Exogenous leptin inhibits the secretion of pancreatic juice via a duodenal CCK1-vagal-dependent mechanism in anaesthetized rats

Leptin originally described as product of the ob gene has been shown to be expressed in various tissues including the gastrointestinal tract. In this study, we investigated the influence of leptin on the secretion of pancreatic juice in biliary-pancreatic duct cannulated anaesthetised rats and in dispersed rat pancreatic acini in vitro. Exogenous leptin was given in boluses intravenously with or without CCK-8 (12 pmol kg(-1) body weight) in the presence or absence pharmacological CCK(1) receptor blockade, cervical vagotomy, and capsaicin pre-treatment. Administration of leptin (0.1, 1 and 10 microg kg(-1) body weight) did not affect the volume of bile and pancreatic juice while the protein and trypsin outputs were reduced in a dose-dependent manner. In the rats, leptin inhibited CCK-8 stimulated protein and trypsin outputs stronger than the basal pancreatic secretion. The inhibition by leptin was abolished by the pharmacological CCK(1) receptor blockade, cervical vagotomy, and capsaicin pre-treatment. In contrast, leptin did not affect basal and CCK-8-stimulated amylase release from the dispersed rat pancreatic acini in vitro. In conclusion, the results of the present study suggest that leptin does not act directly on the rat pancreatic acinar cells but inhibits the secretion of pancreatic enzymes acting indirectly via a neurohormonal CCK-vagal-dependent mechanism.

Increase in neuronal nitric oxide synthase content of the gastroduodenal tract of diabetic rats

This study examined the changes occurring in the pattern of distribution and expression of neuronal nitric oxide synthase (nNOS)-positive nerves in the gastroduodenal tract of streptozotocin-induced diabetic rats. The ganglion cells of the myenteric plexus of the gastric antrum of normal rats contain nNOS. We also observed nNOS-positive neurons and fibres in the myenteric plexus of the duodenum of normal rats. After the onset of diabetes, the number and intensity of staining of nNOS-positive nerve profiles in the gastric antrum and duodenum did not change significantly. However, Western blotting showed a significant increase in the expression of nNOS after the onset of diabetes. In conclusion, diabetes of 4 and 32 weeks duration induced an increase in the tissue content of nNOS in the gastroduodenum of rat. The increase in the level of nNOS in the gastroduodenum of diabetic rats may explain why impaired gastric emptying is common in patients with diabetes.

PKA-mediated inhibition of a novel K+ channel underlies the slow after-hyperpolarization in enteric AH neurons

Postspike after-hyperpolarizations (AHPs) control the excitability of neurons and are important in shaping firing patterns. The duration of some of these events extends to tens of seconds and they can render neurons inexcitable for much of their time course. While consensus is strong that the medium duration (< 1 s AHPs are mediated by the opening of small conductance Ca2+-activated K+ channels, the K+ channels mediating slow AHPs (> 5 s in a subset of enteric (AH) neurons) have an intermediate unit conductance (IKCa). Using whole-cell and excised-patch recording, we have demonstrated that the cAMP-protein kinase A (PKA) pathway regulates the activity of these channels. In whole-cell mode, forskolin (0.003-1 microM) inhibited the current underlying the slow AHP (IsAHP) by 90 %, and this was partially sensitive to inhibition of PKA with internal Rp-cAMPS (500 microM). Rp-cAMPS alone increased the current following break-in and caused a 20 mV hyperpolarization, suggesting that PKA maintains slow AHP channels in the closed state. Internal perfusion of the inhibitory peptide PKI5-24 slightly increased the IsAHP and opposed the inhibitory action of forskolin. Internal perfusion of the catalytic subunit of PKA (PKAcat) suppressed the IsAHP by 50 % without affecting membrane potential or action potential configuration. In inside-out patches containing IKCa-like channels, PKAcat decreased the open probability of IKCa-like channels while alkaline phosphatase activated them. These results suggest that the IKCa-like channels that underlie the slow AHP in myenteric AH neurons are subject to inhibition by PKA-dependent phosphorylation and that PKA plays an integral role in their gating.

