Identification of the cholinergic neurons in guinea-pig sphincter of Oddi ganglia

Effect of four medications associated with gastrointestinal motility on Oddi sphincter in the rabbit

AIM

Modulatory drugs of gastrointestinal (GI) motility are a possibility for use to relieve the main clinical presentation of sphincter of Oddi (SO) dysfunctions which are not easily distinguished from those occurring in high prevalence functional GI disorders. The aim of this study was to investigate the effects of GI motility modulators including pinaverium, domperidone, trimebutine, and tegaserod on the contractile activity of SO stimulated by carbachol in the rabbit.

METHODS

The contraction responses precontracted by carbachol (0.1 microM) of in vitro rabbit SO rings were evaluated before and after the addition of a series concentration (10(-13) to 10(-3)M) of pinaverium, domperidone, trimebutine, and tegaserod.

RESULTS

Pinaverium induced a concentration-dependent relaxation of isolated SO rings (10(-13) vs. 10(-7) vs. 10(-3)M = 16.6 +/- 4.8 vs. 47.1 +/- 5.5 vs. 81.2 +/- 6.2%, p < 0.001 by ANOVA) precontracted with carbachol (0.1 microM). Tegaserod did not significantly effect (10(-13) vs. 10(-7) vs. 10(-3)M = 2.3 +/- 2.2 vs. 6.7+/- 2.1 vs. 10.1 +/- 2.3%, p > 0.05 by ANOVA) SO motility, but domperidone seemed to stimulate SO contractions (10(-12) vs. 10(-7) vs. 10(-3)M = -2.2 +/- 1.5 vs. -13.9 +/- 2.0 vs. -21.0 +/- 2.7%, p < 0.05 by ANOVA). At low doses (10(-13) to 10(-7)M), trimebutine stimulated SO contraction (-8.7 +/- 1.4 vs. -9.3 +/- 2.0%); however, high doses (10(-6) to 10(-3)M) of trimebutine inhibited SO motility (-5.9 +/- 1.7 vs. 14.5 +/- 2.0%, p < 0.05 by ANOVA).

CONCLUSION

Pinaverium totally inhibits contractions induced by carbachol and tegaserod has no effect on carbachol-induced contractions. Domperidone stimulates contractions induced by carbachol. Trimebutine could either stimulate or inhibit SO contractions depending on its dosage.

A new mechanism for diverticular diseases: aging-related vagal withdrawal

It is widely believed that diverticulosis, a common condition among the elderly, results from repeated colonic barotrauma related to low dietary fiber and low stool bulk. Recent evidence has challenged the dietary-barotrauma hypothesis. We propose an alternative hypothesis that diverticulosis may be attributable to colonic smooth muscle dysfunction that results from vagal attrition associated with aging. We previously proposed that broad aging-related attrition of autonomic nerves may unmask intrinsic sympathetic bias of end-organs, leading to the compendium of familiar conditions associated with senility. Unexplained cholinergic hypersensitivity and receptor over-expression in bowel affected by diverticulosis have recently been observed. These findings are highly suggestive of a compensatory response to loss of vagal innervation. The resulting autonomic dysregulation may induce bowel smooth muscle dysfunction, setting the stage for diverticula formation. Thus, diverticular bowel disease may be a manifestation of the aging-related systemic vagal withdrawal. The framework may extend to diverticula formation in other parts of the gastrointestinal and genitourinary tracts. For instance, aging-related vagal attrition may represent the common upstream mechanism that induces both sphincter of Oddi dysfunction and peri-ampullary duodenal diverticula, conditions that frequently occur together. Novel approaches to preventing and treating diverticular diseases by promoting vagal activity are proposed including the electrical or pharmacologic modulation of the autonomic system.

