Common biological pathways in eating disorders and obesity

Food restriction and hyperactivity induce changes in corticolimbic brain dopamine and serotonin levels in female rats

Compelling data support altered dopamine (DA) and serotonin (5-HT) signaling in anorexia nervosa (AN). However, their exact role in the etiopathogenesis of AN has yet to be elucidated. Here, we evaluated the corticolimbic brain levels of DA and 5-HT in the induction and recovery phases of the activity-based anorexia (ABA) model of AN. We exposed female rats to the ABA paradigm and measured the levels of DA, 5-HT, the metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA), and the dopaminergic type 2 (D2) receptors density in feeding- and reward-implicated brain regions (i.e., cerebral cortex, Cx; prefrontal cortex, PFC; caudate putamen, CPu; nucleus accumbens, NAcc; amygdala, Amy; hypothalamus, Hyp; hippocampus, Hipp). DA levels were significantly increased in the Cx, PFC and NAcc, while 5-HT was significantly enhanced in the NAcc and Hipp of ABA rats. Following recovery, DA was still elevated in the NAcc, while 5-HT was increased in the Hyp of recovered ABA rats. DA and 5-HT turnover were impaired at both ABA induction and recovery. D2 receptors density was increased in the NAcc shell. These results provide further proof of the impairment of the dopaminergic and serotoninergic systems in the brain of ABA rats and support the knowledge of the involvement of these two important neurotransmitter systems in the development and progression of AN. Thus, providing new insights on the corticolimbic regions involved in the monoamine dysregulations in the ABA model of AN.

Stomaching rejection: Self-compassion and self-esteem moderate the impact of daily social rejection on restrictive eating behaviours among college women

OBJECTIVE

The present study examined whether having high self-esteem or a self-compassionate perspective help mitigate the impact of daily social rejection on negative affect and restrictive eating behaviours.

DESIGN

Following a baseline survey assessing self-esteem and self-compassion, 121 college women completed online daily diaries for one week.

MAIN OUTCOME MEASURES

Negative affect and restrictive eating behaviours.

RESULTS

On days when women reported more rejection, they also reported higher restrictive eating behaviours and greater negative affect. Effects were moderated by self-esteem and self-compassion, such that the lower participants were in self-esteem or self-compassion, the stronger the positive relation between rejection and negative affect and restrictive eating. However, only the common humanity/isolation dimension of self-compassion significantly moderated daily effects of rejection when controlling for self-esteem. Mediated moderation results reveal different mechanisms by which self-esteem and self-compassion buffer against rejections' effects on affect and restrictive eating.

CONCLUSION

Self-compassion and self-esteem influence the complex impact that social rejection has on affect and restrictive eating. More than other dimensions of self-compassion or self-esteem, remembering one's common humanity can result in a healthier response to social rejection.

Eating Disorders

More than 2 million female Americans have a clinically relevant eating disorder. Although the prevalence and seriousness of this problem has gained increasing attention in recent years, relatively little is known about eating disorder prevention. This article addresses a number of issues related to prevention efforts applied to eating disorders. An overview of putative risk factors that have been identified is presented. In particular, the article emphasizes the importance of understanding the psychological and physical developmental processes during adolescence and the sociocultural context in which eating disorders develop. A summary of empirical investigations of the efficacy of eating disorder prevention programs follows, including an illustration of one of the more promising strategies that has been reported to date. The role of counseling psychologists in further refining eating disorder prevention efforts is discussed.

Under- to over-eating: how do serotonin receptors contribute?

In numerous pathological states, the brain can restrict food intake to a lethal level despite mounting requirements for energy as seen in adolescents with anorexia nervosa. How the brain reduces food intake to the point of death while eating is a cornerstone of survival that remains just as ‘cryptic’ as the association between anorexia and overeating. This review provides a recent snapshot of the neural underpinnings of the rewarding effects of anorexia that may compete with the adaptive decision-making process to eat, and with survival instinct. Among a plethora of factors, impaired activity of the serotonin receptors in the reward system underlies the ability of animals to self-impose food restriction, and the transition from under- to over-eating. However, the triumvirate association between serotonin, overeating and addiction appears unlikely. Considering the implication of the serotonin receptors in the hypothalamus, anorexia and bulimia nervosa could result from an impairment of a ‘synchronic activity’ between the autonomic and voluntary nervous systems.

Can body mass index help predict outcome in patients with bipolar disorder?

OBJECTIVE

Several studies have reported higher prevalence of obesity in patients suffering from bipolar disorder (BD). To study the relation of elevated body mass index (BMI) in patients with BD more closely, we investigated differences in sociodemographic, clinical, and medical characteristics with respect to BMI, with the hypothesis that BMI is related to prognosis and outcome.

