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Background: Although colonoscopy is the standard procedure in the diagnosis of colorectal neoplasia, a significant number of clinically relevant lesions may be missed even by experienced endoscopists using current technology. Particular problems may occur with blind spots behind the semilunar folds and within the right colon. A transparent cap mounted at the tip of a colonoscope may be an easy way to extend the visual field during colonoscopy and may improve the detection rate of mucosal lesions. However, data in the literature are controversial and the quantity of the potential extension of visualization by a transparent cap has not been reported yet., Material and Methods: The significance of cap-assisted colonoscopy (CAC) to increase visualization within different colonic segments (rectum, sigmoid colon, descending colon, transverse colon, ascending colon, cecum) was quantitatively analyzed by randomized back-to-back colonoscopies with and without cap. The investigations were performed in a colonic training model by 5 investigators. The inner colonic surface was stained by a raster of dots and the number of dots counted during colonoscopy served as a measure for the visible surface area of each segment., Results: The time to advance the colonoscope to the respective colonic segments and the overall time to reach the cecum were not significantly different between conventional and CAC. In contrast, overall withdrawal time and withdrawal times for the cecum, ascending colon, descending colon and rectum were significantly longer for CAC, but not for the transverse and sigmoid colon. Visualization of the colonic surface was significantly increased during CAC. Overall, 59.76 ± 2.70 % of the maximal countable dots were visualized without cap and 85.36 ± 9.62 % with cap. The improvement of visualization was only significant for the right colon, but not for the rectum, sigmoid or descending colon., Conclusion: The finding of the present study suggests that the extension of visualization by CAC may be of particular value for the right colon., (© Georg Thieme Verlag KG Stuttgart · New York.)

Background & Aims: Hydrogen sulfide (H(2)S) has been suggested as a novel gasomediator. We explored its unknown neuromodulatory role in human and guinea-pig colon., Methods: We used immunohistochemistry to detect H(2)S-producing enzymes cystathionine gamma-lyase (CSE) and cystathionine beta-synthase (CBS) in enteric neurons, Ussing chambers to measure mucosal ion secretion, and neuroimaging with voltage- and Ca(++)-sensitive dyes to record H(2)S effects on guinea-pig and human enteric neurons., Results: More than 90% of guinea-pig and human submucous and myenteric neurons were colabeled for CSE and CBS. Myenteric interstitial cells of Cajal were CSE-immunoreactive. The exogenous H(2)S donor NaHS (0.2-2.5 mmol/L) concentration-dependently increased chloride secretion in human and guinea-pig submucosa/mucosa preparations, but not in the colonic epithelial cell line T84. The secretory response was reduced significantly by tetrodotoxin (0.5 micromol/L), capsaicin desensitization (10 micromol/L), and the transient receptor potentials vanilloid receptor 1 antagonist capsazepine (10 micromol/L). The endogenous H(2)S donor L-cysteine also induced secretion that was diminished significantly by capsaicin desensitization, the CBS inhibitor amino-oxyacetic acid, and the CSE inhibitor propargylglycine. NaHS increased spike discharge in 23% of guinea-pig and 36% of human submucous neurons, but had no effect on Ca(++) mobilization in cultured guinea-pig enteric neurons. This excitatory response was reduced significantly by capsaicin desensitization and capsazepine, but not by glibenclamide (10 micromol/L)., Conclusions: The presence of H(2)S-producing enzymes in human and guinea-pig enteric neurons, the excitatory action on enteric neurons, and the prosecretory effects of NaHS suggest H(2)S as a novel gut-signaling molecule. Its action mainly involves transient receptor potentials vanilloid receptor 1 receptors on extrinsic afferent terminals, which in turn activate enteric neurons.

