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)     

Control of food intake in children by reinforcement of relevant verbal behavior.

Amounts consumed of 4 foods were recorded for each child in nursery school. 10 children were randomly selected for repeated sessions of verbal conditioning, which occurred shortly before snack time, and consisted of reinforcing the verbal behavior (food term) denoting the food selected for manipulation. The data give evidence that when positive reinforcement is associated with the verbal response denoting a food, then the consumption of that food increases. Conceptually, food can be considered a stimulus that sets up a class of responses, including verbal and eating responses. If the verbal response in that class is reinforced, hence strengthened, then the other responses of that class will be strengthened as well. (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)     

Assessing the role of the growth hormone secretagogue receptor in motivational learning and food intake.

The orexigenic neuropeptide ghrelin is an endogeneous ligand for the growth hormone secretagogue receptor (GHS-R). This orexigen is expressed in both the periphery and in the central system, including portions of mesolimbic dopaminergic circuitry that play a role in affective behaviors. Here we examined pharmacological antagonism of GHS-R in motivational incentive learning, as reflected in Pavlovian-to-instrumental transfer (PIT). Furthermore, it is currently unclear whether the previous effects of ghrelin on food intake are mediated by pre- and/or postingestive influences on ingestive behavior. Thus, the authors also conducted detailed analyses of the temporal dynamics of sucrose licking. Mice received low (50 nmol), moderate (100 nmol), and high (200 nmol) intraperitoneal injections of the GHS-R antagonist GHRP-6 [D-Lys3] prior to subsequent transfer and sucrose consumption tests. Low and moderate doses led to an augmentation of PIT, while high dose injections led to generalized performance deficits. In addition, moderate and high doses of the antagonist resulted in reductions in sucrose intake by reducing palatability of the sucrose. These results suggest dissociable functions of GHS-R in its influence over motivational learning and ingestive behavior. (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)     

Overexpression of ΔFosB is associated with attenuated cocaine-induced suppression of saccharin intake in mice.

Rodents suppress intake of saccharin when it is paired with a drug of abuse (Goudie, Dickins, & Thornton, 1978; Risinger & Boyce, 2002). By the authors' account, this phenomenon, referred to as reward comparison, is thought to be mediated by anticipation of the rewarding properties of the drug (P. S. Grigson, 1997; P. S. Grigson & C. S. Freet, 2000). Although a great deal has yet to be discovered regarding the neural basis of reward and addiction, it is known that overexpression of ΔFosB is associated with an increase in drug sensitization and incentive. Given this, the authors reasoned that overexpression of ΔFosB should also support greater drug-induced devaluation of a natural reward. To test this hypothesis, NSE-tTA × TetOp-ΔFosB mice (Chen et al., 1998) with normal or overexpressed ΔFosB in the striatum were given access to a saccharin cue and then injected with saline, 10 mg/kg cocaine, or 20 mg/kg cocaine. Contrary to the original prediction, overexpression of ΔFosB was associated with attenuated cocaine-induced suppression of saccharin intake. It is hypothesized that elevation of ΔFosB not only increases the reward value of drug, but the reward value of the saccharin cue as well. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Selective serotonin receptor stimulation of the medial nucleus accumbens causes differential effects on food intake and locomotion.

Substantial evidence suggests that pharmacological manipulations of neural serotonin pathways influence ingestive behaviors. Despite the known role of the nucleus accumbens in directing appetitive and consummatory behavior, there has been little examination of the influences that serotonin receptors may play in modulating feeding within nucleus accumbens circuitry. In these experiments, the authors examined the effects of bilateral nucleus accumbens infusions of the 5-HT1/7 receptor agonist 5-CT (at 0.0, 0.5, 1.0, or 4.0 μg/0.5 μl/side), the 5-HT? receptor agonist EMD 386088 (at 0.0, 1.0, and 4.0 μg/0.5 μl/side), or the 5-HT2C preferential agonist RO 60–0175 (at 0.0, 2.0, or 5.0 μg/0.5 μl/side) on food intake and locomotor activity in the rat. Intra-accumbens infusions of 5-CT caused a dose-dependent reduction of food intake and rearing behavior, both in food-restricted animals given 2-hr free access to Purina Protab RMH 3000 Chow, as well as in nondeprived rats offered 2-hr access to a highly palatable fat/sucrose diet. In contrast, stimulation of 5-HT? receptors with EMD 386088 caused a dose-dependent increase of intake under both feeding conditions, without affecting measures of locomotion. Infusions of the moderately selective 5-HT2C receptor agonist RO 60–0175 had no effects on feeding or locomotor measures in food-restricted animals, but did reduce intake of the fat/sucrose in nonrestricted animals at the 2.0 μg, but not the 5.0 μg dose. Intra-accumbens infusions of selective antagonists for the 5-HT? (SB 269970), 5-HT? (SB 252585), and 5-HT2C (RS 102221) receptors did not affect locomotion, and demonstrated no lasting changes in feeding for any of the groups tested. These data are the first to suggest that the activation of different serotonin receptor subtypes within the feeding circuitry of the medial nucleus accumbens differentially influence consummatory behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Expression of flavor preference depends on type of test and on recent drinking history.