Innervation of the extrahepatic biliary tract

The extrahepatic biliary tract is innervated by dense networks of extrinsic and intrinsic nerves that regulates smooth muscle tone and epithelial cell function of extrahepatic biliary tree. Although these ganglia are derived from the same set of precursor neural crest cells that colonize the gut, they exhibit structural, neurochemical, and physiological characteristics that are distinct from the neurons of the enteric nervous system. Gallbladder neurons are relatively inexcitable, and their output is driven by vagal inputs and modulated by hormones, peptides released from sensory fibers, and inflammatory mediators. Gallbladder neurons are cholinergic and they can express a number of other neural active compounds, including substance P, galanin, nitric oxide, and vasoactive intestinal peptide. Sphincter of Oddi (SO) ganglia, which are connected to ganglia of the duodenum, appear to be comprised of distinct populations of excitatory and inhibitory neurons, based on their expression of choline acetyltransferase and substance P or nitric oxide synthase, respectively. While SO neurons likely receive vagal input and their activity is modulated by release of neuropeptides from sensory fibers, a significant source of excitatory synaptic input to these cells arise from the duodenum. This duodenum-SO circuit is likely to play an important role in the coordination of SO tone with gallbladder motility in the process of gallbladder emptying. Now that we have gained a relatively thorough understanding of the innervation of the biliary tree under healthy conditions, the way is paved for future studies of altered neural function in biliary disease.

Electrical activation of common bile duct nerves modulates sphincter of Oddi motility in the Australian possum

BACKGROUND

Sphincter of Oddi (SO) motility is regulated by extrinsic and intrinsic nerves. The existence of neural circuits between the SO and the proximal extrahepatic biliary tree has been reported, but they are poorly understood. Using electrical field stimulation (EFS), we determined if a neural circuit exists between the common bile duct (CBD) and the SO in anaesthetized Australian brush-tailed possums.

METHODS

The gallbladder, cystic duct or CBD were subjected to EFS with a stimulating electrode. Spontaneous SO phasic waves were measured by manometry.

RESULTS

EFS at sites on the distal CBD (12-20 mm proximal to the SO), but less commonly at more proximal CBD, evoked a variety of responses consisting of an excitatory and/or inhibitory phase. Bi-phasic responses consisting of an excitation followed by inhibition were the most common. Tri-phasic responses were also observed as well as excitation or inhibition only. These evoked responses were blocked by topical application of local anaesthetic to the distal CBD or transection of the CBD. EFS at sites on the gallbladder body, neck or cystic duct did not consistently evoke an SO response. Pretreatment with atropine or guanethidine reduced the magnitude of the evoked response by about 50% (p<0.05), pretreatment with hexamethonium had no consistent effect and pretreatment with a nitric oxide synthase inhibitor increased the response.

DISCUSSION

A neural circuit(s) between the SO and the distal CBD modulates SO motility. Damage to this area of the CBD during bile duct exploration surgery could adversely affect SO motility.

The possum sphincter of Oddi pumps or resists flow depending on common bile duct pressure: a multilumen manometry study

The sphincter of Oddi (SO) regulates trans-sphincteric flow (TSF) by acting primarily as a pump or as a resistor in specific species. We used the Australian possum SO, which functions similarly to the human SO, to characterize SO motility responses to different common bile duct (CBD) and duodenal pressures. Possum CBD, SO and attached duodenum (n= 18) was mounted in an organ bath. External reservoirs were used to impose CBD (0-17 mmHg) and duodenal (0, 4, 7 mmHg) pressure. Spontaneous SO activity was recorded using four-lumen pico-manometry and TSF was measured gravimetrically. Temporal analysis of manometric and TSF recordings identified three functionally distinct biliary-SO regions, the proximal-SO (juxta-CBD), body-SO and papilla-SO. At CBD pressures < 3 mmHg the motor activity of these regions was coordinated to pump fluid. Proximal-SO contractions isolated fluid within the body-SO. Peristaltic contraction through the body-SO pumped this fluid through the papilla-SO (17-27 microl contraction), which opened to facilitate flow. CBD pressure > 3.5 mmHg resulted in progressive changes in TSF to predominantly passive 'resistor'-type flow, occurring during proximal-SO-body-SO quiescence, when CBD pressure exceeded the pressure at the papilla-SO. Progression from pump to resistor function commenced when CBD pressure was 2-4 mmHg greater than duodenal pressure. These results imply that TSF is dependent on the CBD-duodenal pressure difference. The papilla-SO is pivotal to TSF, relaxing during proximal-SO-body-SO pumping and closing during proximal-SO-body-SO quiescence. The pump function promotes TSF at low CBD pressure and prevents bile stasis. At higher CBD pressure, the papilla-SO permits TSF along a pressure gradient, thereby maintaining a low pressure within the biliary tract.

