Abdominal surgery inhibits gastrointestinal motility, a phenomenon referred to as postoperative ileus. Since the postoperative ileus disturbs duodenal physiology it is important to minimize the side effects of this condition. Recent experiments in our laboratory show that treatment of anaesthetised rats with parecoxib, a selective cyclooxygenase-2 inhibitor, prevents duodenal postoperative ileus, increases duodenal mucosal bicarbonate secretion and improves other functions as well. One aim of the thesis was to investigate whether removal of luminal chloride affect the parecoxib- and the vasoactive intestinal peptide (VIP)-induced stimulation of duodenal mucosal bicarbonate secretion. The proximal duodenum of anaesthetised Dark Agouti rats was perfused with isotonic solutions containing zero or low Cl- and the effect on luminal alkalinisation determined. The basal as well as the parecoxib-induced increase in alkalinisation, but not that stimulated by VIP, were markedly reduced in the absence of luminal Cl-. One important function of the duodenum is to adjust luminal osmolality towards that in the blood. It is believed that the adjustment of osmolality in the duodenum is achieved by osmosis and diffusion of electrolytes along their concentration gradients and that these processes occur predominately paracellularly. Another aim of the thesis was to examine whether prevention of postoperative ileus affects the duodenal response to luminal hypertonicity. The proximal duodenum of anaesthetised Dark Agouti and Sprague-Dawley rats were perfused with hypertonic solutions of different composition and osmolality and the effects on duodenal motility, alkaline secretion, transepithelial fluid flux, mucosal permeability and the adjustment of luminal osmolality were determined in absence and presence of parecoxib. It is concluded that COX-2 inhibition increases duodenal mucosal bicarbonate secretion by stimulating apical Cl-/HCO3- exchange in duodenocytes. Furthermore, pretreatment of anaesthetised rats with parecoxib improves a number of duodenal functions in both rat strains that contribute to improve the ability to adjust luminal osmolality. The choice of rat strain is another important feature to consider when interpreting the results because the DA strain was more responsive to luminal hypertonicity than the SD strain. Finally, several evidences are provided to suggest that the adjustment of luminal osmolality in the rat duodenum is a regulated process.

Bacterial colonization of the gastrointestinal (GI) tract takes place during the perinatal period, thus coinciding with a critical window of enteric nervous system (ENS) development. Previous work has found that the myenteric plexus of germ free (GF) mice exhibits structural and functional aberrancies in the early postnatal period as compared to specific pathogen free (SPF) and altered Schaedler flora (ASF) mice. These early life disruptions in ENS development in GF mice compared to SPF mice, and more specifically ASF mice, support the notion that a simple intestinal flora is sufficient for directing perinatal ENS development. It has previously been believed that the intrauterine environment during fetal development is sterile. Recent evidence showing successful isolation of microbial communities from embryonic cord blood and newborn meconium that are not of maternal origin suggests that the intrauterine environment is not sterile and is unique to the fetus. Coinciding with this timeline of fetal microbial colonization is the development of the ENS through a population of precursors known as enteric neural crest derived cells (ENCDCs). The prenatal period is characterized by rapid expansion and differentiation of ENCDCs into the many enteric neuron subtypes that comprise the ENS. Terminal differentiation of ENCDCs continues into the early postnatal period. In the current study, we tested the hypothesis that ENCDCs interact directly with microbial products during ENS development. Further, these ENCDC-bacterial product interactions influence the proliferation, apoptosis, and chemical coding of enteric neuron precursors. These objectives were carried out in an in vitro model of ENCDCs isolated from the prenatal period that was established for the first time in our lab using immunoselection. Further, this model was characterized at key timepoints for proliferation, apoptosis, and differentiation. Our results are suggestive of direct ENCDC interactions with lipopolysaccharide (LPS), a TLR4 ligand, and flagellin, a TLR5 ligand, in stimulating ENCDC proliferation and differentiation into early born neurons of nitrergic and serotonergic subtypes. Peptidoglycan derivatives, muramyl dipeptide (MDP) and ƴ-D-Glu-mDAP (iE-DAP), ligands for NOD2 and NOD1 respectively, appear to mainly stimulate differentiation into nitrergic neurons, and possibly serotonergic neurons. The lack of apoptosis in all conditions is consistent with the notion that apoptosis is not an important characteristic of ENCDC maturation and ENS development. Finally, the lack of significance for differentiation into dopaminergic neurons could be further evidence of their late born nature, which has previously been reported to be stimulated by serotonin after the emergence of serotonergic neurons. / Thesis / Master of Science (MSc)