[NERVOUS REGULATION OF BILIARY TRACT MOTILITY].

Aim: The study of mechanisms of regulation of biliary tract motility by divisions of autonomic nervous system (ANS). Material and methods: Experiments were carried out on rabbits, chinchillas weighing 3.5-4 kg using gentle methods of treatment of experimental animals. Electromotor activity of electromotor (EMA) of the gallbladder and sphincter of Oddi was recorded. Irritation of the nerve produces an electrical pulse duration of 2 ms, the amplitude of 1.5-15 V, frequency of 10 Hz. Results: The mechanism of vagal inhibition of sphincter of Oddi motility and unidirectional stimulatory influence of ANS divisions on the motility of the gallbladder and sphincter of Oddi was studied. It was established that in the mechanism of vagal inhibition of sphincter of Oddi motility involved intramural adrenergic neurons synaptically connected with preganglionic parasympathetic fibers. At the stimulatory effect of vagus on biliary tract motility serotonergic intramural neurons are involved transmitting excitation to serotonin receptors of effector tissue.

Innervation of Extrahepatic Biliary Tract, With Special Reference to the Direct Bidirectional Neural Connections of the Gall Bladder, Sphincter of Oddi and Duodenum in Suncus murinus, in Whole-Mount Immunohistochemical Study.

Sphincter of Oddi dysfunction is one of the most important symptoms in post-cholecystectomy syndrome. Using either electrical or mechanical stimulation and retrogradely transported neuronal dyes, it has been demonstrated that there are direct neural pathways connecting gall bladder and the sphincter of Oddi in the Australian opossum and the golden hamster. In the present study, we employed whole-mount immunohistochemistry staining to observe and verify that there are two different plexuses of the extrahepatic biliary tract in Suncus murinus. One, named Pathway One, showed a fine, irregular but dense network plexus that ran adhesively and resided on/in the extrahepatic biliary tract wall, and the plexus extended into the intrahepatic area. On the other hand, named Pathway Two, exhibiting simple, thicker and straight neural bundles, ran parallel to the surface of the extrahepatic biliary tract and passed between the gall bladder and duodenum, but did not give off any branches to the liver. Pathway Two was considered to involve direct bidirectional neural connections between the duodenum and the biliary tract system. For the first time, morphologically, we demonstrated direct neural connections between gall bladder and duodenum in S. murinus. Malfunction of the sphincter of Oddi may be caused by injury of the direct neural pathways between gall bladder and duodenum by cholecystectomy. From the viewpoint of preserving the function of the major duodenal papilla and common bile duct, we emphasize the importance of avoiding kocherization of the common bile duct so as to preserve the direct neural connections between gall bladder and sphincter of Oddi.

The distribution and chemical coding of neurons supplying the sphincter of Oddi in mammals.

The major duodenal papilla (papilla of Vater) is an important structure associated with the biliary tract and, in some species, the pancreas. It usually represents a slight elevation on the intestinal mucosa where the dilated junction (ampulla of Vater) of the commmon bile duct and pancreatic duct enters the duodenum. The ampulla is surrounded by a specifically arranged muscle structure called the sphincter of Oddi (SO) which controls the flow of bile and pancreatic fluid. The function of the sphincter is regulated by a complex system that involves many hormonal and neural factors. The literature in the field contains detailed data on the morphology of the SO in a number of mammalian species. However, the comprehensive information about the anatomy and neurochemistry of the innervation of this structure is very limited. The present review article summarizes the current knowledge on the innervation of the SO in mammals. Special emphasis has been put on the localization and chemical coding of neurons contributing to this nerve supply.

The role of nitric oxide in the electrical field stimulation-induced contractions of sphincter of oddi and gallbladder strips in Guinea pigs.

The aim of this study was to investigate the modulatory role of nitric oxide (NO) in the electrical field stimulation (EFS)-induced contractions of isolated sphincter of Oddi (SO) and gallbladder strips from guinea pigs. EFS was used to activate the intrinsic nerves in SO and gallbladder strips. EFS produced frequency-dependent biphasic contractile responses in the SO strips. A smaller contraction, "on response", occurred during EFS, which was followed by a bigger contraction, "off response". Both responses were completely and irreversibly abolished by tetrodotoxin (TTX) (10(-6) M). Atropine (10(-6) M) inhibited the "on response", but not the "off response". EFS produced frequency-dependent monophasic contractile responses in gallbladder strips, which were completely and irreversibly abolished by TTX (10(-6) M) and atropine (10(-6) M). A nitric oxide synthase (NOS) inhibitor, NG-nitro-L-arginine (10(-4) M and 3 x 10(-4) M, in SO and gallbladder strips, respectively), significantly increased all EFS-induced contractions of SO and gallbladder strips. L-Arginine, but not D-arginine reversed the effect induced by the NOS inhibitor, at all frequencies, in both strips. These results suggested that NO released from nitrergic nerve endings might play a regulatory role in the cholinergic neurotransmission of guinea pig SO and gallbladder strips. The "off response" in he SO preparations might be a rebound increase that was modulated by the nonadrenergic, noncholinergic inhibitory mediator NO.

