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Emerging effects of tryptophan pathway metabolites and intestinal microbiota on metabolism and intestinal function. Amino Acids 2022; 54:57-70. [PMID: 35038025 DOI: 10.1007/s00726-022-03123-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2021] [Accepted: 01/03/2022] [Indexed: 12/14/2022]
Abstract
The metabolism of dietary tryptophan occurs locally in the gut primarily via host enzymes, with ~ 5% metabolized by gut microbes. Three major tryptophan metabolic pathways are serotonin (beyond the scope of this review), indole, kynurenine and related derivatives. We introduce the gut microbiome, dietary tryptophan and the potential interplay of host and bacterial enzymes in tryptophan metabolism. Examples of bacterial transformation to indole and its derivative indole-3 propionic acid demonstrate associations with human metabolic disease and gut permeability, although causality remains to be determined. This review will focus on less well-known data, suggestive of local generation and functional significance in the gut, where kynurenine is converted to kynurenic acid and xanthurenic acid via enzymatic action present in both host and bacteria. Our functional data demonstrate a limited effect on intestinal epithelial cell monolayer permeability and on healthy mouse ileum. Other data suggest a modulatory effect on the microbiome, potentially in pathophysiology. Supportive of this, we found that the expression of mRNA for three kynurenine pathway enzymes were increased in colon from high-fat-fed mice, suggesting that this host pathway is perturbed in metabolic disease. These data, along with that from bacterial genomic analysis and germ-free mice, confirms expression and functional machinery of enzymes in this pathway. Therefore, the host and microbiota may play a significant dual role in either the production or regulation of these kynurenine metabolites which, in turn, can influence both host and microbiome, especially in the context of obesity and intestinal permeability.
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Neale JH, Yamamoto T. N-acetylaspartylglutamate (NAAG) and glutamate carboxypeptidase II: An abundant peptide neurotransmitter-enzyme system with multiple clinical applications. Prog Neurobiol 2019; 184:101722. [PMID: 31730793 DOI: 10.1016/j.pneurobio.2019.101722] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2019] [Revised: 09/24/2019] [Accepted: 11/11/2019] [Indexed: 12/13/2022]
Abstract
N-Acetylaspartylglutamate (NAAG) is the third most prevalent neurotransmitter in the mammalian nervous system, yet its therapeutic potential is only now being fully recognized. Drugs that inhibit the inactivation of NAAG by glutamate carboxypeptidase II (GCPII) increase its extracellular concentration and its activation of its receptor, mGluR3. These drugs warrant attention, as they are effective in animal models of several clinical disorders including stroke, traumatic brain injury and schizophrenia. In inflammatory and neuropathic pain studies, GCPII inhibitors moderated both the primary and secondary pain responses when given systemically, locally or in brain regions associated with the pain perception pathway. The finding that GCPII inhibition also moderated the motor and cognitive effects of ethanol intoxication led to the discovery of their procognitive efficacy in long-term memory tests in control mice and in short-term memory in a mouse model of Alzheimer's disease. NAAG and GCPII inhibitors respectively reduce cocaine self-administration and the rewarding effects of a synthetic stimulant. Most recently, GCPII inhibition also has been reported to be efficacious in a model of inflammatory bowel disease. GCPII was first discovered as a protein expressed by and released from metastatic prostate cells where it is known as prostate specific membrane antigen (PSMA). GCPII inhibitors with high affinity for this protein have been developed as prostate imaging and radiochemical therapies for prostate cancer. Taken together, these data militate in favor of the development and application of GCPII inhibitors in more advanced preclinical research as a prelude to clinical trials.
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Affiliation(s)
- Joseph H Neale
- Department of Biology, Georgetown University, 37(th) and O Sts., NW, Washington, DC, 20057, USA.
