Hippocampal system dysfunction and odor discrimination learning in rats: Impairment of facilitation depending on representational demands.

The performance of normal rats and that of rats with hippocampal system damage were compared on acquisition of different versions of the same two-odor discrimination task that placed different encoding and representational demands on memory. Rats with fornix lesions were impaired when explicit comparisons among multiple odor cues and differential response choices were encouraged. However, when odor-cue comparisons was hindered and explicit cues for response choice were eliminated, rats with fornix lesions out performed normal animals. The results support a hypothesis that the hippocampal system is critical to a memory representation based on encoding relations among multiple percepts, and other brain systems support performance adaptations based on encodings of stimuli individually. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mnemonics for variability: Remembering food delay.

Three experiments with White Carneaux pigeons (Columba livia) investigated memory and decision processes under fixed and variable reinforcement intervals. Response rate was measured during the unreinforced trials in the discrete-trial peak procedure in which reinforced trials were mixed with long unreinforced trials. Two decision models differing in assumptions about memory constraints are reviewed. In the complete-memory model (J. Gibbon et al, see record 1988-09671-001), all interreinforcement intervals were remembered, whereas in the minimax model (D. Brunner et al, see record 84-0343), only estimates of the shortest and longest possible reinforcement times were remembered. Both models accommodated some features of response rate as a function of trial time, but only the second was compatible with the observed cessation of responding. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cocaine-induced suppression of saccharin intake: A model of drug-induced devaluation of natural rewards.

In Experiment 1, water-deprived Sprague-Dawley rats were given 5 min access to saccharin. This tube retracted, an empty tube advanced, and the rats were given 1 hr to lick the empty tube on a fixed-ratio 10 lick contingency to self-administer saline or cocaine (0.33 mg/infusion) via an intravenous catheter. The results showed that rats avoided intake of saccharin after saccharin-cocaine pairings and that greater avoidance of the gustatory cue was associated with greater cocaine self-administration. In Experiment 2, a similar dose-response function was obtained with either the empty tube or a lever as the operant. In Experiment 3, avoidance of the saccharin cue and the propensity to self-administer cocaine were maintained after at least 1 month of abstinence. As such, this paradigm may be useful as a model of cue-induced craving and drug-induced devaluation of natural rewards. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Independent effects of estradiol on water and food intake.

Conducted 6 experiments to examine the effects of estradiol on ingestive behaviors of guinea pigs. Estradiol treatment was found to reduce water intake independently of its actions on food intake and body weight. In the 1st experiment, minimum intake and body weight of 17 intact female guinea pigs coincided with rupture of the vaginal membrane, the estimated time of ovulation. In Exp II, injections of 3 μg of estradiol benzoate (EB)/day to 7 ovariectomized females significantly depressed food intake, water intake, and body weight, compared with 7 Ss that received oil injections. Reducing food rations to 30% below ad lib levels in Exp III by itself had no significant effect on drinking in ovariectomized Ss. In Exp IV, therefore, ovariectomized females were first placed on a food ration 30% below ad lib levels and then injected daily with either 3 μg of EB or oil. Compared with oil injections, these EB injections significantly reduced water intake, while food intake did not decline significantly. Findings indicate that estradiol operates through different mechanisms to affect water intake and food intake. (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Relation of reward from food intake and anticipated food intake to obesity: A functional magnetic resonance imaging study.

The authors tested the hypothesis that obese individuals experience greater reward from food consumption (consummatory food reward) and anticipated consumption (anticipatory food reward) than lean individuals using functional magnetic resonance imaging (fMRI) with 33 adolescent girls (mean age = 15.7, SD = 0.9). Obese relative to lean adolescent girls showed greater activation bilaterally in the gustatory cortex (anterior and mid insula, frontal operculum) and in somatosensory regions (parietal operculum and Rolandic operculum) in response to anticipated intake of chocolate milkshake (vs. a tasteless solution) and to actual consumption of milkshake (vs. a tasteless solution); these brain regions encode the sensory and hedonic aspects of food. However, obese relative to lean adolescent girls also showed decreased activation in the caudate nucleus in response to consumption of milkshake versus a tasteless solution, potentially because they have reduced dopamine receptor availability. Results suggest that individuals who show greater activation in the gustatory cortex and somatosensory regions in response to anticipation and consumption of food, but who show weaker activation in the striatum during food intake, may be at risk for overeating and consequent weight gain. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Internal and external moderators of the effect of variety on food intake.