Exogenous adenosine triphosphate and adenosine stimulate proximal sphincter of oddi motility via neural mechanisms in the anesthetized Australian possum.

We aimed to determine if exogenous adenosine triphosphate or adenosine modulated sphincter of Oddi motility and involved neural mechanisms. Sphincter of Oddi motility was recorded in anesthetized possums by manometry. Adenosine triphosphate or adenosine (1 microM-10 mM) was applied topically to the sphincter before and after pretreatment with tetrodotoxin, hexamethonium, atropine, or Nomega-nitro-L-arginine methyl ester. Sphincter contraction amplitude and frequency were quantified. Adenosine triphosphate induced a concentration-dependent increase in proximal sphincter contraction amplitude and frequency (P < 0.05). This response was reduced by tetrodotoxin and atropine but enhanced by hexamethonium and Nomega-nitro-L-arginine methyl ester. Adenosine concentration dependently increased proximal sphincter contraction amplitude (P < 0.05) only. This response was reduced by tetrodotoxin, atropine, and Nomega-nitro-L-arginine methyl ester, whereas hexamethonium had no effect. We conclude that exogenous adenosine triphosphate and adenosine stimulate proximal sphincter of Oddi motility via neural mechanisms, involving cholinergic motor neurons. Adenosine triphosphate may further modulate sphincter motility via nicotinic and nitrergic pathways.

Decreased distribution of nitric oxide synthase and vasoactive intestinal polypeptide positive nerve cells in the sphincter of Oddi in humans with pancreatobiliary diseases.

To better understand the relationship between innervation in the sphincter of Oddi and pancreatobiliary diseases, nerve cells which possess nitric oxide synthase (NOS) and/or vasoactive intestinal polypeptide (VIP) were studied immunohistochemically in the sphincter of Oddi and duodenum of humans. Specimens from autopsies included 11 cases with pancreatobiliary diseases and 7 cases without such diseases. An elaborate nerve network was revealed with an anti-S-100 antibody in the sphincter of Oddi and duodenum of all specimens. In the sphincter of Oddi of the control group, approximately 47% of the myenteric nerve cells were NOS positive, whereas 54% were VIP positive. Of the NOS positive nerve cells, 21% were also VIP positive. In contrast, 11% of the nerve cells in the sphincter of Oddi of the disease group were NOS positive while 32% were VIP positive. Within the duodenal myenteric plexus of the control group, 35% of all nerve cells were NOS positive while 40% was VIP positive; among them, 23% of the NOS positive cells were VIP positive. Similar results were observed in the duodenum of the disease group. These data indicate that abundant NOS and VIP positive innervation is present in the sphincter of Oddi and duodenum in humans. The lower proportion of NOS positive or VIP positive nerve cells of the disease group may suggest an inadequacy of the sphincter of Oddi to relax.

Mechanism of synergism between sympathetic and parasympathetic autonomic nervous systems in the regulation of motility of the stomach and sphincter of Oddi.

The mechanisms of stimulatory effect of the sympathetic trunk on gastric motor activity and vagal inhibitory effect on electromotor activity of the sphincter of Oddi were studied. Gastric contractions were augmented by preganglionic serotoninergic fibers related synaptically to serotoninergic neurons, while inhibition of electromotor activity of the sphincter of Oddi was elicited by activation of alpha- and beta-adrenoceptors.

Endothelins induce gallbladder contraction independent of elevated blood pressure in vivo in the Australian possum.

