Wright, Alec M.

AbstractBackgroundGastroparesis is defined by delayed gastric emptying (GE) without obstruction. Studies suggest targeting heme oxygenase‐1 (HO1) may ameliorate diabetic gastroparesis. Upregulation of HO1 expression via interleukin‐10 (IL‐10) in the gastric muscularis propria is associated with reversal of delayed GE in diabetic NOD mice. IL‐10 activates the M2 cytoprotective phenotype of macrophages and induces expression of HO1 protein. Here, we assess delivery of HO1 by recombinant adeno‐associated viruses (AAVs) in diabetic mice with delayed GE.MethodsC57BL6 diabetic delayed GE mice were injected with 1 × 1012 vg scAAV9‐cre, scAAV9‐GFP, or scAAV9‐HO1 particles. Changes to GE were assessed weekly utilizing our [13C]‐octanoic acid breath test. Stomach tissue was collected to assess the effect of scAAV9 treatment on Kit, NOS1, and HO1 expression.Key ResultsDelayed GE returned to normal within 2 weeks of treatment in 7/12 mice receiving scAAV9‐cre and in 4/5 mice that received the scAAV9‐GFP, whereas mice that received scAAV9‐HO1 did not respond in the same manner and had GE that took significantly longer to return to normal (6/7 mice at 4–6 weeks). Kit, NOS1, and HO1 protein expression in scAAV9‐GFP‐treated mice with normal GE were not significantly different compared with diabetic mice with delayed GE.Conclusions and InferencesInjection of scAAV9 into diabetic C57BL6 mice produced a biological response that resulted in acceleration of GE independently of the cargo delivered by the AAV9 vector. Further research is needed to determine whether use of AAV mediated gene transduction in the gastric muscularis propria is beneficial and warranted.

AbstractBackgroundThe gut is the only organ system with intrinsic neural reflexes. Intrinsic primary afferent neurons (IPANs) of the enteric nervous system initiate intrinsic reflexes, form gut‐brain connections, and undergo considerable neuroplasticity to cause digestive diseases. They remain inaccessible to study in mice in the absence of a selective marker. Advillin is used as a marker for primary afferent neurons in dorsal root ganglia. The aim of this study was to test the hypothesis that advillin is expressed in IPANs of the mouse jejunum.MethodsAdvillin expression was assessed with immunohistochemistry and using transgenic mice expressing an inducible Cre recombinase under the advillin promoter were used to drive tdTomato and the genetically encoded calcium indicator GCaMP5. These mice were used to characterize the morphology and physiology of advillin‐expressing enteric neurons using confocal microscopy, calcium imaging, and whole‐cell patch‐clamp electrophysiology.Key ResultsAdvillin is expressed in about 25% of myenteric neurons of the mouse jejunum, and these neurons demonstrate the requisite properties of IPANs. Functionally, they demonstrate calcium responses following mechanical stimuli of the mucosa and during antidromic action potentials. They have Dogiel type II morphology with neural processes that mostly remain within the myenteric plexus, but also project to the mucosa and express NeuN and calcitonin gene‐related peptide (CGRP), but not nNOS.Conclusions and InferencesAdvillin marks jejunal IPANs providing accessibility to this important neuronal population to study and model digestive disease.

