Functional studies on blockade by neosurugatoxin of nicotinic receptors in nitroxidergic and sensory nerve terminals and intramural ganglionic cells

In isolated canine cerebral and cutaneous arteries and duodenum, effects of neosurugatoxin (NSTX) on the response to nicotine were compared. Nicotine-induced relaxations are mediated by nitric oxide (NO) from vasodilator nerves in cerebral arteries and by calcitonin gene-related peptide (CGRP) in cutaneous arteries treated with NO synthase inhibitors. Duodenal relaxation to nicotine is mediated by NO from inhibitory nerves. Cerebral arterial strips without endothelium responded to nicotine with relaxations that were inhibited by NSTX (3 x 10(-10) to 3 x 10(-9) M) concentration-dependently. Relaxations to nicotine of duodenal strips were attenuated by NSTX and abolished by tetrodotoxin, whereas those induced by K+ and electrical stimulation were not influenced. In cutaneous arteries treated with N(G)-nitro-L-arginine, nicotine-induced relaxations were attenuated by NSTX as low as 10(-10) M, but unaffected by tetrodotoxin. The inhibitory potency of NSTX was in the order of cutaneous artery > duodenum > cerebral artery. It is concluded that NSTX selectively antagonizes actions on nicotinic receptors in nitroxidergic nerves of cerebral arteries, CGRP-mediated sensory nerves of cutaneous artery and ganglionic cells of the duodenum, but the affinity of this toxin to nicotinic receptors in sensory nerves is the highest.

Glial fibrillary acidic protein (GFAP) immunoreactivity in enteric ganglia of the chick embryo

We examined by immunohistochemistry the expression of glial fibrillary acidic protein (GFAP) in enteric ganglia of the chick embryo, using a polyclonal antibody. The morphology of enteric ganglion cells was examined by electron microscopy. Faint GFAP immunoreactivity was detected in ganglion cells and cell processes from around day 7 in ovo. Later in development the intensity of the immunofluorescence increased and it became more evident that immunoreactive small ganglion cells (interpreted as primitive glial cells), and their processes, surrounded larger negative cell profiles (interpreted as primitive neuronal cells); GFAP immunofluorescence was also evident in intramuscular and mucosal nerve trunks. In colocalization experiments, GFAP immunoreactivity was detected in a proportion of HNK-1/N-CAM immunoreactive ganglion cells, in both the myenteric and submucosal plexus. In addition, we observed GFAP immunoreactive nerves in wholemount preparations of chick gut from as early as day 4.5 in ovo. In the ganglionated nerve of Remak, GFAP immunoreactive satellite and Schwann cells were in evidence from day 5 of incubation. Neuronal markers, such as neurofilament, have been detected very early in development in neural crest cell populations in chick enteric ganglia. In contrast, the expression of markers of the glial phenotype has previously been observed only in the late stages of embryonic development. From our experiments, we conclude that neuronal and glial phenotypes are immunohistochemically distinct from as early as day 4.5 of incubation, even if by ultrastructural criteria glial cells are clearly distinguishable from neurons only after day 16 in ovo.

Activation of neurokinin 1 receptors on interstitial cells of Cajal of the guinea-pig small intestine by substance P

The aims of this work were to determine whether cells that are similar to the interstitial cells of Cajal (ICC) and have immunoreactivity for the neurokinin 1 (NK1) receptor are indeed ICC; to determine whether the agonist, substance P, binds to and activates the receptor on presumptive ICC; and to investigate the relationship between substance P-immunoreactive nerve fibres and ICC. ICC at the level of the myenteric plexus and in the deep muscular plexus in the duodenum and ileum of the guinea-pig were investigated. Immunoreactivities for the ICC marker, Kit, and the NK1 receptor were colocalised in ICC of the myenteric and deep muscular plexuses. In tissue fixed immediately after its removal from the animal, NK1 receptor-immunoreactive ICC were found at the level of the myenteric plexus in the duodenum, but not in the ileum, and in the deep muscular plexus in the duodenum and ileum. The majority of receptor immunoreactivity was on the cell surface. ICC were exposed to substance P (10(-7) M), initially at 4 degrees C for 1 h to allow the agonist to bind, followed by incubation at 37 degrees C to allow receptor internalisation to proceed. Exposure to substance P caused the NK1 receptor immunoreactivity to aggregate in clumps in the cytoplasm of ICC of the myenteric and deep muscular plexuses, including the ICC of the myenteric plexus of the ileum, where NK1 receptor immunoreactivity was not seen if tissue was not exposed to substance P. Substance P, to which the fluorescent label, cyanine 3.18 (Cy-3), was coupled, bound to the ICC. The Cy-3-substance P was internalised with the receptor following warming to 37 degrees C. Many, but not all, ICC were closely apposed by nerve fibres with immunoreactivity for substance P. It is concluded that the NK1 receptor immunoreactivity on ICC represents receptor that is functional in the sense that it binds the natural agonist substance P and undergoes agonist-induced internalisation. ICC are likely to receive excitatory innervation from the close approaches of tachykinin-containing nerve fibres.

Morphological and immunohistochemical identification of neurons and their targets in the guinea-pig duodenum

Nerve circuits within the proximal duodenum were investigated using a combination of immunohistochemistry for individual neuron markers and lesion of intrinsic nerve pathways to determine axon projections. Cell shapes and axonal projections were also studied in cells that had been injected with a marker substance. Several major neuron populations were identified. Calbindin immunoreactivity occurred in a population of myenteric nerve cells with Dogiel type II morphology. These had axons that projected to other myenteric ganglia, to the circular muscle and to the mucosa. All were immunoreactive for the synthesizing enzyme for acetylcholine, choline acetyltransferase, and some were also immunoreactive for calretinin. Myenteric neurons with nitric oxide synthase immunoreactivity projected anally to the circular muscle. These were also immunoreactive for vasoactive intestinal peptide, and proportions of them had enkephalin and/or neuropeptide Y immunoreactivity. It is suggested that they are inhibitory motor neurons to the circular muscle. A very few (about 2%) of nitric oxide synthase-immunoreactive neurons had choline acetyltransferase immunoreactivity. Tachykinin (substance P)-immunoreactive nerve cells were numerous in the myenteric plexus. Some of these projected orally to the circular muscle and are concluded to be excitatory motor neurons. Others projected to the tertiary plexus which innervates the longitudinal muscle and others provided terminals in the myenteric plexus. Two groups of descending interneurons were identified, one with somatostatin immunoreactivity and one with vasoactive intestinal peptide immunoreactivity. The two most common nerve cells in submucous ganglia were neuropeptide Y- and vasoactive intestinal peptide-immunoreactive nerve cells. Both provided innervation of the mucosa. There was also a population of calretinin-immunoreactive submucous neurons that innervated the mucosal glands, but not the villi. Comparison with the ileum reveals similarities in the chemistries and projections of neurons. Differences include the almost complete absence of nitric oxide synthase immunoreactivity from vasoactive intestinal peptide-immunoreactive interneurons in the duodenum, the projection of calbindin-immunoreactive Dogiel type II neurons to the circular muscle and the absence of tachykinin-immunoreactivity from these neurons.

Localization of the neurokinin 1 (NK-1) receptor in the human antrum and duodenum

A newly available antibody to the neurokinin-1 receptor (NK-1r) has made it possible to determine the distribution of the NK-1r receptor in human tissue. In the present study the distribution of the NK-1r and substance P have been determined in the human antrum and duodenum by immunocytochemistry. The NK-1r was present on myenteric and submucosal neurons and nerve fibers of the gastro-enteric nervous system. In addition, the receptor was present on spindle-shaped cells in the circular muscle layer, endothelial cells and a population of mucosal cells. In the submucosal plexus NK-1r immunoreactive neurons were surrounded by substance P containing fibers. These results indicate an extensive cellular expression of the NK-1r in the human antrum and duodenum.