| | - Tatsuo Yamamoto
- Dept. of Anesthesiology, Kumamoto University., Kumamoto, Japan
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Differential effects of R-isovaline and the GABA B agonist, baclofen, in the guinea pig ileum. Eur J Pharmacol 2016; 791:85-90. [PMID: 27521870 DOI: 10.1016/j.ejphar.2016.08.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Revised: 08/02/2016] [Accepted: 08/03/2016] [Indexed: 11/22/2022]
Abstract
R-isovaline is a non-proteinogenic amino acid which produces analgesia in a range of nociceptive assays. Mediation of this effect by metabotropic receptors for γ-aminobutyric acid (GABA) and glutamate, demonstrated by previous work, may depend on the type of tissue or receptor system. The objective of this study was to assess the activity of R-isovaline acting at GABAB and group II metabotropic glutamate receptors in guinea pig ileum, which is known to exhibit well-defined responses to GABAB agonists such as baclofen. The effects of bath-applied R-isovaline and RS-baclofen were examined on electrically evoked contractions of guinea pig ileum and during GABAB antagonism by CGP52432. In separate experiments, the group II metabotropic glutamate receptor agonist, LY354740 was applied to determine the functional presence of these receptors. R-isovaline (1-100mM) decreased the amplitude of ileal muscle contractions and increased tension. RS-baclofen reduced contraction amplitude, but decreased tension. CGP52432 did not prevent the effects of R-isovaline on contraction amplitude, but antagonized effects of RS-baclofen on contraction amplitude. The group II metabotropic glutamate receptor agonist, LY354740, produced no detectable effects on evoked contractions. R-isovaline differed significantly from RS-baclofen in its actions in the guinea pig ileum, indicated in particular by the finding that CGP52432 blocked only the effects of RS-baclofen. The ileal tissue did not respond to a group II metabotropic glutamate receptor agonist, previously shown to co-mediate R-isovaline analgesia. These findings raise the possibility of a novel therapeutic target at unknown receptors for R-isovaline-like compounds in the guinea pig ileum.
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Filpa V, Moro E, Protasoni M, Crema F, Frigo G, Giaroni C. Role of glutamatergic neurotransmission in the enteric nervous system and brain-gut axis in health and disease. Neuropharmacology 2016; 111:14-33. [PMID: 27561972 DOI: 10.1016/j.neuropharm.2016.08.024] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Revised: 07/18/2016] [Accepted: 08/18/2016] [Indexed: 02/07/2023]
Abstract
Several studies have been carried out in the last 30 years in the attempt to clarify the possible role of glutamate as a neurotransmitter/neuromodulator in the gastrointestinal tract. Such effort has provided immunohistochemical, biomolecular and functional data suggesting that the entire glutamatergic neurotransmitter machinery is present in the complex circuitries of the enteric nervous system (ENS), which participates to the local coordination of gastrointestinal functions. Glutamate is also involved in the regulation of the brain-gut axis, a bi-directional connection pathway between the central nervous system (CNS) and the gut. The neurotransmitter contributes to convey information, via afferent fibers, from the gut to the brain, and to send appropriate signals, via efferent fibers, from the brain to control gut secretion and motility. In analogy with the CNS, an increasing number of studies suggest that dysregulation of the enteric glutamatergic neurotransmitter machinery may lead to gastrointestinal dysfunctions. On the whole, this research field has opened the possibility to find new potential targets for development of drugs for the treatment of gastrointestinal diseases. The present review analyzes the more recent literature on enteric glutamatergic neurotransmission both in physiological and pathological conditions, such as gastroesophageal reflux, gastric acid hypersecretory diseases, inflammatory bowel disease, irritable bowel syndrome and intestinal ischemia/reperfusion injury.
