A role of nitric oxide in Hirschsprung's disease

Nitrergic and Substance P Immunoreactive Neurons in the Enteric Nervous System of the Bottlenose Dolphin (Tursiops truncatus) Intestine

Simple Summary

The gastrointestinal tract of the bottlenose dolphin (Tursiops truncatus) differs structurally and functionally from that of terrestrial mammals. In particular, the intestine does not show any macroscopic subdivision and lacks a caecum. In addition, the histological aspect of the intestine is relatively constant, without marked differences between the anterior and posterior parts. Although the intestine of these cetaceans presents differences in comparison with terrestrial mammals, little information is currently available on their enteric nervous system. The aim of the present study was to investigate the morphological and quantitative aspects of neurons immunoreactive (IR) for the neuronal nitric oxide synthase (nNOS) and Substance P (SP) in the intestine of bottlenose dolphins (Tursiops truncatus). In these dolphin specimens, a smaller number of nNOS-IR neurons in the submucosal plexus and a larger number of SP-IR neurons in the myenteric plexus were observed compared to other mammals. Interestingly, no co-localization between nNOS- and SP-IR neurons was detected in either of the plexuses, suggesting the existence of two completely distinct functional classes of neurons in the intestine of the bottlenose dolphin.

Abstract

Compared with other mammals, the digestive system of cetaceans presents some remarkable anatomical and physiological differences. However, the neurochemical features of the enteric nervous system (ENS) in these animals have only been described in part. The present study gives a description of the nitrergic and selected peptidergic systems in the myenteric plexus (MP) and submucosal plexus (SMP) of the intestine of the bottlenose dolphin (Tursiops truncatus). The distribution and morphology of neurons immunoreactive (IR) for the neuronal nitric oxide synthase (nNOS) and Substance P (SP) were immunohistochemically studied in formalin-fixed specimens from the healthy intestine of three animals, and the data were compared with those described in the literature on other mammals (human and non-human). In bottlenose dolphins, the percentages of nitrergic neurons (expressed as median and interquartile range—IQR) were 28% (IQR = 19–29) in the MP and 1% (IQR = 0–2) in the SMP, while the percentages of SP-IR neurons were 31% (IQR = 22–37) in the MP and 41% (IQR = 24–63) in the SMP. Although morphological features of nNOS- and SP-IR neurons were similar to those reported in other mammals, we found some noticeable differences in the percentages of enteric neurons. In fact, we detected a lower proportion of nNOS-IR neurons in the SMP and a higher proportion of SP-IR neurons in the MP compared to other mammals. To the best of the authors’ knowledge, this study represents the first description and quantification of nNOS-IR neurons and the first quantification of SP-IR neurons in the intestine of a cetacean species. As nNOS and SP are important mediators of intestinal functions and the nitrergic population is an important target for many neuroenteropathies, data obtained from a healthy intestine provide a necessary basis to further investigate and understand possible functional differences and motor intestinal dysfunctions/alterations in these special mammals.

A mechanistic model of a PDGFRα(+) cell

A novel platelet-derived growth factor receptor alpha-positive cell (PDGFRα(+)) has recently been identified as part of the purinergic inhibitory neural control mechanism in the gastrointestinal (GI) tract. The mechanism through which PDGFRα(+) cells mediate GI muscle relaxation has been found to be associated with the purine receptors P2Y1 and apamin-sensitive SK3 channels that are highly expressed in these cells. This study aims to develop a mechanistic model elucidating a proposed mechanism through which PDGFRα(+) cells contribute to purinergic inhibitory neuromuscular transmission. In accordance with recent experimental findings, the model describes how the binding of neurotransmitters, released from enteric neurons, triggers the release of Ca(2+) from the endoplasmic reticulum in the PDGFRα(+) cells, and how this subsequently leads to large amplitude transient outward currents, which in turn hyperpolarize the cell. The model has been validated against experimental recordings and good agreement was found under normal and pharmacologically-altered conditions. This model demonstrates the feasibility of the proposed mechanism and provides a basis for understanding the mechanism underlying purinergic control of colonic motility.

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.

