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Hibberd TJ, Costa M, Smolilo DJ, Keightley LJ, Brookes SJ, Dinning PG, Spencer NJ. Mechanisms underlying initiation of propulsion in guinea pig distal colon. Am J Physiol Gastrointest Liver Physiol 2022; 323:G71-G87. [PMID: 35502864 DOI: 10.1152/ajpgi.00055.2022] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Colonic motor complexes (CMCs) are a major neurogenic activity in guineapig distal colon. The identity of the enteric neurons that initiate this activity is not established. Specialized intrinsic primary afferent neurons (IPANs) are a major candidate. We aimed to test this hypothesis. To do this, segments of guineapig distal colon were suspended vertically in heated organ baths and propulsive forces acting on a pellet inside the lumen were recorded by isometric force transducer while pharmacological agents were applied to affect IPAN function. In the absence of drugs, CMCs acted periodically on the pellet, generating peak propulsive forces of 12.7 ± 5 g at 0.56 ± 0.22 cpm, lasting 49 ± 17 s (215 preparations; n = 60). Most but not all CMCs were abolished by nicotinic receptor blockade to inhibit fast excitatory synaptic transmission (50/62 preparations; n = 25). Remarkably, CMCs inhibited by hexamethonium were restored by a pharmacological strategy that aimed to enhance IPAN excitability. Thus, CMCs were restored by increased smooth muscle tension (using BAY K8644, bethanechol or carbachol) and by IPAN excitation using phorbol dibutyrate; NK3 receptor agonist, senktide; and partially by αCGRP. The IPAN inhibitor, 5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazole-2-one (DCEBIO), decreased CMC frequency. CGRP, but not NK3-receptor antagonists, decreased CMC frequency in naive preparations. Finally, CMCs were blocked by tetrodotoxin, and this was not reversed by any drugs listed above. These results support a major role for IPANs that does not require fast synaptic transmission, in the periodic initiation of neurogenic propulsive contractions. Endogenous CGRP plays a role in determining CMC frequency, whereas further unidentified signaling pathways may determine their amplitude and duration.NEW & NOTEWORTHY The colonic motor complex (CMC) initiates propulsion in guinea pig colon. Here, CMCs evoked by an intraluminal pellet were restored during nicotinic receptor blockade by pharmacological agents that directly or indirectly enhance intrinsic primary afferent neuron (IPAN) excitability. IPANs are the only enteric neuron in colon that contain CGRP. Blocking CGRP receptors decreased CMC frequency, implicating their role in CMC initiation. The results support a role for IPANs in the initiation of CMCs.
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Affiliation(s)
- Timothy J Hibberd
- College of Medicine and Public Health, Flinders University, Adelaide, South Australia, Australia
| | - Marcello Costa
- College of Medicine and Public Health, Flinders University, Adelaide, South Australia, Australia
| | - David J Smolilo
- College of Medicine and Public Health, Flinders University, Adelaide, South Australia, Australia
| | - Lauren J Keightley
- College of Medicine and Public Health, Flinders University, Adelaide, South Australia, Australia
| | - Simon J Brookes
- College of Medicine and Public Health, Flinders University, Adelaide, South Australia, Australia
| | - Phil G Dinning
- College of Medicine and Public Health, Flinders University, Adelaide, South Australia, Australia
| | - Nick J Spencer
- College of Medicine and Public Health, Flinders University, Adelaide, South Australia, Australia
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Carbone SE, Veldhuis NA, Gondin AB, Poole DP. G protein-coupled receptor trafficking and signaling: new insights into the enteric nervous system. Am J Physiol Gastrointest Liver Physiol 2019; 316:G446-G452. [PMID: 30702900 DOI: 10.1152/ajpgi.00406.2018] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
G protein-coupled receptors (GPCRs) are essential for the neurogenic control of gastrointestinal (GI) function and are important and emerging therapeutic targets in the gut. Detailed knowledge of both the distribution and functional expression of GPCRs in the enteric nervous system (ENS) is critical toward advancing our understanding of how these receptors contribute to GI function during physiological and pathophysiological states. Equally important, but less well defined, is the complex relationship between receptor expression, ligand binding, signaling, and trafficking within enteric neurons. Neuronal GPCRs are internalized following exposure to agonists and under pathological conditions, such as intestinal inflammation. However, the relationship between the intracellular distribution of GPCRs and their signaling outputs in this setting remains a "black box". This review will briefly summarize current knowledge of agonist-evoked GPCR trafficking and location-specific signaling in the ENS and identifies key areas where future research could be focused. Greater understanding of the cellular and molecular mechanisms involved in regulating GPCR signaling in the ENS will provide new insights into GI function and may open novel avenues for therapeutic targeting of GPCRs for the treatment of digestive disorders.
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Affiliation(s)
- Simona E Carbone
- Drug Discovery Biology Theme, Monash Institute of Pharmaceutical Sciences and Australian Research Council Centre of Excellence in Convergent Bio-Nano Science and Technology, Monash University , Parkville, Victoria , Australia
| | - Nicholas A Veldhuis
- Drug Discovery Biology Theme, Monash Institute of Pharmaceutical Sciences and Australian Research Council Centre of Excellence in Convergent Bio-Nano Science and Technology, Monash University , Parkville, Victoria , Australia
| | - Arisbel B Gondin
- Drug Discovery Biology Theme, Monash Institute of Pharmaceutical Sciences and Australian Research Council Centre of Excellence in Convergent Bio-Nano Science and Technology, Monash University , Parkville, Victoria , Australia
| | - Daniel P Poole
- Drug Discovery Biology Theme, Monash Institute of Pharmaceutical Sciences and Australian Research Council Centre of Excellence in Convergent Bio-Nano Science and Technology, Monash University , Parkville, Victoria , Australia.,Anatomy and Neuroscience, The University of Melbourne , Parkville, Victoria , Australia
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Koussoulas K, Gwynne RM, Foong JPP, Bornstein JC. Cholera Toxin Induces Sustained Hyperexcitability in Myenteric, but Not Submucosal, AH Neurons in Guinea Pig Jejunum. Front Physiol 2017; 8:254. [PMID: 28496413 PMCID: PMC5406514 DOI: 10.3389/fphys.2017.00254] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2017] [Accepted: 04/10/2017] [Indexed: 01/04/2023] Open
Abstract
Background and Aims: Cholera toxin (CT)-induced hypersecretion requires activation of secretomotor pathways in the enteric nervous system (ENS). AH neurons, which have been identified as a population of intrinsic sensory neurons (ISNs), are a source of excitatory input to the secretomotor pathways. We therefore examined effects of CT in the intestinal lumen on myenteric and submucosal AH neurons. Methods: Isolated segments of guinea pig jejunum were incubated for 90 min with saline plus CT (12.5 μg/ml) or CT + neurotransmitter antagonist, or CT + tetrodotoxin (TTX) in their lumen. After washing CT away, submucosal or myenteric plexus preparations were dissected keeping circumferentially adjacent mucosa intact. Submucosal AH neurons were impaled adjacent to intact mucosa and myenteric AH neurons were impaled adjacent to, more than 5 mm from, and in the absence of intact mucosa. Neuronal excitability was monitored by injecting 500 ms current pulses through the recording electrode. Results: After CT pre-treatment, excitability of myenteric AH neurons adjacent to intact mucosa (n = 29) was greater than that of control neurons (n = 24), but submucosal AH neurons (n = 33, control n = 27) were unaffected. CT also induced excitability increases in myenteric AH neurons impaled distant from the mucosa (n = 6) or in its absence (n = 5). Coincubation with tetrodotoxin or SR142801 (NK3 receptor antagonist), but not SR140333 (NK1 antagonist) or granisetron (5-HT3 receptor antagonist) prevented the increased excitability induced by CT. Increased excitability was associated with a reduction in the characteristic AHP and an increase in the ADP of these neurons, but not a change in the hyperpolarization-activated inward current, Ih. Conclusions: CT increases excitability of myenteric, but not submucosal, AH neurons. This is neurally mediated and depends on NK3, but not 5-HT3 receptors. Therefore, CT may act to amplify the secretomotor response to CT via an increase in the activity of the afferent limb of the enteric reflex circuitry.
