Dietary fatty acid composition drives neuroinflammation and impaired behavior in obesity

Nutrient composition in obesogenic diets may influence the severity of disorders associated with obesity such as insulin-resistance and chronic inflammation. Here we hypothesized that obesogenic diets rich in fat and varying in fatty acid composition, particularly in omega 6 (ω6) to omega 3 (ω3) ratio, have various effects on energy metabolism, neuroinflammation and behavior. Mice were fed either a control diet or a high fat diet (HFD) containing either low (LO), medium (ME) or high (HI) ω6/ω3 ratio. Mice from the HFD-LO group consumed less calories and exhibited less body weight gain compared to other HFD groups. Both HFD-ME and HFD-HI impaired glucose metabolism while HFD-LO partly prevented insulin intolerance and was associated with normal leptin levels despite higher subcutaneous and perigonadal adiposity. Only HFD-HI increased anxiety and impaired spatial memory, together with increased inflammation in the hypothalamus and hippocampus. Our results show that impaired glucose metabolism and neuroinflammation are uncoupled, and support that diets with a high ω6/ω3 ratio are associated with neuroinflammation and the behavioral deterioration coupled with the consumption of diets rich in fat.

Microgliosis: a double-edged sword in the control of food intake

Maintaining energy balance is essential for survival and health. This physiological function is controlled by the brain, which adapts food intake to energy needs. Indeed, the brain constantly receives a multitude of biological signals that are derived from digested foods or that originate from the gastrointestinal tract, energy stores (liver and adipose tissues) and other metabolically active organs (muscles). These signals, which include circulating nutrients, hormones and neuronal inputs from the periphery, collectively provide information on the overall energy status of the body. In the brain, several neuronal populations can specifically detect these signals. Nutrient-sensing neurons are found in discrete brain areas and are highly enriched in the hypothalamus. In turn, specialized brain circuits coordinate homeostatic responses acting mainly on appetite, peripheral metabolism, activity and arousal. Accumulating evidence shows that hypothalamic microglial cells located at the vicinity of these circuits can influence the brain control of energy balance. However, microglial cells could have opposite effects on energy balance, that is homeostatic or detrimental, and the conditions for this shift are not totally understood yet. One hypothesis relies on the extent of microglial activation, and nutritional lipids can considerably change it.

Evidence for Constitutive Microbiota-Dependent Short-Term Control of Food Intake in Mice: Is There a Link with Inflammation, Oxidative Stress, Endotoxemia, and GLP-1?

Aims: Although prebiotics, probiotics, and fecal transplantation can alter the sensation of hunger and/or feeding behavior, the role of the constitutive gut microbiota in the short-term regulation of food intake during normal physiology is still unclear. Results: An antibiotic-induced microbiota depletion study was designed to compare feeding behavior in conventional and microbiota-depleted mice. Tissues were sampled to characterize the time profile of microbiota-derived signals in mice during consumption of either standard or high-fat food for 1 h. Pharmacological and genetic tools were used to evaluate the contribution of postprandial endotoxemia and inflammatory responses in the short-term regulation of food intake. We observed constitutive microbial and macronutrient-dependent control of food intake at the time scale of a meal; that is, within 1 h of food introduction. Specifically, microbiota depletion increased food intake, and the microbiota-derived anorectic effect became significant during the consumption of high-fat but not standard food. This anorectic effect correlated with a specific postprandial microbial metabolic signature, and did not require postprandial endotoxemia or an NOD-, LRR-, and Pyrin domain-containing protein 3-inflammasome-mediated inflammatory response. Innovation and Conclusion: These findings show that the gut microbiota controls host appetite at the time scale of a meal under normal physiology. Interestingly, a microbiota-derived anorectic effect develops specifically with a high-fat meal, indicating that gut microbiota activity is involved in the satietogenic properties of foods. Antioxid. Redox Signal. 37, 349-369.

The hepatocyte insulin receptor is required to program the liver clock and rhythmic gene expression

Liver physiology is circadian and sensitive to feeding and insulin. Food intake regulates insulin secretion and is a dominant signal for the liver clock. However, how much insulin contributes to the effect of feeding on the liver clock and rhythmic gene expression remains to be investigated. Insulin action partly depends on changes in insulin receptor (IR)-dependent gene expression. Here, we use hepatocyte-restricted gene deletion of IR to evaluate its role in the regulation and oscillation of gene expression as well as in the programming of the circadian clock in the adult mouse liver. We find that, in the absence of IR, the rhythmicity of core-clock gene expression is altered in response to day-restricted feeding. This change in core-clock gene expression is associated with defective reprogramming of liver gene expression. Our data show that an intact hepatocyte insulin receptor is required to program the liver clock and associated rhythmic gene expression.

Annular aperture arrays: study in the visible region of the electromagnetic spectrum

Baida and Van Labeke recently proposed a structure that exhibits a supertransmission of light through an array of nanometric coaxial apertures in a metallic film that has been named an annular aperture array (AAA) [Opt. Commun. 209, 17 (2002); Phys. Rev. B 67, 155314 (2003); J. Microsc. 213, 140 (2003)]. We present the first experimental study, to our knowledge, of an AAA structure in the visible region. For technological reasons, the structure under study does not produce a supertransmission of 80% as in Baida and Van Labeke [Opt. Commun. 209, 17 (2002)]. We built the nanostructure and experimentally recorded its far-field spectral response. This transmission shows only one broad band with a maximum around lambda = 700 nm, giving a maximum efficiency around 17%. A finite-difference time-domain simulation reproduces quite well the obtained transmission spectrum.

Resonant optical cavity used as a nonradiating source for optical near-field microscopy

Nonradiating sources are emitting devices whose geometry prohibits electromagnetic emission. First, we show that a ring cavity can be substituted for the usual prism in scanning tunneling optical microscopy. Second, we find that near-field detection is an ideal way to explore the behavior of such nonradiating sources.