"Depression" increases "craving" for sweet rewards in animal and human models of depression and craving

Vagus nerve stimulation acutely alters food craving in adults with depression

Vagus nerve stimulation (VNS) is now available as a treatment for epilepsy and treatment-resistant depression. The vagus nerve plays a central role in satiety and short-term regulation of food intake and research suggests a relationship between VNS and weight loss. The underlying mechanisms of this relationship are unknown. The purpose of the current study was to determine whether acute cervical VNS might temporarily alter food cravings. Thirty-three participants were recruited for three groups; depression VNS, depression non-VNS, and healthy controls. Participants viewed 22 computerized images of foods twice in one session and completed ratings for food cravings after each image. The VNS participants' devices were turned on for one viewing of an image and off for the other (randomized order). Participants were blind to VNS condition (on versus off). Acute VNS device activation was associated with a significant change in cravings-ratings for sweet foods. A significant proportion of variability in VNS-related changes in cravings was accounted for by patients' clinical VNS device settings, acute level of depression, and body mass. Further studies are warranted addressing how acute or chronic VNS might modify eating behavior and weight.

A reciprocal interaction between food-motivated behavior and diet-induced obesity

OBJECTIVES

One of the main causes of obesity is overconsumption of diets high in fat and sugar. We studied the metabolic changes and food-motivated behavior when rats were subjected to a choice diet with chow, lard and a 30% sucrose solution (high fat high sugar (HFHS)-choice diet). Because rats showed considerable variations in the feeding response to HFHS-choice diet and in food-motivated behavior, we investigated whether the motivation to obtain a sucrose reward correlated with the development of obesity when rats were subsequently subjected to HFHS-choice diet.

METHOD

We first studied feeding, locomotor activity and body temperature, fat weights and hormonal concentrations when male Wistar rats were subjected to HFHS-choice diet for 1 week. Second, we studied sucrose-motivated behavior, using a progressive ratio (PR) schedule of reinforcement in rats that were subjected to the HFHS-choice diet for at least 2 weeks, compared to control rats on a chow diet. Third, we measured motivation for sucrose under a PR schedule of reinforcement in rats that were subsequently subjected to HFHS-choice diet or a chow diet for 4 weeks. Fat weights were measured and correlated with the motivation to obtain sucrose pellets.

RESULTS

One week on the HFHS-choice diet increased plasma concentrations of glucose and leptin, increased fat stores, but did not alter body temperature or locomotor activity. Moreover, consuming the HFHS-choice diet for several weeks increased the motivation to work for sucrose pellets. Furthermore, the motivation to obtain sucrose pellets correlated positively with abdominal fat stores in rats subsequently subjected to the HFHS-choice diet, whereas this correlation was not found in rats fed on a chow diet.

CONCLUSION

Our data suggest that the motivation to respond for palatable food correlates with obesity due to an obesogenic environment. Conversely, the HFHS-choice diet, which results in obesity, also increased the motivation to work for sucrose. Thus, being motivated to work for sucrose results in obesity, which, in turn, increases food-motivated behavior, resulting in a vicious circle of food motivation and obesity.

Rats with persistently low or high exploratory activity: Behaviour in tests of anxiety and depression, and extracellular levels of dopamine

Behaviour in novel environments is influenced by the conflicting motivators fear and curiosity. Because changes in both of these motivational processes are often simultaneously involved in human affective disorders, we have developed the exploration box test which allows separation of animals belonging to clusters with inherent high neophobia/low motivation to explore and low neophobia/high motivation to explore (LE and HE, respectively). In a novel home-cage, no behavioural differences were found between LE- and HE-rats, suggestive that it is not the general locomotor activity but specific features of the exploration box test that bring about the differences. In studies on both Wistar and Sprague-Dawley rats we found that the trait of exploratory activity remains stable over long periods of time and that LE and HE animals display differences in many other behavioural tests related to mood disorders. Namely, LE animals were found to display enhanced anxiety-like behaviour and to be generally less active in the elevated plus-maze, used more passive coping strategies in the forced swimming test, and acquired a more persistent association between neutral and stressful stimuli in fear conditioning test. LE animals consumed more sucrose solution in non-deprived conditions. We also found that both at baseline and in response to d-amphetamine (0.5mg/kg) administration, LE-rats had lower extracellular dopamine levels in striatum but not in nucleus accumbens. In conclusion, LE-rats appear more inhibited in their activity in typical animal tests of anxiety and are more susceptible to acute stressful stimuli.