Role of extrinsic innervation in release of motilin and patterns of upper gut canine motility

The need for extrinsic neural input to the upper gut in regulation/control of cyclic interdigestive motility and release of motilin remains a topic of controversy. Our aim was to determine whether extrinsic denervation of the upper gut disrupts cyclic release of motilin in relation to the migrating motor complex. Ten dogs underwent transection of all extrinsic innervation and enteric neural input to the stomach, small intestine, colon, pancreas, and liver while enteric neural continuity within this multivisceral complex was maintained. A cyclic pattern of motility occurred during fasting in all dogs in the small bowel (period = 100 +/- 3 min, mean +/- standard error of the mean) and in 8 of 10 dogs in the stomach (period = 98 +/- 4 min). Gastric cycles were temporally coordinated with small bowel cycles. Plasma motilin concentrations cycled temporally with the motility pattern with the greatest concentrations occurring during gastroduodenal phase III-like activity. Exogenous motilin induced a burst of gastric contractions and a premature migrating motor complex in all dogs. Oral meals disrupted cyclic motility and cyclic changes in plasma motilin. Extrinsic innervation to the upper gut is not necessary for cyclic motor activity, for coordinated cyclic release of motilin, or to initiate a premature migrating motor complex-like response to motilin. Central nervous system input (afferent, efferent) is not necessary for cyclic interdigestive activity or cyclic release of motilin.

Interaction between neurokinin A, VIP, prostanoids, and enteric nerves in regulation of duodenal function

Neurokinin A (NKA) induces duodenal motility and increases mucosal permeability and bicarbonate secretion in the in situ perfused duodenum in anesthetized rats. In the present study, the NKA-induced increase in mucosal permeability was potentiated by luminal perfusion with lidocaine and diminished by vasoactive intestinal peptide (VIP) but unaltered by elevated intraluminal pressure. Elevation of intraluminal pressure, however, potentiated the stimulatory effect of NKA on bicarbonate secretion. In contrast, the tachykinin decreased the rate of alkalinization in rats subjected to elevated intraluminal pressure and treated with indomethacin. Similarly, NKA partially inhibited the VIP-stimulated bicarbonate secretion. Luminal lidocaine did not affect the secretory response to NKA. The motility induced by NKA was unaffected by VIP or lidocaine but decreased by elevated intraluminal pressure. It is concluded that the NKA-induced increase in duodenal mucosal bicarbonate secretion is independent of neurons and possibly mediated by prostanoids. The increase in mucosal permeability in response to NKA may be suppressed by mucosal nerves, perhaps utilizing VIP as one of the transmitters.

Mucosal mast cells are involved in CCK disruption of MMC in the rat intestine

Our aim was to determine if mucosal mast cells could be activated by endogenous CCK and, as a consequence, mediate CCK actions in the small intestine. Rats were prepared for electromyography to record electrical activity in the small intestine. In another group of animals, the duodenum was perfused to measure rat mast cell protease II (RMCP II) as indicative of mast cell degranulation. Endogenous CCK release was induced by administration of soybean trypsin inhibitor (SBTI) in conscious rats or by intraduodenal perfusion of ovalbumin hydrolysate (OVH) in anesthetized rats. CCK concentration was measured by bioassay on pancreatic acini. SBTI in control rats disrupted migrating motor complexes (MMC) for >40 min. In rats treated with the mast cell stabilizer ketotifen, SBTI did not induce any change in the MMC pattern. RMCP II concentration in the duodenal perfusate significantly increased after OVH. Perfusate from ketotifen-treated animals did not show any significant increase in RMCP II values during OVH perfusion, although CCK plasma concentration was not different from the control group. Furthermore, infusion of the CCK-B receptor antagonist L-365,260 significantly blocked the increase of RMCP II concentration after OVH. Our results indicate that mucosal mast cells are degranulated by endogenous CCK release through stimulation of CCK-B receptors. Therefore mucosal mast cells participate in CCK intestinal actions.

Distributional pattern and targets of GABA-containing neurons in the porcine small and large intestine

In the rat and guinea-pig enteric nervous system, gamma-aminobutyric acid (GABA) has been shown to act as a neurotransmitter in interneurons innervating both excitatory and inhibitory motor neurons, thus modulating peristalsis and acid secretion. The present study reports on the distribution of GABA-containing neurons in the porcine intestine by the use of immunocytochemistry. Duodenal, jejunal, ileal and distal colonic segments were exposed in vitro to exogenous GABA (10(-8) M) prior to fixation and immunocytochemical staining to supplement endogenous stores of GABA. In contrast to the guinea-pig intestine, where GABA-immunoreactive (IR) nerve cell bodies were common in myenteric ganglia but very rare in the submucosa, in the pig intestine the nerve cell bodies expressing GABA-immunoreactivity were found predominantly in the ganglia and nerve strands of the inner submucous plexus, while a small number were also found in the myenteric plexus. Most of the neurons were small-sized and had a multidendritic uniaxonal appearance. Their varicose axonal processes protruded within the same ganglion to other nerve cells, including GABA-IR ones, or ran into connecting nerve strands towards neighbouring ganglia. Some of the bigger GABA-IR neurons in the myenteric plexus, however, displayed either a lamellar multidendritic uniaxonal or a bipolar appearance. The density of GABA-IR neurons in the inner submucous plexus varied from duodenum to colon, being highest in ileum and lowest in duodenum. Double-immunolabelling of GABA with substance P revealed that approximately 40% of the GABA-IR neurons in the inner submucous plexus of the ileum also stained for substance P. Our results suggest that in the porcine enteric nervous system, GABA-containing neurons are primarily involved in the modulation of secretory processes rather than in the modulation of peristalsis.

The deep muscular plexus of the pig duodenum: a histochemical and ultrastructural study with special reference to the interstitial cells

The aim of the present study was to describe the deep muscular plexus of the pig duodenum and to characterize its cellular components. Numerous nerve varicosities have been detected in the deep muscular plexus using anti-synaptophysin antibodies. Nerve fibres were also detected here in the outer circular muscle layer, whereas no nerve fibres were observed in the inner circular muscle layer. In the deep muscular plexus, nerve fibres projected to interstitial cells which were characterized at the ultrastructural level. The interstitial cells were of two kinds: the interstitial fibroblastic-like cells (FLC) and the interstitial dense cells (IDC), both of which were interposed between nerve fibres and smooth muscle cells. The FLC were characterized by their elongated bipolar shape, the lack of basal lamina, a well-developed endoplasmic reticulum, a Golgi apparatus, and intermediate filaments. They were closely apposed to axon terminals containing small clear synaptic vesicles and/or dense-cored vesicles. They were frequently connected to each other and to smooth muscle cells of the inner and outer circular layer by desmosomes and more rarely by gap junctions. The IDC are myoid-like cells. They had a stellate appearance and were characterized by a dense cell body, numerous caveolae, and a discontinuous basal lamina. The IDC were always closely apposed to nerve fibres and were connected to smooth muscle cells by desmosomes and small gap junctions. The present results show the unique pattern of cellular organization of the deep muscular plexus of the pig small intestine. They suggest that the interstitial cells in the deep muscular plexus are involved in the integration and transmission of nervous inputs from myenteric neurons to the inner and outer circular muscle layers. The clear-cut distinction observed here between the two types of interstitial cells (fibroblastic and myoid-like) suggests that the interstitial cells of each type may also be involved in some other specific activity, which still remains to be determined.

Inhibitory NANC neurotransmission in choledocho-duodenal junction of rabbits--a possible role of PACAP

The pharmacological properties of non-adrenergic non-cholinergic (NANC) inhibitory neurotransmission were investigated in the rabbit choledocho-duodenal junction (CDJ), using the microelectrode and tension recording methods. L-NAME (10(-4) M) and apamin (5 X 10 (-6) M) suppressed NANC relaxation evoked by electrical field stimulation (EFS) in the presence of atropine and guanethidine (each 10(-6) M) to a similar extent (to about 40% of the initial control). However, combined application of L-NAME (10(-4) M) and apamin (5 X 10(-6) M) did not abolish it. EFS also evoked biphasic inhibitory junction potentials (IJPs) consisting of initial fast and slow sustained components in the presence of atropine and guanethidine (each 10(-6) M). Apamin (5 X 10(-8)-5 X 10(-6) M) dose-dependently suppressed the initial fast component by about 70%. In contrast, L-NAME (10(-4) M) did not affect either the amplitude of IJP or the resting membrane potential. PACAP-38 (> 10(-8) M) dose-dependently hyperpolarized the smooth muscle membrane of rabbit CDJ followed by a slow repolarization to the original level. After pretreatment with apamin (5 X 10(-7) M), PACAP-38 (10(-6) M) failed to evoke membrane hyperpolarization. During repolarization in the continued presence of PACAP-38, the amplitude of initial fast component of IJP was reduced to about 40-60% of control value, while that of the slow one was unaffected. A similar suppression of initial fast component of IJP (about 40% of the control value) also occurred after application of PACAP (6-38), a PACAP antagonist, or prolonged treatment with monoclonal antibodies to PACAP-27 or PACAP-38. Furthermore, the substantial part of residual fast IJP in the presence of PACAP (6-38) was suppressed by desensitization to alpha,beta-methylene ATP (10(-3) M). These results indicate that in rabbit CDJ NANC relaxation consists mainly of apamin- and L-NAME-sensitive components, which occur in a membrane potential dependent (through membrane hyperpolarization) and independent fashion, respectively. It has further been suggested that PACAP, together with a smaller contribution of ATP, may be involved as the principal apamin-sensitive transmitter in NANC relaxation of this muscle.

