The role of enteric inhibitory motoneurons in peristalsis in the isolated guinea-pig small intestine

Afferent nerve activity in a mouse model increases with faster bladder filling rates in vitro, but voiding behavior remains unaltered in vivo

Storage and voiding functions in urinary bladder are well-known, yet fundamental physiological events coordinating these behaviors remain elusive. We sought to understand how voiding function is influenced by the rate at which the bladder fills. We hypothesized that faster filling rates would increase afferent sensory activity and increase micturition rate. In vivo, this would mean animals experiencing faster bladder filling would void more frequently with smaller void volumes. To test this hypothesis, we measured afferent nerve activity during different filling rates using an ex vivo mouse bladder preparation and assessed voiding frequency in normally behaving mice noninvasively (UroVoid). Bladder afferent nerve activity depended on the filling rate, with faster filling increasing afferent nerve activity at a given volume. Voiding behavior in vivo was measured in UroVoid cages. Male and female mice were given access to tap water or, to induce faster bladder filling rates, water containing 5% sucrose. Fluid intake increased dramatically in mice consuming 5% sucrose. As expected, micturition frequency was elevated in the sucrose group. However, even with the greatly increased rate of urine production, void volumes were unchanged in both genders. Although faster filling rates generated higher afferent nerve rates ex vivo, this did not translate into more frequent, smaller-volume voids in vivo. This suggests afferent nerve activity is only one factor contributing to the switch from bladder filling to micturition. Together with afferent nerve activity, higher centers in the central nervous system and the state of arousal are likely critical to coordinating the micturition reflex.

The role of enteric inhibitory neurons in intestinal motility

The enteric nervous system controls much of the mixing and propulsion of nutrients along the digestive tract. Enteric neural circuits involve intrinsic sensory neurons, interneurons and motor neurons. While the role of the excitatory motor neurons is well established, the role of the enteric inhibitory motor neurons (IMNs) is less clear. The discovery of inhibitory transmission in the intestine in the 1960's in the laboratory of Geoff Burnstock triggered the search for the unknown neurotransmitter. It has since emerged that most neurons including the IMNs contain and may utilise more than one transmitter substances; for IMNs these include ATP, the neuropeptide VIP/PACAP and nitric oxide. This review distinguishes the enteric neural pathways underlying the 'standing reflexes' from the pathways operating physiologically during propulsive and non-propulsive movements. Morphological evidence in small laboratory animals indicates that the IMNs are located in the myenteric plexus and project aborally to the circular muscle, where they act by relaxing the muscle. There is ongoing 'tonic' activity of these IMNs to keep the intestinal muscle relaxed. Accommodatory responses to content further activate enteric pathways that involve the IMNs as the final neural element. IMNs are activated by mechanical and chemical stimulation induced by luminal contents, which activate intrinsic sensory enteric neurons and the polarised interneuronal ascending excitatory and descending inhibitory reflex pathways. The latter relaxes the muscle ahead of the advancing bolus, thus facilitating propulsion.

Neurotransmitters responsible for purinergic motor neurotransmission and regulation of GI motility

Classical concepts of peripheral neurotransmission were insufficient to explain enteric inhibitory neurotransmission. Geoffrey Burnstock and colleagues developed the idea that ATP or a related purine satisfies the criteria for a neurotransmitter and serves as an enteric inhibitory neurotransmitter in GI muscles. Cloning of purinergic receptors and development of specific drugs and transgenic mice have shown that enteric inhibitory responses depend upon P2Y₁ receptors in post-junctional cells. The post-junctional cells that transduce purinergic neurotransmitters in the GI tract are PDGFRα⁺ cells and not smooth muscle cells (SMCs). PDGFRα⁺ cells express P2Y₁ receptors, are activated by enteric inhibitory nerve stimulation and generate Ca²⁺ oscillations, express small-conductance Ca²⁺-activated K⁺ channels (SK3), and generate outward currents when exposed to P2Y₁ agonists. These properties are consistent with post-junctional purinergic responses, and similar responses and effectors are not functional in SMCs. Refinements in methodologies to measure purines in tissue superfusates, such as high-performance liquid chromatography (HPLC) coupled with etheno-derivatization of purines and fluorescence detection, revealed that multiple purines are released during stimulation of intrinsic nerves. β-NAD⁺ and other purines, better satisfy criteria for the purinergic neurotransmitter than ATP. HPLC has also allowed better detection of purine metabolites, and coupled with isolation of specific types of post-junctional cells, has provided new concepts about deactivation of purine neurotransmitters. In spite of steady progress, many unknowns about purinergic neurotransmission remain and require additional investigation to understand this important regulatory mechanism in GI motility.

Nitric Oxide Is Essential for Generating the Minute Rhythm Contraction Pattern in the Small Intestine, Likely via ICC-DMP

Nitrergic nerves have been proposed to play a critical role in the orchestration of peristaltic activities throughout the gastrointestinal tract. In the present study, we investigated the role of nitric oxide, using spatiotemporal mapping, in peristaltic activity of the whole ex vivo mouse intestine. We identified a propulsive motor pattern in the form of propagating myogenic contractions, that are clustered by the enteric nervous system into a minute rhythm that is dependent on nitric oxide. The cluster formation was abolished by TTX, lidocaine and nitric oxide synthesis inhibition, whereas the myogenic contractions, occurring at the ICC-MP initiated slow wave frequency, remained undisturbed. Cluster formation, inhibited by block of nitric oxide synthesis, was fully restored in a highly regular rhythmic fashion by a constant level of nitric oxide generated by sodium nitroprusside; but the action of sodium nitroprusside was inhibited by lidocaine indicating that it was relying on neural activity, but not rhythmic nitrergic nerve activity. Hence, distention-induced activity of cholinergic nerves and/or a co-factor within nitrergic nerves such as ATP is also a requirement for the minute rhythm. Cluster formation was dependent on distention but was not evoked by a distention reflex. Block of gap junction conductance by carbenoxolone, dose dependently inhibited, and eventually abolished clusters and contraction waves, likely associated, not with inhibition of nitrergic innervation, but by abolishing ICC network synchronization. An intriguing feature of the clusters was the presence of bands of rhythmic inhibitions at 4-8 cycles/min; these inhibitory patches occurred in the presence of tetrodotoxin or lidocaine and hence were not dependent on nitrergic nerves. We propose that the minute rhythm is generated by nitric oxide-induced rhythmic depolarization of the musculature via ICC-DMP.

Diminished enteric neuromuscular transmission in the distal colon following experimental spinal cord injury

Neurogenic bowel following spinal cord injury (SCI) leads to decreased colonic motility, remodeling of the neuromuscular compartment and results in chronic evacuation difficulties. The distal colon of the rat serves a dual role for fluid absorption and storage that is homologous to the descending colon of humans. Dysmotility of the descending colon is one component of neurogenic bowel. We investigated the integrity of the enteric neuromuscular transmission responsible for the generation of excitatory and inhibitory junction potentials (EJPs and IJPs, respectively) in the distal colon of rats. We previously demonstrated a chronic reduction in colonic enteric neurons from rats with acute and chronic high-thoracic (T3) SCI and hypothesized that neurogenic bowel following T3-SCI results from diminished enteric neuromuscular transmission. Immunohistochemical labeling for myenteric neuronal nitric oxide synthase (nNOS) and choline acetyltransferase (ChAT) neurons demonstrated a significant loss of presumptive nitric oxide (NO) and acetylcholine (ACh) immunoreactive neurons in both 3-day and 3-week injured animals. Colonic neuromuscular transmission in response to transmural electrical stimulation of the colon was significantly reduced 3-days and 3-weeks following SCI in male rats. Specifically, cholinergic-mediated excitatory junction potentials (EJPs) and nitrergic-mediated slow inhibitory junction potentials (IJPs) were significantly reduced while ATP-mediated fast IJPs remained unaffected. We conclude that a reduction in excitatory and inhibitory enteric neuromuscular transmission contributes to neurogenic bowel observed following SCI, and that these loss-of-function changes involve enteric-mediated cholinergic and nitrergic pathways.

TRPA1 Channel Activation Inhibits Motor Activity in the Mouse Colon

There is a growing awareness of the role that TRP channels play in regulating sensory and motor functions in the gastrointestinal tract. In this study we used an in-vitro murine model of colonic peristaltic-like complexes (CPMCs) to evaluate the role of exogenous and endogenous TRPA1 signaling processes in regulating colonic motility. Using in-vitro recordings of intraluminal pressure to monitor the presence of CPMCs in colonic segments we performed a series of experiments on male CD1 mice (2 months of age) and found that CPMC activity was attenuated by TRPA1 agonists. Bath application of the TRPA1 antagonist HC-030031 had no effect upon basal CPMC activity whereas application of the synthetic TRPA1 agonist ASP7663 caused a reversible dose dependent decrease in CPMC frequency that was blocked by HC-030031. Cinnamaldehyde and 4-hydroxy-2-nonenal elicited long lasting decreases in CPMC frequency that were blocked by HC-030031 whereas the decreased CPMC activity invoked by AITC could not be blocked by HC-030031. Our results show that any potential mechanosensory function of TRPA1 doesn’t involve contributing to distension induced colonic motor activity and that a role for TRPA1 in the colon is through regulating motility through exogenous and endogenous agonist induced inhibitory effects.

