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  • 1
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    Phenotypic characterization of taste cells of the mouse small intestine
    American Physiological Society ; 2007
    In:  American Journal of Physiology-Gastrointestinal and Liver Physiology Vol. 292, No. 5 ( 2007-05), p. G1420-G1428
    Details
    In: American Journal of Physiology-Gastrointestinal and Liver Physiology, American Physiological Society, Vol. 292, No. 5 ( 2007-05), p. G1420-G1428
    Abstract: Nutrient-evoked gastrointestinal reflexes are likely initiated by specialized epithelial cells located in the small intestine that detect luminal stimuli and release mediators that activate vagal endings. The G-protein α-gustducin, a key signal molecule in lingual taste detection, has been identified in mouse small intestine, where it may also subserve nutrient detection; however, the phenotype of α-gustducin cells is unknown. Immunohistochemistry was performed throughout the mouse small intestine for α-gustducin, enteroendocrine cell markers 5-HT and glucagon-like peptide-1 (GLP-1), and brush cell markers neuronal nitric oxide synthase and Ulex europaeus agglutinin-1 (UEA-1) lectin binding, singly, and in combination. α-Gustducin was expressed in solitary epithelial cells of the mid to upper villus, which were distributed in a regional manner with most occurring within the midjejunum. Here, 27% of α-gustducin cells colabeled for 5-HT and 15% for GLP-1; 57% of α-gustducin cells colabeled UEA-1, with no triple labeling. α-Gustducin cells that colabeled for 5-HT or GLP-1 were of distinct morphology and exhibited a different α-gustducin immunolabeling pattern to those colabeled with UEA-1. Neuronal nitric oxide synthase was absent from intestinal epithelium despite strong labeling in the myenteric plexus. We conclude that subsets of enteroendocrine cells in the midjejunum and brush cells (more generally distributed) are equipped to utilize α-gustducin signaling in mice. Intestinal taste modalities may be signaled by these enteroendocrine cells via the release of 5-HT, GLP-1, or coexpressed mediators or by brush cells via a nonnitrergic mediator in distinct regions of the intestine.
    Type of Medium: Online Resource
    ISSN: 0193-1857 , 1522-1547
    URL: Article
    DOI: 10.1152/ajpgi.00504.2006
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2007
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  • 2
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    Roles of muscarinic receptor subtypes in small intestinal motor dysfunction in acute radiation enteritis
    American Physiological Society ; 2007
    In:  American Journal of Physiology-Gastrointestinal and Liver Physiology Vol. 293, No. 1 ( 2007-07), p. G121-G127
    Details
    In: American Journal of Physiology-Gastrointestinal and Liver Physiology, American Physiological Society, Vol. 293, No. 1 ( 2007-07), p. G121-G127
    Abstract: Administration of abdominal radiotherapy results in small intestinal motor dysfunction. We have developed a rat radiation enteritis model that, after exposure in vivo, shows high-amplitude, long-duration (HALD) pressure waves in ex vivo ileal segments. These resemble in vivo dysmotility where giant contractions migrate both antegradely and retrogradely. Mediation of these motor patterns is unclear, although enteric neural components are implicated. After the induction of acute radiation enteritis in vivo, ileal segments were isolated and arterially perfused. TTX, hexamethonium, atropine, or the selective muscarinic antagonists pirenzepine (M 1 ), methoctramine (M 2 ), and 1,1-dimethyl-4-diphenylacetoxypiperidinium iodide (4-DAMP; M 3 ) were added to the perfusate. The baseline mean rate per minute per channel of HALD pressure waves was 0.35 ± 0.047. This was significantly reduced by TTX (83.3%, P 〈 0.01), hexamethonium (90.3%, P 〈 0.03), and atropine (98.4%, P 〈 0.01). The HALD pressure wave mean rate per minute per channel was significantly reduced by pirenzepine (81.1%, P 〈 0.03), methoctramine (96.8%, P 〈 0.001), and 4-DAMP (93.1%, P 〈 0.03) compared with predrug baseline data. As an indicator of normal motility patterns, the frequency of low-amplitude, short-duration pressure waves was also assessed. The mean rate per minute per channel of 5.15 ± 0.98 was significantly increased by TTX (19%, P 〈 0.05) but significantly reduced by pirenzepine (35.1%, P 〈 0.02) and methoctramine (75%, P 〈 0.0003). However, the rate of small-amplitude pressure waves was not affected by hexamethonium, atropine, or the M 3 antagonist 4-DAMP. The data indicate a role for neuronal mechanisms and the specific involvement of cholinergic receptors in generating dysmotility in acute radiation enteritis. The effect of selective M 3 receptor antagonism suggests that M 3 receptors may provide specific therapeutic targets in acute radiation enteritis.