Deficiency of purinergic P2Y receptors in aganglionic intestine in Hirschsprung's disease

Hirschsprung's disease is characterized by the absence of ganglion cells in the distal bowel and extends proximally for varying distances. In recent years, the purinergic P2Y receptors have begun to receive much attention as they have been recognised as major ATP receptors in many regions of the body, including the intestine. ATP has long been established as an inhibitory neurotransmitter in the enteric nervous system. The aim of our study was to analyse the expression of P2Y1 and P2Y2 receptors in the intestine of patients with Hirschsprung's disease. Frozen sections were cut from rectal tissue segments taken from both the aganglionic and ganglionic regions of patients with Hirschsprung's disease, as well as tissue from normal rectal biopsies, which were used as controls. Sections were incubated overnight with P2Y1 and P2Y2 receptor antibodies and results were analysed by light microscopy. Both P2Y1 and P2Y2 immunoreactivity was absent from the submucosal and myenteric plexuses of aganglionic tissue compared to ganglionic tissue and normal controls, in which large number of immunoreactive neurons were evident, arranged in ganglia in both plexuses and positive nerve fibres, in both the smooth and circular muscles. Our results show a lack of expression of P2Y1 and P2Y2 receptors in the aganglionic gut in Hirschsprung's disease. The absence of these receptors suggests the absence of the inhibitory neurotransmitter ATP, which may help to explain the contracted state of the aganglionic gut in Hirschsprung's disease.

Stimulation of the nitric oxide-guanosine 3', 5'-cyclic monophosphate pathway by sildenafil: effect on rectal muscle tone, distensibility, and perception in health and in irritable bowel syndrome

OBJECTIVES

Nitric oxide, a neurotransmitter in the noncholinergic, nonadrenergic nervous system, is a mediator of relaxation of GI smooth muscle and of visceral nociception mainly studied in vitro. Sildenafil stimulates the nitric oxide guanosine 3', 5'-cyclic monophosphate (NO-cGMP) pathway through inhibition of phosphodiesterase 5. The aims of this study were to evaluate in vivo the effect of stimulation of the NO-cGMP pathway on rectal tone, distensibility, and perception in healthy individuals and in patients with irritable bowel syndrome (IBS).

METHODS

In eight healthy subjects and four patients with IBS rectal tone, distensibility and perception thresholds were measured with an electronic barostat both before and 60 min after administration of sildenafil (50 mg p.o.). Perception was scored on a graded scale of 0-6. At the end of a distension series an anatomic questionnaire was filled out by the subjects.

RESULTS

Sildenafil significantly reduced rectal tone in healthy subjects (intrabag volume predrug: 145.5 +/- 18.7 ml vs postdrug: 164.4 +/- 16.9 ml, p = 0.01) and IBS (111.3 +/- 25.2 ml vs 136.5 +/- 33.3 ml; p = 0.01) but did not alter rectal compliance (healthy subjects: 5.8 +/- 0.4 vs 6.3 +/- 0.6 ml/mm Hg, p > 0.05; IBS subjects: 6.1 +/- 0.6 vs 7.1 +/- 1.0 ml/mm Hg, p > 0.05). Intrabag pressure and rectal wall tension to reach perception thresholds for initial sensation, sensation of stool, and urgency were not altered by sildenafil. However, intrabag volumes to reach these thresholds were significantly increased by sildenafil both in healthy subjects and in patients with IBS. Viscerosomatic referral was unchanged.

CONCLUSIONS

Stimulation of the NO-cGMP pathway decreases rectal tone but does not influence rectal distensibility. Relaxation of the rectum is accompanied by an increase in rectal volumes to reach perception thresholds in healthy subjects and in patients with IBS, but no direct effect on rectal perception can be demonstrated.

