Ruth B. S. Harris

Effect of repeated stress on body weight and body composition of rats fed low- and high-fat diets

Exposure to the moderate stressor of 3-h restraint for 3 consecutive days causes a temporary drop in food intake but a permanent reduction in body weight in adult rats. Young rats did not show the same response. Food intake of adult rats exposed to repeated restraint was significantly lower than that of controls for 4 days after the end of stress, and there was no rebound hyperphagia. Body weight remained significantly lower for at least 40 days after stress. When the rats were fed a high-fat diet of 80% chow and 20% vegetable shortening (48% kcal fat, 16% protein), lean body mass accounted for all of the weight loss in stressed rats. When the experiment was repeated with a purified high-fat diet containing corn oil and coconut oil as the source of fat (41% kcal fat, 16% protein), weight loss consisted of both lean and fat tissue. There were no sustained changes in single time point measures of corticosterone, insulin, or leptin that could account for the reduced body weight in these rats.Exposure to the moderate stressor of 3-h restraint for 3 consecutive days causes a temporary drop in food intake but a permanent reduction in body weight in adult rats. Young rats did not show the same response. Food intake of adult rats exposed to repeated restraint was significantly lower than that of controls for 4 days after the end of stress, and there was no rebound hyperphagia. Body weight remained significantly lower for at least 40 days after stress. When the rats were fed a high-fat diet of 80% chow and 20% vegetable shortening (48% kcal fat, 16% protein), lean body mass accounted for all of the weight loss in stressed rats. When the experiment was repeated with a purified high-fat diet containing corn oil and coconut oil as the source of fat (41% kcal fat, 16% protein), weight loss consisted of both lean and fat tissue. There were no sustained changes in single time point measures of corticosterone, insulin, or leptin that could account for the reduced body weight in these rats.

The role of CRF2 receptors in corticotropin-releasing factor- and urocortin-induced anorexia

THE experiments presented in this study were designed to assess corticotropin-releasing factor (CRF) receptor subtype mediation of CRF-and urocortin (UCN)-induced decrease in food intake. Male Sprague—Dawley rats were treated with antisense and sense oligo-nucleotides (ON) to CRF2 receptor mRNAs for 3 6 h and then received an intracerebroventricular (i.c.v.) injection of CRF, UCN β3 μg) or saline. Antisense treatment significantly attenuated CRF-and UCN-induced suppression in food intake and HPA activation. Administration of CRF1 receptor antagonist did not affect the decrease in food intake or activation of the HPA axis induced by ICV infusion of 3μg CRF. The data suggest that down-regulation of CRF2 receptors selectively attenuates CRF-and UCN-induced anorexia and hypothalamo-pituitary-adrenocortical activation in rats.

Sleep Deprivation by the “Flower Pot” Technique and Spatial Reference Memory

This study investigated whether paradoxical, or rapid eye movement (REM), sleep deprivation (SD) affected spatial memory. SD was induced in male Wistar rats by housing them on small platforms over water. They fell into the water if they lost muscle tone. Controls were either housed in tanks with large platforms (TC) or in normal cages (CC). All rats had free access to food and water. Each day they were tested in a place-learning set task using a Morris water maze. The rats were released from 6 different starting points (sets) and allowed 2 min to find a submerged platform. Two trials were conducted from each starting point. SD caused a significant decrement in performance in Trial 1 from Day 2. By Day 4, when distance swum to find the platform was plotted against set, area under the curve was doubled in SD compared to that in TC and CC rats, indicating a significant impairment in reference spatial memory. There was no consistent effect on working memory, indicated by Trial 2. SD caused weight loss and increased serum corticosterone compared to that in CC rats. There were no differences in concentrations of hypothalamic, hippocampal, or cortical catecholamines or their metabolites. Serotonin metabolism was elevated in the hypothalamus and hippocampus in SD rats. These results indicate that SD induced in rats housed on small platforms causes a substantial impairment of reference memory. The memory deficit may not be specific to SD because the rats are physically stressed and lose some nonREM sleep when housed in these conditions.

Failure to Change Exploration or Saccharin Preference In Rats Exposed to Chronic Mild Stress

Chronic mild stress (CMS) exposes animals to unpredictable stressors. Reduced consumption of sucrose or saccharin solutions by CMS rats has been used as a putative measure of anhedonia, typical of depression. Our objective was to determine whether saccharin consumption and preference and suppression of exploratory and rearing behaviors in the open field were reliable indicators of CMS-induced behavioral depression. In Experiment 1, male Wistar rats subjected to 6 weeks of CMS consumed significantly less food and gained less weight than controls. CMS did not effect saccharin intake, or preference, measured in a two-bottle test with water. CMS rats exposed to a novel open field showed increased exploration and rearing. In a second test, performed immediately after a novel stress of restraint, there were no differences in exploratory or rearing behavior of CMS and control rats. In Experiment 2, CMS was reduced to 3 weeks and rats were single or group housed in their home cages. Open field activity of CMS rats was similar to that in Experiment 1. Saccharin preference of CMS rats was significantly suppressed when tested after 24 hours of water deprivation, but was not different from controls after 5 hours of water deprivation. In the final experiment Sprague Dawley rats behaved the same as Wistar rats in the CMS paradigm. Therefore, the CMS protocol used in these experiments did not induce behaviors indicative of depression but did cause a mild anorexia and weight loss. Saccharin intake of CMS rats was dependent upon their dehydration state and could not be attributed to stress-induced anhedonia.