Tachykinins mediate slow excitatory postsynaptic transmission in guinea pig sphincter of Oddi ganglia

Intracellular recording techniques were used to test whether tachykinins could be mediators of slow excitatory postsynaptic potentials (EPSPs) in guinea pig sphincter of Oddi (SO) ganglia. Application of the tachykinin substance P (SP) onto SO neurons caused a prolonged membrane depolarization that was reminiscent of the slow EPSP in these cells. Pressure ejection of the neurokinin 3 (NK3) receptor-specific agonist senktide caused a similar depolarization; however, no responses were detected on application of NK1 or NK2 receptor agonists. The NK3 receptor antagonist SR-142801 (100 nM) significantly inhibited both SP-induced depolarization and the stimulation-evoked slow EPSP, as did NK3 receptor desensitization with senktide. Capsaicin, which causes the release of SP from small-diameter afferent fibers, induced a depolarization that was similar to the evoked slow EPSP in both amplitude and duration. The capsaicin-induced depolarization was significantly attenuated in the presence of SR-142801. These data indicate that tachykinins, released from extrinsic afferent fibers, act via NK3 receptors to provide slow excitatory synaptic input to SO neurons.

Direct neuronal interactions between the duodenum and the sphincter of Oddi

The sphincter of Oddi (SO) is a complex structure that must function in coordination with the motor activities of the gallbladder and the duodenum. It is now clear that a neural circuit exists between the duodenum and the SO, and it is likely that this network is largely responsible for the regulation of SO motility. Recent studies have demonstrated that this circuit provides excitatory cholinergic input to SO ganglia that can be activated by electrical stimulation of the duodenal mucosa, distention of the duodenum, and increased motor activity of the duodenum.

Duodenal neurons provide nicotinic fast synaptic input to sphincter of Oddi neurons in guinea pig

We have investigated the existence of neural connections between the duodenum and the sphincter of Oddi (SO). Stimulation of duodenal myenteric fiber bundles elicited synaptic responses in SO neurons, which included nicotinic fast excitatory postsynaptic potentials (EPSPs), slow EPSPs, and alpha(2)-adrenoreceptor-mediated inhibitory postsynaptic potentials. After 48 h in organ culture, when extrinsic fibers had diminished, only the fast EPSPs persisted. Duodenal mucosal stimulation also elicited nicotinic fast EPSPs in SO neurons. There was no association between the SO neurons that received duodenal input and their chemical coding. A reciprocal projection also exists from the SO to the duodenum. In acute and cultured preparations, duodenal myenteric stimulation caused antidromic responses in 20% of SO neurons. Furthermore, 45.6 +/- 10.5 neurons in SO ganglia were retrogradely labeled from dye application sites in the duodenum. It is proposed that bidirectional neural communication occurs between the duodenum and the SO and that duodenal neurons provide excitatory fast synaptic input to SO neurons through a reflex that can be activated at the duodenal mucosa.

5-HT is present in nerves of guinea pig sphincter of Oddi and depolarizes sphincter of Oddi neurons

This study involved immunohistochemistry and intracellular electrophysiology to investigate serotonergic neurotransmission in the sphincter of Oddi (SO). 5-Hydroxytryptamine (HT)-positive neurons (14 cells/preparation) and nerve fibers were observed in the ganglionated plexus. Serotonergic nerve fibers, which persisted under 2- to 6-day organ culture, were densely distributed, with varicose endings encircling some SO neurons. When 5-HT was applied to SO neurons, it elicited three different responses: 1) a fast depolarization to 5-HT in 31 of 62 cells was mimicked by 2-methyl-5-HT and blocked by LY-278584 (1 microM); 2) a prolonged depolarization to 5-HT in 21 of 62 cells evoked an increase in input resistance and was attenuated by the 5-HT1P antagonist renzapride (1 microM) but not by the 5-HT4 antagonist SDZ-205557 (0.1-10 microM); and 3) an indirect depolarization blocked by TTX or atropine was observed in 32 of 62 cells. 5-HT superfusion elicited a dose-dependent monophasic depolarization (EC50 = 2 microM, n=14). In conclusion, 5-HT is present in nerves of the SO and elicits both 5-HT3 and 5-HT1P receptor-mediated depolarizations, supporting the concept that 5-HT plays a role in SO regulation.