The persistence of a conditioned flavor preference was examined in 3 experiments. All contained an initial acquisition phase in which half the rats were given almond odor mixed with sucrose (AS) in some sessions and water (W) only in other sessions, whereas the other half (controls) were given explicitly unpaired exposures to almond (A) and sucrose (S) in separate sessions. Subsequent 2-bottle choice tests revealed a persistent preference for A, despite extinction exposure to A or S, but this depended on the choice offered on test: Exposure to A did not extinguish the preference for A over W but did reduce the preference for AS over S; conversely, exposure to S did not extinguish the preference for AS over S but did reduce the preference for A over W. These results indicate that flavor preferences can be resistant to extinction procedures but suggest that the expression of such preferences in choice tests depends on an adaptation-level process. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Various aspects of feeding behavior can be partially dissociated in the rat by the incentive properties of food and the physiological state.

The authors investigated the role of food incentive properties and homeostatic state on the motivational, anticipatory, and consummatory aspects of feeding. Behavioral tests were carried out on food-sated and food-restricted rats that were presented with 2 kinds of food differing in their palatability level. Both food-sated and food-restricted rats consumed large quantities and were highly motivated when presented with very palatable food. In contrast, only food-restricted rats developed anticipatory responses, regardless of the kind of food presented. These data suggest that food incentive properties play a key role in the control of consummatory and motivational components of feeding but seem less involved in the regulation of anticipatory behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Individual differences in the "Greek effect" on risky drinking: The role of self-consciousness.

Although the environmental influence of Greek affiliation on drinking has been established, little is known about intrapersonal characteristics that make individuals susceptible to this influence. Self-consciousness (attending to one's self) was hypothesized to represent dispositional vulnerability to environmental influence. The potential moderating effect of self-consciousness on the relation between Greek involvement and drinking was examined longitudinally among college students (N = 319). The effect of Greek status was moderated by private and public self-consciousness and by gender. Specifically, non-Greek members' drinking was not influenced by self-consciousness. However, sorority members increased drinking as private self-consciousness increased, whereas fraternity members increased drinking as private and public self-consciousness decreased. These findings indicate that the "Greek effect" interacts with individual characteristics to affect drinking. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Characterization of the role of medial prefrontal cortex dopamine receptors in cocaine-induced locomotor activity.

Medial prefrontal cortex (mPFC) dopamine (DA) modulates the motor-stimulant response to cocaine. The present study examined the specific mPFC DA receptor subtypes that mediate this behavioral response. Intra-mPFC injection of the DA D?-like receptor agonist quinpirole blocked cocaine-induced motor activity, an effect that was prevented by coadministration of the D2 receptor antagonist sulpiride. Intra-mPFC injection of the selective D? receptor agonist PD 168,077 or the selective D? receptor agonist SKF 81297 did not alter the motor-stimulant response to cocaine. Finally, it was found that an intermediate dose of quinpirole, which only attenuated cocaine-induced motor activity, was not altered by SKF 81297 coadministration, suggesting a lack of synergy between mPFC D?, and D? receptors. These results suggest that D? receptor mechanisms in the mPFC are at least partly responsible for mediating the acute motor-stimulant effects of cocaine. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Examining the role of drinking motives in college student alcohol use and problems.

A motivational model of alcohol involvement (M. L. Cooper, M. R. Frone, M. Russell, & P. Mudar, 1995) was replicated and extended by incorporating social antecedents and motives and by testing this model cross-sectionally and longitudinally in a sample of college students. Participants (N = 388) completed a questionnaire battery assessing alcohol use and problems, alcohol expectancies, sensation seeking, negative affect, social influences, and drinking motives. Associations among psychosocial antecedents, drinking motives, and alcohol involvement differed from those found by M. L. Cooper et al. (1995). These findings point to the importance of social influences and of positive reinforcement motives but not to the centrality of drinking motives in this population. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Timing of Meals.

In most individuals, food intake occurs as discrete bouts or meals, and little attention has been paid to the factors that normally determine when meals will occur when food is freely available. On the basis of experiments using rats, the authors suggest that when there are no constraints on obtaining food and few competing activities, 3 levels of interacting controls normally dictate when meals will start. The first is the genetically determined circadian activity pattern on which nocturnal animals tend to initiate most meals in the dark. The second is the regularly occurring changing of the light cycle: These changes provide temporal anchors. The third relates to the size of the preceding meal, such that larger meals cause a longer delay until the onset of the next meal. Superimposed on these 3 are factors related to learning, convenience, and opportunity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Insular cortex lesions and morphine-induced suppression of conditioned stimulus intake in the rat.