Exposure to seawater increases intestinal motility in euryhaline rainbow trout (Oncorhynchus mykiss)

Upon exposure to seawater, euryhaline teleosts need to imbibe and desalinate seawater to allow for intestinal ion and water absorption, as this is essential for maintaining osmotic homeostasis. Despite the potential benefits of increased mixing and transport of imbibed water for increasing the efficiency of absorptive processes, the effect of water salinity on intestinal motility in teleosts remains unexplored. By qualitatively and quantitatively describing in vivo intestinal motility of euryhaline rainbow trout (Oncorhynchus mykiss), this study demonstrates that, in freshwater, the most common motility pattern consisted of clusters of rhythmic, posteriorly propagating contractions that lasted ∼1-2 min followed by a period of quiescence lasting ∼4-5 min. This pattern closely resembles mammalian migrating motor complexes (MMCs). Following a transition to seawater, imbibed seawater resulted in a significant distension of the intestine and the frequency of MMCs increased twofold to threefold with a concomitant reduction in the periods of quiescence. The increased frequency of MMCs was also accompanied by ripple-type contractions occurring every 12-60 s. These findings demonstrate that intestinal contractile activity of euryhaline teleosts is dramatically increased upon exposure to seawater, which is likely part of the overall response for maintaining osmotic homeostasis as increased drinking and mechanical perturbation of fluids is necessary to optimise intestinal ion and water absorption. Finally, the temporal response of intestinal motility in rainbow trout transitioning from freshwater to seawater coincides with previously documented physiological modifications associated with osmoregulation and may provide further insight into the underlying reasons shaping the migration patterns of salmonids.

Regulation of Gastrointestinal Smooth Muscle Function by Interstitial Cells

Interstitial cells of mesenchymal origin form gap junctions with smooth muscle cells in visceral smooth muscles and provide important regulatory functions. In gastrointestinal (GI) muscles, there are two distinct classes of interstitial cells, c-Kit(+) interstitial cells of Cajal and PDGFRα(+) cells, that regulate motility patterns. Loss of these cells may contribute to symptoms in GI motility disorders.

Upregulation of L-type calcium channels in colonic inhibitory motoneurons of P/Q-type calcium channel-deficient mice

Enteric inhibitory motoneurons use nitric oxide and a purine neurotransmitter to relax gastrointestinal smooth muscle. Enteric P/Q-type Ca2+ channels contribute to excitatory neuromuscular transmission; their contribution to inhibitory transmission is less clear. We used the colon from tottering mice (tg/tg, loss of function mutation in the α1A pore-forming subunit of P/Q-type Ca2+ channels) to test the hypothesis that P/Q-type Ca2+ channels contribute to inhibitory neuromuscular transmission and colonic propulsive motility. Fecal pellet output in vivo and the colonic migrating motor complex (ex vivo) were measured. Neurogenic circular muscle relaxations and inhibitory junction potentials (IJPs) were also measured ex vivo. Colonic propulsive motility in vivo and ex vivo was impaired in tg/tg mice. IJPs were either unchanged or somewhat larger in tissues from tg/tg compared with wild-type (WT) mice. Nifedipine (L-type Ca2+ channel antagonist) inhibited IJPs by 35 and 14% in tissues from tg/tg and WT mice, respectively. The contribution of N- and R-type channels to neuromuscular transmission was larger in tissues from tg/tg compared with WT mice. The resting membrane potential of circular muscle cells was similar in tissues from tg/tg and WT mice. Neurogenic relaxations of circular muscle from tg/tg and WT mice were similar. These results demonstrate that a functional deficit in P/Q-type channels does not alter propulsive colonic motility. Myenteric neuron L-type Ca2+ channel function increases to compensate for loss of functional P/Q-type Ca2+ channels. This compensation maintains inhibitory neuromuscular transmission and normal colonic motility.

Spontaneous Ca(2+) transients in interstitial cells of Cajal located within the deep muscular plexus of the murine small intestine

KEY POINTS

Interstitial cells of Cajal at the level of the deep muscular plexus (ICC-DMP) in the small intestine generate spontaneous Ca(2+) transients that consist of localized Ca(2+) events and limited propagating Ca(2+) waves. Ca(2+) transients in ICC-DMP display variable characteristics: from discrete, highly localized Ca(2+) transients to regionalized Ca(2+) waves with variable rates of occurrence, amplitude, duration and spatial spread. Ca(2+) transients fired stochastically, with no cellular or multicellular rhythmic activity being observed. No correlation was found between the firing sites in adjacent cells. Ca(2+) transients in ICC-DMP are suppressed by the ongoing release of inhibitory neurotransmitter(s). Functional intracellular Ca(2+) stores are essential for spontaneous Ca(2+) transients, and the sarco/endoplasmic reticulum Ca(2+) -ATPase (SERCA) pump is necessary for maintenance of spontaneity. Ca(2+) release mechanisms involve both ryanodine receptors (RyRs) and inositol triphosphate receptors (InsP3 Rs). Release from these channels is interdependent. ICC express transcripts of multiple RyRs and InsP3 Rs, with Itpr1 and Ryr2 subtypes displaying the highest expression.

ABSTRACT

Interstitial cells of Cajal in the deep muscular plexus of the small intestine (ICC-DMP) are closely associated with varicosities of enteric motor neurons and generate responses contributing to neural regulation of intestinal motility. Responses of ICC-DMP are mediated by activation of Ca(2+) -activated Cl(-) channels; thus, Ca(2+) signalling is central to the behaviours of these cells. Confocal imaging was used to characterize the nature and mechanisms of Ca(2+) transients in ICC-DMP within intact jejunal muscles expressing a genetically encoded Ca(2+) indicator (GCaMP3) selectively in ICC. ICC-DMP displayed spontaneous Ca(2+) transients that ranged from discrete, localized events to waves that propagated over variable distances. The occurrence of Ca(2+) transients was highly variable, and it was determined that firing was stochastic in nature. Ca(2+) transients were tabulated in multiple cells within fields of view, and no correlation was found between the events in adjacent cells. TTX (1 μm) significantly increased the occurrence of Ca(2+) transients, suggesting that ICC-DMP contributes to the tonic inhibition conveyed by ongoing activity of inhibitory motor neurons. Ca(2+) transients were minimally affected after 12 min in Ca(2+) free solution, indicating these events do not depend immediately upon Ca(2+) influx. However, inhibitors of sarco/endoplasmic reticulum Ca(2+) -ATPase (SERCA) pump and blockers of inositol triphosphate receptor (InsP3 R) and ryanodine receptor (RyR) channels blocked ICC Ca(2+) transients. These data suggest an interdependence between RyR and InsP3 R in the generation of Ca(2+) transients. Itpr1 and Ryr2 were the dominant transcripts expressed by ICC. These findings provide the first high-resolution recording of the subcellular Ca(2+) dynamics that control the behaviour of ICC-DMP in situ.

Temporal sequence of activation of cells involved in purinergic neurotransmission in the colon

KEY POINTS

Platelet derived growth factor receptor α (PDGFRα(+) ) cells in colonic muscles are innervated by enteric inhibitory motor neurons. PDGFRα(+) cells generate Ca(2+) transients in response to exogenous purines and these responses were blocked by MRS-2500. Stimulation of enteric neurons, with cholinergic and nitrergic components blocked, evoked Ca(2+) transients in PDGFRα(+) and smooth muscle cells (SMCs). Responses to nerve stimulation were abolished by MRS-2500 and not observed in muscles with genetic deactivation of P2Y1 receptors. Ca(2+) transients evoked by nerve stimulation in PDGFRα(+) cells showed the same temporal characteristics as electrophysiological responses. PDGFRα(+) cells express gap junction genes, and drugs that inhibit gap junctions blocked neural responses in SMCs, but not in nerve processes or PDGFRα(+) cells. PDGFRα(+) cells are directly innervated by inhibitory motor neurons and purinergic responses are conducted to SMCs via gap junctions.

ABSTRACT

Interstitial cells, known as platelet derived growth factor receptor α (PDGFRα(+) ) cells, are closely associated with varicosities of enteric motor neurons and suggested to mediate purinergic hyperpolarization responses in smooth muscles of the gastrointestinal tract (GI), but this concept has not been demonstrated directly in intact muscles. We used confocal microscopy to monitor Ca(2+) transients in neurons and post-junctional cells of the murine colon evoked by exogenous purines or electrical field stimulation (EFS) of enteric neurons. EFS (1-20 Hz) caused Ca(2+) transients in enteric motor nerve processes and then in PDGFRα(+) cells shortly after the onset of stimulation (latency from EFS was 280 ms at 10 Hz). Responses in smooth muscle cells (SMCs) were typically a small decrease in Ca(2+) fluorescence just after the initiation of Ca(2+) transients in PDGFRα(+) cells. Upon cessation of EFS, several fast Ca(2+) transients were noted in SMCs (rebound excitation). Strong correlation was noted in the temporal characteristics of Ca(2+) transients evoked in PDGFRα(+) cells by EFS and inhibitory junction potentials (IJPs) recorded with intracellular microelectrodes. Ca(2+) transients and IJPs elicited by EFS were blocked by MRS-2500, a P2Y1 antagonist, and absent in P2ry1((-/-)) mice. PDGFRα(+) cells expressed gap junction genes, and gap junction uncouplers, 18β-glycyrrhetinic acid (18β-GA) and octanol blocked Ca(2+) transients in SMCs but not in neurons or PDGFRα(+) cells. IJPs recorded from SMCs were also blocked. These findings demonstrate direct innervation of PDGFRα(+) cells by motor neurons. PDGFRα(+) cells are primary targets for purinergic neurotransmitter(s) in enteric inhibitory neurotransmission. Hyperpolarization responses are conducted to SMCs via gap junctions.