Sensory and biomechanical responses to ramp-controlled distension of the human duodenum

The aim of this study was to develop a new method for investigation of the relationship among the mechanical stimulus, the biomechanical properties, and the visceral perception evoked by volume/ramp-controlled distension in the human duodenum in vivo. An impedance planimetric probe for balloon distension was placed in the third part of the duodenum in seven healthy volunteers. Distension of the duodenum was done at infusion rates of 10, 25, and 50 ml/min. The pump was reversed when level 7 was reached on a visual analog scale ranging from 0 to 10. Distensions were done with and without the administration of the antimuscarinic drug butylscopolamine. The total circumferential tension (T(total)) and the passive circumferential tension (T(passive)) were determined from the distension tests without and with the administration of butylscopolamine, respectively. T(total) and T(passive) showed an exponential behavior as a function of strain (a measure of deformation). The active circumferential tension (T(active)) was computed as T(total)-T(passive) and showed a bell-shaped behavior as a function of strain. At low distension intensities, the intensity of sensation at 10 ml/min was significantly higher than that obtained at 25 and 50 ml/min. The coefficient of variation at the pain threshold for circumferential strain (average 4.34) was closer to zero compared with those for volume (8.72), pressure (31.22), and circumferential tension (31.55). This suggests that the mechanoreceptors in the gastrointestinal wall depend primarily on circumferential strain. The stimulus-response functions provided evidence for the existence of low- and high-threshold mechanoreceptors in the human duodenum. Furthermore, the data suggest that high-threshold receptors are nonadapting.

Expression of 5-HT3 receptors by extrinsic duodenal afferents contribute to intestinal inhibition of gastric emptying

Intestinal perfusion with carbohydrates inhibits gastric emptying via vagal and spinal capsaicin-sensitive afferent pathways. The aim of the present study was to determine the role of 1) 5-hydroxytryptamine (5-HT)(3) receptors (5-HT(3)R) in mediating glucose-induced inhibition of gastric emptying and 2) 5-HT(3)R expression in vagal and spinal afferents in innervating the duodenum. In awake rats fitted with gastric and duodenal cannulas, perfusion of the duodenum with glucose (50 and 100 mg) inhibited gastric emptying. Intestinal perfusion of mannitol inhibited gastric emptying only at the highest concentration (990 mosm/kgH(2)O). Pretreatment with the 5-HT(3)R antagonist tropisetron abolished both glucose- and mannitol-induced inhibition of gastric emptying. Retrograde labeling of visceral afferents by injection of dextran-conjugated Texas Red into the duodenal wall was used to identify extrinsic primary afferents. Immunoreactivity for 5-HT(3)R, visualized with an antibody directed to the COOH terminus of the rat 5-HT(3)R, was found in >80% of duodenal vagal and spinal afferents. These results show that duodenal extrinsic afferents express 5-HT(3)R and that the receptor mediates specific glucose-induced inhibition of gastric emptying. These findings support the hypothesis that enterochromaffin cells in the intestinal mucosa release 5-HT in response to glucose, which activates 5-HT(3)R on afferent nerve terminals to evoke reflex changes in gastric motility. The primary glucose sensors of the intestine may be mucosal enterochromaffin cells.

Electro-acupuncture stimulation effects on duodenal motility in anesthetized rats

The effect of electro-acupuncture stimulation (EAS) on duodenal motility was examined in anesthetized, artificially ventilated rats. EAS was applied to the abdominal area or to a hindpaw for 30 s at stimulus intensities of 0.1-10.0 mA with a stimulus frequency of 20 Hz. The duodenal motility was measured using the balloon method at a position about 1.5 cm caudal from the pylorus. Duodenal motility was inhibited by EAS at intensities of more than 5.0 mA (suprathreshold of group IV afferent excitation) when applied to the abdominal area. The duodenal inhibitory response existed after bilateral vagotomy or spinal transection, but was abolished by sectioning bilateral splanchnic nerves. Duodenal motility was facilitated by EAS at intensities of more than 2.0 mA (subthreshold of group IV, and suprathreshold for groups II+III afferent excitation) when applied to a hindpaw. The duodenal facilitatory response by EAS to a hindpaw existed after sectioning the splanchnic nerves, but disappeared after bilateral vagotomy or spinal transection. Furthermore, repetitive electrical stimulation of vagal efferent nerves enhanced duodenal motility, while repetitive electrical stimulation of the splanchnic efferent nerves inhibited the motility. It was concluded that the inhibitory response of duodenal motility elicited by EAS to the abdominal area is a spinal reflex response involving splanchnic inhibitory efferent nerves, and the enhanced response of duodenal motility by EAS to a hindpaw is a supraspinal reflex response involving vagal excitatory nerves.

