Leptin concentrations in response to acute stress predict subsequent intake of comfort foods

Stress-induced behavioral and metabolic adaptations lead to an obesity-prone phenotype in ewes with elevated cortisol responses

The underlying cause of predisposition to obesity is complex but one marker is cortisol responsiveness. Selection of sheep for high (HR) or low (LR) cortisol responses to adrenocorticotropin shows that HR are more likely to become obese. Increased propensity to obesity is associated with reduced skeletal muscle thermogenesis. We sought to determine whether metabolic or behavioral responses to stress also contribute to altered propensity to obesity in LR and HR. Animals (n=5-10/group) were exposed to 3 stressors and we measured food intake and thermogenesis (recorded with dataloggers implanted into muscle). Stressors were hypoglycaemia (0.125 units/kg insulin, IV), a barking dog and immune challenge (200 ng/kg lipopolysaccharide--LPS, IV). LR animals showed a greater catabolic state in response to both immune and psychosocial stressors. LPS reduced (P<0.01) food intake in both groups but LR showed a greater (P<0.05) reduction in food intake and a more substantial (P<0.05) rise in muscle temperature. Introduction of the barking dog reduced (P<0.05) food intake in LR only. These metabolic differences coincided with differences in cortisol responsiveness, where HR animals had increased (P<0.05) cortisol in response to both immune and psychosocial stressors. We also assessed behavior in the following paradigms: 1, isolation in the open field test; 2, response to a human intruder; and 3, food competition. LR had greater (P<0.05) activity, reduced fearfulness and displayed a proactive coping style of behavior. Thus we demonstrate that high cortisol responsiveness identifies animals with stress-induced metabolic and behavioral traits that may contribute to susceptibility to obesity.

Neuroendocrine circuits governing energy balance and stress regulation: functional overlap and therapeutic implications

Significant comorbidities between obesity-related metabolic disease and stress-related psychological disorders suggest important functional interactions between energy balance and brain stress integration. Largely overlapping neural circuits control these systems, and this anatomical arrangement optimizes opportunities for mutual influence. Here we first review the current literature identifying effects of metabolic neuroendocrine signals on stress regulation, and vice versa. Next, the contributions of reward-driven food intake to these metabolic and stress interactions are discussed. Lastly, we consider the interrelationships between metabolism, stress, and reward in light of their important implications in the development of therapies for metabolism- or stress-related disease.

Biological and psychological markers of stress in humans: focus on the Trier Social Stress Test

Validated biological and psychological markers of acute stress in humans are an important tool in translational research. The Trier Social Stress Test (TSST), involving public interview and mental arithmetic performance, is among the most popular methods of inducing acute stress in experimental settings, and reliably increases hypothalamic-pituitary-adrenal axis activation. However, although much research has focused on HPA axis activity, the TSST also affects the sympathetic-adrenal-medullary system, the immune system, cardiovascular outputs, gastric function and cognition. We critically assess the utility of different biological and psychological markers, with guidance for future research, and discuss factors which can moderate TSST effects. We outline the effects of the TSST in stress-related disorders, and if these responses can be abrogated by pharmacological and psychological treatments. Modified TSST protocols are discussed, and the TSST is compared to alternative methods of inducing acute stress. Our analysis suggests that multiple readouts are necessary to derive maximum information; this strategy will enhance our understanding of the psychobiology of stress and provide the means to assess novel therapeutic agents.

Reconstruction of the drive underlying food intake and its control by leptin and dieting

The intake of food and the expenditure of calories is modelled by a system of differential equations. The state variables are the amount of calories stored in adipose tissue and the level of plasma leptin. The model has as input a drive that controls the intake of food. This drive consists of a collective of physiological and psychological incentives to eat or to stop eating. An individual based approach is presented by which the parameters of the system can be set using data of a subject. The method of analysis is fully worked out using weight data of two persons. The model is prone to extensions by transferring incentives being part of the input to the collection of state variables.

Serum leptin and loss of control eating in children and adolescents

BACKGROUND

Both insufficiency and resistance to the actions of the adipocyte-derived hormone leptin promote hunger, increased food intake and greater body weight. Some studies suggest that adults reporting binge eating have increased serum leptin compared with those without binge eating, even after adjusting for the greater adiposity that characterizes binge eaters. Pediatric binge or loss of control (LOC) eating are prospective risk factors for excessive weight gain and may predict development of metabolic abnormalities, but whether LOC eating is associated with higher leptin among children is unknown. We therefore examined leptin and LOC eating in a pediatric cohort.

METHODS

A convenience sample of 506 lean and obese youth (7-18 years) was recruited from Washington, DC and its suburbs. Serum leptin was collected after an overnight fast. Adiposity was measured by dual-energy X-ray absorptiometry or air displacement plethysmography. LOC eating was assessed by interview methodology.

RESULTS

Leptin was strongly associated with fat mass (r=0.79, P<0.001). However, even after adjusting for adiposity and other relevant covariates, youth with LOC eating had higher serum leptin compared with those without LOC episodes (15.42±1.05 vs 12.36±1.04 ng ml(-1), P<0.001). Neither reported amount of food consumed during a recent LOC episode nor number of LOC episodes in the previous month accounted for differences in leptin (P>0.05). The relationship between LOC eating and leptin appeared to be significant for females only (P=0.002).

CONCLUSIONS

Reports of LOC eating were associated with higher fasting leptin in youth, beyond the contributions of body weight. Prospective studies are required to elucidate whether LOC eating promotes greater leptin or whether greater leptin resistance may promote LOC eating.