K+ channels stimulated by glucose: a new energy-sensing pathway

Insights into how sugar can turn off cell activity are emerging from studies of hypothalamic neurons. Brain states are coordinated by hypothalamic orexin/hypocretin neurons, whose loss leads to narcoleptic instability of consciousness and inability to rouse when hungry. Recent studies indicate that glucose blocks the electrical activity of orexin cells by opening K+ channels in their membrane. This new energy-sensing mechanism is so sensitive that even small changes in glucose levels, of the type occurring between meals, can turn orexin cells on and off. Glucose-stimulated K+ channels share biophysical properties with "leak" (two-pore domain) K+ channels, the newest and least understood K+ channel family. A hypothesis is outlined whereby the stimulation of brain K+ channels by sugar could relieve stress and enhance reward, although probably at a cost of increased sleepiness.

Facial and affective reactions to tastes and their modulation by sadness and joy

This study examined adults' affective and facial reactions to tastes which differ in quality and valence, and the impact of sadness and joy on these reactions. Thirty-six male and female subjects participated voluntarily. Subjects each tasted 6 ml of a sweet chocolate drink, a bitter quinine solution (0.0015 M) and a bitter-sweet soft drink. Following a baseline period, either joy or sadness was induced using film clips before the same taste stimuli were presented for a second time. Subjects rated the drinks' pleasantness and intensity of taste immediately after each stimulus presentation. Facial reactions were videotaped and analysed using the Facial Action Coding System (FACS [P. Ekman, W.V. Friesen, Facial Action Coding System: Manual. Palo Alto, CA: Consulting Psychologists Press; 1978., P. Ekman, W. Friesen, J. Hager, Facial Action Coding System. Salt Lake City, Utah: Research Nexus; 2002.]). The results strongly indicated that the tastes produced specific facial reactions that bear strong similarities to the facial reactivity patterns found in human newborns. The data also suggest that some adults' facial reactions serve additional communicative functions. Emotions modulated taste ratings, but not facial reactions to tastes. In particular, ratings of the sweet stimulus were modulated in congruence with emotion quality, such that joy increased and sadness decreased the pleasantness and sweetness of the sweet stimulus. No emotion-congruent modulation was found for the pleasantness and intensity ratings of the bitter or the bitter-sweet stimulus. This 'robustness' of bitter taste ratings may reflect a biologically meaningful mechanism.

Mood state effects of chocolate

BACKGROUND

Chocolate consumption has long been associated with enjoyment and pleasure. Popular claims confer on chocolate the properties of being a stimulant, relaxant, euphoriant, aphrodisiac, tonic and antidepressant. The last claim stimulated this review.

METHOD

We review chocolate's properties and the principal hypotheses addressing its claimed mood altering propensities. We distinguish between food craving and emotional eating, consider their psycho-physiological underpinnings, and examine the likely 'positioning' of any effect of chocolate to each concept.

RESULTS

Chocolate can provide its own hedonistic reward by satisfying cravings but, when consumed as a comfort eating or emotional eating strategy, is more likely to be associated with prolongation rather than cessation of a dysphoric mood.

LIMITATIONS

This review focuses primarily on clarifying the possibility that, for some people, chocolate consumption may act as an antidepressant self-medication strategy and the processes by which this may occur.

CONCLUSIONS

Any mood benefits of chocolate consumption are ephemeral.