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Affiliation(s)
- Katerina Koussoulas
- Enteric Neuroscience Laboratory, Department of Physiology, University of MelbourneParkville, VIC, Australia
| | - Rachel M Gwynne
- Enteric Neuroscience Laboratory, Department of Physiology, University of MelbourneParkville, VIC, Australia
| | - Jaime P P Foong
- Enteric Neuroscience Laboratory, Department of Physiology, University of MelbourneParkville, VIC, Australia
| | - Joel C Bornstein
- Enteric Neuroscience Laboratory, Department of Physiology, University of MelbourneParkville, VIC, Australia
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Gwynne RM, Clarke AJ, Furness JB, Bornstein JC. Both exogenous 5-HT and endogenous 5-HT, released by fluoxetine, enhance distension evoked propulsion in guinea-pig ileum in vitro. Front Neurosci 2014; 8:301. [PMID: 25285066 PMCID: PMC4168689 DOI: 10.3389/fnins.2014.00301] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2014] [Accepted: 09/03/2014] [Indexed: 12/11/2022] Open
Abstract
The roles of 5-HT3 and 5-HT4 receptors in the modulation of intestinal propulsion by luminal application of 5-HT and augmentation of endogenous 5-HT effects were studied in segments of guinea-pig ileum in vitro. Persistent propulsive contractions evoked by saline distension were examined using a modified Trendelenburg method. When 5-HT (30 nM), fluoxetine (selective serotonin reuptake inhibitor; 1 nM), 2-methyl-5-HT (5-HT3 receptor agonist; 1 mM), or RS 67506 (5-HT4 receptor agonist, 1 μM) was infused into the lumen, the pressure needed to initiate persistent propulsive activity fell significantly. A specific 5-HT4 receptor antagonist, SB 207266 (10 nM in lumen), abolished the effects of 5-HT, fluoxetine, and RS 67506, but not those of 2-methyl-5-HT. Granisetron (5-HT3 receptor antagonist; 1 μM in lumen) abolished the effect of 5-HT, fluoxetine, RS 67506, and 2-methyl-5-HT. The NK3 receptor antagonist SR 142801 (100 nM in lumen) blocked the effects of 5-HT, fluoxetine, and 2-methyl-5-HT. SB 207266, granisetron, and SR 142801 had no effect by themselves. Higher concentrations of fluoxetine (100 and 300 nM) and RS 67506 (3 and 10 μM) had no effect on the distension threshold for propulsive contractions. These results indicate that luminal application of exogenous 5-HT, or increased release of endogenous mucosal 5-HT above basal levels, acts to lower the threshold for propulsive contractions in the guinea-pig ileum via activation of 5-HT3 and 5-HT4 receptors and the release of tachykinins. The results further indicate that basal release of 5-HT is insufficient to alter the threshold for propulsive motor activity.
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Affiliation(s)
- Rachel M Gwynne
- Department of Physiology, University of Melbourne Parkville, VIC, Australia
| | - Amanda J Clarke
- Department of Physiology, University of Melbourne Parkville, VIC, Australia
| | - John B Furness
- Departments of Anatomy and Cell Biology, University of Melbourne Parkville, VIC, Australia
| | - Joel C Bornstein
- Department of Physiology, University of Melbourne Parkville, VIC, Australia
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Localisation and activation of the neurokinin 1 receptor in the enteric nervous system of the mouse distal colon. Cell Tissue Res 2014; 356:319-32. [PMID: 24728885 DOI: 10.1007/s00441-014-1822-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2013] [Accepted: 01/20/2014] [Indexed: 12/31/2022]
Abstract
The substance P neurokinin 1 receptor (NK1R) regulates motility, secretion, inflammation and pain in the intestine. The distribution of the NK1R is a key determinant of the functional effects of substance P in the gut. Information regarding the distribution of NK1R in subtypes of mouse enteric neurons is lacking and is the focus of the present study. NK1R immunoreactivity (NK1R-IR) is examined in whole-mount preparations of the mouse distal colon by indirect immunofluorescence and confocal microscopy. The distribution of NK1R-IR within key functional neuronal subclasses was determined by using established neurochemical markers. NK1R-IR was expressed by a subpopulation of myenteric and submucosal neurons; it was mainly detected in large multipolar myenteric neurons and was colocalized with calcitonin gene-related peptide, neurofilament M, choline acetyltransferase and calretinin. The remaining NK1R-immunoreactive neurons were positive for nitric oxide synthase. NK1R was expressed by most of the submucosal neurons and was exclusively co-expressed with vasoactive intestinal peptide, with no overlap with choline acetyltransferase. Treatment with substance P resulted in the concentration-dependent internalisation of NK1R from the cell surface into endosome-like structures. Myenteric NK1R was mainly expressed by intrinsic primary afferent neurons, with minor expression by descending interneurons and inhibitory motor neurons. Submucosal NK1R was restricted to non-cholinergic secretomotor neurons. These findings highlight key differences in the neuronal distribution of NK1R-IR between the mouse, rat and guinea-pig, with important implications for the functional role of NK1R in regulating intestinal motility and secretion.
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Sridharan R, Zuber J, Connelly SM, Mathew E, Dumont ME. Fluorescent approaches for understanding interactions of ligands with G protein coupled receptors. BIOCHIMICA ET BIOPHYSICA ACTA 2014; 1838:15-33. [PMID: 24055822 PMCID: PMC3926105 DOI: 10.1016/j.bbamem.2013.09.005] [Citation(s) in RCA: 86] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2013] [Revised: 09/03/2013] [Accepted: 09/08/2013] [Indexed: 11/18/2022]
Abstract
G protein coupled receptors are responsible for a wide variety of signaling responses in diverse cell types. Despite major advances in the determination of structures of this class of receptors, the underlying mechanisms by which binding of different types of ligands specifically elicits particular signaling responses remain unclear. The use of fluorescence spectroscopy can provide important information about the process of ligand binding and ligand dependent conformational changes in receptors, especially kinetic aspects of these processes that can be difficult to extract from X-ray structures. We present an overview of the extensive array of fluorescent ligands that have been used in studies of G protein coupled receptors and describe spectroscopic approaches for assaying binding and probing the environment of receptor-bound ligands with particular attention to examples involving yeast pheromone receptors. In addition, we discuss the use of fluorescence spectroscopy for detecting and characterizing conformational changes in receptors induced by the binding of ligands. Such studies have provided strong evidence for diversity of receptor conformations elicited by different ligands, consistent with the idea that GPCRs are not simple on and off switches. This diversity of states constitutes an underlying mechanistic basis for biased agonism, the observation that different stimuli can produce different responses from a single receptor. It is likely that continued technical advances will allow fluorescence spectroscopy to play an important role in continued probing of structural transitions in G protein coupled receptors. This article is part of a Special Issue entitled: Structural and biophysical characterisation of membrane protein-ligand binding.
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Affiliation(s)
- Rajashri Sridharan
- Department of Biochemistry and Biophysics, P.O. Box 712, University of Rochester Medical Center, Rochester, NY 14642
| | - Jeffrey Zuber
- Department of Biochemistry and Biophysics, P.O. Box 712, University of Rochester Medical Center, Rochester, NY 14642
| | - Sara M. Connelly
- Department of Biochemistry and Biophysics, P.O. Box 712, University of Rochester Medical Center, Rochester, NY 14642
| | - Elizabeth Mathew
- Department of Biochemistry and Biophysics, P.O. Box 712, University of Rochester Medical Center, Rochester, NY 14642
| | - Mark E. Dumont
- Department of Biochemistry and Biophysics, P.O. Box 712, University of Rochester Medical Center, Rochester, NY 14642
- Department of Pediatrics, P.O. Box 777, University of Rochester Medical Center, Rochester, NY 14642
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Mondal A, Aizawa S, Sakata I, Goswami C, Oda SI, Sakai T. Mechanism of ghrelin-induced gastric contractions in Suncus murinus (house musk shrew): involvement of intrinsic primary afferent neurons. PLoS One 2013; 8:e60365. [PMID: 23565235 PMCID: PMC3614873 DOI: 10.1371/journal.pone.0060365] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2012] [Accepted: 02/26/2013] [Indexed: 12/13/2022] Open
Abstract
Here, we have reported that motilin can induce contractions in a dose-dependent manner in isolated Suncus murinus (house musk shrew) stomach. We have also shown that after pretreatment with a low dose of motilin (10(-10) M), ghrelin also induces gastric contractions at levels of 10(-10) M to 10(-7) M. However, the neural mechanism of ghrelin action in the stomach has not been fully revealed. In the present study, we studied the mechanism of ghrelin-induced contraction in vitro using a pharmacological method. The responses to ghrelin in the stomach were almost completely abolished by hexamethonium and were significantly suppressed by the administration of phentolamine, prazosin, ondansetron, and naloxone. Additionally, N-nitro-l-arginine methylester significantly potentiated the contractions. Importantly, the mucosa is essential for ghrelin-induced, but not motilin-induced, gastric contractions. To evaluate the involvement of intrinsic primary afferent neurons (IPANs), which are multiaxonal neurons that pass signals from the mucosa to the myenteric plexus, we examined the effect of the IPAN-related pathway on ghrelin-induced contractions and found that pretreatment with adenosine and tachykinergic receptor 3 antagonists (SR142801) significantly eliminated the contractions and GR113808 (5-hydroxytryptamine receptor 4 antagonist) almost completely eliminated it. The results indicate that ghrelin stimulates and modulates suncus gastric contractions through cholinergic, adrenergic, serotonergic, opioidergic neurons and nitric oxide synthases in the myenteric plexus. The mucosa is also important for ghrelin-induced gastric contractions, and IPANs may be the important interneurons that pass the signal from the mucosa to the myenteric plexus.