Specific localization of gap junction protein, connexin45, in the deep muscular plexus of dog and rat small intestine

Cellular networks of pacemaker activity in intestinal movements are still a matter of debate. Because gap-junctional intercellular communication in the intestinal wall may provide important clues for understanding regulatory mechanisms of intestinal movements, we have attempted to clarify the distribution patterns of three types of gap junction proteins. Using antibodies for connexin40, connexin43, connexin45, smooth muscle actin, and vimentin, immunocytochemical observations were made with the confocal laser scanning microscope on cryosections of fresh-frozen small intestine and colon of the dog and rat. Connexin 45 was localized along the deep muscular plexus of the small intestine in both dog and rat. Double labeling studies revealed that connexin45 overlapped with vimentin -, but not actin-positive areas, indicating the fibroblast-like nature of the cells, rather than their being smooth muscle-like. Connexin43 immunoreactivity appeared along the smooth muscle cell surface in the outer circular layer of the small intestine of both animals. Connexin 40 immunoreactivity was not observed in the muscle layer other than in the wall of large blood vessels. It is suggested that connexin45-expressing cells along the deep muscular plexus of dog and rat small intestine are likely to act as a constituent of a pacemaker system, which may include a conductive system, by forming a cellular network operating via specific types of gap junctions.

Serum cholinesterase activity in children with gastroduodenitis or peptic ulcer disease

Serum cholinesterase /ChE/ investigation in children with gastroduodenitis or peptic ulcer disease indicate its low activity, specially in children with peptic ulcer disease. These investigation can be index of parasympathetic tonus in digestive tract disease.

Duodenal nutrient exposure elicits nutrient-specific gut motility and vagal afferent signals in rat

Volume and chemical characteristics of meals in the gut have been proposed to generate vagal afferent signals that mediate the negative feedback control of ingestion and gastric emptying. Furthermore, duodenal nutrients elicit changes in gastrointestinal motility that may stimulate mechanosensitive vagal afferents. The degree to which the activity of an individual vagal afferent fiber can be modified by moth mechanical and nutrient properties in the gut remains unclear. The present studies evaluated the relationships between distal antral and proximal duodenal load-sensitive vagal afferent activity and gastroduodenal motility in response to duodenal nutrient exposure in ketamine-xylazine-anesthetized rats. Duodenal carbohydrate (glucose) and amino acid (peptone) infusions (0.2 ml/min, 0.2-0.5 kcal/ml) stimulated concentration-dependent increases in 1) antroduodenal contractions and 2) antral and duodenal vagal afferent activity beyond those attributable to osmolarity alone. In addition, duodenal peptone was more effective than equicaloric glucose in eliciting this vagal activity. These data demonstrate that the proximal duodenum can discriminate its nutrient chemical contents and that gastroduodenal load-sensitive vagal afferents indirectly transduce nutrient chemical information.

Modulation of electrically evoked responses in rat duodenum by activation of nicotinic cholinoceptors

1. The effect of activation of nicotinic cholinoceptors in rat duodenal segments following electrical field stimulation (EFS) was investigated. 2. Electrical field stimulation elicited a two-component response: transient relaxation followed by contraction. The EFS-evoked response was tetrodotoxin (TTX; 1 mumol/L) sensitive. The relaxation component was NG-nitro-L-arginine (L-NNA; 100 mumol/L) sensitive, while the contractile response was atropine (1 mumol/L) sensitive. 3. 1,1-Dimethyl-4-phenyl-piperazinium iodide (DMPP; 20 mumol/L) induced relaxation of spontaneously active preparations that was L-NNA sensitive. L-Arginine (1 mmol/L) reversed the effects of L-NNA on DMPP-induced relaxation. 4. When EFS was applied, DMPP increased the amplitude of the relaxation component of the response and reduced the contractile component. 5. In the presence of L-NNA, the effect of DMPP on the relaxation component of the response to EFS was reduced, but the contractile response was not affected. L-Arginine partly reduced this effect of L-NNA. 6. Neither propranolol (1 mumol/L) nor yohimbine (1 mumol/L) had any effect on the actions of DMPP on EFS-evoked responses, but prazosin (1 mumol/L) strongly reduced the effect of DMPP on the contractile component of the response to EFS and slightly reduced the effect of DMPP on the relaxation response. 7. Histochemical studies demonstrated that, in the myenteric plexus of the rat duodenum, there are many reduced nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d)-positive neurons and that their number decreased after treatment with L-NNA. In the presence of L-arginine and L-NNA, the number of NADPH-d-positive neurons was similar to that found in control samples. 8. The data suggest that activation of nicotinic cholinoceptors modulates EFS-evoked responses in the rat duodenum as a result of the potentiation of nitrergic and adrenergic neurotransmission.

Postsynaptic enhancement by motilin of muscarinic receptor cation currents in duodenal smooth muscle

We have investigated a potential role of motilin in amplifying the postsynaptic muscarinic responses in the rabbit duodenal smooth muscle cells, using the whole cell variant of patch-clamp technique. Stimulation of motilin receptors by exogenously applied motilin (1 nM) resulted in a large increase in carbachol (CCh)-induced atropine-sensitive cation current (ICCh) at threshold concentrations of CCh (0.3-1 microM) at 30 degrees C. This potentiation was abolished in the presence of a specific blocker of motilin receptor (GM109) and was attenuated with increased concentrations of either motilin or CCh, being virtually absent with maximally effective concentrations of these agonists. Motilin failed to potentiate ICCh when the ambient temperature was reduced to 20 degrees C or if the cation current had been directly activated by internal perfusion with guanosine 5'-O-(3-thiotriphosphate) (50 microM) bypassing the muscarinic receptor. These results suggest that some biochemical processes, such as enzymatic reactions, might be involved in the motilin-induced potentiation and that its site of action might be the muscarinic receptor and/or associated G proteins.

Correlation of electrophysiological and morphological characteristics of myenteric neurons of the duodenum in the guinea-pig

Intracellular recording, dye filling and immunohistochemistry were used to investigate neurons of the proximal duodenum of the guinea-pig. Recordings were made from neurons of the myenteric plexus in the presence of nicardipine to quell muscle contractions, using microelectrodes that contained the marker substance Neurobiotin. Preparations were subsequently processed histochemically to reveal nerve cell shapes and immunoreactivity for calbindin, calretinin or nitric oxide synthase. Neurons were distinguished by their shapes and axonal projections as Dogiel type II, Dogiel type I, filamentous descending interneurons and small filamentous neurons. Dogiel type II cells had large cell bodies and multiple axon processes. They each had a broad action potential (mean half-width, 2.9 ms) and a prominent inflection (hump) on the falling phase of the action potential. The majority (70%) of Dogiel type II cells were AH neurons, defined by their having a prolonged hyperpolarizing potential that followed a soma action potential and lasted more than 2 s. Fast excitatory postsynaptic potentials were not recorded from Dogiel type II neurons. Two thirds of Dogiel type II neurons fired phasically in response to intracellularly injected 500 ms depolarizing current pulses and one-third fired tonically. Calbindin immunoreactivity occurred in 70% of Dogiel type II neurons. Dogiel type I neurons had lamellar dendrites and a single axon. They had brief action potentials (mean half-width, 1.7 ms) with no, or a slight hump. They responded to fibre tract stimulation with fast excitatory postsynaptic potentials. Only 2/21 exhibited a prolonged hyperpolarization following action potentials. The majority of Dogiel type I neurons thus belong to the S neuron category. Nine Dogiel type I neurons fired phasically in response to 500 ms depolarizing current pulses, while 12 fired tonically. Filamentous descending interneurons had long, branching filamentous dendrites and a single anally-projecting axon which gave rise to varicose branches in myenteric ganglia. Action potential characteristics of filamentous interneurons ranged between those of Dogiel type II and type I neurons. Small neurons. Small neurons with short filamentous, or few simple dendrites were also characterized. They had single axons, which could be traced either locally to the circular muscle, or to the longitudinal muscle. None of 12 filamentous interneurons or of 10 small filamentous neurons exhibited a prolonged post-spike hyperpolarization, whereas fast excitatory postsynaptic potentials were recorded from a majority. It is concluded that the morphological types of neuron that are encountered in the ileum also occur in the duodenum, but the electrophysiological characteristics of the neurons are more variable for each morphological class. Thus, it is not always possible to predict the morphology of myenteric neurons in the duodenum from their electrophysiological properties. Part of the electrophysiological variability appears to be due to duodenal neurons being more excitable than ileal neurons.