Problemessen vs. Spaßessen

Zusammenfassung. Das Zusammenspiel von negativem Affekt und nachfolgender Affektregulation auf das Essverhalten wurde mit 70 Versuchspersonen (Vpn) experimentell untersucht. Nach einer Imaginationsinduktion von negativem Affekt wurden die Vpn in eine positive oder in eine negative Selbstaktivierungsgruppe eingeteilt. Die Diätintention der Probanden wurde durch eine “Neujahrsvorsatz-Methode“ erfasst. Es ergaben sich folgende Interaktionen zwischen Selbstaktivierung und Diätintention: (a) Vpn mit negativer Selbstaktivierung und niedriger Diätintention aßen mehr Schokolade als Vpn in allen anderen Bedingungen. (b) Vpn mit positiver Selbstaktivierung und hoher Diätintention aßen mehr Kekse als Vpn in allen anderen Bedingungen. Die Befunde sind nicht mit der Hypothese von Tice, Bratslavsky und Baumeister (2001) vereinbar, die eine einfache Beziehung zwischen negativem Affekt und nachfolgendem Verlust der Impulskontrolle beim Essen postulierten. Es gab darüber hinaus positive Korrelationen zwischen der Menge der verzehrten Schokolade und Persönlichkeitsdispositionen mit Beziehung zu Depressivität. Implikationen der Befunde für eine Diät und die Gesundheit werden diskutiert.

Everyday mood and emotions after eating a chocolate bar or an apple

Emotional changes after eating chocolate were examined in everyday life. Thirty-seven healthy, normal-weight women ate a chocolate bar, an apple or nothing and rated their subjective state 5, 30, 60 and 90min after eating. Both chocolate and the apple reduced hunger, elevated mood and increased activation, but the effects of the chocolate were stronger. Eating chocolate was also followed by joy and, in some women, by guilt. Guilt responders experienced less intense positive emotions. Whereas positive emotional responses appear to be due to sensory pleasure and it's anticipation and may also be related to reduced hunger, guilt responses are probably induced by negative food-related cognitions.

Emotional influences on food choice: sensory, physiological and psychological pathways

Sensory, physiological and psychological mechanisms are reviewed that underlie emotional influences on food choice. Both moods and emotions are considered. Eating a meal will reliably alter mood and emotional predisposition, typically reducing arousal and irritability, and increasing calmness and positive affect. However, this depends on the meal size and composition being close to the eater's habit, expectations and needs. Unusual meals--e.g. too small, unhealthy--may negatively affect mood. Sweetness, and sensory cues to high energy density, such as fatty texture, can improve mood and mitigate effects of stress via brain opioidergic and dopaminergic neurotransmission. However, adaptation in these pathways, perhaps enhanced by inherited sensitivity, with chronic exposure to such sensory qualities, could lead to overeating of energy-dense foods and consequent obesity. Sweet, fatty foods low in protein may also provide alleviation from stress in vulnerable people via enhanced function of the serotonergic system. Moreover, in rats, such foods seem to act as part of a feedback loop, via release of glucocorticoid hormones and insulin, to restrain activity of the hypothalamic pituitary adrenal axis during stress. However, this effect is also associated with abdominal obesity. In humans, a number of psychological characteristics predict the tendency to choose such foods when stressed, such as restrained or emotional eating, neuroticism, depression and premenstrual dysphoria, all of which could indicate neurophysiological sensitivity to reinforcing effects of such foods. Greater understanding of such predictive traits and the underlying mechanisms could lead to tailoring of diet to meet personal emotional needs.

Chronic mild stress (CMS) revisited: consistency and behavioural-neurobiological concordance in the effects of CMS

The chronic mild stress (CMS) model of depression has high validity but has in the past been criticized for being difficult to replicate. However, a large number of recent publications have confirmed that CMS causes behavioural changes in rodents that parallel symptoms of depression. This review summarizes studies from over sixty independent research groups that have reported decreases in reactivity to rewards, and a variety of other depression-like behaviours, in rats or mice, following exposure to CMS. Together, these changes are referred to as a 'depressive' behavioural profile. Almost every study that has examined the effects of chronic antidepressant treatment in these procedures has reported that antidepressants were effective in reversing or preventing these 'depressive' behavioural changes. (The single exception is a study in which the duration of treatment was too brief to constitute an adequate trial.) There are also a handful of reports of CMS causing significant effects in the opposite direction, termed here an 'anomalous' behavioural profile. There are six neurobiological parameters that have been studied in both 'anhedonic' and 'anomalous' animals: psychostimulant and place-conditioning effects of dopamine agonists; dopamine D2 receptor number and message; inhibition of dopamine turnover by quinpirole, and beta-adrenergic receptor binding. On all six measures, CMS caused opposite effects in animals displaying 'depressive' and 'anomalous' profiles. Thus, there is overwhelming evidence that under appropriate experimental conditions, CMS can cause antidepressant-reversible depressive-like effects in rodents; however, the 'anomalous' profile that is occasionally reported appears to be a genuine phenomenon, and these two sets of behavioural effects appear to be associated with opposite patterns of neurobiological changes.

