on the ileocolon. The effects of yohimbine on colonic motility and defecation were also studied in the presence of various antagonists (atropine, hexamethonium, ondansetron, FK224, and naloxone). Yohimbine evoked giant migrating contractions and defecation in a dose-independent manner in neurally intact dogs. These stimulatory effects of yohimbine were abolished by atropine and hexamethonium. In dogs with extrinsic denervation, yohimbine induced giant migrating contractions in the colon but did not stimulate defecation. In dogs with ileocolonic loops, yohimbine induced colonic motor complexes but not giant migrating contractions in the enterically isolated colon. These results indicate that alpha(2)-adrenoceptors in the peripheral nervous system regulate giant migrating contractions by controlling the release of acetylcholine, while those in the central nervous system must be important in the regulation of defecation.

24: Effect of extrinsic denervation on NANC innervation with substance P and VIP in longitudinal smooth muscle of the rat jejunum

Obligate extrinsic denervation may contribute to enteric motor dysfunction of the transplanted gut. We showed that chronic extrinsic denervation decreased response to exogenous Substance P (Sub P) and abdominal operations transiently increased sensitivity to exogenous Vasoactive intestinal polypeptide (VIP) (Neurogastroenterol Motil 18:779, 2006). Aim: To determine effects of extrinsic denervation mediated by endogenous release of the nonadrenergic, noncholinergic (NANC) neurotransmitters Sub P and VIP. Methods: Jejunal longitudinal muscle strips were obtained from 3 groups of Lewis rats (n ≥ 6/group): NC (naive controls); 8 wks after jejunal and ileal transaction/anastomosis to disrupt enteric myoneuronal continuity (T/A-8), and after syngeneic (no immune rejection) jejunoileal transplantation (SBT-8). Endogenously released Sub P and VIP were studied using electrical field stimulation (EFS; voltage 10V, pulse width 0.5msec, duration 10sec) at 50Hz (excitatory) and 6Hz (inhibitory) frequencies under NANC-conditions (atropine, propranolol, phentolamine) with and without Sub P antagonist ([D-Pro2,D-Trp7,9]-Sub P), VIP antagonist ([D-p-Cl-Phe6,Leu17]-VIP), and the NO-synthase inhibitor L-NNA (L-NG-nitro arginine). Data are Mean±SEM in % of baseline contractile activity or seconds of inhibition. Results: EFS at 50 Hz increased contractile activity in NC but not in T/A-8 and SBT-8 and the Sub P antagonist blocked contractile activity during EFS at 50Hz in NC (146±18 vs. 85±22%; (without vs. with Sub P antagonist); p=0.04), SBT-8 (92±24 vs. 33±14%; p=0.005), but not in T/A-8 (98±43vs. 95±40 %; p=0.92). VIP antagonist had no effect. Inhibition caused by EFS at 50Hz was of longer duration in SBT-8 vs. NC (5.1±0.7 vs. 2.9±0.2sec; p<0.02). Neither Sub P nor VIP antagonist altered duration of inhibition. EFS at 6Hz inhibited contractile activity markedly in all groups (NC: 46±12; T/A-8: 23±12; SBT-8: 29±11%; p<0.02); this inhibition was reversed by L-NNA in all groups (NC: 103±11; T/A-8: 77±22; SBT-8: 66±29%; p<0.02), but not by the VIP antagonist. In the presence of both L-NNA and VIP antagonist, contractile activity at 6Hz was greater in NC compared to T/A-8 and SBT-8 (154±24 vs. 66±18 and 52±20%; p<0.02), while the duration of inhibition was longer in SBT-8 vs. NC (7.2±.0.6 vs. 4.4±0.3sec; p<0.02). Conclusions: Our data suggest that the chronic effects of denervation as induced by T/A and SBT may blunt the release of excitatory NANC neurotransmitters; Sub P release after SBT is preserved. In contrast, changes in VIP signaling are acute and reversible. Changes in the NANC inhibitory response after extrinsic denervation appear to be mediated via NO rather than VIP. These effects to extrinsic denervation may alter enteric motor function after small bowel transplantation.

