High-fat diet impairs duodenal barrier function and elicits glia-dependent changes along the gut-brain axis that are required for anxiogenic and depressive-like behaviors

Background Mood and metabolic disorders are interrelated and may share common pathological processes. Autonomic neurons link the brain with the gastrointestinal tract and constitute a likely pathway for peripheral metabolic challenges to affect behaviors controlled by the brain. The activities of neurons along these pathways are regulated by glia, which exhibit phenotypic shifts in response to changes in their microenvironment. How glial changes might contribute to the behavioral effects of consuming a high-fat diet (HFD) is uncertain. Here, we tested the hypothesis that anxiogenic and depressive-like behaviors driven by consuming a HFD involve compromised duodenal barrier integrity and subsequent phenotypic changes to glia and neurons along the gut-brain axis. Methods C57Bl/6 male mice were exposed to a standard diet or HFD for 20 weeks. Bodyweight was monitored weekly and correlated with mucosa histological damage and duodenal expression of tight junction proteins ZO-1 and occludin at 0, 6, and 20 weeks. The expression of GFAP, TLR-4, BDNF, and DCX were investigated in duodenal myenteric plexus, nodose ganglia, and dentate gyrus of the hippocampus at the same time points. Dendritic spine number was measured in cultured neurons isolated from duodenal myenteric plexuses and hippocampi at weeks 0, 6, and 20. Depressive and anxiety behaviors were also assessed by tail suspension, forced swimming, and open field tests. Results HFD mice exhibited duodenal mucosa damage with marked infiltration of immune cells and decreased expression of ZO-1 and occludin that coincided with increasing body weight. Glial expression of GFAP and TLR4 increased in parallel in the duodenal myenteric plexuses, nodose ganglia, and hippocampus in a time-dependent manner. Glial changes were associated with a progressive decrease in BDNF, and DCX expression, fewer neuronal dendritic spines, and anxiogenic/depressive symptoms in HFD-treated mice. Fluorocitrate (FC), a glial metabolic poison, abolished these effects both in the enteric and central nervous systems and prevented behavioral alterations at week 20. Conclusions HFD impairs duodenal barrier integrity and produces behavioral changes consistent with depressive and anxiety phenotypes. HFD-driven changes in both peripheral and central nervous systems are glial-dependent, suggesting a potential glial role in the alteration of the gut-brain signaling that occurs during metabolic disorders and psychiatric co-morbidity.

The Enteric Nervous System and Its Emerging Role as a Therapeutic Target

The gastrointestinal (GI) tract is innervated by the enteric nervous system (ENS), an extensive neuronal network that traverses along its walls. Due to local reflex circuits, the ENS is capable of functioning with and without input from the central nervous system. The functions of the ENS range from the propulsion of food to nutrient handling, blood flow regulation, and immunological defense. Records of it first being studied emerged in the early 19th century when the submucosal and myenteric plexuses were discovered. This was followed by extensive research and further delineation of its development, anatomy, and function during the next two centuries. The morbidity and mortality associated with the underdevelopment, infection, or inflammation of the ENS highlight its importance and the need for us to completely understand its normal function. This review will provide a general overview of the ENS to date and connect specific GI diseases including short bowel syndrome with neuronal pathophysiology and current therapies. Exciting opportunities in which the ENS could be used as a therapeutic target for common GI diseases will also be highlighted, as the further unlocking of such mechanisms could open the door to more therapy-related advances and ultimately change our treatment approach.

The Enteric Nervous System and Its Emerging Role as A Therapeutic Target

The gastrointestinal (GI) tract is innervated by the enteric nervous system (ENS), an extensive neuronal network that traverses along its walls. Due to local reflex circuits, the ENS is capable of functioning with and without input from the central nervous system. The functions of the ENS range from the propulsion of food to nutrient handling, blood flow regulation and immunological defense. Records of it first being studied emerged in the early 19th century when the submucosal and myenteric plexuses were discovered. This was followed by extensive research and further delineation of its development, anatomy, and function during the next two centuries. The morbidity and mortality associated with the underdevelopment, infection or inflammation of the ENS highlights its importance and the need for us to completely understand its normal function. This review will provide a general overview of the ENS to date and connect specific GI disorders such as short bowel syndrome with neuronal pathophysiology. Exciting opportunities in which the ENS could be used as a therapeutic target for common GI diseases will also be highlighted, as the further unlocking of such mechanisms could open the door to more therapy-related advances, and ultimately change our approach to GI disorders.

