Presynaptic inhibitory effects of the peptides NPY, PYY and PP on nicotinic EPSPs in guinea-pig gastric myenteric neurones

Supraphysiological effects of pancreatic polypeptide on gastric motor function and nutrient tolerance in humans

Pancreatic polypeptide (PP) is known to affect food intake. In this exploratory study, we set out to investigate its supraphysiological effect on food tolerance, gastric accommodation, and emptying. In 12 healthy volunteers, 0, 3, or 10 pmol*kg-1 *min-1 PP was administered intravenously (PP0, PP3 or PP10). Thirty minutes thereafter, nutrient drink infusion (60 ml*min-1 ) through a nasogastric feeding tube was started until maximum satiation. Gastric accommodation was assessed by measuring the intragastric pressure (IGP; nasogastric manometry). In a separate test, the effect of PP0 or PP10 on gastric emptying was tested in 10 healthy volunteers and assessed using the 13 C breath test. Results are presented as mean ± SEM, and p < 0.05 was considered significant. For the IGP test, PP increased ingested nutrient volume: 886 ± 93, 1059 ± 124, and 1025 ± 125 ml for PP0, PP3, and PP10, respectively (p = 0.048). In all groups, Nadir IGP values were reached upon food intake (transformed values: 1.5 ± 0.2, 1.7 ± 0.3, and 1.6 ± 0.3 mmHg for PP0, PP3, and PP10, respectively; NS) to return to baseline thereafter. For the gastric emptying study, volunteers ingested a similar nutrient volume: 802 ± 119 and 1089 ± 128 ml (p = 0.016), and gastric half-emptying time was 281 ± 52 and 249 ± 37 min for PP0 and PP10, respectively (NS). No significant correlation between tolerated nutrient volume and IGP drop (R² < 0.01; p = 0.88 for PP0 vs. PP3 and R² =0.07; p = 0.40 for PP0 vs. PP10, respectively) or gastric half-emptying time (R² = 0.12; p = 0.32) was found. A supraphysiological PP dose enhances food tolerance; however, this effect is not mediated through gastric motility. CLINICAL TRIAL REGISTRY NUMBER: NCT03854708 is obtained from clinicaltrials.gov.

Importance of the enteric nervous system in the control of the migrating motility complex

The migrating motility complex (MMC), a cyclical phenomenon, represents rudimentary motility pattern in the gastrointestinal tract. The MMC is observed mostly in the stomach and gut of man and numerous animal species. It contains three or four phases, while its phase III is the most characteristic. The mechanisms controlling the pattern are unclear in part, although the neural control of the MMC seems crucial. The main goal of this article was to discuss the importance of intrinsic innervation of the gastrointestinal tract in MMC initiation, migration, and cessation to emphasize that various MMC-controlling mechanisms act through the enteric nervous system. Two main neural regions, central and peripheral, are able to initiate the MMC. However, central regulation of the MMC may require cooperation with the enteric nervous system. When central mechanisms are not active, the MMC can be initiated peripherally in any region of the small bowel. The enteric nervous system affects the MMC in response to the luminal stimuli which can contribute to the initiation and cessation of the cycle, and it may evoke irregular phasic contractions within the pattern. The hormonal regulators released from the endocrine cells may exert a modulatory effect upon the MMC mostly through the enteric nervous system. Their central action could also be considered. It can be concluded that the enteric nervous system is involved in the great majority of the MMC-controlling mechanisms.

Vagal neurocircuitry and its influence on gastric motility

A large body of research has been dedicated to the effects of gastrointestinal peptides on vagal afferent fibres, yet multiple lines of evidence indicate that gastrointestinal peptides also modulate brainstem vagal neurocircuitry, and that this modulation has a fundamental role in the physiology and pathophysiology of the upper gastrointestinal tract. In fact, brainstem vagovagal neurocircuits comprise highly plastic neurons and synapses connecting afferent vagal fibres, second order neurons of the nucleus tractus solitarius (NTS), and efferent fibres originating in the dorsal motor nucleus of the vagus (DMV). Neuronal communication between the NTS and DMV is regulated by the presence of a variety of inputs, both from within the brainstem itself as well as from higher centres, which utilize an array of neurotransmitters and neuromodulators. Because of the circumventricular nature of these brainstem areas, circulating hormones can also modulate the vagal output to the upper gastrointestinal tract. This Review summarizes the organization and function of vagovagal reflex control of the upper gastrointestinal tract, presents data on the plasticity within these neurocircuits after stress, and discusses the gastrointestinal dysfunctions observed in Parkinson disease as examples of physiological adjustment and maladaptation of these reflexes.