Postprandial Augmentation of Absorption of Water and Electrolytes in Jejunum Is Neurally Modulated: Implications for Segmental Small Bowel Transplantation

Postprandial augmentation of absorption of water and electrolytes is believed to occur in the jejunum. Neural mechanisms of control, however, have not been studied in the in situ jejunum or in the transplanted bowel. The aim of this study was to determine if postprandial augmentation of absorption occurs in the in situ jejunum and to evaluate neural mechanisms controlling postprandial jejunal absorption. Based on our previous work, we hypothesized that postprandial augmentation of absorption does not occur in the jejunum in situ and that extrinsic denervation of the jejunum is associated with decreased postprandial absorption. Absorption was studied in an 80 cm, in situ jejunal segment in six dogs by using an isosmolar electrolyte solution alone, or with 80 mmol/L glucose before and after jejunal transection to disrupt intrinsic neural continuity of the study segment with the remaining gut. Net absorptive fluxes of water and electrolytes were measured in the fasted state and after a 400-kcal meal. Another six dogs were studied 3 weeks after our validated model of extrinsic denervation of jejunoileum; identical fasting and postprandial absorptive states were evaluated. Postprandial augmentation of absorption of water and electrolytes did occur in the jejunum (P < 0.03) both in the absence and in the presence of intraluminal glucose. After intrinsic neural transection or extrinsic denervation, no postprandial augmentation of absorption occurred, with or without glucose. Postprandial augmentation of absorption of water and electrolytes occurs in the in situ jejunum. Disrupting intrinsic neural continuity or extrinsic denervation (as after intestinal transplantation) abolishes postprandial augmentation.

Physiological Modulation of Intestinal Motility by Enteric Dopaminergic Neurons and the D2Receptor: Analysis of Dopamine Receptor Expression, Location, Development, and Function in Wild-Type and Knock-Out Mice

Dopaminergic neurons are present in both plexuses of the murine bowel and are upregulated after extrinsic denervation but play unknown roles in enteric nervous system (ENS) physiology. Transcripts encoding dopamine (DA) receptors D1-D5 were analyzed by reverse transcription-PCR in stomach approximately duodenum approximately ileum approximately proximal > > distal colon. Dissected muscle and myenteric plexus contained transcripts encoding D1-D3 and D5, whereas mucosa contained D1 and D3-D5. D1-D5 expression began in fetal gut [embryonic day 10 (E10)], before the appearance of neurons (E12), and was sustained without developmental regulation through postnatal day 1. In situ hybridization revealed that subsets of submucosal and myenteric neurons contained mRNA encoding D2 or D3. Immunoblots confirmed that D1, D2, and D5 receptor proteins were present from stomach through distal colon. Subsets of submucosal and myenteric neurons were also D1, D2, or D3 immunoreactive. When double labeled by in situ hybridization, these neurons contained mRNA encoding the respective receptors. Total gastrointestinal transit time (TGTT) and colonic transit time (CTT) were measured in mice lacking D2, D3, or D2 plus D3. Both TGTT and CTT were decreased significantly (motility increased) in D2 and D2 plus D3, but not D3, knock-out animals. Mice lacking D2 and D2 plus D3 but not D3 were smaller than wild-type littermates, yet ate significantly more and had greater stool frequency, water content, and mass. Because motility is abnormal when D2 is absent, the net inhibitory DA effect on motility is physiologically significant. The early expression of DA receptors is also consistent with the possibility that DA affects ENS development.

