Regulation of energy balance in two models of reversible obesity in the rat.

Reports on 2 experiments with 114 adult male Sprague-Dawley rats. Ss were made obese either by tube feeding varying fractions (34, 47, 68, or 75%) of their normal food intake or by offering them a varied and palatable diet (cafeteria diet). After 17–30 days of these regimens, the treatments were withdrawn, and Ss were allowed free access to the normal stock diet. Tube-fed Ss precisely adjusted voluntary food intake to compensate for the energy delivered by tube but nevertheless became obese as a result of an increased metabolic efficiency. Cafeteria-fed Ss were hyperphagic and became obese without any apparent change in metabolic efficiency. Recovery from obesity was more rapid in cafeteria Ss and was due to a pronounced increase in heat production as well as concomitant hypophagia. Ss previously made obese by tube feeding exhibited hypophagia and returned to normal weight without any change in heat production. The relevance of these results to the concept of lipostasis and the relative roles of energy intake and expenditure in the regulation of energy balance are discussed. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Some extraordinary facts about obese humans and rats.

Examined similarities between experimental findings with obese human Ss and lesioned hyperphagic rats. In comparison to normals, obese Ss (a) eat more of a good- and less of a bad-tasting food; (b) eat fewer meals/day, eat more/meal, and eat more rapidly; (c) react more emotionally; (d) eat more when food is easy to procure and less when it is difficult; (e) do not regulate food consumption when preloaded with solids, but do when preloaded with liquids; and (f) are less active. N. Mrosovosky's theory that the ventromedial hypothalamus is functionally quiescent in obese Ss is discussed. The function of the hypothalamus is examined. It is hypothesized that obese Ss are stimulus-bound. Experiments reveal that obese Ss (a) do better on recall tests, (b) respond faster with fewer errors on complex RT tasks, (c) are more distractible, and (d) work harder for food when food cues are prominent. Reexamining the activity levels of Ss, it was found that beyond a given stimulus intensity, Ss are more reactive than normals. Difficulties with the comparison and formulation are noted. (38 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of septal, preoptic, and habenula ablations on thirst-motivated behaviors in rats.

Two experiments used a total of 59 male Sprague-Dawley rats. Bilateral septal lesions dramatically enhanced barpressing rates generated under progressive ratio schedules of reinforcement. This increased barpressing was dependent on deprivation level but independent of the type of deprivation (i.e., food or water). Equivalent effects on barpressing were observed in Ss with bilateral medial forebrain bundle lesions at the level of the lateral preoptic area. Septal lesions, medial forebrain bundle lesions, and habenula lesions did not result in a hyperreactivity to bitter quinine solutions. Hyperreactivity to quinine was observed only in Ss with medial preoptic lesions. This medial preoptic lesion also impaired operant responding for water on a progressive ratio schedule of reinforcement. It is suggested that the medial preoptic lesion produced a deficit in thirst-motivated behavior. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hypothalamic knife cuts: Effects on eating, drinking, irritability, aggression, and copulation in the male rat.

Describes 2 experiments with a total of 43 male hooded rats. In Exp. I, Ss with parasagittal knife cuts that separated the medial from the lateral hypothalamic areas (a) became hyperphagic, hyperdipsic, obese, and irritable; (b) did not change their level of aggressive responses against mice; and (c) copulated at an impaired rate or not at all. In Exp. II, 2 groups of Ss were subjected to coronal cuts restricted between the fornices at levels either anterior or posterior to the ventromedial hypothalamic nuclei. Most of the anterior-cut Ss increased their food and water intake, and some became irritable. Of the posterior-cut Ss, none increased and 1/2 decreased their food intake, some became hyperdipsic, and 1 became irritable. Neither of the coronal-cut groups changed levels of aggressive or sexual responses. It is concluded that the mediolateral hypothalamic connections are important for eating, irritability, and copulation. (42 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Diet palatability modulates sham feeding in VMH-lesion and normal rats: Implications for finickiness and evaluation of sham-feeding data.

Examined the capacity for taste cues to modulate the food intake of 24 ventromedial hypothalamic (VMH) and normal Long-Evans rats. Ss were implanted with a chronically indwelling gastric cannula and sham fed (cannula open) or normally fed (cannula closed) liquid diets varying in sucrose content. VMH Ss were maintained at control body-weight levels. For both groups, the discrepancy in consumption between sham and normal feeding situations depended on the sweetness of the diet. The implications of this finding for studies using sham feeding to assess putative feeding control signals are discussed. VMH lesions exaggerated the sensory control of food intake. Under sham-feeding conditions, increases in the sweetness of the diet led to disproportionately large increments of food intake in VMH Ss relative to controls. Data support the existence of a finickiness component in the VMH syndrome and allude to the nature of the physiological disturbance underlying this behavior change. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hyperphagia in rats with experimental diabetes mellitus: A response to a decreased supply of utilizable fuels.

