Effects Of Extrinsic Denervation Research Articles

Effects of extrinsic denervation on innervation with VIP and substance P in circular muscle of rat jejunum1

Extrinsic denervation contributes to enteric motor dysfunction after small bowel transplantation (SBT). Our aim was to determine changes in nonadrenergic, noncholinergic innervation with vasoactive intestinal polypeptide (VIP) and substance P (Sub P) in rat jejunal circular muscle after SBT. Muscle strips were studied in tissue chambers from six groups of rats (n > or = 6 per group): naïve controls (NC), animals 1 week after anaesthesia/sham celiotomy (SC-1), and 1 and 8 weeks after jejunal and ileal transection/reanastomosis (TA-1, TA-8) and after syngeneic, orthotopic SBT (SBT-1, SBT-8). Response to exogenous VIP and Sub P and their endogenous release during electrical field stimulation (EFS) were studied. Exogenous VIP and Sub P caused a dose-dependent inhibition and stimulation of mechanical activity in all groups respectively (P < 0.05). The responses to VIP and Sub P were decreased (compared to NC) in all groups at 1 and 8 weeks postoperatively. The VIP antagonist ([D-p-Cl-Phe(6),Leu(17)]-VIP) did not prevent the inhibition by exogenous VIP in any group, while the Sub P antagonist ([D-Pro(2),D-Trp(7,9)]-Sub P) prevented the effect of exogenous Sub P in NC, TA-8 and SBT-8 (P < 0.05). Responses to exogenous VIP were unaffected by the nitric oxide synthase inhibitor l-N(G)-nitro arginine and precontraction of muscle strips with Sub P. Endogenous release of VIP and Sub P during EFS was preserved after SBT. In circular muscle of rat jejunum, changes in neuromuscular transmission with VIP and Sub P during the first 8 weeks after SBT are not mediated by extrinsic denervation.

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.

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

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

Role of extrinsic innervation in modulating nitrergic transmission in the canine ileocolonic region

The human colon can dilate, often to life-threatening proportions. Our aim was to explore nitrergic mechanisms underlying colonic dilation in conscious dogs with enterically isolated ileocolonic loops either extrinsically innervated (n = 4) or extrinsically denervated (n = 4). We recorded phasic pressures in ileum and ileocolonic sphincter (ICS), colonic tone, compliance, and relaxation during ileal distension. By NADPH-diaphorase histochemistry, we assessed effects of extrinsic denervation and enteric isolation on nitrergic fibers. Extrinsic denervation increased phasic pressures in ileum, ICS, and colon and abolished ICS and colonic relaxation in response to ileal distension. The nitric oxide synthase (NOS) inhibitor N(omega)-nitro-L-arginine (L-NNA) increased phasic pressures at all sites and ICS tone but did not abolish colonic relaxation during ileal distension in innervated loops. L-NNA reduced compliance and induced colonic high-amplitude propagated contractions in denervated loops. The NOS substrate donor L-arginine reversed effects of L-NNA. The number of NADPH-diaphorase fibers increased in both enterically isolated preparations. Nonnitrergic extrinsic nerve pathways mediate reflex colonic relaxation during ileal distension. Enteric isolation augments the number of NOS fibers, an effect not modified by extrinsic denervation.

Effects of extrinsic denervation with or without ischemia-reperfusion injury on constitutional mucosal characteristics in porcine jejunoileum.

We investigated the effects of jejunoileal denervation with or without ischemia-reperfusion on mucosal characteristics and small intestinal structure. Growing pigs underwent sham laparotomy, jejunal transection, or extrinsic jejunoileal denervation with or without in situ ischemia-reperfusion. Small intestinal morphology, crypt cell proliferation, enterocyte ultrastructure, and disaccharidase activities were analyzed from jejunum and ileum after eight weeks. Immunohistological analysis of the ileum showed no staining of catecholaminergic neurons after extrinsic denervation. Neural isolation of the jejunoileum with or without ischemia-reperfusion injury reduced weight gain and villous enterocyte density in the ileum, abolished the proximodistal gradient of sucrase activity, and increased mucosal thickness, villus height, and villus surface area in the ileum. However, gross jejunoileal morphology, crypt cell proliferation, and enterocyte ultrastructure remained unchanged. In conclusion, jejunoileal denervation in growing pigs selectively modulates constitutional mucosal characteristics in the ileum, presumably due to altered enterocyte turnover, without a decrease in small intestinal absorptive surface area. These changes are independent of short ischemia and subsequent reperfusion.

Effect of extrinsic denervation in a canine model of jejunoileal autotransplantation on mechanical and electrical activity of jejunal circular smooth muscle.

