A qualitative and quantitative study on the enkephalinergic innervation of the pig gastrointestinal tract

Gastric ulcer induced changes in substance P and Nk1, Nk2, Nk3 receptors expression in different stomach localizations with regard to intrinsic neuronal system

Gastric ulceration, a focal tissue damage accompanied by inflammation, can influence other parts of the stomach. Substance P and its receptors are strongly involved in regulation of gastrointestinal motility, secretion and inflammation. The enteric nervous system is one of the regulators of gastrointestinal functioning and contributes to tissue response to the pathology. The pig, an omnivorous animal, is a valuable species for gastrointestinal experiments. Thus, the objective of the study was to verify whether the antral ulceration induces changes in the expression of substance P and tachykinin receptors in the neighboring (antrum) and distanced (corpus, pylorus) porcine gastric tissues and therein localized myenteric and submucosal perikarya as well as in the intrinsic descending neurons supplying pyloric sphincter. The experiment was performed on healthy pigs and pigs with experimentally induced gastric ulcers. Stomach samples from the corpus, antrum (adjacent to the ulcer in experimental pigs) and pylorus were analyzed by: (1) double immunofluorescence for changes in the number of SP-positive myenteric and submucosal neurons (2) Real-Time PCR for changes in expression of mRNA encoding SP and Nk1, Nk2, Nk3 receptors. Additionally, gastric descending neurons supplying pyloric sphincter were immunostained for SP. In experimental animals, only the number of SP-positive myenteric perikarya significantly increased in all stomach localizations studied. Q-PCR revealed increased expression for: SP, Nk1, Nk3 in the corpus; Nk2 and Nk3 in the pylorus; In the antrum, expression of Nk3 was increased but Nk2-decreased. Antral ulcers induced significant changes in the expression of SP and tachykinin receptors in the wide stomach area indicating sophisticated tissue reaction.

Distribution and chemical coding patterns of cocaine- and amphetamine-regulated transcript-like immunoreactive (CART-LI) neurons in the enteric nervous system of the porcine stomach cardia

The aim of this study was to determine the presence of cocaine- and amphetamine-regulated transcript-like immunoreactive (CART-LI) neurons and co-localisation of CART with vesicular acetylcholine transporter (VAChT), neuronal nitric oxide synthase (n-NOS), vasoactive intestinal polypeptide (VIP), substance P (SP) and leu-enkephalin (LENK) in the enteric nervous system of the porcine gastric cardia by using a double-labelling immunofluorescence technique. CART-LI neurons were observed in the myenteric plexus (18.2±2.6%). A dense network of CART-LI nerve fibers was mainly observed in the muscular layer. CART showed co-localization mainly with VAChT, n-NOS, VIP and to a lesser degree with LENK and SP. Distribution of CART and its co-localization with other neurotransmitters suggest that this peptide plays an important role in gastric motility in the pig.

The Influence of Prolonged Acetylsalicylic Acid Supplementation-Induced Gastritis on the Neurochemistry of the Sympathetic Neurons Supplying Prepyloric Region of the Porcine Stomach

This experiment was designed to establish the localization and neurochemical phenotyping of sympathetic neurons supplying prepyloric area of the porcine stomach in a physiological state and during acetylsalicylic acid (ASA) induced gastritis. In order to localize the sympathetic perikarya the stomachs of both control and acetylsalicylic acid treated (ASA group) animals were injected with neuronal retrograde tracer Fast Blue (FB). Seven days post FB injection, animals were divided into a control and ASA supplementation group. The ASA group was given 100 mg/kg of b.w. ASA orally for 21 days. On the 28^th day all pigs were euthanized with gradual overdose of anesthetic. Then fourteen-micrometer-thick cryostat sections were processed for routine double-labeling immunofluorescence, using primary antisera directed towards tyrosine hydroxylase (TH), dopamine β-hydroxylase (DβH), neuropeptide Y (NPY), galanin (GAL), neuronal nitric oxide synthase (nNOS), leu 5-enkephalin (LENK), cocaine- and amphetamine- regulated transcript peptide (CART), calcitonin gene-related peptide (CGRP), substance P (SP) and vasoactive intestinal peptide (VIP). The data obtained in this study indicate that postganglionic sympathetic nerve fibers supplying prepyloric area of the porcine stomach originate from the coeliac-cranial mesenteric ganglion complex (CCMG). In control animals, the FB-labelled neurons expressed TH (94.85 ± 1.01%), DβH (97.10 ± 0.97%), NPY (46.88 ± 2.53%) and GAL (8.40 ± 0.53%). In ASA group, TH- and DβH- positive nerve cells were reduced (85.78 ± 2.65% and 88.82 ± 1.63% respectively). Moreover, ASA- induced gastritis resulted in increased expression of NPY (76.59 ± 3.02%) and GAL (26.45 ± 2.75%) as well as the novo-synthesis of nNOS (6.13 ± 1.11%) and LENK (4.77 ± 0.42%) in traced CCMG neurons. Additionally, a network of CART-, CGRP-, SP-, VIP-, LENK-, nNOS- immunoreactive (IR) nerve fibers encircling the FB-positive perikarya were observed in both intact and ASA-treated animals. The results of this study indicate involvement of these neuropeptides in the development or presumably counteraction of gastric inflammation.