In 2 experiments with male Sprague-Dawley rats, alloxan-diabetic rats were hyperphagic when fed diets containing little fat, but they ate normal amounts of food when given diets rich in fat. Normal Ss increased food intake to the same degree when the caloric density of their diet was decreased by reducing the content of fats or carbohydrates in isocaloric amounts. Diabetic Ss did not respond substantially to changes in caloric density of their diet which were produced by altering the content of dietary carbohydrates, but they systematically increased food intake as the amount of fat in their diet was reduced. Diabetic Ss ate normal amounts of a high-fat diet despite continued loss of nutrients in urine and persisting impairments in glucose utilization, fat storage, and liver glycogen deposition. Findings suggest that hyperphagia in experimental diabetes mellitus is a compensatory response to a lack of utilizable fat fuels rather than the result of a metabolic disturbance per se. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of degree of obesity, food deprivation, and palatability on eating behavior of humans.

Monitored the eating behavior of 20 obese and 20 normal weight Ss in the context of tasting tests. Intake was measured following a solid food preload and following a period of food deprivation. All Ss participated in both conditions. Under all experimental conditions obese Ss ate more than normal weight Ss. The effect of a preload was similar in both groups. Obese Ss, however, were more responsive to their preference functions than were normal weight Ss. The fruitfulness of using brief exposure tests for determining differential modes of eating behavior is discussed. (24 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rats define different body weights depending on palatability and accessibility of their food.

Normal adult Long-Evans rats lived on powdered diets adulterated to contain as much as 1.6% quinine sulfate, on a palatable high-fat diet, or in Skinner boxes with 45-mg Noyes pellets available on FR schedules as high as FR-256. They maintained lower body weights over periods of months in proportion to the percentage of quinine adulteration or the FR. Ss on the high-fat diet overate as much and gained weight as rapidly as Ss recovering from food deprivation, and became moderately obese. Ss having become lean or obese contingent on the palatability or accessibility of their diet defended body weight by eating more in the cold, less when force-fed by gavage, and more to restore weight after food deprivation. Yet on chow they restored and defended body weights typical of Ss whose diet had been confined to commercially prepared chow. Results are inconsistent with motivational models that rigidly distinguish drive from incentive, that treat body weight changes as evidence for failure to regulate energy balance or body weight, or that rely exclusively on deprivation of food or reduction of body weight for definitions of need for calories. Instead, caloric homeostasis in rats may incorporate ecological constraints. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Competition between lateral hypothalamus and ventromedial tegmentum in electrical self-stimulation in the rat.

Used 14 male Sprague-Dawley rats with 2 bipolar electrodes, one in the lateral hypothalamus (LH) and the other in the ventromedial tegmentum (VMT). After training, barpressing rates for LH and VMT self-stimulation were studied separately by switching the stimulation alternately to LH and to VMT (single-bar test), or were studied in a choice test where Ss had to choose between LH and VMT stimulation by pressing 2 independent bars. In the single-bar test when threshold currents were used, Ss self-stimulated significantly more in LH than in VMT, but the reverse was observed at high current intensities. Some negative behaviors observed in LH with strong currents did not generalize when stimulation was switched to the VMT probe, suggesting a relative independence between LH and VMT. The comparison between the relative preference of Ss for LH or VMT stimulation in the choice test and the barpressing rates in the single-bar test shows that in this last test barpressing rates reflect the rewarding value of stimulation only when weak current intensities are used. (French summary) (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioral and neurochemical effects of neonatal administration of monosodium {l}-glutamate in mice.

Studied the feeding behavior, activity level, and thermoregulatory ability of 117 CL-1 mice made obese by neonatal administration of monosodium {l}-glutamate (MSG). The degree of obesity and other characteristics of the syndrome depended on age, diet, and housing condition. Carcass fat determinations demonstrated the presence of obesity in all MSG Ss; however, body weight was elevated over control levels only in adult mice caged in groups. Group-housed MSG Ss also failed to increase food intake in response to food deprivation and were both hypoactive and hypothermic. Individually caged MSG Ss showed normal activity levels and body temperature, an attenuated response to food deprivation, and an enhanced response to a high-fat diet. Since MSG obesity may be the consequence of damage to the dopamine-rich arcuate nucleus of the hypothalamus, a 2nd goal was to measure central catecholamines and examine any changes in the MSG S's behavioral responses to catecholaminergic drugs. Ss treated with MSG sustained some loss of hypothalamic dopamine, but no systematic relation between central catecholamines and behavioral aspects of the syndrome could be discerned. (46 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Suckling behavior and intake control in the developing rat pup.