Nervous control of alkaline secretion in the duodenum as studied by the use of cholera toxin in the anaesthetized rat

There is experimental evidence for an axon reflex control of alkaline secretion in the rat duodenum. We have investigated if there is also an intramural reflex control of alkaline secretion similar to that demonstrated with regard to the control of the fluid transport in the rat jejunum. Alkaline secretion in the duodenum of an anesthetized rat was continuously monitored using an in situ titration technique. The segment was extrinsically denervated. Exposing the duodenal segment to 80 microg cholera toxin markedly increased alkaline secretion. This response was abolished by hexamethonium (28 micromol (10 mg) kg(-1) body wt), a nicotinic receptor blocker, lidocaine (0.5 mL of a 1% solution on the serosal surface), a local anaesthetic, and nifedipine (5.75 micromol (2 mg) kg(-1) body wt i.v.), a calcium channel blocker. The response to cholera toxin was partially abolished by granisetron (0.11 micromol (40 microg) kg(-1) body wt i.v.), a 5-HT3 receptor blocker. Atropine (1.7 micromol (0.5 mg) kg(-1) body wt i.v.), a muscarinic receptor blocker, had no effect. We therefore conclude that the alkaline secretion in the rat jejunum evoked by cholera toxin exhibits the same pharmacological properties as the fluid secretion caused by the toxin in the jejunum. This suggests that the alkaline secretion in the rat duodenum is controlled not only by an axon reflex but also by an intramural secretory reflex similar to that controlling fluid transport in the rat jejunum.

Motilin controls cyclic release of insulin through vagal cholinergic muscarinic pathways in fasted dogs

The effect of motilin on insulin release has not been studied in the interdigestive state. Adult mongrel dogs were chronically implanted with force transducers in the stomach and duodenum to monitor contractile activity, and the plasma motilin and insulin concentrations were measured by a specific radioimmunoassay and enzyme immunoassay, respectively. The concentration of insulin in plasma was found to fluctuate in close association with that of motilin and phase III of the interdigestive migrating contractions in the stomach. This spontaneous release of insulin was mimicked by intravenous infusion of motilin at a dose of 0.3 microgram.kg-1.h-1. Exogenous motilin (0.01-0.3 microgram/kg) dose dependently stimulated insulin release, which was abolished by atropine, hexamethonium, ondansetron, and truncal vagotomy. Phentolamine significantly enhanced, whereas propranolol inhibited, motilin-induced insulin release. In a perifusion system using islet cells from the canine pancreas, motilin did not affect insulin release. In conclusion, motilin stimulates insulin release through vagal cholinergic, muscarinic receptors on pancreatic beta-cells, and the effect appears to be modulated by adrenergic nerves.

Duodenal motility in fasting dogs: humoral and neural pathways mediating the colonic brake

We have previously described a negative feedback loop that inhibits duodenal motility when nutrients are infused into the ileum and colon. In the present study, we examined the role of extrinsic innervation and plasma levels of peptide YY (PYY) in mediating this phenomenon. We perfused neurally intact (n = 5 dogs) or extrinsically denervated (n = 6 dogs) isolated loops of proximal colon with isomolar NaCl or a mixed-nutrient solution at 2 and 6 ml/min for 4 h during fasting or for 2 h beginning 15 min after a meal. Both rates of infusion with NaCl prolonged the cycle length of the duodenal migrating motor complex (MMC) in the group with neurally intact loops but not in the group with extrinsically denervated loops. Nutrient infusions increased the MMC cycle length in both groups. Integrated plasma concentrations of PYY were increased by nutrients but not by NaCl in both groups. These data suggest that increased volumes and unabsorbed nutrients in the proximal colon alter proximal small bowel motility. Volume-induced effects are mediated via extrinsic nerves, whereas nutrient-induced effects may be mediated by humoral factors, such as plasma PYY.

Activity-dependent changes in intracellular calcium in myenteric neurons

The spatial distribution and changes in intracellular calcium concentration ([Ca2+]i) in myenteric neurons were measured using fura 2 in the longitudinal muscle-myenteric plexus preparation from the guinea pig duodenum. These measurements were made simultaneously with intracellular voltage recordings. The generation of action potentials in the cell bodies of both S- and AH-type neurons increased [Ca2+]i in the processes and cell bodies. There was no measurable delay between the [Ca2+]i changes in the somata and the processes, indicating that these changes were caused by the spread of electrical signals and not by diffusion. The rate of Ca2+ removal was faster in the processes than in the somata, apparently due to the large surface-to-volume ratio in the former. In AH neurons, the [Ca2+]i transient was shorter than the duration of the after-spike hyperpolarization. It is concluded that the two main types of myenteric neurons possess voltage-gated Ca2+ channels in both somata and processes.

Gastroduodenal resistance and neural mechanisms involved in saline flow decrease elicited by acute blood volume expansion in anesthetized rats

We have previously demonstrated that blood volume (BV) expansion decreases saline flow through the gastroduodenal (GD) segment in anesthetized rats (Xavier-Neto J, dos Santos AA & Rola FH (1990) Gut, 31: 1006-1010). The present study attempts to identify the site(s) of resistance and neural mechanisms involved in this phenomenon. Male Wistar rats (N = 97, 200-300 g) were surgically manipulated to create four gut circuits: GD, gastric, pyloric and duodenal. These circuits were perfused under barostatically controlled pressure (4 cmH2O). Steady-state changes in flow were taken to reflect modifications in circuit resistances during three periods of time: normovolemic control (20 min), expansion (10-15 min), and expanded (30 min). Perfusion flow rates did not change in normovolemic control animals over a period of 60 min. BV expansion (Ringer bicarbonate, 1 ml/min up to 5% body weight) significantly (P < 0.05) reduced perfusion flow in the GD (10.3 +/- 0.5 to 7.6 +/- 0.6 ml/min), pyloric (9.0 +/- 0.6 to 5.6 +/- 1.2 ml/min) and duodenal (10.8 +/- 0.4 to 9.0 +/- 0.6 ml/min) circuits, but not in the gastric circuit (11.9 +/- 0.4 to 10.4 +/- 0.6 ml/min). Prazosin (1 mg/kg) and yohimbine (3 mg/kg) prevented the expansion effect on the duodenal but not on the pyloric circuit. Bilateral cervical vagotomy prevented the expansion effect on the pylorus during the expansion but not during the expanded period and had no effect on the duodenum. Atropine (0.5 mg/kg), hexamethonium (10 mg/kg) and propranolol (2 mg/kg) were ineffective on both circuits. These results indicate that 1) BV expansion increases the GD resistance to liquid flow, 2) pylorus and duodenum are important sites of resistance, and, 3) yohimbine and prazosin prevented the increase in duodenal resistance and vagotomy prevented it partially in the pylorus.

Light microscopy of the enteric nervous system of horses with or without equine dysautonomia (grass sickness): its correlation with the motor effects of physostigmine

Light microscopy was undertaken on sections from the caudal flexure of the duodenum and the terminal ileum proximal to the ileocaecal fold in 5 control horses, 5 horses with acute grass sickness (AGS), and 5 horses with chronic grass sickness (CGS). With the exception of the ileal submucous plexus of the CGS group, the AGS group had the lowest number of neurons as measured using a subjective scoring scheme. The proportion of abnormal neurons in the AGS group was similar in both plexuses and both regions, whereas the values for the CGS group were much higher in the duodenal region than in the ileal region. The motility of tissue adjacent to that used for histology was measured isometrically in vitro. The increase in the rate of contractions following exposure to physostigmine was greatest for the AGS group, both from the duodenal and from the ileal region. The latency was longest for the AGS group, suggesting that the material from this group had the least number of active cholinergic neurons. The studies with physostigmine thus indicated that the most severe functional damage occurred in cases of AGS. These findings confirm that extensive damage occurs in the enteric neurons in equine grass sickness. There was good correlation between the functional cholinergic responses and the extent of neuronal degeneration.