CART in the dorsal vagal complex: sources of immunoreactivity and effects on Fos expression and food intake

CART-peptide (CARTp) has been shown to suppress food intake, particularly when injected into the 4th ventricle of rats, and the presence of CART in nodose ganglia suggested a role in satiation. Based on retrograde tracing from the DVC combined with CART immunohistochemistry and supranodose vagotomy, we found that CART immunoreactivity in varicose fibers of the dorsal vagal complex originates from vagal afferents, sparse projections from the medullary reticular formation and the arcuate/retrochiasmatic nucleus of the hypothalamus, and most likely also from local CART neurons in the area postrema and NTS. In the nodose ganglia, 17% of neurons with projections to the stomach and 41% to the duodenum express CART-IR. CART-IR vagal afferents significantly contribute to the rich fiber plexus in mainly the commissural NTS and the adjacent area postrema. Injections of CARTp into the 4th ventricle strongly suppressed sucrose drinking and stimulated expression of c-Fos in the NTS. Injections of CARTp directly into various subnuclei of the NTS were less effective in suppressing food intake. The findings suggest that the critical site for CART's suppression of food intake is not in the termination zone of CART-containing vagal afferents in the commissural NTS, and that CART release from vagal afferent terminals plays a minor role in satiation. The functional role of CART in vagal afferents and the site of food intake suppression by 4th ventricular CARTp remain to be determined.

Ruthenium red-sensitive cation channels, but not calcitonin gene-related peptide or substance P-mediated mechanisms, protect duodenal villi against acid-induced damage

Intestinal mucosal capsaicin-sensitive afferent nerves mediate, in part, the protective mesenteric hyperemia after intraduodenal acidification. Mechanisms associated the sensory neuropeptides, e.g. calcitonin gene-related peptide (CGRP), substance P, and ruthenium red-sensitive cation channels contribute to acid-induced mesenteric hyperemia, but whether they play a role in protection against acid-induced duodenal villous damage is not known. We tested the hypothesis that in doses that attenuate acid-induced hyperemia, inhibitors of these mechanisms will exacerbate acid-induced duodenal villous damage. Intravenous vehicle, specific receptor antagonists of CGRP (CGRP(8-37)), substance P (CP 96345), intraduodenal ruthenium red or vehicle was administered, followed by intraduodenal perfusion with 0.1 N HCl. Duodenal tissue was processed for hematoxylin and eosin staining. Villous damage was scored by blinded observers. Deep villous injury was significantly increased after treatment with ruthenium red, but not with CGRP(8-37) or CP 96345. These findings support the hypothesis that ruthenium red-sensitive cation channels, but not neuropeptides associated with intestinal mucosal afferent nerves, are involved in the acid-sensing mechanism which mediates the protection against acid-induced duodenal villous damage.

Neuronal activation of brain vagal-regulatory pathways and upper gut enteric plexuses by insulin hypoglycemia

Neuronal activation of brain vagal-regulatory nuclei and gastric/duodenal enteric plexuses in response to insulin (2 U/kg, 2 h) hypoglycemia was studied in rats. Insulin hypoglycemia significantly induced Fos expression in the paraventricular nucleus of the hypothalamus, locus coeruleus, dorsal motor nucleus of the vagus (DMN), and nucleus tractus solitarii (NTS), as well as in the gastric/duodenal myenteric/submucosal plexuses. A substantial number of insulin hypoglycemia-activated DMN and NTS neurons were choline acetyltransferase and tyrosine hydroxylase positive, respectively, whereas the activated enteric neurons included NADPH- and vasoactive intestinal peptide neurons. The numbers of Fos-positive cells in each above-named brain nucleus or in the gastric/duodenal myenteric plexus of insulin-treated rats were negatively correlated with serum glucose levels and significantly increased when glucose levels were lower than 80 mg/dl. Acute bilateral cervical vagotomy did not influence insulin hypoglycemia-induced Fos induction in the brain vagal-regulatory nuclei but completely and partially prevented this response in the gastric and duodenal enteric plexuses, respectively. These results revealed that brain-gut neurons regulating vagal outflow to the stomach/duodenum are sensitively responsive to insulin hypoglycemia.

Selective loss of vagal intramuscular mechanoreceptors in mice mutant for steel factor, the c-Kit receptor ligand