1. Using a Ussing chamber and neuronal retrograde tracing with 1,1'-didodecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) we characterized the afferent and efferent neuronal pathways which mediated distension-evoked secretion in the guinea-pig distal colon. 2. Acute capsaicin application (10 microM) to the serosal site of the Ussing chamber evoked a secretory response which was blocked by tetrodotoxin (1 microM), the combined application of the NK1 and NK3 receptor antagonists CP-99,994-1 and SR 142801 (1 microM), and by combined application of atropine (10 microM) and the VIP receptor antagonist VIP(6-28) (10 microM). Functional desensitization of extrinsic primary afferents by long-term application of capsaicin significantly diminished distension-evoked secretion by 46 %. 3. After functional desensitization by capsaicin, serosal application of gadolinium (100 microM) inhibited the distension-evoked chloride secretion by 54 %; the L-type Ca(2+) channel blocker nifedipine (1 microM) and the 5-HT(1P) receptor antagonist renzapride (1 microM) had no effect. The combination of atropine and VIP(6-28) or the combination of NK1 and NK3 receptor antagonists almost abolished distension-evoked secretion. 4. The secretory response evoked by electrical field stimulation, carbachol (1 microM) or VIP (1 microM) was not attenuated by gadolinium. Field stimulation-evoked chloride secretion was not affected by blockade of NK1 and NK3 receptors. 5. Twelve per cent of DiI-labelled submucosal neurones with projections to the mucosa were immunoreactive for choline acetyltransferase, substance P and calbindin and very probably represented intrinsic primary afferent neurones. 6. Distension-evoked chloride secretion was mediated by capsaicin-sensitive extrinsic primary afferents and by stretch-sensitive intrinsic primary afferent neurones. Both the extrinsic and intrinsic afferents converge on common efferent pathways. These pathways consist of VIPergic and cholinergic secretomotor neurones that are activated via NK1 and NK3 receptors.

We investigated the role of tachykinin receptor subtypes on secretory responses in the guinea-pig distal colon using Ussing chamber experiments and intracellular recordings from submucosal neurones. Choline acetyltransferase (ChAT) and vasoactive intestinal polypeptide (VIP) were demonstrated in submucosal neurones by immunohistochemistry. In Ussing chamber experiments substance P (SP), the NK1-receptor agonist [SAR9,Met(O2)11]-SP and the NK-3-receptor agonist (MePhe7)-NKB increased dose-dependently short-circuit currents. The NK-2-receptor agonist (betaAla8)-NKA(4-10) had no effect. Responses to 1-100 nM SP, [(SAR9,Met(O2)11]-SP and (MePhe7)-NKB were tetrodotoxin-sensitive but hexamethonium-insensitive. While (MePhe7)-NKB-responses were atropine-sensitive at all concentrations, the atropine sensitivity of the secretory responses to SP and [SAR9,Met(O2)11]-SP dramatically decreased with increasing concentrations. [SAR9,Met(O2)11]-SP and (MePhe7)-NKB effects were blocked by the selective NK-I and NK-3 antagonists CP-99,994-1 (1 microM) and SR 142801 (1 microM), respectively. Combination of both antagonists blocked the SP-response. SR 142801 also suppressed the response to [SAR9,Met(O2)11]-SP. Desensitization with [SAR9,Met(O2)11]-SP significantly decreased (MePhe7)-NKB-responses but not vice versa. In intracellular recordings 90% of submucosal neurones were activated by both ISAR9,Met(O2)11]-SP and (MePhe7)-NKB as indicated by membrane depolarisation and enhanced spike discharge. These effects were tetrodotoxin-resistant and potentiated by atropine. NK-1-and NK-3-mediated responses occurred equally in ChAT-positive and in VIP-positive neurones. The results suggest the importance of NK-1- and NK-3-receptors on cholinergic and non-cholinergic submucosal neurones for secretory processes in the guinea-pig distal colon.

Intracellular recording techniques were used to investigate the effects of norepinephrine on submucous neurones in the guinea-pig distal colon. In 81% of the neurones, pressure microejection of norepinephrine produced a membrane hyperpolarization associated with a decrease in excitability and input resistance. Microejection of clonidine (1 microM) mimicked the norepinephrine-induced hyperpolarization, whereas both phentolamine (1 microM) and yohimbine (1 microM) reversibly suppressed it. Superfusion of norepinephrine (1 nM - 10 microM) hyperpolarized the cells in a concentration-dependent manner. Norepinephrine and clonidine (1 nM - 10 microM) caused a concentration-dependent presynaptic inhibition of stimulus-evoked cholinergic fast excitatory postsynaptic potential. Slow inhibitory post-synaptic potentials (sISPSs) were induced by focal electrical stimulation of the interganglionic fibre tracts in 43% of the neurones tested. Superfusion of both phentolamine (1 microM) and yohimbine (1 microM) reduced the sIPSPs while prazosin (1 microM) had no significant effect. We concluded that norepinephrine acted post- and presynaptically via alpha 2-adrenoreceptors to have an inhibitory effect on the guinea-pig colonic submucous. In addition, our study strongly supported the role of norepinephrine as a mediator of the sIPSPs. As a result, norepinephrine would primarily suppress information transfer within the neuronal circuits in guinea-pig colonic submucosal plexus.