Spontaneous transient hyperpolarizations in the rabbit small intestine

Four types of electrical activity were recorded and related to cell structure by intracellular recording and dye injection into impaled cells in muscles of rabbit small intestine. The specific cell types from which recordings were made were longitudinal smooth muscle cells (LSMCs), circular smooth muscle cells (CSMCs), interstitial cells of Cajal distributed in the myenteric region (ICC-MY) and fibroblast-like cells (FLCs). Slow waves (slow wavesSMC) were recorded from LSMCs and CSMCs. Slow waves (slow wavesICC) were of greatest amplitude (>50 mV) and highest maximum rate of rise (>10 V s(-1)) in ICC-MY. The dominant activity in FLCs was spontaneous transient hyperpolarizations (STHs), with maximum amplitudes above 30 mV. STHs were often superimposed upon small amplitude slow waves (slow wavesFLC). STHs displayed a cyclical pattern of discharge irrespective of background slow wave activity. STHs were inhibited by MRS2500 (3 μm), a P2Y1 antagonist, and abolished by apamin (0.3 μm), a blocker of small conductance Ca(2+)-activated K(+) channels. Small amplitude STHs (<15 mV) were detected in smooth muscle layers, whereas STHs were not resolved in cells identified as ICC-MY. Electrical field stimulation evoked purinergic inhibitory junction potentials (IJPs) in CSMCs. Purinergic IJPs were not recorded from ICC-MY. These results suggest that FLCs may regulate smooth muscle excitability in the rabbit small intestine via generation of rhythmic apamin-sensitive STHs. Stimulation of P2Y1 receptors modulates the amplitudes of STHs. Our results also suggest that purinergic inhibitory motor neurons regulate the motility of the rabbit small intestine by causing IJPs in FLCs that conduct to CSMCs.

Gastrointestinal effect of methanol extract of Radix Aucklandiae and selected active substances on the transit activity of rat isolated intestinal strips

CONTEXT

Radix Aucklandiae, the dry rhizome of Aucklandia lappa Decne (Asteraceae), enjoyed traditional popularity for its antidiarrheal effects. Although there are many investigations on its chemical constituents and pharmacologic actions, few studies explaining its activity and mechanism in gastrointestinal disorders are available.

OBJECTIVE

In this paper, we focused on the effects of the methanol extract of R. Aucklandiae (RA ext) on gastrointestinal tract, so as to assess some of the possible mechanisms involved in the clinical treatment.

MATERIALS AND METHODS

In vivo, in neostigmine-induced mice and normal mice, after intragastric administration, RA ext (100, 200, 300, and 400 mg/kg) was studied on gastrointestinal transit including gastric emptying and small intestinal motility. Meanwhile, in vitro, the effect of it (0.1, 0.2, 0.3, and 0.4 mg/mL) on the isolated tissue preparations of rat jejunum was also investigated, as well as costunolide and dehydrocostuslactone which were the main constituents.

RESULTS

In vivo, the gastric emptying increased and intestinal transit decreased after the administration of RA ext in normal mice. However, RA ext inhibited the gastric emptying and the intestinal transit throughout the concentrations in neostigmine-induced mice. In vitro, RA ext caused inhibitory effect on the spontaneous contraction of rat-isolated jejunum in a dose-dependent manner ranging from 0.1 to 0.4 mg/mL, and it also relaxed the acetylcholine chloride (Ach, 10(-5) M), 5-hydroxytryptamine (5-HT, 200 μM)-induced, and K(+) (60 mM)-induced contractions. RA ext shifted the Ca(2+) concentration-response curves to right, similar to that caused by verapamil (0.025 mM). The Ca(2+) concentration-response curves were shifted by costunolide (CO) (5.4, 8.1, and 10.8 μg/mL), dehydrocostuslactone (DE) (4.6, 6.9, and 9.2 μg/mL), costunolide-dehydrocostuslactone (CO-DE) (5.4-4.6, 8.1-6.9, and 10.8-9.2 μg/mL) to the right, similar to that caused by verapamil (0.01 mM).

DISCUSSION AND CONCLUSION

These results indicate that RA ext played a spasmolytic role in gastrointestinal motility, which is probably mediated through the inhibition of muscarinic receptors, 5-HT receptors, and calcium influx. The presence of cholinergic and calcium antagonist constituents may be the compatibility of CO and DE. All these results provide a pharmacological basis for its clinical use in the gastrointestinal tract.

Inhibitory effect of cannabichromene, a major non-psychotropic cannabinoid extracted from Cannabis sativa, on inflammation-induced hypermotility in mice

BACKGROUND AND PURPOSE

Cannabichromene (CBC) is a major non-psychotropic phytocannabinoid that inhibits endocannabinoid inactivation and activates the transient receptor potential ankyrin-1 (TRPA1). Both endocannabinoids and TRPA1 may modulate gastrointestinal motility. Here, we investigated the effect of CBC on mouse intestinal motility in physiological and pathological states.

EXPERIMENTAL APPROACH

Inflammation was induced in the mouse small intestine by croton oil. Endocannabinoid (anandamide and 2-arachidonoyl glycerol), palmitoylethanolamide and oleoylethanolamide levels were measured by liquid chromatography-mass spectrometry; TRPA1 and cannabinoid receptors were analysed by quantitative RT-PCR; upper gastrointestinal transit, colonic propulsion and whole gut transit were evaluated in vivo; contractility was evaluated in vitro by stimulating the isolated ileum, in an organ bath, with ACh or electrical field stimulation (EFS).

KEY RESULTS

Croton oil administration was associated with decreased levels of anandamide (but not 2-arachidonoyl glycerol) and palmitoylethanolamide, up-regulation of TRPA1 and CB₁ receptors and down-regulation of CB₂ receptors. Ex vivo CBC did not change endocannabinoid levels, but it altered the mRNA expression of TRPA1 and cannabinoid receptors. In vivo, CBC did not affect motility in control mice, but normalized croton oil-induced hypermotility. In vitro, CBC reduced preferentially EFS- versus ACh-induced contractions. Both in vitro and in vivo, the inhibitory effect of CBC was not modified by cannabinoid or TRPA1 receptor antagonists.

CONCLUSION AND IMPLICATIONS

CBC selectively reduces inflammation-induced hypermotility in vivo in a manner that is not dependent on cannabinoid receptors or TRPA1.

P2Y1 purinoreceptors are fundamental to inhibitory motor control of murine colonic excitability and transit

Activation of enteric inhibitory motor neurons causes inhibitory junctional potentials (IJPs) and muscle relaxation in mammalian gastrointestinal (GI) muscles, including humans. IJPs in many GI muscles are bi-phasic with a fast initial hyperpolarization (fIJP) due to release of a purine neurotransmitter and a slower hyperpolarization component (sIJP) due to release of nitric oxide. We sought to characterize the nature of the post-junctional receptor(s) involved in transducing purinergic neural inputs in the murine colon using mice with genetically deactivated P2ry1. Wild-type mice had characteristic biphasic IJPs and pharmacological dissection confirmed that the fIJP was purinergic and the sIJP was nitrergic. The fIJP was completely absent in P2ry1(−/−) mice and the P2Y1 receptor antagonist MRS2500 had no effect on electrical activity or responses to electrical field stimulation of intrinsic nerves in these mice. Contractile experiments confirmed that purinergic responses were abolished in P2ry1(−/−) mice. Picospritzing of neurotransmitter candidates (ATP and its primary metabolite, ADP) and β-NAD (and its primary metabolite, ADP-ribose, ADPR) caused transient hyperpolarization responses in wild-type colons, but responses to β-NAD and ADPR were completely abolished in P2ry1(−/−) mice. Hyperpolarization and relaxation responses to ATP and ADP were retained in colons of P2ry1(−/−) mice. Video imaging revealed that transit of fecal pellets was significantly delayed in colons from P2ry1(−/−) mice. These data demonstrate the importance of purinergic neurotransmission in regulating colonic motility and confirm pharmacological experiments suggesting that purinergic neurotransmission is mediated via P2Y1 receptors.

Myostimulating effect of sesamum radiatum aqueous leaf extract in isolated Guinea-pig Taenia caeci contractile activity

This study was carried to examine the effects of the aqueous leaf extract of Sesamum radiatum, a laxative plant on the contractile activity of Taenia caeci, an intestinal smooth muscle. Strips of Taenia caeci were rapidly removed from guinea-pig and were suspended between two L-shaped stainless steel hooks in a 10 ml organ bath with Mac Ewen solution. The isometric contractile force of the Taenia caeci strips were recorded by using a strain gauge. S. radiatum aqueous leaf extract (ESera) is a spasmogenic substance. This myostimulant effect is characterized by the increase of the rhythm and the amplitude of isolated guinea-pig Taenia caeci smooth muscle in normal solution and by the development of contracture in modified solution and in solution without calcium. A similar effect was observed with ACh which caused a graded increase of the contractile activity of Taenia caeci. The effects induced by ESera and ACh were reversed in the presence of atropine. The spasmogenic effect induced by ESera could justify partially the use of S. radiatum as laxative in traditional medicine.

Laxative activities of Mareya micrantha (Benth.) Müll. Arg. (Euphorbiaceae) leaf aqueous extract in rats

Background

Mareya micrantha (Benth.) Müll. Arg. (Euphorbiaceae) is a shrub that is commonly used in Côte d'Ivoire (West Africa) for the treatment of constipation and as an ocytocic drug. The present study was carried out to investigate the laxative activity of Mareya micrantha in albino's Wistar rats.

Methods

Rats were divided in 5 groups of 5 animals each, first group as control, second group served as standard (sodium picosulfate) while group 3, 4 and 5 were treated with leaf aqueous extract of Mareya micrantha at doses of 100, 200 and 400 mg/kg body weight (b.w.), per os respectively. The laxative activity was determined based on the weight of the faeces matter. The effects of the leaves aqueous extract of Mareya micrantha and castor oil were also evaluated on intestinal transit, intestinal fluid accumulation and ions secretion.