Prevention of stress-induced weight loss by third ventricle CRF receptor antagonist.

We previously reported that rats exposed to repeated restraint (3 h/day for 3 days) experience temporary hypophagia and a sustained reduction in body weight compared with nonrestrained controls. Studies described here determined the involvement of central corticotropin-releasing factor (CRF) receptors in the initiation of this chronic response to acute stress. In experiment 1, Sprague-Dawley rats were fitted with cannulas in the lateral ventricle and infused with 50 μg of αhCRF-(9-41) or saline immediately before restraint on each of the 3 days of restraint. The receptor antagonist inhibited hypophagia and weight loss on day 1 of restraint but not on days 2 and 3. In experiment 2, 10 μg of αhCRF-(9-41) or saline were infused into the third ventricle immediately before each restraint. The receptor antagonist totally blocked stress-induced hypophagia and weight loss. These results demonstrate that CRF receptors located in or near the hypothalamus mediate the acute responses to stress that lead to a permanent change in the hormonal or metabolic processes that determine body weight and body composition.We previously reported that rats exposed to repeated restraint (3 h/day for 3 days) experience temporary hypophagia and a sustained reduction in body weight compared with nonrestrained controls. Studies described here determined the involvement of central corticotropin-releasing factor (CRF) receptors in the initiation of this chronic response to acute stress. In experiment 1, Sprague-Dawley rats were fitted with cannulas in the lateral ventricle and infused with 50 micrograms of alphahCRF-(9-41) or saline immediately before restraint on each of the 3 days of restraint. The receptor antagonist inhibited hypophagia and weight loss on day 1 of restraint but not on days 2 and 3. In experiment 2, 10 micrograms of alphahCRF-(9-41) or saline were infused into the third ventricle immediately before each restraint. The receptor antagonist totally blocked stress-induced hypophagia and weight loss. These results demonstrate that CRF receptors located in or near the hypothalamus mediate the acute responses to stress that lead to a permanent change in the hormonal or metabolic processes that determine body weight and body composition.

The regulation of total body fat: lessons learned from lipectomy studies.

Surgical removal of body fat (partial lipectomy) is a means of directly reducing fat such that metabolic and behavioral responses can be readily attributed to the lipid deficit. If total body fat is regulated, then lipectomy should trigger compensatory increases in nonexcised white adipose tissue (WAT) mass and/or regrowth at excision sites. Many species, including laboratory rats and mice, show lipectomy-induced compensatory recovery of body fat. Those animals exhibiting naturally occurring annual adiposity cycles, such as ground squirrels and hamsters, do so most impressively reaching seasonally appropriate body fat levels indistinguishable from controls. Reparation of the lipid deficit occurs without an increase in food intake, and generally through enlargement of non-excised WAT mass, rather than regrowth of excised WAT. A body fat regulatory system involving humoral and sensory neural inputs to the brain as well as sympathetic neural outputs from brain to adipose tissue is presented. Collectively, the lipectomy model appears useful for testing mechanisms controlling adiposity, or individual depot growth, and offers insight into how lipid stores fluctuate naturally.

Early and late stimulation of ob mRNA expression in meal-fed and overfed rats

ob protein is hypothesized to be a circulating feedback signal in the regulation of energy balance. Obese, overfed rats have high levels of ob mRNA expression and suppressed voluntary food intake, indicating the presence of a potent satiety factor. The objectives of this experiment were to determine whether feeding rats their normal daily intake in three meals, compared with ad libitum feeding, increased ob mRNA expression and to determine the degree of obesity required to stimulate expression of ob mRNA. Rats were fed ad libitum, were tube-fed their normal intake in three meals a day, or were tube-fed twice normal intake, ob mRNA was measured by Northern blot analysis after 0, 2, 7, 14, 21, and 32 d of tube-feeding. After only 2 d ob mRNA was threefold higher in tube-fed animals than in ad libitum controls. By day 21 there was a further increase in ob mRNA expression in overfed rats which were at 130% control weight. These results suggest that a metabolic consequence of meal-feeding increases ob mRNA expression in the absence of increased food intake or weight gain. There is a further increase in ob mRNA expression once significant obesity is established.