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Affiliation(s)
- Anupom Mondal
- Area of Regulatory Biology, Graduate School of Science and Engineering, Saitama University, Saitama, Japan
| | - Sayaka Aizawa
- Area of Regulatory Biology, Graduate School of Science and Engineering, Saitama University, Saitama, Japan
| | - Ichiro Sakata
- Area of Regulatory Biology, Graduate School of Science and Engineering, Saitama University, Saitama, Japan
| | - Chayon Goswami
- Area of Regulatory Biology, Graduate School of Science and Engineering, Saitama University, Saitama, Japan
| | - Sen-ichi Oda
- Laboratory of Animal Management and Resources, Department of Zoology, Okayama University of Science, Okayama, Japan
| | - Takafumi Sakai
- Area of Regulatory Biology, Graduate School of Science and Engineering, Saitama University, Saitama, Japan
- * E-mail:
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King SK, Sutcliffe JR, Ong SY, Lee M, Koh TL, Wong SQ, Farmer PJ, Peck CJ, Stanton MP, Keck J, Cook DJ, Chow CW, Hutson JM, Southwell BR. Substance P and vasoactive intestinal peptide are reduced in right transverse colon in pediatric slow-transit constipation. Neurogastroenterol Motil 2010; 22:883-92, e234. [PMID: 20529207 DOI: 10.1111/j.1365-2982.2010.01524.x] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
BACKGROUND Slow-transit constipation (STC) is recognized in children but the etiology is unknown. Abnormalities in substance P (SP), vasoactive intestinal peptide (VIP) and nitric oxide (NO) have been implicated. The density of nerve fibers in circular muscle containing these transmitters was examined in colon from children with STC and compared to other pediatric and adult samples. METHODS Fluorescence immunohistochemistry using antibodies to NO synthase (NOS), VIP and SP was performed on colonic biopsies (transverse and sigmoid colon) from 33 adults with colorectal cancer, 11 children with normal colonic transit and anorectal retention (NAR) and 51 with chronic constipation and slow motility in the proximal colon (STC). The percentage area of nerve fibers in circular muscle containing each transmitter was quantified in confocal images. KEY RESULTS In colon circular muscle, the percentage area of nerve fibers containing NOS > VIP > SP (6 : 2 : 1). Pediatric groups had a higher density of nerve fibers than adults. In pediatric samples, there were no regional differences in NOS and VIP, while SP nerve fiber density was higher in sigmoid than proximal colon. STC children had lower SP and VIP nerve fiber density in the proximal colon than NAR children. Twenty-three percent of STC children had low SP nerve fiber density. CONCLUSIONS & INFERENCES There are age-related reductions in nerve fiber density in human colon circular muscle. NOS and VIP do not show regional variations, while SP nerve fiber density is higher in distal colon. 1/3 of pediatric STC patients have low SP or VIP nerve fiber density in proximal colon.
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Affiliation(s)
- S K King
- Department of General Surgery, Royal Children's Hospital, Melbourne, Australia
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Gwynne RM, Bornstein JC. Synaptic transmission at functionally identified synapses in the enteric nervous system: roles for both ionotropic and metabotropic receptors. Curr Neuropharmacol 2010; 5:1-17. [PMID: 18615154 DOI: 10.2174/157015907780077141] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2006] [Revised: 11/28/2006] [Accepted: 12/04/2006] [Indexed: 12/18/2022] Open
Abstract
Digestion and absorption of nutrients and the secretion and reabsorption of fluid in the gastrointestinal tract are regulated by neurons of the enteric nervous system (ENS), the extensive peripheral nerve network contained within the intestinal wall. The ENS is an important physiological model for the study of neural networks since it is both complex and accessible. At least 20 different neurochemically and functionally distinct classes of enteric neurons have been identified in the guinea pig ileum. These neurons express a wide range of ionotropic and metabotropic receptors. Synaptic potentials mediated by ionotropic receptors such as the nicotinic acetylcholine receptor, P2X purinoceptors and 5-HT(3) receptors are seen in many enteric neurons. However, prominent synaptic potentials mediated by metabotropic receptors, like the P2Y(1) receptor and the NK(1) receptor, are also seen in these neurons. Studies of synaptic transmission between the different neuron classes within the enteric neural pathways have shown that both ionotropic and metabotropic synaptic potentials play major roles at distinct synapses within simple reflex pathways. However, there are still functional synapses at which no known transmitter or receptor has been identified. This review describes the identified roles for both ionotropic and metabotropic neurotransmission at functionally defined synapses within the guinea pig ileum ENS. It is concluded that metabotropic synaptic potentials act as primary transmitters at some synapses. It is suggested identification of the interactions between different synaptic potentials in the production of complex behaviours will require the use of well validated computer models of the enteric neural circuitry.
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Affiliation(s)
- R M Gwynne
- Department of Physiology, University of Melbourne, Parkville, Victoria 3010, Australia.
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Dénes V, Wilhelm M, NÉMeth A, GÁBriel R. Interactions of Serotoninergic, Cholinergic, and Tachykinin-Containing Nerve Elements in the Rabbit Small Intestine. Anat Rec (Hoboken) 2009; 292:1548-58. [DOI: 10.1002/ar.20956] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Foong JPP, Bornstein JC. mGluR(1) Receptors Contribute to Non-Purinergic Slow Excitatory Transmission to Submucosal VIP Neurons of Guinea-Pig Ileum. Front Neurosci 2009; 3:46. [PMID: 20582273 PMCID: PMC2695390 DOI: 10.3389/neuro.21.001.2009] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2009] [Accepted: 05/14/2009] [Indexed: 11/23/2022] Open
Abstract
Vasoactive intestinal peptide (VIP) immunoreactive secretomotor neurons in the submucous plexus are involved in mediating bacterial toxin-induced hypersecretion leading to diarrhoea. VIP neurons become hyperexcitable after the mucosa is exposed to cholera toxin, which suggests that the manipulation of the excitability of these neurons may be therapeutic. This study used standard intracellular recording methods to systematically characterize slow excitatory postsynaptic potentials (EPSPs) evoked in submucosal VIP neurons by different stimulus regimes (1, 3 and 15 pulse 30 Hz stimulation), together with their associated input resistances and pharmacology. All slow EPSPs were associated with a significant increase in input resistance compared to baseline values. Slow EPSPs evoked by a single stimulus were confirmed to be purinergic, however, slow EPSPs evoked by 15 pulse trains were non-purinergic and those evoked by 3 pulse trains were mixed. NK1 or NK3 receptor antagonists did not affect slow EPSPs. The group I mGluR receptor antagonist, PHCCC reduced the amplitude of purinergic and non-purinergic slow EPSPs. Blocking mGluR1 receptors depressed the overall response to 3 and 15 pulse trains, but this effect was inconsistent, while blockade of mGluR5 receptors had no effect on the non-purinergic slow EPSPs. Thus, although other receptors are almost certainly involved, our data indicate that there are at least two pharmacologically distinct types of slow EPSPs in the VIP secretomotor neurons: one mediated by P2Y receptors and the other in part by mGluR1 receptors.
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12
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Gwynne RM, Ellis M, Sjövall H, Bornstein JC. Cholera toxin induces sustained hyperexcitability in submucosal secretomotor neurons in guinea pig jejunum. Gastroenterology 2009; 136:299-308.e4. [PMID: 19026646 DOI: 10.1053/j.gastro.2008.09.071] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/04/2008] [Revised: 09/16/2008] [Accepted: 09/25/2008] [Indexed: 02/01/2023]
Abstract
BACKGROUND & AIMS Neural mechanisms underlying cholera toxin (CT)-induced intestinal hypersecretion remain unclear. We investigated long-term excitability changes in vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) secretomotor neurons after prolonged luminal exposure to CT. METHODS Isolated segments of guinea pig jejunum were incubated with saline or CT +/- neurotransmitter antagonist in the lumen; the submucosal plexus was then dissected clear, circumferentially adjacent to intact mucosa. Synaptic inputs and firing properties of S neurons in ganglia next to the mucosa in control saline were studied using intracellular recording. Neurons were processed for VIP and NPY immunoreactivity. RESULTS Thirty S neurons (20 VIP(+), 7 NPY(+), 3 VIP(-)/NPY(-)) from CT-treated preparations and 27 control S neurons (19 VIP(+), 4 NPY(+), 4 VIP(-)/NPY(-)) in ganglia adjacent to intact mucosa were analyzed. VIP(+) and NPY(+) neurons in CT-treated preparations fired significantly more action potentials and for longer periods during injected depolarizing current pulses (50-350 pA) than control neurons. Addition of tetrodotoxin, hexamethonium, granisetron, or the neurokinin-1 (NK1) antagonist SR140333 during the CT incubation blocked CT-induced effects in both neuron types. The NK3 antagonist SR142801 blocked CT-induced effects in NPY(+) neurons and reduced the number of action potentials in VIP(+) neurons. Synaptic activity was unaffected by CT. CONCLUSIONS CT induces specific and sustained hyperexcitability of secretomotor neurons in enteric pathways. CT acts in the mucosa. Its effect is neurally mediated and depends on 5-hydroxytryptamine-3, nicotinic, and NK1 receptors. This system represents a unique model to understand the neural mechanisms of action of CT and to identify therapeutic targets.
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Affiliation(s)
- Rachel M Gwynne
- Department of Physiology, University of Melbourne, Parkville, Victoria, Australia.