Induction and recovery of colonic motility/defecatory disorders after extrinsic denervation of the colon and rectum in rats

Anterior resection for rectal disease is associated with extrinsic autonomic denervation of the neorectum, which may influence the myenteric plexus, and subsequently the motility/defecatory status after operation. A rat model with denervated neorectum was constructed. Colonic contractile activity in vivo, the amount of generic neuron marker (PGP 9.5) and nitric oxide synthase (NOS) were measured periodically. The responses of the muscle strip in each period to electrical field stimulation were evaluated using various neurotransmitters. In rats with denervated neorectum, giant migrating contractions (GMCs) of the distal colon, the number of fecal lumps per day and their small size, significantly increased in the early phase postoperatively, although both recovered in the late-phase period. The contractile response of the muscle strip of the denervated colon to acetylcholine was reduced throughout the period; however, contraction of the denervated colon under the addition of NO inhibitor (l-NAME) was enhanced significantly in the late-phase period, and recovered to the control level by atropine. Neuronal NOS, but not PGP 9.5 concentration, in the myenteric plexus at the distal denervated colon, significantly increased in the late-phase period. None of the above items differed from the control at other colonic portions throughout the period. Extrinsic autonomic denervation causes abnormal hyper-motility in the neorectum, which may be associated with multiple evacuations in the early phase postoperatively. Increased acetylcholine and the subsequent increase of neuronal NOS in the myenteric plexus may be an adaptive mechanism to compensate for such abnormal colonic motility after extrinsic denervation.

Acute denervation alters the epithelial response to adrenoceptor activation through an increase in α1‐adrenoceptor expression on villus enterocytes

Loss of sympathetic input due to intestinal denervation results in hypersensitivity and increased intestinal secretion. It is unknown whether denervation-induced alterations in intestinal epithelial physiology are the result of changes in adrenoceptors on enterocytes (ENTs). The purpose of this study was to examine adrenoceptor distribution and pharmacology on small intestinal ENTs following acute intestinal denervation. Lewis rats underwent small bowel transplantation (SBT) or sham operation and proximal small intestinal segments were harvested 1, 2 and 4 weeks postoperatively. Intestinal electrolyte movement was assessed using short-circuit current (Isc) measurements of stripped epithelial sheets following stimulation with phenylephrine (PE), an alpha(1)-adrenoceptor agonist. The presence of adrenoceptor subtypes on separated villus and crypt ENTs was assessed using flow cytometry. Alpha(1)-adrenoceptors were found on approximately 27% of jejunal villus ENTs, but not crypt ENTs, following acute extrinsic denervation. ENTs from the Lewis rat have few beta-adrenoceptors. Alpha(1)-adrenoceptor stimulation of acutely denervated intestinal epithelial sheets decreased Isc by -13.45%. This effect was mediated by a reduction in chloride (Cl(-)) secretion; the absence of Cl(-) reversed the Isc to +13.79%. In conclusion, loss of sympathetic innervation to the gastrointestinal epithelium causes acute upregulation of alpha(1)-adrenoceptors on villus ENTs, leading to inhibition of Cl(-) secretion at the villus tip. The increase in adrenoceptors may reflect a compensatory mechanism to combat the increased secretory state of the bowel due to the loss of the sympathetic innervation and tonic control over intestinal secretion.

Inhibition by nitric oxide and nonadrenergic, noncholinergic (NANC) nerves is preserved in a canine model of extrinsic denervation: Implications for small bowel transplantation

Small bowel transplantation (SBT) is complicated by changes in graft motility, especially in the early postoperative period. This dysmotility may be related in part to the extrinsic denervation necessitated by the procedure, but specific neurotransmitter response to SBT is incompletely understood. The aim of this study was to evaluate the role of nitric oxide and nonadrenergic, noncholinergic (NANC) enteric neural input in the nonimmunologic etiology of the dysmotility seen after SBT. A technique of jejunoileal extrinsic denervation (without disruption of mesenteric vascular supply) was used as a model of canine jejunoileal autotransplantation to avoid potential confounding factors such as ischemia-reperfusion and postallotransplant immunologic effects. Longitudinal smooth muscle strips from ileum and jejunum were studied with in vitro tissue chamber methodology at 0, 2, and 8 weeks after this experimental model to explore early and late effects of denervation. Effects of exogenous nitric oxide (NO) and electric field stimulation (EFS), which releases native, endogenous enteric neurotransmitters) were evaluated in neurally intact control dogs and those undergoing extrinsic denervation. Exogenous NO caused a dose-dependent inhibition of spontaneous contractile activity and in some muscle strips a decrease in basal tone in both groups of dogs. These effects were unchanged by neural blockade with tetrodotoxin and preserved after extrinsic denervation. EFS produced inhibition of spontaneous contractile activity in ileum and a complex, inconsistent response in jejunum. The response to EFS in both ileum and jejunum was unchanged after extrinsic denervation. Nitric oxide inhibits contractile activity in canine longitudinal muscle of small bowel. Motility changes seen after this large animal model of extrinsic denervation are not caused by changes in NO or NANC neural function. The variability observed between different segments of intestine is important to consider in the context of SBT.