    Type of Medium: Online Resource
    ISSN: 0193-1857 , 1522-1547
    URL: Article
    DOI: 10.1152/ajpgi.00469.2006
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2007
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  • 3
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    Distinct afferent innervation patterns within the human proximal and distal esophageal mucosa
    American Physiological Society ; 2015
    In:  American Journal of Physiology-Gastrointestinal and Liver Physiology Vol. 308, No. 6 ( 2015-03-15), p. G525-G531
    Details
    In: American Journal of Physiology-Gastrointestinal and Liver Physiology, American Physiological Society, Vol. 308, No. 6 ( 2015-03-15), p. G525-G531
    Abstract: Little is known about the mucosal phenotype of the proximal human esophagus. There is evidence to suggest that the proximal esophagus is more sensitive to chemical and mechanical stimulation compared with the distal. This may have physiological relevance (e.g., in prevention of aspiration of gastroesophageal refluxate), but also pathological relevance (e.g., in reflux perception or dysphagia). Reasons for this increased sensitivity are unclear but may include impairment in mucosal barrier integrity or changes in sensory innervation. We assessed mucosal barrier integrity and afferent nerve distribution in the proximal and distal esophagus of healthy human volunteers. In 10 healthy volunteers baseline proximal and distal esophageal impedance was measured in vivo. Esophageal mucosal biopsies from the distal and proximal esophagus were taken, and baseline transepithelial electrical resistance (TER) was measured in Ussing chambers. Biopsies were examined immunohistochemically for presence and location of calcitonin gene-related peptide (CGRP)-immunoreactive nerve fibers. In a further four healthy volunteers we investigated for colocalization of CGRP and protein gene product (PGP) 9.5 immunoreactivity in nerve fibers. Baseline impedance was higher in the proximal than in the distal esophagus [2,936 Ω (SD578) vs. 2,229 Ω (SD821); P = 0.03] , however, baseline TER was not significantly different between them. Mucosal CGRP-immunoreactive nerves were found in the epithelium of both proximal and distal esophagus, but were located more superficially in the proximal mucosa compared with the distal [11.5 (SD7) vs. 21.7 (SD5) cell layers from lumen, P = 0.002] 19% of proximal, and 10% of distal mucosal PGP-immunoreactive fibers colocalized with CGRP. PGP-immunoreactive fibers were also significantly closer to the luminal surface in the proximal compared with the distal esophagus ( P 〈 0.001). We conclude that mucosal barrier integrity is similar in proximal and distal esophagus, but proximal mucosal afferent nerves are in a more superficial location. The enhanced sensitivity to reflux-evoked symptoms of the proximal esophagus most likely has an anatomical basis.
    Type of Medium: Online Resource
    ISSN: 0193-1857 , 1522-1547
    URL: Article
    DOI: 10.1152/ajpgi.00175.2014
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2015
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  • 4
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    GABA B R expressed on vagal afferent neurones inhibit gastric mechanosensitivity in ferret proximal stomach
    American Physiological Society ; 2001
    In:  American Journal of Physiology-Gastrointestinal and Liver Physiology Vol. 281, No. 6 ( 2001-12-01), p. G1494-G1501
    Details
    In: American Journal of Physiology-Gastrointestinal and Liver Physiology, American Physiological Society, Vol. 281, No. 6 ( 2001-12-01), p. G1494-G1501
    Abstract: GABA B -receptor (GABA B R) agonists reduce transient lower esophageal sphincter relaxation (TLESR) and reflux episodes through an action on vagal pathways. In this study, we determined whether GABA B R are expressed on vagal afferent neurones and whether they modulate distension-evoked discharge of vagal afferents in the isolated stomach. Vagal mehanoreceptor activity was recorded following distensions of the isolated ferret proximal stomach before and after perfusion with the GABA B R-selective agonists baclofen and 3-aminopropylphosphinic acid (3-APPiA). Retrograde labeling and immunohistochemistry were used to identify GABA B R located on vagal afferent neurones in the nodose ganglia. Vagal afferent fibers responded to isovolumetric gastric distension with an increase in discharge. The GABA B -receptor agonists baclofen (5 × 10 −5 M) and 3-APPiA (10 −6 to 10 −5 M) but not muscimol (GABA A -selective agonist: 1.3 × 10 −5 M) significantly decreased afferent distension-response curves. The effect of baclofen (5 × 10 −5 M) was reversed by the GABA B -receptor antagonist CGP 62349 (10 −5 M). Over 93% of retrogradely labeled gastric vagal afferents in the nodose ganglia expressed immunoreactivity for the GABA B R. GABA B R expressed on vagal afferent fibers directly inhibit gastric mechanosensory activity. This is likely a contributing mechanism to the efficacy of GABA B -receptor agonists in reducing TLESR and reflux episodes in vivo.