Cultured nestin-positive cells from postnatal mouse small bowel differentiate ex vivo into neurons, glia, and smooth muscle

Little is known about postnatal enteric nervous system (ENS) development, but some reports suggest that the postnatal bowel may contain neural stem cells. Therefore, we created an in vitro model of desegregation using an enzymatic and mechanical tissue technique. This approach yielded a group of cells from the small intestine of lactating and adult mice, which ex vivo attach to the culture dish; actively proliferate; and express nestin, vimentin, and the pro-neural transcription factors neurogenin-2 (ngn-2), Sox-10, and Mash-1. In the conditions grown, double immunostains suggest that they differentiate into various cell types, particularly neurons, smooth muscle, and glia including 04 protein-positive cells. They also express the neurotrophic-protein tyrosine kinase (Trk) receptors TrkA, TrkB, and TrkC; the low-affinity neurotrophin receptor p75NTR; and the glial-derived neurotrophic factor receptors (GFR)alpha-1, GFRalpha-2, and GFRalpha-3. The neurons expressed several sensory and motor neurotransmitters present in the central and enteric nervous systems, including calcitonin gene-related peptide, neuropeptideY, peptideYY, substance P, vasoactive intestinal polypeptide, and galanin; along with glia, these neurons formed elaborate intercellular connections. They also express c-KIT, CD34, CD20, and CD45RO, suggesting they either have a hematogenous origin or may differentiate toward hematogenous lines. These findings suggest that these cells may be enteric neural stem cells (ENSCs); may normally be present in the small intestine; and may have the capacity to proliferate and differentiate into neurons, glia, and smooth muscle. Further identification and purification of intestinal ENSCs will provide a means to study the regulation of their differentiation and should give insight into the mechanisms involved in development and remodeling of the ENS. The possible therapeutic application of postnatal stem cells such as ENSCs needs to be evaluated, including their use for transplantation in the central nervous system.

Physiological role of neuropeptide Y in the regulation of the ascending phase of the peristaltic reflex

The physiological role of neuropeptide Y (NPY) and of specific NPY receptors in regulating the intestinal peristaltic reflex was examined in three-compartment flat-sheet preparations of rat colon. Graded muscle stretch or mucosal stimulation applied to the central compartment inhibited NPY release in the orad compartment where ascending contraction was measured. NPY and the Y1-receptor agonist [Leu31, Pro34]NPY inhibited, whereas the selective Y1-receptor antagonist BIBP 3226 augmented ascending contraction and substance P (SP) release in the orad compartment induced by muscle stretch or mucosal stimulation. Neither agonist nor antagonist had any effect on descending relaxation or VIP release in the caudad compartment. The Y2-receptor agonist NPY13-36 and antagonist BIIE 0246 had no effect on peptide release or mechanical response. The results indicate that suppression of a tonic inhibitory influence of NPY neurons on excitatory neurotransmitter release contributes substantially to the orad contractile phase of the peristaltic reflex. The effect of NPY on neurotransmitter release is mediated by Y1 receptors.

Projections and neurochemistry of interneurones in the myenteric plexus of the guinea-pig gastric corpus

Recently, motor neurones of the myenteric plexus innervating the muscle layers or the mucosa have been identified in the guinea-pig stomach. We applied the neuronal tracer DiI (1,1'-didodecyl-3,3,3', 3'-tetramethylindocarbocyanine perchlorat) onto myenteric ganglia in order to identify populations of interneurones in the myenteric plexus of the guinea-pig stomach. The tracing was combined with the immunohistochemical detection of calbindinD28k (CALB), choline acetyltransferase (ChAT), neuropeptide Y (NPY) and 5-hydroxytryptamine (serotonin) (5-HT) and the results were compared to the neurochemical coding of target specific motor neurones. Long projecting ( approximately 5.4 mm) ChAT/CALB/+/-5-HT-, nitric oxide synthase (NOS)/CALB- and short projecting ( approximately 1.1 mm) ChAT/NPY-neurones were identified as descending interneurones. CALB positive ascending interneurones contained ChAT but rarely 5-HT (code: ChAT/CALB). This study identified ascending and descending interneurones in the gastric myenteric plexus and revealed the neurochemical coding of some of the interneurone populations.

