The effects of differential psychological stress and infantile handling on plasma triglyceride and aortic cholesterol levels in rats

Drosophila serotonin 2A receptor signaling coordinates central metabolic processes to modulate aging in response to nutrient choice

It has been recognized for nearly a century that diet modulates aging. Despite early experiments suggesting that reduced caloric intake augmented lifespan, accumulating evidence indicates that other characteristics of the diet may be equally or more influential in modulating aging. We demonstrate that behavior, metabolism, and lifespan in Drosophila are affected by whether flies are provided a choice of different nutrients or a single, complete medium, largely independent of the amount of nutrients that are consumed. Meal choice elicits a rapid metabolic reprogramming that indicates a potentiation of TCA cycle and amino acid metabolism, which requires serotonin 2A receptor. Knockdown of glutamate dehydrogenase, a key TCA pathway component, abrogates the effect of dietary choice on lifespan. Our results reveal a mechanism of aging that applies in natural conditions, including our own, in which organisms continuously perceive and evaluate nutrient availability to promote fitness and well-being.

The foods we eat can affect our lifespan, but it is also possible that thinking about food may have effects on our health. Choosing what to eat is one of the main ways we think about food, and most animals, including the fruit fly Drosophila melanogaster, choose their foods. The effects of these choices can affect health via a chemical in the brain called serotonin. This chemical interacts with proteins called serotonin 2A receptors in the brain, which then likely primes the body to process nutrients.

To understand how serotonin affected the lifespan and health of fruit flies, Lyu et al. compared flies that were offered a single food to those that could choose between several foods. The flies that had a choice of foods lived shorter lives and produced more serotonin, but these effects were reversed when Lyu et al. limited the amount of a protein called glutamate dehydrogenase, which helps cells process nutrients.

These results suggest that choosing what we eat can impact lifespan, ageing and health. Human and fly brains share many similarities, but human brain chemistry is more complex, as is our experience of food. This work demonstrates that food choices can affect lifespan. More research into this phenomenon may shed further light onto how our thoughts and decision-making impact our health.

Comparison of the effects of acute and chronic psychological stress on metabolic features in rats

This study was aimed to compare the effects of acute and chronic psychological stress on metabolic factors. Forty-two male Wistar rats were divided into control and stressed groups. Stress was applied by a communication box acutely (1 d) and chronically (15 and 30 d). Blood sampling was carried out by retro-orbital-puncture method. The plasma levels of glucose, cholesterol, triglyceride, insulin, and corticosterone were measured. In addition, feed and water intake, latency to eat and drink, adrenal and body weights were determined. Acute and chronic psychological stress did not significantly change basal plasma corticosterone levels. However, immediately (1 min) after acute exposure to stress, plasma corticosterone level increased compared to that before stress exposure. Acute stress increased plasma insulin levels significantly. Fifteen days of stress exposure resulted in plasma glucose increase. Chronic stress significantly increased feed intake, latency to eat, and adrenal weight compared to acute stress. The body weights of both control and stressed groups increased markedly during the experiment. Homeostasis model assessment of insulin resistance (HOMA-IR) index did not change significantly in the stressed group. In conclusion, application of acute and chronic psychological stress leads to different metabolic and/or behavioral changes but the metabolic changes resulting from acute exposure to stress seem to be more pronounced.

Angiotensin-converting enzyme inhibition changes the metabolic response to neuroglucopenic stress

