Dopamine neuron activity evoked by sucrose and sucrose-predictive cues is augmented by peripheral and central manipulations of glucose availability

Food deprivation drives eating through multiple signals and circuits. Decreased glucose availability (i.e., cytoglucopenia) drives eating and also increases the value of sucrose. Ventral tegmental area (VTA) dopamine neurons (DANs) contribute to the evaluation of taste stimuli, but their role in integrating glucoprivic signals remains unknown. We monitored VTA DAN activity via Cre-dependent expression of a calcium indicator with in vivo fibre photometry. In ad libitum fed rats, intraoral sucrose evoked a phasic increase in DAN activity. To manipulate glucose availability, we administered (intraperitoneal, lateral or fourth ventricular) the antiglycolytic agent 5-thio-D-glucose (5TG), which significantly augmented the phasic DAN activity to sucrose. 5TG failed to alter DAN activity to water or saccharin, suggesting the response was selective for caloric stimuli. 5TG enhancement of sucrose-evoked DAN activity was stronger after fourth ventricular administration, suggesting a critical node of action within the hindbrain. As 5TG also increases blood glucose, in a separate study, we used peripheral insulin, which stimulates eating, to decrease blood glucose-which was associated with increased DAN activity to intraoral sucrose. DAN activity developed to a cue predictive of intraoral sucrose. While 5TG augmented cue-evoked DAN activity, its action was most potent when delivered to the lateral ventricle. Together, the studies point to central glucose availability as a key modulator of phasic DAN activity to food and food-cues. As glucose sensing neurons are known to populate the hypothalamus and brainstem, results suggest differential modulation of cue-evoked and sucrose-evoked DAN activity.

The influence of insulin on anticipation and consummatory reward to food intake: A functional imaging study on healthy normal weight and overweight subjects employing intranasal insulin delivery

Aberrant responses within homeostatic, hedonic and cognitive systems contribute to poor appetite control in those with an overweight phenotype. The hedonic system incorporates limbic and meso-limbic regions involved in learning and reward processing, as well as cortical regions involved in motivation, decision making and gustatory processing. Equally important within this complex, multifaceted framework are the cognitive systems involved in inhibitory control and valuation of food choices. Regions within these systems display insulin receptors and pharmacologically increasing central insulin concentrations using intranasal administration (IN-INS) has been shown to significantly reduce appealing food cue responsiveness and also food intake. In this work we describe a placebo-controlled crossover pharmacological functional magnetic resonance imaging (fMRI) study that looks at how IN-INS (160 IU) affects anticipatory and consummatory responses to sweet stimuli and importantly how these responses differ between healthy normal weight and overweight male individuals. This work shows that age matched normal weight and overweight (not obese) individuals respond similarly to both the anticipation and receipt of sweet stimuli under placebo conditions. However, increased central insulin concentrations produce marked differences between groups when anticipating sweet stimuli within the prefrontal cortex and midbrain as well as observed differences in the amygdala during consummatory responses.

Wistar Kyoto Rats Display Anhedonia In Consumption but Retain Some Sensitivity to the Anticipation of Palatable Solutions

The Wistar Kyoto (WKY) rat has been proposed as a model of depression-like symptoms. However, anhedonia—a reduction in the response to normatively rewarding events—as a central depression symptom has yet to be fully assessed in this model. We compared WKY rats and Wistar controls, with stress-susceptibility examined by applying mild unpredictable stress to a subset of each group. Anhedonia-like behavior was assessed using microstructural analysis of licking behavior, where mean lick cluster size reflects hedonic responses. This was combined with tests of anticipatory contrast, where the consumption of a moderately palatable solution (4% sucrose) is suppressed in anticipation of a more palatable solution (32% sucrose). WKY rats displayed greatly attenuated hedonic reactions to sucrose overall, although their reactions retained some sensitivity to differences in sucrose concentration. They displayed normal reductions in consumption in anticipatory contrast, although the effect of contrast on hedonic reactions was greatly blunted. Mild stress produced overall reductions in sucrose consumption, but this was not exacerbated in WKY rats. Moreover, mild stress did not affect hedonic reactions or the effects of contrast. These results confirm that the WKY substrain expresses a direct behavioral analog of anhedonia, which may have utility for increasing mechanistic understanding of depression symptoms.

