Orexins (hypocretins) contribute to fear and avoidance in rats exposed to a single episode of footshocks.

Orexins (hypocretins) are peptides that have been shown to regulate behavioral arousal and wakefulness. Recent evidence indicates that orexin neurons are activated by stress and that orexins play a role in anxiety. The present paper describes a series of experiments that examined whether orexins are involved in the anxiety that resulted from exposing rats to an acute episode of footshocks (5 × 2 s of 1.5 mA shocks). We found that prepro-orexin (ppOX) mRNA was elevated in rats at 6 and 14 days after exposure to footshock and that ppOX mRNA levels were correlated with fear at 14 days post-shock. Systemic injections of the non-selective dual orexin receptor antagonist TCS-1102 (10 and 20 mg/kg, i.p.) were found to decrease fear and anxiety in rats 14 days after exposure to footshock. We also found that rats that exhibited a high level of immobility to a novel tone the day after the footshock episode (high responders, HR) showed significantly elevated levels of ppOX mRNA at 14 days post-shock compared to control rats. Furthermore, TCS-1102 (10 mg/kg, i.p.) was found to have anxiolytic effects that were specific for HR when tested in the elevated T-maze. This study provides evidence linking the orexin system to the anxiety produced by exposure of rats to a single episode of footshocks. It also provides preclinical evidence in support of the use of orexin antagonists for the treatment of anxiety in response to an acute episode of stress.

Y2Y4 receptor double knockout protects against obesity due to a high-fat diet or Y1 receptor deficiency in mice.

Neuropeptide Y receptors are critical regulators of energy homeostasis, but the functional interactions and relative contributions of Y receptors and the environment in this process are unknown. We measured the effects of an ad libitum diet of normal or high-fat food on energy balance in mice with single, double, or triple deficiencies of Y1, Y2, or Y4 receptors. Whereas wild-type mice developed diet-induced obesity, Y2Y4 double knockouts did not. In contrast, Y1 knockout or Y1Y2 or Y1Y4 receptor double knockout mice developed an exacerbated diet-induced obesity syndrome. Remarkably, the antiobesity effect of Y2Y4 deficiency was stronger than the obesogenic effect of Y1 deficiency, since Y1Y2Y4 triple knockouts did not develop obesity on the high-fat diet. Resistance to diet-induced obesity in Y2Y4 knockouts was associated with reduced food intake and improved glucose tolerance in the absence of changes in total physical activity. Fecal concentration of free fatty acids was significantly increased in Y2Y4 knockouts in association with a significantly reduced bile acid pool and marked alterations in intestinal morphology. In addition, hypothalamic proopiomelanocortin expression was decreased in diet-induced obesity (in both wild-type and Y1 receptor knockout mice) but not in obesity-resistant Y2Y4 receptor knockout mice fed a high-fat diet. Therefore, deletion of Y2 and Y4 receptors synergistically protects against diet-induced obesity, at least partially via changes in food intake and hypothalamic proopiomelanocortin expression.

Exposure to smoke during development: fetal programming of adult disease.

It is well established that smoking has potent effects on a number of parameters including food intake, body weight, metabolism, and blood pressure. For example, it is well documented that 1) there is an inverse relationship between smoking and body weight, and 2) smoking cessation is associated with weight gain. However, there is increasing evidence that smoking can exert deleterious effects on energy balance through maternal exposure during fetal development. Specifically, there appears to be an increased incidence of metabolic disease (including obesity), and cardiovascular disease in children and adults that were exposed to smoke during fetal development. The present review will examine the relationship between maternal smoke and adult disease in offspring. The epidemiological studies highlighting this relationship will be reviewed as well as the experimental animal models that point to potential mechanisms underlying this relationship. A better understanding of how smoking effects changes in energy balance may lead to treatments to ameliorate the long-lasting effects of perinatal exposure to smoke as well as increasing the health benefits associated with smoking cessation.

Identification of leptin receptors in lung and isolated fetal type II cells.

Leptin is a cytokine involved in regulation of the satiety response. Receptors for this protein have been identified in brain as well as many other peripheral tissues. Some of the highest levels of receptor concentration occur in the lung. Considering the cellular diversity of lung, neither the localization nor the function of leptin in pulmonary tissues has been delineated. The purpose of the present study was to determine if fetal and adult rabbit lung displayed specific binding for leptin, to identify the binding sites, and to explore a potential functional role for leptin in lung surfactant production. Frozen sections of adult and fetal rabbit (24th gestational day) lung were prepared and incubated with increasing concentrations of [125I]leptin in the presence or absence of 1-microM-unlabeled leptin. Sections were removed and radioactivity measured. Concurrently, sections were coated with nuclear Trac emulsion and incubated in the dark at -30 degrees C. Lung showed specific binding for leptin. Microscopically, [125I]leptin was localized to acinar-lining epithelium of developing fetal lung. Larger cells within the epithelial layer appeared to bind leptin more avidly than adjacent cells. Antibodies to the leptin receptor were used to identify binding sites in adult lung and isolated fetal lung type II cells. In adult lung, both the K20 (against the extracellular amino-terminal) and the M18 antibody (against the intracellular carboxy-terminal) displayed several binding sites. In contrast, the isolated fetal type II cells showed only a single binding site for both antibodies. The apparent molecular mass of the receptor using the K20 antibody appeared to be approximately 125 kD. A protein of similar mass bound the M18 antibody suggesting that functional receptor is present in lung and expressed by fetal type II cells. Incubation of isolated fetal type II cells with leptin (0.01-10 microg/ml) stimulated [3H]choline incorporation in disaturated phosphatidylcholine. These results show that fetal and adult lung bind leptin specifically, and fetal type II cells in particular, may be responsive to leptin stimulation of phospholipid production. Leptin may therefore be important in regulating maturation of cells of the fetal lung.