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Affiliation(s)
- Viviana Filpa
- Department of Clinical and Experimental Medicine, University of Insubria, via H. Dunant 5, I-21100 Varese, Italy
| | - Elisabetta Moro
- Department of Internal Medicine and Therapeutics, Section of Pharmacology, via Ferrata 9, I-27100 Pavia, Italy
| | - Marina Protasoni
- Department of Surgical and Morphological Sciences, University of Insubria, via F. Guicciardini 9, I-21100 Varese, Italy
| | - Francesca Crema
- Department of Internal Medicine and Therapeutics, Section of Pharmacology, via Ferrata 9, I-27100 Pavia, Italy
| | - Gianmario Frigo
- Department of Internal Medicine and Therapeutics, Section of Pharmacology, via Ferrata 9, I-27100 Pavia, Italy
| | - Cristina Giaroni
- Department of Clinical and Experimental Medicine, University of Insubria, via H. Dunant 5, I-21100 Varese, Italy
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Seifi M, Swinny JD. Immunolocalization of AMPA receptor subunits within the enteric nervous system of the mouse colon and the effect of their activation on spontaneous colonic contractions. Neurogastroenterol Motil 2016; 28:705-20. [PMID: 26867789 DOI: 10.1111/nmo.12768] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/17/2015] [Accepted: 12/08/2015] [Indexed: 12/14/2022]
Abstract
BACKGROUND The appropriate expression of specific neurotransmitter receptors within the cellular networks that compose the enteric nervous system (ENS) is central to the regulation of gastrointestinal (GI) functions. While the ENS expression patterns of the neurotransmitter glutamate have been well documented, the localization of its receptors on ENS neurons remains to be fully characterized. We investigated the expression patterns of glutamate receptor AMPA subunits within ENS neurons of the mouse colon and the consequences of their pharmacological activation on spontaneous colonic contractility. METHODS RT-PCR was used to detect individual AMPA receptor (GluR 1-4) subunit expression at the mRNA level in mouse colon tissue. Immunohistochemistry and confocal microscopy was used to localize the expression of the GluR1 and 4 subunits in colon tissue. Brain tissue was used as a positive control. Organ bath preparations were used to determine the effect of AMPA receptors activation on the force and frequency of colonic longitudinal smooth muscle spontaneous contractions. KEY RESULTS GluR1, 3, 4 mRNA was detected in the mouse colon. Immunoreactivity for GluR1 and 4 subunits was detected on the somatic and dendritic surfaces of subpopulations of neurochemically defined ENS neurons. The pharmacological activation of AMPA receptors increased the force but not frequency of spontaneous colonic contractions. CONCLUSIONS & INFERENCES Molecularly distinct AMPA receptor subtypes are differentially expressed within the neural networks of the mouse colon and have a direct role in motility. These data provide the rationale for the development of AMPA-selective ligands for the therapeutic delivery to the GIT in motility disorders.
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Affiliation(s)
- M Seifi
- Institute for Biomedical and Biomolecular Sciences, School of Pharmacy and Biomedical Sciences, University of Portsmouth, Portsmouth, UK
| | - J D Swinny
- Institute for Biomedical and Biomolecular Sciences, School of Pharmacy and Biomedical Sciences, University of Portsmouth, Portsmouth, UK
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Julio-Pieper M, Flor PJ, Dinan TG, Cryan JF. Exciting times beyond the brain: metabotropic glutamate receptors in peripheral and non-neural tissues. Pharmacol Rev 2011; 63:35-58. [PMID: 21228260 DOI: 10.1124/pr.110.004036] [Citation(s) in RCA: 139] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Metabotropic glutamate (mGlu) receptors are G-protein-coupled receptors expressed primarily on neurons and glial cells, where they are located in the proximity of the synaptic cleft. In the central nervous system (CNS), mGlu receptors modulate the effects of l-glutamate neurotransmission in addition to that of a variety of other neurotransmitters. However, mGlu receptors also have a widespread distribution outside the CNS that has been somewhat neglected to date. Based on this expression, diverse roles of mGlu receptors have been suggested in a variety of processes in health and disease including controlling hormone production in the adrenal gland and pancreas, regulating mineralization in the developing cartilage, modulating lymphocyte cytokine production, directing the state of differentiation in embryonic stem cells, and modulating gastrointestinal secretory function. Understanding the role of mGlu receptors in the periphery will also provide a better insight into potential side effects of drugs currently being developed for neurological and psychiatric conditions. This review summarizes the new potential roles of mGlu receptors and raises the possibility of novel pharmacological targets for various disorders.