Investigating the Effect of Physiological Need States on Palatability and Motivation Using Microstructural Analysis of Licking

The study of consummatory responses during food intake represents a unique opportunity to investigate the physiological, psychological and neurobiological processes that control ingestive behavior. Recording the occurrence and temporal organization of individual licks across consumption, also called lickometry, yields a rich data set that can be analyzed to dissect consummatory responses into different licking patterns. These patterns, divided into trains of licks separated by pauses, have been used to deconstruct the many influences on consumption, such as palatability evaluation, incentive properties, and post-ingestive processes. In this review, we describe commonly used definitions of licking patterns and how various studies have defined and measured these. We then discuss how licking patterns can be used to investigate the impact of different physiological need states on processes governing ingestive behavior. We also present new data showing how licking patterns are changed in an animal model of protein appetite and how this may guide food choice in different protein-associated hedonic and homeostatic states. Thus, recording lick microstructure can be achieved relatively easily and represents a useful tool to provide insights, beyond the measurement of total intake, into the multiple factors influencing ingestive behavior.

Patients With Obsessive-Compulsive Disorder Exhibit Deficits in Consummatory but Not Anticipatory Pleasure

Background: Reward dysfunctions have been reported in obsessive-compulsive disorder (OCD), which implicates a high possibility of anhedonia for this disease. However, several components of anhedonia, such as consummatory and anticipatory pleasure, has not been substantially studied in OCD patients. Methods: The Chinese version of the Temporal Experience of Pleasure Scale (CV-TEPS) was used to evaluate both the consummatory and anticipatory pleasure in 130 OCD patients, 89 major depressive disorder (MDD) patients, and 95 healthy controls (HCs). The Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) and the Beck Depression Inventory (BDI) were scored for assessing the severity of obsessive and compulsive symptoms and depressive symptoms, respectively. Analyses of covariance (ANCOVA) were used to compare the differences of anhedonia among the three groups with the severity of depression controlled. Regression analyses were also used to analyze the relationship between consummatory and anticipatory pleasure and clinical variables in OCD patients. Results: After controlling for the effect of depression, there were significant differences in TEPS scores among the three groups (p < 0.05). Compared with HCs, OCD patients had lower scores on the consummatory subscale, but not the anticipatory subscale, of the TEPS. MDD patients had lower scores on both the consummatory and anticipatory subscales than HCs. Conclusion: OCD patients exhibit deficits in consummatory but not anticipatory pleasure, which is distinct from MDD patients.

Optogenetic activation of amygdala projections to nucleus accumbens can arrest conditioned and unconditioned alcohol consummatory behavior

Following a Pavlovian pairing procedure, alcohol-paired cues come to elicit behavioral responses that lead to alcohol consumption. Here we used an optogenetic approach to activate basolateral amygdala (BLA) axonal terminals targeting the shell of nucleus accumbens (AcbSh) and investigated a possible influence over cue-conditioned alcohol seeking and alcohol drinking, based on the demonstrated roles of these areas in behavioral responding to Pavlovian cues and in feeding behavior. Rats were trained to anticipate alcohol or sucrose following the onset of a discrete conditioned stimulus (CS). Channelrhodopsin-mediated activation of the BLA-to-AcbSh pathway concurrent with each CS disrupted cued alcohol seeking. Activation of the same pathway caused rapid cessation of alcohol drinking from a sipper tube. Neither effect was accompanied by an overall change in locomotion. Finally, the suppressive effect of photoactivation on cued-triggered seeking was also evidenced in animals trained with sucrose. Together these findings suggest that photoactivation of BLA terminals in the AcbSh can override the conditioned motivational properties of reward-predictive cues as well as unconditioned consummatory responses necessary for alcohol drinking. The findings provide evidence for a limbic-striatal influence over motivated behavior for orally consumed rewards, including alcohol.