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De Man JG, De Winter BY, De Schepper HU, Herman AG, Pelckmans PA. Differential role of tachykinin NK3 receptors on cholinergic excitatory neurotransmission in the mouse stomach and small intestine. Br J Pharmacol 2008; 155:1195-203. [PMID: 18806817 DOI: 10.1038/bjp.2008.357] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
BACKGROUND AND PURPOSE Tachykinin NK(3) receptors are widely expressed in the mouse gastrointestinal tract but their functional role in enteric neuromuscular transmission remains unstudied in this species. We investigated the involvement of NK(3) receptors in cholinergic neurotransmission in the mouse stomach and small intestine. EXPERIMENTAL APPROACH Muscle strips of the mouse gastric fundus and ileum were mounted in organ baths for tension recordings. Effects of NK(3) agonists and antagonists were studied on contractions to EFS of enteric nerves and to carbachol. KEY RESULTS EFS induced frequency-dependent tetrodotoxin-sensitive contractions, which were abolished by atropine. The cholinergic contractions to EFS in the stomach were enhanced by the NK(3) antagonist SR142801, but not affected by the NK(3) agonist senktide or neurokinin B. The cholinergic contractions to EFS in the small intestine were not affected by SR142801, but dose-dependently inhibited by senktide and neurokinin B. This inhibitory effect was prevented by SR142801 but not by hexamethonium. SR142801, senktide or neurokinin B did not induce any response per se in the stomach and small intestine and did not affect contractions to carbachol. CONCLUSIONS AND IMPLICATIONS NK(3) receptors modulate cholinergic neurotransmission differently in the mouse stomach and small intestine. Blockade of NK(3) receptors enhanced cholinergic transmission in the stomach but not in the intestine. Activation of NK(3) receptors inhibited cholinergic transmission in the small intestine but not in the stomach. This indicates a physiological role for NK(3) receptors in mouse stomach contractility and a pathophysiological role in mouse intestinal contractility.
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Affiliation(s)
- J G De Man
- Faculty of Medicine, Laboratory of Experimental Medicine and Paediatrics, Division of Gastroenterology, University of Antwerp, Universiteitsplein 1, Antwerp, Belgium.
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Poole DP, Amadesi S, Rozengurt E, Thacker M, Bunnett NW, Furness JB. Stimulation of the neurokinin 3 receptor activates protein kinase C epsilon and protein kinase D in enteric neurons. Am J Physiol Gastrointest Liver Physiol 2008; 294:G1245-56. [PMID: 18308856 DOI: 10.1152/ajpgi.00521.2007] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Tachykinins, acting through NK(3) receptors (NK(3)R), contribute to excitatory transmission to intrinsic primary afferent neurons (IPANs) of the small intestine. Although this transmission is dependent on protein kinase C (PKC), its maintenance could depend on protein kinase D (PKD), a downstream target of PKC. Here we show that PKD1/2-immunoreactivity occurred exclusively in IPANs of the guinea pig ileum, demonstrated by double staining with the IPAN marker NeuN. PKCepsilon was also colocalized with PKD1/2 in IPANs. PKCepsilon and PKD1/2 trafficking was studied in enteric neurons within whole mounts of the ileal wall. In untreated preparations, PKCepsilon and PKD1/2 were cytosolic and no signal for activated (phosphorylated) PKD was detected. The NK(3)R agonist senktide evoked a transient translocation of PKCepsilon and PKD1/2 from the cytosol to the plasma membrane and induced PKD1/2 phosphorylation at the plasma membrane. PKCepsilon translocation was maximal at 10 s and returned to the cytosol within 2 min. Phosphorylated-PKD1/2 was detected at the plasma membrane within 15 s and translocated to the cytosol by 2 min, where it remained active up to 30 min after NK(3)R stimulation. PKD1/2 activation was reduced by a PKCepsilon inhibitor and prevented by NK(3)R inhibition. NK(3)R-mediated PKCepsilon and PKD activation was confirmed in HEK293 cells transiently expressing NK(3)R and green fluorescent protein-tagged PKCepsilon, PKD1, PKD2, or PKD3. Senktide caused membrane translocation and activation of kinases within 30 s. After 15 min, phosphorylated PKD had returned to the cytosol. PKD activation was confirmed through Western blotting. Thus stimulation of NK(3)R activates PKCepsilon and PKD in sequence, and sequential activation of these kinases may account for rapid and prolonged modulation of IPAN function.
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Affiliation(s)
- D P Poole
- Department of Anatomy and Cell Biology and Centre for Neuroscience, University of Melbourne, Parkville, VIC, Australia.
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15
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Poole DP, Matsuyama H, Nguyen TV, Eriksson EMY, Fowler CJ, Furness JB. Inflammation and inflammatory agents activate protein kinase C epsilon translocation and excite guinea-pig submucosal neurons. Gastroenterology 2007; 133:1229-39. [PMID: 17765238 DOI: 10.1053/j.gastro.2007.07.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/25/2007] [Accepted: 05/17/2007] [Indexed: 01/16/2023]
Abstract
BACKGROUND & AIMS Properties of enteric neurons are transformed by inflammation and protein kinase C (PKC) isoforms are involved both in long-term changes in enteric neurons, and in transducing the effects of substances released during inflammation. We investigated roles of PKCepsilon in submucosal neurons by studying translocation in response to inflammatory mediators, effects on neuron excitability, and the changes in PKCepsilon distribution in a trinitrobenzene sulphonate model of ileitis. METHODS Immunohistochemical detection and analysis of association with membrane and cytosolic fractions, and Western blot analysis of cytosolic and particulate fractions were used to quantify translocation. Electrophysiology methods were used to measure effects on neuron excitability. RESULTS All submucosal neurons were immunoreactive for the novel PKC, PKCepsilon, and direct PKC activators, phorbol 12,13-dibutyrate, ingenol 3,20-dibenzoate, and the PKCepsilon-specific activator, transactivator of transduction-Psiepsilon receptor for activated C kinase, all caused PKCepsilon translocation from cytoplasm to surfaces of the neurons. Electrophysiologic studies showed that the stimulant of novel PKCs, ingenol (1 micromol/L), increased excitability of all neurons. Stimulation of protease-activated receptors caused PKCepsilon translocation selectively in vasoactive intestinal peptide secretomotor neurons, whereas a neurokinin 3 tachykinin receptor agonist caused translocation in neuropeptide Y and calretinin neurons. In all cases translocation was reduced significantly by a PKCepsilon-specific translocation inhibitor peptide. Increased PKCepsilon at the plasma membrane occurred in all neurons 6-7 days after an inflammatory stimulus. CONCLUSIONS Major targets for PKCepsilon include ion channels near the plasma membrane. PKCepsilon is likely to have a significant role in controlling the excitability of submucosal neurons and is probably an intermediate in causing hyperexcitability after inflammation.
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Affiliation(s)
- Daniel P Poole
- Department of Anatomy and Cell Biology, Centre for Neuroscience, University of Melbourne, Parkville, Victoria, Australia
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Sanger GJ, Tuladhar BR, Bueno L, Furness JB. Defensive and pathological functions of the gastrointestinal NK3 receptor. Vascul Pharmacol 2006; 45:215-20. [PMID: 16901762 DOI: 10.1016/j.vph.2005.08.026] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2005] [Accepted: 08/01/2005] [Indexed: 10/24/2022]
Abstract
In general, normal gut functions are unaffected by selective NK(3) receptor antagonists such as talnetant (SB-223412), osanetant (SR 142901) or SB-235375. However, NK(3) receptors may mediate certain defensive or pathological intestinal processes. The precise mechanisms, by which this role is achieved, are not fully understood. In summary, intense stimulation of the intrinsic primary afferent neurones (IPANs) of the enteric nervous system is thought to release tachykinins from these neurones, to induce slow excitation (slow EPSPs) of connecting IPANs. This is hypothesised to cause hypersensitivity and disrupt intestinal motility, at least partly explaining why NK(3) receptor antagonism can reduce the level of disruption caused by supramaximal distension pressures in vitro. Tachykinin release from IPANs may also increase C-fibre sensitivity, directly or indirectly. Thus, NK(3) receptor antagonists can inhibit nociception associated with intestinal distension, in normal animals or after pre-sensitisation by restraint stress. Importantly, such inhibition has been found with SB-235375, a peripherally restricted antagonist. SB-235375 can also reduce a visceromotor response to brief colorectal distension without affecting similar responses to skin pinch, providing additional evidence for intestinal-specific activity. NK(3) receptor biology is, therefore, revealing a novel pathway by which disruptions in intestinal motility and nociception can be induced.
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Van Nassauw L, Wu M, De Jonge F, Adriaensen D, Timmermans JP. Cytoplasmic, but not nuclear, expression of the neuronal nuclei (NeuN) antibody is an exclusive feature of Dogiel type II neurons in the guinea-pig gastrointestinal tract. Histochem Cell Biol 2005; 124:369-77. [PMID: 16049694 DOI: 10.1007/s00418-005-0019-7] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/12/2005] [Indexed: 01/20/2023]
Abstract
This study aimed to reveal if NeuN, a neuronal nuclei (NeuN) antibody, is a selective marker of intrinsic primary afferent neurons (IPANs) in the guinea-pig gastrointestinal tract as previously hypothesised. The NeuN immunoreactivity was found in the enteric nervous system with exception of the esophagus. Two groups of NeuN-expressing neurons were observed: neurons with immunostained nuclei and cytoplasm (NeuN(NC)) and neurons only expressing immunoreactivity in their nuclei (NeuN(N)). The NeuN(N)-immunoreactive neurons were found in the myenteric plexus of the stomach and the colon. In the stomach, none of the NeuN(N)-expressing neurons, of which 55+/-3% co-expressed calbindin, had a Dogiel type I or II morphology. The NeuN(N)-positive neurons of the colon, which did not express calbindin, did not resemble a Dogiel type II morphology either, but were small-sized neurons. The NeuN(NC)-immunoreactive neurons were observed in both the small and large intestine. These neurons were smooth-contoured and bigger-sized, resembling a Dogiel type II morphology. Some of these neurons co-expressed calbindin. The present data reveal the existence of two populations of Dogiel type II neurons, exhibiting NeuN(NC)+/calbindin+ or NeuN(NC)+/calbindin- immunoreactivity, in the intestine. Assuming that all IPANs exhibit a Dogiel type II morphology, we conclude that the cytoplasmic expression of NeuN is an exclusive feature of IPANs.