The present experiment examined the influence of insular cortex (IC) lesions on the intake of a taste stimulus in a consummatory procedure that used morphine as the unconditioned stimulus. In normal rats, morphine caused a rapid reduction in saccharin intake when the taste was novel but not when it was familiar. Irrespective of stimulus novelty, morphine had little influence on the saccharin consumption of IC-lesioned rats. The results are discussed in terms of a lesion-induced disruption of (i) a reward comparison mechanism and (ii) the perception of taste novelty. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Eat, drink, and be merry, for tomorrow we diet: Effects of anticipated deprivation on food intake in restrained and unrestrained eaters.

This study examined the effect of anticipated food deprivation on intake in restrained and unrestrained eaters. Participants were randomly assigned to a diet condition, in which they expected to diet for a week, or to a control (no-diet) condition. Immediately after being assigned to a condition, participants completed a taste-rating task in which food consumption was measured. Restrained eaters in the diet condition consumed significantly more food than did restrained eaters in the no-diet condition or unrestrained eaters in either condition. Unrestrained eaters consumed the same amount regardless of condition. These results confirm that merely planning to go on a diet can trigger overeating in restrained eaters, reflecting the dynamic connection between dieting and overeating. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of insulin in the glucostatic control of food intake

Insulin, a primary metabolic hormone, plays a dominant role in the regulation of food intake. An increase in the level of circulating insulin produced by its prandial release from endogenous stores is associated with the state of satiety. On the other hand, an increase in the insulin level produced by its exogenous administration, as well as by its excessive and prolonged release in certain pathological states or during the period of nocturnal overeating, paradoxically gives rise to the sensation of hunger. This differential effect of endogenous and exogenous insulin is analyzed in view of experimental and clinical evidence concerning the principal mechanisms in the regulation of food intake. These include the interrelation of central and peripheral glucosensitive systems, the involvement of the enteroinsular axis, and the effects on these regulatory mechanisms of the physiological state produced by changes in circulating insulin levels. The essential role of the vagus nerve in mediating the hunger and satiety induced by the lack of excess of glucose for cellular oxidation places the short-term glucostatic control in the periphery where the insulin is primarily acting. A unifying hypothesis concerning the role of insulin in the regulation of good intake is proposed and its clinical implications suggested.     

The role of work habits in the motivation of food safety behaviors.

The authors considered work habits within an integrated framework of motivated behavior. A distinction made between automatic and controlled action led to 2 measures of work habits: a habit strength measure reflecting the 4 characteristics of automaticity and a measure of work routines under conscious control. Workers at a turkey processing plant (N = 162) responded to an extensive survey of these work habits measures with regard to food safety. Results indicated that attitudes and subjective norms predicted food safety intentions. These intentions, along with perceived behavior control and work habits, predicted reports of food safety behaviors. A mediation analysis indicated that the work routines measure accounted for the variance in self-reported behavior and mediated any effect of the habit strength measure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Weight suppression is a robust predictor of outcome in the cognitive-behavioral treatment of bulimia nervosa.

This study examined weight suppression (difference between highest premorbid weight and pretreatment weight) as a predictor of outcome in 188 outpatients with bulimia nervosa enrolled in a cognitive- behavioral therapy intervention. Participants who dropped out of treatment had significantly higher levels of weight suppression than treatment completers. Of participants who completed treatment, those who continued to engage in binge eating or purging had significantly higher levels of weight suppression than those who were abstinent from bingeing and purging. Results did not change when body mass index, dietary restraint, weight and shape concerns, or other relevant variables were controlled. Relinquishing bulimic behaviors and adopting normal eating patterns may be most feasible for patients who are closest to their highest premorbid weights. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Familiarity-based stimulus generalization of conditioned suppression in rats is dependent on the perirhinal cortex.

We report that bilateral, excitoxic lesions of the perirhinal cortex attenuate rats' familiarity-based stimulus generalization. After surgery, rats were preexposed either to 2 auditory stimuli (A and B) or to only 1 auditory stimulus (B). Following preexposure, all rats received pairings of A and a footshock before assessment of generalized responding (conditioned suppression) to B. Sham rats' generalization was greater when preexposure was to both A and B than when preexposure was to B only. That pattern was abolished in lesioned rats, though no general deficiency was found in other measures of auditory processing. Our findings suggest that the perirhinal cortex is required for rats to encode familiarity as part of stimulus representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Aging and the depth of binocular rivalry suppression.

Two experiments were designed to examine the effect of aging on the strength of binocular rivalry suppression. To produce rivalry, orthogonally oriented sine-wave luminance gratings were presented dichoptically. The observers were then required either to discriminate the spatial location of a probe spot presented to the dominant or suppressed eye's view or to detect the presence or absence of the probe. The observers in the younger and older age groups exhibited typical rivalry suppression for both tasks (i.e., the probe was more difficult to detect or discriminate when presented to the suppressed eye), but the magnitude of the suppression was significantly larger in the older observers. This increased suppression that accompanies aging can be explained by a reduction in the inhibition produced by the binocular matching circuitry of S. R. Lehky and R. Blake's (1991) model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)