Anticipatory and consummatory pleasure and displeasure in major depressive disorder: An experience sampling study

Pleasure and displeasure can be parsed into anticipatory and consummatory phases. However, research on pleasure and displeasure in major depressive disorder (MDD), a disorder characterized by anhedonia, has largely focused on deficits in the consummatory phase. Moreover, most studies in this area have been laboratory-based, raising the question of how component processes of pleasure and displeasure are experienced in the daily lives of depressed individuals. Using experience sampling, we compared anticipatory and consummatory pleasure and displeasure for daily activities reported by adults with MDD (n = 41) and healthy controls (n = 39). Participants carried electronic devices for one week and were randomly prompted eight times a day to answer questions about activities to which they most and least looked forward. Compared to healthy controls, MDD participants reported blunted levels of both anticipatory and consummatory pleasure and elevated levels of both anticipatory and consummatory displeasure for daily activities. Independent of MDD status, participants accurately predicted pleasure but overestimated displeasure. These results are the first to provide evidence that, across both anticipatory and consummatory phases, individuals with MDD experience blunted pleasure and elevated displeasure for daily activities. Our findings clarify the disturbances in pleasure and displeasure that characterize MDD and may inform treatment for this debilitating disorder. (PsycINFO Database Record

The behavioral economics of drug self-administration: a review and new analytical approach for within-session procedures

RATIONALE

Behavioral-economic demand curve analysis offers several useful measures of drug self-administration. Although generation of demand curves previously required multiple days, recent within-session procedures allow curve construction from a single 110-min cocaine self-administration session, making behavioral-economic analyses available to a broad range of self-administration experiments. However, a mathematical approach of curve fitting has not been reported for the within-session threshold procedure.

OBJECTIVES

We review demand curve analysis in drug self-administration experiments and provide a quantitative method for fitting curves to single-session data that incorporates relative stability of brain drug concentration.

METHODS

Sprague-Dawley rats were trained to self-administer cocaine, and then tested with the threshold procedure in which the cocaine dose was sequentially decreased on a fixed ratio-1 schedule. Price points (responses/mg cocaine) outside of relatively stable brain cocaine concentrations were removed before curves were fit. Curve-fit accuracy was determined by the degree of correlation between graphical and calculated parameters for cocaine consumption at low price (Q(0)) and the price at which maximal responding occurred (P(max)).

RESULTS

Removing price points that occurred at relatively unstable brain cocaine concentrations generated precise estimates of Q(0) and resulted in P (max) values with significantly closer agreement with graphical P(max) than conventional methods.

CONCLUSION

The exponential demand equation can be fit to single-session data using the threshold procedure for cocaine self-administration. Removing data points that occur during relatively unstable brain cocaine concentrations resulted in more accurate estimates of demand curve slope than graphical methods, permitting a more comprehensive analysis of drug self-administration via a behavioral-economic framework.

Microdialysis of ethanol during operant ethanol self-administration and ethanol determination by gas chromatography

Operant self-administration methods are commonly used to study the behavioral and pharmacological effects of many drugs of abuse, including ethanol. However, ethanol is typically self-administered orally, rather than intravenously like many other drugs of abuse. The pharmacokinetics of orally administered drugs are more complex than intravenously administered drugs. Because understanding the relationship between the pharmacological and behavioral effects of ethanol requires knowledge of the time course of ethanol reaching the brain during and after drinking, we use in vivo microdialysis and gas chromatography with flame ionization detection to monitor brain dialysate ethanol concentrations over time. Combined microdialysis-behavioral experiments involve the use of several techniques. In this article, stereotaxic surgery, behavioral training and microdialysis, which can be adapted to test a multitude of self-administration and neurochemical centered hypotheses, are included only to illustrate how they relate to the subsequent phases of sample collection and dialysate ethanol analysis. Dialysate ethanol concentration analysis via gas chromatography with flame-ionization detection, which is specific to ethanol studies, is described in detail. Data produced by these methods reveal the pattern of ethanol reaching the brain during the self-administration procedure, and when paired with neurochemical analysis of the same dialysate samples, allows conclusions to be made regarding the pharmacological and behavioral effects of ethanol.

Relative food preference and hedonic judgments in schizophrenia

There is a well-documented disruption of the neural network associated with reward evaluation in schizophrenia. This same system is involved in coding the incentive value of food in healthy individuals, but few studies to date have examined anhedonia and its relation to food hedonicity and preference in schizophrenia. Relative preference and hedonic food ratings were examined in schizophrenia patients and healthy controls. In the relative preference task, subjects viewed photographs of food items and selected the one that they most preferred. Hedonic ratings were obtained by asking subjects how much they liked the food stimulus on a scale of 1-5. There were no overall response time differences between the two groups in the relative preference task, but schizophrenia patients showed subtle differences in their hedonic ratings of foods compared with control subjects. Schizophrenia patients gave more positive hedonic ratings for food than did controls, and the use of fewer positive ratings was associated with increased anhedonia, particularly with loss of sexual interest. These results suggest that while making relative preference judgments may be intact, hedonic values attached to food may be altered in schizophrenia, and they may be related to dysfunction in more basic vegetative systems.

