The mucosa of the small intestine is clearly able to discriminate specific chemical components of ingested meals to stimulate gastrointestinal feedback pathways and reduce further food intake. Luminal carbohydrates delay gastric emptying and initiate satiation, which are mediated by reflexes via the vagus nerve upon activation of vagal afferent endings in the mucosa. Nutrients activate these nerve fibres through intermediary epithelial cells, which release neuromediators upon transduction of luminal signals through the apical membrane. 5-hydroxytryptamine (5-HT) and glucagon-like peptide-1 (GLP-1) are released from enteroendocrine cells in response to luminal carbohydrates and both slow gastric emptying and inhibit food intake via vagal afferent pathways. The molecular mechanisms for carbohydrate detection and transduction leading to 5-HT and GLP-1 release are unknown. However molecules key to transduction of taste by receptor cells in the lingual epithelium are expressed in the gastrointestinal mucosa. The studies in this thesis aimed to investigate 1) the possibility that taste molecules expressed in the intestine form part of the carbohydrate sensing pathway that leads to 5-HT and GLP-1 release, which in turn activate mucosal vagal afferents and 2) to gauge any alterations in taste molecule expression that may relate to adaptation of carbohydrate-induced gastric motility reflexes that occurs in dietary and disease states. Firstly these studies show key taste molecules, including sweet taste receptors T1R2 and T1R3, the Gprotein gustducin (alpha-subunit Gαgust), and the taste transduction channel TRPM5, are expressed in the mouse gastrointestinal mucosa shown by RT-PCR and were further localised to individual epithelial ‘taste’ cells using immunohistochemistry. Quantification of transcript levels by real time RT-PCR revealed the proximal small intestine as the preferential site of sweet taste receptor expression along the gastrointestinal tract. This finding was also confirmed in humans using gastric and intestinal mucosal biopsies obtained at enteroscopy with significantly higher transcript expression levels in the small intestine compared to stomach. In the mouse, double label immunohistochemistry with Gα[subscript]gust antibody, as a marker of intestinal taste cells, was performed using lectin UEA-1, a marker of intestinal brush cells, and 5-HT or GLP-1 to link intestinal taste transduction to 5-HT and GLP-1 release. Results show Gα[subscript]gust is expressed within a subset of all three cell types in the small intestine but predominantly within UEA-1-expressing cells. Although Gα[subscript]gust, 5-HT and GLP-1 are largely expressed in mutually exclusive cells, within the jejunum a portion Gαgust positive cells coexpressed 5-HT or GLP-1. This Indicates a subpopulation of intestinal taste cells may be dedicated to carbohydrate-evoked gastrointestinal reflexes through 5-HT and GLP-1 mediated pathways, however, taste transduction within the small intestine appears to predominantly link to alternate mediators. After nutrient detection at the luminal surface, activation of mucosal afferents by 5-HT released from enterochromaffin cells is well documented, however although vagal afferents express GLP-1 receptors direct activation has not been demonstrated. For this purpose the effects of GLP-1 on gastrointestinal vagal afferents were investigated through single fibre recordings in in vitro tissue preparations. GLP-1 had no effect on the activity of mouse gastroesophageal vagal afferents but a rat duodenal preparation proved too problematic to be able to test GLP-1 specifically on duodenal vagal afferents. Altered gastric motility in response to carbohydrate meals due to prior dietary patterns and diabetes mellitus suggest adaptation in feedback mechanisms. Towards the second aim of this thesis taste molecule expression was quantified in fed and fasted mice by real time RT-PCR and revealed taste gene transcription is altered with the changing luminal environment, specifically transcription of taste genes was significantly decreased after feeding compared to the fasted state. Studies comparing expression in the duodenum of type 2 diabetics and non-diabetic controls show no significant difference in taste transcript levels between the two groups. However taste molecule expression was correlated to blood glucose levels in diabetics suggesting transcription of these signal molecules is adapted to both luminal and systemic carbohydrate levels. Findings in both the mouse and human gastrointestinal tract in terms of intestinal chemosensing are discussed. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1363582 / Thesis (Ph.D.) -- University of Adelaide, School of Molecular and Biomedical Sciences, 2009