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Affiliation(s)
- Luc Van Nassauw
- Laboratory of Cell Biology and Histology, University of Antwerp, Groenenborgerlaan 171, 2020, Antwerp, Belgium
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Patton D, O'Reilly M, Vanner S. Sensory peptide neurotransmitters mediating mucosal and distension evoked neural vasodilator reflexes in guinea pig ileum. Am J Physiol Gastrointest Liver Physiol 2005; 289:G785-90. [PMID: 15976390 DOI: 10.1152/ajpgi.00027.2005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The aim was to determine the role CGRP and/or tachykinins released from sensory neural mechanisms in enteric neural vasodilator pathways. These pathways project through the myenteric plexus to submucosal vasodilator neurons. Submucosal arterioles were exposed in the distal portion of an in vitro combined submucosal-myenteric guinea pig ileal preparation, and dilation was monitored with videomicroscopy. Vasodilator neural reflexes were activated by gently stroking the mucosa with a fine brush or by distending a balloon placed beneath the flat-sheet preparation in the proximal portion. Dilations evoked by mucosal stroking were inhibited 64% by the CGRP 8-37 and 37% by NK3 (SR 142801) antagonists. When the two antagonists were combined with hexamethonium, only a small vasodilation persisted. Balloon distension-evoked vasodilations were inhibited by NK3 antagonists (66%) but were not altered by CGRP 8-37. In preparations in which myenteric descending interneurons were directly activated by electrical stimulation, combined application of CGRP 8-37 and the NK antagonists had no effect. Stimulation of capsaicin sensitive nerves in the myenteric plexus did not activate these vasodilator reflexes. These findings suggest that mucosal-activated reflexes result from the release of CGRP and tachykinins from enteric sensory neurons. Distension-evoked responses were significantly blocked by NK3 antagonists, suggesting that stretch activation of myenteric sensory neurons release tachykinins that activate NK3 receptors on myenteric vasodilator pathways.
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Affiliation(s)
- D Patton
- Gastrointestinal Diseases Research Unit, Queen's University, Kingston, Ontario, Canada K7L 5G2
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De Schepper HU, De Winter BY, Seerden TC, Herman AG, Pelckmans PA, De Man JG. Functional characterisation of tachykinin receptors in the circular muscle layer of the mouse ileum. ACTA ACUST UNITED AC 2005; 130:105-15. [PMID: 15935491 DOI: 10.1016/j.regpep.2005.04.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2005] [Revised: 04/11/2005] [Accepted: 04/11/2005] [Indexed: 11/20/2022]
Abstract
OBJECTIVES Tachykinins are important mediators in neuromuscular signalling but have not been thoroughly characterised in the mouse gut. We investigated the participation of tachykinin receptors in contractility of circular muscle strips of the mouse ileum. RESULTS Electrical field stimulation (EFS) of excitatory nonadrenergic noncholinergic (NANC) nerves induced frequency-dependent contractions which were mimicked by substance P (SP). Desensitisation of SP and NK(1), NK(2) or NK(3) receptors significantly reduced contractions to EFS. The NK(1) receptor blocker RP67580 significantly inhibited NANC contractions to EFS. The NK(2) and NK(3) receptor blockers nepadutant and SR142801 did not affect NANC contractions per se but increased the RP67580-induced inhibition of NANC contractions to EFS. Contractions to SP were significantly reduced by RP67580 but not affected by nepadutant or SR142801. The NK(1) and NK(2) receptor agonists, septide and [beta-ala(8)]-NKA 4-10 (beta-A-NKA), respectively, but not the NK(3) receptor agonist senktide-induced dose-dependent contractions. Atropine inhibited and l-NNA augmented contractions to septide. Contractions to beta-A-NKA were insensitive to atropine but augmented by l-NNA. CONCLUSIONS Tachykinins mediate NANC contractions to EFS in the mouse small intestine. Endogenously released tachykinins activate mainly NK(1) receptors, located on cholinergic nerves and smooth muscle cells and, to a lesser degree, NK(2) and NK(3) receptors, most likely located presynaptically.
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Affiliation(s)
- Heiko U De Schepper
- Division of Gastroenterology, Faculty of Medicine, University of Antwerp, Universiteitsplein 1, Wilrijk B-2610, Belgium
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Abalo R, José Rivera A, Vera G, Isabel Martín M. Ileal myenteric plexus in aged guinea-pigs: loss of structure and calretinin-immunoreactive neurones. Neurogastroenterol Motil 2005; 17:123-32. [PMID: 15670272 DOI: 10.1111/j.1365-2982.2004.00612.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Myenteric plexus controls gastrointestinal motility by means of well organized circuits which are comprised of sensory neurones, interneurones and motor neurones to the muscular layers. Calretinin (CR) is a calcium-binding protein that, in guinea-pig ileum, has only been found in ascending interneurones, which also express neurofilament triplet proteins (NFT), and excitatory longitudinal muscle motor neurones, which do not. In spite of some evidence that age affects both function and structure of the myenteric plexus, little is known about the possible selectivity of the process regarding specific myenteric neuronal phenotypes. The influence of age on both the structure of the myenteric plexus and the presence of CR-immunoreactive (CR-IR) neurones was studied using conventional immunohistochemical procedures applied to ileal whole-mount preparations from guinea-pigs. Both a reduction in ganglionic size and changes in the distribution of neurones inside and outside the ganglia, together with a general neuronal loss were found in preparations from aged guinea-pigs. More interestingly, a relatively more pronounced age-related loss of CR-IR neurones, especially those lacking of NFT expression, was found. Specific myenteric neuronal phenotypes may show differential sensitivity to ageing, and this could, under certain circumstances, alter the functional balance of gastrointestinal motility in aged individuals.
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Affiliation(s)
- Raquel Abalo
- Area Farmacología, Depto. Ciencias de la Salud, Facultad de Ciencias de la Salud, Universidad Rey Juan Carlos, Avda. de Atenas s/n, Alcorcón, Madrid, Spain
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Shafton AD, Bogeski G, Kitchener PD, Lewis VA, Sanger GJ, Furness JB. Effects of the peripherally acting NK receptor antagonist, SB-235375, on intestinal and somatic nociceptive responses and on intestinal motility in anaesthetized rats. Neurogastroenterol Motil 2004; 16:223-31. [PMID: 15086876 DOI: 10.1111/j.1365-2982.2004.00501.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
We investigated the effects of the selective NK(3) tachykinin receptor antagonist, SB-235375, on noxious signalling from gut and skin and on intestinal motility in anaesthetized rats. We also measured penetrance into brain and spinal cord. Nociceptive responses in reaction to colorectal distension and skin pinch were assessed by recording the electromyogram (EMG) from the external oblique muscle (a visceromotor response). Motility was measured by recording intraluminal pressure waves during changes in baseline pressure in the jejunum. Colorectal compliance was assessed by measuring luminal pressure change during isovolumic distension. SB-235375 (20 mg kg(-1), by i.v. bolus) reduced the EMG response to colorectal distension by over 90%. The reduction was slow at onset, peaked at about 60 min, and lasted for over 2 h. Responses to noxious skin pinch were unchanged. Amplitudes of propulsive waves in the jejunum were slightly reduced, but their frequency of occurrence was unchanged. SB-235375 decreased colorectal compliance by 5-10%. There was undetectable penetration of i.v. SB-235375 into brain or spinal cord. We conclude that SB-235375 acts peripherally to substantially reduce nociceptive signalling from colorectum without affecting noxious signalling from skin and with little effect on intestinal motility.
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Affiliation(s)
- A D Shafton
- Department of Anatomy and Cell Biology and Centre for Neuroscience, University of Melbourne, Parkville, Victoria, Australia
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Sanger GJ. Neurokinin NK1 and NK3 receptors as targets for drugs to treat gastrointestinal motility disorders and pain. Br J Pharmacol 2004; 141:1303-12. [PMID: 15023866 PMCID: PMC1574901 DOI: 10.1038/sj.bjp.0705742] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
NK1 and NK3 receptors do not appear to play significant roles in normal GI functions, but both may be involved in defensive or pathological processes. NK1 receptor antagonists are antiemetic, operating via vagal sensory and motor systems, so there is a need to study their effects on other gastro-vagal functions thought to play roles in functional bowel disorders. Interactions between NK1 receptors and enteric nonadrenergic, noncholinergic motorneurones suggest a need to explore the role of this receptor in disrupted colonic motility. NK1 receptor antagonism does not exert consistent analgesic activity in humans, but similar studies have not been carried out against pain of GI origin, where NK1 receptors may have additional influences on mucosal inflammatory or "irritant" processes. NK3 receptors mediate certain disruptions of intestinal motility. The activity may be driven by tachykinins released from intrinsic primary afferent neurones (IPANs), which induce slow EPSP activity in connecting IPANs and hence, a degree of hypersensitivity within the enteric nervous system. The same process is also proposed to increase C-fibre sensitivity, either indirectly or directly. Thus, NK3 receptor antagonists inhibit intestinal nociception via a "peripheral" mechanism that may be intestine-specific. Studies with talnetant and other selective NK3 receptor antagonists are, therefore, revealing an exciting and novel pathway by which pathological changes in intestinal motility and nociception can be induced, suggesting a role for NK3 receptor antagonism in irritable bowel syndrome.
