Cytoplasmic delayed neuronal death in the myenteric plexus of the rat small intestine after ischemia

Resveratrol promotes myenteric neuroprotection in the ileum of rats after ischemia-reperfusion injury

AIMS

The present study evaluated the effects of resveratrol in the myenteric plexus after intestinal ischemia-reperfusion (I/R) injury caused by occluding the superior mesenteric artery for 45min, followed by 7days of reperfusion.

MAIN METHODS

Forty-two male Wistar rats were divided into seven groups: control (C group), untreated sham surgery control (SC group), sham surgery control treated with resveratrol before surgery (STA group), sham surgery control treated with resveratrol before and after surgery (STAD group), ischemic control (IRC group), ischemic treated before I/R (IRTA group), and ischemic treated before and after I/R (IRTAD group). Resveratrol (10mg/kg) was administered for 4days and 2h prior to surgery and/or 7days later. Morphometric analyses were performed, and the density of the general neuronal population (HuC/D-immunoreactive [IR]), nitrergic subpopulation (neuronal nitric oxide synthase [nNOS]-IR), vasoactive intestinal peptide (VIP)ergic varicosities (VIP-IR), and glial cells (S100-IR) was determined.

KEY FINDINGS

Injury that was caused by I/R significantly reduced (p<0.01) the HuC/D-IR general neuronal population. Treatment with resveratrol before and after ischemia had a neuroprotective effect. Morphometric changes caused by I/R in nitrergic neurons and varicosities were also attenuated by resveratrol. Ischemia/reperfusion promoted the proliferation of enteric glial cells, and resveratrol treatment before and after I/R reversed this effect.

SIGNIFICANCE

Resveratrol had neuroprotective effects, showing promise for application in intestinal surgery and transplants.

The Effect of Ischemia and Reperfusion on Enteric Glial Cells and Contractile Activity in the Ileum

BACKGROUND

We investigated the effects of ischemia followed by different periods of reperfusion (I/R) on immunoreactive S100β-positive glial and Hu-immunoreactive neurons co-expressing the P2X2 receptor in the myenteric plexus of the rat ileum.

METHODS

The ileal artery was occluded for 35 min with an atraumatic vascular clamp. The animals were killed 24 h, 72 h, and 1 week after ischemia. Sham animals were not submitted to ileal artery occlusion. The relative density, size, and co-localization of P2X2 receptor-expressing cells in relation to S100β-immunoreactive glial and Hu-immunoreactive neuronal cells were evaluated. Additionally, we analyzed the effects of I/R on gastrointestinal transit and ileum contractile activity.

RESULTS

The cellular density of P2X2 receptor and neuronal Hu immunoreactivity/cm(2) decreased after I/R, whereas glial S100β immunoreactivity/cm(2) increased. No significant differences between sham and I/R groups were observed regarding the perikarya area of Hu-positive neurons. The area of S100β-immunoreactive glial cells increased by 24.1 % 1 week after I/R compared with the 24 h group. Methylene blue progression along the small intestine decreased (P < 0.05) from 24.5 ± 2.3 % in the sham group to 17.2 ± 2.0 % 1 week post-ischemia. We noted a significant (P < 0.05) decrease in the maximal contraction amplitude triggered by electrical field stimulation in the presence of ATP in preparations submitted to 24 h of I/R.

CONCLUSIONS

Changes in the P2X2 receptor density parallel myenteric neuronal loss following I/R of the rat ileum. This, together with the increase in the activated (oversized) glial cells, may contribute to decreased GI motility after I/R.

Effects of ischemia and reperfusion on subpopulations of rat enteric neurons expressing the P2X7 receptor

BACKGROUND

Intestinal ischemia followed by reperfusion (I/R) may occur following intestinal obstruction. In rats, I/R in the small intestine leads to structural changes accompanied by neuronal death.

AIM

To analyze the impact of I/R injury on different neuronal populations in the myenteric plexus of rat ileum.

METHODS

The ileal artery was occluded for 35 min and animals were euthanized 6, 24, and 72 h, and 1 week later. Immunohistochemistry was performed with antibodies against the P2X7 receptor as well as nitric oxide synthase (NOS), calbindin, calretinin, choline acetyltransferase (ChAT), or the pan-neuronal marker anti-HuC/D.