Electroacupuncture at ST-36 accelerates colonic motility and transit in freely moving conscious rats

Acupuncture is useful for functional bowel diseases, such as constipation and diarrhea. However, the mechanisms of beneficial effects of acupuncture on colonic function have scarcely ever been investigated. We tested the hypothesis that electroacupuncture (EA) at ST-36 stimulates colonic motility and transit via a parasympathetic pathway in conscious rats. Hook-shaped needles were inserted at bilateral ST-36 (lower limb) or BL-21 (back) and electrically stimulated at 10 Hz for 20 min. We also studied c-Fos expression in response to EA at ST-36 in Barrington's nucleus of the pons. EA at ST-36, but not BL-21, significantly increased the amplitude of motility at the distal colon. The calculated motility index of the distal colon increased to 132 +/- 9.9% of basal levels (n = 14, P < 0.05). In contrast, EA at ST-36 had no stimulatory effects in the proximal colon. EA at ST-36 significantly accelerated colonic transit [geometric center (GC) = 6.76 +/- 0.42, n = 9, P < 0.001] compared with EA at BL-21 (GC = 5.23 +/- 0.39, n = 7). The stimulatory effect of EA at ST-36 on colonic motility and transit was abolished by pretreatment with atropine. EA-induced acceleration of colonic transit was also abolished by extrinsic nerve denervation of the distal colon (GC = 4.69 +/- 0.33, n = 6). The number of c-Fos-immunopositive cells at Barrington's nucleus significantly increased in response to EA at ST-36 to 8.1 +/- 1.1 cells/section compared with that of controls (2.4 +/- 0.5 cells/section, n = 3, P < 0.01). It is concluded that EA at ST-36 stimulates distal colonic motility and accelerates colonic transit via a sacral parasympathetic efferent pathway (pelvic nerve). Barrington's nucleus plays an important role in mediating EA-induced distal colonic motility in conscious rats.

Extrinsic denervation alters postprandial absorption of glucose and glutamine in the ileum: implications for small bowel transplantation.

In the postprandial period, augmentation of absorption of water, electrolytes, and taurocholate is believed to occur in the ileum. The role of extrinsic innervation in this postprandial augmentation has not been well studied and may be an important concept in small bowel transplantation. Our aim was to investigate extrinsic neural mechanisms mediating postprandial absorptive patterns. The study hypothesis was that postprandial augmentation of absorption in the ileum is blunted in transplanted (extrinsically denervated) bowel. Ileal absorption was studied in six dogs with an 80-cm in situ ileal segment via a triple-lumen perfusion technique using an iso-osmolar, ileal-like electrolyte solution alone and containing either glucose 2.5 mM, glutamine 2.5 mM, oleic acid 5 mM, or taurocholate 5 mM. Net absorptive fluxes of each substrate, as well as water and electrolytes, were measured in both the fasted state and after a 400-Kcal mixed meal before and at 2 and 12 weeks after our validated model of complete extrinsic denervation of the jejunoileum. At baseline, there were no differences in absorption of water, electrolytes, or any nutrient postprandially compared with the fasted state. Two weeks after extrinsic denervation, absorption of glucose at both 1 and 2 hours postprandially was decreased compared with absorption during fasting. Glutamine absorption was also decreased at 2 hours postprandially. At 12 weeks after extrinsic denervation, net postprandial absorption of glucose and glutamine returned toward normal and was not different from fasting absorption. No differences were noted in postprandial absorption of oleic acid or taurocholate at any time point. Decreases in absorption of nutrients postprandially after extrinsic denervation (which is necessitated by small bowel transplantation) may play an important role in post-transplant enteric absorptive dysfunction. The previously described postprandial augmentation in net absorption may be a function of enterically isolated gut and does not appear to occur in the in situ ileum.