Studied the behavioral development of suckling and intake control in 2 experiments with Charles River CD strain rat pups. Ss were observed at the initiation, during the course, and at the termination of suckling from their anesthetized mothers. Diet was delivered intraorally through a fine tongue cannula which enabled control of timing and volume. The control of diet intake and the behavior at termination of suckling showed correlated changes from 5 to 20 days of age. When deprived of suckling (and food and water) for 8 hr, 5- and 10-day-old Ss consumed large volumes of diet (10% of body weight or greater) and terminated suckling only in the presence of extreme gastrointestinal filling. These Ss were immediately lethargic and slept after intake termination. Five-day-old Ss persisted in reattaching to the nipple when manually stimulated; 10-day-old Ss eventually refused to reattach. In contrast, 20-day-old Ss consumed more moderate volumes of diet (5% of body weight). These Ss also remained awake for a period after feeding and engaged in the exploratory and grooming activities characteristic of adult rats at the termination of feeding. These observations demonstrate major changes in suckling behavior during development. They suggest that intake control processes shift from indirect to direct and become more effective and specifically food intake related in older pups. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of lipostatic mechanism in regulation by feeding of energy balance in rats.

Conducted 6 experiments to investigate the existence of a fat-feeding diurnal cycle in normal and hyperphagic male and female Wistar rats. Such a cycle was found in normal but not in hyperphagic Ss. By using 14C-labeled food eaten either at night or day, it was directly shown that metabolites eaten and stored at night were mobilized during the subsequent day and predominantly used during the hours preceding the onset of each meal. From other results on relationships between fat synthesis and overeating at night, and lipolysis and undereating in the day, diurnal is concluded that a lipostatic mechanism modulates-both within the diurnal cycle and from day to day-the glucosensitive short-term control system of food intake. Disruption of this lipostatic mechanism in ventromedial hypothalamus (VMH) lesioned Ss suggests that VMH nuclei are key sites for the neuroendocrine basis of the lipostatic control of food intake. (49 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Motivated feeding in the absence of glucoprivic control of feeding in rats.

Feeding to decreased intracellular glucose utilization was assessed in 13 Sherman female albino rats with bilateral damage to the medial forebrain bundle and in 7 normal rats. Brain-damaged Ss that did not feed to glucoprivation, those that ate normally to glucoprivation, and normal Ss were tested on 3 traditional indices of food-motivated behavior: quinine adulteration of diet, barpressing on a variable-interval schedule of 30 sec, and barpressing on a schedule with a progressive ratio of 2. 4 of the 7 brain-damaged Ss that did not eat to glucoprivation performed like normal Ss on all 3 motivational indices, while all 7 performed normally on at least 2 of the 3. Results support the conclusion that the glucoprivic mechanisms is not necessary for the occurrence of normal food-motivated behavior. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gustation and ingestive behavior in the rat.

Studied the contribution of taste to the quantitative control of intake and body weight in 15 male Wistar rats. Gustatory deafferentation was produced by combined bilateral section of the chorda tympani and glossopharyngeal nerves and the pharyngeal branch of the vagus nerve. The procedure did not affect the condition of the mouth, impair orientation to sensory stimuli, or severely disrupt the consummatory sequence. Nevertheless, deafferented Ss showed reduced responsiveness to food and water, elevated quinine HCl aversion thresholds, and impaired feeding efficiency. Food and water intake and body weight remained below control levels for at least 40–50 days postoperatively. Food intake deficits were not observed when Ss were offered ad lib pablum, a result suggesting that increased palatability could compensate for decreased gustatory input. The order of recovery of food intake through different diet types suggests a heightened responsiveness to taste stimuli. The effects of gustatory deafferentation are compared with those seen after section of trigeminal orosensory nerves, and the differential contributions of oral taste and oral touch are discussed. (42 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of desalivation on drinking and air licking induced by water deprivation and hypertonic saline injections.

Previous studies show that desalivate (DS) rats drink more water than controls when maintained on a diet of dry food, but drink less than controls after a period of water deprivation. In the present series of studies, a total of 14 male and 2 female naive hooded rats served as Ss. Results show that DSs ate less food than sham operates (SHs), indicating that DSs' body fluids probably do not become as hyperosmotic as those of the SHs. When Ss were maintained on a moist mash during water deprivation, subsequent water intake and air licking were about the same for DSs and SHs. After combined food and water deprivation, both groups air-licked at greatly reduced rates. After subcutaneous injections of hypertonic saline, DSs air-licked just as much as SHs. It is concluded that DSs drink less after water deprivation because they eat less dry food than SHs during deprivation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Estrus- and ovariectomy-induced body weight changes: Evidence for two estrogenic mechanisms.