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Affiliation(s)
- Gareth J Sanger
- Gastrointestinal Research Department, Neurology-Gastroenterology CEDD, GlaxoSmithKline, Harlow, Essex, CM19 5AW, UK.
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Johnson PJ, Bornstein JC. Neurokinin-1 and -3 receptor blockade inhibits slow excitatory synaptic transmission in myenteric neurons and reveals slow inhibitory input. Neuroscience 2004; 126:137-47. [PMID: 15145080 DOI: 10.1016/j.neuroscience.2004.03.021] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/18/2004] [Indexed: 11/24/2022]
Abstract
Recent studies have shown that tachykinins mediate slow synaptic transmission to myenteric AH (afterhyperpolarising) neurons via neurokinin-3 receptors (NK(3)R). This study investigated a similar role for neurokinin-1 receptors (NK(1)R) and compared the effect of selective receptor antagonists on non-cholinergic slow excitatory post-synaptic potentials (EPSPs) recorded in myenteric AH neurons of the guinea-pig ileum. Slow EPSPs evoked by electrical stimulation of circumferentially oriented presynaptic nerves were mimicked by application of senktide, an NK(3)R agonist. [Sar(9),Met(O(2))(11)]-substance P, an NK(1)R agonist, depolarised a smaller number of neurons. SR142801, a selective NK(3)R antagonist (100 nM), inhibited slow EPSPs and responses to senktide, but had no effect on depolarisations evoked by forskolin, an activator of adenylate cyclase. SR140333, a selective NK(1)R antagonist, inhibited slow EPSPs in a subset of neurons and blocked responses to [Sar(9),Met(O(2))(11)]-substance P, but not to senktide or forskolin. Slow EPSPs that were predominantly mediated by NK(1)R had significantly shorter latencies than those due to activation of NK(3)R. After blockade of slow EPSPs, slow hyperpolarizing responses to presynaptic nerve stimulation were revealed in one-third of neurons. These events, which were associated with a decrease in input resistance and blocked by tetrodotoxin, were equated with slow inhibitory postsynaptic potentials. They were abolished by the 5-hydroxytryptamine(1A) receptor antagonist 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl]-piperazine (NAN-190), but unaffected by phentolamine, an alpha-adrenoceptor antagonist. In conclusion, these results provide the first direct evidence that NK(1)R mediate some slow excitatory synaptic input to myenteric AH neurons, and suggest that NK(1)R and NK(3)R activate distinct signal transduction pathways. These results also demonstrate that slow inhibitory synaptic transmission, which may be mediated by 5-hydroxytryptamine, is more prevalent in the myenteric plexus than previously indicated.
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Affiliation(s)
- P J Johnson
- Department of Physiology, University of Melbourne, Parkville, Victoria 3010, Australia.
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Abstract
Fluorescent molecules bound to receptors can show their location and, if binding is reversible, can provide pharmacological information such as affinity and proximity between interacting molecules. The spatial precision offered by visualisation transcends the diverse localisation and low molecular concentration of receptor molecules. Consequently, the relationships between receptor location and function and life cycles of receptors have become better understood as a result of fluorescent labeling. Each of these aspects contributes new insights to drug action and potential new targets. The relationships between spatial distribution of receptor and function are largely unknown. This is particularly apparent for native receptors expressed in their normal host tissues where communication between heterogeneous cell types influences receptor distribution and function. In cultured cell systems, particularly for G-protein-coupled receptors (GPCR), fluorescence-based methods have enabled the visualisation of the cycle of agonist-stimulated receptor clustering, endocytic internalisation to the perinuclear region, degradation of the receptor-ligand complex, and recycling back to the surface membrane. Using variant forms of green fluorescent protein (GFP), antibodies, or fluorescent ligands, it is possible to detect or visualise the formation of oligomeric receptor complexes. Careful selection of fluorescent molecules based on their spectral properties enables resonance energy transfer and multilabel visualisation with colocalisation studies. Fluorescent agonist and antagonist ligands are now being used in parallel with GFP to study receptor cycling in live cells. This review covers how labeling and visualisation technologies have been applied to the study of major pharmacologically important receptors and illustrates this by giving examples of recent techniques that have relied on GFP, antibodies, or fluorescent ligands alone or in combination for the purpose of studying GPCR.
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Affiliation(s)
- Craig J Daly
- Faculty of Biomedical and Life Sciences, Division of Neuroscience and Biomedical Systems, University of Glasgow, Wolfson Building (Office 448), West Medical Building (Lab 440), University Avenue, G12 8QQ, Glasgow, UK.
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St John JA, Clarris HJ, McKeown S, Royal S, Key B. Sorting and convergence of primary olfactory axons are independent of the olfactory bulb. J Comp Neurol 2003; 464:131-40. [PMID: 12898607 DOI: 10.1002/cne.10777] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Primary olfactory axons expressing the same odorant receptor gene sort out and converge to fixed sites in the olfactory bulb. We examined the guidance of axons expressing the P2 odorant receptor when they were challenged with different cellular environments in vivo. In the mutant extratoes mouse, the olfactory bulb is lacking and is replaced by a fibrocellular mass. In these animals, primary olfactory axons form glomerular-like loci despite the absence of normal postsynaptic targets. P2 axons are able to sort out from other axons in this fibrocellular mass and converge to form loci of like axons. The sites of these loci along mediolateral and ventrodorsal axes were highly variable. Similar convergence was observed for larger subpopulations of axons expressing the same cell surface carbohydrates. The sorting out and convergence of like axons also occurred during regeneration following bulbectomy. Olfactory axon behaviour in these models demonstrates that sorting and convergence of axons are independent of the target, which instead provides distinct topographic cues for guidance.
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Affiliation(s)
- James A St John
- Department of Anatomy and Developmental Biology, School of Biomedical Sciences, University of Queensland, Brisbane, Queensland 4072, Australia
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26
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Affiliation(s)
- J C McGrath
- Autonomic Physiology Unit, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland.
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Coutts AA, Irving AJ, Mackie K, Pertwee RG, Anavi-Goffer S. Localisation of cannabinoid CB(1) receptor immunoreactivity in the guinea pig and rat myenteric plexus. J Comp Neurol 2002; 448:410-22. [PMID: 12115703 DOI: 10.1002/cne.10270] [Citation(s) in RCA: 121] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Activation of cannabinoid CB(1) receptors inhibits gastrointestinal motility, propulsion, and transit, whereas selective antagonism of these receptors has the opposite effects, suggesting the presence of endocannabinoid tone. Supporting evidence for presynaptic CB(1) receptors on myenteric neurons has been found in vitro. In this study, selective CB(1) receptor antibodies and neuronal markers were used to identify and characterise myenteric neurons expressing cannabinoid receptors. Whole mounts of rat and guinea pig myenteric preparations were dually labelled with antibodies against the CB(1) receptor and choline acetyltransferase, neurofilament proteins, calbindin, calretinin, synapsin I, microtubule-associated protein-2, calcitonin gene-related peptide, or substance P. The pattern of CB(1) receptor labelling and the neurochemical classification of CB(1) receptor-positive cells were markedly influenced by the species and fixation procedure. Virtually all choline acetyltransferase-immunoreactive myenteric neurons expressed CB(1) receptors in ganglia from both species. Subpopulations of neurons identified with calbindin, calretinin, and microtubule-associated protein-2 did not express CB(1) receptors. A few calcitonin gene-related peptide- and substance P-positive somata coexpressed CB(1) receptor immunoreactivity but showed little colocalisation on individual fibres. There was a close association between CB(1) receptor immunoreactivity and fibres labelled for synaptic protein, suggesting a role in the modulation of transmitter release. Functional responses to cannabinoids in the presence of hexamethonium suggest further that CB(1) receptors occur on excitatory motoneurons. In conclusion, CB(1) receptors are expressed on a variety of cholinergic sensory, interneuronal, and motor neurons in myenteric ganglia.
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Affiliation(s)
- Angela A Coutts
- Department of Biomedical Sciences, University of Aberdeen, Aberdeen, Scotland AB25 2ZD, United Kingdom.