Little is known about the acute and chronic effects of the intestinal transplantation on smooth muscle contractile physiology. Our aim was to determine the effects of the denervation necessitated by jejunoileal autotransplantation on membrane potential and contractile activity. Six dogs underwent a model of jejunoileal autotransplantation that specifically avoids ischemia/reperfusion injury (by maintaining blood flow to the gut during the "transplantation" procedure). Strips of jejunal circular muscle were studied sequentially before and 2 and 8 weeks after denervation by recording mechanical and intracellular electrical activities in vitro. The amplitude of spontaneous contractions (X +/- SD) was increased (P < 0.05) at 2 compared to 0 weeks (126 +/- 19 vs 77 +/- 32 g/g; P < 0.05) but markedly decreased at 8 weeks (7 +/- 2 g/g). Contraction frequency, resting membrane potential, and amplitude of slow waves were unchanged across these time points. Bethanechol (10(-7)-10(-4) M) and substance P (10(-8)-10(-6) M) dose-dependently increased contractile activity at all time points, but the absolute change in amplitude was decreased at 8 weeks. The amplitude of inhibitory junction potentials (IJPs) and duration of inhibition of contractile activity in the presence of cholinergic and adrenergic blockade increased at 2 and 8 weeks; off-contraction amplitude was decreased at 8 weeks (P < 0.05). These effects may occur via changes in neurotransmitter release, changes in regulation of membrane receptors, or alteration of characteristics of the membrane threshold potential.

Effects of extrinsic denervation or capsaicin on PACAP innervation of the rat gastrointestinal tract

Effects of extrinsic denervation or capsaicin on PACAP innervation of the rat gastrointestinal tract

Rat jejunal absorptive function after intestinal transplantation

Jejunal absorptive function was evaluated following small intestinal transplantation to determine the effects of extrinsic denervation. In particular, water and sodium absorption were measured following transplantation (denervated) and compared to a control group (Thiry-Vella). Water flow was initially secretory two days after transplantation (-41 +/- 27 microliters/min/g dry tissue weight) but became absorptive at day 8 (25 +/- 25). Water flow in the Thiry-Vella group was not significantly different (P > 0.05) from the transplant group at days 8 (17 +/- 7) and 10 (47 +/- 42). Sodium flows were also initially secretory in the transplant group and became absorptive. This study refutes previous claims that small bowel transplants have a deficiency of water absorption due to extrinsic denervation of the bowel and suggests normal absorptive function of water, electrolytes, and protein.

Effect of extrinsic denervation on the rate of net water transport of the feline gall bladder.

The influence on the concentrating ability of the gall bladder after extrinsic denervation was studied in anaesthetised cats, previously subjected to truncal vagotomy and/or coeliacectomy , and compared with sham operated controls. Net water absorption was studied by perfusion techniques. Acute experiments were performed under basal conditions and alpha-adrenoceptor stimulation (intra-arterial infusion of noradrenaline). Gall bladder biopsies were studied by fluorescence microscopy and cytofluorimetry to visualise and quantify catecholamines. Three weeks after coeliacectomy basal absorption had decreased significantly. In the short term vagotomy group no changes were shown. In the long term vagotomy group, however, there was a four-fold increase in absorptive capacity, which decreased to control levels after alpha-adrenoceptor blockade (phentolamine). Long term vagotomy with subsequent coeliacectomy caused no significant changes. Infusion of noradrenaline increased net water absorption by 60 +/- 11% in all experimental groups except in long term vagotomised animals, where the high basal absorption was not further augmented. One hour after noradrenaline infusion controls returned to basal absorption rate, while denervated cats remained at stimulated levels. In long term vagotomised gall bladders there were morphological signs of adrenergic proliferation (increased total number of nerve terminals, sprouting and raised levels of intraneuronal noradrenaline). These results suggest that the adrenergic nervous system is important for full absorptive capacity of the gall bladder. The increased absorption after long term vagotomy, abolished after alpha-adrenoceptor blockade, might well be explained by the parallel adrenergic proliferation. This hypothesis was further corroborated in animals with long term vagotomy, where subsequent surgical adrenergic denervation restored basal absorption to control levels.