Identification of neurons that express stem cell factor in the mouse small intestine

BACKGROUND & AIMS

Enteric neurons in the murine intestine express stem cell factor (SCF), which may provide an important signal in the development of the interstitial cells of Cajal (ICC). Our aim was to identify the subpopulation(s) of myenteric neurons that express SCF.

METHODS

Myenteric plexus preparations from postnatal SCF-lacZ mice were processed for beta-galactosidase histochemistry followed by immunohistochemistry.

RESULTS

Approximately 60% of the nitric oxide synthase-immunoreactive neurons, which projected to myenteric ganglia and to circular muscle, expressed SCF, and more than 80% of the calbindin-immunoreactive neurons, which projected exclusively to myenteric ganglia, expressed SCF. A small subpopulation of calretinin-immunoreactive neurons expressed SCF transiently. Many of the remainder of SCF-expressing neurons were choline acetyltransferase immunoreactive, but their projections are unknown.

CONCLUSIONS

SCF-expressing neurons that project within the myenteric plexus may be an important source of SCF for the development of Kit-expressing ICC at this level. The only possible neuronal source of SCF for the ICC of the deep muscular plexus is a subpopulation of nitric oxide synthase-immunoreactive neurons.

The identification and chemical coding of cholinergic neurons in the small and large intestine of the mouse

BACKGROUND

The recent availability of antisera to the vesicular acetylcholine transporter (VAChT) and choline acetyltransferase (ChAT) that demonstrate peripheral cholinergic neurons has made possible the anatomical identification of cholinergic neurons in the enteric nervous system. In this study, we localised cholinergic neurons in the mouse small and large intestine and identified which substances are found colocalised in the cholinergic neurons.

METHODS

Immunohistochemical single and double staining techniques were used on whole mount preparations and frozen sections to examine the localisation and chemical coding of cholinergic neurons in the small and large intestine of the mouse. Cholinergic neurons were identified using antisera to ChAT or VAChT.

RESULTS

In both the small and large intestine, numerous ChAT-immunoreactive nerve cell bodies were present in the myenteric and submucous ganglia, and ChAT- and VAChT-immunoreactive nerve terminals were abundant in the myenteric and submucous plexuses and the external muscle. Previous studies have identified two major classes of myenteric neurons in the small intestine of the mouse--those containing calretinin plus substance P, and those containing nitric oxide synthase (NOS) plus vasoactive intestinal peptide (VIP). Double-label studies showed that the vast majority of the calretinin/substance P neurons were cholinergic neurons, whereas only a small proportion of the NOS/VIP cells were cholinergic; the noncholinergic NOS/VIP neurons were motor neurons or interneurons, whereas the cholinergic NOS/VIP neurons appeared to be exclusively interneurons. In the small intestine, all of the 5-HT-loaded neurons and a subpopulation of the calbindin neurons were also cholinergic. In the large intestine, there was a pattern of overlaps similar to that found in the small intestine, except that in the large intestine approximately 25% of the calretinin cells were not cholinergic. Only approximately one third of the GABA-loaded neurons in the large intestine were cholinergic.

CONCLUSIONS

Large subpopulations of motor neurons and interneurons in the mouse small intestine are cholinergic neurons.

Choledochosphincter inhibitory reflex: identification of the reflex in dogs and its significance

BACKGROUND

The sphincter of Oddi (SO) may undergo functional disorders. The mechanism of action of this sphincter is as yet not fully explored; the current study aims at studying some aspects of this mechanism.

METHODS

Twelve mongrel dogs (mean weight 15.3 +/- 2. 9 SD kg, 8 male, 4 female) were studied. Under general anesthesia, the abdomen was opened and the gall bladder, common bile duct (CBD), and duodenum were exposed. Through separate punctures in the CBD, a balloon-tipped 2F catheter was introduced into the CBD and a 2F manometric catheter was placed within the SO. The positioning of the catheters was controlled fluoroscopically. The pressure response of the CBD and SO to CBD balloon distension with CO2, without and with separate anesthetization of either the CBD or SO, was recorded.