Immunohistochemical Diagnosis of Hirschsprung’s Disease and Allied Disorders

Summary Introduction. Hirschsprung’s disease accounts for approximately 20% of neonatal bowel obstruction and has a mortality rate of 20 to 25%. As the pathology severely affects a child’s quality of life, quick and precise diagnosis is mandatory. For years, diagnosis relied completely on histopathological analysis of rectal biopsies using haematoxylin-eosin and acetylcholinesterase stains. However, there have been many attempts to find an immunohistochemical marker that would simplify diagnosis of Hirschsprung’s disease. Acceptable markers should be highly sensitive and specific, easy to use and reliable. Aim of the study. The aim is to disclose the full morphological scope of Hirschsprung’s disease and allied disorders by using data available at the Children’s Clinical University Hospital (Riga, Latvia) and to identify the most sensitive and specific immunohistochemical marker for the diagnosis of Hirschsprung’s disease and allied disorders. Material and methods. In a retrospective study, all patients diagnosed with Hirschsprung’s disease and allied disorders at the Pathology Bureau of the Children’s Clinical University Hospital between April 2010 and October 2014 were identified. Immunohistochemical visualisation of calretinin, chromogranin A and synaptophysin was carried out. A conjugated polymer system EnVision was used to detect the bound primary antibodies. The study was controlled by findings in the bowel wall of adults and children lacking aganglionosis. The intensity and pattern of ganglion cell and nerve fibre staining were evaluated semi-quantitatively on a scale of one to three in both submucosal and myenteric plexuses of bowel. The specificity and sensitivity of each immunohistochemical marker were determined with a MedCalc online calculator. Results. During the relevant period, Hirschsprung’s disease (23) and allied disorders (12) were diagnosed in 35 patients. Among these children, 45.7% were diagnosed during the first year of life. Three types of Hirschsprung’s disease were present - short segment disease (73.9%), long segment disease (21.8%) and total colonic aganglionosis (4.3%). Allied Hirschsprung’s disorders were of three different types - hypoganglionosis (75%), zonal aganglionosis (16.7%) and immaturity of ganglion cells (8.3%). After evaluation of the reactivity of immunohistochemical markers, calretinin, synaptophysin and chromogranin showed staining intensity of ganglion cells of 2.47, 0.58 and 0.63, respectively, while nerve plexus staining intensity was 1.84 for calretinin, 2.68 for synaptophysin and 1.79 for chromogranin. Calretinin was characterised by sensitivity/ specificity as high as 90.5%/ 92.9% while these parameters were only 52.4%/ 100.0% for chromogranin A and 33.3%/ 14.3% for synaptophysin. Conclusions. In Latvia, the diagnosis of Hirschsprung’s disease or allied disorder is made later in life than it is in other countries. Hirschsprung’s disease was more frequent than the allied disorders. It can present as short segment disease, long segment disease and total colonic aganglionosis. Calretinin showed the highest reactivity to ganglion cells and proved to be the most specific and sensitive marker for diagnosis of Hirschsprung’s disease and allied disorders. Synaptophysin showed strong staining of myenteric plexuses and can be used for assessment of extrinsic nerve fibres despite its low reactivity to ganglion cells.

Presence of intramucosal neuroglial cells in normal and aganglionic human colon

The enteric nervous system (ENS) is composed of neural crest-derived neurons (also known as ganglion cells) the cell bodies of which are located in the submucosal and myenteric plexuses of the intestinal wall. Intramucosal ganglion cells are known to exist but are rare and often considered ectopic. Also derived from the neural crest are enteric glial cells that populate the ganglia and the associated nerves, as well as the lamina propria of the intestinal mucosa. In Hirschsprung disease (HSCR), ganglion cells are absent from the distal gut because of a failure of neural crest-derived progenitor cells to complete their rostrocaudal migration during embryogenesis. The fate of intramucosal glial cells in human HSCR is essentially unknown. We demonstrate a network of intramucosal cells that exhibit dendritic morphology typical of neurons and glial cells. These dendritic cells are present throughout the human gut and express Tuj1, S100, glial fibrillary acidic protein, CD56, synaptophysin, and calretinin, consistent with mixed or overlapping neuroglial differentiation. The cells are present in aganglionic colon from patients with HSCR, but with an altered immunophenotype. Coexpression of Tuj1 and HNK1 in this cell population supports a neural crest origin. These findings extend and challenge the current understanding of ENS microanatomy and suggest the existence of an intramucosal population of neural crest-derived cells, present in HSCR, with overlapping immunophenotype of neurons and glia. Intramucosal neuroglial cells have not been previously recognized, and their presence in HSCR poses new questions about ENS development and the pathobiology of HSCR that merit further investigation.