Octreotide in the treatment of small intestinal dysfunction after a model of jejunoileal autotransplantation in the pig.

Enteric denervation and ischemic injury contribute to dysmotility and malabsorption following intestinal transplantation. We hypothesized that, by prolonging bowel transit and by ameliorating dysmotility, octreotide (OT) may improve cholesterol and bile acid absorption after jejunoileal autotransplantation. Seventeen pigs with fixed food intake underwent either jejunal transection (n = 6), or jejunoileal autotransplantation, which includes extrinsic autonomic denervation, lymphatic interruption, and in situ cold ischemia (n = 11). Five randomly chosen autotransplanted animals received intramuscular long-acting OT (10 mg) once a month. After 8 weeks, weight gain, intestinal transit time, fecal excretion of bile acids and cholesterol, and fractional cholesterol absorption were determined. Jejunal and ileal specimens were collected for histochemical analyses. Plasma cholestenol and campesterol, respective markers of cholesterol synthesis and absorption, were measured after 2 and 8 weeks. Following jejunoileal autotransplantation, octreotide treatment significantly increased the median intestinal transit time from 22.8 to 24.8 h and the median body weight gain from 166 to 187%. Jejunoileal autotransplantation significantly increased fecal bile acid excretion, plasma cholestenol, and bacterially modified fecal neutral sterols, and decreased absorption of cholesterol, plasma campesterol, and biliary cholesterol secretion. These changes were not significantly modified by OT treatment. Bowel wall and mucosal structure, mucosal proliferation, and weight or microvilli showed no statistically significant differences between autotransplanted animals with or without OT treatment. Findings of the present study suggest that octreotide prolongs intestinal transit time and improves weight gain after jejunoileal autotransplantation, but has no effect on malabsorption of cholesterol and bile acids.

Growth hormone selectively improves intestinal cholesterol absorption after jejunoileal autotransplantation in pigs

Background/Purpose Small bowel transplantation impairs enteric function and causes malabsorption of cholesterol and bile acids. Growth hormone stimulates intestinal absorptive function. The authors hypothesized that long-term growth hormone therapy could improve absorption of bile acids and cholesterol after autotransplantation of the jejunoileum. Methods Sixteen pigs with similar food, cholesterol, and fat intake underwent either sham laparotomy or a model of jejunoileal autotransplantation, including extrinsic autonomic denervation, lymphatic interruption, and in situ cold ischemia. Five randomly chosen autotransplanted animals received daily growth hormone treatment for 8 weeks. Serum lipids, absorption, and excretion of cholesterol, bile acids, and fat were determined after 8 weeks. Mucosal morphometrics, proliferation, and enzyme activities were determined. Plasma cholesterol precursors and plant sterols, respective markers of cholesterol synthesis and absorption, were measured after 2 and 8 weeks. Results After jejunoileal autotransplantation, growth hormone treatment significantly increased body weight gain, cholesterol absorption efficiency from 45.1% to 62.1%, plasma campesterol to cholesterol proportions, and biliary secretion of cholesterol. With or without growth hormone treatment, autotransplantation significantly increased fecal bile acid excretion, plasma cholesterol precursors, fecal bacterially modified neutral sterols, mucosal thickness of the ileum (but not jejunum), and intestinal transit time when compared with sham-operated animals. Crypt cell proliferation, mucosal enzyme activities, and microvilli showed no differences between the groups. Conclusions These findings suggest that growth hormone treatment selectively improves cholesterol, but not bile acid absorption, after autotransplantation of the jejunoileum.

Enteric dopaminergic neurons: definition, developmental lineage, and effects of extrinsic denervation.