Role of nitric oxide in the internal anal sphincter of Hirschsprung's disease

It is not clear what contribution the internal anal sphincter (IAS) makes to the impaired motility observed in patients with Hirschsprung's disease (HD). Nitric oxide (NO) has recently been shown to be a neurotransmitter in the nonadrenergic noncholinergic (NANC) inhibitory nerves in the human gut. To clarify the physiologic significance of NO in the IAS of HD (aganglionosis), we investigated the enteric nerve responses on lesional (aganglionic) and normal IAS muscle strips above the dentate line. Lesional and normal IAS muscle strips above the dentate line were derived from patients with HD (10 cases) and patients who underwent rectal amputation for low rectal cancer (12 cases). A mechanographic technique was used to evaluate in vitro muscle responses to electrical field stimulation (EFS) before and after treatment with various autonomic nerve blockers, N(G)-L-nitroarginine, and L-arginine. The following results were obtained: (1) Cholinergic nerves are mainly involved in the regulation of enteric nerve responses to EFS in the normal IAS. (2) The aganglionic IAS of patients with HD was more strongly innervated by cholinergic nerves than the normal IAS (p < 0.05). (3) NANC inhibitory nerves were found to act on the normal IAS but had no effect on the enteric nerves in patients with aganglionosis. (4) NO was found to act on normal IAS, but no effect was observed in the aganglionic IAS. These findings suggest that innervation of the cholinergic nerves and a loss of NO mediation of NANC inhibitory nerves play an important role in the impaired motility observed in the IAS with HD.

The role of nitrergic system on the contractility of colonic circular smooth muscle in Hirschsprung's disease

The contribution of nitrergic tone on the contractility of colonic smooth muscle in Hirschsprung's disease (HD) was investigated.

METHODS

Ganglionic and aganglionic bowel specimens were taken from 8 patients with HD during pull-through operations and electrical field stimulation (EFS)-induced isometric contractions of the circular smooth muscle were recorded in vitro. Isolated circular muscle strips prepared from colonic segments of sex- and age-matched patients (n = 3) who underwent surgery for nonmotility-related colonic diseases formed the control group. Statistical analysis was performed by two way analysis of variance and unpaired Student's ttest.

RESULTS

The amplitude of spontaneous rhythmic activity was lower in aganglionic segments than in ganglionic ones. The amplitudes of contractile responses were significantly greater in aganglionic segments. In ganglionic preparations, N(omega)-nitro-L-arginine (L-NNA) addition into the medium increased the contractile responses to the level of aganglionic preparations. This increase was completely blocked by L-arginine application. Neither L-NNA nor L-arginine produced any change in aganglionic segments. A relaxation phase was detected in both ganglionic and aganglionic segments. In ganglionic preparations, this relaxation phase was completely inhibited by L-NNA and restored by L-arginine, whereas no effect was detected in aganglionic ones. Responses obtained from the control group were similar to the ganglionic segments of HD patients.

CONCLUSIONS

In normal colon and as well as in ganglionic segments of HD, the evoked contractile activity and relaxations are under the tonic influence of the nitrergic system. Aganglionic segments totally lack the nitrergic activity in both evoked contraction and relaxation responses, while still maintaining an inefficient relaxation capacity under unknown mechanisms.

Turnover of radioactive mucin precursors in the colon of patients with Hirschsprung's disease correlates with the development of enterocolitis

BACKGROUND/PURPOSE

Mucin glycoproteins (mucins) in the colonic mucus gel layer interact with pathogens performing protective functions by a variety of mechanisms. It is recognised that patients with Hirschsprung's disease (HD) are prone to episodes of enterocolitis even after corrective surgery, the aetiology of which is poorly understood. The authors correlated the turnover of radioactive mucin precursors in organ culture of the proximal ganglionated colon at the time of pull-through with the development of postoperative enterocolitis.

METHODS

The colonic mucins in the retained proximal ganglionated colon of nine HD patients at the time of pull-through were studied. Organ culture of intact mucosa was performed with radioactive mucin precursors 35S-sulphate and 3H-glucosamine. Mucins in the secretions and epithelial cells were then purified by gel filtration. Turnover of the isotopes was determined by relating radioactivity to tissue DNA content. These patients were followed up prospectively for a mean duration of 30.8 months. The patients were assigned to one of two groups according to the criteria of requiring hospital admission for enterocolitis during this period. There were five patients in the group that remained well after corrective surgery and four in the group that developed entercolitis. The turnover values of both radioisotopes were analysed for differences in the two groups of patients.

RESULTS

Patients in the enterocolitis group had a median value for turnover of 331 dpm/microg DNA, and the group that was well had a median value of 2044 dpm/microg DNA. These differences were statistically significant (Mann-Whitney, P = .037).