RESULTS

Upon CBD distension by 0.5 ml of CO2, the pressure in the CBD rose (P < 0.001) and in the SO dropped (P < 0.01). The SO pressure drop was momentary and did not change significantly (P > 0. 05) with increase in the volume of CBD distension. The pressure response was blocked on separate anesthetization of the CBD and SO.

CONCLUSIONS

The SO opening on CBD distension is suggested to be reflex and not hydromechanical. It seems to be mediated through a reflex which we call "choledochosphincter inhibitory reflex." Derangement of this reflex might result in functional disorders of the SO.

The identification and chemical coding of cholinergic neurons in the small and large intestine of the mouse

BACKGROUND

The recent availability of antisera to the vesicular acetylcholine transporter (VAChT) and choline acetyltransferase (ChAT) that demonstrate peripheral cholinergic neurons has made possible the anatomical identification of cholinergic neurons in the enteric nervous system. In this study, we localised cholinergic neurons in the mouse small and large intestine and identified which substances are found colocalised in the cholinergic neurons.

METHODS

Immunohistochemical single and double staining techniques were used on whole mount preparations and frozen sections to examine the localisation and chemical coding of cholinergic neurons in the small and large intestine of the mouse. Cholinergic neurons were identified using antisera to ChAT or VAChT.

RESULTS

In both the small and large intestine, numerous ChAT-immunoreactive nerve cell bodies were present in the myenteric and submucous ganglia, and ChAT- and VAChT-immunoreactive nerve terminals were abundant in the myenteric and submucous plexuses and the external muscle. Previous studies have identified two major classes of myenteric neurons in the small intestine of the mouse--those containing calretinin plus substance P, and those containing nitric oxide synthase (NOS) plus vasoactive intestinal peptide (VIP). Double-label studies showed that the vast majority of the calretinin/substance P neurons were cholinergic neurons, whereas only a small proportion of the NOS/VIP cells were cholinergic; the noncholinergic NOS/VIP neurons were motor neurons or interneurons, whereas the cholinergic NOS/VIP neurons appeared to be exclusively interneurons. In the small intestine, all of the 5-HT-loaded neurons and a subpopulation of the calbindin neurons were also cholinergic. In the large intestine, there was a pattern of overlaps similar to that found in the small intestine, except that in the large intestine approximately 25% of the calretinin cells were not cholinergic. Only approximately one third of the GABA-loaded neurons in the large intestine were cholinergic.

CONCLUSIONS

Large subpopulations of motor neurons and interneurons in the mouse small intestine are cholinergic neurons.

Correlation of electrophysiology, neurochemistry and axonal projections of guinea-pig sphincter of Oddi neurones

Sphincter of Oddi (SO) ganglia are comprised of two main types of neurones based either on their electrical or neurochemical properties. This study investigated whether any correlation exists between the electrical and neurochemical properties of these cells. SO neurones were characterized electrically as either Tonic or Phasic cells, labelled with neurobiotin, fixed, and processed for beta-nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-DA) staining and choline acetyltransferase immuno-reactivity to identify whether electrically characterized neurones were nitrergic or cholinergic. A total of 119 cells were analysed in this manner; 45% of cells were Tonic and 37% were Phasic. An equivalent number of Tonic (58.1%, 18/31) and Phasic cells (60%, 21/35) were choline acetyltransferase (ChAT) positive. Three of 34 Phasic cells were NADPH-DA positive, whereas 11/33 Tonic cells were NADPH-DA positive. In none of the preparations was ChAT immunoreactivity and NADPH-DA reactivity ever observed in the same neurone. Calretinin immunoreactivity was present in a subpopulation of both Tonic and Phasic neurones. No correlation was observed between the direction of axon projections and the electrophysiological or neurochemical properties of the cell. These results suggest that there is a lack of correlation between the electrical properties and the neurochemical content of SO neurones. Various explanations for these findings are discussed.