The existence of enteric dopaminergic neurons has been suspected; however, the innervation of the gut by sympathetic nerves, in which dopamine (DA) is the norepinephrine precursor, complicates analyses of enteric DA. We now report that transcripts encoding tyrosine hydroxylase (TH) and the DA transporter (DAT) are present in the murine bowel (small intestine > stomach or colon; proximal colon > distal colon). Because sympathetic neurons are extrinsic, transcripts encoding TH and DAT in the bowel are probably derived from intrinsic neurons. TH protein was demonstrated immunocytochemically in neuronal perikarya (submucosal >> myenteric plexus; small intestine > stomach or colon). TH, DA, and DAT immunoreactivities were coincident in subsets of neurons (submucosal > myenteric) in guinea pig and mouse intestines in situ and in cultured guinea pig enteric ganglia. Surgical ablation of sympathetic nerves by extrinsic denervation of loops of the bowel did not affect DAT immunoreactivity but actually increased numbers of TH-immunoreactive neurons, expression of mRNA encoding TH and DAT, and enteric DOPAC (the specific dopamine metabolite). The fetal gut contains transiently catecholaminergic (TC) cells. TC cells are the proliferating crest-derived precursors of mature neurons that are not catecholaminergic and, thus, disappear after embryonic day (E) 14 (mouse) or E15 (rat). TC cells appear early in ontogeny, and their development/survival is dependent on mash-1 gene expression. In contrast, the intrinsic TH-expressing neurons of the murine bowel appear late (perinatally) and are mash-1 independent. We conclude that the enteric nervous system contains intrinsic dopaminergic neurons that arise from a mash-1-independent lineage of noncatecholaminergic precursors.

Chronic extrinsic denervation of the small bowel: effect on adrenergic and cholinergic contractile mechanisms in canine ileal circular muscle

Background Small bowel transplantation necessitates chronic extrinsic denervation and is often followed by enteric dysfunction. Our aim was to study canine ileal contractile activity after extrinsic denervation. Methods In vitro dose responses to cholinergic and adrenergic agonists were evaluated in canine ileal muscle strips in control subjects and after jejunoileal extrinsic denervation (EX DEN) at 0, 2, and 8 weeks after operative preparation. Results Spontaneous activity and the increased activity after tetrodotoxin (enteric nerve blockade) did not differ between groups. Response to acetylcholine and bethanechol did not differ at any time in the control or EX DEN group. In contrast, the EX DEN group demonstrated a procontractile hypersensitivity to norepinephrine at 2 and 8 weeks that was not seen in the control group. This adrenergic hypersensitivity in the EX DEN group was insensitive to intramural neural blockade with tetrodotoxin. Conclusions Extrinsic denervation does not affect basal contractile activity, augmented contractile activity to intramural neural blockade, nor response to cholinergic agonists. However, it induces a procontractile adrenergic hypersensitivity in canine ileal circular muscle mediated at the level of the smooth muscle and not at the enteric nervous system.

Effects of transection and extrinsic denervation and a model of autotransplantation of the porcine jejunoileum on cholesterol biodynamics

Background/Purpose: Small bowel transplantation impairs enteric function, necessitating transection, extrinsic denervation, and ischemia-reperfusion of the small intestine. The authors investigated how each of these nonimmunologic insides of the transplantation procedure modulates biodynamics of cholesterol and absorption of lipids. Methods: Twenty-three pigs with similar food, cholesterol, and fat intake underwent sham laparotomy (group 1), transection (group 2), extrinsic jejunoileal denervation (group 3), or a model of autotransplantation, including extrinsic jejunoileal denervation with in situ ischemia-reperfusion (group 4). Serum lipids, absorption, and excretion of cholesterol, bile acids, and fat were determined after 8 weeks. Plasma cholesterol precursors and plant sterols, respective markers of cholesterol synthesis, and absorption, were measured after 2 and 8 weeks. Results: When compared with sham laparotomy and transection groups, denervation and autotransplantation significantly decreased weight gain and increased plasma cholesterol precursors and fecal excretion of bile acids. In relation to sham operated animals, transection alone modestly increased plasma plant sterols at 2 weeks and biliary secretion and mass absorption of cholesterol. The latter changes were not observed after denervation or autotransplantation, ie, fractional and total absorption of cholesterol were significantly decreased in autotransplanted pigs when compared with transected controls. As compared with all the other groups, autotransplantion significantly increased bacterial metabolites of neutral sterols in feces and net fecal elimination of cholesterol, mainly as bile acids. Conclusions: Extrinsic autonomic denervation of the jejunoileum, with or without synchronous ischemia-reperfusion, results in increased cholesterol synthesis, bile acid malabsorption, and decreased weight gain. Cholesterol malabsorption may develop gradually after intestinal autotransplantation, and even a short period of ischemia further impairs absorptive function of the denervated jejunoileum, resulting in increased fecal elimination of cholesterol mainly as bile acids.