ACE inhibition by enalaprilate stimulates duodenal mucosal alkaline secretion via a bradykinin pathway in the rat

The effects of enalaprilate on duodenal mucosal alkaline secretion (in situ titration) and mean arterial blood pressure were investigated in chloralose-anesthetized male rats. A bolus injection of enalaprilate (0.7 mg/kg intravenously) increased alkaline secretion by about 60%, and this response was resistant to guanethidine (5 mg/kg intravenously), splanchnicotomy, and vagotomy. Furthermore, angiotensin II infusion (0.25-2.5 microg/kg/hr intravenously) following the administration of enalaprilate failed to influence this response. Bradykinin (10(-6)-10(-4) M) applied topically to the serosal surface of the duodenal segment under study increased dose-dependently the duodenal mucosal alkaline secretion, an effect that could be blocked by the selective bradykinin receptor subtype-2 antagonist HOE140 (100 nmol/kg intravenously). HOE140 also antagonized the response to enalaprilate. These data suggest that enalaprilate increases duodenal mucosal alkaline secretion via a local bradykinin pathway involving receptors of the bradykinin receptor subtype-2 antagonist, rather than by blockade of endogenous angiotensin II or by central autonomic neural regulation.

High-affinity CCK-A receptors on the vagus nerve mediate CCK-stimulated pancreatic secretion in rats

Cholecystokinin (CCK) receptors are found on vagal afferent fibers. In pancreatic acini, CCK receptors exist in high- and low-affinity states. The aim of this study was to identify the vagal CCK-A receptor affinity state that mediates the effect of CCK on pancreatic protein secretion. Using a rat model with a pancreatic-biliary cannula, we studied the effects of CCK-JMV-180 on exocrine pancreatic function. CCK-JMV-180 acts as an agonist on high-affinity CCK receptors and as an antagonist on low-affinity CCK receptors. Infusion of CCK-JMV-180 (22-88 micrograms.kg-1.h-1) caused dose-dependent increases in pancreatic protein secretion, which were blocked by the CCK-A receptor antagonist L-364,718. Acute vagotomy in anesthetized rats and perivagal application of capsaicin in conscious rats abolished pancreatic responses to CCK-JMV-180 at 22 and 44 micrograms.kg-1.h-1. CCK-JMV-180 did not reduce pancreatic responses to CCK octapeptide infusion at 20 and 40 pmol.kg-1.h-1. To demonstrate that endogenously released CCK also acts on high-affinity CCK-A receptors, we showed that in conscious rats intraduodenal infusion of 18% casein produced a threefold increase in protein secretion and elevated plasma CCK levels from 0.7 to 8.4 pM. Infusion of CCK-JMV-180 at 44 micrograms.kg-1.h-1 failed to inhibit pancreatic responses to casein. In separate studies, perivagal application of 1% capsaicin inhibited 95% and 90% of the pancreatic responses to casein and casein combined with intravenous CCK-JMV-180, respectively. The neurotoxic effect of capsaicin on small-diameter sensory vagal fibers was verified by immunohistochemical and retrograde tracing studies. In conclusion, we demonstrated that in contrast to their effect on satiety, which is mediated by vagal low-affinity CCK-A receptors, exogenous CCK and endogenous CCK under physiological conditions act through high-affinity CCK-A receptors to mediate pancreatic protein secretion. These findings suggest that different affinity states of the vagal CCK receptors mediate different digestive functions.

Duodenal juxtapyloric retroperistalsis in the interdigestive state in humans

BACKGROUND

The last part of phase III of the migrating motor complex (MMC) is characterized by retroperistalsis in the descending duodenum. This study focused on MMC-related juxtapyloric peristalsis.

METHODS

Antroduodenal manometry was performed in 10 healthy subjects. Pressure was recorded in the distal antrum and in four consecutive subsegments (DS1-DS4), 15 mm each, in the juxtapyloric duodenum.

RESULTS

In the period with ongoing antral phase-III activity (early duodenal phase III) the antral pressure waves were antegrade, but in the juxtapyloric duodenum (DS1) retrograde waves predominated (median, 66%; interquartile range (IQR), 33-83%); that is, most duodenal pressure waves were directed against the antral ones. More distally, in DS3 and DS4, only 17% and 25% (IQR, 0-17, 0-33%, respectively) of the pressure waves were retrograde in this period. After the end of antral phase III--that is, in late duodenal phase III--the proportion of retrograde pressure waves increased successively to 91.5% (IQR, 66-100%) in DS2, 74.5% (IQR, 50-100%) in DS3, and 66% (IQR, 8.2-95.8%) in DS4, respectively, before the onset of duodenal motor quiescence. In phase II antegrade pressure waves predominated (63-76%, medians) in all four duodenal subsegments examined.

CONCLUSIONS

During the interdigestive phase III the antral perstalsis is antegrade, but most juxtapyloric duodenal pressure waves are retrograde; that is, antral and duodenal contractions are on a collision course. In the proximal part of the descending duodenum the end of duodenal phase III shows retroperistalsis after the onset of phase I in the gastric antrum. These motor patterns may be important for regulation of the chemical milieu in the juxtapyloric area.

Afferent innervation of gastrointestinal tract smooth muscle by the hepatic branch of the vagus

To survey the vagal hepatic branch afferent projections to and the terminal specializations in the gastrointestinal tract, male Sprague-Dawley rats were given subdiaphragmatic vagotomies, sparing only the common hepatic branch, and were injected with 3 microl of 8% wheat germ agglutinin-horseradish peroxidase in the left nodose ganglion. The nodose ganglia, the stomach, the first 8 cm of duodenum, and the cecum were prepared as wholemounts and were processed with tetramethyl benzidine. Hepatic afferent innervation of the ventral stomach consisted of one or more bundles entering at the lower esophageal sphincter and coursing to the forestomach, where they branched into distinct terminal fields. The only fibers on the dorsal forestomach were distal branches and terminals that wrapped around the greater curvature from the ventral side. Hepatic afferents supplied the forestomach with both intraganglionic laminar endings (IGLEs; putative mechanosensors that coordinate peristalsis) and intramuscular arrays (IMAs; considered tension receptors). IGLEs were located primarily on the ventral wall of the stomach, whereas IMAs were distributed symmetrically. Afferents were also supplied to the distal antrum and the pylorus, with pyloric innervation consisting almost exclusively of IMAs. Innervation of the proximal duodenum was denser in the first 3 cm and decreased progressively caudally, with only meager innervation after 6 cm. Cecal innervation consisted of a few fibers at the ileocecal junction. Duodenal and cecal endings were predominately IGLEs. These results indicate that the hepatic branch carries sensory information from the forestomach, antrum, pylorus, duodenum, and cecum. Furthermore, the different terminals it supplies suggest that the branch mediates a multiplicity of gastrointestinal functions.

Vagal preganglionic projections to the enteric nervous system characterized with Phaseolus vulgaris-leucoagglutinin

The patterns and extent of vagal preganglionic divergence and convergence within the gastrointestinal tract of the rat were characterized with the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L). Three weeks after tracer was iontophoretically injected into two to four sites within the dorsal motor nucleus of the vagus, wholemounts of perfused gut organs (stomach, duodenum, cecum) were prepared, counterstained with Cuprolinic blue, and processed for PHA-L using the avidin biotin complex with diaminobenzidine. Controls included animals injected with PHA-L after intracranial deafferentations. Well-positioned injections labeled an extremely dense and intricate network of varicose efferent axons throughout the gastric myenteric plexus (including that of the fundus). Individual fibers collateralized extensively, forming a variety of pericellular arborizations and terminal complexes made up of both en passant and end swellings. Single axons frequently innervated subsets of neurons within ganglia. Most enteric neurons were contacted by varicosities of more than one vagal fiber. The patterns of vagal preganglionic fibers in the duodenal and cecal myenteric plexuses resembled the organization in the stomach in many aspects, but the projections in each organ had distinctive characteristics, and label was less dense in the intestines than in the stomach. Vagal preganglionic fibers directly innervated submucosal ganglia, although sparsely. Brainstem injections of PHA-L retrogradely labeled a few myenteric neurons in the corpus, fundus, and duodenum: These "gastrobulbar" and "duodenobulbar" neurons received reciprocal vagal preganglionic innervation. Finally, the PHA-L that spread to the nucleus of the solitary tract occasionally produced transganglionic labeling of afferent intramuscular arrays (gastric fundus). The results of this paper provide strong evidence that the traditional "command neuron" or "mother cell" hypotheses of vagal-enteric organization should be abandoned for an integrative neural network model.