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Furness JB, Kumano K, Larsson H, Murr E, Kunze WAA, Vogalis F. Sensitization of enteric reflexes in the rat colon in vitro. Auton Neurosci 2002; 97:19-25. [PMID: 12036182 DOI: 10.1016/s1566-0702(02)00003-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
We have investigated sensitization of reflexes in the isolated rat colon in order to develop a model that might prove useful for investigating how the sensitivity of enteric reflexes can be altered by prior stimulation. Records were taken of circular muscle tension, 7-10 mm oral and anal to radial distension exerted by a hook passed through the wall of the colon. A test stimulus of 1.5 g produced consistent contractions both oral and anal to the distension. A conditioning protocol, consisting of repeated application of 3 g for 30 s with 30 s between the stimuli for 30 min, doubled the amplitudes of reflex contractions that were evoked by the test stimuli but did not change the sensitivity of the muscle to the direct action of carbachol. The enhanced responses persisted for at least 40 min. The enhancement of reflexes was not reduced by antagonists of tachykinin NK3 receptors or of 5-HT3 receptors, but the reflex oral to stimulation was reduced by NK1 and NK3 antagonists added together. Sensitization was abolished by the cyclo-oxygenase and thromboxane synthase inhibitor, indomethacin. We conclude that sensitization can be reliably induced in vitro and that the model described in the present work can be used to investigate drugs that interfere with the sensitization process.
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Affiliation(s)
- John B Furness
- Department of Anatomy and Cell Biology, University of Melbourne, Parkville VIC, Australia.
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Lin Z, Gao N, Hu HZ, Liu S, Gao C, Kim G, Ren J, Xia Y, Peck OC, Wood JD. Immunoreactivity of Hu proteins facilitates identification of myenteric neurones in guinea-pig small intestine. Neurogastroenterol Motil 2002; 14:197-204. [PMID: 11975720 DOI: 10.1046/j.1365-2982.2002.00317.x] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Hu proteins, together with neurone-specific enolase (NSE), protein gene product 9.5 (PGP-9.5), microtubule-associated protein-2 (MAP-2) and tubulin beta III isoform, were evaluated immunohistochemically as neuronal markers in whole-mount preparations and cultures obtained from the myenteric plexus of guinea-pig small intestine. Anti-Hu immunostaining marked the ganglion cell somas and nuclei without staining of the neuronal processes in the whole-mounts and cultures. The ganglion cell bodies were not obscured by staining of multiple neuronal fibres and this facilitated accurate counting of the neurones. MAP2 immunostaining also provided clear images of individual neurones in both whole mounts and cultures. Immunoreactivity for NSE, PGP-9.5 and tubulin beta III isoform provided sharp images of the ganglion cells in culture, but not in whole-mount preparations. Strong staining of the neuronal processes in the whole-mount preparations obscured the profiles of the ganglion cell bodies to such an extent that accurate counting of the total neuronal population was compromised. Anti-Hu immunostaining was judged to be an acceptable method for obtaining reliable estimates of total numbers of myenteric neurones in relation to other specific histochemical properties such as histamine binding.
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Affiliation(s)
- Z Lin
- Department of Physiology and Cell Biology, College of Medicine and Public Health, The Ohio State University, Columbus, Ohio 43210, USA
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30
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Hu HZ, Gao N, Lin Z, Gao C, Liu S, Ren J, Xia Y, Wood JD. Chemical coding and electrophysiology of enteric neurons expressing neurofilament 145 in guinea pig gastrointestinal tract. J Comp Neurol 2001. [DOI: 10.1002/cne.1424] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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31
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Holzer P, Holzer-Petsche U. Tachykinin receptors in the gut: physiological and pathological implications. Curr Opin Pharmacol 2001; 1:583-90. [PMID: 11757813 DOI: 10.1016/s1471-4892(01)00100-x] [Citation(s) in RCA: 107] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The tachykinins substance P and neurokinin A participate in the regulation of gastrointestinal motility, secretion, vascular permeability and pain sensitivity. Advances made during the past two years corroborate a causal involvement of tachykinins in inflammation-induced disturbances of gut function, such as dysmotility, secretory diarrhoea, oedema and hyperalgesia. It would therefore appear that tachykinin receptors, which in the digestive system are expressed in a cell-specific manner, represent attractive targets for novel therapeutics in gastroenterology.
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Affiliation(s)
- P Holzer
- Department of Experimental and Clinical Pharmacology, University of Graz, Austria.
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Alex G, Kunze WA, Furness JB, Clerc N. Comparison of the effects of neurokinin-3 receptor blockade on two forms of slow synaptic transmission in myenteric AH neurons. Neuroscience 2001; 104:263-9. [PMID: 11311548 DOI: 10.1016/s0306-4522(01)00064-1] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
AH neurons are intrinsic sensory neurons of the intestine that exhibit two types of slow synaptic event: slow excitatory postsynaptic potentials which increase their excitability for about 2-4 min, and sustained slow postsynaptic excitation which can persist for several hours, and may be involved in long-term changes in the sensitivity of the intestine to sensory stimuli. The effects of the neurokinin-3 tachykinin receptor antagonist, SR142801, on these two types of synaptic event in AH neurons of the myenteric ganglia of guinea-pig small intestine were compared. Slow excitatory postsynaptic potentials were evoked by stimulation of synaptic inputs at 10-20 Hz for 1s, and sustained slow postsynaptic excitation was evoked by stimulation of inputs at 1Hz for 4 min. SR142801 (1microM) reduced the amplitude of the slow excitatory postsynaptic potential to 26% of control, and also reduced the increase in input resistance and the extent of anode break excitation associated with the slow excitatory postsynaptic potential. In contrast, SR142801 did not reduce the increase in excitability, the increase in input resistance or the depolarisation that occur during the sustained slow postsynaptic excitation. SR142801 did not change the resting membrane potential or the resting input resistance. We conclude that tachykinins, acting through neurokinin-3 receptors, are involved in the generation of the slow excitatory postsynaptic potential, but not in the sustained slow postsynaptic excitation, and that the release of transmitters from synaptic inputs to AH neurons is frequency coded.
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Affiliation(s)
- G Alex
- Department of Anatomy and Cell Biology, University of Melbourne, VIC 3052, Parkville, Australia
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Portbury AL, Grkovic I, Young HM, Furness JB. Relationship between postsynaptic NK(1) receptor distribution and nerve terminals innervating myenteric neurons in the guinea-pig ileum. THE ANATOMICAL RECORD 2001; 263:248-54. [PMID: 11455533 DOI: 10.1002/ar.1088] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The amounts of neurokinin 1 (NK(1)) receptor immunolabelling on the membranes of myenteric cell bodies at appositions with tachykinin-immunoreactive nerve terminals, other nerve terminals, and glial cells were compared at the ultrastructural level using pre-embedding, double-label immunocytochemistry. NK(1) receptor immunoreactivity was revealed using silver-intensified, 1 nm gold, and tachykinin-immunoreactive nerve terminals were revealed using diaminobenzidine. The density of NK(1) receptor immunolabelling (silver particles per length of cell membrane) on the membrane at appositions with tachykinin-immunoreactive nerve terminals was not significantly different from that at appositions with other (nonimmunoreactive) nerve terminals or with glial cells. Synaptic specializations ("active zones") were present at a small proportion of the appositions between NK(1) receptor-immunoreactive cell bodies and tachykinin-immunoreactive or other nerve terminals. The density of NK(1) receptor immunolabelling at synaptic specializations was lower than that at regions of appositions where no synaptic specializations were present. The presence of NK(1) receptor on the cell surface in areas not directly apposed to tachykinin-containing nerve terminals suggests that tachykinins that diffuse away from their site of release may still exert an action via NK(1) receptors. Although NK(1) receptors do not appear to be targetted to particular sites on the surfaces of myenteric nerve cell bodies and proximal dendrites, they are reduced in density at regions of the membrane-forming synaptic specializations.
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Affiliation(s)
- A L Portbury
- Department of Anatomy and Cell Biology, University of Melbourne, 3010, VIC, Australia
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Southwell BR, Furness JB. Immunohistochemical demonstration of the NK(1) tachykinin receptor on muscle and epithelia in guinea pig intestine. Gastroenterology 2001; 120:1140-51. [PMID: 11266378 DOI: 10.1053/gast.2001.23251] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
BACKGROUND AND AIMS Previous immunohistochemical studies failed to reveal neurokinin (NK)(1) tachykinin receptors on intestinal muscle, despite convincing pharmacologic data indicating their presence. This study aimed to apply optimal immunohistochemical methods to reveal the receptors. METHODS NK(1)-receptor immunoreactivity was examined by confocal microscopy in tissue incubated with or without 10(-7) mol/L substance P (SP), 10(-7) mol/L SP plus 10(-6) mol/L NK(1) receptor antagonist (CP99994), or with fluorescent cyanine 3.18 (Cy3) SP. RESULTS Without incubation, NK(1)-receptor immunoreactivity was strong on muscle of the rectum and distal colon and weak in proximal colon and small intestine. NK(1) receptor was located on the surface of muscle cells in all gut regions. Exposure to SP increased the intensity of immunoreactivity, and the receptor moved into the cytoplasm. Mobilization of the receptor by SP was blocked by the NK(1)-receptor antagonist CP99994. Cy3-SP was internalized by muscle cells and colocalized with the receptor. NK(1)-receptor immunoreactivity occurred on crypt epithelial cells in the small intestine and the base of glands in the proximal colon. CONCLUSIONS The NK(1) receptor occurs on the external muscle throughout the small and large intestines. SP binds and triggers NK(1)-receptor aggregation and internalization in the muscle.