Results

Phytochemicals screening of the extract revealed the presence of flavonoids, alkaloids, tannins, polyphenols, sterols and polyterpenes. The aqueous extract of Mareya micrantha applied orally (100, 200 and 400 mg/kg; p.o.), produced significant laxative activity and reduced loperamide induced constipation in dose dependant manner. The effect of the extract at 200 and 400 mg/kg (p.o.) was similar to that of reference drug sodium picosulfate (5 mg/kg, p.o). The same doses of the extract (200 and 400 mg/kg, p.o.) produced a significant increase (p < 0.01) of intestinal transit in comparison with castor oil (2 mL) (p < 0.01). Moreover, the extract induced a significant enteropooling and excretion of Cl^-, Na⁺, K⁺ and Ca²⁺ in the intestinal fluid (p < 0.01).

Conclusions

The results showed that the aqueous extract of Mareya micrantha has a significant laxative activity and supports its traditional use in herbal medicine.

Purinergic mechanisms in the control of gastrointestinal motility

For many years, ATP and adenosine have been implicated in movement regulation of the gastrointestinal tract. They act through three major receptor subtypes: adenosine or P1 receptors, P2X receptors and P2Y receptors. Each of these major receptor types can be subdivided into several different classes and is widely distributed amongst various neurons, muscle types, glia and interstitial cells that regulate intestinal functions. Several key roles for the different receptors and their endogenous ligands have been identified in physiological and pharmacological studies. For example, adenosine acting at A(1) receptors appears to inhibit intestinal motility in various pathological conditions. Similarly, ATP acting at P2Y receptors is an important component of inhibitory neuromuscular transmission, acting as a cotransmitter with nitric oxide. ATP acting at P2X and P2Y(1) receptors is important for synaptic transmission in simple descending excitatory and inhibitory reflex pathways. Some P2Y receptor subtypes prefer uridine nucleotides over purine nucleotides. Thus, roles for UTP and UDP as enteric transmitters in place of ATP cannot be excluded. ATP also appears to be important for sensory transduction, especially in chemosensitive pathways that initiate local inhibitory reflexes. Despite this evidence, data are lacking about the roles of either adenosine or ATP in more complex motility patterns such as segmentation or the interdigestive migrating motor complex. Clarification of roles for purinergic transmission in these common, but understudied, motility patterns will depend on the use of subtype-specific antagonists that in some cases have not yet been developed.

Mechanisms underlying nutrient-induced segmentation in isolated guinea pig small intestine

Mechanisms underlying nutrient-induced segmentation within the gut are not well understood. We have shown that decanoic acid and some amino acids induce neurally dependent segmentation in guinea pig small intestine in vitro. This study examined the neural mechanisms underlying segmentation in the circular muscle and whether the timing of segmentation contractions also depends on slow waves. Decanoic acid (1 mM) was infused into the lumen of guinea pig duodenum and jejunum. Video imaging was used to monitor intestinal diameter as a function of both longitudinal position and time. Circular muscle electrical activity was recorded by using suction electrodes. Recordings from sites of segmenting contractions showed they are always associated with excitatory junction potentials leading to action potentials. Recordings from sites oral and anal to segmenting contractions revealed inhibitory junction potentials that were time locked to those contractions. Slow waves were never observed underlying segmenting contractions. In paralyzed preparations, intracellular recording revealed that slow-wave frequency was highly consistent at 19.5 (SD 1.4) cycles per minute (c/min) in duodenum and 16.6 (SD 1.1) c/min in jejunum. By contrast, the frequencies of segmenting contractions varied widely (duodenum: 3.6-28.8 c/min, median 10.8 c/min; jejunum: 3.0-27.0 c/min, median 7.8 c/min) and sometimes exceeded slow-wave frequencies for that region. Thus nutrient-induced segmentation contractions in guinea pig small intestine do not depend on slow-wave activity. Rather they result from a neural circuit producing rhythmic localized activity in excitatory motor neurons, while simultaneously activating surrounding inhibitory motor neurons.

Mapping 5-HT inputs to enteric neurons of the guinea-pig small intestine

5-HT released by gastrointestinal mucosa and enteric interneurons has powerful effects on gut behavior. However, the targets of 5-HT-containing neurons within enteric circuits are not well characterized. We used antisera against 5-HT and selected markers of known enteric neuron types to investigate the connections made by 5-HT-containing neurons in the guinea-pig jejunum. Confocal microscopy was used to quantify the number of 5-HT-immunoreactive varicosities apposed to immunohistochemically identified cell bodies. Large numbers of varicosities were identified apposing cholinergic secretomotor neurons, immunoreactive for neuropeptide Y, in both myenteric and submucous plexuses. Subgroups of neurons identified by calretinin (ascending interneurons) and nitric oxide synthase (descending interneurons and inhibitory motor neurons) immunoreactivity were also apposed by many varicosities. Longitudinal muscle motor neurons (calretinin immunoreactive) and AH/Dogiel type II (sensory) neurons (calbindin immunoreactive) were apposed by small numbers of varicosities. Combined retrograde tracing and immunohistochemistry were used to identify excitatory circular muscle motor neurons; these were encircled by 5-HT-immunoreactive varicosities, but the appositions could not be quantified. We suggest that 5-HT-containing interneurons are involved in secretomotor pathways and pathways to subgroups of other interneurons, but not longitudinal muscle motor neurons. There also appear to be connections between 5-HT-containing interneurons and excitatory circular muscle motor neurons. Physiological evidence demonstrates a functional connection between 5-HT-containing interneurons and AH/Dogiel type II neurons, but few 5-HT-immunoreactive varicosities were observed apposing calbindin-immunoreactive cell bodies. Taken together these results suggest that neural 5-HT may have significant roles in excitatory pathways regulating both motility and secretion.

Nucleotide regulation of the voltage-dependent nonselective cation conductance in murine colonic myocytes

ATP is proposed to be a major inhibitory neurotransmitter in the gastrointestinal (GI) tract, causing hyperpolarization and smooth muscle relaxation. ATP activates small-conductance Ca(2+)-activated K(+) channels that are involved in setting the resting membrane potential and causing inhibitory junction potentials. No reports are available examining the effects of ATP on voltage-dependent inward currents in GI smooth muscle cells. We previously reported two types of voltage-dependent inward currents in murine proximal colonic myocytes: a low-threshold voltage-activated, nonselective cation current (I(VNSCC)) and a relatively high-threshold voltage-activated (L-type) Ca(2+) current (I(L)). Here we have investigated the effects of ATP on these currents. External application of ATP (1 mM) did not affect I(VNSCC) or I(L) in dialyzed cells. ATP (1 mM) increased I(VNSCC) and decreased I(L) in the perforated whole-cell configuration. UTP and UDP (1 mM) were more potent than ATP on I(VNSCC). ADP decreased I(L) but had no effect on I(VNSCC). The order of effectiveness was UTP = UDP > ATP > ADP. These effects were not blocked by pyridoxal phosphate-6-azo(benzene-2,4-disulfonic acid) (PPADS), but the phospholipase C inhibitor U-73122 reversed the effects of ATP on I(VNSCC). ATP stimulation of I(VNSCC) was also reversed by protein kinase C (PKC) inhibitors chelerythrine chloride or bisindolylmaleimide I. Phorbol 12,13-dibutyrate mimicked the effects of ATP. RT-PCR showed that P2Y(4) is expressed by murine colonic myocytes, and this receptor is relatively insensitive to PPADS. Our data suggest that ATP activates I(VNSCC) and depresses I(L) via binding of P2Y(4) receptors and stimulation of the phospholipase C/PKC pathway.

Spatiotemporal electrical and motility mapping of distension-induced propagating oscillations in the murine small intestine

Since the development of knockout animals, the mouse has become an important model to study gastrointestinal motility. However, little information is available on the electrical and contractile activities induced by distension in the murine small intestine. Spatiotemporal electrical mapping and mechanical recordings were made from isolated intestinal segments from different regions of the murine small intestine during distension. The electrical activity was recorded with 16 extracellular electrodes while motility was assessed simultaneously by tracking the border movements with a digital camera. Distension induced propagating oscillatory contractions in isolated intestinal segments. These propagating contractions were dictated by the underlying propagating slow wave with superimposed spikes. The frequencies, velocities, and direction of the propagating oscillations strongly correlated with the frequencies (r = 0.86), velocities (r = 0.84), and direction (r = 1) of the electrical slow waves. N(omega)-nitro-L-arginine methyl ester decreased the maximal diameter of the segment and reduced the peak contraction amplitude of the propagating oscillatory contractions, whereas atropine and verapamil blocked the propagating oscillations. Tetrodotoxin had little effect on the maximal diameter and peak contraction amplitude. In conclusion, distension in the murine small intestine does not initiate peristaltic reflexes but induces a propagating oscillatory motor pattern that is determined by propagating slow waves with superimposed spikes. These spikes are cholinergic and calcium dependent.

Endogenous nitric oxide modulates small intestinal nutrient transit and activity in healthy adult humans

OBJECTIVE

Nitric oxide (NO) mechanisms have been shown to modulate fasting small intestinal motility in humans, but a role in the regulation of human postprandial small intestinal motility has not been assessed. The aim of this study was to evaluate the effect of the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA) on the regulation of small intestinal nutrient transit and postprandial small intestinal motility in healthy humans.

MATERIAL AND METHODS

Seven healthy male volunteers (18-27 years) underwent antroduodenal manometry recordings for 4 h on 2 occasions after intraduodenal instillation of a 500 KJ [120 Kcal] test meal. The meal was administered 15 min after the commencement of a 60-min intravenous infusion of L-NMMA (4 mg kg-1 h-1) or saline (0.9%). Studies were separated, performed in randomized order and >3 days apart. The frequency and amplitude of duodenal pressure waves together with time to return of fasting motility (phase III) was determined. On each day, small intestinal transit was measured using a lactulose breath test.