Endothelin levels are elevated in shock, sepsis, and cholestatic jaundice, and an effect on biliary motility may be postulated. The aim of this study was to determine whether (1) endothelin-1 and endothelin-3 induce gallbladder contraction in vivo, (2) the response is caused by changes in blood pressure, and (3) the response is nerve mediated. Gallbladder pressure and blood pressure were measured in 38 anesthetized possums. Endothelin-1 or endothelin-3 (5 to 200 pmol/kg) was administered by close intra-arterial injection. Tetrodotoxin (9 microg/kg) or the mixed endothelin antagonist tezosentan was infused at a rate of 10 or 100 nmol/kg/min (close intra-arterial injection). Maximum changes in gallbladder pressure (% of carbachol-induced contraction) and blood pressure (mm Hg) were determined. Statistical analysis was carried out by means of repeated-measures analysis of variance and Kruskal-Wallis test. Both endothelin-1 and endothelin-3 induced dose-dependent increases in gallbladder pressure and blood pressure (P < 0.05), which were unaffected by pretreatment with tetrodotoxin. The endothelin-1-induced gallbladder pressure but not blood pressure was reduced by the higher dose of tezosentan (P < 0.03). The lower dose of tezosentan also produced a decrease in the endothelin-3-induced gallbladder pressure (P < 0.02) but not in blood pressure, whereas the higher dose reduced the blood pressure with no further reduction in gallbladder pressure (P < 0.05). Endothelins increase gallbladder motility in vivo, acting directly on the smooth muscle and independent of changes in blood pressure.

Impairment by lovastatin of neural relaxation of the rabbit sphincter of Oddi.

We sought whether inhibition of cholesterol biosynthesis by lovastatin influenced the nitrergic relaxation response of the sphincter of Oddi. Rabbit sphincters of Oddi rings were tested for changes in isometric tension in response to field stimulation in the presence of 4 microM guanethidine and 1 microM atropine. Tissue samples were then analyzed for cAMP and cGMP content by radioimmunoassay for nitric oxide concentration by electron spin resonance and for vasoactive intestinal peptide and calcitonin gene-related peptide (CGRP) release by radioimmunoassay. Membrane G(salpha) protein was determined by Western blot analysis. Field stimulation relaxed the preparations with an increase in nitric oxide, cAMP and cGMP concentrations at increased calcitonin gene-related peptide and vasoactive intestinal polypeptide (VIP) release. Preparations from rabbits pre-treated with lovastatin (5 mg/kg/day intragastrically, over 5 days) contracted under the same conditions with an attenuated cGMP-increase at preserved increase in NO content and neuropeptide release. The relaxation was recaptured combining lovastatin with farnesol (1 mg/kg intravenously, twice a day for 5 days). The field stimulation-induced increase in cyclic nucleotides was also restored. Lovastatin decreased membrane G(salpha) protein content, which was re-normalized by farnesol. Farnesol treatment reinstates neurogenic relaxation of the sphincter of Oddi deteriorated by lovastatin possibly by normalizing G-protein coupling.

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.

Distribution and chemical coding of orphanin FQ/nociceptin-immunoreactive neurons in the myenteric plexus of guinea pig intestines and sphincter of Oddi.

Longitudinal muscle-myenteric plexus preparations of guinea pig intestines and sphincter of Oddi (SO) were immunostained for orphanin FQ/nociceptin. Orphanin FQ-immunoreactive (OFQ-IR) neurons and nerve fibers were relatively abundant in the SO, duodenum, ileum, cecum, and distal colon, with fewer neurons and nerve fibers observed in the proximal colon. Double staining with antibodies directed against the neuron-specific RNA binding protein Hu revealed that while the numbers of OFQ-IR neurons per ganglion decreased along the gut tube, similar proportions (7-9%) of neurons in these regions were OFQ-IR, whereas <1% of the neurons in the proximal colon were OFQ positive. In the ileum, where 8% of the myenteric neurons were OFQ-IR, all OFQ-IR neurons expressed choline acetyltransferase. In addition, multiple-label immunohistochemistry demonstrated that 58% of the OFQ-IR neurons were calretinin-IR, 52% were substance P-IR, and 28% were enkephalin-IR. Nitric oxide synthase immunoreactivity was observed in about 5% of OFQ-IR neurons, or 0.4% of the total population, and a similar proportion of the OFQ-IR neurons was positive for vasoactive intestinal peptide. No OFQ-IR neurons were immunoreactive for calbindin, somatostatin, or serotonin. These results, combined with previous studies of chemical coding and projection patterns in the guinea pig myenteric plexus, indicate that OFQ-IR is expressed preferentially in excitatory motor neurons projecting to the longitudinal and circular muscle layers, as well as a small subgroup of descending interneurons. Because OFQ is expressed by excitatory motor neurons, and because this peptide inhibits excitatory neurotransmission in the guinea pig ileum, it is likely that OFQ acts through a feedback autoinhibitory mechanism.