Neuronal Adrenergic and Muscular Cholinergic Contractile Hypersensitivity in Canine Jejunum After Extrinsic Denervation

Extrinsic denervation may be responsible for motor dysfunction after small bowel transplantation. The aim of this study was to examine the role of extrinsic innervation of canine jejunum on contractile activity. An in vitro dose response of cholinergic and adrenergic agonists was evaluated in canine jejunal strips of circular muscle at 0, 2, and 8 weeks in a control group and after jejunoileal extrinsic denervation (EX DEN). Neurons in circular muscle were quantitated by means of immunohistochemical techniques. Adrenergic and cholinergic responses did not differ at any time in the control group. However, at 2 and 8 weeks, extrinsic denervation caused an increased sensitivity to the procontractile effects of the cholinergic agonist bethanechol at the level of the smooth muscle cells, and increased sensitivity to the inhibitory effects of the adrenergic agent norepinephrine mediated at the level of the enteric nervous system. Immunohistochemical analysis showed a reduction in all neurons and a complete lack of adrenergic fibers in the EX DEN group after 2 and 8 weeks. Extrinsic denervation induces enteric neuronal cholinergic and adrenergic smooth muscle hypersensitivity in canine jejunal circular muscle. ( J Gastrointest Surg 2003;7:572–582).

Pathophysiological significance of neuronal nitric oxide synthase in the gastrointestinal tract.

It has been demonstrated that nitric oxide (NO) is a major inhibitory nonadrenergic, noncholinergic (NANC) neurotransmitter in the gastrointestinal (GI) tract. NO released in response to nerve stimulation of the myenteric plexus causes relaxation of the smooth muscle. NO is synthesized by the activation of neuronal NO synthase (nNOS) in the myenteric plexus. Released NO plays an important physiological role in various parts of the GI tract. NO regulates the muscle tone of the sphincter in the lower esophagus, pylorus, sphincter of Oddi, and anus. NO also regulates the accommodation reflex of the fundus and the peristaltic reflex of the intestine. Previous studies have shown that NOS inhibitors delay gastric emptying and colonic transit. The reduction of nNOS expression, associated with impaired local production of NO, may be responsible for motility disorders in the GI tract. There is accumulated evidence that dysfunction of NO neurons in the myenteric plexus may cause various GI diseases. These reports are reviewed and possible mechanisms of altered nNOS expression are discussed in this article. In particular, impaired nNOS synthesis of the myenteric plexus seems to be an important contributing factor to the pathogenesis of achalasia, diabetic gastroparesis, infantile hypertrophic pyloric stenosis, Hirschsprung's disease, and Chagas' disease. Reduced NO release and/or nNOS expression are suspicious in a subset of patients with functional dyspepsia. Although the etiology of intestinal pseudo-obstruction remains unknown, it is conceivable that extrinsic denervation may upregulate nNOS expression, resulting in enhanced muscular relaxation and disturbed peristalsis. An animal model of colitis showed impaired nNOS expression in the colonic myenteric plexus. Antecedent infection may be associated with the impaired NO pathways observed in functional dyspepsia, colitis, and Chagas' disease.