1. Neuronal retrograde tracing with the dye DiI (1,1'-didodecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate), in combination with immunohistochemical detection of choline acetyltransferase (ChAT) and vasoactive intestinal peptide (VIP), were used to identify the innervation of the mucosa of the guinea-pig proximal colon by submucosal neurones. Ussing chamber experiments were performed to measure changes in short circuit current (delta Isc) evoked by electrical stimulation of the oral or anal end of the preparation. 2. The tracing studies revealed that the mucosa was primarily innervated by descending neurones (78%); the vast majority of these were VIP positive (85%). The numerically smaller ascending pathway (13%) was predominantly ChAT positive (69%). A small population (9%) of DiI-labelled neurones projected circumferentially. 3. Ussing chamber experiments revealed that oral electrical stimulation induced a significantly larger delta Isc than anal stimulation. The VIP antagonist VIP(6-28) significantly reduced only orally induced delta Isc. Anally induced delta Isc were significantly more atropine sensitive that orally induced delta Isc. Tissue incubation with carbachol or VIP significantly potentiated delta Isc induced by VIP and carbachol, respectively, indicating cross-potentiation. 4. This study provides the first functional demonstration of polarized innervation patterns from submucosal neurones to enteric mucosa. The ascending ChAT and descending VIP pathways suggest the existence of reflexes resulting in preferential release of VIP or acetylcholine. The distinct pathways might favour the observed cross-potentiation of cholinergic and VIPergic mediated secretion.

Bi-directional interactions between the enteric nervous system and the immune system play an important role in gut inflammation. We therefore investigated the effects of the inflammatory mediators, prostaglandin (PGD2, PGE2, PGI2, and PGF2 alpha) and leukotriene (LTC4), on guinea-pig colonic secretion and on electrophysiological behaviour of submucosal neurones. In Ussing chambers, all inflammatory mediators evoked a dose-dependent increase in short circuit current (Isc) that represented electrogenic chloride secretion. The secretory response was significantly reduced by tetrodotoxin (TTX) and atropine suggesting involvement of cholinergic submucosal neurones. Long-term application of prostaglandins and LTC4 induced TTX- and atropine-sensitive cyclical chloride secretions. Intracellular recordings revealed activation of submucosal neurones by all inflammatory mediators. This activation consisted of depolarisation of the membrane associated with increased spike discharge. Frequently, prostaglandins and LTC4 induced spontaneous occurrence of cholinergic fast excitatory postsynaptic potentials. Results suggest that the role of the enteric nervous system in neuroimmune interactions consists of a potentiation of the direct epithelial effect of inflammatory mediators by the activation of submucosal neurones. Ongoing nerve-mediated cyclical changes in chloride secretion may be interpreted as the induction of intrinsic alarm programs. The effects of inflammatory mediators may serve as a defense mechanism to dilute noxious substances in the lumen.

Short term exposure to leukotrienes evoked a well known nerve mediated increase in short circuit current. It is unknown whether leukotrienes evoke in addition oscillations in chloride secretion, as has been reported for some of the other mediators released during inflammation. Therefore, the aim of this study was to characterize the effects of a long time exposure of leukotrienes on mucosal functions. Conventional Ussing chamber, and intracellular recording techniques were used to investigate the actions of leukotriene D4 and C4 on short-circuit current and excitability of submucosal neurons in guinea-pig distal colon. In Ussing chambers, long term exposure to leukotriene D4 or C4 evoked rhythmic oscillations in short-circuit current in 35% and 50% of tissues, respectively. These current bursts were blocked by tetrodotoxin, atropine, hexamethonium and piroxicam. Secretory response to short term exposure of leukotrienes was significantly higher in tissues exhibiting current bursts. Likewise, the potentiating effects of leukotrienes on the response to field stimulation was only observed in tissues exhibiting current bursts. In intracellular recording experiments, leukotriene C4 evoked activation of submucosal neurons that was partly sensitive to indomethacin; no oscillations in neuronal excitability could be demonstrated. Results suggested that long term exposure to leukotrienes evoked current bursts that were mediated by neural, cholinergic mechanisms as well as endogeneous prostaglandins.