Vagal intramuscular arrays are mechanoreceptors that innervate smooth muscle fibers and intramuscular interstitial cells of Cajal of the proximal GI tract. C-Kit mutant mice that lack intramuscular interstitial cells of Cajal also lack intramuscular arrays. Mice mutant for steel factor, the ligand for the c-Kit receptor, were studied to extend and validate these previous findings and to characterize associated changes in food intake. Injections of wheat germ agglutinin-horseradish peroxidase and of dextran into the nodose ganglion were employed to label intramuscular arrays and intraganglionic laminar endings, the other vagal mechanoreceptors found in the gut wall. These two receptor types were inventoried in wholemounts of the stomach and duodenum using a standardized sampling and quantification regime. Steel mutants exhibited a paucity of normal intramuscular arrays and lacked intramuscular interstitial cells of Cajal in the forestomach, whereas their intraganglionic laminar endings appeared normal in number, distribution, and morphology. These observations suggest that intramuscular array losses in steel and c-Kit mutants are specific and result from the elimination of the intramuscular interstitial cells of Cajal, the effect common to both mutations, not from interactions peculiar to background strains or non-specific effects. Double-labeling analyses of intramuscular arrays and intramuscular interstitial cells of Cajal reinforced the hypothesis based on previous findings in the c-Kit mice that these interstitial cells have a trophic effect on intramuscular array development and/or maintenance. Finally, meal pattern analyses revealed decreased meal size and increased meal frequency in steel mutants, with normal daily intake. These alterations suggest short-term feeding controls are affected by the loss of intramuscular arrays and/or intramuscular interstitial cells of Cajal, though long-term controls are unimpaired.

Neurokinin-1 and neurokinin-3 receptors are expressed in vagal efferent neurons that innervate different parts of the gastro-intestinal tract

Vagal efferent neurons innervating the digestive tract are mainly contained in the dorsal motor nucleus of the vagus. Previous studies have suggested that neurokinins and their neurokinin-1 and neurokinin-3 receptors are involved in the parasympathetic control of digestive functions. The purpose of the present study was to analyze the distribution of neurokinin-1 and neurokinin-3 receptors amongst vagal efferent neurons innervating the stomach, the duodenum, the ileum and the cecum. The immunocytochemical detection of neurokinin-1 and neurokinin-3 receptors was combined with the immunocytochemical detection of retrogradely transported cholera toxin-B subunit, previously injected in the gut wall. Neurokinin-1 and neurokinin-3 receptors were present in 19+/-7% and 8+/-3% of retrogradely labeled neurons innervating the stomach. Almost half of the labeled neurons innervating the duodenum (46+/-7%) expressed neurokinin-1 receptors but less than 0.5% contained neurokinin-3 receptors. None of the retrogradely labeled vagal efferent neurons innervating the ileum and the cecum were immunoreactive for neurokinin-1 and neurokinin-3 receptors. We conclude that neurokinin-1 and neurokinin-3 receptors are located on vagal efferent neurons which innervate the stomach and that neurokinin-1 receptors are common, whereas neurokinin-3 receptors are rare on neurons projecting to the duodenum. Additionally, the distal part of the rat small intestine is innervated by vagal efferent neurons that do not express neurokinins receptors on their membrane. This suggests that neurokinins may influence the parasympathetic control of different regions of the gastro-intestinal tract in specific ways.

Biliary sphincter motility after neural isolation of the pancreatoduodenal region in conscious dogs

BACKGROUND

Several neural and hormonal factors are known to affect the motility of the sphincter of Oddi. However, the precise mechanisms of the control of sphincter motility have not been completely explored. We investigated the relationship of canine biliary sphincter motility when it is extrinsically denervated by neural isolation of the pancreatoduodenal region.

METHODS

Interdigestive and postprandial sphincter motility in a denervated pancreatoduodenal segment and effects of cholecystokinin-octapeptide were studied in 7 conscious dogs. Data were compared with those of 7 neurally intact control dogs.

RESULTS

After extrinsic denervation of the pancreatoduodenal region, sphincter motility exerted a cyclic change in concert with the duodenal myoelectric cycles; this change involved short cyclic bursts of motor activity, which gradually increased in intensity. The increase in the cyclic bursts of motor activity was also cyclic and associated with an increase in the plasma motilin concentration. Neural isolation of the pancreatoduodenal region increased sphincter basal pressure and motility index (integral per minute). In the denervated biliary sphincter, the feeding pattern and temporary inhibitory effect of feeding, as seen in controls, were absent, which suggests the role of extrinsic nerves in delivering bile into the duodenum after feeding. In the denervated dogs, cholecystokinin-octapeptide caused excitation of the sphincter activity, instead of relaxation observed in controls.

CONCLUSIONS

Extrinsic innervation to the pancreatoduodenal region has an inhibitory effect on biliary sphincter motility. Abnormalities in extrinsic innervation to the biliary sphincter might increase the resistance of the sphincter to the bile flow and induce bile stagnation.