Neuroglucopenia induced by 2-deoxy-D-glucose (2DG) activates hypothalamic glucoreceptors leading to increased hepatic glucose production and insulin inhibition. This response is similar to what is observed with intravenous injection of angiotensin II (Ang II). However, the involvement of an angiotensin-converting enzyme inhibitor on neuroglucopenia has not been investigated. The aim of this study was to determine the effects of chronic enalapril treatment on plasma glucose, insulin and lipid levels in response to neuroglucopenia. Male Holtzman rats (120-170 g) were chronically treated with enalapril (10 mg/kg per day) in the drinking water for two weeks. On the day of experiment the animals received an i.v. enalapril final dose one hour before the neuroglucopenic stress by 2DG infusion (500 mg/kg), and blood samples were drawn before and 5, 10, 20, 30 and 60 minutes following infusion. The hyperglycaemic response to 2DG was not significantly changed by enalapril treatment. The enalapril-treated group exhibited a peak of plasma insulin higher than controls. Plasma triglyceride showed a significant increase only in the enalapril group after neuroglucopenic stress (p < 0.05).These data show that chronic enalapril treatment changes insulin and triglyceride responses to neuroglucopenia, suggesting an effect on glucose-induced insulin secretion and the storage of triglycerides.

Regulation by chronic-mild stress of glucocorticoids, monocyte chemoattractant protein-1 and adiposity in rats fed on a high-fat diet

Stress has been reported as a widespread problem and several studies have linked obesity and inflammation-related diseases. Moreover, the combination of suffering from chronic stress and high energy intake might be related to the onset of some metabolic diseases. To study the possible relationships between stress, inflammatory status and obesity, a chronic-mild stress (CMS) paradigm with a high-fat dietary intake model (Cafeteria diet) was implemented on male Wistar rats for 11 weeks. Stress and dietary intake effects on animal adiposity, serum biochemical as well as glucocorticoids and inflammation markers were all analyzed. As expected, consuming a high-fat diet increased body weight, adiposity and insulin resistance in non-stressed animals. A decrease of total white adipose tissue (WAT) and an increase of fecal glucocorticoids, as well as angiotensinogen, and monocyte chemoattractant protein-1 (MCP-1) expression level in retroperitoneal WAT were found only on control-stressed rats. Regarding the serum MCP-1, a decrease was observed on animals under CMS while being fed Cafeteria diet. Furthermore, 11β-hydroxysteroid dehydrogenase activity, a glucocorticoid and obesity biomarker in the liver, was influenced by high-fat diet intake but not by stress. Finally, statistical analysis showed a strong relation between MCP-1 expression levels in retroperitoneal WAT, fecal corticosterone and total WAT. This trial proved that CMS induced a glucocorticoid-mediated response, which was reduced by the intake of a Cafeteria diet. These findings suggest that a high-fat diet could protect against a stress condition and revealed a different behavior to a stressful environment depending on the nutritional status.

The effects of immobilization stress on serum triglycerides, nonesterified fatty acids, and total cholesterol in male rats after dietary modifications

The effects of acute immobilization stress on triglycerides, nonesterified fatty acids (NEFA) and total cholesterol were determined in serum samples obtained by indwelling jugular catheters from male Sprague-Dawley rats. Stress was evaluated in three groups of rats: (1) those maintained on a regular Purina Chow diet and then fasted for 24 hours; (2) those maintained on this same diet but not fasted (nonfasted) before experimentation; and (3) those maintained on a Purina Chow diet supplemented with cholesterol (1%) and fat (10%) for 6 weeks and nonfasted prior to experimentation. Samples were taken by catheter in the home cage prior to, four times during a one hour stress/nonstress period and thirty minutes after being returned to the home cage for recovery. Nonstressed rats remained in the home cage during the entire 90 minute period. In each dietary state studied, stress affected serum triglycerides and NEFA but not total cholesterol levels. Triglyceride levels in fasted rats increased during the stress period. On the other hand, triglycerides decreased in response to stress in nonfasted rats. In stressed, nonfasted high cholesterol-fed animals, triglycerides were elevated in comparison to their nonstressed counterparts. In both fasted, regular diet-fed and nonfasted, cholesterol-fed rats, NEFA sharply declined from baseline after 5 minutes of stress; NEFA did however increase after fifteen minutes. NEFA levels in both stressed and nonstressed, nonfasted rats also rapidly decreased from baseline and never recovered throughout the session. Total cholesterol did not change in response to stress or dietary modifications. The rats maintained on a high cholesterol diet showed only a diet-induced increase in total cholesterol. Thus, acute immobilization stress affected serum triglyceride and NEFA values and these effects were diet- and time-dependent. Total cholesterol levels were unaffected by stress.