We have applied conventional flux-chamber and intracellular recording methods to investigate the effects of the prostaglandins PGF2 alpha and PGI2 upon epithelial ion transport and on the electrical behaviour of submucosal neurones in guinea-pig colon. In flux-chamber experiments on segments of colon, both prostaglandins evoked a dose-dependent increase in short-circuit current that was reduced in chloride-depleted Krebs solution and by serosal addition of tetrodotoxin or atropine, but was unaffected by hexamethonium. These results indicate activation of chloride secretion via submucosal neurones. The response to PGF2 alpha was decreased by piroxicam. Application of PGF2 alpha or PGI2 to submucosal neurones evoked depolarization of the membrane potential associated with an enhanced spike discharge. The depolarizing response was tetrodotoxin insensitive, indicating a direct effect of the prostaglandins on the impaled neurones. Membrane depolarization was frequently associated with the occurrence of fast excitatory postsynaptic potentials, suggesting in addition that part of the excitatory effect is mediated by the activation of neural circuits that drive the impaled neurone synaptically. The results of this study indicate that the secretory effects of prostaglandins are mediated in part by submucosal neurones and further suggest that the colonic submucosal plexus may function as an amplifier to enhance the epithelial response to inflammatory mediators.

We investigated electrical and synaptic behavior of neurons in the colonic submucous plexus during exposure to beta-lactoglobulin in guinea pigs sensitized by ingestion of milk. Microelectrodes were used to record electrical and synaptic behavior in neurons from milk-sensitized and nonsensitized age-matched animals during exposure to beta-lactoglobulin. Neurons in sensitized animals were hyperexcitable. Application of the histamine H2 antagonist cimetidine reversed the hyperexcitability, suggesting endogenously released histamine as one of the responsible factors. Antigenic exposure suppressed stimulus-evoked nicotinic cholinergic fast excitatory postsynaptic potentials (EPSPs). This was blocked by the selective histamine H3 antagonist burimamide. Suppression of the EPSPs resulted from presynaptic inhibition of acetylcholine release. Increased neuronal excitability and suppression of synaptic transmission was only found in milk-sensitized intestine, not in the intestine from age-matched nonsensitized animals. We concluded that signaling from mucosal mast cells to the enteric nervous system is important in colonic defense against antigenic threats. Histamine is a paracrine messenger in the communication network.

Background/aims: Enteric neuroimmune communication in gastrointestinal hypersensitivity responses includes antigen detection by mast cells and release of chemical messages to the enteric nervous system. The aim of this study was to analyze the electrical and synaptic behavior of neurons in the colonic submucous plexus during exposure to Trichinella spiralis antigen in animals infected earlier with the parasite., Methods: Microelectrodes were used to record in submucous neurons of guinea pig distal colon during application of Trichinella antigen., Results: Neurons in sensitized animals were more excitable than in controls. Hyperexcitability was seen as a greater probability of spontaneous action potential discharge and repetitive firing to depolarizing current or exposure to acetylcholine. Application of histaminergic antagonists reversed the augmented excitability, suggesting endogenously released histamine as a responsible factor. Antigenic exposure increased neuronal excitability and suppressed nicotinic transmission at fast cholinergic synapses only in sensitized animals. Effects on excitability, but not presynaptic inhibitory effects, were blocked by cimetidine., Conclusions: Signaling between mucosal mast cells and the enteric nervous system is involved in colonic anaphylactic responses to sensitizing antigens. Histamine is a paracrine signal in the communication pathway.