Effects of feed on plasma leptin and ghrelin concentrations in crib-biting horses

The reason why some horses begin an oral stereotypy such as crib-biting is not known. The aim of this study was to measure ghrelin and leptin concentrations in plasma concentrations to determine whether there is a link to crib-biting in horses. Plasma samples (n=3) were collected for plasma leptin and ghrelin assay before and during the morning first feeding in the usual environments of 15 horses with stereotypic crib-biting and 15 matched controls. The crib-biting intensity was scored in three 5-min phases, and a subgroup of verified crib-biters (n=8) was defined as horses that were seen to crib-bite during this study. Plasma leptin concentration (mean and 95% confidence interval [CI]) was lower in horses observed to crib-bite before and after feeding of concentrates (1.2, CI 0.8-1.7 ng/mL and 1.0, CI 0.6-1.7) than in non-crib-biters (2.3, CI 1.6-3.4 and 2.3, CI 1.6-3.4 ng/mL, respectively) and correlated negatively with crib-biting intensity. Crib-biting intensity was significantly higher shortly after feeding than before or 30 min later. Plasma ghrelin concentration was significantly higher before feeding concentrate than before hay feeding or after the concentrate, but did not differ between groups. There was a significant negative correlation between body composition score and plasma ghrelin concentration. These findings suggest that leptin concentrations may be associated with crib-biting behaviour in horses.

Obesity as malnutrition: the dimensions beyond energy balance

The aetiology of obesity is seemingly simple to understand: individuals consume more energy than they expend, with the excess energy being stored in adipose tissue. Public health campaigns therefore promote dietary restraint and physical exercise, and emphasize individual responsibility for these behaviours. Increasingly, however, researchers are switching from thermodynamic to metabolic models of obesity, thereby clarifying how specific environmental factors promote lipogenesis. Obesity can best be explained not by counting 'calories in and out', but by understanding how specific dietary products and activity behaviours perturb cellular metabolism and promote net lipogenesis. This metabolic approach can furthermore be integrated with more sophisticated models of how commercial practices drive the consumer trends that promote obesogenic behaviours. Notably, obesity treatment has proven more effective if it bypasses individual responsibility, suggesting that a similar approach placing less emphasis on individual responsibility would improve the efficacy of obesity prevention. Successful obesity prevention campaigns are likely to emerge only when the public receive better 'protection' from the commercial practices that are driving the global obesity epidemic. Rather than populations failing to heed governments' public health advice, governments are currently failing the public by abandoning their responsibility for regulating commercial activities.

Enhanced brain performance in mice following postnatal stress

The double postnatal stress model (brief maternal separation plus sham injection daily applied from birth to weaning) induces metabolic alterations similar to type 2 diabetes in young-adult male mice. We verify whether 1) the stress also induces brain metabolic-functional alterations connected to diabetes and 2) different alterations are modulated selectively by two stress-damaged endogenous systems (opioid- and/or ACTH-corticosteroid-linked). Here, diabetes-like metabolic plus neurophysiologic-neurometabolic parameters are studied in adult mice following postnatal stress and drug treatment. Surprisingly, together with 'classic' diabetes-like alterations, the stress model induces in young-adult mice significantly enhanced brain neurometabolic-neurophysiologic performances, consisting of decreased latency to flash-visual evoked potentials (- ~8%); increased level (+ ~40%) and reduced latency (- ~30%) of NAD(P)H autofluorescence postsynaptic signals following electric stimuli; enhanced passive avoidance learning (+ ~135% latency); and enhanced brain-derived neurotrophic factor level (+ ~70%). Postnatal treatment with the opioid receptor antagonist naloxone prevents some alterations, moreover the treatment with antisense (AS; AS vs proopiomelanocortin mRNA) draws all parameters to control levels, thus showing that some alterations are bound to endogenous opioid-system hyper-functioning, while others depend on ACTH-corticosterone system hyper-functioning. Our stress model induces diabetes-like metabolic alterations coupled to enhanced brain neurometabolic-neurophysiologic performances. Taken all together, these findings are compatible with an 'enduring acute-stress' reaction, which puts mice in favorable survival situations vs controls. However, prolonged hormonal-metabolic imbalances are expected to also produce diabetes-like complications at later ages in stressed mice.

Cafeteria diet-induced obesity plus chronic stress alter serum leptin levels

Obesity is a disease that has become a serious public health issue worldwide, and chronic stressors, which are a problem for modern society, cause neuroendocrine changes with alterations in food intake. Obesity and chronic stress are associated with the development of cardiovascular diseases and metabolic disorders. In this study, a rat model was used to evaluate the effects of a hypercaloric diet plus chronic restraint stress on the serum leptin and lipids levels and on the weight of specific adipose tissue (mesenteric, MAT; subcutaneous, SAT and visceral, VAT). Wistar rats were divided into the following 4 groups: standard chow (C), hypercaloric diet (HD), stress plus standard chow (S), and stress plus hypercaloric diet (SHD). The animals in the stress groups were subjected to chronic stress (placed inside a 25 cm × 7 cm plastic tube for 1h per day, 5 days per week for 6 weeks). The following parameters were evaluated: the weight of the liver, adrenal glands and specific adipose tissue; the delta weight; the Lee index; and the serum levels of leptin, corticosterone, glucose, total cholesterol, and triglycerides. The hypercaloric diet induced obesity in rats, increasing the Lee index, weight, leptin, triglycerides, and cholesterol levels. The stress decreased weight gain even in animals fed a hypercaloric diet but did not prevent a significant increase in the Lee index. However, an interaction between the independent factors (hypercaloric diet and stress) was observed, which is demonstrated by the increased serum leptin levels in the animals exposed to both protocols.