Inhibitory effects of NPY on ganglionic transmission in myenteric neurones of the guinea-pig descending colon

Intracellular recordings were made from myenteric neurones of the guinea-pig descending colon. Neuropeptide Y (NPY) and related pancreatic polypeptides were applied by superfusion and the effects upon the amplitude of fast excitatory synaptic potentials (ESPs) and the ratio of paired fast ESPs evoked by stimulation of internodal fibre tracts were noted. NPY produced a concentration-dependent inhibition in fast ESP amplitude in the majority of neurones (17/21) with a calculated IC50 value of 7 nM; in some neurones this inhibition was mediated via the local release of noradrenaline. Peptide YY (PYY) (eight out of 11 neurones; IC50 = 1 nM), NPY(3-36) (three out of three neurones) and [Leu31, Pro34]NPY (four out of five neurones) also decreased the amplitude of fast ESPs. The effects of two or more pancreatic polypeptides or analogues on fast synaptic transmission were compared directly in six neurones; the apparent relative potency of agonists suggested the involvement of Y2-receptors and at least one other Y-receptor type. In the absence of any direct postsynaptic effects of pancreatic polypeptides on the active or passive properties of myenteric neurones, or on their sensitivity to ionophoretically applied acetylcholine, inhibition of fast ganglionic transmission was presumed to be presynaptic in origin. It is concluded that, in addition to their previously described depressant actions on neuro-effector transmission to colonic smooth muscle, pancreatic polypeptides can exert powerful inhibitory effects on myenteric neurones of the descending colon.

Expression and physiological actions of neuropeptide Y in guinea pig parasympathetic cardiac ganglia

Guinea pig atrial whole mount preparations containing the parasympathetic cardiac ganglia were used to establish the expression, distribution and actions of neuropeptide Y (NPY) in atrial tissues. NPY-immunoreactive fibers densely innervated the atrial myocardium and blood vessels. Fibers containing NPY also innervated intrinsic parasympathetic cardiac neurons. Four percent of the cardiac neurons, identified using microtubule associated protein-2 antiserum, were NPY-positive. An endogenous source of NPY was confirmed with reverse transcription PCR which demonstrated the presence of proNPY mRNA. Sixty percent of the parasympathetic cardiac neurons were hyperpolarized by local application of NPY. NPY also decreased the amplitude and duration of the action potential after hyperpolarization in 60% of the neurons and decreased the fast excitatory postsynaptic potential in about 50% of the cells. These observations indicate that NPY is anatomically positioned to directly alter the output of the parasympathetic cardiac ganglia either by hyperpolarizing the cardiac neurons or by decreasing the fast synaptic input which drives individual neurons.

Subpopulations of gastric myenteric neurons are differentially activated via distinct serotonin receptors: projection, neurochemical coding, and functional implications

The enteric nervous system coordinates various gut functions. Functional studies suggested that neurotransmitters and neuromodulators, one of the most prominent among them being 5-HT, may act through a specific modulation of ascending and descending enteric pathways. However, it is still mostly unknown how particular components of enteric reflex circuits are controlled. This report describes experiments aimed at identifying a differential activation of enteric pathways by 5-HT. Electrophysiological and immunohistochemical methods were combined to investigate the projection pattern and the transmitter phenotype of 5-HT-sensitive gastric myenteric neurons. Of 294 intracellularly labeled neurons, 60.5% showed responses mediated via 5-HT3 receptors, 11.3% were 5-HT1P-responsive, 3.7% exhibited both 5-HT3 and 5-HT1P receptor-mediated depolarization, and 24.5% were not responding to 5-HT. The 5-HT3-responsive cells were mainly cholinergic (79%) and had ascending projections, whereas the 5-HT1P-responsive cells had primarily descending projections and were nitrergic (67%). Substance P-positive neurons were cholinergic; most of the cells (75%) exhibited 5-HT3 mediated responses and had ascending projections. Muscle strip recordings supported the functional significance of the differential location of 5-HT receptor subtypes. Thus, contractile responses of gastric circular muscle strips were dose-dependently increased by a 5-HT3 and decreased by a 5-HT1P agonist. Results indicated that excitatory ascending enteric pathways consisting of cholinergic, substance Pergic neurons were activated by 5-HT3 receptors, whereas 5-HT1P receptors were involved in activation of inhibitory descending pathways using nitrergic neurons. This suggested that different effects of 5-HT on gastric functions are related to specific activation of receptors located on different subsets of enteric neurons.