Localization and neurochemical characteristics of the extrinsic sympathetic neurons projecting to the pylorus in the domestic pig

The pylorus, an important part of the digestive tract controlling the flow of chyme between the stomach and the duodenum, is widely innervated by intrinsic and extrinsic nerves. To determine the locations of postganglionic sympathetic perikarya that innervate the pylorus of the domestic pig, a retrograde tracing method with application of Fast Blue tracer was used. All positive neuronal cell bodies (ca. 1750) were found in the celiac-cranial mesenteric ganglion complex (CSMG), however, the coeliac poles of this complex provided the major input to the pylorus. Afterwards, the immunohistochemical staining procedure was applied to determine biologically active substances expressed in the FB-labeled perikarya. Approximately 77% of the FB-positive cell bodies contained tyrosine hydroxylase (TH), 87% dopamine β-hydroxylase (DβH), 40% neuropeptide Y (NPY), 12% somatostatin (SOM) and 7% galanin (GAL). The presence of all these substances in the ganglion tissue was confirmed by RT-PCR technique. Double immunocytochemistry revealed that all of the TH-positive perikarya contained DβH, about 40% NPY, 12% SOM and 8% GAL. Additionally, all above-cited immunohistochemical markers as well as VIP, PACAP, ChAT, LEU, MET, SP and nNOS were observed within nerve fibers associated with the FB-positive perikarya. Immunocytochemical labeling of the pyloric wall tissue disclosed that TH+, DβH+ and NPY+ nerve fibers innervated ganglia of the myenteric and submucosal plexuses, blood vessels, both muscular layers and the muscularis mucosae; nerve fibers immunoreactive to GAL mostly innervated both muscular layers, while SOM+ nerve fibers were observed within the myenteric plexus. Presented study revealed sources of origin and immunohistochemical characteristics of the sympathetic postganglionic perikarya innervating the porcine pylorus.

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

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

Chemical coding of myenteric neurons with different axonal projection patterns in the porcine ileum

The aim of this study was to perform an immunohistochemical characterization of two different myenteric neuron types of the pig displaying opposite axonal projections. These were type I neurons equipped with lamellar dendrites that projected mainly orally, and type VI neurons that displayed typical axonal dendrites and projected anally. Double immunostainings of longitudinal muscle/myenteric plexus wholemounts from ileal segments of four pigs were performed to visualize neurofilaments (NF) in combination with calcitonin gene-related peptide (CGRP), leu-enkephalin (ENK) and substance P (SP), respectively. Triple immunostainings of wholemounts, using antibodies against neuronal nitric oxide synthase (nNOS) and vasoactive intestinal peptide (VIP) as well as against VIP and galanin (GAL), were performed. We found that 78% of type I neurons immunoreacted to ENK, 21% to CGRP and 24% to SP. The NF-positive type I neurons co-reactive for one of the three above markers displayed mostly frayed outlines of both their somal contours and their broadened dendritic endings. By contrast, most of the non-coreactive type I neurons displayed rather sharply outlined somata and dendrites. No type I neuron immunoreacted to nNOS, VIP or GAL and none of the type VI NF-reactive neurons reacted to CGRP, ENK or SP. All type VI neurons investigated displayed immunoreactivity for nNOS, 92% of which were co-reactive for VIP. Co-reactivity for VIP and GAL was found in 69% of type VI neurons, 21% were positive for VIP but negative for GAL, 9% were negative for both GAL and VIP, and 1% were positive for GAL but negative for VIP. We conclude that there are two subpopulations of morphological type I neurons. One of these displays mainly oral projections and could not be further characterized in this study. The other, which may correspond to neurons innervating the longitudinal and circular muscle layers, were partly immunoreactive for ENK, CGRP and/or SP. Type VI neurons are immunoreactive for nNOS frequently co-localized with VIP and, partly, also GAL. These may be inhibitory motor neurons and are different from VIP/GAL-coreactive minineurons described earlier.

beta-Casomorphin-7 regulates the secretion and expression of gastrointestinal mucins through a mu-opioid pathway

We have recently shown that beta-casomorphin-7, a milk opioid peptide, strongly stimulates mucin secretion in the rat jejunum through a nervous pathway and opioid receptor activation. In this study, the hypothesis that beta-casomorphin-7 may also act directly on intestinal goblet cells was investigated in vitro in rat and human intestinal mucin-producing cells (DHE and HT29-MTX) using quantitative and semiquantitative RT-PCR and ELISA. The presence of mu-opioid receptors was demonstrated in rat goblet cells in the upper half of the colonic crypt and in the two cell lines by immunohistochemistry and RT-PCR. In rat DHE cells, beta-casomorphin-7 increased the expression of rat mucin (rMuc)2 and rMuc3 but not rMuc1, rMuc4, and rMuc5AC. This effect was time and dose dependent, with the maximum of increase in transcripts being noticed for a concentration of 10(-4) M after 2 h of stimulation for rMuc2 (225% of controls) and 4 h of stimulation for rMuc3 (208% of controls). Mucin secretion was maximally increased after 8 h of stimulation. Interestingly, these effects were prevented by pretreatment of the cells with the mu-opioid antagonist cyprodime. In human HT29-MTX cells, beta-casomorphin-7 (10(-4) M) also increased MUC5AC mRNA levels (219% after 24 h of stimulation) and the secretion of this mucin (169% of controls). In conclusion, beta-casomorphin-7 may contribute significantly to mucin production via a direct effect on intestinal goblet cells and the activation of mu-opioid receptors. Because intestinal mucins have a crucial mucosal protective function, dairy products containing beta-casomorphin-7 may improve intestinal protection and could have dietary and health applications.