In vitro characterisation of intramural neural pathways between the duodenum and the sphincter of Oddi of the brush-tailed possum

The aims of this study were to determine if neural pathways between the duodenum and sphincter of Oddi are intramural, activated by duodenal electrical field stimulation (EFS) in vitro, and contain capsaicin-sensitive primary afferents. The possible involvement of cholinergic (muscarinic and/or nicotinic) and adrenergic receptors in these pathways were also investigated. Duodenal EFS (5-60 Hz, 70 V, 0.5 ms duration, 10 s train) at sites 2 cm oral and 2 cm anal to the sphincter of Oddi-duodenal junction produced frequency-dependent excitatory responses in the sphincter of Oddi, measured by manometry (n = 3). Excitatory responses from duodenal circular muscle were also evident. Tetrodotoxin (1 microM; n = 7) pretreatment abolished both sphincter of Oddi and duodenal responses to duodenal EFS. Crushing the duodenum between the site of stimulation and the sphincter of Oddi-duodenal junction also abolished sphincter of Oddi response. The sphincter of Oddi responses to duodenal EFS at the oral and anal sites were reduced by pretreatment with (i) atropine (100 nM: n = 7) to 19 +/- 6% (P < 0.05) and 22 +/- 8% (P < 0.05) of control respectively. (ii) hexamethonium (100 microM: n = 9) to 10 +/- 2% (P < 0.01) and 6.0 + 2.5% (P < 0.01) of control respectively and (iii) guanethidine (1 microM; n = 6) to 75 +/- 6% (P < 0.05) and 78 +/- 10% (P < 0.05) of control, respectively. Combined pretreatment with phentolamine and propranolol (both 1 microM; n = 7) was without effect, as was capsaicin (1 microM; n = 12) pretreatment. Excitatory intramural pathways between the sphincter of Oddi and the duodenum are primarily cholinergic in nature and contain an adrenergic component. Capsaicin-sensitive primary afferents are not involved.

Mechanisms of peptide YY release induced by an intraduodenal meal in rats: neural regulation by proximal gut

Peptide YY (PYY) release in anaesthetized rats was studied during the 2 h following the intraduodenal administration of a semi-liquid meal of 21 kJ. Surgical and pharmacological manipulations were performed in order to analyse the mechanisms of PYY release. Postprandial PYY release was suppressed or strongly decreased by caecocolonectomy, truncal vagotomy, tetrodotoxin, hexamethonium, sensory denervation by perivagal capsaicin, and by the NO-synthase inhibitor L-N-arginine methyl ester, while atropine, adrenergic blockers, antagonists of type-A or type-B cholecystokinin (CCK) receptors or bombesin receptors had no effect. Comparing the digestive transit of the semi-liquid meal with the amount of PYY contained in the small bowel wall showed that nutrients had not reached the area rich in cells containing PYY by 30 min, the time at which there was a large PYY release in plasma. By 120 min, the meal front had travelled 72% of the small intestine length, just beginning to reach the PYY-rich part of the ileum. We conclude that the main postprandial PYY release studied in this model comes from ileal and colonic L-cells indirectly stimulated through a neural mechanism originating in the proximal gut and involving sensory vagal fibres, nicotinic synapses and NO release, while CCK and bombesin do not seem to be physiologically involved.

The role of gastric and postgastric sites in glucose-conditioned flavor preferences in rats

Two experiments examined the role of gastric and postgastric contributions in the development of flavor preferences in rats. During training trials, food-deprived rats consumed, on alternate days, a cue flavor paired with glucose infusions and another flavor paired with water infusions. Preferences were assessed in choice tests between the two cue flavors without infusions. The first experiment compared preferences conditioned to a flavor paired with intraduodenal (ID) glucose infusions to those paired with intragastric (IG) infusions. ID glucose-conditioned preferences were as strong as that of IG glucose. The second experiment examined whether the actions of glucose in the stomach alone were sufficient to condition flavor preferences. Glucose infusions were restricted to the stomach with an inflated pyloric cuff and then removed at the end of 30-min training sessions before the cuff was deflated. Rats trained with this procedure did not develop a reliable flavor preference. Flavor preferences were obtained, however, when the cuff was inflated for 30 min after the end of the daily training sessions, or when the cuff was inflated during the training sessions but then deflated without removing the infused glucose. Both of these procedures allowed at least some of the infused glucose to empty into the intestine. Taken together, the results indicate that information from the stomach is neither necessary nor sufficient to produce glucose-conditioned flavor preferences. Such preferences are reinforced by the intestinal and/or postabsorptive actions of glucose.

Morphological and quantitative study of the myenteric plexus of the duodenum of streptozotocin-induced diabetic rats

The purpose of this work was to study the morphological and quantitative alterations of the myenteric plexus neurons of the duodenum of rats with acute and chronic streptozotocin-induced diabetes and establish a comparison with non-diabetic animals. Samples of duodenum were destined to histological sections stained by Hematoxilin-Eosin and to membrane preparings stained by the Giemsa and NADH-diaphorasis methods. Small, medium and large neurons were found, with a predominance of medium ones on chronic and acute diabetic animals. It was verified that most of the neurons of diabetic and non-diabetic animals have an eccentrical nucleus and thus this characteristic is not an indicative of degenerative process. It was observed that in diabetes there is a decrease in the number of myenteric neurons. It is argued that this initial decrease is due to the toxic effects of the drug and not to the physiopathology of diabetes itself, and also that the expressive smaller proportion of neurons on the chronically diabetic animals is due to the immediate loss related to streptozotocin and the further consequences of aging during nine weeks of diabetes.

Endotoxin induces biphasic alterations in small intestinal myoelectric activity in fasted newborn piglets

Previous studies have shown that i.v. endotoxin infusion causes gastrointestinal dysfunction and intestinal injury in piglets. The aim of this study was to investigate the effects of endotoxin on intestinal myoelectric activity in newborn swine and to correlate this with gastrointestinal and hemodynamic events. Three pairs of electrodes were implanted in the jejunal wall of piglets, and after recovery, intestinal myoelectric activity was continuously recorded in the conscious, fasted condition. The intestinal myoelectric activity on the control day showed regular, repeating migrating myoelectric complex (MMC) cycles, each of which was composed of the classic phases I, II, and III. Mean cycle duration was 67.0 +/- 18.7 min (+/- SD), and phase III comprised 9.1 +/- 2.2% of each cycle. On the next day, infusion of 30 micrograms/kg endotoxin caused an initial, prolonged quiescent period and delayed the appearance of the first postendotoxin phase III complex. After the quiescent period, there was a period of irregular spiking activity followed by several shortened MMC cycles (47.9 +/- 22.7 min, p < 0.01 versus control) with a prolongation of the percentage of time spent in phase III (15.4 +/- 11.3%, p < 0.01). Endotoxin thus produced biphasic alterations in intestinal myoelectric activity characterized by an initial quiescence followed by increased gastrointestinal smooth muscle activity. Animals developed diarrhea, hypotension, and tachycardia about 1 h after endotoxin infusion in temporal association with increased spiking activity and MMC cycling. These studies are the first to show this biphasic response to endotoxin.