Enteric glia are important components of the enteric nervous system (ENS) that control critical functions of the alimentary canal including motility, fluid and ion transport, and immune barrier. Anatomical assessments of enteric glia to date have utilized microdissected whole‐mount tissue or thin sections to visualize cells in the optically dense matrix of the bowel. The aim of this study was to assess the morphological features of enteric glia throughout the small and large intestines of the mouse in intact full‐thickness preparations. B6.Cg‐Polr2atm1(CAG‐GCaMP5g,‐tdTomato)Tvrd/J mice were bred to homozygosity with B6.Cg‐Tg(SOX10‐cre/ERT2)Vpa mice which were maintained as hemizygous. Mice received a gavage of tamoxifen (5mg in 0.2ml corn oil) for five days at seven to eight weeks of age to induce tdTomato (tdT) expression in glia. Mice were euthanized by CO2 inhalation at 10–20 weeks of age. Jejunum and mid colon segments were opened on the mesenteric border, fixed in 4% paraformaldehyde, immunostained for anti‐S100β, and cleared with Ce3D solution. Tissues were imaged using confocal microscopy and 3D reconstructions were made using Analyze. SOX10‐tdT cells were found in the bowel throughout all layers. In the muscularis externa of both the jejunum and colon, there were extensive networks within myenteric ganglia, intraganglionic fiber tracts, within the circular muscle layer, along fiber tracts ascending through the circular muscle, and rare cells were observed in the longitudinal muscle layer. In the submucosal layer of both the jejunum and colon, SOX‐tdT cells were in submucosal ganglia, along intraganglionic fibers and formed a regular network of processes that extended within the lamina propria surrounding the base of intestinal crypts. In the mucosa, SOX10‐tdT distribution differed between the jejunum and colon. In the colonic mucosa, there were two distinct bands of SOX10‐tdT networks oriented perpendicular to and surrounding all colonic glands which were approximately 120μm in height. These bands were located approximately 20μm and 60μm from the base of the glands. SOX10‐tdT cells were very rarely observed near the luminal surface of the colonic glands. In the jejunal mucosa, there were extensive SOX10‐tdT networks throughout the lamina propria surrounding crypts and extending to the tips of villi. Overlap of SOX10‐tdT and S100β immunoreactivity was nearly 100% throughout all glial populations with two exceptions, only 10–20% of SOX10‐tdT cells had S100β immunoreactivity in the jejunum mucosa and there were submucosal neurons that expressed S100β that did not contain SOX10‐tdT. Collectively, these data demonstrate significant complexity of the glial networks of the intestines with distinct morphological differences between mucosal glia of the colon and jejunum that may implicate different functions of enteric glia in the small and large intestines. Support or Funding Information Supported by NIH grants R01DK106011, P30DK084567 and DP2AT010875 and Department of Defense grant W81XWH‐18‐1‐0218. Representative SOX10‐tdT fluorescence in projections of 409 or 139 1.22μm‐thick confocal images through the full thickness of either jejunum (left) or colon (right), respectively. Figure 1

Abstract Background Gastric emptying is a complex physiological process regulating the division of a meal into smaller partitions for the small intestine. Disrupted gastric emptying contributes to digestive disease, yet current measures may not reflect different mechanisms by which the process can be altered. Methods We have developed high temporal resolution solid and liquid gastric emptying breath tests in mice using [ 13 C]‐octanoic acid and off axis‐ integrated cavity output spectroscopy ( OA ‐ ICOS ). Stretched gamma variate and 2‐component stretched gamma variate models fit measured breath excretion data. Key Results These assays detect acceleration and delay using pharmacological (7.5 mg/kg atropine) or physiological (nutrients, cold exposure stress, diabetes) manipulations and remain stable over time. High temporal resolution resolved complex excretion curves with 2 components, which was more prevalent in mice with delayed gastric emptying following streptozotocin‐induced diabetes. There were differences in the gastric emptying of Balb/c vs C57Bl6 mice, with slower gastric emptying and a greater occurrence of two‐phase gastric emptying curves in the latter strain. Gastric emptying of C57Bl6 could be accelerated by halving the meal size, but with no effect on the occurrence of two‐phase gastric emptying curves. A greater proportion of two‐phase gastric emptying was induced in Balb/c mice with the administration of PYY (8‐80 nmol) 60 min following meal ingestion. Conclusions and Inferences Collectively, these results demonstrate the utility of high temporal resolution gastric emptying assays. Two‐phase gastric emptying is more prevalent than previously reported, likely involves intestinal feedback, but contributes little to the overall rate of gastric emptying.