Many factors contribute to how much we eat. One such factor is the variety of different foods available. The current article reviews the variety literature with a specific focus on the factors that moderate the effects of variety on food intake and that moderate the processes that may underlie the variety effect (i.e., sensory-specific satiety and monotony). The moderators have been categorized as being of either an internal nature or an external nature. The literature suggests that internal moderators, including characteristics such as gender, weight, and dietary restraint, do not act as moderators of the variety effect. One possible exception to the absence of internal moderators is old age. Alternatively, external moderators, such as particular properties of food and the eater’s perception of the situation, appear to affect the strength of the variety effect on intake to some degree. An evolutionary hypothesis may account for the distinct roles that internal and external variables play in moderating the variety effect. (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)     

Haloperidol attenuates rewarding and aversively conditioned suppression of saccharin solution intake: Reevaluation of the anhedonia hypothesis of dopamine blocking.

The dopamine (DA) antagonist, haloperidol, affected the conditioned suppression of a saccharin solution intake (the conditioned stimulus, CS) induced by amphetamine (AMPH) and lithium chloride (LiCl) unconditioned stimuli (USs). Four experiments showed that (a) haloperidol by itself did not reduce saccharin solution intake. (b) When haloperidol was injected between the CS and the US, the conditioned suppression was attenuated; however, (c) this did not occur when haloperidol was injected after the US, indicating that haloperidol affected the perception of the US. (d) This attenuation was found with both rewarding AMPH and aversive LiCl treatments, indicating that the valence of the US was unimportant. Thus, the so-called "anhedonia response" might be due to weakening of US impact. A general salient-stimulus hypothesis was proposed, with the anhedonia hypothesis of DA blocking as its subset. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of gastric loads and food deprivation on subsequent food intake in suckling rats.

In 4 experiments, a total of 478 suckling Charles River rats were subjected to deprivation periods of 6-8 hrs. Intake following deprivation was greater in deprived than in nondeprived Ss but did not increase with increasing deprivation. Gastric loads of NaCl solutions depressed subsequent intake; 3% NaCl was more effective than .9% NaCl. Other gastric loads of varying osmotic and caloric values also depressed subsequent intake. In order of increasing effectiveness in depressing intake, the gastric loads were protein hydrolystate, heavy cream, water, milk, lactose, glucose, and corn oil. Effectiveness was unrelated to osmotic or caloric value of the load. Gastric fill and, possibly, some property of carbohydrate appeared to be important determinants of satiety in the S. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Memory of lectures: Effect of delay and distractor type.

Tested recognition memory for critical sentences from a classroom lecture as a function of lecture instructions, length of retention interval, and type of recognition test items, using 85 undergraduates. When tested immediately after the lecture, Ss differentiated the original sentences from reworded and inferential statements that were similar in meaning. At longer delays, however, only the inferences were recognized as not having been presented in the lecture. Labeling a lecture statement as important had little effect on recognition of the original item, although it did enhance recognition of the other item types. Findings confirm other recent reports of verbatim memory for natural speech. (4 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Proximity of food, sex, and access to running wheels: Effects on food intake in rats.

To test the hypothesis that the addition and withdrawal of a running wheel affects food intake because of a manipulation of the proximity of the rat to the food dish, a 2nd source of food was made available to the rat when in the running wheel. Ss were 24 male and 24 female ARS/Sprague-Dawley albino rats. Results fail to support the hypothesis. Additional findings were that both sexes showed the reduction in food intake when given access to running wheels, but only the males showed an increase in food intake when deprived of access to running wheels. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of aldosterone and deoxycorticosterone on food intake and body weight.

Conducted an experiment with 48 female adrenalectomized Sprague-Dawley rats, who were injected daily with aldosterone (.25 mg/kg) or deoxycorticosterone (3 mg/kg) in combination with corticosterone. The mineralocorticoids increased food intake and weight gain well beyond that of controls receiving only corticosterone injections. The weight gain was not wholly dependent on increased food intake, as separate groups of Ss maintained on a restricted diet (10 g of laboratory chow/day) also displayed significant mineralocorticoid-stimulated weight gain. Although carcass composition was not directly determined, the undifferentiated wet/dry tissue ratios, hematocrit values, and nasoanal lengths found across groups suggested that the observed effect of mineralocorticoids was on body fat. Aldosterone and deoxycorticosterone can have important actions on energy metabolism as well as on sodium regulation. (9 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Decrease in the high frequency QRS components depending on the local conduction delay

The high frequency components contained in the QRS complex (HF-QRS) are a powerful indicator for the risk of sudden cardiac death. However, it is controversial whether conduction delay increases or decreases the HF-QRS. In 21 anesthetized, open-chest dogs, the right atrium was constantly paced. A cannula was inserted into the left anterior descending artery and flecainide, lidocaine or disopyramide was infused to slow the local conduction. Sixty unipolar electrograms were recorded from the entire ventricular surface and were signal-averaged. Data were filtered (30-250 Hz) by using fast-Fourier transform. The HF-QRS was calculated by integrating the filtered QRS signal. Activation time (AT; dV/dt minimum) was delayed and the HF-QRS was reduced in the area perfused by flecainide, lidocaine or disopyramide. The percent increase in AT closely correlated the percentage decrease in the HF-QRS; the correlation coefficients were 0.75, 0.83 and 0.76 for flecainide, lidocaine and disopyramide infusion, respectively, (p<0.001). Decrease in the HF-QRS linearly correlated with the local conduction delay. This study proved that conduction delay decreases the HF-QRS, and that the HF-QRS is a potent indicator of disturbed local conduction.     