i.r. Beta-endorphin, corticosterone, cholesterol and triglyceride concentrations in rat plasma after stress, cingulotomy or both

Plasma i.r. beta-endorphin, corticosterone, cholesterol and triglyceride concentrations were determined in male Sprague-Dawley rats after exposure to running or swimming stressors or after surgical ablation of the cingulum bundle. While cingulotomy alone altered only the plasma triglyceride concentrations, the combination of cingulotomy plus running stress significantly increased plasma i.r. beta-endorphin and triglyceride concentrations above those seen in animals receiving only a running stress. Triglyceride concentrations in cingulotomy plus swimming stress were significantly elevated above those in animals receiving a severe stress only. While the exposure to running and swimming increased plasma beta-endorphin significantly above control levels, plasma corticosterone was not affected by these stressors. Changes in plasma cholesterol and triglycerides were also differentially affected by cingulotomy or stress exposure. These results indicate that various stress hormones are affected differentially by exposure to various experimental procedures which are employed as stressors.

Effects of stress and ovariectomy on the plasma cholesterol, serum triglyceride, and aortic cholesterol levels of female rats

Female Sprague-Dawley rats were either ovariectomized or sham-operated prior to puberty. As adults, they were maintained on a cholesterol-supplemented diet and subjected to either predictable, controllable shock; unpredictable, uncontrollable shock; or no shock for 30 days (51-min daily sessions). Sham-operated rats had higher plasma cholesterol levels than ovariectomized rats, but neither group showed an effect of stress treatments. For both groups, serum triglyceride and aortic cholesterol levels were lower in stressed than nonstressed rats. Additionally, the ovariectomized rats had higher levels of serum triglycerides than sham-operated controls.

Sensitivity of corticosterone and some metabolic variables to graded levels of low intensity stresses in adult male rats

Adult male rats were subjected to different acute stressors, whose intensity was gradually increased, and their corticosterone, glucose, and serum lipid levels were studied. Serum corticosterone was sensitive to graded levels of stress intensities. Glucose followed the same trend. However, serum lipid responses were not related to the intensity of stress. Our results indicate that these latter variables were not sensitive indices of the emotional arousal elicited by brief stress stimuli.

Reduction of chronic psychosocial hypertension in mice by decaffeinated tea

The effects of decaffeinated green tea on CBA mice have been contrasted with those of water during 3 to 5 months of exposure to various intensities of social stress. Intensity was modified by using different types of caging: Henry-Stephens complex population cages for maximum stress, open field population cages for intermediate levels, and siblings in standard mouse boxes for minimal stress. Two population densities were used: high, with 16 males and 16 females per population cage; and low, with approximately half this number. In three sets of experiments, 58 comparisons were made between body weight, blood pressure, pulse rate, scarring, blood urea nitrogen (BUN), adrenal and heart weights, plasma corticosterone, adult male mortality, and number of weanlings of those on decaffeinated green tea and matched groups on water. Twenty-five of the comparisons indicated less arousal with the decaffeinated green tea and in none was the water favored. Blood pressure fell from 150 to 133 mm Hg. These results support the proposal that the polyphenols (bioflavonoids) of tea may have a beneficial sedative action.

Stress and immune function in diabetes mellitus

Type I diabetic men were found to have a greater number of stresses, more perceived stress per episode, greater anxiety, poorer immune function, and less metabolic control than Type II diabetic men. Degree of family support and compliance with the medical regimen did not differ. Correlation of perceived stress with immune function and metabolic control showed that Type I had more correlates than Type II, with more perceived stress associated with more depressed immune responses.