Conventional flux chamber and intracellular recording methods were used to investigate the mode of action of prostaglandin D2 (PGD2) on ion transport in muscle-stripped segments of guinea pig colon and on colonic submucosal ganglion cells. Application of PGD2 resulted in a dose-dependent increase in short-circuit current that was reduced by serosal addition of bumetanide, tetrodotoxin, atropine, or piroxicam, but not hexamethonium. Application of PGD2 to submucosal neurons evoked a depolarization of the membrane potential that was associated with an enhanced spike discharge. In AH/type 2 neurons, postspike afterhyperpolarizations were reduced in amplitude and duration. The depolarizing responses to PGD2 were not affected by tetrodotoxin, indicative of a direct effect of PGD2 on the impaled neurons. Whereas fast excitatory postsynaptic potentials (EPSPs) were not affected by PGD2, slow EPSPs were reduced by a presynaptic effect, indicating presynaptic suppression of noncholinergic neurotransmitter release. The study demonstrates that PGD2 acts as a neuromodulator to evoke nerve-mediated chloride secretion, predominantly through activation of cholinergic submucosal neurons. The results further indicate that PGD2 released from lamina propria immune cells during antigenic stimulation may influence mucosal function by altering electrical behavior of submucosal neurons.

Conventional flux chamber methods were applied to investigate the mode of action of rhein, an active metabolite derived from colonic microbial fermentation of the naturally occurring sennoside laxatives, in muscle-stripped segments of guinea pig colon. Mucosal or serosal application of rhein (10 nmol/1 to 0.5 mmol/l) resulted in a dose-dependent increase in short-circuit current (Isc) that was superimposed by irregular fluctuations in Isc. The response to electrical field stimulation was increased. The rhein-evoked increase in Isc was reduced by serosal addition of 50 mumol/l bumetanide, 1 mumol/l tetrodotoxin, 1 mumol/l atropine and 10 mumol/l piroxicam but not 100 mumol/l hexamethonium, 1 mumol/l ICS 205 930 or 10 mumol/l cimetidine. The study suggests that rhein activates chloride secretion by excitation of submucosal neurons and release of acetylcholine and endogenous prostaglandins, but not by release of histamine or serotonin.

Intracellular microelectrodes were used to investigate the actions of histamine in the submucous plexus of the distal colon of the guinea pig. Three effects resulted from application of histamine to submucous neurons. The first was membrane depolarization associated with increased input resistance and augmented excitability. The second was presynaptic suppression of acetylcholine release at nicotinic synapses. The third occurred during long-term application and consisted of recurrent trains of action potentials associated with periodic depolarization of membrane potential. Pharmacological analysis, with selective agonists and antagonists, suggested mediation of the first and third response by postsynaptic histamine H2 receptors. The second response was mediated by presynaptic histamine H3 receptors. These actions of histamine represent a mechanism for neuroimmune signaling between mucosal mast cells and submucous neurons in gastrointestinal type 1 hypersensitivity reactions to allergens.

Muscle-stripped segments of distal colon from guinea pigs were mounted in modified flux chambers to determine the effect of distension on mucosal secretion. Ion secretion was monitored as changes in short-circuit current (Isc). Distending forces were pressure gradients established by controlled reduction in liquid volume of the submucosal compartment of the chamber. Volume removal for 10 s or 5 min evoked a monophasic or biphasic increase in Isc, which returned to baseline within 5-20 min. The amplitude of the response correlated with the volume removed and was reduced by bumetanide and Cl-free solutions but not by tetraethylammonium or amiloride. Tetrodotoxin and atropine also suppressed the response. Neither the nicotinic receptor antagonist mecamylamine, the 5-hydroxytryptamine3 (5-HT3) receptor antagonist ICS 205-930, or the prostaglandin synthesis inhibitor piroxicam altered the response. Addition of prostaglandin D2 to the submucosal bath significantly enhanced the response. The results suggest that distension of the colon evokes anion secretion by activation of reflex circuits with cholinergic neurons and muscarinic synapses. Prostaglandins and 5-hydroxytryptamine acting at 5-HT3 receptors appear not to be signal substances in the reflex pathway, which evokes the secretory response to distension.