RESULTS

The test meal interrupted fasting small intestinal motility in all subjects. The time to recurrence of fasting motility following its postprandial disruption was similar (L-NMMA versus saline 1.6+/-0.2 h versus 1.9+/-0.1 h; p>0.05). Duodenocaecal transit was delayed by infusion of L-NMMA compared with saline (L-NMMA versus saline 92.1+/-3.9 min versus 66.4+/-6.4 min; p<0.005). Infusion of L-NMMA significantly increased the frequency (L-NMMA versus saline 50.4+/-6.6 versus 34.8+/-5.5 waves per 30 min; p<0.05) and amplitude (L-NMMA versus saline 20.4+/-1.5 versus 15.5+/-1.1 mmHg; p<0.01) of duodenal pressure waves.

CONCLUSIONS

These data suggest that endogenous NO may play a role in the regulation of small intestinal nutrient transit by regulating small intestinal motility in healthy individuals.

5-HT7 receptors modulate peristalsis and accommodation in the guinea pig ileum

BACKGROUND & AIMS

The 5-hydroxytryptamine 7 (5-HT7) receptors mediate intestinal smooth muscle relaxation. In this study, we evaluated the expression of 5-HT7 receptors in the guinea pig ileum and their role in peristalsis and accommodation of the circular muscle.

METHODS

We used immunohistochemistry and confocal microscopy with whole tissue and cultured myenteric neurons. Peristalsis was induced by delivering a solution into the oral end of an isolated ileal segment. The effect of the selective 5-HT7 receptor antagonist SB-269970 (100 nmol/L) on peristaltic activity was evaluated at 30, 60, and 90 minutes and compared with control.

RESULTS

5-HT7 receptor immunoreactivity was localized to numerous myenteric neurons, a few submucosal neurons, and a few smooth muscle cells of the ileum. In enteric cultured neurons, 5-HT7 receptor immunoreactivity was observed in subpopulations of after hyperpolarizing neurons and descending neurons as identified by neuron-specific nuclear protein or calbindin and neuronal nitric oxide synthase or vasoactive intestinal peptide antibodies, respectively. SB-269970 significantly increased the threshold pressure by 33.3% +/- 2.2% (P < .001) and by 27.2% +/- 1.6% (P < .05) at 60 and 90 minutes, respectively, without modifying the threshold volume. The accommodation significantly decreased by 27.5% both at 60 and 90 minutes (P < .05).

CONCLUSIONS

Our results indicate that endogenous 5-HT is involved in the modulation of circular muscle accommodation during the preparatory phase of peristalsis via the activation of 5-HT7 receptors expressed by neurons in addition to smooth muscle cells. Overstimulation of these receptors leading to an exaggerated accommodation of circular muscle might contribute to abdominal symptoms in functional bowel disorders.

Effect of sodium fluoride on gastric emptying and intestinal transit in mice

Fluoride, a well-recognised harmful substance, is easily absorbed by the gastrointestinal mucosa. It is therefore conceivable that any alteration of the gastrointestinal motility can affect the rate of absorption of fluoride and leads to aggravation of its toxic effects. The effects of fluoride on gastric emptying and intestinal transit were studied in the mouse using a carboxymethyl cellulose (CMC) solution as a non-nutrient meal. The participation of the cholinergic and nitrergic systems in these effects was also evaluated. Oral gavage of 5 mM NaF had no significant effect on gastric emptying and intestinal transit of the CMC meal, whereas a decrease of gastric emptying (-33%, P<0.05) and an increase in intestinal transit (+20.7%, P<0.05) were observed with 20 mM NaF. Atropine injection induced a significant decrease of gastric emptying. Combined treatment of atropine with 20 mM NaF brought about a further, but not significant decrease in gastric emptying. N-G-nitro-L-arginine-methyl ester (L-NAME) treatment with or without oral administration of NaF decreased gastric emptying. Atropine treatment significantly depressed intestinal transit from 56.5% to 37.7% in the absence of NaF and from 70.1% to 42.8% in its presence. In contrast, L-NAME administration either alone or with fluoride increased intestinal transit (P<0.05). The present results suggest that fluoride alter gastrointestinal motility, an effect that may partly involve the cholinergic pathway.

Measurement of the propelled liquid by isolated hamster ileum as a parameter to evaluate peristalsis

We present a method to measure the volume of liquid propelled by peristaltic movements of isolated hamster ileum as a novel means to assess peristaltic activity. The oral and aboral ends of the dissected ileum were attached to cannulas fixed horizontally. The application of intraluminal pressure by raising the level of liquid in the bottle connected to the oral end evoked peristalsis and intermittent propulsion of the intraluminal liquid. The inhibition of intrinsic neurons by tetrodotoxin stopped propulsion; this indicated that the liquid propulsion was correlated with neuron-regulated peristalsis. The volume of liquid propelled by one complete peristaltic movement was significantly greater than that by incomplete peristalsis, whereas recordings of pressure changes were indistinguishable. Inhibitors of nitric oxide synthase decreased the volume of liquid propelled by peristaltic movements, suggesting a role of nitrergic neurons in peristalsis. Our data show that the method described above might be suitable for analyzing peristalsis.

Nitrergic prejunctional inhibition of purinergic neuromuscular transmission in the hamster proximal colon

Neurogenic ATP and nitric oxide (NO) may play important roles in the physiological control of gastrointestinal motility. However, the interplay between purinergic and nitrergic neurons in mediating the inhibitory neurotransmission remains uncertain. This study investigated whether neurogenic NO modulates the purinergic transmission to circular smooth muscles of the hamster proximal colon. Electrical activity was recorded from circular muscle cells of the hamster proximal colon by using the microelectrode technique. Intramural nerve stimulation with a single pulse evoked a fast purinergic inhibitory junction potential (IJP) followed by a slow nitrergic IJP. The purinergic component of the second IJP evoked by paired stimulus pulses at pulse intervals between 1 and 3 s became smaller than that of the first IJP. This purinergic IJP depression could be observed at pulse intervals <3 s, but not at longer ones, and failed to occur in the presence of NO synthase inhibitor. Exogenous NO (0.3-1 microM), at which no hyperpolarization is produced, inhibited purinergic IJPs, without altering the nitrergic IJP and exogenously applied ATP-induced hyperpolarization. In the presence of both purinoceptor antagonist and nitric oxide synthase (NOS) inhibitor, intramural nerve stimulation with 5 pulses at 20 Hz evoked vasoactive intestinal peptide (VIP)-associated IJPs, suggesting that VIP component may be masked in the IJPs of the hamster proximal colon. Our results suggest that neurogenic NO may modulate the purinergic transmission to circular smooth muscles of the hamster proximal colon via a prejunctional mechanism. In addition, VIP may be involved in the neurotransmitter in the hamster proximal colon.

Propagating contractions of the circular muscle evoked by slow stretch in flat sheets of guinea-pig ileum

Flat sheet preparations of guinea-pig ileum were stretched circumferentially and the propagation of circular muscle contractions along the preparation was investigated. Slow stretch, at 100 microm s-1, of a 50-mm long flat sheet of intestine, evoked circular muscle contraction orally, which propagated, without decrement, for up to 30 mm. This occurred despite circular muscle shortening being prevented, and in the absence of propulsion of contents. Thus, propagation in this flat sheet preparation could not explained on the basis of neuro-mechanical interactions, as previously proposed. Irrespective of the length of preparations, contraction amplitude decreased significantly in the most aboral 10-15 mm of intestine. This was not due to descending inhibitory pathways, but was associated with interruption of ascending excitatory pathways near the aboral end. Slow waves were not detected in circular muscle cells in any preparation (n=8). Smooth muscle action potentials evoked in circular muscle cells, in the presence of tetrodotoxin (TTX, 0.6 micromol L-1), did not propagate for more than 1 mm in the longitudinal axis. Propagation of circular muscle activity, evoked by slow stretch of flat sheet preparations, reveals the presence of a mechanism other than myogenic spread or the neuro-mechanical interactions previously proposed to account for propagation; the nature of this mechanism remains to be determined.

Enhanced colonic peristalsis by impairment of nitrergic enteric neurons in spontaneously diabetic rats

Changes in enteric neurons containing various neurotransmitters in the colon have been described in diabetic rats; however, how these changes are related to colonic motility disorders remains unclear. Nitric oxide (NO) is known to be an important inhibitory neurotransmitter in the enteric nervous system. In the present study, we investigated the peristaltic reflex using our modified Trendelenburg's method to evaluate the differences in enteric nitrergic neurons of the distal colon between spontaneously diabetic rats and their sibling control rats. We measured maximum intraluminal pressure, threshold pressure and propagation distance of the reflex contraction. These diabetic rats showed a greater maximum intraluminal pressure than that in the control rats. NG nitro-L-arginine methyl ester (L-NAME) significantly increased the maximum pressure in the control rats. Although L-arginine did not change the maximum pressure, sodium nitroprusside (SNP) significantly decreased it in these diabetic rats. Nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase reactivities in the myenteric plexus were much weaker in the diabetic rats than those in the control rats. These results indicate that the colonic peristaltic reflex is enhanced by impairment of enteric nitrergic inhibitory neurons in spontaneously diabetic rats.