Site-specific gene expression of nNOS variants in distinct functional regions of rat gastrointestinal tract

5' mRNA variants of neuronal nitric oxide synthase (nNOS) are generated either by alternative promoter usage resulting in different mRNAs that encode for the same protein (nNOSalpha) or alternative splicing encoding NH(2)-terminally truncated proteins (nNOSbeta/gamma) that lack the PDZ/GLGF domain for protein-protein interaction of nNOSalpha. We studied the expression of 5' nNOS mRNA forms and nNOS-interacting proteins (postsynaptic density protein-95; PSD-95) in the rat gastrointestinal tract and analyzed the more distinct localization of nNOS protein variants in the duodenum by immunohistochemistry with COOH- and NH(2)-terminal nNOS antibodies. 5' nNOS mRNA variants showed a site-specific expression along the gastrointestinal tract with presence of all forms (nNOSalpha-a, -b, -c; nNOSbeta) in the muscle layer of esophagus, stomach, duodenum, longitudinal muscle layer of jejunum/ileum, proximal colon, and rectum. In contrast, a lack of nNOSalpha-a and nNOSbeta mRNA was observed in pylorus, circular muscle layer of jejunum/ileum, and cecum. Expression of nNOSalpha and nNOSbeta cDNAs revealed proteins of ~155 kDa and 135/125 kDa, respectively. Immunohistochemistry showed a differential distribution of COOH- and NH(2)-terminal nNOS immunoreactivity in distinct layers of rat duodenum, suggesting a cell-specific expression and distinct compartmentalization of nNOS proteins. Observed distribution of 5' nNOS mRNA variants and proteins argue for a complex control of nNOS expression by usage of separate promoters, cell- and site-specific splicing mechanisms, and translational initiation. These mechanisms could be involved in gastrointestinal motor diseases and may explain the phenotype of nNOSalpha knockout mice with gastric stasis and pyloric stenosis, due to a total loss of nNOS in the pyloric sphincter region.

Characterization of circular muscle motor neurons of the duodenum and distal colon in the Australian brush-tailed possum

The motor innervation of the duodenum and distal colon remains uncharacterized within the same species. Our aim was to compare the projections and neurochemical properties of duodenal and distal colon circular muscle motor neurons. Circular muscle motor neurons were retrogradely traced by using a neural tracer in vitro, processed for choline acetyltransferase (ChAT) and nitric oxide synthase (NOS) immunoreactivity and then visualized by using indirect immunofluorescence. A mean of 372 +/- 64 and 156 +/- 23 neurons (mean +/- SEM) were tracer-labeled within the duodenum and colon, respectively. The ChAT+/NOS- neurons comprised 57.6 +/- 6.6% and 39.6 +/- 4.4% of all labeled cells in the duodenum and colon, respectively, and projected mainly in the oral direction. Of all labeled cells, the ChAT-/NOS+ neurons comprised 8.5 +/- 2.3% in the duodenum and 46.6 +/- 5.0% in the distal colon and projected mainly in the anal direction. Of the remainder, 20.6 +/- 5.0% and 8.2 +/- 2.4% were ChAT+/NOS+ and 13.2 +/- 0.9% and 5.6 +/- 1.4% were ChAT-/NOS- in the duodenum and distal colon, respectively. Within both regions, the distribution of the ChAT+/NOS- and ChAT-/NOS+ neurons are consistent with the ascending excitatory and descending inhibitory reflexes. The proportion of ChAT-/NOS+ neurons is greater within the colon in comparison with the duodenum. A considerable proportion of duodenal motor neurons were ChAT+/NOS+ and ChAT-/NOS-. These two classes may underlie nonperistaltic motor patterns, which predominate within the duodenum. These findings demonstrate regional differences in the innervation of intestinal circular muscle.

Vagal afferents innervating the gastrointestinal tract and CCKA-receptor immunoreactivity

A large body of evidence derived from electrophysiological recording and pharmacological/behavioral experiments suggests the presence of CCKA-receptors on vagal primary afferent fibers innervating the gastrointestinal tract. With the availability of antibodies specific for the CCKA-receptor, we wanted to demonstrate its presence and distribution on identified vagal afferent fibers and different types of terminals in the mucosa, myenteric plexus, and external muscle layers of the stomach and duodenum. In the duodenal mucosa, neither a C-terminal (Ab-1) nor an N-terminal (Ab-2) specific antibody produced any specific staining; in the myenteric plexus, non-vagal enteric neurons and their processes, but not vagal intraganglionic laminar endings (IGLEs), exhibited CCKAR-immunoreactivity. Similarly, in the gastric myenteric plexus, a population of enteric neurons and their processes, but not identified vagal IGLEs, were labeled by both antibodies. In both external muscle layers of the stomach, CCKAR-immunoreactive axons were in close register with labeled vagal afferent intramuscular arrays, but the two labels were not contained in the same varicosities. Ab-1 immunoreactivity was found in the cell membrane of vagal afferent perikarya in the nodose ganglia and in pancreatic acinar cells. The failure to detect CCKAR-immunoreactivity in peripheral vagal afferent terminals cannot be due to methodological problems because it was present in enteric neurons in the same sections, and because it did not stain structures resembling IGLEs in material without the potentially masking vagal afferent label. We conclude that CCKA-receptors on vagal afferent terminals: 1) are below the immunohistochemical detection threshold, 2) exhibit a conformation or affinity state inaccessible to the two antibodies, or 3) are not transported to the peripheral terminals.