Intracellular microelectrodes were used to investigate the neuropharmacology of 5-hydroxytryptamine (5-HT) in the submucous plexus of the distal colon of the guinea pig. Three effects resulted from application of 5-HT to submucous neurons. Two of the effects were components of a biphasic depolarization mediated by receptors on the neuronal cell body. The third was suppression of acetylcholine release at nicotinic synapses on the cell bodies and was mediated by presynaptic 5-HT receptors. The initial component of the biphasic depolarization was a rapidly activating response characterized by increased ionic conductance and a tendency for rapid desensitization. Pharmacological analysis with selective agonists and antagonists suggested mediation of this response by the 5-HT3 receptor subtype. The second component of the depolarizing response was a slowly activating and long-lasting depolarization associated with decreased ionic conductance. Analysis of this response suggested it was mediated by the 5-HT1P receptor subtype. Identification of the presynaptic receptors for 5-HT was equivocal. These receptors did not behave like 5-HT3 or 5-HT1P receptor subtypes. The putative 5-HT4 agonist 5-methoxytryptamine was equipotent with 5-HT in producing presynaptic inhibition at the fast nicotinic synapses.

The effects of 5-hydroxytryptamine (5-HT) on epithelial short-circuit current (Isc) were determined and related to the 5-HT effects on electrical and synaptic behavior of neurons in the submucosal plexus of the guinea pig colon. 5-HT evoked a biphasic increase in Isc that was reduced by bumetanide, Cl(-)-free solutions, atropine, and mecamylamine and abolished by tetrodotoxin. The 5-HT response was mimicked by 2-methyl-5-HT, but not by 5-hydroxyindalpine, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane, and 5-methoxytryptamine (5-MeOT). ICS 205-930 suppressed the 5-HT response. Electrical field stimulation of submucosal neurons evoked an increase in Isc indicative of Cl- secretion that was reduced by 5-MeOT and enhanced by 2-methyl-5-HT. Application of 5-HT to submucosal neurons by micropressure ejection resulted in membrane depolarization, augmented excitability, and repetitive spike discharge. The depolarization was biphasic, consisting of rapidly and slowly activating components. The rapidly activating component was suppressed by ICS 205-930. Fast excitatory postsynaptic potentials evoked by electrical stimulation of interganglionic connectives were suppressed by 5-HT and 5-MeOT. These results suggest that 5-HT activates 5-HT3 receptors, which mediate fast excitatory responses in submucosal neurons, leading to release of acetylcholine at nicotinic and muscarinic synapses and stimulation of Cl- secretion. Presynaptic inhibition suppresses acetylcholine release and results in attenuation of neurally evoked Cl- secretion.

Intracellular recording methods were used in vitro to study the electrophysiological behavior of neurons in ganglia of the submucosal plexus in the distal colon of the guinea pig. The results revealed subpopulations of submucosal ganglion cells that corresponded to the AH/type 2, S/type 1, type 3, and type 4 subpopulations found elsewhere in the intestine. Electrical behavior of colonic submucosal neurons differed from the myenteric plexus of the colon, rectum, and stomach and the small intestinal submucosal plexus mainly in the relative proportions of the different subpopulations. Regional differences in this respect may be a reflection of functional specialization in the diverse regions of the alimentary canal.

Intracellular electrical recording was used to investigate synaptic behavior of ganglion cells in the neural networks of the submucosal plexus of the guinea pig distal colon. Fast excitatory postsynaptic potentials (EPSPs), mediated by nicotinic receptors, were found in all S/type 1 neurons, 70% of AH/type 2, 75% of type 3, and 95% of type 4 neurons. Slow EPSPs were characterized by membrane depolarization, increased input resistance, enhanced action potential discharge, and suppression of hyperpolarizing afterpotentials in 64% of the S/type 1 neurons, 74% of AH/type 2, 31% of type 3, and 70% of type 4 neurons. Micropressure application of acetylcholine evoked a two-component depolarizing response consisting of an initial transient with decreased input resistance followed by a prolonged depolarization associated with increased input resistance. The transient response was suppressed by nicotinic-blocking drugs. Muscarinic antagonists suppressed the prolonged response. Acetylcholine acted also at presynaptic muscarinic receptors to suppress stimulus-evoked fast EPSPs. No stimulus-evoked inhibitory synaptic potentials were observed. Norepinephrine, applied by microejection, acted at alpha 2-adrenoceptors to hyperpolarize the membrane potential in association with decreased neuronal input resistance.