    Type of Medium: Online Resource
    ISSN: 0193-1857 , 1522-1547
    URL: Article
    DOI: 10.1152/ajpgi.2001.281.6.G1494
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2001
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  • 5
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    GABA B receptors on vagal afferent pathways: peripheral and central inhibition
    American Physiological Society ; 2001
    In:  American Journal of Physiology-Gastrointestinal and Liver Physiology Vol. 280, No. 4 ( 2001-04-01), p. G658-G668
    Details
    In: American Journal of Physiology-Gastrointestinal and Liver Physiology, American Physiological Society, Vol. 280, No. 4 ( 2001-04-01), p. G658-G668
    Abstract: To investigate GABA B receptors along vagal afferent pathways, we recorded from vagal afferents, medullary neurons, and vagal efferents in ferrets. Baclofen (7–14 μmol/kg iv) reduced gastric tension receptor and nucleus tractus solitarii neuronal responses to gastric distension but not gastroduodenal mucosal receptor responses to cholecystokinin (CCK). GABA B antagonists CGP-35348 or CGP-62349 reversed effects of baclofen. Vagal efferents showed excitatory and inhibitory responses to distension and CCK. Baclofen (3 nmol icv or 7–14 μmol/kg iv) reduced both distension response types but reduced only inhibitory responses to CCK. CGP-35348 (100 nmol icv or 100 μmol/kg iv) reversed baclofen's effect on distension responses, but inhibitory responses to CCK remained attenuated. They were, however, reversed by CGP-62349 (0.4 nmol icv). In conclusion, GABA B receptors inhibit mechanosensitivity, not chemosensitivity, of vagal afferents peripherally. Mechanosensory input to brain stem neurons is also reduced centrally by GABA B receptors, but excitatory chemosensory input is unaffected. Inhibitory mechano- and chemosensory inputs to brain stem neurons (via inhibitory interneurons) are both reduced, but the pathway taken by chemosensory input involves GABA B receptors that are insensitive to CGP-35348.
    Type of Medium: Online Resource
    ISSN: 0193-1857 , 1522-1547
    URL: Article
    DOI: 10.1152/ajpgi.2001.280.4.G658
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2001
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  • 6
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    Peripheral versus central modulation of gastric vagal pathways by metabotropic glutamate receptor 5
    American Physiological Society ; 2007
    In:  American Journal of Physiology-Gastrointestinal and Liver Physiology Vol. 292, No. 2 ( 2007-02), p. G501-G511
    Details
    In: American Journal of Physiology-Gastrointestinal and Liver Physiology, American Physiological Society, Vol. 292, No. 2 ( 2007-02), p. G501-G511
    Abstract: Metabotropic glutamate receptors (mGluR) are classified into group I, II, and III mGluR. Group I (mGluR1, mGluR5) are excitatory, whereas group II and III are inhibitory. mGluR5 antagonism potently reduces triggering of transient lower esophageal sphincter relaxations and gastroesophageal reflux. Transient lower esophageal sphincter relaxations are mediated via a vagal pathway and initiated by distension of the proximal stomach. Here, we determined the site of action of mGluR5 in gastric vagal pathways by investigating peripheral responses of ferret gastroesophageal vagal afferents to graded mechanical stimuli in vitro and central responses of nucleus tractus solitarius (NTS) neurons with gastric input in vivo in the presence or absence of the mGluR5 antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP). mGluR5 were also identified immunohistochemically in the nodose ganglia and NTS after extrinsic vagal inputs had been traced from the proximal stomach. Gastroesophageal vagal afferents were classified as mucosal, tension, or tension-mucosal (TM) receptors. MPEP (1–10 μM) inhibited responses to circumferential tension of tension and TM receptors. Responses to mucosal stroking of mucosal and TM receptors were unaffected. MPEP (0.001–10 nmol icv) had no major effect on the majority of NTS neurons excited by gastric distension or on NTS neurons inhibited by distension. mGluR5 labeling was abundant in gastric vagal afferent neurons and sparse in fibers within NTS vagal subnuclei. We conclude that mGluR5 play a prominent role at gastroesophageal vagal afferent endings but a minor role in central gastric vagal pathways. Peripheral mGluR5 may prove a suitable target for reducing mechanosensory input from the periphery, for therapeutic benefit.