Peripheral neurotensin participates in the modulation of pre- and postprandial intestinal motility in rats

The present study was undertaken to determine whether neurotensin is involved in the regulation of the intestinal postprandial motor response and, if so, whether the regulatory pathway depends upon peripheral or central neurotensin secretion. Neurotensin, injected by the i.v. route (5 micrograms/kg) during the fasting state, induced firstly an increased irregular spiking activity during 30-40 min. This effect was followed by an increase of frequency of the myoelectrical complexes during 60 min. When injected by the i.c.v. route, neurotensin (0.5 microgram/kg) reinforced the fasting motility pattern of the small intestine after a latency of 70 min. Neurotensin was ineffective on the colon. The neurotensin receptor antagonist SR 48692 (200 micrograms/kg i.v.) reduced the duration of the postprandial motor response of the small intestine and blocked the late postprandial phase on the proximal colon while it suppressed the early postprandial phase on the distal colon. When administered i.c.v. (20 micrograms/kg), SR 48692 had no effect. It is concluded that neurotensin modulates intestinal postprandial motility essentially by a peripheral regulatory pathway. Endogenous neurotensin is involved in the maintenance of the postprandial motility pattern on the small intestine and the proximal colon while it is involved in the initiation of this response on the distal colon. This suggests that endogenous neurotensin acts via both endocrine and nervous mechanisms.

Primary afferent nerves mediate in part beta-adrenoceptor stimulation-induced mesenteric hyperemia in rats

We tested the hypothesis that in the rat duodenum and intestine the mesenteric hyperemia due to beta-adrenoceptor stimulation is mediated by capsaicin-sensitive afferent nerves. Superior mesenteric artery blood flow was measured by pulsed Doppler flowmetry in the anesthetized rat. Functional ablation of afferent nerves was accomplished by subcutaneous 125 mg/kg capsaicin pretreatment 10 to 14 days before blood flow studies. Blockade of capsaicin-sensitive cation-selective ion channels of the duodenal and intestinal mucosal afferent nerves was achieved by intraduodenal 0.1% ruthenium red given 15 min prior to the intraduodenal administration of 5 mg/kg isoproterenol. Functional ablation of the afferent nerves and blockade of the capsaicin-sensitive cation-selective ion channels alone or in combination resulted in a significant reduction of mesenteric hyperemia induced by intraduodenal isoproterenol. These data support the hypothesis that beta-adrenoceptor stimulation by intraduodenal isoproterenol induces mesenteric hyperemia in part through afferent nerves in the rat duodenal and intestinal mucosa. The results suggest for the first time a link between beta-adrenoceptor function and peripheral capsaicin-sensitive afferent nerve-mediated mechanism in the rat gut.

Association between H. pylori, duodenal mechanosensory thresholds, and small intestinal motility in chronic unexplained dyspepsia

Alterations of small intestinal sensory thresholds and small intestinal dysmotility are associated with functional dyspepsia. Because gastric and duodenal afferents partly project to the same areas, we postulated that patients with functional dyspepsia and H. pylori infection would be characterized by lower duodenal sensory thresholds. We evaluated 16 patients with functional dyspepsia and 16 age- and sex-matched controls. All patients had undergone an extensive diagnostic work-up to exclude organic lesions. Mechanosensitive function was tested in the third portion of duodenum utilizing a barostat device, and small intestinal motility was assessed before and during duodenal nutrient infusion with a five-channel low-compliance perfusion system. H. pylori status was assessed by a validated serological test. Small intestinal sensory thresholds (first perception and maximal tolerated pressure) were significantly lower in patients (21.1 +/- 2.1 and 30.9 +/- 1.8 mm Hg) compared to controls (33.0 +/- 2.2 and 38.8 +/- 0.9 mm Hg, all P < 0.003). Nine of 16 patients compared with five of 16 controls were H. pylori positive (P = 0.15). Thresholds for H. pylori-negative (28.7 +/- 2.8 and 36.5 +/- 1.1 mm Hg) or -positive subjects (25.0 +/- 3.0 and 32.7 +/- 2.4 mm Hg) were overall not significantly different (P > 0.3). However, in patients with defined high H. pylori titers (>50 units/ml) defined a priori, thresholds for first perception were significantly lower (14.7 +/- 2.9 mm Hg, N = 5) compared to patients with H. pylori titers below this threshold (24.3 +/- 2.9 mm Hg, N = 4) or without H. pylori infection (23.8 +/- 3.4 mm Hg, P < 0.05). During duodenal nutrient infusion, the duodenal motility index increased (P < 0.03). This increase was not significantly different in patients and controls or in H. pylori-negative or -positive subjects. Sensory abnormalities are present in patients with functional dyspepsia. In a small subgroup of patients with high H. pylori titers, sensory abnormalities may be linked to H. pylori infection.

Effects of maternal proteic undernutrition on the neurons of the myenteric plexus of the duodenum of rats

The purpose of this study was to verify the effects of proteic undernutrition on the neurons of the myenteric plexus from the duodenum of Wistar rats. Twenty-four animals at the age of 60 days were divided in four groups, which were named according to the period their mothers received hypoproteic ration (8%). Some segments of duodenum were subjected to histological treatment and stained with hematoxilin-eosin and some were used for whole mount preparations stained with Giemsa. We observed small, medium-sized and large neurons grouped in ganglia of various shapes. It was concluded that the maternal proteic undernutrition does not affect the organization of the myenteric plexus and that animals submitted to undernutrition during gestation and lactation, when normally fed, show neurons with strongly basophilic cytoplasm and larger cellular bodies than those from control animals.

Determination on functional basis of presynaptic alpha 2-adrenoceptor subtypes in guinea-pig duodenum

The effects of several alpha 2-adrenoceptor agonists and antagonists were examined on the cholinergic twitch contractions evoked by electrical field stimulation of guinea-pig duodenum. Oxymetazoline, xylazine, noradrenaline, alpha-methyl-noradrenaline or medetomidine (0.01-30 microM) were nearly equieffective in inhibiting duodenal twitch responses. The effects of xylazine were competitively counteracted by antagonists tested (0.03-10 microM) with the following order of potency: RX 821002 = idazoxan > rauwolscine = yohimbine = BRL 44408 >> prazosin = ARC 239 = BRL 41992. According to the current classification, it is suggested that alpha 2-heteroadrenoceptors involved in the modulation of duodenal cholinergic neurotransmission belong to the alpha ZD subtype.

Jejunoileal transplantation. Effects on characteristics of canine jejunal motor activity in vivo

This study was designed to determine if extrinsic innervation and intrinsic neural continuity with the duodenum (neuroenteric physiologic pathways disrupted during intestinal transplantation) modulate the characteristics of interdigestive motor activity in the canine small bowel. Five dogs served as neurally intact controls (group 1) and 10 dogs (group 2) underwent a model of jejunal autotransplantation involving in situ neural isolation of the jejunoileum. Fasting duodenal and jejunal motor activity was recorded on-line to a microcomputer using closely spaced duodenal and jejunal manometry catheters. Characteristics of global motor patterns, the migrating motor complex (MMC), and local motor patterns, including individual contractions and grouped clustered contractions, were determined. Neural isolation of the jejunoileum disrupted coordination of duodenal and jejunal phase III activity, increased the variability of cycling of the MMC, decreased the period of the jejunal MMC, and increased motility indices in the neurally isolated jejunum. In contrast, single pressure waves and clustered contractions in the neurally isolated jejunum were not altered significantly in incidence or direction, distance, or velocity of spread. In situ neural isolation of the jejunoileum leads to temporal dissociation of the MMC between the transplanted segment (jejunum) and the duodenum but does not appear to alter markedly the characteristics of local contractile activity as measured by individual or grouped contractions. The occurrence of interdigestive jejunal motor patterns and the local organization of individual and grouped small intestinal contractions are not controlled by extrinsic innervation or intrinsic neural continuity with the duodenum.

Aging impairs afferent nerve function in rat intestine. Reduction of mesenteric hyperemia induced by intraduodenal capsaicin and acid

The high incidence of peptic ulcer disease despite decreased acid secretion in the elderly suggests an impairment of mucosal defense mechanism with aging. Stimulation of the intestinal mucosal afferent nerves by intraduodenal application of capsaicin or hydrochloric acid (HCl) increases superior mesenteric artery (SMA) blood flow and protects the duodenal mucosa against deep damage. We tested the hypothesis that the intestinal hyperemia induced by intraduodenal capsaicin or HCL is significantly reduced in older (12 months) rats compared with younger (2 months) rats. Mesenteric blood flow was measured by pulsed Doppler flowmetry in anesthetized rats with the flow probe around the SMA. Two milliliters per kilogram of 160 microM capsaicin or 0.1 N HCl administered intraduodenally increased SMA blood flow significantly in both age groups. The peak response in SMA blood flow, however, was significantly smaller in the older rats than in the younger rats. These observations support the hypothesis that impairment of afferent nerve function occurs with aging in the rat intestine.