RESULTS

Double immunolabeling demonstrated that 100% of NOS-, calbindin-, calretinin-, and ChAT-immunoreactive neurons in all groups expressed the P2X7 receptor. Following I/R, neuronal density decreased by 22.6% in P2X7 receptor-immunoreactive neurons, and decreased by 46.7, 38, 39.8, 21.7, and 20% in NOS-, calbindin-, calretinin-, ChAT-, and HuC/D-immunoreactive neurons, respectively, at 6, 24, and 72 h and 1 week following injury compared to the control and sham groups. We also observed a 14% increase in the neuronal cell body profile area of the NOS-immunoreactive neurons at 6 and 24 h post-I/R and a 14% increase in ChAT-immunoreactive neurons at 1 week following I/R. However, the average size of the calretinin-immunoreactive neurons was reduced by 12% at 6 h post-I/R and increased by 8% at 24 h post-I/R.

CONCLUSIONS

This work demonstrates that I/R is associated with a significant loss of different subpopulations of neurons in the myenteric plexus accompanied by morphological changes, all of which may underlie conditions related to intestinal motility disorder.

The relationship between glial distortion and neuronal changes following intestinal ischemia and reperfusion

BACKGROUND

Damage to mucosal epithelial cells, muscle cells and enteric neurons has been extensively studied following intestinal ischemia and reperfusion (I/R). Interestingly, the effects of intestinal I/R on enteric glia remains unexplored, despite knowledge that glia contribute to neuronal maintenance. Here, we describe structural damage to enteric glia and associated changes in distribution and immunoreactivity of the neuronal protein Hu.

METHODS

The mouse small intestine was made ischemic for 3 h and reperfused from 1 to 12 h. Immunohistochemical localisation of glial fibrillary acidic protein (GFAP), Hu and TUNEL were used to evaluate changes.

KEY RESULTS

At all time points glial cells became distorted, which was evident by their altered GFAP immunoreactivity, including an unusual appearance of bright perinuclear GFAP staining and the presence of GFAP globules. The numbers of neurons per ganglion area were significantly fewer in ganglia that contained distorted glia when compared with ganglia that contained glia of normal appearance. The distribution of Hu immunoreactivity was altered at all reperfusion time points. The presence of vacuoles and Hu granules in neurons was evident and an increase in nuclear Hu, relative to cytoplasmic Hu, was observed in ganglia that contained both normal and distorted glial cells. A number of neurons appeared to lose their Hu immunoreactivity, most noticeably in ganglia that contained distorted glial cells. TUNEL reaction occurred in a minority of glial cells and neurons.

CONCLUSIONS & INFERENCES

Structural damage to gliofilaments occurs following I/R and may be associated with damage to neighboring neurons.

The involvement of nitric oxide synthase neurons in enteric neuropathies

Nitric oxide (NO), produced by the neural nitric oxide synthase enzyme (nNOS) is a transmitter of inhibitory neurons supplying the muscle of the gastrointestinal tract. Transmission from these neurons is necessary for sphincter relaxation that allows the passage of gut contents, and also for relaxation of muscle during propulsive activity in the colon. There are deficiencies of transmission from NOS neurons to the lower esophageal sphincter in esophageal achalasia, to the pyloric sphincter in hypertrophic pyloric stenosis and to the internal anal sphincter in colonic achalasia. Deficits in NOS neurons are observed in two disorders in which colonic propulsion fails, Hirschsprung's disease and Chagas' disease. In addition, damage to NOS neurons occurs when there is stress to cells, in diabetes, resulting in gastroparesis, and following ischemia and reperfusion. A number of factors may contribute to the propensity of NOS neurons to be involved in enteric neuropathies. One of these is the failure of the neurons to maintain Ca(2+) homeostasis. In neurons in general, stress can increase cytoplasmic Ca(2+), causing a Ca(2+) toxicity. NOS neurons face the additional problem that NOS is activated by Ca(2+). This is hypothesized to produce an excess of NO, whose free radical properties can cause cell damage, which is exacerbated by peroxynitrite formed when NO reacts with oxygen free radicals.

Effects of ischemia and reperfusion on P2X2 receptor expressing neurons of the rat ileum enteric nervous system

PURPOSE

We investigated the effects of ischemia/reperfusion in the intestine (I/R-i) on purine receptor P2X2-immunoreactive (IR) neurons of the rat ileum.

METHODS

The superior mesenteric artery was occluded for 45 min with an atraumatic vascular clamp and animals were sacrificed 4 h later. Neurons of the myenteric and submucosal plexuses were evaluated for immunoreactivity against the P2X2 receptor, nitric oxide synthase (NOS), choline acetyl transferase (ChAT), calbindin, and calretinin.