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Affiliation(s)
- Marcela Julio-Pieper
- Laboratory of Neurogastroenterology, Alimentary Pharmabiotic Centre, University College Cork, Cork, Ireland
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Boutry C, Matsumoto H, Airinei G, Benamouzig R, Tomé D, Blachier F, Bos C. Monosodium glutamate raises antral distension and plasma amino acid after a standard meal in humans. Am J Physiol Gastrointest Liver Physiol 2011; 300:G137-45. [PMID: 21030612 DOI: 10.1152/ajpgi.00299.2010] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The consumption of monosodium glutamate (MSG) is advocated to elicit physiological and metabolic effects, yet these effects have been poorly investigated directly in humans and in particular in the postprandial phase. Thirteen healthy adults were supplemented for 6 days with a nutritional dose of MSG (2 g) or sodium chloride (NaCl) as control, following a crossover design. On the 7th day, they underwent a complete postprandial examination for the 6 h following the ingestion of the same liquid standard meal (700 kcal, 20% of energy as [(15)N]protein, 50% as carbohydrate, and 30% as fat) supplemented with MSG or NaCl. Real-ultrasound measures of antral area indicated a significant increased distension for the 2 h following the meal supplemented with MSG vs. NaCl. This early postprandial phase was also associated with significantly increased levels of circulating leucine, isoleucine, valine, lysine, cysteine, alanine, tyrosine, and tryptophan after MSG compared with NaCl. No changes to the postprandial glucose, insulin, glucagon-like peptide (GLP)-1, and ghrelin were noted between MSG- and NaCl-supplemented meals. Subjective assessments of hunger and fullness were neither affected by MSG supplementation. Finally, the postprandial fate of dietary N was identical between dietary conditions. Our findings indicate that nutritional dose of MSG promoted greater postprandial elevations of several indispensable amino acids in plasma and induced gastric distension. Further work to elucidate the possible sparing effect of MSG on indispensable amino acid first-pass uptake in humans is warranted. This trial was registered at clinicaltrials.gov as NCT00862017.
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Affiliation(s)
- Claire Boutry
- INRA, Research Center for Human Nutrition-IdF, UMR914, Paris, France
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Julio-Pieper M, Hyland NP, Bravo JA, Dinan TG, Cryan JF. A novel role for the metabotropic glutamate receptor-7: modulation of faecal water content and colonic electrolyte transport in the mouse. Br J Pharmacol 2010; 160:367-75. [PMID: 20423346 DOI: 10.1111/j.1476-5381.2010.00713.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
BACKGROUND AND PURPOSE Increasing evidence implicates metabotropic glutamate receptor mGlu(7) in the pathophysiology of stress-related disorders such as depression and anxiety. Mood disorders are frequently associated with gastrointestinal (GI) dysfunction; however, the role of mGlu(7) receptors outside the CNS is unknown. This present study investigated the expression and possible functional role of mGlu(7) receptors in the mouse colon. EXPERIMENTAL APPROACH Expression of mGlu(7) receptor mRNA and protein was studied in mouse colon by in situ hybridization and Western blotting. Effects of the selective mGlu(7) receptor agonist AMN082 on defecation and faecal parameters were studied in an isolation-induced stress model. AMN082 effects on ion transport and neuronal intracellular signalling were examined via Ussing chambers and calcium imaging. KEY RESULTS mGlu(7) receptor mRNA and protein were highly expressed in colon mucosa. Stress-induced faecal output was unaffected by AMN082, although faecal water content was increased. In mucosa/submucosa preparations, 100 nM and 1 microM AMN082 increased bethanechol-induced changes in short-circuit current in the Ussing chamber. This was sensitive to tetrodotoxin. Also, 100 nM AMN082 significantly increased calcium signalling in a subset of submucosal neurons. CONCLUSIONS AND IMPLICATIONS Activating mGlu(7) receptors increased colonic secretory function in vivo and ex vivo. In a group of submucosal neurons, AMN082 strongly induced calcium signalling and the presence of submucosal nerves was required for the AMN082-dependent increase in secretion. These data suggest that targeting mGlu(7) receptors may be useful in the treatment of central components of stress disorders and also stress-associated GI dysfunction such as diarrhoea or constipation.