    Type of Medium: Online Resource
    ISSN: 0193-1857 , 1522-1547
    URL: Article
    DOI: 10.1152/ajpgi.00353.2006
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2007
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  • 7
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    Effect of the artificial sweetener, sucralose, on gastric emptying and incretin hormone release in healthy subjects
    American Physiological Society ; 2009
    In:  American Journal of Physiology-Gastrointestinal and Liver Physiology Vol. 296, No. 4 ( 2009-04), p. G735-G739
    Details
    In: American Journal of Physiology-Gastrointestinal and Liver Physiology, American Physiological Society, Vol. 296, No. 4 ( 2009-04), p. G735-G739
    Abstract: The incretin hormones, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), play an important role in glucose homeostasis in both health and diabetes. In mice, sucralose, an artificial sweetener, stimulates GLP-1 release via sweet taste receptors on enteroendocrine cells. We studied blood glucose, plasma levels of insulin, GLP-1, and GIP, and gastric emptying (by a breath test) in 7 healthy humans after intragastric infusions of 1) 50 g sucrose in water to a total volume of 500 ml (∼290 mosmol/l), 2) 80 mg sucralose in 500 ml normal saline (∼300 mosmol/l, 0.4 mM sucralose), 3) 800 mg sucralose in 500 ml normal saline (∼300 mosmol/l, 4 mM sucralose), and 4) 500 ml normal saline (∼300 mosmol/l), all labeled with 150 mg 13 C-acetate. Blood glucose increased only in response to sucrose ( P 〈 0.05). GLP-1, GIP, and insulin also increased after sucrose ( P = 0.0001) but not after either load of sucralose or saline. Gastric emptying of sucrose was slower than that of saline ( t 50 : 87.4 ± 4.1 min vs. 74.7 ± 3.2 min, P 〈 0.005), whereas there were no differences in t 50 between sucralose 0.4 mM (73.7 ± 3.1 min) or 4 mM (76.7 ± 3.1 min) and saline. We conclude that sucralose, delivered by intragastric infusion, does not stimulate insulin, GLP-1, or GIP release or slow gastric emptying in healthy humans.
    Type of Medium: Online Resource
    ISSN: 0193-1857 , 1522-1547
    URL: Article
    DOI: 10.1152/ajpgi.90708.2008
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2009
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  • 8
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    Ghrelin selectively reduces mechanosensitivity of upper gastrointestinal vagal afferents
    American Physiological Society ; 2007
    In:  American Journal of Physiology-Gastrointestinal and Liver Physiology Vol. 292, No. 5 ( 2007-05), p. G1376-G1384
    Details
    In: American Journal of Physiology-Gastrointestinal and Liver Physiology, American Physiological Society, Vol. 292, No. 5 ( 2007-05), p. G1376-G1384
    Abstract: Ghrelin is a peptide released from gastric endocrine cells that has an orexigenic effect via a vagal pathway. Here we determine the effect of ghrelin on mechanosensitivity of upper-intestinal vagal afferent fibers in ferret and mouse. The responses of gastroesophageal vagal afferents to graded mechanical stimulation were determined in vitro before and during application of ghrelin to their peripheral endings. Three types of vagal afferent were tested: tension receptors responding to circumferential tension, mucosal receptors responding only to mucosal stroking, and tension/mucosal (TM) receptors in ferret esophagus that responded to both stimuli. In the mouse, ghrelin did not significantly affect the response of mucosal receptors to mucosal stroking with calibrated von Frey hairs. However, it significantly reduced responses of tension receptors to circumferential tension ( P 〈 0.005; two-way ANOVA) by up to 40%. This inhibition was reversed by the ghrelin receptor antagonist [d-Lys-3]-growth hormone-releasing peptide (GHRP)-6. In the ferret, ghrelin significantly reduced the response of mucosal and TM receptors to mucosal stroking with calibrated von Frey hairs. Surprisingly, ghrelin did not significantly alter the response to circumferential tension in either tension or TM receptors. RT-PCR analysis indicated that both ghrelin and its receptor are expressed in vagal afferent cell bodies in mouse nodose ganglia. In conclusion, ghrelin selectively inhibits subpopulations of mechanically sensitive gastroesophageal vagal afferents; there is also potential for ghrelin release from vagal afferents. However, the subpopulation of afferents inhibited differs between species. These data have broad implications for ghrelin's role in food intake regulation and reflex control of gastrointestinal function.