RESULTS

Following I/R-i, we observed a decrease in P2X2 receptor immunoreactivity in the cytoplasm and surface membranes of neurons of the myenteric and submucosal plexuses. These studies also revealed an absence of calbindin-positive neurons in the I/R-i group. In addition, the colocalization of the P2X2 receptor with NOS, ChAT, and calretinin immunoreactivity in the myenteric plexus was decreased following I/R-i. Likewise, the colocalization between P2X2 and calretinin in neurons of the submucosal plexus was also reduced. In the I/R-i group, there was a 55.8% decrease in the density of neurons immunoreactive (IR) for the P2X2 receptor, a 26.4% reduction in NOS-IR neuron, a 25% reduction in ChAT-IR neuron, and a 47% reduction in calretinin-IR neuron. The density of P2X2 receptor and calretinin-IR neurons also decreased in the submucosal plexus of the I/R-i group. In the myenteric plexus, P2X2-IR, NOS-IR, ChAT-IR and calretinin-IR neurons were reduced in size by 50%, 49.7%, 42%, and 33%, respectively, in the I/R-i group; in the submucosal plexus, P2X2-IR and calretinin-IR neurons were reduced in size by 56% and 72.6%, respectively.

CONCLUSIONS

These data demonstrate that ischemia/reperfusion of the intestine affects the expression of the P2X2 receptor in neurons of the myenteric and submucosal plexus, as well as density and size of neurons in this population. Our findings indicate that I/R-i induces changes in P2X2-IR enteric neurons that could result in alterations in intestinal motility.

Damaging effects of ischemia/reperfusion on intestinal muscle

Periods of ischemia followed by restoration of blood flow cause ischemia/reperfusion (I/R) injury. In the intestine, I/R damage to the mucosa and neurons is prominent. Functionally, abnormalities occur in motility, most conspicuously a slowing of transit, possibly as a consequence of damage to neurons and/or muscle. Here, we describe degenerative and regenerative changes that have not been previously reported in intestinal muscle. The mouse small intestine was made ischemic for 1 h, followed by re-perfusion for 1 h to 7 days. The tissues were examined histologically, after hematoxylin/eosin and Masson's trichrome staining, and by myeloperoxidase histochemistry to detect inflammatory reactions to I/R. Histological analysis revealed changes in the mucosa, muscle, and neurons. The mucosa was severely but transiently damaged. The mucosal surface was sloughed off at 1-3 h, but re-epithelialization occurred by 12 h, and the epithelium appeared healthy by 1-2 days. Longitudinal muscle degeneration was followed by regeneration, but little effect on the circular muscle was noted. The first signs of muscle change were apparent at 3-12 h, and by 1 and 2 days, extensive degeneration within the muscle was observed, which included clear cytoplasm, pyknotic nuclei, and apoptotic bodies. The muscle recovered quickly and appeared normal at 7 days. Histological evidence of neuronal damage was apparent at 1-7 days. Neutrophils were not present in the muscle layers and were infrequent in the mucosa. However, they were often seen in the longitudinal muscle at 1-3 days and were also present in the circular muscle. Neutrophil numbers increased in the mucosa in both I/R and sham-operated animals and remained elevated from 1 h to 7 days. We conclude that I/R causes severe longitudinal muscle damage, which might contribute to the long-term motility deficits observed after I/R injury to the intestine.

The reactions of specific neuron types to intestinal ischemia in the guinea pig enteric nervous system

Damage following ischemia and reperfusion (I/R) is common in the intestine and can be caused during abdominal surgery, in several disease states and following intestinal transplantation. Most studies have concentrated on damage to the mucosa, although published evidence also points to effects on neurons. Moreover, alterations of neuronally controlled functions of the intestine persist after I/R. The present study was designed to investigate the time course of damage to neurons and the selectivity of the effect of I/R damage for specific types of enteric neurons. A branch of the superior mesenteric artery supplying the distal ileum of anesthetised guinea pigs was occluded for 1 h and the animals were allowed to recover for 2 h to 4 weeks before tissue was taken for the immunohistochemical localization of markers of specific neuron types in tissues from sham and I/R animals. The dendrites of neurons with nitric oxide synthase (NOS) immunoreactivity, which are inhibitory motor neurons and interneurons, were distorted and swollen by 24 h after I/R and remained enlarged up to 28 days. The total neuron profile areas (cell body plus dendrites) increased by 25%, but the sizes of cell bodies did not change significantly. Neurons of type II morphology (intrinsic primary afferent neurons), revealed by NeuN immunoreactivity, were transiently reduced in cell size, at 24 h and 7 days. These neurons also showed signs of minor cell surface blebbing. Calretinin neurons, many of which are excitatory motor neurons, were unaffected. Thus, this study revealed a selective damage to NOS neurons that was observed at 24 h and persisted up to 4 weeks, without a significant change in the relative numbers of NOS neurons.