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Affiliation(s)
- M Julio-Pieper
- Alimentary Pharmabiotic Centre, University College Cork, Ireland
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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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Effects of exogenous glutamate and kainate on electric field-stimulated contractions of isolated human ureter. Urology 2008; 73:1136-9. [PMID: 18400280 DOI: 10.1016/j.urology.2008.02.057] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2007] [Revised: 01/31/2008] [Accepted: 02/19/2008] [Indexed: 11/24/2022]
Abstract
OBJECTIVES A neurotransmitter role for glutamate in the autonomous nervous system was recently demonstrated in the gastrointestinal tract, and its stimulatory effect on spontaneous motility of human ureter was shown. The aim of our study was to investigate the effects of glutamate on the release of neurotransmitters from intramural nerves of the human ureter. METHODS The effects of exogenous glutamate were tested on electric field-stimulated contractions of isolated human ureter, taken from 16 adult patients after nephrectomy. The longitudinal tension and intraluminal pressure of the isolated ureter were recorded simultaneously. The electric field stimulation was done with square wave pulses (20 V through electrodes, 400 mA, duration 1 ms, frequency 16 Hz). The pulse trains lasted for 30 s, a with 30-s pause. RESULTS Glutamate (7.9 x 10(-6) M/L to 10.6 x 10(-3) M/L) and kainic acid (6.3 x 10(-8) M/L to 2.2 x 10(-5) M/L) produced a concentration-dependent decrease in the electric field-stimulated activity of the isolated preparations. However, N-methyl-D-aspartic acid (9.1 x 10(-8) M/L to 3.1 x 10(-5) M/L), (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (7.2 x 10(-8) M/L to 3.2 x 10(-6) M/L) and (+/-)-1-Aminocyclopentane-trans-1,3-dicarboxylic acid (7.7 x 10(-8) M/L to 6.5 x 10(-5) M/L) were ineffective. The electric field-stimulated contractions of isolated ureter were also inhibited by lidocaine (3.70 x 10(-4)M/L) and atropine (1.00 x 10(-6)M/L). CONCLUSIONS The results of our study suggest that glutamate inhibits electric field-stimulated release of acetylcholine in the human ureter through activation of kainate ionotropic receptors, located on the intramural nerve fibers.
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Jankovic SM, Jankovic SV, Stojadinovic D, Jakovljevic M, Milovanovic D. Effect of exogenous glutamate and N-Methyl-D-aspartic acid on spontaneous activity of isolated human ureter. Int J Urol 2007; 14:833-7. [PMID: 17760751 DOI: 10.1111/j.1442-2042.2007.01834.x] [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] [Indexed: 11/27/2022]
Abstract
OBJECTIVES While the neurotransmitter role of glutamate in the gastrointestinal tract has been shown, its effects on smooth muscle of the human ureter have not previously been investigated. In our study we have investigated the effects of exogenous glutamate on the spontaneous activity of isolated human ureter, taken from 14 adult patients after nephrectomy. METHODS The segment of ureter, excised 3 cm distal from the pyeloureteral junction, was isolated in an organ bath. Both longitudinal tension and intraluminal pressure of the segment were recorded simultaneously. RESULTS Glutamate administered in the lumen of the isolated ureteral segments (7.8 x 10(-7) M/L-3.5 x 10(-2) M/L) was ineffective. When added to the isolated organ bath from the serous side of the ureteral segment, glutamate (7.9 x 10(-6) M/L-10.6 x 10(-3) M/L) and N-Methyl-D-aspartic acid (NMDA) (9.1 x 10(-8) M/L-3.1 x 10(-5) M/L) produced a concentration-dependent increase in spontaneous activity of the isolated preparations, while kainic acid (6.3 x 10(-8) M/L-10.5 x 10(-5) M/L) and (+/-)-trans-1-Aminocyclopentane-trans-1,3-dicarboxylic acid (ACPD) (7.7 x 10(-8) M/L -6.5 x 10(-5) M/L) were ineffective. CONCLUSIONS The results of our study suggest that an excitatory neurotransmitter glutamate stimulates spontaneous activity of the human ureter through activation of NMDA ionotropic receptors, located on smooth muscle cells or intramural nerve fibers.
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Affiliation(s)
- Slobodan M Jankovic
- Pharmacology Department, Medical Faculty, University of Kragujevac, Kragujevac, Serbia.
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Raab M, Neuhuber WL. Glutamatergic functions of primary afferent neurons with special emphasis on vagal afferents. INTERNATIONAL REVIEW OF CYTOLOGY 2007; 256:223-75. [PMID: 17241909 DOI: 10.1016/s0074-7696(07)56007-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Glutamate has been identified as the main transmitter of primary afferent neurons. This was established based on biochemical, electrophysiological, and immunohistochemical data from studies on glutamatergic receptors and their agonists/antagonists. The availability of specific antibodies directed against glutamate and, more recently, vesicular glutamate transporters corroborated this and led to significant new discoveries. In particular, peripheral endings of various classes of afferents contain vesicular glutamate transporters, suggesting vesicular storage in and exocytotic release of glutamate from peripheral afferent endings. This suggests that autocrine mechanisms regulate sensory transduction processes. However, glutamate release from peripheral sensory terminals could also enable afferent neurons to influence various cells associated with them. This may be particularly relevant for vagal intraganglionic laminar endings, which could represent glutamatergic sensor-effector components of intramural reflex arcs in the gastrointestinal tract. Thus, morphological analysis of the relationships of putative glutamatergic primary afferents with associated tissues may direct forthcoming studies on their functions.