Subpopulations of gastric myenteric neurons are differentially activated via distinct serotonin receptors: projection, neurochemical coding, and functional implications

The enteric nervous system coordinates various gut functions. Functional studies suggested that neurotransmitters and neuromodulators, one of the most prominent among them being 5-HT, may act through a specific modulation of ascending and descending enteric pathways. However, it is still mostly unknown how particular components of enteric reflex circuits are controlled. This report describes experiments aimed at identifying a differential activation of enteric pathways by 5-HT. Electrophysiological and immunohistochemical methods were combined to investigate the projection pattern and the transmitter phenotype of 5-HT-sensitive gastric myenteric neurons. Of 294 intracellularly labeled neurons, 60.5% showed responses mediated via 5-HT3 receptors, 11.3% were 5-HT1P-responsive, 3.7% exhibited both 5-HT3 and 5-HT1P receptor-mediated depolarization, and 24.5% were not responding to 5-HT. The 5-HT3-responsive cells were mainly cholinergic (79%) and had ascending projections, whereas the 5-HT1P-responsive cells had primarily descending projections and were nitrergic (67%). Substance P-positive neurons were cholinergic; most of the cells (75%) exhibited 5-HT3 mediated responses and had ascending projections. Muscle strip recordings supported the functional significance of the differential location of 5-HT receptor subtypes. Thus, contractile responses of gastric circular muscle strips were dose-dependently increased by a 5-HT3 and decreased by a 5-HT1P agonist. Results indicated that excitatory ascending enteric pathways consisting of cholinergic, substance Pergic neurons were activated by 5-HT3 receptors, whereas 5-HT1P receptors were involved in activation of inhibitory descending pathways using nitrergic neurons. This suggested that different effects of 5-HT on gastric functions are related to specific activation of receptors located on different subsets of enteric neurons.

Action of FMRFamide-like peptides on porcine gastrointestinal motility in vitro

Mechanical activity was recorded in circular and longitudinal smooth muscle preparations isolated from extensive regions of the porcine gastrointestinal tract in response to the FMRFamide-like neuropeptides F8Famide and A18Famide. In all preparations, the peptides were about equipotent in producing phasic contractions or enhancing spontaneous activity. The most prominent responses were observed in jejunal longitudinal strips which were on the average 91% (+/- 4% SEM, n = 15; 10(-6) M) of the histamine (10(-5) M) responses. The peptide-induced phasic activity was completely abolished by nifedipine but was unaffected by tetrodotoxin, atropine, phentolamine, yohimbine, phenoxybenzamine, propranolol, methysergide, cimetidine, indomethacin, levallorphane or naloxone. Both peptides enhanced acetylcholine-induced contractions. However, bovine ileum and guinea-pig taenia coli was not affected by these peptides. The results indicate that F8F- and A18F-amide contract porcine gastrointestinal smooth muscle by acting directly via non-opioid receptors on L-type calcium channels. In addition an increase of the sensitivity to cholinergic stimulation occurs.

Differential mechanism of peptide YY and neuropeptide Y in inhibiting motility of guinea-pig colon

The effect of peptide YY on contractility, acetylcholine release and noradrenaline release was examined in the isolated guinea-pig colon, and findings were compared with those for neuropeptide Y. Peptide YY and neuropeptide Y inhibited the twitch contractions mediated by the stimulation of cholinergic neurons. Peptide YY, neuropeptide Y, [Leu31,Pro34]neuropeptide Y and neuropeptide Y-(13-36) inhibited the electrically stimulated release of acetylcholine. Neuropeptide Y, but not peptide YY, inhibited the high K(+)-stimulated tetrodotoxin-resistant release of acetylcholine, while the inhibitory effect of neuropeptide Y disappeared after treatment with yohimbine. Neuropeptide Y, but not peptide YY or neuropeptide Y analogues, evoked the release of noradrenaline. After desensitization to the effects of neuropeptide Y, peptide YY inhibited electrically stimulated acetylcholine release. Thus, peptide YY inhibits acetylcholine release through stimulation of a receptor, distinct from the site of action of neuropeptide Y, located on cholinergic neurons as well as the neuropeptide Y Y1 and Y2 receptors in the guinea-pig colon. Neuropeptide Y inhibits acetylcholine release due to the noradrenaline release mediated by stimulation of a receptor distinct from neuropeptide Y Y1 and Y2 receptors, located on adrenergic neurons.