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MESH Headings
- Animals
- Carbocyanines/metabolism
- Carbocyanines/pharmacology
- Colon/cytology
- Colon/innervation
- Endocytosis/drug effects
- Epithelial Cells/chemistry
- Epithelial Cells/metabolism
- Female
- Fluorescent Dyes/metabolism
- Fluorescent Dyes/pharmacology
- Guinea Pigs
- Immunohistochemistry
- Intestinal Mucosa/chemistry
- Intestinal Mucosa/cytology
- Intestinal Mucosa/innervation
- Intestine, Small/cytology
- Intestine, Small/innervation
- Male
- Muscle, Smooth/chemistry
- Muscle, Smooth/innervation
- Nerve Fibers/chemistry
- Neurokinin-1 Receptor Antagonists
- Piperidines/pharmacology
- Receptors, Neurokinin-1/analysis
- Receptors, Neurokinin-1/metabolism
- Receptors, Neurokinin-2/analysis
- Receptors, Neurokinin-2/metabolism
- Receptors, Neurokinin-3/analysis
- Receptors, Neurokinin-3/metabolism
- Rectum/drug effects
- Rectum/physiology
- Substance P/pharmacology
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Affiliation(s)
- B R Southwell
- Department of Gastroenterology, Murdoch Children's Research Institute, Parkville, Victoria 3052, Australia.
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Tonini M, Spelta V, De Ponti F, De Giorgio R, D'Agostino G, Stanghellini V, Corinaldesi R, Sternini C, Crema F. Tachykinin-dependent and -independent components of peristalsis in the guinea pig isolated distal colon. Gastroenterology 2001; 120:938-45. [PMID: 11231947 DOI: 10.1053/gast.2001.22526] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
BACKGROUND & AIMS In the intestine, tachykinins regulate motility by participating in neuromuscular and neuro-neuronal transmission. The aim of this study was to test the hypothesis that colonic propulsion is regulated by an interplay between tachykinergic and cholinergic transmission. METHODS Propulsion was elicited by intraluminal distention of a thin rubber balloon, which traveled from the oral to the anal end of guinea pig isolated distal colon segments. The overall contribution of endogenous tachykinins to colonic propulsion was examined by blocking NK1, NK2, and NK3 receptors simultaneously. RESULTS NK2-receptor blockade by MEN 11420 inhibited propulsion, whereas blockade of NK(1) by SR 140333 or of NK3 receptors by SR 142801 had minor effects on motility. Blockade of muscarinic or nicotinic receptors by hyoscine or hexamethonium decelerated peristalsis up to propulsion arrest. In the presence of partial muscarinic receptor blockade, the NK1-receptor antagonist SR 140333 and the NK2-receptor antagonist MEN 11420 markedly inhibited propulsion. Propulsion was also inhibited by the NK3-receptor antagonist SR 142801 in the presence of partial nicotinic receptor blockade. The simultaneous administration of the 3 tachykinin antagonists inhibited propulsion by 50%. CONCLUSIONS This study demonstrates the existence of an interplay between tachykinergic and cholinergic pathways during peristalsis and the importance of endogenous tachykinins acting at multiple receptor sites in the control of colonic propulsion.
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Affiliation(s)
- M Tonini
- Department of Internal Medicine and Therapeutics, Division of Clinical and Experimental Pharmacology, University of Pavia, Italy.
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Jenkinson KM, Mann PT, Southwell BR, Furness JB. Independent endocytosis of the NK(1) and NK(3) tachykinin receptors in neurons of the rat myenteric plexus. Neuroscience 2001; 100:191-9. [PMID: 10996469 DOI: 10.1016/s0306-4522(00)00259-1] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In the myenteric plexus of rat ileum, NK(1) and NK(3) receptors are co-located almost exclusively on neurons of a single population. This study compares endocytosis of NK(1) and NK(3) receptors in these neurons. In the absence of agonist, 26.2+/-2.8% of NK(1) receptor and 29.1+/-1.1% of NK(3) receptor was located in the cytoplasm of the neurons; the remaining receptor was on the surface. The tachykinin neurotransmitters, substance P (10 pM-10 microM) and neurokinin A (10 pM-100 microM), both induced concentration-dependent endocytosis of NK(1) and NK(3) receptors. The selective NK(1) receptor agonist, [Sar(9),Met(O(2))(11)]-substance P (1 microM), induced endocytosis of NK(1) receptor (64.2+/-1.5% in cytoplasm) but not NK(3) receptor (32.9+/-5.0%). The NK(1) receptor endocytosis was reduced by the selective NK(1) receptor antagonist, CP-99994 (100 nM), but not by the selective NK(3) receptor antagonist, SR-142801 (1 microM). The selective NK(3) receptor agonist, senktide (10 nM), induced endocytosis of NK(3) receptor (61.2+/-5.4%) but not NK(1) receptor (34.0+/-4.5%). The NK(3) receptor endocytosis was blocked by SR-142801 but not by CP-99994. We also investigated the effects of monensin, which generally blocks recycling of endocytosed receptor. In the absence or presence of exogenous agonist, monensin caused a build-up of NK(1) receptor, but not NK(3) receptor, in the cytoplasm of neurons.The results demonstrate independent, agonist-induced endocytosis of NK(1) and NK(3) receptors in neurons of the myenteric plexus of rat ileum and suggest that the mechanisms of recycling of NK(1) and NK(3) receptors differ.
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Affiliation(s)
- K M Jenkinson
- Department of Anatomy and Cell Biology, University of Melbourne, 3010, Victoria, Australia.
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Bian X, Bertrand PP, Bornstein JC. Descending inhibitory reflexes involve P2X receptor-mediated transmission from interneurons to motor neurons in guinea-pig ileum. J Physiol 2000; 528:551-60. [PMID: 11060131 PMCID: PMC2270162 DOI: 10.1111/j.1469-7793.2000.00551.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
The role of P2X receptors in descending inhibitory reflexes evoked by distension or mucosal distortion in the guinea-pig ileum was studied using intracellular recording from the circular muscle in a two-chambered organ bath. This allowed separate superfusion of the sites of reflex stimulation and recording, thereby allowing drugs to be selectively applied to different parts of the reflex pathway. Inhibitory junction potentials (IJPs) evoked by electrical field stimulation (EFS) in the recording chamber were compared with those evoked during reflexes to control for effects of P2 receptor antagonists on neuromuscular transmission. The P2 receptor antagonists suramin (100 microM) and pyridoxal phosphate-6-azophenyl-2',4'-disulphonic acid (10 and 60 microM; PPADS), when added to the recording chamber, depressed reflexly evoked IJPs significantly more than those evoked by EFS. In particular, 10 microM PPADS depressed IJPs evoked by distension or mucosal distortion by about 50 %, but had little effect on IJPs evoked by EFS. Blockade of synaptic transmission in the stimulation chamber with a low Ca2+-high Mg2+ solution depressed, but did not abolish, IJPs evoked by distension. The residual reflex IJPs were unaffected by PPADS (10 microM), hyoscine (1 microM), hyoscine plus hexamethonium (200 microM), or hysocine plus hexamethonium plus PPADS in the recording chamber. We conclude that P2X receptors are important for synaptic transmission from descending interneurons to inhibitory motor neurons in descending inhibitory reflex pathways of guinea-pig ileum. Transmission from anally directed axons of distension-sensitive intrinsic sensory neurons to inhibitory motor neurons is unlikely to involve P2X, muscarinic or nicotinic receptors.
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Affiliation(s)
- X Bian
- Department of Physiology, University of Melbourne, Parkville, Victoria 3010, Australia.
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Schneider DA, Galligan JJ. Presynaptic nicotinic acetylcholine receptors in the myenteric plexus of guinea pig intestine. Am J Physiol Gastrointest Liver Physiol 2000; 279:G528-35. [PMID: 10960351 DOI: 10.1152/ajpgi.2000.279.3.g528] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Presynaptic nicotinic acetylcholine receptors (nAChRs) were studied in myenteric plexus preparations from guinea pig ileum using intracellular electrophysiological methods. Microapplication of nicotine (1 mM) caused a biphasic depolarization in all AH neurons (n = 30) and in 36 of 49 S neurons. Cytisine (1 mM) caused fast depolarizations in S neurons and no response in AH neurons. Mecamylamine (10 microM) blocked all responses caused by nicotine and cytisine. TTX (0.3 microM) blocked slow excitatory synaptic potentials in S and AH neurons but had no effect on fast depolarizations caused by nicotine. Nicotine-induced slow depolarizations were reduced by TTX in two of twelve AH neurons (79% inhibition) and four of nine S neurons (90+/-12% inhibition). Slow nicotine-induced depolarizations in the remaining neurons were TTX resistant. TTX-resistant slow depolarizations were inhibited after neurokinin receptor 3 desensitization caused by senktide (0.1 microM); senktide desensitization inhibited the slow nicotine-induced depolarization by 81+/-5% and 63+/-15% in AH and S neurons, respectively. A low-calcium and high-magnesium solution blocked nicotine-induced slow depolarizations in AH neurons. In conclusion, presynaptic nAChRs mediate the release of substance P and/or neurokinin A to cause slow depolarizations of myenteric neurons.
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Affiliation(s)
- D A Schneider
- Department of Pharmacology and Toxicology and Neuroscience Program, Michigan State University, East Lansing, Michigan 48824-1317, USA
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