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Affiliation(s)
- Marion Raab
- Institut für Anatomie, Universität Erlangen-Nürnberg, Erlangen, Germany
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Soares A, Schoffen JPF, De Gouveia EM, Natali MRM. Effects of the neonatal treatment with monosodium glutamate on myenteric neurons and the intestine wall in the ileum of rats. J Gastroenterol 2006; 41:674-80. [PMID: 16933005 DOI: 10.1007/s00535-006-1839-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/10/2006] [Accepted: 04/05/2006] [Indexed: 02/04/2023]
Abstract
BACKGROUND The neonatal administration of a 4 mg/g dose of monosodium glutamate (MSG) to rodents leads to neuronal death in the hypothalamus arcuate nucleus, which leads in turn to obesity in the adult animal. However, few studies have investigated the effects on the enteric nervous system. This study evaluated the effects of the neonatal administration of MSG on the frequency and morphometry of the myenteric as well as the ileum wall morphometry of adult Wistar male rats. METHODS Whole-mount preparations of ileum samples were stained by the Giemsa or NADH-diaphorase histochemical methods. For histological processing, hematoxylin and eosin staining was used. RESULTS The treatment with MSG led to obesity, as shown by the higher values for Lee's index and the weights of periepididimal and retroperitoneal adipose tissues. The Giemsa staining revealed a significantly larger neuronal density in the MSG group, which is explained by smaller physical growth and a reduction in the weight of the small intestine. The mean neuronal profile did not change between groups. The NADH-diaphorase-positive neuronal subpopulation kept its neuronal density but its average cellular profile was reduced in the MSG group. A morphometric analysis of the intestinal wall, muscular layer, villi, and intestinal crypts showed that their characteristics did not change. CONCLUSIONS The treatment with MSG did not cause alteration of the total myenteric population of the ileum, but it influenced the NADH-diaphorase-positive subpopulation. From the maintenance of the morphometric parameters of the ileum intestinal wall, we inferred that intestinal function was preserved in obese animals.
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Affiliation(s)
- Angélica Soares
- Enteric Neurons Laboratory, Department of Morphophysiological Sciences, State University of Maringá, Av. Colombo 5790, Maringá-Paraná, PR, 87020-900, Brazil
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Weiland TJ, Anthony-Harvey-Beavis D, Voudouris NJ, Kent S. Metabotropic glutamate receptors mediate lipopolysaccharide-induced fever and sickness behavior. Brain Behav Immun 2006; 20:233-45. [PMID: 16242909 DOI: 10.1016/j.bbi.2005.08.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/06/2005] [Revised: 08/20/2005] [Accepted: 08/31/2005] [Indexed: 11/18/2022] Open
Abstract
Several mechanisms have been proposed for neuroimmune communication supporting the sickness syndrome (fever, anorexia, inactivity, and cachexia) following infection. We examined the role of glutamate as a neurochemical intermediary of sickness behavior induced by intraperitoneal lipopolysaccharide (LPS). Mice implanted with biotelemetry devices capable of detecting body temperature (Tb) were administered LPS (50 or 500 microg/kg i.p., serotype 0111:B4) with or without i.p. pretreatment with vehicle or broad-spectrum antagonists selective for N-methyl-d-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic (AMPA)/kainite, or metabotropic glutamate (mGlu) receptors. While NMDA and AMPA/kainate receptor antagonism failed to attenuate LPS-induced sickness behavior, antagonism of metabotropic receptors with l(+)-AP3 reduced the febrile (0-11h: control: 37.32+/-0.16 degrees C, l(+)-AP3: 36.66+/-0.27), anorexic (control: -87+/-5%, l(+)-AP3: 48+/-12% scotophase food intake), and cachexic (control: -8.9+/-0.4%, l(+)-AP3: -6.1+/-1.3% body weight) effects of 500 microg/kg LPS, and produced a biphasic Tb effect in response to 50 microg/kg LPS (1h: -0.90+/-0.26; 6h: 1.78+/-0.35 degrees C relative to baseline). At this dose the Tb of l(+)-AP3-treated mice was 1.18 degrees C lower than controls 2h post-injection, and 0.68 degrees C greater that controls 8h post-injection. These results suggest a role for mGlu receptors in mediating fever, anorexia, and cachexia possibly via activation of extra-vagal pathways, since the attenuating effect of l(+)-AP3 increased with increasing dosages of LPS. Given the critical role ascribed to mGlu receptors in neurotransmitter release and astrocytic processes, it is possible that these observations reflect an l(+)-AP3-induced attenuation of these systems.