Anhedonia in schizophrenia: distinctions between anticipatory and consummatory pleasure

Research on anhedonia in schizophrenia has revealed mixed results, with patients reporting greater anhedonia than healthy controls on self-report measures and semi-structured interviews, but also reporting comparable experiences of positive emotions in response to pleasurable stimuli. Basic science points to the importance of distinguishing between anticipatory and consummatory (or in-the-moment) pleasure experiences, and this distinction may help to reconcile the mixed findings on anhedonia in schizophrenia. In two studies, we tested the hypothesis that anhedonia in schizophrenia reflects a deficit in anticipatory pleasure but not consummatory pleasure. In Study 1, we used experience sampling methodology to assess reported experiences of consummatory and anticipated pleasure among schizophrenia patients and controls. In Study 2, schizophrenia patients and controls completed a self-report trait measure of anticipatory and consummatory pleasure and interviews that assessed negative symptoms, including anhedonia, and community functioning. In both studies, we found evidence for an anticipatory but not a consummatory pleasure deficit in schizophrenia. In addition, anticipatory pleasure was related to clinical ratings of anhedonia and functional outcome. Clinical and research implications of these findings are discussed.

Facilitation of sexual behavior and enhanced dopamine efflux in the nucleus accumbens of male rats after D-amphetamine-induced behavioral sensitization

Behavioral sensitization caused by repeated and intermittent administration of psychostimulants, such as cocaine and D-amphetamine, is accompanied by enhanced function in limbic-motor circuitry that is involved in the generation of motivated behavior. The present microdialysis study investigated the effect of D-amphetamine-induced sensitization on dopamine (DA) efflux in the nucleus accumbens (NAC) of male rats during sexual behavior. Male rats were given one injection of D-amphetamine (1.5 mg/kg, i.p.) or saline every other day for a total of 10 injections. Three weeks after discontinuation of drug treatment, rats were tested for sexual behavior during a test in which microdialysis was performed. There was an augmented efflux of DA in the NAC of D-amphetamine-sensitized rats compared with nonsensitized control rats when a receptive female was present behind a screen (35 vs 17%). Sensitized rats exhibited facilitated sexual behavior when the screen was removed, as indicated by a significantly shorter latency to mount and an overall increase in the amount of copulatory behavior. Although there was a significant increase in NAC DA concentrations from baseline in both sensitized and nonsensitized rats during copulation, there was a greater increase in DA efflux in the NAC of sensitized rats during the first 10 min copulatory sample (60 vs 37%). These results demonstrate that behavioral sensitization caused by repeated psychostimulant administration can "cross-sensitize" to a natural behavior, such as sex, and that increased NAC DA release may contribute to the facilitation of appetitive and consummatory aspects of this behavior.

Dynamic changes in nucleus accumbens dopamine efflux during the Coolidge effect in male rats

The Coolidge effect describes the reinitiation of sexual behavior in a "sexually satiated" animal in response to a novel receptive mate. Given the role of the mesolimbic dopamine (DA) system in the initiation and maintenance of motivated behavior, microdialysis was used to monitor nucleus accumbens (NAC) DA transmission during copulation, sexual satiety, and the reinitiation of sexual behavior. In agreement with earlier reports, the presentation of an estrous female behind a screen and copulation were associated with significant increases in NAC DA efflux. Return of NAC DA concentrations to baseline values coincided with a period of sexual satiety, although concentrations of the DA metabolites, dihydroxyphenylacetic acid and homovanillic acid, remained elevated. The presentation of a novel receptive female behind a screen resulted in a slight increase in NAC DA, which was augmented significantly during renewed copulation with the novel female. The present data suggest that the stimulus properties of a novel receptive female may serve to increase NAC DA transmission in a sexually satiated male rat, and this, in turn, may be related to the reinitiation of sexual behavior.