Histamine in the control of porcine and human sphincter of Oddi activity.

Histamine decreases sphincter of Oddi (SO) contractility in vivo in opossum, but increases contractility in vitro in guinea-pig. In resistor-like SO, such as in pig and man, the histamine effect is poorly known. We investigated the effect of histamine on pig SO in vivo and in vitro and on human SO in vitro. Perfusion manometry catheter and two silver electrodes for simultaneous pressure and electromyography registration were inserted into the SO transduodenally by laparotomy in six anaesthetized pigs weighing for 25-28 kg. Histamine (5-10 microgram kg-1) was infused intra-arterially (i.a.) into the pancreaticoduodenal artery with and without diphenhydramine (75 microgram kg-1) i.a. premedication. Acetylcholine (4 microgram kg-1) i.a., a potent SO stimulator, was used as positive control. After these experiments, the SO was removed and, together with seven human SO from Whipple specimens, were cut into 1.0-1.5 mm thick transverse sections (rings). The rings were placed between two hooks in oxygenated organ bath solution at 37 degrees C. The SO contraction force was measured with isometric force-displacement transducers and registered on a polygraph. SO rings were incubated with histamine (10-100 micromol L-1) and acetylcholine (100 micromol L-1) with or without diphenhydramine (10 micromol L-1), cimetidine (10 micromol L-1), or atropine (1 micromol L-1). Acetylcholine induced huge electrical bursts, and basal SO pressure increased by 20 +/- 10 mmHg. Histamine (10 microgram kg-1) induced strong SO contraction and the SO remained oedematous for over 10 min. Histamine (5 microgram kg-1) resulted in electromyographic burst activity with phasic SO contractions and increase in basal SO pressure by 34 +/- 19 mmHg for over 15 min. Diphenhydramine did not alter acetylcholine-induced SO motility, but significantly decreased histamine-induced contractions and almost abolished electrical activity. In vitro, acetylcholine induced SO contractions in pig (335 +/- 111 mg) and in man (323 +/- 54 mg). Histamine did not change SO tone in man, but in pig it induced dose-dependent contractions in the same way as acetylcholine. These contractions could be inhibited by diphenhydramine, but not by cimetidine or atropine. We conclude that histamine has a stimulatory effect, mediated by H1-receptor, on the pig SO motility. The SO response to histamine is different in adult humans from that observed in young pigs.

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.

Proximal and distal segments of the possum sphincter of Oddi respond differently to neural and cholecystokinin octapeptide stimulation in vitro.

BACKGROUND/AIMS: Previous studies have demonstrated separate pancreatic duct (PD) and bile duct (BD) components of the sphincter of Oddi (SO) and suggested distinct proximal and distal functional segments. This study was designed to determine if proximal and distal segments of the BD component of the SO (BD-SO) and PD component of the SO (PD-SO) responded equally to (1) activation of SO-duodenal neural pathways, and (2) exogenous cholecystokinin octapeptide (CCK-8). METHODS: Intact SO-duodenum preparations from Australian brush-tailed possums (n = 6) were mounted in organ baths. SO activity was recorded from the proximal and distal segments of BD-SO and PD-SO +/- electrical activation of duodenal nerves at two separate sites. Full thickness muscle strips from the proximal and distal segments of the BD-SO and PD-SO were prepared (n = 8), mounted in organ baths, and exposed to CCK-8 (10(-9)- 10(-6) M), +/- tetrodotoxin. RESULTS: Activation of duodenal nerves evoked different responses in some segments of the BD-SO and PD-SO, depending on the site of duodenal electrical stimulation. CCK-8 induced a concentration-dependent, tetrodotoxin-insensitive decrease in the contraction amplitude of SO muscle strips from the proximal but not the distal SO. BD-SO and PD-SO strips were not different. CONCLUSIONS: The SO is composed of BD and PD components each of which contains proximal and distal segments that can respond independently to appropriate stimuli.

Neurological damage and duodenopancreatic reflux in the pathogenesis of alcoholic pancreatitis.