Effects of extrinsic denervation on net water transport and motility of the feline gallbladder in vivo

The influence on the concentrating ability of the gallbladder after extrinsic denervation was studied in anesthetized cats, previously subjected to truncal vagotomy, and/or celiacectomy, and compared with sham-operated controls. Net water absorption was studied by perfusion techniques. Acute experiments were performed under basal conditions and α-adrenoceptor stimulation (iv infusion of norepinephrine (NE), 1 μg/kg · min). Gallbladder biopsies were studied by fluorescence microscopy to visualize and quantitate catecholamines. Three weeks after celiacectomy basal absorption had decreased significantly. In the short-term vagotomy group no changes were demonstrated. However, in the long-term vagotomy group there was a fourfold increase in absorptive capacity, which decreased to control levels after α-adrenoceptor blockade (phentolamine 1 mg/kg iv). Long-term vagotomy with subsequent celiacectomy caused no significant changes. Infusion of NE increased net water absorption by 70 ± 16% in all experimental groups except in long-term vagotomized animals, where the high basal absorption was not further augmented. One hour after NE infusion controls returned to basal absorption rate, while denervated cats remained at stimulated levels. In long-term vagotomized gallbladders there were morphological signs of adrenergic proliferation (increased total number of nerve terminals, sprouting, and elevated levels of intraneuronal NE). In conclusion these results suggest that the adrenergic nervous system is important for full absorptive capacity of the gallbladder. The increased absorption after long-term vagotomy, abolished after α-adrenoceptor blockade, might well be explained by the parallel adrenergic proliferation. This hypothesis was further corroborated in animals with long-term vagotomy, where subsequent surgical adrenergic denervation restored basal absorption to control levels. There was no motility response to NE in controls or short-term vagotomy animals, but after previous celiacectomy a short relaxation was seen indicating denervation supersensitivity of β-adrenoceptors. After long-term vagotomy there was a contractile response indicating activation of α-adrenoceptors as outlined in the absorption study.

Peptide-containing neurons intrinsic to the gut wall. An experimental study in the pig.

Nerve fibers containing substance P, VIP, enkephalin or somatostatin are numerous in the porcine gut wall. They are particularly numerous in the submucosal and myenteric plexuses where peptide-containing cell bodies are also observed. Peptide-containing nerve fibers occur also in the vagus nerves, suggesting that the gut receives and extrinsic supply of peptidergic nerves. The extrinsic contribution to the peptide-containing nerve supply of the gut wall has not yet been quantitatively assessed. In an attempt to clarify this question pigs were subjected to bilateral subdiaphragmatic vagotomy. Another group of animals was subjected to complete extrinsic denervation by autotransplantation of a jejunal segment. The pigs were killed at various time intervals after the operations; the longest time interval studied was four months. Following vagotomy the innervation pattern of the jejunum appeared completely unaffected. Following complete extrinsic denervation the adrenergic nerve fibers disappeared, while peptide-containing and acetylcholinesterase-positive nerve fibers remained apparently unaltered. This was confirmed chemically in the case of substance P. The motor activity of smooth muscle from the jejunum was studied in vitro. At low stimulation frequencies the smooth muscle from control jejunum responded by relaxation; upon cessation of stimulation a contraction occurred. With increasing stimulation frequencies the duration of the relaxation decreased; at high frequency stimulation only a contraction was recorded. In the autotransplant low frequency stimulation induced no or only a weak relaxation; high frequency stimulation induced contraction. After cholinergic and adrenergic blockade, the muscle responded with relaxation at all frequencies; the response was similar in innervated and denervated specimens. On the whole, the effects of extrinsic denervation on the motor activity of smooth muscle from porcine jejunum were minor, possibly reflecting the high degree of autonomy of the gut.

Effects of Extrinsic Denervation on the Fluorescence of Monoamines in the Small Intestine of the Cat

AbstractAhlman, H., L. Enerback, J. Kewenter and B. Storm. Effects of extrinsic denervation on the fluorescence of monoamines in the small intestine of the cat. Acta physiol. scand. 1973. 89. 429–435.The effects of section of the nerves supplying the small intestine in the cat were studied in vivo at different times after the operation. Before denervation, biopsies from the jejunum and ileum were studied by a fluorescence method in order to observe the adrenergic innervation and the presence of 5‐hydroxytryptamine (5‐HT). In addition to the adrenergic fibres terminating around the ganglion cells of the intestinal nervous plexuses, other adrenergic fibres were seen in close connection with the muscle fibres in both muscular layers. The only location of 5‐HT seemed to be in the enterochromaffin cells of the mucosa. After nerve section the completeness of the denervation was established in an acute experiment by means of electrical stimulation of the vagal and splanchnic nerves while registering the motility of a jejunal and an ileal loop. Afterwards the small intestinal wall was studied with the same histochemical fluorescence method. No changes were found in the towel habits or in the general state of nutrition of the animals. The intestinal adrenergic innervation completely disappeared after denervation. The adrenergic innervation does not seem to be necessary for adequate peristaltic activity in the small intestine. 5‐HT did not disappear after denervation but was found unchanged in the enterochromaffin cells.