Within-meal gut feedback signaling

During a meal, multiple gastrointestinal sites are stimulated by ingested nutrients and their digestion products, initiating local gastrointestinal actions and producing a variety of potential feedback signals that can contribute to meal termination. During ingestion, gastric emptying is rapid, allowing a significant portion of ingested nutrients to enter the intestine. Gastric and duodenal vagal afferent fibers increase their electrophysiological activity in relation to the mechanical presence of ingested nutrients. On reaching the duodenum, nutrients also activate vagal chemosensitive elements and stimulate the release of a variety of brain gut peptides including cholecystokinin (CCK). CCK also activates vagal afferent fibers directly and modifies the response properties of vagal mechanosensitive fibers to gastric and duodenal loads. Blocking or eliminating these feedback signals results in increased meal size demonstrating their role in meal termination.

The innervation of the human antro-pyloric region: organization and composition

Although the composition of the gastric innervation has been determined in animal models, relatively little known about the innervation of the human antro-pyloric region. We used immunocytochemical techniques to establish the localization and co-expression of neuropeptides and nitric oxide in the human antrum and upper duodenum. Our results demonstrate the existence of a clearly defined submucosal plexus in the antral region that is absent in rats and guinea pigs. The abundant innervation of the lamina propria contains 3 major nerve populations: VIP- and NOS-, SP- and CGRP-, and GRP-immunoreactive. For the first time, NOS-containing nerve fibers were observed throughout the length of the antral glands. Within the antrum somatostatin was confined to endocrine cells, however, at the pyloric sphincter both enteric plexi contained immunoreactive neurons and nerve fibres. Within the pyloric sphincter CGRP- and SP-immunoreactive fibres were significantly increased, correlating with the presence of large ganglia in the submucosal plexus. In conclusion, the organization and composition of the innervation of human antro-pylorus differed substantially from that reported in other mammals. The presence of an abundant mucosal innervation paralled by a well-defined submucosal plexus indicates that the functional regulation of the gastric-pyloric region will be distinct from that of smaller animal models.

Neurotrophin-4 deficient mice have a loss of vagal intraganglionic mechanoreceptors from the small intestine and a disruption of short-term satiety

Intraganglionic laminar endings (IGLEs) and intramuscular arrays (IMAs) are the two putative mechanoreceptors that the vagus nerve supplies to gastrointestinal smooth muscle. To examine whether neurotrophin-4 (NT-4)-deficient mice, which have only 45% of the normal number of nodose ganglion neurons, exhibit selective losses of these endings and potentially provide a model for assessing their functional roles, we inventoried IGLEs and IMAs in the gut wall. Vagal afferents were labeled by nodose ganglion injections of wheat germ agglutinin-horseradish peroxidase, and a standardized sampling protocol was used to map the terminals in the stomach, duodenum, and ileum. NT-4 mutants had a substantial organ-specific reduction of IGLEs; whereas the morphologies and densities of both IGLEs and IMAs in the stomach were similar to wild-type patterns, IGLEs were largely absent in the small intestine (90 and 81% losses in duodenum and ileum, respectively). Meal pattern analyses revealed that NT-4 mutants had increased meal durations with solid food and increased meal sizes with liquid food. However, daily total food intake and body weight remained normal because of compensatory changes in other meal parameters. These findings indicate that NT-4 knock-out mice have a selective vagal afferent loss and suggest that intestinal IGLEs (1) may participate in short-term satiety, probably by conveying feedback about intestinal distension or transit to the brain, (2) are not essential for long-term control of feeding and body weight, and (3) play different roles in regulation of solid and liquid diet intake.

Heterogeneous distribution of a gap junction protein, connexin43, in the gastroduodenal junction of the guinea pig

The gastroduodenal junction differs in morphology and function from the stomach and the duodenum. We studied the immunohistochemical distribution of the gap junction protein, connexin43, and the nerve terminal proteins, SNAP-25 and synaptotagmin, in the musculature of the guinea pig gastroduodenal junction. Connexin43-immunopositive structures were distributed throughout the circular layer of the gastroduodenal junction, most densely in the duodenal circular layer. The difference in the distribution patterns of these structures between the stomach and the duodenum was readily observed in the gastroduodenal junction. In the inner part of the circular muscle layer of the gastroduodenal junction, the connexin43-immunopositive structures were relatively few or non-existent, whereas the SNAP-25-containing nerve fibers and synaptotagmin-containing nerve terminals, clearly observed, were numerous. These findings show a heterogeneous distribution of the gap junctions and nerves in the gastroduodenal junction. The results suggest that the gastroduodenal junction has heterogeneous electrical connections among smooth muscle cells via gap junctions, and specific nerve innervation, which regulates gastroduodenal motility.