Somatostatin decreases food intake of rats and baboons.

Somatostatin is a peptide hormone found in the CNS and the gastrointestinal tract. It has the ability to modify a number of metabolic factors associated with food intake. The purpose of the 7 experiments reported here was to determine the effect of somatostatin on the intake of individual meals of 2 species, the rat (131 female Wistar, 20 male Wistar and Long Evans) and the baboon (4 male Papio cynocephalus). In one set of experiments, Ss received somatostatin (10 ng–2 μg/kg) or a control solution ip. There was a dose-dependent decrease of food intake relative to vehicle-injected controls. In subsequent experiments, these doses had no effect on water intake and did not cause a conditioned taste aversion. Findings suggest that somatostatin acts relatively selectively on food intake and probably does not induce nausea or illness. The administration of somatostatin into cerebrospinal fluid had no effect on food intake. Therefore, somatostatin apparently works peripherally to reduce food intake in both rats and baboons. (46 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prefrontal cortex and the regulation of food intake in the rat.

Studied the postoperative regulation of food and water intake in a total of 103 male Wistar albino rats with aspiration lesions to either the medial frontal or orbital frontal projection fields of thalamic nucleus medialis dorsalis (prefrontal cortex). These projection fields proved functionally dissociable in that orbital frontal lesions impaired immediate postoperative regulation of food and water intake for up to 2 wks, while medial frontal lesions produced finickiness. Neither lesion affected response to cellular dehydration or recovery from extended deprivation. Data are consistent with data from rhesus monkeys with prefrontal lesions and differ from animals with lateral hypothalamic lesions. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Caloric regulation of food intake in man.

Investigated caloric regulation in normal 18-36 yr old human Ss on a liquid diet. In Exp I, 8 Ss failed to compensate for changes in the caloric density of a preload (.25-1.8 kcal/ml) by adjusting meal size within 1 meal or from 1 meal to the next. In Exp II, 15 Ss were required to ingest nothing but the liquid diet for 10-21 days. They were given adlib access to a standard liquid diet (1.0 kcal/ml) for 4-9 days followed by 4-14 days on a diluted diet (.5 kcal/ml). 9 Ss failed to regulate their caloric intake in the time allowed. 6 Ss failed to regulate their caloric intake in the time allowed. 6 Ss compensated dramatically for the caloric dilution by increasing both meal size and meal frequency. Regulation was slow to occur (2-5 days) and usually was not perfect (mean level of 87%). Results are discussed in the light of work with animals and man on the mechanisms controlling regulation of food intake. (30 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Chronic lithium chloride infusions: Conditioned suppression of food intake and preference.

Developed a modified learned food aversion paradigm that simulated the prolonged food and illness exposure likely to characterize nutrient deficiencies or tumor growth. In this paradigm, a continuously available food was associated with a slow, continuous infusion of LiCl provided by an osmotic minipump. In Exps I and II, 68 rats were implanted with minipumps with LiCl or with empty pumps and exposed to novel or familiar diets. In Exp III, conducted with 40 Ss, the variable was prior exposure to the same diet. Significant aversions were acquired when the available diet was novel but not when it was familiar. Effects of drug infusions on daily food intake paralleled those on aversion formation. Marked, persistent suppression of food intake was seen in drug-treated Ss consuming a novel diet, but only transient declines were seen in those with a familiar diet. By separating the direct from the conditioned effects on food intake of chronic drug infusions, these studies provided strong evidence that learned food aversions can lead to anorexia. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Tumor growth in rats: Conditioned suppression of food intake and preference.

In 4 experiments, 140 male syngeneic Wistar-Furth rats were implanted with tumors or received control incisions. Ss with experimental tumors developed strong aversions to a novel diet they consumed during tumor growth. Aversions were not evident when the food available during tumor growth was familiar laboratory chow. The impact of learned food aversions on tumor anorexia was evidenced by more severe and long-lasting hypophagia in tumor-bearing Ss maintained on a novel diet than in those maintained on laboratory chow. Thus, when a diet was a salient target for the development of learned aversions, the aversions that developed to it could make substantial contributions to the overall syndrome of tumor anorexia. Frequent changes of the diet offered to tumor-bearing Ss were associated with milder anorexia than that produced by a constant diet. Results suggest that, the prevention of learned food aversions, or the repeated replacement of aversive foods, can minimize the impact of learned food aversions and attentuate anorexia in tumor-bearing animals. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)