Estrogenic modulation of body weight in female rats is usually thought to result indirectly from estrogenic modulation of food intake. However, present data from 5 experiments with 79 female albino rats suggest that estrogens influence body weight by at least 2 mechanisms, 1 of which is independent of changes in food intake. When Ss were ovariectomized (Ovx) and food intake was limited to preoperative levels, Ovx Ss nonetheless gained large amounts of body weight. Although Ovx Ss gained more weight than controls on the same amount of food, during 33 hrs of food deprivation Ovx and control Ss lost weight at the same rate, indicating that the prefasting metabolic rates of the 2 groups were similar. During the 1st 40 days after surgery, the ano-nasal lengths of Ovx Ss increased twice as fast as that of intact Ss, which suggests a mechanism for the gradual increase in weight induced by Ovx. The weights of intact Ss followed a regular 4-day cycle during ad lib feeding, but when the estrus-associated decrease in food intake was prevented, the cyclic weight changes were altered. Thus estrogens appear to regulate body weight by modulation of food intake and modulation of ano-nasal growth or other metabolic processes. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Thiamin deprivation in ventromedial hypothalamic hyperphagic rats: Anorexia, specificity of food aversion, and a dietary consideration.

In 3 studies, the anorexic consequence of thiamine deprivation was investigated in ventromedial hypothalamic (VMH) hyperphagic CD male rats under either high-fat or low-fat (HF and LF, respectively) thiamine-free diet conditions. The LF diet maintained feeding significantly longer in thiamine-deprived VMH Ss than in intact Ss, whereas the HF diet sustained feeding in thiamine-deficient intact Ss and accelerated anorexia onset in vitamin-B1-deprived VMH Ss. This effect was noted under both ad lib and pair-feeding conditions. Thiamine-deprived VMH Ss subjected to weight control developed anorexia sooner than intact Ss regardless of the diet employed. The VMH Ss fed an HF diet failed to resume feeding after thiamine readministration, which is interpreted as a permanent aversion to this diet. The relation between dietary intake and conditioned taste aversion is discussed with reference to the VMH and intact rats. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Genetic versus hypothalamic obesity: Studies of intake and dietary manipulations in rats.

Studied feeding behavior in 4 experiments with a total of 86 Zucker rats. Ad-lib food and water intakes were significantly greater for the genetically obese rats (fatties) than for their nonobese littermates. The ratio of water intake per gram of food intake was not different for the 2 groups. The ability to regulate caloric intake was then tested in 4 groups of rats: genetically obese, ventromedial hypothalamic lesioned (VMH) obese, sham operated, and normal controls. In response to caloric dilution and quinine adulteration the genetically obese Ss behaved more like normal Ss than like VMH-lesioned Ss. Sensitivity to quinine increased with age in the Zucker fatty. The fact that Ss with genetic obesity and Ss with hypothalamic obesity displayed different behaviors suggests that obesity is not merely a unitary disorder. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Control of prolactin and growth hormone secretion in mice by obesity

Prolactin (PRL) and growth hormone (GH) secretions in mice rendered obese by the administration of gold thioglucose (GTG) are abnormal. The objective of the present experiments was to determine whether the effects were related to the drug or to the resultant obesity. Perphenazine-induced PRL release in normal mice and in GTG-injected non-obese mice was compared to that of GTG-injected obese mice after the initial development of obesity, after body weight reduction by diet control and after the resumption of obesity by ad lib. feeding. The GTG-injected mice which did not become obese had greater (50%) than normal levels of serum PRL following perphenazine stimulation in 2 of 3 experiments. This suggested that the injection of GTG directly affected the control mechanism for PRL secretion, but that the abnormal PRL secretion was probably not the cause of obesity that develops after GTG treatment. Perphenazine-induced PRL levels in mice rendered obese with GTG were much greater (2-3 times higher than normal). However, the unusually high levels of PRL were totally abolished when the body weights of these mice were brought down to normal by dietary restriction. Conversely, when obesity was permitted to recur by giving the mice free access to food, PRL levels reverted back to the original obese pattern. The concentrations of GH were usually lower than normal in GTG-obese mice, and these levels were also more often associated with the development of obesity than with the injection of GTG. The data show a marked influence of obesity on the control of PRL and GH secretions in the mouse.     

Conditioned taste aversion in lean and obese rats with ventromedial hypothalamic knife cuts.

Assessed the development of a conditioned taste aversion (CTA) in 60 female Sprague-Dawley rats made hyperphagic with parasagittal knife cuts in the ventromedial hypothalamus (VMH). Ss were water deprived and presented with a .1% saccharin solution paired with injections of either LiCl or NaCl. In Exp I, VMH Ss tested at a nonobese weight level did not differ from sham-operated controls in acquisition and extinction of the CTA. In Exp II, moderately obese VMH Ss displayed a stronger CTA than did sham-operated controls as evidenced by slower extinction. A 2nd group of obese VMH Ss given an amount of LiCl equivalent to that given to the controls also displayed retarded extinction of the CTA. Results reflect an obesity-induced suppression in appetitive motivation. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)