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Affiliation(s)
- Tracey J Weiland
- School of Psychological Science, La Trobe University, Bundoora, Vic. 3086, Australia.
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Ewald P, Neuhuber WL, Raab M. Vesicular glutamate transporter 1 immunoreactivity in extrinsic and intrinsic innervation of the rat esophagus. Histochem Cell Biol 2005; 125:377-95. [PMID: 16231188 DOI: 10.1007/s00418-005-0083-z] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/13/2005] [Indexed: 01/19/2023]
Abstract
Encouraged by the recent finding of vesicular glutamate transporter 2 (VGLUT2) immunoreactivity (-ir) in intraganglionic laminar endings (IGLEs) of the rat esophagus, we investigated also the distribution and co-localization patterns of VGLUT1. Confocal imaging revealed substantial co-localization of VGLUT1-ir with selective markers of IGLEs, i.e., calretinin and VGLUT2, indicating that IGLEs contain both VGLUT1 and VGLUT2 within their synaptic vesicles. Besides IGLEs, we found VGLUT1-ir in both cholinergic and nitrergic myenteric neuronal cell bodies, in fibers of the muscularis mucosae, and in esophageal motor endplates. Skeletal neuromuscular junctions, in contrast, showed no VGLUT1-ir. We also tested for probable co-localization of VGLUT1-ir with markers of extrinsic and intrinsic esophageal innervation and glia. Within the myenteric neuropil we found, besides co-localization of VGLUT1 and substance P, no further co-localization of VGLUT1-ir with any of these markers. In the muscularis mucosae some VGLUT1-ir fibers were shown to contain neuronal nitric oxide synthase (nNOS)-ir. VGLUT1-ir in esophageal motor endplates was partly co-localized with vesicular acetylcholine transporter (VAChT)/choline acetyltransferase (ChAT)-ir, but VGLUT1-ir was also demonstrated in separately terminating fibers at motor endplates co-localized neither with ChAT/VAChT-ir nor with nNOS-ir, suggesting a hitherto unknown glutamatergic enteric co-innervation. Thus, VGLUT1-ir was found in extrinsic as well as intrinsic innervation of the rat esophagus.
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Affiliation(s)
- P Ewald
- Department of Anatomy I, University of Erlangen-Nuremberg, Krankenhausstr. 9, 91054, Erlangen, Germany
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16
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Tsai LH. Function of GABAergic and glutamatergic neurons in the stomach. J Biomed Sci 2005; 12:255-66. [PMID: 15917994 DOI: 10.1007/s11373-005-1357-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2004] [Accepted: 11/18/2004] [Indexed: 11/26/2022] Open
Abstract
Gamma-aminobutyric acid (GABA) and L-glutamic acid (L-Glu) are transmitters of GABAergic and glutamatergic neurons in the enteric interneurons, targeting excitatory or inhibitory GABA receptors or glutamate receptors that modulate gastric motility and mucosal function. GABAergic and glutamatergic neuron immunoreactivity have been found in cholinergic enteric neurons in the stomach. GABA and L-Glu may also subserve hormonal and paracrine signaling. Disruption in gastrointestinal function following perturbation of enteric GABA receptors and glutamate receptors presents potential new target sites for drug development.
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Affiliation(s)
- Li Hsueh Tsai
- Department of Physiology, School of Medicine, Taipei Medical University, Taipei, 11014, Taiwan.