Disturbance of peristalsis in the guinea-pig isolated small intestine by indomethacin, but not cyclo-oxygenase isoform-selective inhibitors

1. Since the cyclo-oxygenase (COX) isoform-nonselective inhibitor indomethacin is known to modify intestinal motility, we analysed the effects of COX-1 and COX-2 inhibition on intestinal peristalsis. 2. Peristalsis in isolated segments of the guinea-pig small intestine was triggered by a rise of the intraluminal pressure and recorded via the pressure changes associated with peristalsis. 3. The COX-1 inhibitor SC-560, the COX-2 inhibitor NS-398 (both at 0.1 -- 1 microM) and the isoform-nonselective inhibitors flurbiprofen (0.01 - 10 microM) and piroxicam (0.1 - 50 microM) were without major influence on peristalsis, whereas indomethacin and etodolac (0.1 -- 10 microM) disturbed the regularity of peristalsis by causing nonpropulsive circular muscle contractions. 4. Radioimmunoassay measurements showed that SC-560, NS-398, indomethacin and etodolac (each at 1 microM) suppressed the release of 6-keto-prostaglandin F(1 alpha) (6-keto-PGF(1 alpha)) from the intestinal segments. 5. Reverse transcription - polymerase chain reaction tests revealed that, relative to glyceraldehyde-3 phosphate dehydrogenase ribonucleic acid, the expression of COX-1 mRNA increased by a factor of 2.0 whereas that of COX-2 mRNA rose by a factor of 7.9 during the 2 h experimental period. 6. Pharmacological experiments indicated that the action of indomethacin to disturb intestinal peristalsis was unrelated to inhibition of L-type calcium channels, adenosine triphosphate-sensitive potassium channels or phosphodiesterase type IV. 7. These results show that selective inhibition of COX-1 and COX-2 does not grossly alter peristaltic motor activity in the guinea-pig isolated small intestine and that the effect of indomethacin to disturb the regular pattern of propulsive motility in this species is unrelated to COX inhibition.

Tachykinin-dependent and -independent components of peristalsis in the guinea pig isolated distal colon

BACKGROUND & AIMS

In the intestine, tachykinins regulate motility by participating in neuromuscular and neuro-neuronal transmission. The aim of this study was to test the hypothesis that colonic propulsion is regulated by an interplay between tachykinergic and cholinergic transmission.

METHODS

Propulsion was elicited by intraluminal distention of a thin rubber balloon, which traveled from the oral to the anal end of guinea pig isolated distal colon segments. The overall contribution of endogenous tachykinins to colonic propulsion was examined by blocking NK1, NK2, and NK3 receptors simultaneously.

RESULTS

NK2-receptor blockade by MEN 11420 inhibited propulsion, whereas blockade of NK(1) by SR 140333 or of NK3 receptors by SR 142801 had minor effects on motility. Blockade of muscarinic or nicotinic receptors by hyoscine or hexamethonium decelerated peristalsis up to propulsion arrest. In the presence of partial muscarinic receptor blockade, the NK1-receptor antagonist SR 140333 and the NK2-receptor antagonist MEN 11420 markedly inhibited propulsion. Propulsion was also inhibited by the NK3-receptor antagonist SR 142801 in the presence of partial nicotinic receptor blockade. The simultaneous administration of the 3 tachykinin antagonists inhibited propulsion by 50%.

CONCLUSIONS

This study demonstrates the existence of an interplay between tachykinergic and cholinergic pathways during peristalsis and the importance of endogenous tachykinins acting at multiple receptor sites in the control of colonic propulsion.

Role of muscle tone in peristalsis in guinea-pig small intestine

We investigated the involvement of muscle tone and circular muscle (CM) contraction in peristalsis in isolated guinea-pig small intestine. A segment of jejunum (approximately 13 cm) was mounted into a three chambered partitioned bath. Peristaltic waves were initiated in the oral chamber either by: (1) infusing fluid into the oral end of the jejunum; the ejected fluid was diverted via a cannula from reaching the intermediate and anal chambers, or by (2) intraluminal balloon distension of the empty oral segment. Tension of the circular muscle was measured in all three chambers. Peristaltic waves elicited by fluid infusion were evoked at an abrupt threshold. In contrast, peristaltic waves elicited by distension could be graded in amplitude according to stimulus intensity. Peristaltic waves evoked in an empty intestine exhibited similar propagation velocities to peristaltic waves associated with fluid propulsion. Nifedipine (200-400 nM) added to the intermediate chamber to block muscle contraction did not prevent peristaltic waves elicited by either stimulus from propagating into the anal chamber, although their amplitude was attenuated. Nifedipine to the site of stimulation (oral chamber) abolished peristaltic waves generated by either stimulus. Tetrodotoxin (1-2 microM), or a low Ca2+-high Mg2+ solution to the intermediate chamber abolished the propagation of peristalsis from the oral to anal chambers. In conclusion, graded peristaltic waves can occur in an empty intestine. Therefore peristalsis is not necessarily an "all-or-none" phenomenon. Peristalsis depends on the spread of nervous activity along the bowel, rather than the reactivation of neural circuits caused by displacement of fluid in the lumen. However, local muscle tone and contraction are important for the initiation and maintenance of peristaltic propagation.

Neural mechanisms underlying migrating motor complex formation in mouse isolated colon

1. Little is known about the intrinsic enteric reflex pathways associated with migrating motor complex (MMC) formation. Acetylcholine (ACh) mediates the rapid component of the MMC, however a non-cholinergic component also exists. The present study investigated the possible role of endogenous tachykinins (TKs) in the formation of colonic MMCs and the relative roles of excitatory and inhibitory pathways. 2. MMCs were recorded from the circular muscle at four sites (proximal, proximal-mid, mid-distal and distal) along the mouse colon using force transducers. 3. The tachykinin (NK(1) and NK(2)) receptor antagonists SR-140 333 (250 nM) and SR-48 968 (250 nM) reduced the amplitude of MMCs at all recording sites, preferentially abolishing the long duration contraction. Residual MMCs were abolished by the subsequent addition of atropine (1 microM). 4. The neuronal nitric oxide synthase inhibitor, N(omega)nitro-L-arginine (L-NOARG, 100 microM), increased MMC amplitude in the distal region, whilst reducing the amplitude in the proximal region. In preparations where MMCs did not migrate to the distal colon, addition of L-NOARG resulted in the formation of MMCs. Subsequent addition of apamin (250 nM) or suramin (100 microM) further increased MMC amplitude in the distal region, whilst suramin increased MMC amplitude in the mid-distal region. Apamin but not suramin reduced MMC amplitude in the proximal region. Subsequent addition of SR-140 333 and SR-48 968 reduced MMC amplitude at all sites. Residual MMCs were abolished by atropine (1 microM). 5. In conclusion, TKs, ACh, nitric oxide (NO) and ATP are involved in the neural mechanisms underlying the formation of MMCs in the mouse colon. Tachykinins mediate the long duration component of the MMC via NK(1) and NK(2) receptors. Inhibitory pathways may be involved in determining whether MMCs are formed.

Regulation of guinea pig intestinal peristalsis by endogenous endothelin acting at ET(B) receptors

BACKGROUND & AIMS

Endothelins are expressed in many enteric neurons of the gut. Because activation of endothelin ET(A) and ET(B) receptors is known to alter intestinal muscle activity, the effect of ET(A) and ET(B) receptor agonists and antagonists on propulsive peristalsis was examined.

METHODS

Repetitive peristalsis in fluid-perfused segments of the guinea pig isolated small intestine was elicited by a rise of the intraluminal pressure and recorded via the pressure changes generated by the peristaltic waves.

RESULTS

Endothelin 1 (0.3-10 nmol/L added to the organ bath) stimulated peristalsis as shown by a decrease in the pressure threshold at which peristaltic waves were triggered, whereas the endothelin analog sarafotoxin 6c (0.3-10 nmol/L) inhibited peristalsis as reflected by an increase in the pressure threshold. The ET(A) receptor antagonist BQ-123 (3 micromol/L) converted the properistaltic action of endothelin 1 to an antiperistaltic action, whereas the ET(B) receptor antagonist BQ-788 (3 micromol/L) prevented the antiperistaltic action of sarafotoxin 6c. BQ-788, but not BQ-123, facilitated peristalsis on its own. Additional experiments indicated that the properistaltic action of endothelin 1 is mediated by enteric neurons, whereas the peristaltic motor effects of sarafotoxin 6c and BQ-788 are caused by a direct action on the muscle.

CONCLUSIONS

ET(A) receptor activation stimulates, whereas ET(B) receptor activation inhibits, intestinal peristalsis. The ability of BQ-788 to facilitate peristalsis per se points to a physiologic role of ET(B) receptors in peristaltic motor regulation.

Differences in circular muscle contraction and peristaltic motor inhibition caused by tachykinin NK1 receptor agonists in the guinea-pig small intestine

The tachykinin NK1 receptor agonist substance P methyl ester (SPOME) impedes intestinal peristalsis by releasing nitric oxide (NO) from inhibitory motor neurones. Since NK1 receptor agonists differ in their receptor interaction, we set out to compare a range of NK1 receptor agonists including SPOME, septide and GR-73 632 in their effects on propulsive peristalsis and circular muscle activity in the guinea-pig isolated small intestine. SPOME (100-300 nM) inhibited peristalsis by a rise of the pressure threshold at which peristaltic waves were triggered, whereas septide and GR-73 632 (30-300 nM) interrupted peristalsis by causing circular muscle spasms. Separate experiments showed that all three NK1 receptor agonists caused contraction of the circular muscle, which was enhanced by the NO synthase inhibitor NG-nitro-L-arginine methyl ester (300 mM) and the P2X purinoceptor antagonist suramin (300 mM). In contrast, tetrodotoxin (300 nM) augmented the contractile effect of septide and GR-73 632 but not that of SPOME. It is concluded that the motor response to NK1 receptor agonists involves release of NO and adenosine triphosphate from inhibitory motor neurones. However, the NK1 receptor agonists differ in the mechanism by which they cause inhibitory transmitter release, which corresponds to differences in their antiperistaltic action.