CONCLUSIONS

A reduced turnover of mucins as shown by incorporation of radioactive precursors will give rise to a defective colonic mucus-defensive barrier. It can be inferred that the lower the turnover, the more prone a patient is to postoperative enterocolitis. It is therefore possible that organ culture with radioactive mucin precursors of the proximal ganglionated mucosa performed at the time of pull-through has a predictive value in the development of postoperative enterocolitis.

The role of motilin and cisapride in the enteric nervous system of the lower esophageal sphincter in humans

To assess the pharmacophysiological significance of the enteric nervous system and the responses of the human lower esophageal sphincter (LES) to motilin and cisapride, the mechanical responses of esophageal tissues from six patients with esophageal cancer and seven patients with gastric cancer were investigated. Circular muscle reactions were recorded to evaluate the in vitro esophageal responses to electrical field stimulation (EFS), motilin, and cisapride, evoking the adrenergic and cholinergic nerves before and after treatment with various autonomic nerve blockers. The findings of this study revealed that: cholinergic nerves are mainly involved in the regulation of enteric nerves in the steady state, while non-adrenergic non-cholinergic (NANC) inhibitory nerves also exist; motilin may act both via nerves and also directly on the LES smooth muscle; and cisapride releases acetylcholine from the end of the postganglionic fiber of the cholinergic nerve in human LES thereby inducing contraction of the LES. These results suggest that cholinergic and NANC inhibitory nerves play an important role in human LES, and that motilin and cisapride is clinically useful for improving the impaired LES of patients with gastroesophageal reflux.

Functional innervation of the aganglionic segment in Hirschsprung's disease--a comparison of the short- and long-segment type

The authors examined the neuro-effector transmission in the aganglionic segment from 13 patients with Hirschsprung's disease, 10 patients had short-segment type and three patients had long-segment type. Circular muscle strips were prepared and the responses to transmural electrical field stimulation were examined using the isometric tension recording technique. In the ganglionic preparations from the short- and long-segment cases, the stimulation evoked a biphasic response consisting of a relaxation and an atropine-sensitive contraction. The relaxation was partly inhibited by N-omega-nitro-L-arginine (NNLA, a nitric oxide [NO] synthase inhibitor), and the effect of NNLA was abolished completely in the presence of L-arginine, which suggested the presence of NO-mediated inhibitory innervation. In the aganglionic preparations from the short-segment-type cases, stimulation evoked only an atropine-sensitive contraction, while in the aganglionic preparations from the long-segment-type cases, a weak inhibitory response persisted after the contractile response was abolished by atropine. This NO-mediated inhibitory response was frequently detected as the examined region approached the ganglionic segment. These results suggest that the aganglionic segment in the long-segment-type cases might therefore receive NO-mediated inhibitory input from the proximal ganglionic segment.

Relationship between nitric oxide and non-adrenergic non-cholinergic inhibitory nerves in human lower esophageal sphincter

Nitric oxide (NO) has recently been shown to be a neurotransmitter in the non-adrenergic non-cholinergic (NANC) inhibitory nerves in the gastrointestinal tract. To clarify the the role of NO in the human lower esophageal sphincter (LES), enteric nerve responses in lower esophageal tissue specimens obtained from patients with esophageal cancer (n = 7) and patients with gastric cancer (n = 6) were investigated. A mechanographic technique was used to evaluate in vitro LES muscle responses to electrical field stimulation (EFS) of adrenergic and cholinergic nerves before and after treatment with various autonomic nerve blockers, including NG-nitro-L-arginine (L-NNA) and L-arginine. Findings were: (1) Cholinergic nerves were those mainly involved in the regulation of enteric- nerve responses to EFS in the steady state, and NANC inhibitory nerves acted on the LES; (2) L-NNA concentration-dependently inhibited the relaxation in response to EFS in the LES; and (3) this inhibitory effect in the LES was reversed by L-arginine. These findings suggest that cholinergic and NANC inhibitory nerves play important roles in regulating contraction and relaxation of the human LES, and that NO plays an important role as a neurotransmitter in NANC inhibitory nerves of the human LES.