Behavioural and neurochemical effects induced by chronic mild stress applied to two different rat strains

Chronic mild stress (CMS) has been reported to induce an anhedonic-like state in rats that resembles some of the symptoms of endogenous depression in humans. In the present study, CMS-induced behavioural responses along with neurochemical alterations in dopaminergic and serotonergic function in prefrontal cortex, striatum, hypothalamus and hippocampus were examined following treatment with imipramine in Wistar and Sprague-Dawley rats. The CMS procedure lasted 7 weeks in total. Once per week, a 1-h preference test for 1% sucrose solution was conducted. Treatment with imipramine (10mg/kg i.p., once daily) commenced after experimental week 3. CMS induced significant reductions in absolute and relative sucrose intake and sucrose preference in both rat strains but their temporal pattern was different especially during the weeks 0-3. These effects were reversed by IMI. An increase in the dopaminergic and a decrease in the serotonergic activity were observed in the prefrontal cortex in both rat strains following CMS. A decrease in the striatal dopaminergic activity and an increased hippocampal serotonergic activity were also seen in both rat strains following CMS. In Wistar rats, dopaminergic and serotonergic activities were enhanced in the hypothalamus whereas in Sprague-Dawley rats no such stress-induced changes were observed. Notably, the clear decrease in sucrose consumption observed in stressed Wistar rats could be directly associated with a respective increase in the dopaminergic hypothalamic activity. Chronic treatment with imipramine normalized all neurochemical alterations induced by CMS. Our results suggest that a specific and regionally differentiated serotonin-dopamine interaction is directly related to the observed stress-induced anhedonia.

Chocolate cravings are susceptible to visuo-spatial interference

The study investigated the specificity of visuo-spatial working memory-based techniques as a means to reduce chocolate cravings. Twenty-four self-identified chocolate cravers and 24 non-cravers formed and maintained images of chocolate-containing foods elicited by pictures, while performing a visuo-spatial task (loading the visuo-spatial sketch pad) or an auditory task (loading the phonological loop). Vividness and craving intensity were rated for each image. Concurrent visuo-spatial processing was found to render chocolate images significantly less vivid and cravings less intense compared to concurrent verbal processing, for both cravers and non-cravers. Chocolate cravers did, however, report higher levels of chocolate craving and intake than non-cravers. It was concluded that visuo-spatial tasks provide an effective craving reduction mechanism for the management of chocolate cravings. Such techniques may be particularly useful in populations for whom eating problems are triggered by chocolate craving.

Emotionsbedingtes Essverhalten: Die Bedeutung der Emotionen

Zusammenfassung. Wirkungen von Emotionen auf das Essverhalten variieren in Abhängigkeit von Person- und Emotionsmerkmalen. Bisherige Untersuchungen waren größtenteils auf den Einfluss von Personmerkmalen gerichtet. Sie zeigten, dass ein gezügelter sowie ein emotionaler Ess-Stil zu gesteigerter Nahrungsaufnahme bei negativen Emotionen prädisponieren. Weitere Untersuchungen verweisen auf den Einfluss von Emotionsmerkmalen wie Intensität und Valenz. Der vorliegende Beitrag fasst den Forschungsstand zusammen und unterteilt die Wirkungen von Emotionen auf das Essverhalten in fünf Varianten, die sich durch definierte Person- und Emotionsmerkmale vorhersagen lassen: emotionale Steuerung der Nahrungswahl, emotionale Hemmung des Essverhaltens, emotionale Enthemmung gezügelten Essverhaltens, emotional-instrumentelles Essverhalten und emotionkongruente Modulation des Essverhaltens.