The mucosa of the small intestine is clearly able to discriminate specific chemical components of ingested meals to stimulate gastrointestinal feedback pathways and reduce further food intake. Luminal carbohydrates delay gastric emptying and initiate satiation, which are mediated by reflexes via the vagus nerve upon activation of vagal afferent endings in the mucosa. Nutrients activate these nerve fibres through intermediary epithelial cells, which release neuromediators upon transduction of luminal signals through the apical membrane. 5-hydroxytryptamine (5-HT) and glucagon-like peptide-1 (GLP-1) are released from enteroendocrine cells in response to luminal carbohydrates and both slow gastric emptying and inhibit food intake via vagal afferent pathways. The molecular mechanisms for carbohydrate detection and transduction leading to 5-HT and GLP-1 release are unknown. However molecules key to transduction of taste by receptor cells in the lingual epithelium are expressed in the gastrointestinal mucosa. The studies in this thesis aimed to investigate 1) the possibility that taste molecules expressed in the intestine form part of the carbohydrate sensing pathway that leads to 5-HT and GLP-1 release, which in turn activate mucosal vagal afferents and 2) to gauge any alterations in taste molecule expression that may relate to adaptation of carbohydrate-induced gastric motility reflexes that occurs in dietary and disease states. Firstly these studies show key taste molecules, including sweet taste receptors T1R2 and T1R3, the Gprotein gustducin (alpha-subunit Gαgust), and the taste transduction channel TRPM5, are expressed in the mouse gastrointestinal mucosa shown by RT-PCR and were further localised to individual epithelial ‘taste’ cells using immunohistochemistry. Quantification of transcript levels by real time RT-PCR revealed the proximal small intestine as the preferential site of sweet taste receptor expression along the gastrointestinal tract. This finding was also confirmed in humans using gastric and intestinal mucosal biopsies obtained at enteroscopy with significantly higher transcript expression levels in the small intestine compared to stomach. In the mouse, double label immunohistochemistry with Gα[subscript]gust antibody, as a marker of intestinal taste cells, was performed using lectin UEA-1, a marker of intestinal brush cells, and 5-HT or GLP-1 to link intestinal taste transduction to 5-HT and GLP-1 release. Results show Gα[subscript]gust is expressed within a subset of all three cell types in the small intestine but predominantly within UEA-1-expressing cells. Although Gα[subscript]gust, 5-HT and GLP-1 are largely expressed in mutually exclusive cells, within the jejunum a portion Gαgust positive cells coexpressed 5-HT or GLP-1. This Indicates a subpopulation of intestinal taste cells may be dedicated to carbohydrate-evoked gastrointestinal reflexes through 5-HT and GLP-1 mediated pathways, however, taste transduction within the small intestine appears to predominantly link to alternate mediators. After nutrient detection at the luminal surface, activation of mucosal afferents by 5-HT released from enterochromaffin cells is well documented, however although vagal afferents express GLP-1 receptors direct activation has not been demonstrated. For this purpose the effects of GLP-1 on gastrointestinal vagal afferents were investigated through single fibre recordings in in vitro tissue preparations. GLP-1 had no effect on the activity of mouse gastroesophageal vagal afferents but a rat duodenal preparation proved too problematic to be able to test GLP-1 specifically on duodenal vagal afferents. Altered gastric motility in response to carbohydrate meals due to prior dietary patterns and diabetes mellitus suggest adaptation in feedback mechanisms. Towards the second aim of this thesis taste molecule expression was quantified in fed and fasted mice by real time RT-PCR and revealed taste gene transcription is altered with the changing luminal environment, specifically transcription of taste genes was significantly decreased after feeding compared to the fasted state. Studies comparing expression in the duodenum of type 2 diabetics and non-diabetic controls show no significant difference in taste transcript levels between the two groups. However taste molecule expression was correlated to blood glucose levels in diabetics suggesting transcription of these signal molecules is adapted to both luminal and systemic carbohydrate levels. Findings in both the mouse and human gastrointestinal tract in terms of intestinal chemosensing are discussed. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1363582 / Thesis (Ph.D.) -- University of Adelaide, School of Molecular and Biomedical Sciences, 2009