Exposure of Escherichia coli to intestinal myoelectrical activity-related electric field induces resistance against subsequent UV(254 nm) (UVC) irradiation

Survival of Escherichia coli K-12 AB1157 irradiated with UVC (UV(254 nm)) was enhanced after pre-treatment with a low-tension electric field (EF). The EF used was identical to the electrical field generated by the small intestine (myoelectrical migrating complex--MMC), registered in a healthy calf and transmitted into the memory of an EF generator. The EF emitted by the generator was transmitted via electrodes placed in shaken bacterial cultures. The protective effects of the EF on the E. coli survival after exposure to UV were: (i) observed only for the dnaJ(+)dnaK(+) strain, and not for the DeltadnaJdnaK heat shock mutant; (ii) strictly dependent on the temperature at which the bacteria were grown; (iii) most obvious when the bacteria were incubated at 37 degrees C. Moreover, the MMC-related EF and a higher temperature (40 degrees C) show a similar protective effect against UV-irradiation. The results point to the involvement of the heat shock response in the low-tension EF-induced protection of bacterial cells against UVC-irradiation. Additionally, treatment with the MMC-related EF affects total protein contents and their pattern in E. coli cells. The EF-treatment did not show any influence on the level of the argE3(ochre) --> Arg(+) reversions.

Changes in serotonin levels and 5-HT receptor activity in duodenum of streptozotocin-diabetic rats

Few previous studies have discussed the changes in serotonin receptor activity in the small intestine of diabetic animals. Therefore, we examined serotonin content in duodenal tissue and dose-dependent effects of serotonin agonists and antagonists on the motor activity of ex vivo vascularly perfused duodenum of streptozotocin (STZ)-diabetic rats. Serotonin content was significantly increased in enterochromaffin cells but not altered in serotonin-containing neurons in STZ-diabetic rats. Motor activity assessed by frequency, amplitude, and percent motility index per 10 min of pressure waves was reduced in the duodenum of diabetic rats, and this reduction was reversed by insulin treatment. Serotonin dose dependently increased the motor activity in control rat duodenum but only a higher concentration of serotonin increased the motor activity in diabetic rats. The 5-hydroxytryptamine (5-HT) receptor subtype 4 (5-HT(4)) antagonist SB-204070 dose dependently reduced motor activity in both control and diabetic rats, whereas the 5-HT(3) receptor antagonist azasetron, even at a higher concentration, failed to affect motor activity in diabetic rat duodenum but dose dependently reduced motor activity in control rat duodenum. These results suggest that 5-HT(3) receptor activity was impaired but 5-HT(4) receptor activity was intact in STZ-diabetic rat duodenum. Such an impairment of 5-HT(3) receptor activity may induce the motility disturbance in the small intestine of diabetes mellitus.

Neuropeptides in the duodenal mucosa of chronic alcoholic heavy drinkers

Previous studies have shown that patients with chronic alcohol ingestion may show a variety of morphological and functional alterations in the small intestine. In this study, we have focused on the neuroendocrine system in the duodenal mucosa in chronic alcoholics; an area little studied. Twenty-three defined chronic alcoholics admitted to the hospital for detoxification underwent clinical examination, followed by upper gastrointestinal endoscopy and blood tests on average 4 days after the most recent alcohol intake. Biopsy specimens were taken from the distal part of the descending duodenum for both immunohistochemical and routine histological examination. The control group consisted of 25 patients referred for upper endoscopy mainly because of dyspepsia (ulcer, reflux type), but who were otherwise healthy. A normal carbohydrate-deficient transferrin and a history of low alcohol consumption (<40 g/week) were required for inclusion in the control group. The tissue specimens were studied using antisera for the following neuropeptides: cholecystokinin, galanin, gastric inhibitory peptide (GIP), glucagon, motilin, neuropeptide Y, pituitary adenylyl cyclase activating peptide, secretin, serotonin, somatostatin, substance P, vasoactive intestinal polypeptide and protein gene product, as a general marker for neurones and cells of the diffuse neuroendocrine system. The density of nerve fibres was evaluated semi-quantitatively and the number of endocrine cells per unit length of mucosa was counted in sections cut perpendicularly to the mucosal surface. All the different peptidergic nerve fibres in the alcohol group showed higher densities than the corresponding controls. However, this was not a statistically significant difference. A slightly significant increase (P = 0.02) in the numbers of glucagon and GIP cells was seen in the alcohol group. Gastrointestinal symptoms were frequently present (87%) in chronic alcoholics. We suggest that chronic alcohol consumption in man may have a general effect on the peptidergic nerve system and some endocrine cell types in the duodenal mucosa.