Psychostimulant withdrawal as an inducing condition in animal models of depression

A large body of evidence indicates that the withdrawal from high doses of psychostimulant drugs in humans induces a transient syndrome, with symptoms that appear isomorphic to those of major depressive disorder. Pharmacological treatment strategies for psychostimulant withdrawal in humans have focused mainly on compounds with antidepressant properties. Animal models of psychostimulant withdrawal have been shown to demonstrate a wide range of deficits, including changes in homeostatic, affective and cognitive behaviors, as well as numerous physiological changes. Many of these behavioral and physiological sequelae parallel specific symptoms of major depressive disorder, and have been reversed by treatment with antidepressant drugs. These combined findings provide strong support for the use of psychostimulant withdrawal as an inducing condition in animal models of depression. In the current review we propound that the psychostimulant withdrawal model displays high levels of predictive and construct validity. Recent progress and limitations in the development of this model, as well as future directions for research, are evaluated and discussed.

Rats with congenital learned helplessness respond less to sucrose but show no deficits in activity or learning

Inbred rat strains for congenital learned helplessness (cLH) and for congenital resistance to learned helplessness (cNLH) were investigated as a model to study genetic predisposition to major depression. Congenitally helpless rats respond less to sucrose under a progressive ratio schedule. This is not confounded by locomotor hypoactivity: in contrast, cLH rats show a slight hyperactivity during the first 5 min of an open field test. cLH rats acquire operant responding to sucrose as readily as cNLH rats and exhibit normal memory acquisition and retrieval in the Morris water maze, thus ruling out general learning deficits as the cause of the decreased response to sucrose. Reduced total responses and reduced breaking points for sucrose in the cLH strain argue for anhedonia, which is an analogue to loss of pleasure essential for the diagnosis of major depressive episodes, and thus confirm the validity of congenitally learned helpless rats as a model of major depression.

Performance of the marmoset monkey on computerized tasks of attention and working memory

The CAmbridge Neuropsychological Test Automated Battery (CANTAB) is a computerised battery of neuropsychological tests presented as stimuli on a touch-sensitive computer screen that has been used to assess a wide range of cognitive functions in neuropsychiatric patients, healthy volunteers, and species of non-human primate, primarily the rhesus macaque. The common marmoset is a small-bodied, tractable simian primate that breeds well under laboratory conditions. This primate has been quite extensively studied in terms of its abilities and limitations with respect to appetitive cognitive conditioning. However, the CANTAB versions of sustained/divided attention and working memory tasks have to-date not been studied in the marmoset. Here we describe adult marmoset performance on the CANTAB five-choice serial reaction time task, a delayed match-to-position task, and a task derived from the CANTAB visuo-spatial paired associates learning task that constituted two, concurrent delayed match-to-position tasks. The acquisition and stable longitudinal performance of these tasks provide strong evidence that the marmoset, in addition to the macaque, can be the species of choice for CANTAB-based drug and lesion studies of cognitive function, using tasks similar to those deployed in the study of human cognition and diagnosis of neuropsychiatric disorders.

Sweet babies: chocolate consumption during pregnancy and infant temperament at six months

BACKGROUND

Chocolate contains several biologically active components potentially having behavioral and psychological consequences.

AIMS

We tested whether chocolate consumption and stress experiences during pregnancy predict mother-rated infant temperament at 6 months.

DESIGN AND SUBJECTS

Prenatal frequency of chocolate consumption and intensity of psychological stress experience of the mothers, and temperament characteristics of the infants 6 months postpartum were evaluated in 305 consecutive, healthy mother-infant dyads.

RESULTS

Mothers who reported daily consumption of chocolate rated more positively the temperament of their infants at 6 months. Maternal prenatal stress predicted more negatively tuned ratings of the infant temperament, particularly among those who reported never/seldom chocolate consumption. However, this effect was not observed among the mothers reporting weekly or daily chocolate consumption.