Modulation of peristalsis by cannabinoid CB(1) ligands in the isolated guinea-pig ileum

The effect of cannabinoid drugs on peristalsis in the guinea-pig ileum was studied. Peristalsis was induced by delivering fluid into the oral end of an isolated intestinal segment. Longitudinal muscle reflex contraction, threshold pressure and threshold volume to trigger peristalsis, compliance of the intestinal wall during the preparatory phase (a reflection of the resistance of the wall to distension) and maximal ejection pressure during the emptying phase of peristalsis were measured. The cannabinoid agonists WIN 55,212-2 (0.3 - 300 nM) and CP55,940 (0.3 - 300 nM) significantly decreased longitudinal muscle reflex contraction, compliance and maximal ejection pressure, while increased threshold pressure and volume to elicit peristalsis. These effects were not modified by the opioid antagonist naloxone (1 microM) and by the alpha-adrenoceptor antagonist phentolamine (1 microM). The inhibitory effect of both WIN 55,212-2 and CP55,940 on intestinal peristalsis was antagonized by the cannabinoid CB(1) receptor antagonist SR141716A (0.1 microM), but not by the cannabinoid CB(2) receptor antagonist SR144528 (0.1 microM). In absence of other drugs, the CB(1) receptor antagonists SR141716A (0.01 - 1 microM) and AM281 (0.01 - 1 microM) slightly (approximatively 20%) but significantly increased maximal ejection pressure during the empty phase of peristalsis without modifying longitudinal muscle reflex contraction, threshold pressure, threshold volume to trigger peristalsis and compliance. It is concluded that activation of CB(1) receptors reduces peristalsis efficiency in the isolated guinea-pig, and that the emptying phase of peristalsis could be tonically inhibited by the endogenous cannabinoid system.

Contribution of NK(2) tachykinin receptors to propulsion in the rabbit distal colon

The role of the tachykinin neurokinin (NK)(2) receptors on rabbit distal colon propulsion was investigated by using two selective NK(2)-receptor antagonists, MEN-10627 and SR-48968. Experiments on colonic circular muscle strips showed that contractile responses to [beta-Ala(8)]NKA-(4-10) (1 nM-1 microM), a selective NK(2)-receptor agonist, were competitively antagonized by MEN-10627 (1-100 nM), whereas SR-48968 (0.1-10 nM) caused an insurmountable antagonism, thus confirming the difference in the mode of action of the two compounds. Colonic propulsion was elicited by distending a mobile rubber balloon with 0.3 ml (submaximal stimulus) or 1.0 ml (maximal stimulus) of water. The velocity of anal displacement of the balloon (mm/s) was considered the main propulsion parameter. At low concentrations (1.0-100 nM and 0.1-10 nM, respectively), MEN-10627 and SR-48968 facilitated the velocity of propulsion, whereas at high concentrations (100 nM and 1 microM, respectively) they decelerated propulsion. The excitatory and inhibitory effects of both antagonists were observed only with submaximal stimulus. We focused on the hypothesis that the facilitatory effect on propulsion may result from blockade of neuronal NK(2) receptors and the inhibitory effect from suppression of the excitatory transmission mediated by NK(2) receptors on smooth muscle cells. In the presence of N(G)-nitro-L-arginine (300 microM), a nitric oxide synthase inhibitor, MEN-10627, at a concentration (10 nM) that was found to accelerate propulsion in control experiments inhibited the velocity of propulsion. In the presence of threshold (1-10 nM) or full (1 microM) concentration of atropine, which inhibited to a great extent the velocity of propulsion, the inhibitory effect of MEN-10627 (1 microM) was markedly increased. In conclusion, in the rabbit distal colon NK(2) receptors may decelerate propulsion by activating a nitric oxide-dependent neuronal mechanism and may accelerate it by a postjunctional synergistic interaction with cholinergic muscarinic receptors.

Different receptors mediating the inhibitory action of exogenous ATP and endogenously released purines on guinea-pig intestinal peristalsis

1 Adenosine 5'-triphosphate (ATP) is an enteric neurotransmitter which acts at purine receptors on intestinal nerve and muscle. This study set out to shed light on the receptor mechanisms by which exogenous and endogenous ATP influences intestinal peristalsis. 2 Peristalsis in isolated segments of the guinea-pig small intestine was triggered by a perfusion-induced rise of the intraluminal pressure. Motor changes were quantified by alterations of the peristaltic pressure threshold (PPT) at which propulsive muscle contractions were elicited. 3 ATP (>/= 3 microM) increased PPT and abolished peristalsis at concentrations of 100-300 microM. Adenosine 5'-O-2-thiodiphosphate (ADPbetaS, 3-100 microM) was more potent, whereas alpha,beta-methylene ATP (alpha,beta-meATP, 3-100 microM) was less potent, than ATP in depressing peristalsis. 4 8-Phenyltheophylline (10 microM) attenuated the anti-peristaltic effect of 10 and 30 microM ATP but not that of higher ATP concentrations. Apamin (0.5 microM) counteracted the ability of ATP, ADPbetaS and alpha,beta-meATP to enhance PPT. Suramin (300 microM) and pyridoxal phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS, 150 microM) antagonized the inhibitory effect of alpha,beta-meATP on peristalsis but did not alter the effect of ATP and ADPbetaS. 5 PPADS (50-150 microM) reduced PPT by as much as 50%. This stimulant effect on peristalsis was prevented by suramin (300 microM) but left unaltered by apamin (0.5 microM) and NG-nitro-L-arginine methyl ester (300 microM). 6 These data show that exogenous and endogenous ATP inhibits intestinal peristalsis via different apamin-sensitive purinoceptor mechanisms. Exogenous ATP depresses peristalsis mostly via suramin- and PPADS-insensitive P2 receptors, whereas endogenous purines act via P2 receptors sensitive to both suramin and PPADS.

Cannabinoid inhibition of guinea-pig intestinal peristalsis via inhibition of excitatory and activation of inhibitory neural pathways

Since activation of cannabinoid CB1 receptors inhibits gastrointestinal transit in the mouse, this study analyzed the action of the cannabinoid receptor agonist methanandamide on distension-induced propulsive motility. Peristalsis in luminally perfused segments of the guinea-pig isolated ileum was elicited by a rise of the intraluminal pressure. The pressure threshold at which peristaltic contractions were triggered was used to quantify drug effects. Methanandamide (0.1-3 microM) inhibited peristalsis as deduced from a concentration-related increase in the peristaltic pressure threshold, an action that was prevented by the CB1 receptor antagonist SR141716A (1 microM) per se, which had no effect on peristalsis. The distension-induced ascending reflex contraction of the circular muscle was likewise depressed by methanandamide in a SR141716A-sensitive manner, whereas indomethacin-induced phasic contractions of the circular muscle were left unchanged by methanandamide. The anti-peristaltic action of methanandamide was inhibited by apamin (0.5 microM), attenuated by N-nitro-L-arginine methyl ester (300 microM) and left unaltered by suramin (300 microM), pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid (150 microM) and naloxone (0.5 microM). It is concluded that methanandamide depresses intestinal peristalsis via activation of CB1 receptors on enteric neurons, which results in blockade of excitatory motor pathways and facilitation of inhibitory pathways operating via apamin-sensitive K+ channels and nitric oxide.

Does the guinea-pig ileum obey the 'law of the intestine'?

1. We report the first simultaneous mechanical reflex responses of the longitudinal muscle (LM) and circular muscle (CM) layers of the guinea-pig ileum following mucosal stimulation and distension in vitro. 2. Dissection techniques were used to prevent mechanical interaction between the LM and CM layers both oral and anal to a stimulus site. 3. All graded stimuli produced graded contractions of both the LM and CM orally and anally to the stimulus. Contractions occurred synchronously in the LM and CM and under no circumstances were inhibitory responses recorded in either muscle layer, despite the presence of ongoing cholinergic tone in both the LM and CM. Contractions were abolished by tetrodotoxin (1.6 microM). 4. Local brush stroking of the mucosa evoked a peristaltic wave which readily conducted distally over 13 cm, without the presence of fluid in the lumen. No descending relaxation was observed. 5. Apamin (300 nM) disrupted evoked peristaltic waves and significantly increased the rate-of-rise of the LM and CM contractions anal to a stimulus, and the LM oral to a stimulus. 6. Nomega-nitro-L-arginine (100 microM), a nitric oxide synthesis inhibitor, had no overall significant effect on the characteristics of the LM and CM contractions, although on occasion an enhancement in their peak amplitude was noted. 7. It is suggested that the guinea-pig ileum does not conform to the 'law of the intestine' as postulated by Bayliss & Starling (1899). Rather, local physiological stimulation of the ileum elicits a contraction both orally and anally to a stimulus, which occurs synchronously in both the CM and LM layers. Apamin-sensitive inhibitory neurotransmission modulates the rate-of-rise of the anal contraction of the CM, possibly to generate distal propulsion.

Quantitative analysis of peristalsis in the guinea-pig small intestine using spatio-temporal maps

1. Peristalsis was evoked in guinea-pig small intestine by slow fluid infusion and recorded onto video and digitized. Spatio-temporal maps of diameter and longitudinal movement were constructed and parameters of motion were calculated. 2. During the filling of the isolated segments of intestine, rhythmic local longitudinal movements were observed at several points along the preparation. These phasic longitudinal muscle contractions were associated with small but significant local increases in diameter and probably reflect a passive mechanical coupling by connective tissue in the gut wall. In addition, occasional synchronized longitudinal muscle contractions caused net shortening of the preparation and always preceded the onset of peristaltic emptying. 3. Peristaltic emptying was characterized by a contraction of the circular muscle which usually started at the oral end of the preparation, that propagated aborally, propelling the contents. However, in 19 % of trials, the first circular muscle contraction occurred in the aboral half of the preparation. 4. The propagation of peristalsis consisted of separate sequential circular muscle contractions several centimetres long, particularly in the oral half of the preparation, giving a 'step-like' appearance to the spatio-temporal map. The gut was transiently distended aboral to the propagating circular muscle contraction due to the propulsion of contents. 5. At each point in the preparation, the longitudinal muscle remained contracted during the propulsive part of the circular muscle contraction. Only when the circular muscle contraction became lumen occlusive did lengthening of the longitudinal muscle take place. 6. Spatio-temporal maps are a powerful tool to visualize and analyse the complexity of gastrointestinal motility patterns.