Voluntary Wheel Running Decreases Adipose Tissue Mass and Expression of Leptin mRNA in Osborne-Mendel Rats

The purpose of this study was to assess the effects of voluntary wheel running on the expression of leptin mRNA in rats that are either sensitive (OM) or resistant (S5B/P1) to diet-induced obesity. Male OM and S5B/P1 rats had ad libitum access to standard rodent diet and water. At 3–5 weeks of age, animals of both strains were randomly assigned to either an exercise or sedentary control group. The exercise groups had 24-h access to a running wheel, and they trained for 7 weeks. During weeks 1–4, animals in both OM and S5B/P1 exercise groups progressively increased their running. During weeks 5–7, S5B/P1 exercisers tended to run more than did OM (∼60 vs. 45 km/week), but by the end of the study both groups had an equally greater heart weight (mg/g body weight) and planteris citrate synthase activity than their sedentary controls. Oral glucose tolerance tests performed during the last week of training revealed that compared with their appropriate controls, insulin sensitivity was enhanced (P < 0.05) in OM but not in the S5B/P1 wheel-running groups. Inguinal, epididymal, and retroperitoneal fat pads weighed less in the running than in the nonrunning groups of both strains (P < 0.01). Additionally, exercised animals had an increased percentage of smaller cells (40–60 µm; P < 0.05) and a decreased percentage of larger cells (120–160 µm; P < 0.05) in the epididymal fat depot. Epididymal leptin mRNA measured by Northern blot analysis was reduced in the exercise-trained rats of both strains (P < 0.05). Furthermore, serum leptin was reduced in exercise-trained compared with the control animals of both strains. In comparison to S5B/P1, control OM animals exhibited both a higher expression and higher circulating levels of leptin (P < 0.05). While serum leptin levels were decreased and food intake was increased in the exercise-trained animals of both strains (P < 0.05), the exact relationship between exercise, leptin, and food intake in this rat model of dietary obesity remains to be determined. Nonetheless, these results suggest that the expression and secretion of leptin can be influenced by exercise training and that these changes (i.e., reduced expression and secretion of protein) can occur independently of changes in whole-body insulin sensitivity and susceptibility to diet-induced obesity.

CRF Receptor Antagonist Attenuates Immobilization Stress-Induced Norepinephrine Release in the Prefrontal Cortex in Rats

Neuroanatomical, neurophysiological, and behavioral studies suggest that brain stem nucleus locus coeruleus (LC) plays an important role in stress response. The present study was designed to clarify, whether infusion of CRF antagonist, alpha hCRF, into LC could attenuate or block stress-induced changes in norepinephrine (NE) concentrations in microdialysates collected from the medial prefrontal cortex (PFM). Rats were implanted with a bilateral cannulae assembly aimed in the LC and a microdialysis probe (4 mm active membrane length) into the LC. Immobilization of animals significantly increased the concentration of NE in microdialysates from PFM to a maximum of 170.8 +/- 12.8% of the baseline ten minutes after the onset of stressor. Concentration of NE in dialysates remained significantly elevated for the next 40 min. Infusion of alpha hCRF into the LC significantly attenuated stress-induced increase in PFM NE concentration in samples collected at 10, 20, 30, and 50 min after the onset of immobilization. Infusion of alpha hCRF alone (no immobilization) did not change concentrations at any time during sample collection. These results are consistent with other studies and suggest that stress can facilitate NE release in the PFM through the activation of the CRF system in the brain.

Apolipoprotein-E deficiency results in an altered stress responsiveness in addition to an impaired spatial memory in young mice

It has been suggested that Alzheimers disease (AD) is associated with an altered neurotrophic function of apolipoprotein-E (ApoE) and abnormal neuroendocrine activities. In the present study we investigated stress responsiveness of ApoE-deficient mice. Firstly, two sessions of restraint were introduced, 20 min per day for two (session 1) and three (session 2) consecutive days. In session 1, there was no difference between genotypes in open-field activity in response to restraint stress. In session 2, spatial memory was assessed in a Morris Water Maze Place Learning Set task immediately following stress. Restraint stress caused a significant impairment of spatial memory in wild-type mice. The non-restraint ApoE-deficient mice showed a severe impairment of spatial memory similar to that of the restrained wild-type mice. Restraint stress had no obvious effect on spatial memory in ApoE-deficient mice until the third day of testing, when there was a decrease in reference memory compared with their non-restraint controls. In addition, the first session of restraint stress had an inhibitory effect on food intake in wild-type but not ApoE-deficient mice, and a longer-lasting effect on body weight in the wild-type than ApoE-deficient mice. ApoE-deficient mice showed a weaker corticosterone response to the initial restraint stress and a slower descending rate in serum corticosterone level during a 30-min post-stress period than their wild-type controls. However, higher baseline levels and stronger corticosterone responses were observed in ApoE-deficient mice than in wild-type mice when exposed to repeated restraint stress. The expression of ApoE mRNA was upregulated in the hypothalamus in wild-type mice exposed to repeated restraint stress. Taken together, these results demonstrate that ApoE deficiency causes a memory impairment and an altered stress responsiveness in mice.