OBJECTIVE: To present a new theory on the pathogenesis of acute alcoholic pancreatitis based on experimental data, the significance of which has not been recognized, and on evidence from the current literature. HYPOTHESIS: That chronic alcoholism damages muscarinic receptors in the pancreas, duodenum, and Oddi sphincter, producing heightened sensitivity to acetylcholine, stimulation of protein-rich pancreatic juice, hypertonicity of the duodenum and esophagus, relaxation of the Oddi sphincter, and intraduodenal pressures exceeding those shown to cause duodenopancreatic reflux and acute pancreatitis in humans and experimental animals. OUTCOME: The duodenopancreatic reflux mechanism can explain all of the clinical features of acute alcohol pancreatitis, including the intraductal site and rapid activation of zymogens by enterokinase, the recurrent episodes of pancreatitis, the precipitation of protein plugs by partial proteolytic hydrolysis, the severe vascular changes, the relation to infection by the most direct route, and the progression to chronic pancreatitis via the necrosis-fibrosis sequence. CONCLUSIONS: Damage to the nervous system, with a time lag of 5 to 15 years between the onset of heavy drinking and the development of neurological disorders (peripheral neuropathy and cerebellar degeneration), is a characteristic complication of chronic alcoholism. The similarity to events in alcoholic pancreatitis is striking.

Functional innervation of the biliary sphincter of the guinea-pig revealed by anti-autonomic drugs.

1. The roles of excitatory and inhibitory intrinsic motor nerves on contractions reflexly evoked by wall distension were investigated in the isolated sphincter of Oddi of the guinea-pig (SO-GP). 2. Distension of the terminal bile duct for 30-60 s time periods increased the frequency of contractions from about 2 to 12 min(-1) (n = 16). 3. Hexamethonium (HEX; 300 microM) largely prevented the distension-evoked increase in contraction frequency (4.5 min(-1), n = 8) as did atropine (ATR; 1 microM) (0.8 min(-1), n = 6), while tetrodotoxin (TTX; 1 microM) blocked the contractions triggered during distension. 4. L-nitroarginine (L-NA; 100 microM) significantly increased the frequency of contractions during and in the absence distension while apamin (APAM; 0.5 microM) significantly increased their frequency and doubled their mean amplitude during distension. 5. These results suggest that distension activates excitatory cholinergic motor nerves to increase the frequency of contractions in the SO-GP. These actions are modulated by the concomitant activation of intrinsic nitrergic and non-nitrergic inhibitory motor nerves.

Somatic electrical nerve stimulation regulates the motility of sphincter of Oddi in rabbits and cats: evidence for a somatovisceral reflex mediated by cholecystokinin.

Cholecystokinin (CCK) plays an important role in regulating the biliary motility in herbivorous and carnivorous animals. Little is known about how the motility of the sphincter of Oddi (SO) is regulated through a somatic stimulation. It was our aim to test the hypothesis that somatic electrical nerve stimulation (SENS) affects SO motility in animals with different types of SO through CCK-related mechanisms. The activity of SO in anesthetized rabbits and cats was measured by using a continuously perfused open-tip manometric method. SENS was brought about by applying an electric current (2/15 Hz alternatively, 20 min) to two needles positioned near spinal nerves in the 6th and 7th intercostal space in the right midclavicular line. The SO motility before and X min after the start of SENS, designated as pre-SENS and SENS-X respectively, were recorded and saved in a computer equipped with off-line analysis software. The SO activity in rabbits, in terms of phasic contraction pressure and duration of summation peak during SENS were significantly higher than that before SENS. The phasic contraction pressure of pre-SENS, SENS-10, and SENS-16 were 6.83 +/- 0.39 mm Hg, 9.23 +/- 0.83 mm Hg and 10.46 +/- 0.81 mm Hg, respectively (P < 0.03, N = 13). The duration of summation peak in pre-SENS, SENS-10, and SENS-16 were 7.26 +/- 0.41 sec, 10.22 +/- 0.46 sec, and 13.49 +/- 2.31 sec, respectively (P < 0.05, N = 13). The SENS-induced SO hyperactivity was not inhibited by pretreatment with atropine, propranolol, phentolamine, or naloxone, but was blocked by pretreatment with the CCK receptor antagonist, proglumide, and by injection of anti-CCK-8 antibody during SENS in a dose-dependent manner. In contrast, SENS induced an inhibitory SO response in cats. However, in both circumstances, an obvious elevation of plasma CCK level determined by radioimmunoassay was noted after SENS. We conclude that SENS causes secretion of CCK, which in turn affects biliary tract motility in animals with different types of SO. This provides an easily applicable method for those patients who have hyperactive SO function.

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.