METHODS

We measured the BMI of 276 subjects of a tertiary care sample from the Maritime Bipolar Registry. Subjects were 16 to 83 years old, with psychiatric diagnoses of bipolar I disorder (n = 186), bipolar II disorder (n = 85), and BD not otherwise specified (n = 5). The registry included basic demographic data and details of the clinical presentation. We first examined the variables showing a significant association with BMI; subsequently, we modeled the relationship between BMI and psychiatric outcome using structural equation analysis.

RESULTS

The prevalence of obesity in our sample was 39.1%. We found higher BMI in subjects with a chronic course (p < 0.001) and longer duration of illness (p = 0.02), lower scores on the Global Assessment of Functioning Scale (p = 0.02), and on disability (p = 0.002). Overweight patients had more frequent comorbid subthreshold social (p = 0.02) and generalized anxiety disorders (p = 0.05), diabetes mellitus type II (p < 0.001), and hypertension (p = 0.001). Subjects who achieved complete remission of symptoms on lithium showed significantly lower BMI (p = 0.01).

CONCLUSIONS

Our findings suggest that BMI is associated with the prognosis and outcome of BD. Whether this association is causal remains to be determined.

Genetic disruption of both tryptophan hydroxylase genes dramatically reduces serotonin and affects behavior in models sensitive to antidepressants

The neurotransmitter serotonin (5-HT) plays an important role in both the peripheral and central nervous systems. The biosynthesis of serotonin is regulated by two rate-limiting enzymes, tryptophan hydroxylase-1 and -2 (TPH1 and TPH2). We used a gene-targeting approach to generate mice with selective and complete elimination of the two known TPH isoforms. This resulted in dramatically reduced central 5-HT levels in Tph2 knockout (TPH2KO) and Tph1/Tph2 double knockout (DKO) mice; and substantially reduced peripheral 5-HT levels in DKO, but not TPH2KO mice. Therefore, differential expression of the two isoforms of TPH was reflected in corresponding depletion of 5-HT content in the brain and periphery. Surprisingly, despite the prominent and evolutionarily ancient role that 5-HT plays in both vertebrate and invertebrate physiology, none of these mutations resulted in an overt phenotype. TPH2KO and DKO mice were viable and normal in appearance. Behavioral alterations in assays with predictive validity for antidepressants were among the very few phenotypes uncovered. These behavioral changes were subtle in the TPH2KO mice; they were enhanced in the DKO mice. Herein, we confirm findings from prior descriptions of TPH1 knockout mice and present the first reported phenotypic evaluations of Tph2 and Tph1/Tph2 knockout mice. The behavioral effects observed in the TPH2 KO and DKO mice strongly confirm the role of 5-HT and its synthetic enzymes in the etiology and treatment of affective disorders.

Dopamine and monogamy

Social attachments play a central role in human society. In fact, such attachments are so important that deficits in the ability to form meaningful social bonds are associated with a variety of psychological disorders. Although mother-infant bonding has been studied for many years, we only recently have begun to examine the processes that underlie social bonds between adults. Over the past decade, central dopamine has become a focus of such research, especially its role in pair bonding between mates in species that display monogamous life strategies. Neuroanatomical and pharmacological studies in rodents have firmly established central dopamine systems, especially the mesocorticolimbic dopamine circuitry, in the formation, expression, and maintenance of monogamous pair bonds. As this research has progressed, it has become apparent that there is considerable overlap between the processes that underlie pair bonding and those that mediate responses to abused substances. This suggests that social bonding and substance abuse each may affect the other. Herein we review the current state of knowledge of central dopamine involvement in pair bond formation, expression, and maintenance. We first describe the neuroanatomical substrate within which dopamine exerts its effects on social bonding. We then describe dopamine receptor subtype-specific influences on pair bonding and how dopamine receptor activation may interact with activation of other neurochemical systems. Finally, we describe possible interactions between social bonding and substance abuse.

The role of dopamine in motivation for food in humans: implications for obesity

Obesity is a major public health problem. The increasing number of obese individuals in the US adds urgency to the efforts to understand the mechanisms underlying pathological overeating. Imaging studies using positron emission tomography implicate the involvement of brain dopamine (DA) in normal and pathological food intake in humans. In normal body weight, fasting subjects, food presentation that could not be consumed was associated with increases in striatal extracellular DA, which provides evidence of an involvement of DA in non-hedonic motivational properties of food intake. In pathologically obese subjects, the authors showed reductions in striatal D2 receptor availability that were inversely associated with the weight of the subject. The involvement of the DA system in reward and reinforcement has led to the hypothesis that low brain DA activity in obese subjects predisposes them to excessive use of food. A better understanding of the role of the DA system in the motivation for food intake will help the development of better therapeutic interventions.