Developmental changes in heme-oxygenase-2 and bNOS expression in enteric neurons in the pig duodenum

There exists much parallelism between carbon monoxide- and nitric oxide-generating systems. Therefore, we wondered whether developmental and functional differences along the duodenum similarly affect, part of them, namely, heme oxygenase-2-(HO-2) and neural isoform of nitric oxide synthase- (nNOS) expressing neurons. By applying NADPH diaphorase histochemistry and HO-2 immunohistochemistry on whole-mount preparations and by using stereologic methods, a qualitative and quantitative description of HO-2 and nNOS expression was obtained. Examinations were carried out on the duodenum of fetal, neonatal and weaned pigs. At all ages, three enteric plexuses were readily distinguished. The presence of both enzymes fits in with other morphological and physiological reports. However, the expression of both enzymes significantly changed during development. The number of HO-2-IR neurons increased approximately 20-fold in the inner submucous and almost doubled in the myenteric plexus. In addition, the number of nNOS-expressing neurons displayed a significant decrease in the outer submucous plexus after weaning. High levels of glucocorticoids may cause the perinatally increased HO-2 expression, whereas an influence on nNOS expression is doubtful. Therefore, it seems that notwithstanding the high similarity between both systems, their expression is regulated differently in the pig duodenum.

Locations and innervation of cell bodies of sympathetic neurons projecting to the gastrointestinal tract in the rat

The locations of cell bodies of sympathetic neurons projecting to the stomach, the duodenum, the ileum, the colon, the spleen and the pancreas have been studied using retrograde tracing. Projections arose from both pre- and paravertebral ganglia. In the rat, the prevertebral ganglia are the paired coeliac ganglia lying caudo-lateral to the root of the coeliac artery, paired splanchnic ganglia in the abdominal segments of the greater splanchnic nerves, unpaired superior mesenteric and inter-renal ganglia and the inferior mesenteric ganglia. The projections from the prevertebral sympathetic ganglia to the different parts of the gut were organised somatotopically. The most rostral ganglia (splanchnic, coeliac, and superior mesenteric ganglia) contained neurons innervating all regions of the gastrointestinal tract, the pancreas and the spleen. The inter-renal and inferior mesenteric ganglia, located more caudally, contained neurons innervating the distal part of the gut (distal ileum and colon). The innervation of the spleen and the pancreas came from the closest ganglia (sympathetic chains, splanchnic and coeliac ganglia). This organotopic organisation was not found in the sympathetic chain ganglia; the innervation of all organs came predominantly from the lower part of the thoracic chains. A large proportion of the retrogradely labelled nerve cells in the splanchnic ganglia received nitric oxide synthase immunoreactive innervation probably from the spinal cord. In the other prevertebral ganglia, most of the neurons received nitric oxide synthase immunoreactive innervation and/or bombesin immunoreactive innervation. This leads to the conclusion that, in these ganglia, many neurons receive projections from the gastrointestinal tract in addition to the spinal cord.

Effect of surgical alteration of the rat gastrointestinal tract on the growth and development of Hymenolepis diminuta

Eight groups of rats were used to study the involvement of the enteric (ENS) and central (CNS) nervous systems in the development of Hymenolepis diminuta using surgical intestinal transection, or CNS denervation, or both procedures. The transection procedure was used to isolate the ENS of the small intestine from either orad and/or caudal portions of the alimentary system, while the CNS denervation was used to eliminate direct visceral efferent inputs from the CNS. Nine days after the surgical procedures, all rats were infected with 35 cysticercoids of H. diminuta. On 20 days postinfection, the infection intensity, tapeworm dry weight, tapeworm morphology, intestine length, and intestinal wet weight were recorded. Only the combination of the duodenal and ileal transections with a CNS denervation reduced infection intensity and prevented the increased intestinal length normally observed in infected rats. In contrast, none of the various intestinal transection procedures alone or CNS denervation alone had any effect on the survival, ability to produce oncospheres or morphology of the tapeworms. In conclusion, tapeworm survival is decreased when both CNS and ENS inputs into the small intestine are altered or absent.