Relationships between the morphology and function of gastric and intestinal distention-sensitive neurons in the dorsal motor nucleus of the vagus

The activity of vagal motor neurons is influenced by sensory information transmitted to the brainstem. In particular, there is evidence that distention of the stomach increases activity of motor neurons in the dorsal vagal motor nucleus, whereas distention of the duodenum, small intestine, and colon reduces neuron firing. In this study, we determined 1) the response of vagal motor neurons to distention of the stomach and duodenum and 2) whether the response properties were associated with specific morphological features. Using the single-cell recording and iontophoretic injection technique, we identified four groups of vagal motor neurons affected by gastric and/or duodenal distention. Group 1 neurons responded to either gastric or duodenal stimulation. Neurons in groups 2, 3, and 4 were affected by both gastric and duodenal distention. Group 2 neurons were excited by duodenal distention and were inhibited by gastric distention. Group 3 neurons were inhibited by duodenal distention and were excited by gastric distention. Most neurons belonged to group 4. Neurons in this group were inhibited by both gastric and duodenal distention. Our analyses revealed that the neurons affected by both stimuli had distinctive structural features. Neurons in group 2 had the largest somata, the most dendritic branches, and the greatest cell surface area. Neurons in group 3 were the smallest and had the shortest dendritic length. In addition, we were able to demonstrate that the neurons in group 4 had a smaller total dendritic length and a smaller cell volume than neurons in group 2 and had more dendritic branch segments than neurons in group 3. These results suggest that morphological features are associated with specific response properties of vagal motor neurons.

Relationships between the morphology and function of gastric and intestinal distention-sensitive neurons in the dorsal motor nucleus of the vagus

The activity of vagal motor neurons is influenced by sensory information transmitted to the brainstem. In particular, there is evidence that distention of the stomach increases activity of motor neurons in the dorsal vagal motor nucleus, whereas distention of the duodenum, small intestine, and colon reduces neuron firing. In this study, we determined 1) the response of vagal motor neurons to distention of the stomach and duodenum and 2) whether the response properties were associated with specific morphological features. Using the single-cell recording and iontophoretic injection technique, we identified four groups of vagal motor neurons affected by gastric and/or duodenal distention. Group 1 neurons responded to either gastric or duodenal stimulation. Neurons in groups 2, 3, and 4 were affected by both gastric and duodenal distention. Group 2 neurons were excited by duodenal distention and were inhibited by gastric distention. Group 3 neurons were inhibited by duodenal distention and were excited by gastric distention. Most neurons belonged to group 4. Neurons in this group were inhibited by both gastric and duodenal distention. Our analyses revealed that the neurons affected by both stimuli had distinctive structural features. Neurons in group 2 had the largest somata, the most dendritic branches, and the greatest cell surface area. Neurons in group 3 were the smallest and had the shortest dendritic length. In addition, we were able to demonstrate that the neurons in group 4 had a smaller total dendritic length and a smaller cell volume than neurons in group 2 and had more dendritic branch segments than neurons in group 3. These results suggest that morphological features are associated with specific response properties of vagal motor neurons.

Effect of neural blockades, gastrointestinal regulatory peptides, and diversion of gastroduodenal contents on periodic pancreatic secretion in the preruminant calf

The role of nerves, gastrointestinal peptides, and gastroduodenal contents in the regulation of pancreatic periodic function were studied in preruminant calves. Nine male, Friesian calves were surgically fitted with pancreatic and duodenal catheters, abomasal and duodenal cannulae, and duodenal electrodes. Pancreatic secretion oscillated in phase with the duodenal migrating myoelectric complex. Pancreatic secretion and duodenal motility were abolished by intravenous atropine (5 micrograms.kg-1.min-1). The frequency of pancreatic and duodenal cycles was similarly increased by motilin and decreased by pituitary adenylate cyclase activating polypeptide-27; secretin lengthened duodenal but not pancreatic cycles, resulting in loss of synchronization; cholecystokinin-8 and secretin increased pancreatic secretion (all infusions at 120 pmol.kg-1.h-1); intraduodenal lidocaine (2%) or diversion of gastroduodenal contents reduced pancreatic secretion without altering periodicity. In conclusion, generation of pancreatic as well as of duodenal periodicity in the calf depends upon cholinergic neural efferent input. Secretin, cholecystokinin-8, pituitary adenylate cyclase activating polypeptide, duodenal contents, and mucosal afferent receptors seem to have relatively minor regulatory roles but can modulate the level of pancreatic secretion. The importance of enteric neural influence from the duodenum and the role of motilin in the regulation of pancreatic periodicity and its synchronization with the duodenal motility cycle remain to be determined.

Rat duodenum nitrergic-induced relaxations are cGMP-independent and apamin-sensitive

The effects of the K+ channel blockers, apamin, tetraethylammonium and 4-aminopyridine, upon the relaxations of the isolated rat proximal duodenum induced by nitregic nerve activation, nitric oxide (NO), the NO donor 3-morpholinosydnonimine (SIN-1) and Br-cyclic GMP were determined. The effects of the guanylate cyclase inhibitors, cystamine and N-methylhydroxylamine, on NO-, SIN-1- and nitrergic nerve-induced responses were also investigated. Apamin inhibited nitrergic nerve-, NO-and SIN-1-induced relaxations but did not affect those induced by Br-cGMP. Tetraethylammonium and 4-aminopyridine as well as cystamine and N-methylhydroxylamine failed to affect the relaxations caused by any of the agents tested. These findings indicate that, in the rat proximal duodenum, nitrergic nerve activation as well as exogenous nitric oxide cause relaxation through a cGMP-independent, apamin sensitive mechanism.

Effect of enteric nonnutrient infusions on motor patterns in neurally intact and neurally isolated canine jejunum

Previous work in our laboratory has shown that nonnutrient mechanical factors initiate changes in motility patterns in local and remote regions of the small intestine. Our aims were to determine how isolated duodenal and jejunoileal nonnutrient infusions alter interdigestive motor patterns locally and distantly and whether these effects are neurally mediated. Ten dogs were prepared with duodenal and proximal jejunal infusion and manometry catheters and a proximal jejunal diverting cannula. Five of these dogs served as neurally intact controls (Group 1) and five also underwent in situ neural isolation of the entire jejunoileum (Group 2: extrinsic denervation; disruption of enteric myoneural continuity with duodenum). After recovery, nonnutrient infusions at 0-15 ml/min for 5 hr into proximal duodenum or jejunum did not consistently affect cycling of the migrating motor complex (MMC). The period and duration of individual phases of the MMC and time to first phase III after the start of infusion were similar in both groups. In Group 2, duodenal characteristics (period and duration of phase II, time to first phase III) increased slightly with increasing rates of jejunal but not duodenal infusion. Motility indices, although greater in Group 2, were not altered by enteric infusions. Differing rates of nonnutrient enteric flow limited to duodenum or jejunoileum did not affect markedly local or distant motor patterns. Alterations in interdigestive motility patterns by postprandial nonnutrient intraluminal content are not mediated directly by intraluminal flow.

Effects of nitric oxide inhibition on duodenal function in rat: involvement of neural mechanisms

This study examines the integrative response of several duodenal functions to nitric oxide synthase inhibition. Effects of the nitric oxide synthase inhibitor N-nitro-L-arginine methyl ester (L-NAME) were studied in anesthetized rats, using in situ duodenal perfusion. L-NAME increased bicarbonate secretion, permeability, and fluid secretion and induced motility. Injection of L-arginine abolished L-NAME-induced motility and lowered the secretion of bicarbonate and fluid. Pretreatment with the nicotinic receptor antagonist hexamethonium prevented the rise in bicarbonate secretion and motility in response to L-NAME but did not affect the increase in mucosal permeability. Atropine diminished the L-NAME-induced increases in permeability, motility, and fluid secretion. The adrenolytic drug guanethidine did not alter the responses to the inhibitor. These results suggest that nitric oxide inhibits duodenal motility and bicarbonate secretion by suppressing a stimulatory, nicotinic receptor-dependent, neural mechanism. The L-NAME-induced contractions involve both a cholinergic, atropine-sensitive pathway and nonadrenergic, noncholinergic neural transmission. Muscarinic receptors also mediate part of the L-NAME-induced increases in mucosal permeability and fluid secretion.