Lifelong food restriction prevents senile osteopenia and hyperparathyroidism in F344 rats

Studies were carried out on male F344 rats to examine the influence of aging and life-prolonging food restriction on bone and circulating parathyroid hormone levels. In ad libitum fed animals, the weight, density and calcium content of the femur increased with age and achieved their peak levels by 12 months of age. These levels remained stable until about 24 months and by 27 months of age the ad libitum fed animals had lost appreciable amounts of bone. The maturation of the femurs of the animals maintained on 60% of the ad libitum food intake was delayed and their bones were lighter, less dense and contained less calcium than bones from ad libitum fed rats of corresponding ages. But at 6, 12 and 24 months of age, the femur strength to body weight ratios were very highly significantly greater (P < 0.0001) for the restricted animals compared to the ad libitum fed controls. Circulating immunoreactive parathyroid hormone increased progressively with aging in the animals fed ad libitum and the animals that experienced bone loss at advanced age also had the highest level of the hormone. In contrast, in the food restricted animals aging was not associated with a marked increase in serum parathyroid hormone or with senile bone loss. The data are discussed in relation to the mechanism of the observed changes.     

Schedule and quinine induced deprivation in feeding and refeeding

Twenty female albino rats were adapted to either 0 or 23 hr of food deprivation. Half of each group was then fed 0.125% quinine sulfate adulterated diet for seven days. Following the quinine feeding, ad lib feeding (refeeding) was instituted for 14 days. Several conclusions were drawn from the results: (1) rats on a deprivation schedule fail to show a predicted change to regulation on the basis of taste rather than calories; (2) rats on food deprivation actually increase their relative intake of water; (3) refeeding after a deprivation schedule does not lead to depression of initial intake below normal, but otherwise the process of recovery follows the same course as after total starvation.     

Flavor preferences,food intake,and weight gain in baboons (Papio sp.)

To evaluate the influence of flavor on ad lib consumption and on associated changes in body weight, female baboons, 7–15 years of age, served in two experiments with seven monkey chows which were identical except for flavor: lemon, orange, apple, sugar, fruit punch, chocolate, and unflavored. In the first experiment, two groups of animals (n=7 and 4) received five of the seven flavors, presented in daily pair-wise combinations. Analysis of quantities consumed demonstrated marked and consistent flavor preferences in individual baboons. Although specific preference varied between animals, total amounts consumed of the various flavors differed significantly, with rank ordering clearly evident. Overall food intake and body weights increased significantly over baseline values obtained with a standard, unflavored chow. In the second experiment, three baboons received chow of a preferred flavor for nine weeks. Amounts consumed and body weights increased significantly over baseline. These results indicate that flavored chows may be useful for producing a nonhuman primate behavioral model of obesity and for inducing animals to eat otherwise unpalatable diets.     

Fat in the intestine as a regulator of appetite--role of CCK

The present review summarizes the appetite-suppressing effects of intestinal fat in the regulation of food intake in humans, with a special focus on the role of cholecystokinin (CCK). Current evidence supports a role for intestinal fat (especially long-chain free fatty acids) acting via the peptide CCK as a physiological satiety pathway. The regulation of satiety is, however, complex and it is not surprising that multiple control systems exist. It is interesting to note that nutrients, such as hydrolysis products of fat in the small intestine, stimulate the release of satiety peptides, such as CCK or PYY, that serve as satiety signals. CCK, released from the gastrointestinal tract by the local action of digested food, exerts various functions: stimulation of gallbladder contraction and exocrine pancreatic secretion, inhibition of gastric emptying, and inhibition of appetite. CCK functions therefore (1) as a positive feedback signal to stimulate digestive processes and (2) as negative feedback signal to limit the amount of food consumed during an individual meal.     

A selective modulation of the olfactory bulb electrical activity in relation to the learning of palatability in hungry and satiated rats

We attempted to determine whether a neutral odor which had become palatable as a result of learning had also acquired the property of activating the mitral cells of the olfactory bulb of hungry rats to the same extent as the odor of their usual nutriment. Male Wistar rats have been accustomed for various times to eat, during a single daily meal, exclusively a synthetic diet, either flavoured or not with eucalyptol. The mitral cell multiunit electrical activity was recorded in chronically implanted hungry and satiated animals. It was shown that: (1) in the rats having received the flavoured diet for one month when grown up, eucalyptol behaved as a nonalimentary odor towards mitral cells; (2) in the rats having received the flavoured diet (already given to the mothers) from weaning to the test period, eucalyptol behaved as a food odor at the mitral cell level, but amyl acetate, a control odor, did not activate mitral cells in hungry animals; (3) the odor of the diet with or without eucalyptol activated mitral cells at first in hungry rats, and this property was reinforced, for either diet, by its consumption beginning early and maintained continuously. It was concluded that palatability is dynamically related to the animal's previous experience, and that its modifications induce various degrees of mitral activation in hungry rats. This property allowed an electrophysiological measure of odor palatability to be proposed. The results are discussed in relation to the behavioral and neurophysiological maturation of animals.     

Initiation of mouse-killing behavior following amygdaloid lesions in the rat(author's transl)]

Long-Evans hooded rats were tested for emotionality and observed by pairs in an open field for 6 consecutive days. Postoperative observations indicated that both emotionality and social cohesiveness were dramatically altered by ventromedial and anterolateral hypothalamic lesions. Tegmental, interpeduncular and habenular lesions were shown to have no effect on these behaviors. Alterations in behavior observed following hypothalamic ablations were related to septal and amygdaloid effects, and the possibility of separate projection systems for emotionality and social cohesiveness was discussed.     