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Jankovic SM, Jankovic SV, Milovanovic DR. Effect of the exogenous glutamate and the NMDA on electric field-stimulated contractions of isolated rat ileum. Pharmacol Res 2004; 50:529-32. [PMID: 15458775 DOI: 10.1016/j.phrs.2004.02.011] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 02/24/2004] [Indexed: 11/24/2022]
Abstract
While neurotransmitter role of glutamate in gastrointestinal intrinsic nervous system was shown, its effects in various segments of gastrointestinal tract were not yet understood completely. In our study, we have investigated effects of exogenous glutamate on electric field-stimulated contractions of isolated rat ileum. The ilea from forty Wistar rats of both sexes were isolated in an organ bath, according to the Magnus mounting method, and exposed to field stimulation with square wave pulses (20 V over the electrodes, 400 mA, 1 ms duration, frequency 16 Hz, pulse trains for 30 s with 30 s pause). The stimulation produced tonic contractions and relaxations recorded with an isometric system. Atropine (2.3 x 10(-6) M/l) completely abolished contractions of isolated rat ileum produced by the field stimulation, while relaxations remained unaffected. Glutamate (from 7.8 x 10(-6) to 3.5 x 10(-3) M/l) and N-Methyl-D-aspartic acid (NMDA) (from 9.1 x 10(-9) to 1.3 x 10(-5) M/l) caused concentration-dependent inhibition of the field-stimulated contractions of isolated rat ileum (EC50 was 90.17 +/- 1.81 x 10(-5) and 53.51 +/- 3.68 x 10(-9) M/l, respectively) while not affecting the field-stimulated relaxations. On the other hand, (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) (from 6.0 x 10(-9) to 9.3 x 10(-6) M/l), kainic acid (from 5.8 x 10(-9) to 8.3 x 10(-6) M/l) and (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid ((+/-)-trans-ACPD) (from 7.0 x 10(-9) to 1.1 x 10(-5) M/l) did not influence both the field-stimulated contractions and the field-stimulated relaxations of isolated rat ileum. The results of our study suggest inhibitory effect of glutamate on acetylcholine release from intrinsic neurons of rat ileum, mediated through NMDA receptors.
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Affiliation(s)
- Slobodan M Jankovic
- Medical Faculty, University of Kragujevac, Ul. Svetozara Markovica 69, P.O. Box 124, 34000 Kragujevac, Serbia and Montenegro.
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Chen WP, Kirchgessner AL. Activation of group II mGlu receptors inhibits voltage-gated Ca2+ currents in myenteric neurons. Am J Physiol Gastrointest Liver Physiol 2002; 283:G1282-9. [PMID: 12388194 DOI: 10.1152/ajpgi.00216.2002] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The enteric nervous system (ENS) contains functional ionotropic and group I metabotropic glutamate (mGlu) receptors. In this study, we determined whether enteric neurons express group II mGlu receptors and the effects of mGlu receptor activation on voltage-gated Ca(2+) currents in these cells. (2R,4R)-4-aminopyrrolidine-2,4-dicarboxylate (2R,4R-APDC), a group II mGlu receptor agonist, reversibly suppressed the Ba(2+) current in myenteric neurons isolated from the guinea pig ileum. Significant inhibition was also produced by L-glutamate and the group II mGlu receptor agonists, (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG-IV) and (2S,1'S,2'S)-2-(2-carboxycyclopropyl)glycine (L-CCG-I), with a rank order potency of 2R,4R-APDC > DCG-IV > L-glutamate > L-CCG-I, and was reduced by the group II mGlu receptor antagonist LY-341495. Pretreatment of neurons with pertussis toxin (PTX) reduced the action of mGlu receptor agonists, suggesting participation of G(i)/G(o) proteins. Finally, omega-conotoxin GVIA blocked current suppression by DCG-IV, suggesting modulation of N-type calcium channels. mGlu2/3 receptor immunoreactivity was displayed by neurons in culture and in the submucosal and myenteric plexus of the ileum. A subset of these cells displayed a glutamatergic phenotype as shown by the expression of vesicular glutamate transporter 2. These results provide the first evidence for functional group II mGlu receptors in the ENS and show that these receptors are PTX sensitive and negatively coupled to N-type calcium channels. Inhibition of N-type calcium channels produced by activation of group II mGlu receptors may modulate enteric neurotransmission.
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Affiliation(s)
- Wei-Ping Chen
- Department of Physiology and Pharmacology, State University of New York Downstate Medical Center, Brooklyn, New York 11203, USA
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