Lessons from the porcine enteric nervous system

The porcine intestinal tract possesses functional and pathological similarities to the human digestive tract and the organization of the porcine enteric nervous system, like that of the human, appears to be more complex than that of commonly investigated guinea-pig intestine. Intrinsic primary afferent neurones appear to differ in the intestines of large and small animals in terms of their chemical coding, distribution over enteric neural networks, electrophysiological behaviour and synaptic properties. Opioid receptors on afferent and motor neurones in the porcine small intestine are predominately of the delta type, whereas those in guinea-pig ileum are mu. Moreover, delta-opioid receptors associated with the myenteric and submucosal plexuses of porcine ileum that, respectively, modulate neurogenic smooth muscle contractions and mucosal ion transport appear to differ in their pharmacological characteristics. These profound interspecies and interregional differences underscore the complexity of the enteric nervous system, and the development of new drugs designed to treat human neurogastrointestinal disorders should be based on the results of investigations in homologous animal models, such as the pig.

Predominance of delta-opioid-binding sites in the porcine enteric nervous system

The antidiarrheal and constipating actions of opioids are mediated in part by enteric neurons, which lie within the wall of the small intestine and colon, but the differential expression of specific, high-affinity opioid-binding sites in ganglionated plexuses within functionally distinct intestinal segments has not been examined. We determined the saturation binding characteristics under Na+-free conditions of the nonselective opioid receptor (OPR) ligand [3H][(5alpha,7alpha)-17-(cyclopropylmethyl)-4,5-epoxy-18,19-dihydro-3-hydroxy-6-methoxy-alpha, alpha-dimethyl-6,14-ethenomorphinan-7-methanol] (diprenorphine) and the respective delta-, kappa-, and mu-OPR ligands [3H]naltrindole, D-(5alpha,7alpha,8beta)-(-)-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxoaspiro-(4,5)dec-8-yl]benzeneacetamide ([3H]U-69,593), and [3H][D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO) in neuronal membranes isolated from myenteric and submucosal plexuses of porcine small intestine and colon. Naloxone-displaceable [3H]diprenorphine-binding sites (KD values ranging from 0.2-0.5 nM and Bmax = 50-95 fmol/mg of protein) were found in both subregions from all gut segments examined. High-affinity [3H]naltrindole sites (KD = 60-140 pmol) were at highest densities (approximately 60 fmol/mg of protein) in submucosal plexus of the ileum and distal colon myenteric plexus and were at lowest densities (8-9 fmol/mg of protein) in the submucosal plexuses of cecum and distal colon. [3H]U-69,593 sites (KD = 0.3-4 nM) were present only in the myenteric plexuses of all segments examined, with highest densities in cecum and proximal colon (44-47 fmol/mg of protein). [3H]DAMGO-binding sites were expressed at relatively low densities in the enteric plexuses of all gut regions. These results indicate that delta-OPRs predominate in the porcine enteric nervous system with a more circumscribed expression of kappa- and mu-OPRs.

Endogenous opiates: 2000

This paper is the twenty-third installment of the annual review of research concerning the opiate system. It summarizes papers published during 2000 that studied the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects, although stress-induced analgesia is included. The specific topics covered this year include stress; tolerance and dependence; learning, memory, and reward; eating and drinking; alcohol and other drugs of abuse; sexual activity, pregnancy, and development; mental illness and mood; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; gastrointestinal, renal, and hepatic function; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Opioid, cannabinoid and vanilloid receptor localization on porcine cultured myenteric neurons

Opioids and cannabinoids have profound inhibitory actions on intestinal motility which are mediated in part by their cognate receptors in the enteric nervous system. In the present study, we examined the expression of immunoreactivity for delta- and kappa-opioid receptors, CB(1)-cannabinoid receptors and type 1 vanilloid receptors by immunocytochemistry and confocal laser scanning microscopy on ileal myenteric neurons, isolated from juvenile pigs, that were <70 microm diameter in either axis and maintained for 1-2 weeks in primary culture. Immunoreactivities for delta-opioid and cannabinoid receptors were present in neurons immunoreactive for the cholinergic marker, choline acetyltransferase. Some neurons with delta-opioid receptor-like immunoreactivity were also immunoreactive for kappa-opioid, cannabinoid or vanilloid receptors. These observations indicate that receptors for cannabinoids or vanilloids are co-localized in opioid receptor-expressing myenteric neurons which modulate intestinal sensorimotor function.