Neurochemical coding of enteric neurons in the guinea pig stomach

The aim of this study was to investigate the neurochemical coding of myenteric neurons in the guinea pig gastric corpus by using immunohistochemical methods. Antibodies and antisera against calbindin (CALB), calretinin (CALRET), choline acetyltransferase (ChAT), calcitonin gene-related peptide (CGRP), dopamine beta-hydroxylase (DBH), beta-endorphin (ENK), neuropeptide Y (NPY), neuron-specific enolase (NSE), nitric oxide synthase (NOS), protein gene product 9.5 (PGP), parvalbumin (PARV), serotonin (5-HT), somatostatin (SOM), substance P (SP), tyrosine hydroxylase (TH), and vasoactive intestinal peptide (VIP) were used. Double- and triple-labeling studies revealed colocalization of certain transmitters and enabled the identification of distinct subpopulations of gastric enteric neurons. NPY/VIP/NOS/ENK were present in 28% of all neurons, whereas 11% had NPY/VIP/DBH/ChAT; NOS-only neurons made up 2% of the population. The combination SP/ChAT/ENK occurred in 21% of the population, whereas SP/ChAT/ENK/CALRET and SP/CHAT/SOM/ +/- CALRET was identified in 5% and 6% of all cells, respectively. 5-HT-containing neurons comprised 2% of all cells and could be further classified by the presence of additional antigens as 5-HT/SP/(ChAT) or 5-HT/VIP/(ChAT). Approximately 21% of all neurons contained only ChAT with no additional antigen present and are referred to as ChAT/-. Gastric myenteric ganglion cells were not immunoreactive for CALB, PARV, CGRP, or TH. The results of this study indicate that gastric myenteric neurons can be characterized on the basis of different chemical coding. Neurochemical coding of corpus myenteric neurons revealed some similarities and significant differences in comparison with other regions of the gut. These differences might reflect adaptation of enteric nerves according to regional specialization and the distinct functions of the proximal stomach as a gastric reservoir.

Distribution of enteric neural peptide YY in the dog gastrointestinal tract

Various regions of the dog gastrointestinal tract were investigated for the distribution of peptide YY (PYY) neurons using immunocytochemistry and radioimmunoassay. PYY neurons that encircled non-PYY-immunoreactive neurons were mainly observed in the myenteric plexus from the stomach to the colon. There was more PYY-like immunoreactivity in the muscle layer of the stomach and ileum than in the other intestines. The results of high performance liquid chromatography revealed that neural PYY-immunoreactive substance is identical to authentic PYY. PYY was not localized in the cholinergic neurons. These results indicate that PYY, as a neuropeptide, is involved in the regulation of gastrointestinal function.

Y2-receptor-mediated selective inhibition of slow, inhibitory postsynaptic potential in submucous neurones of guinea-pig caecum

1. The subtype of neuropeptide Y receptor mediating the selective inhibition of the slow inhibitory postsynaptic potential (i.p.s.p.) of submucous neurones in guinea-pig caecum was investigated by use of conventional intracellular electrophysiological recording techniques. 2. Neuropeptide Y (NPY) (1-300 nM) was found to depress or abolish reversibly the slow i.p.s.p. evoked by focal stimulation of internodal fibre tracts. At low concentrations (1-30 nM), a reduction in the duration of the slow i.p.s.p. was often apparent before any inhibition of the amplitude of this synaptic potential. 3. These inhibitory effects of NPY were mimicked by peptide YY (PYY; 0.3-100 nM), NPY13-36 (1-300 nM) and NPY22-36 (10-100 nM); [Leu31,Pro34]NPY ([Pro34]NPY) and bovine pancreatic polypeptide (bPP) were without pre- or postsynaptic effects at concentrations of up to 300 nM. The IC50 +/- s.e. mean values for PYY, NPY, and NPY13-36 were 2.7 +/- 0.3, 7.8 +/- 2.1 and 30 +/- 4.8 nM, respectively, and were significantly different from each other. Thus, the apparent rank order of potency was PYY > NPY > NPY13-36 >> [Pro34]NPY and bPP. 4. In concentrations of up to 300 nM, NPY and its analogues had no depressant effects on the active and passive properties of the impaled neurone and did not affect the amplitude or duration of either cholinergic fast synaptic potentials or non-cholinergic, slow excitatory postsynaptic potentials (e.p.s.ps). Furthermore, none of these peptides altered the amplitude or time-course of changes in membrane potential induced by focal application of acetylcholine or noradrenaline. 5. It is, therefore, concluded that the selective inhibition of the slow i.p.s.p. is mediated by Y2-receptors,located presynaptically on noradrenergic nerve terminals.