Enteric dopaminergic neurons: Definition, developmental lineage, and effects of extrinsic denervation

Enteric dopaminergic neurons: Definition, developmental lineage, and effects of extrinsic denervation

Total antioxidant capacity following extrinsic denervation and small intestinal transplantation in the rat

Transplantation of small intestine in a rat model has been shown to affect expression of neurochemicals within enteric inhibitory nerves. However, the mechanism for altered expression of inhibitory neurochemicals is uncertain. Based on our previous studies, we hypothesized that small intestinal transplantation would result in altered intestinal levels of antioxidant capacity. Glutathione, total antioxidant capacity, and lipid peroxide levels were measured at 3 months following (1) transection of rat small intestine, (2) transection and extrinsic denervation of rat intestine, and (3) isotransplantation of rat ileum or (4) allotransplantation of rat ileum with cyclosporine therapy to suppress rejection. Glutathione levels were not significantly different among the four groups. There were trends toward increased lipid peroxide levels following isografting and extrinsic denervation. Total antioxidant capacity was increased following extrinsic denervation ( P=0.05). Increased intestinal total antioxidant capacity in response to extrinsic denervation may represent a compensatory mechanism for protection against oxidative stress. This result enhances our understanding of the relationship between tissue antioxidant levels and alteration of enteric nerves.

Ileal resection enhances jejunal absorptive adaptation for water and electrolytes to extrinsic denervation: Implications for segmental small bowel transplantation

Background/Purpose: Segmental small bowel transplantation (SBT) may be an alternative to whole jejunoileal SBT. The aim of this study was to evaluate adaptability of extrinsically denervated jejunum after ileectomy. Methods: Baseline absorption of an isomolar, nonnutrient electrolyte solution was measured in an 80-cm in situ jejunal segment. Control (CON) and extrinsically denervated dogs (EXT DEN) then underwent distal 50% enterectomy; EXT DEN dogs also underwent a complete extrinsic denervation of remnant jejunum. Absorption was remeasured 2 and 12 weeks later; jejunal biopsies at 12 weeks were compared with baseline. Results: All dogs experienced weight loss and diarrhea, which resolved by 10 weeks in CON but persisted in EXT DEN dogs. Net absorptive fluxes of water, Na+, K+, and Cl−, however, remained unchanged in both groups 2 weeks and 12 weeks after denervation. Morphometric evaluation showed an increase in crypt depth in both groups at the 12-week time-point. Conclusions: Despite a clinical short bowel syndrome, more weight loss, and diarrhea in EXT DEN, there were no temporal differences in net absorptive fluxes of water and electrolytes within or between these 2 groups, and both developed increased crypt depth at 12 weeks. Extrinsic denervation does not blunt jejunal adaptive response to ileectomy. J Pediatr Surg 38:502-507. Copyright 2003, Elsevier Science (USA). All rights reserved.

Small Bowel Extrinsic Denervation Does Not Alter Water and Electrolyte Absorption From the Colon in the Fasting or Early Postprandial State

Small bowel transplantation (SBT) causes watery diarrhea. The decreases shown previously in absorption of water, electrolytes, and bile salts in the jejunum and ileum, although present, are not dramatic and seem not to be great enough to explain the diarrhea. Our aim was to determine changes in water and electrolyte absorption in the colon during fasting and postprandially in a canine preparation of jejunoileal extrinsic denervation, which serves as a model of jejunoileal autotransplantation. We hypothesized that colonic absorption of water and electrolytes decreases transiently in the colon after SBT. Six dogs had cannulas implanted in the colon to study absorption of an ileal-like basal electrolyte solution with or without 10 mmol/L glucose. Absorption during fasting and postprandially was measured before and 2 and 12 weeks after a validated preparation of jejunoileal extrinsic denervation. All dogs developed diarrhea after SBT. Net colonic absorptive fluxes of water and electrolytes in the colon did not change from baseline values at 2 or 12 weeks after extrinsic denervation, either during fasting or postprandially; glucose in the infusate did not alter absorptive fluxes during fasting or postprandially. Extrinsic denervation of the small intestine does not appear to alter colonic absorption of water or electrolytes during fasting or postprandially. These observations suggest that the neurally intact colon has a minimal role in the diarrhea after SBT. ( J Gastrointest Surg 2003;7:347–353.)