Visual parameters define the phase and the load of contractions in isolated guinea pig ileum

How the movements of the intestinal walls relate to luminal pressures and outflow remains incompletely understood. We triggered the peristaltic reflex in the isolated ileum of the guinea pig and quantified wall movements through computerized measurements of diameter changes. Contractions developed as indentations close to the upstream end of the loop. The indentations deepened and expanded in length. The downstream shoulder of contractions started and stopped to propagate before the upstream shoulder. Shoulders differed in their length and gradient over most of the duration of the contraction, and this gives the contraction an axial asymmetry. Over the course of individual contractions, the length of the indented segment correlated well with the luminal pressure. Contractions in response to large volumes generated long indented segments and high luminal pressures. The onset and the end of pressure waves and of outflow did not necessarily coincide with the onset and end of visual parameters of contractions. These findings indicate that objective visual parameters might be useful to describe and to classify contractions.

Stimulant action of pituitary adenylate cyclase-activating peptide on normal and drug-compromised peristalsis in the guinea-pig intestine

1. Pituitary adenylate cyclase-activating peptide (PACAP) is known to influence the activity of intestinal smooth muscle. This study set out to examine the action of PACAP on normal and drug-inhibited peristalsis and to shed light on its site and mode of action. 2. Peristalsis in isolated segments of the guinea-pig small intestine was elicited by distension through a rise of the intraluminal pressure. Drug-induced motility changes were quantified by alterations of the peristaltic pressure threshold at which aborally moving peristaltic contractions were triggered. 3. PACAP (1-30 nM) stimulated normal peristalsis as deduced from a concentration-related decrease in the peristaltic pressure threshold (maximum decrease by 55%). The peptide's stimulant effect remained intact in segments pre-exposed to apamin (0.5 microM), N-nitro-L-arginine methyl ester (300 microM), naloxone (0.5 microM), atropine (1 microM) plus naloxone (0.5 microM) or hexamethonium (100 microM) plus naloxone (0.5 microM). 4. PACAP (10 nM) restored peristalsis blocked by morphine (10 microM), noradrenaline (1 microM) or N6-cyclopentyladenosine (0.3 microM) and partially reinstated peristalsis blocked by Rp-adenosine-3',5'-cyclic monophosphothioate triethylamine (100 microM) but failed to revive peristalsis blocked by hexamethonium (100 microM) or atropine (1 microM). The peptide's spectrum of properistaltic activity differed from that of naloxone (0.5 microM) and forskolin (0.3 microM). 5. The distension-induced ascending reflex contraction of the circular muscle was facilitated by PACAP (1-30 nM) which itself evoked transient nerve-mediated contractions of intestinal segment preparations. 6. These data show that PACAP stimulates normal peristalsis and counteracts drug-induced peristaltic arrest by a stimulant action on excitatory enteric motor pathways, presumably at the intrinsic sensory neurone level. The action of PACAP seems to involve multiple signalling mechanisms including stimulation of adenylate cyclase.

Initiation of peristalsis by circumferential stretch of flat sheets of guinea-pig ileum

1. Segments of isolated guinea-pig intestine, 12 mm long, were distended slowly by intraluminal fluid infusion or by mechanical stretch as either a tube or flat sheet. In all cases, at a constant threshold length, a sudden, large amplitude contraction of the circular muscle occurred orally, corresponding to the initiation of peristalsis. 2. Circumferential stretch of flat sheet preparations evoked graded contractions of the longitudinal muscle (the 'preparatory phase'), which were maintained during circular muscle contraction. This suggests that the lengthening reported during the emptying phase of peristalsis is due to mechanical interactions. 3. The threshold for peristalsis was lower with more rapid stretches and was also lower in long preparations (25 mm) compared with short preparations (5-10 mm), indicating that ascending excitatory pathways play a significant role in triggering peristalsis. 4. Stretching a preparation beyond the threshold for peristalsis evoked contractions of increasing amplitude; thus peristalsis is graded above its threshold. However, during suprathreshold stretch maintained at a constant length, contractions of the circular muscle quickly declined in amplitude and frequency. 5. Circular muscle cells had a resting membrane potential approximately 6 mV more negative than the threshold for action potentials. During slow circumferential stretch, subthreshold graded excitatory motor input to the circular muscle occurred, prior to the initiation of peristalsis. However, peristalsis was initiated by a discrete large excitatory junction potential (12 +/- 2 mV) which evoked bursts of smooth muscle action potentials and which probably arose from synchronized firing of ascending excitatory neuronal pathways.

The neurology and enterology of equine grass sickness: a review of basic mechanisms

Autonomic dysfunction constitutes a prominent clinical feature of equine grass sickness (EGS). Significant injury to the nervous control of the alimentary system is life threatening, partly because of dysphagia but also because of the failure of the unique regulatory mechanisms in equine digestion involving water and electrolyte balance. The neuropathology also indicates the presence of a somatic polyneuropathy. The morphological features of EGS are similar to those of excitotoxic neuronal degeneration, which resembles neuronal apoptosis. It is difficult to ascertain from published accounts the degree of damage to central neurones: the distribution is well documented and selective but the proportion of damage is poorly quantified. If lesions involve a significant number of regulatory neurones they should produce functional deficits. Any clinical assessment of horses, especially those with chronic EGS, should include a thorough neurological examination. Although this will not necessarily improve the outcome of the case, it may enable the rational selection of animals with a reasonable prognosis for recovery which is partly determined by the extent of CNS lesions. The evidence supports the following pathogenesis. There is an initial lesion in the enteric nervous system of susceptible horses. In the acute form of EGS, massive enteric neuronal damage occurs first functionally, then structurally leading to generalized alimentary smooth muscle atony, enhanced secretions and altered fluid fluxes. Severe distension of the stomach and small intestines rapidly develops, which augments the intestinal ileus by intersegmental inhibitory reflexes and causes colic and dehydration. In subacute cases, failure of intestinal bicarbonate buffer together with alimentary stasis rapidly reduces caecal-colonic fermentation. Thus the osmolality of large intestinal digesta reduces and water travels out of the bowel along osmotic gradients. Water returns to the circulation, but is eventually lost in the gastric and small intestinal secretions. The observation that pathological lesions may not be seen in the prevertebral ganglia within the first few days of acute cases supports the view that a functional deficit precedes structural lesions which may be secondary to a retrograde degeneration. It is therefore possible to resolve the observations that less damage may be seen in prevertebral ganglia and elsewhere in peracute and acute cases with the more common finding that greater neuronal damage is present in acute than in chronic cases. These different observations are probably time dependent. Chronic EGS occurs when there is less initial enteric nerve damage which may lead to less secondary prevertebral ganglionic pathology, and more time for functional and structural compensatory mechanisms to develop. Denervation hypersensitivity develops at target sites both in the gut and in peripheral somatic nerves which may account, in part, for the clinical signs of patchy sweating and muscle tremors. Raised circulating adrenaline levels may also account for generalized sweating, may contribute to gastrointestinal atony and may affect pacemakers at the pelvic flexure. Many of the features of EGS make worthwhile the re-investigation of Clostridium botulinum Group III toxins, which are known to prevent vesicular exocytosis, stimulate neurosecretion, produce neuronal chromatolysis and inhibit neutrophil migration. Also, evidence from other species suggests that increased nitrergic neuronal activity can account for many of the clinical signs of EGS, namely dysphagia, generalized ileus, gastric dilatation, sweating, peripheral vasodilatation, tachycardia, salivary hypersecretion, muscle wastage and cachexia.

Immunohistochemical distribution of c-Kit-positive cells and nitric oxide synthase-positive nerves in the guinea-pig small intestine

Anatomical relationships between c-Kit-positive cells and nitric oxide synthase-positive nerves in the small intestine were examined by double-labeling immunohistochemistry. Cryosections and whole mount preparations of the guinea-pig small intestine were double-immunolabeled using anti-c-Kit and neuronal nitric oxide synthase antibodies, and were observed using confocal laser scanning microscopy. The c-Kit-like immunoreactivity constituted dense reticular networks in the deep muscular plexus and myenteric plexus of the intestinal wall. The nitric oxide synthase-like immunoreactivity occurred in the circular muscle layer, most densely at the deep muscular plexus, as well as within the ganglion strands or connecting strands of the myenteric plexus. Close association between c-Kit-like immunoreactivity and nitric oxide synthase-like immunoreactivity was evident in the deep muscular plexus. Specimens immunolabeled with the anti-nitric oxide synthase antibody were further examined under transmission electron microscopy. Axon profiles with nitric oxide synthase-like immunoreactivity lay closely adjacent to the interstitial cells in the deep muscular plexus as well as to smooth muscle cells of the circular muscle layer, whereas there was a considerable distance (> 500 nm) between interstitial cells and axon profiles with nitric oxide synthase-like immunoreactivity in the myenteric plexus. These results suggest that the interstitial cells in the deep muscular plexus serve as mediators of the nitrergic neurotransmission to the musculature in the small intestine, playing a role in the regulation of intestinal movement.