CONCLUSIONS

In addition to producing subjective feelings of psychological well being, chocolate may have effects at multiple environmental and psychological levels.

Reinterpretation of Basal Glucocorticoid Feedback: Implications to Behavioral and Metabolic Disease

A number of metabolic (e.g., abdominal obesity) and psychological (e.g., depression) pathologies commonly present together and have been associated with dysregulation in the hypothalamo-pituitary-adrenal (HPA) axis. Glucocorticoid hormones represent the final product of this classic neuroendocrine axis, and these steroids modulate neuroendocrine, metabolic, and behavioral function. A primary characteristic of the HPA axis is a negative feedback loop, and glucocorticoids act through the brain to inhibit drive to this neuroendocrine system. Slight and chronic perturbations in glucocorticoid levels, below or above normal, throughout the body lead to metabolic (e.g., abdominal obesity) and behavioral (e.g., depression) pathology. Appropriate feedback in the HPA axis is, therefore, critical, and determining how and where glucocorticoids act to impart their feedback effects have been the focus of many laboratories. However, the answer to these questions remain, in part, elusive. In this chapter, I review findings that have led me to reinterpret glucocorticoid feedback in the HPA axis. I propose that, under basal (nonstress) conditions, glucocorticoid feedback is a consequence of the metabolic actions of the adrenal steroid, not a direct effect on brain. This new perspective may provide insight into the etiology of diseases such as major depression and the metabolic syndrome X, and might explain the commonly observed coexistence of affective and metabolic disturbances.

Amphetamine withdrawal does not produce a depressive-like state in rats as measured by three behavioral tests

Administration of amphetamine (AMPH) can induce symptoms of psychosis in humans and locomotor sensitization in rats; in contrast, withdrawal from a period of AMPH intake is most often associated with symptoms of human endogenous depression. The aim of this study was to determine whether AMPH withdrawal produces a depressive-like state in rats. The present study examined the effects of withdrawal from an escalating-dose AMPH schedule (ESC; three daily injections over 6 days, 1-5 mg/kg, i.p.) and an intermittent-dose AMPH schedule (INT; one daily injection over 6 days, 1.5 mg/kg, i.p.) on animals' performance in three behavioral paradigms related to depression: the Porsolt swim test, the learned helplessness assay and operant responding for sucrose on a progressive ratio schedule. ESC and INT AMPH withdrawal had no effect on any of these tests or on stress responsiveness as measured by increased plasma levels of corticosterone (CORT) and adrenocorticotropin following the swim test, although basal CORT levels were higher in AMPH-withdrawn animals compared to controls. Finally, we confirmed the presence of locomotor sensitization for both AMPH schedules after 30 days of withdrawal. Our results suggest that the ability of AMPH withdrawal to produce symptoms of depression may not be evident in all behavioral screens for depressive symptoms in the rat.

Chocolate eating in healthy men during experimentally induced sadness and joy

The study compared influences of qualitatively different emotions on eating. Motivation to eat, affective responses to chocolate and chewing of chocolate were investigated in healthy normal weight males during experimentally induced emotions. Subjects abstained from eating 2 h (n = 24) or 8 h (n = 24) before testing. They received pieces of chocolate after viewing film clips presented to induce anger, fear, sadness and joy. Motivation to eat and most affective responses to eating chocolate were higher after 8 h than after 2 h of deprivation. Sadness and joy affected motivation to eat in opposite directions: joy increased and sadness decreased appetite (p < 0.001). In joy, a higher tendency to eat more chocolate was reported (p < 0.001), and chocolate tasted more pleasant (p < 0.001) and was experienced as more "stimulating" than in sadness (p < 0.01). No effects of deprivation could be found for chewing time and number of chews. Results indicate that the quality of emotions can affect motivation to eat and affective responses to eating chocolate. Our findings on decreased eating responses to sadness in healthy males and the contradictory increased eating responses to sadness reported by others supports two types of emotion-induced changes of eating: emotion-congruent modulation of eating and eating to regulate emotions.