Infiltration of mast cells in rat colon is a consequence of ischemia/reperfusion

Intestinal ischemia as well as mastocytosis occur in patients with inflammatory bowel disease and irritable bowel syndrome. Our aim was to clarify how ischemia with reperfusion (I/R) affects the structure, enteric neurons, and immune cells in the colon. Rats were subjected to colon ischemia for 1 h and reperfused for 1 day up to 20 weeks; sham-operated rats were used as controls. No structural remodeling of the intestinal segment was detected after I/R. The number and distribution of eosinophils were not affected by I/R. Local areas containing numerous mast cells were detected in the muscle layers, the serosa, and in and around the myenteric ganglia 4-20 weeks post ischemia. It was notable that myenteric ganglionic formations within mast-cell-rich areas virtually lacked neurons. Mast cells were rarely found in controls. In conclusion, I/R of the colon attracts mast cells, and death of myenteric neurons occurs in such locations.

Acute colonic ischaemia in rats results in long-term structural changes without alterations of colonic sensitivity

Colonic ischaemia and mast cells have been involved in the pathophysiology of the functional gastrointestinal disorder irritable bowel syndrome, although the cause-effect relationships remain unknown. We assessed long-term histopathological and functional changes associated to an acute ischaemic episode (1 h) of the colon, followed by 8-week recovery, in rats. Functional colonic alterations [sensitivity during colorectal distension (CRD), compliance and propulsive motility] were assessed regularly during the recovery. Colonic histopathology (presence of inflammation, morphometric alterations and variations in neuronal density in the enteric nervous system) 8-week postischaemia was assessed. Following ischaemia, none of the functional parameters tested (motility, sensitivity and compliance) were affected. At necropsy, the colon presented an overall normal appearance with an increase in weight of the ischaemic area (mg/cm: 99 +/- 6; P < 0.05 vs. control: 81 +/- 4 or sham ischaemia: 81 +/- 3). Histopathological evaluations revealed the presence of a local infiltrate of mast cells in the area of ischaemia (nb of mast cells: 142 +/- 50; P < 0.05 vs. control, 31 +/- 14 or sham ischaemia: 40 +/- 16), without other significant alterations. Animals subjected to colonic ischaemia and treated 8 weeks later with the mast cell degranulator, compound 48/80, showed no changes in CRD-related pain responses. These studies show that acute colonic ischaemia is associated with the presence of a long-term local infiltration of mast cells, located within the serosa and muscle layers, despite the absence of functional changes, including colonic sensitivity. Considering the important pathophysiological functions of mast cells, the observed mast cell infiltration may be involved in ischaemia-induced functional changes yet to be characterized.

Changes in intestinal motility and in the myenteric plexus in a rat model of intestinal ischemia-reperfusion

BACKGROUND/PURPOSE

Early histologic changes induced by intestinal ischemia-reperfusion injury (IIRI) have been extensively studied using animal models. However, information regarding late effects on intestinal motility is lacking. The aim of this study was to investigate the late effects of IIRI on myenteric plexus histology and intestinal motility.

MATERIALS AND METHODS

Thirty-two postweaning male rats weighing between 58 and 103 g were divided randomly into 4 groups: Control (unoperated), Sham (celiotomy), 30-minute ischemia (celiotomy and superior mesenteric artery ischemia for 30 minutes), and 45-minute ischemia (celiotomy and superior mesenteric artery ischemia for 45 minutes). Postoperative intestinal motility was assessed by weighing total fecal output for 24 hours on the 3rd, 7th, 14th, and 21st day after surgery. Segments of duodenum, jejunum, and ileum were examined at light microscopy for changes in the myenteric plexus.

RESULTS

Three weeks after IIRI, the ganglion cells from the myenteric plexus appeared in light microscopy, spongy or foamy, containing many vacuoles in their cytoplasm. The neuronal nucleus became irregular, with degenerative signs. These alterations did not occur among animals from the control or sham groups. Although the animals of the 45-minute ischemia group showed a significant drop in fecal output in the 21st postoperative day, this appeared to have no effect on weight gain.

CONCLUSIONS

The results suggest that intestinal ischemia-reperfusion causes late neuronal damage. These changes resulted in alterations of intestinal motility, which, within the conditions of the present study, had no repercussion on general weight gain.

