Vagal afferent neurons in high fat diet-induced obesity; intestinal microflora, gut inflammation and cholecystokinin.

The vagal afferent pathway is the major neural pathway by which information about ingested nutrients reaches the CNS and influences both GI function and feeding behavior. Vagal afferent neurons (VAN) express receptors for many of the regulatory peptides and molecules released from the intestinal wall, pancreas, and adipocytes that influence GI function, glucose homeostasis, and regulate food intake and body weight. As such, they play a critical role in both physiology and pathophysiology, such as obesity, where there is evidence that vagal afferent function is altered. This review will summarize recent findings on changes in vagal afferent function in response to ingestion of high fat diets and explore the hypothesis that changes in gut microbiota and integrity of the epithelium may not only be important in inducing these changes but may be the initial events that lead to dysregulation of food intake and body weight in response to high fat, high energy diets.

Propensity to high-fat diet-induced obesity in rats is associated with changes in the gut microbiota and gut inflammation.

Consumption of diets high in fat and calories leads to hyperphagia and obesity, which is associated with chronic "low-grade" systemic inflammation. Ingestion of a high-fat diet alters the gut microbiota, pointing to a possible role in the development of obesity. The present study used Sprague-Dawley rats that, when fed a high-fat diet, exhibit either an obesity-prone (DIO-P) or obesity-resistant (DIO-R) phenotype, to determine whether changes in gut epithelial function and microbiota are diet or obese associated. Food intake and body weight were monitored daily in rats maintained on either low- or high-fat diets. After 8 or 12 wk, tissue was removed to determine adiposity and gut epithelial function and to analyze the gut microbiota using PCR. DIO-P but not DIO-R rats exhibit an increase in toll-like receptor (TLR4) activation associated with ileal inflammation and a decrease in intestinal alkaline phosphatase, a luminal enzyme that detoxifies lipopolysaccharide (LPS). Intestinal permeability and plasma LPS were increased together with phosphorylation of myosin light chain and localization of occludin in the cytoplasm of epithelial cells. Measurement of bacterial 16S rRNA showed a decrease in total bacterial density and an increase in the relative proportion of Bacteroidales and Clostridiales orders in high-fat-fed rats regardless of phenotype; an increase in Enterobacteriales was seen in the microbiota of DIO-P rats only. Consumption of a high-fat diet induces changes in the gut microbiota, but it is the development of inflammation that is associated with the appearance of hyperphagia and an obese phenotype.

Cocaine- and amphetamine-regulated transcript mediates the actions of cholecystokinin on rat vagal afferent neurons.

BACKGROUND & AIMS: Cholecystokinin (CCK) acts on vagal afferent neurons to inhibit food intake and gastric emptying; it also increases expression of the neuropeptide cocaine- and amphetamine-regulated transcript (CART), but the significance of this is unknown. We investigated the role of CARTp in vagal afferent neurons. METHODS: Release of CART peptide (CARTp) from cultured vagal afferent neurons was determined by enzyme-linked immunosorbent assay. Expression of receptors and neuropeptides in rat vagal afferent neurons in response to CARTp was studied using immunohistochemistry and luciferase promoter reporter constructs. Effects of CARTp and CCK were studied on food intake. RESULTS: CCK stimulated CARTp release from cultured nodose neurons. CARTp replicated the effect of CCK in stimulating expression of Y2R and of CART itself in these neurons in vivo and in vitro, but not in inhibiting cannabinoid-1, melanin-concentrating hormone, and melanin-concentrating hormone-1 receptor expression. Effects of CCK on Y2R and CART expression were reduced by CART small interfering RNA or brefeldin A. Exposure of rats to CARTp increased the inhibitory action of CCK on food intake after short-, but not long-duration, fasting. CONCLUSIONS: The actions of CCK in stimulating CART and Y2R expression in vagal afferent neurons and in inhibiting food intake are augmented by CARTp; CARTp is released by CCK from these neurons, indicating that it acts as an autocrine excitatory mediator.