Although a vast literature attests to the belief that psychosocial disturbance is an important component of functional gastrointestinal disorders (FGID), the relation of life stress, psychological distress and personality to the development of these disorders is poorly understood. The broad objective of this thesis is to provide data on relations between psychosocial factors and FGID, especially irritable bowel syndrome (IBS) and functional dyspepsia (FD), in representative outpatient samples. Issues not previously addressed are examined in a series of studies. The first two studies are concerned with relations between psychosocial factors, extraintestinal (somatic) symptoms and the number and type of FGID syndromes present at consultation and, in IBS patients, the prospective relation of psychosocial factors to changes in symptom intensity over 16 months. The last three studies relate psychosocial factors to gastrointestinal (GI) transit, motor, and sensory function in FGID, abnormalities in these parameters representing the putative origin of symptoms in FGID. In total, 350 patients participated, representing a 95% participation rate. Important features of the methodology include the use of a recently standardised symptom-based classification system for FGID, an objective and reliable interview-based life stress instrument (The Life Events and Difficulties Schedule), and sophisticated and sensitive technologies to assess GI transit, motor and sensory function. Novel measures, which conceptually take into account the chronic, fluctuating and recurrent course of IBS and FD syndromes, and the tendency of these syndromes to coexist, are also included. Thus, measures of symptom outcome assess the number of syndromes present, while the symptom intensity variable reflects the severity and frequency of both FD and IBS symptoms, if both are present. Similarly, with respect to altered transit, and motor and sensory function, physiological outcome variables reflect not only the presence of an abnormality but the number of regions affected, and the type and number of abnormalities present. Cross-sectional findings showed for the first time that psychosocial disturbance is associated with FGID symptomatology in a quantitative manner, that chronic life stress threat is central to this process and this stress-related process is a prominent feature of a particular group of syndromes (ie IBS/FD) defined primarily by the presence of pain and discomfort. A combination of psychological, social and biological factors combined to predict the number of FGID syndromes present at entry into the study. Prominent among them was an angry, reactive and anxious (neurotic) personality, chronic life stress threat, increased coping, poor emotional support and increased age. In addition to a greater number of FD/IBS syndromes, individuals with an anger-reactive response style had experienced more intense pain and discomfort, and displayed more complete sensorimotor disturbance. Longitudinal data demonstrated (also for the first time) the strength, consistency and unequivocal direction of the relation of chronic threat to symptom intensity over time. Almost all of the within subject variance in symptom intensity levels (assessed on 3 occasions over a 16 month period) was explained by the severity of chronic threat during the previous 6 months or more. For 76% of IBS patients, the presence vs the absence of one or more highly threatening chronic stressors predicted with considerable precision, the long-term clinical outcome. Thus, no patient exposed to even one such stressor improved clinically (ie by at least 50%) over the follow-up period, while in contrast, all patients who improved clinically did so in the absence of such a stressor. For 24% of patients, however, failure to improve clinically could not be explained by any psychological, social (including life stress) or demographic factor included in this study. Key risk indicators of a poor outcome at 16 months were identified - chronic life stress threat, the severity of baseline GI symptomatology, and female gender. Life stress is important because it alone determined the magnitude and direction of change in symptom intensity over time, while the severity of baseline GI symptomatology revealed the extent of improvement required to achieve a recovery, and female gender predicted the presence of a larger number of FD/IBS syndromes in women long-term. Widespread hypomotility, which was almost exclusive to women in this study, represents one factor that may inhibit improvement (or rate of improvement) for women over time. Finally, these findings have identified a psychophysiological subgroup, with underlying psychosocial, motor (and perhaps also sensory) dysfunctions that are more specific for women than men, and which does not seem to be distinctive of any particular FGID subgroup.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniversitet, 2005. / Härtill 4 uppsatser.

Diss. (sammanfattning) Linköping : Univ., 2001. / Härtill 6 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2002. / Härtill 5 uppsatser.

Diss. (sammanfattning) Linköping : Univ., 2001. / Härtill 5 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 4 uppsatser.

Thesis (M.D.) -- University of Adelaide, Dept. of Medicine, 2000. / Includes bibliographical references.

Diss. (sammanfattning) Göteborg : Göteborgs universitet, 2007. / Härtill 4 uppsatser.