Altered responsiveness of the guinea-pig isolated ileum to smooth muscle stimulants and to electrical stimulation after in situ ischemia

1. We evaluated changes in contractility of the guinea-pig isolated ileum, using intact segments and myenteric plexus-longitudinal muscle (MPLM) preparations, after several times (5-160 min) of ischemia in situ. 2. Intestinal ischemia was produced by clamping the superior mesenteric artery. Ischemic and nonischemic segments, obtained from the same guinea-pig, were mounted in organ baths containing Krebs-bicarbonate (K-B) solution, maintained at 37 degrees C and gassed with 95% O2/5% CO2. The preparations were allowed to equilibrate for 60 min under continuous superfusion of warm K-B solution and then electrically stimulated at 40 V (0.3 Hz, 3.0 ms). Thereafter, complete noncumulative concentration-response curves were constructed for acetylcholine (ACh), histamine (HIS), potassium chloride (KCl), and barium chloride (BaCl2). Mean Emax (maximal response) values were calculated for each drug. 3. Our study shows that alterations of chemically and electrically evoked contractions are dependent on ischemic periods. It also demonstrates that contractile responses of ischemic tissues to neurogenic stimulation decreases earlier and to a significantly greater extent than the non-nerve mediated responses of the intestinal smooth muscle. Contractile responses to smooth muscle stimulants were all similarly affected by ischemia. Electron microscopy images indicated necrotic neuronal death. The decrease in reactivity of ischemic tissues to electrical stimulation was ameliorated by dexrazoxane, an antioxidant agent. 4. We consider the guinea-pig isolated ileum as a useful model system to study the processes involved in neuronal ischemia, and we propose that the reduction in maximal responses to electrical stimulation is a useful parameter to study neuroprotection.

Substance P and vasoactive intestinal peptide in rat small-bowel isografts

BACKGROUND

It is established that substance P (SP) is released by stimulation of nonadrenergic noncholinergic (NANC) excitatory nerves and vasoactive intestinal peptide (VIP) by stimulation of NANC inhibitory nerves. To evaluate the function of peptidergic nerves such as SP and VIP in small-bowel isografts, we examined the enteric nerve responses to SP and VIP in the isografted rat jejunum, using the normal rat jejunum as a control.

METHODS

Orthotopic entire small bowel transplantation (SBT) with portocaval drainage was performed from Lewis rats to Lewis rats. Grafted tissue specimens were obtained 130 days after SBT (n = 9). As controls, normal segments of the jejunum were obtained from untransplanted Lewis rats (n = 22). A mechanograph was used to evaluate in vitro jejunal responses to electrical field stimulation of the enteric nervous system before and after treatments with various autonomic nerve blockers and neuropeptides (SP and VIP).

RESULTS

SP concentration-dependently mediated the contraction reaction of NANC excitatory nerve in the isografted jejunum and to a lesser extent in the normal jejunum. In addition, there were significant diferences in the percentages showing contraction at 1 x 10(-8) and 1 x 10(-6)g/mL SP between the normal and isografted jejunal muscle strips (P < .05, respectively). VIP concentration dependently mediated the relaxation reaction of NANC inhibitory nerve in the normal jejunum and to a lesser extent in the isografted jejunum. In addition, there was a significant difference between the relaxation frequencies of the normal and those of isografted jejunal muscle strips at 1 x 10(-6) g/mL SP (P < .01).

CONCLUSIONS

Contraction reactions of SP were observed in both the normal and isografted jejunum but were increased in the isografted jejunum. Relaxation reactions of VIP were also observed in both the normal and isografted jejunum but were decreased in the isografted jejunum. The increase of the effects of SP via NANC excitatory nerves and the decrease of the effects of VIP in mediating NANC inhibitory nerves may be largely related to the peristaltic abnormalities seen in the isografted LEW rat jejunum.

Structural and neuronal changes in rat ileum after ischemia with reperfusion

Intestinal ischemia/reperfusion (I/R) is of profound importance in many clinical situations. The present study investigates short- and long-term changes, in particular in enteric neurons, but also with respect to the presence of eosinophilic leukocytes, goblet cells, and mast cells in the intestinal wall using an experimental model for intestinal I/R. Structural changes were also examined. Specimens from untreated, sham-operated, and ischemia (60 min)/reperfusion (1 hr-10 weeks) rat ileum were studied using histochemistry and morphometry. After I/R a marked acidophilia was noted in both submucous and myenteric neurons. This preceded a loss of myenteric, but not submucous, neurons. A low number of acidophilic neurons was noted also in sham-operated segments. Eosinophils and mast cells gradually increased after I/R and were notably found in smooth muscle and myenteric ganglia. Structural changes included mucosal shedding followed by restitution with an epithelium transiently containing a high number of goblet cells and a marked thickening of the muscular layers.