A new animal model of binge eating: key synergistic role of past caloric restriction and stress

Dieting and stress are important in the etiology and maintenance of eating disorders, and dieting strongly predicts stress-induced overeating in humans. We hypothesized that caloric restriction and stress interact in a unique manner to promote binge eating. To test this hypothesis, a group of young female rats were cycled through a restriction period (4 days of 66% of control food intake) followed by 6 days of free feeding prior to being stressed by acute foot shock. After three of these cycles, the food intake of rats exposed only to restriction (R), or only to stress (S), did not differ from controls. However, R+S rats that were restricted and refed, despite normal body weight and food intake after free feeding, engaged in a powerful bout of hyperphagia when stressed (Experiment 1). The R + S effect was replicated in an older group of rats (Experiment 2). The hyperphagia was characteristically binge-like, it constituted a 40% selective increase in highly palatable (HP) food (P < .001) over a discrete period of time (within 24 h post-stress), and reflected feeding for reward (higher HP:chow ratio) over metabolic need as occurred after restriction (higher chow:HP ratio). Subsequent experiments revealed that binge eating did not occur if only chow was available (Experiment 3) or if restriction-refeeding (R-R) did not proximally precede stress (Experiment 4). Experiment 5 revealed that a history of R-R cycles followed by only one stress episode was sufficient to increase intake to 53% above controls as early as 2 h after stress (P < .001). This animal model of binge eating should facilitate investigations into the neurochemical changes induced by dieting and environmental stress to produce disordered eating and provide a preclinical tool to test preventive strategies and treatments more relevant to bulimia nervosa, multiple cases of binge eating disorder (BED) and binge-purge type anorexia nervosa.     

Influence of dietary protein level on protein self-selection and plasma and brain amino acid concentrations

Control of protein intake was studied in young rats that were allowed to choose between either protein-free and 55% casein diets or 15% and 55% casein diets. Animals on the protein-free vs. 55% casein regimen exhibited a lower weight gain, a lower cumulative energy intake and a greater cumulative total protein intake during the 13-day study compared to rats selecting between 15% and 55% casein. The daily average proportion of total food selected as casein by animals choosing between protein-free and 55% casein diets increased from 15% to 38% during the course of the study. In contrast, rats choosing between 15% and 55% casein chose 18-22% of total food as protein throughout the entire study. Long-term protein intake or protein selection did not correlate significantly with whole-brain contents of 5-HT or 5-HIAA. Our results suggest that protein intake is not regulated at a constant proportion of total calories, but is controlled between a minimum level that will support rapid growth and a maximum that, if exceeded, would require the animal to undergo substantial metabolic adaptation. The mechanism controlling protein selection may involve diet-induced changes in the brain content of total free indispensable amino acids.     

Energetic limits on reproduction: Maternal food intake

We examined the factors influencing maternal food intake and pup growth in Norway rats. Mother rats allowed pups in naturally large litters to grow at a slower rate than pups in naturally small litters. Pups reared by dams in a warm ambience (26°C) gained weight more slowly than dams at 22°C, and maternal food intake but not weight gain was depressed in the high ambient temperature. Pup growth at 18°C was unimpaired, with those dams eating no more and gaining no less weight than dams at 22°C. Nest material, however, was found to be essential for the successful rearing of young at cooler ambient temperatures. While restriction of food during gestation resulted in a marginally lower weight gain for the pups during the first 2 weeks postpartum, the dams appeared not to mobilize corporal stores or increase their food intake during lactation. Heavy body weight mothers did not eat any more, nor did they gain any less weight nor rear larger pups than light body weight dams. Rat mothers increased their consumption of a diet diluted with non-nutritive fiber to equal the nutritive intake of their controls, with their pups not differing in their growth rate. Pups reared by dams eating a high quality diet grew faster than pups with dams on the control diet. Food intake by mother rats is required during lactation relative to the amount of milk that is delivered to the pups, rather than to an absolute amount of food. Lactating females with a concurrent pregnancy neither increase their food intake nor appear to mobilize their corporal stores to deal with the added energetic drain of pregnancy. Indeed, their young grew somewhat more quickly than pups nursed by dams that were simply lactating. Taken as a whole, these results suggest that Norway rat dams apparently do not monitor and defend a maximal pup growth rate. Rather, rat dams seem to continue to defend their own homeostasis, and by doing so, allow the young to grow and survive under a wide variety of circumstances.     

L-tryptophan injection fails to alter nutrient selection by rats

Nutritional studies on rats given a choice between two diets differing in protein content have led to the proposal that brain 5-HT content regulates protein intake [2]. Pharmacologic studies under similar conditions of dietary self-selection suggest that brain 5-HT controls carbohydrate intake [41]. We tested the effect of elevating brain 5-HT via tryptophan injection (100 mg/kg) on short-term food intake and selection by rats choosing between two diets differing in protein and carbohydrate content. Under these conditions neither total food intake nor protein and carbohydrate selection were affected despite increases of 50% in brain concentrations of 5-HT and 5-HIAA. The effect of Trp administration was selective to serotonin metabolism as brain concentrations of NE, DA and DOPAC were not affected. These results suggest that alterations in brain 5-HT content which may occur following meal ingestion may not be of physiological importance in regulating nutrient intake and selection.