    Type of Medium: Online Resource
    ISSN: 0193-1857 , 1522-1547
    URL: Article
    DOI: 10.1152/ajpgi.00536.2006
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2007
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  • 9
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    Inhibition of transient LES relaxations and reflux in ferrets by GABA receptor agonists
    American Physiological Society ; 1999
    In:  American Journal of Physiology-Gastrointestinal and Liver Physiology Vol. 277, No. 4 ( 1999-10), p. G867-G874
    Details
    In: American Journal of Physiology-Gastrointestinal and Liver Physiology, American Physiological Society, Vol. 277, No. 4 ( 1999-10), p. G867-G874
    Type of Medium: Online Resource
    ISSN: 0193-1857 , 1522-1547
    URL: Article
    DOI: 10.1152/ajpgi.1999.277.4.G867
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1999
    detail.hit.zdb_id: 1477329-6
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  • 10
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    Opioid modulation of ferret vagal afferent mechanosensitivity
    American Physiological Society ; 2008
    In:  American Journal of Physiology-Gastrointestinal and Liver Physiology Vol. 294, No. 4 ( 2008-04), p. G963-G970
    Details
    In: American Journal of Physiology-Gastrointestinal and Liver Physiology, American Physiological Society, Vol. 294, No. 4 ( 2008-04), p. G963-G970
    Abstract: Despite universal use of opioids in the clinic to inhibit pain, there is relatively little known of their peripheral actions on sensory nerve endings, where in fact they may be better targeted with more widespread applications. Here we show differential effects of μ-, κ-, and δ-opioids on mechanosensitive ferret esophageal vagal afferent endings investigated in vitro. The effects of selective agonists [d-Ala 2 ,N-Me-Phe 4 ,Gly-ol 5 ]-enkephalin (DAMGO), 2-(3, 4-dichlorophenyl)- N-methyl- N-[(1S)-1phenyl-2-(1-pyrrolidinyl) ethyl] acetamide hydrochlorine (ICI 199441), and (+)-4-[(αR)-α-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]- N, N-diethylbenzamide (SNC-80), respectively, on mechanosensory stimulus-response functions were quantified. DAMGO (10 −7 to 10 −5 M) reduced the responses of tension receptors to circumferential tension (1–5 g) by up to 50%, and the responses of mucosal receptors to mucosal stroking (10–1,000 mg von Frey hair) by 〉 50%. DAMGO effects were reversed by naloxone (10 −5 M). Tension/mucosal (TM) receptor responses to tension and stroking were unaffected by DAMGO. ICI 199441 (10 −6 to 10 −5 M) potently inhibited all responses except TM receptor responses to tension, and SNC-80 (10 −5 to 10 −3 M) had no effect other than a minor inhibition of mucosal receptor responses to intense stimuli at 10 −3 M. We conclude that μ- and κ-opioids have potent and selective peripheral effects on esophageal vagal afferents that may have applications in treatment of disorders of visceral sensation.
    Type of Medium: Online Resource
    ISSN: 0193-1857 , 1522-1547
    URL: Article
    DOI: 10.1152/ajpgi.00562.2007
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2008
    detail.hit.zdb_id: 1477329-6
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