Carbohydrate ingestion, blood glucose and mood

A series of studies have reported that a high carbohydrate meal, or diets high in carbohydrate, were associated with feeling less energetic. However, after a drink containing pure sugar most studies report no effect. Meals almost exclusively carbohydrate increase the availability of tryptophan and hence serotonin synthesis in the brain, however, a small amount of protein blocks this mechanism making it an uncommon response. In many individuals, poor mood stimulates the eating of palatable high carbohydrate/high fat foods that stimulate the release of endorphins. There is a tendency for those with lower blood glucose, when performing cognitively demanding tasks, to report poorer mood. In a range of situations an association between a tendency for blood glucose levels to fall rapidly, and irritability, has been found. Differences in the ability to control blood glucose levels influence the association between carbohydrate intake and mood. There is a need in future research to contrast the impact of carbohydrate on mood in those distinguished because of their pre-existing psychological and physiological functioning.

Sucrose intake and corticosterone interact with cold to modulate ingestive behaviour, energy balance, autonomic outflow and neuroendocrine responses during chronic stress

In adrenalectomized (ADX) rats, either corticosterone replacement or increased sucrose intake will restore body weight gain, uncoupling protein-1, fat depot mass, food intake and corticotropin-releasing factor mRNA expression to normal. Here, we tested the potential interactions between sucrose intake and circulating corticosterone on behavioural, metabolic, autonomic and neuroendocrine responses to the stress of cold. Rats were left intact, sham-ADX, or ADX and replaced with pellets that provided normal, basal (30%B) or high stress (100%B) constant circulating concentrations of corticosterone +/- sucrose. More calories were consumed in cold than at room temperature (RT), provided that corticosterone concentrations were elevated above mean daily basal values in cold. Neither increased sucrose nor increased chow ingestion occurred in cold if the rats were ADX and replaced with 30%B. However, sucrose drinking in this group markedly ameliorated other responses to cold. By contrast, ADX30%B rats not drinking sucrose fared poorly, and none of the metabolic or endocrine variables were similar to those in sham-ADX controls. ADX100%B group in cold, resembled intact rats without sucrose; however, this group was metabolically abnormal at RT. We conclude that drinking sucrose lowers stress-induced corticosterone secretion while reducing many responses to cold; elevated corticosterone concentrations in the stress-response range are essential for the normal integrated cold-induced responses to occur.

A new perspective on glucocorticoid feedback: relation to stress, carbohydrate feeding and feeling better

Input to and regulation of activity in the hypothalamic-pituitary-adrenal (HPA) axis is diverse and complex. Glucocorticoid feedback is a major component that determines activity in this classic neuroendocrine axis and, while feedback occurs through the brain, the pathways that mediate glucocorticoid feedback remain unknown. In this review, I discuss findings that have led us to view glucocorticoid feedback in the HPA axis in a new light. Much of what has precipitated this view comes from a very surprising finding in our laboratory; sucrose ingestion normalizes feeding, energy balance and central corticotropin releasing factor expression in adrenalectomized (ADX) rats. Since this discovery, a diverse set of literature that supports this view of glucocorticoid feedback has been found. Taken together, recent findings of the well-known importance of glucocorticoids to feeding and energy balance, and the modulatory actions of carbohydrate ingestion on both basal and stress-induced activity in the HPA axis, strongly suggest that many metabolic (e.g. obesity) and psychological (e.g. depression) pathologies, which often present together and have been associated with stress and HPA dysregulation, might, in part, be understood in light of our new view of glucocorticoid feedback.

Chronic variable stress and partial 5-HT denervation by parachloroamphetamine treatment in the rat: effects on behavior and monoamine neurochemistry

Chronic variable stress (CVS) and manipulations of 5-HT-ergic neurotransmission are increasingly used as animal models of depression. In the present study, CVS for 2 weeks and a partial lesion of 5-HT projections by a small dose of parachloroamphetamine (PCA, 2 mg/kg) were applied independently or in combination. CVS reduced significantly the gain in body weight and increased the number of defecations in the open field test. PCA reduced body weight only within the first 24 h after its administration. Consumption of sucrose solution and its preference to water in non-deprived rats were significantly higher in PCA-pretreated rats 2 weeks after CVS compared to control animals. In the forced swimming test, both PCA and CVS treatments reduced immobility on the first but not the second session. Both treatments reduced significantly the time rats spent in social interaction. CVS also elicited an increase in the weight of the right adrenal, but this effect was not present in the PCA-pretreated group. PCA reduced 5-HT and 5-HIAA levels in the frontal cortex, hippocampus, and septum by approximately 20%. CVS increased HVA levels in the frontal cortex. Applied together, PCA pretreatment and CVS increased dopamine turnover in the frontal cortex. Conclusively, this study has provided evidence that chronic variable stress, which elicited expected physiological and neurochemical changes, does not reduce sucrose intake or preference in non-deprived animals, but, instead, may increase it after partial 5-HT-ergic denervation; and that partial 5-HT-ergic denervation by a low dose PCA treatment has a long-lasting effect on forced swimming and social behavior similar to chronic stress.

Mood and carbohydrate cravings

The relationship between mood and carbohydrate cravings, and the possible role of gender in these associations, was investigated in a sample of 113 males and 138 female college students. Participants completed a Cravings Questionnaire and several mood inventories (profile of mood states, Beck Depression Inventory, and the Vitality Inventory) in groups of 25. Individuals classifying themselves as "carbohydrate cravers" reported foods rich in carbohydrates, and "protein cravers" reported protein-rich foods as being the ones they most strongly craved. Carbohydrate cravers reported feeling distressed prior to their cravings and satisfied, happy/good and relaxed following carbohydrate consumption. Protein cravers reported feeling anxious or hungry prior to their cravings and happy, normal, bored, and energetic following protein-rich food consumption. A non-significant correlation existed between "protein" cravers' ratings of craving intensity and mood, but a significant positive correlation existed between "carbohydrate" cravers' ratings of craving intensity and almost all mood scales assessed for both male and female "carbohydrate" cravers. The correlation between craving intensity and mood existed predominately with individuals who craved sweet carbohydrate-rich foods.

The effects of nutrients on mood

A recent major theory was that a meal high in carbohydrate increased the rate that tryptophan enters the brain, leading to an increase in the level of the neurotransmitter serotonin that modulates mood. Although such a mechanism may be important under laboratory conditions it is unlikely to be of significance following the eating of any typical meal. As little as 2-4% of the calories of a meal as protein will prevent an increased availability of tryptophan. Arguably the food with the greatest impact on mood is chocolate. Those who crave chocolate tend to do so when they feel emotionally low. There have been a series of suggestions that chocolate's mood elevating properties reflect 'drug-like' constituents including anandamines, caffeine, phenylethylamine and magnesium. However, the levels of these substances are so low as to preclude such influences. As all palatable foods stimulate endorphin release in the brain this is the most likely mechanism to account for the elevation of mood. A deficiency of many vitamins is associated with psychological symptoms. In some elderly patients folate deficiency is associated with depression. In four double-blind studies an improvement in thiamine status was associated with improved mood. Iron deficiency anaemia is common, particularly in women, and is associated with apathy, depression and rapid fatigue when exercising.

Chronic mild stress has no effect on responding by rats for sucrose under a progressive ratio schedule

Exposure of rats to chronic unpredictable mild stress (CMS) has been shown to produce a syndrome in which a wide range of consummatory behaviors are attenuated, resembling a state of anhedonia, which may be reversed by treatment with antidepressant drugs. The aim of the present study was to determine whether CMS would also affect a rat's motivation to respond for a sucrose solution, as assessed by its performance under a progressive ratio (PR) schedule of reinforcement. Control studies demonstrated that break points in nonstressed rats were sensitive to both the concentration of sucrose solution used, as well as the period of food and water deprivation used prior to testing. Exposure of rats to CMS had no effect upon break points when responding under a progressive ratio schedule for either a 1% or 7% sucrose solution, although subjects did display the typical reduction in consumption of a freely consumed 1% sucrose solution. These results are not readily understood within the theoretical framework of the CMS model of anhedonia and imply instead that both the neural and psychological correlates of motivation may be less susceptible to modulation by the effects of CMS than the free consumption of sweet solutions.