Binge size increases with body mass index in women with binge-eating disorder

OBJECTIVE

To determine whether meal size is related to body mass index (BMI) in obese subjects with binge-eating disorder (BED).

RESEARCH METHODS AND PROCEDURES

Five groups of subjects each consumed two laboratory-test meals on nonconsecutive days. Forty-two women, categorized by BMI and BED diagnosis, were instructed to "binge" during one meal and to eat "normally" during another. Eighteen women had BMI values >38 kg/m(2) (more-obese) and 17 had BMI values between 28 to 32 kg/m(2) (less-obese). Twelve of the more-obese and nine of the less-obese individuals met Diagnostic and Statistical Manual (DSM)-IV criteria for BED. Seven normal-weight women also participated as controls.

RESULTS

Subjects with BED ate significantly more in both meals than subjects without BED. Binge meals were significantly larger than normal meals only among subjects with BED. The more-obese subjects with BED ate significantly more than the less-obese subjects with BED, but only when they were asked to binge. Intake of the binge meal was significantly, positively correlated with BMI among subjects with BED. Subjects with BED reported significantly higher satiety ratings after the binge than after the normal meal, but subjects without BED reported similar ratings after both meals. Regardless of instructions and diagnosis, obese subjects consumed a significantly higher percentage of energy from fat (38.5%) than did normal-weight subjects (30.8%).

DISCUSSION

During binge meals, the energy intake of subjects with BED is greater than that of individuals of similar body weight without BED and is positively correlated with BMI.

Integrating the prevention of eating disorders and obesity: feasible or futile?

The rate of obesity in adults and youth has doubled in the past 20 years; during this same period there has been an increase in the prevalence of "dysfunctional eating behaviors," including eating disorders and unhealthy weight loss practices. Despite the fact that obesity, eating disorders, and unhealthy weight loss practices are cultivated in the same cultural context-an increasingly "toxic" environment regarding food and weight-these problems are regarded as distinct, with different origins, courses, and approaches to prevention and treatment. In this article, we present conceptual and practical reasons for adopting an integrated approach to the prevention of the spectrum of problems related to eating and weight (i.e., eating disorders, obesity, and unhealthy weight loss practices), suggest personal, socioenvironmental, and behavioral factors to be included in an integrated approach to prevention, and provide some ideas for developing an integrated program using a media literacy/advocacy approach. We conclude with a discussion of challenges to the development of interventions aimed at the broad spectrum of weight-related problems and suggestions for addressing these challenges.

Effects of restraint stress and serotonin on macronutrient selection: a rat model of stress-induced anorexia

The present study investigated the effects of brief (20 min), acute (2 hr) and chronic restraint stress (2 hr/day for five days) at the time of dark onset on macronutrient selection in female Wistar rats. The role of 5-HT1A receptors in nutrient intake was also examined in a dose-response study (100-700 microg/kg body weight) of 8-hydroxy-2-(di-n-propylamino) tetralin (DPAT) in an acute restraint model. A total of 200 rats aged 6-12 months were tested. In all cases, the restraint stress took the form of confinement within tight-fitting cylinder tubes. In the brief and acute paradigms, the intake of pure carbohydrate (CHO), protein (PRO), and fat was measured for 40 min after a single exposure to stress; in the chronic model, nutrient intake was assessed for 40 min only after the final restraint stress session on day 5. In the DPAT paradigm, intraperitoneal injections of the 5-HT1A agonist were given prior to acute restraint and a 40 min session of nutrient self-selection. Statistical analysis using the t-test for independent samples revealed that neither PRO nor total intake was significantly altered by restraint in the brief, acute or chronic restraint experiments, whereas CHO consumption was suppressed by acute (p=0.02) and chronic restraint (p=0.021), and fat intake was suppressed by brief (p=0.010), acute (p=0.002) and chronic restraint (p=0.001). In the DPAT paradigm, acute restraint stress suppressed CHO (p=0.0001), fat (p=0.000001) and total intake (p=0.003). These effects were not reversed by DPAT, and the administration of 300 pg/kg actually further reduced fat intake. In conclusion, fat intake is more sensitive to the suppressive effects of restraint stress than CHO intake, whereas protein intake is unaffected. Furthermore, 5-HT1A receptors do not seem to play a role in the effects of acute restraint on CHO and fat intake.

Mouse models of serotonin receptor function: toward a genetic dissection of serotonin systems

Central serotonin (5-hydroxytryptamine, 5-HT) systems regulate a wide variety of complex behaviors, and are targeted by drugs used in the treatment of diverse neuropsychiatric disorders. The actions of 5-HT are mediated by a large and heterogeneous family of 5-HT receptor subtypes. Studies of the functional significance of individual subtypes have been complicated by the limited availability of selective receptor agonist and antagonist drugs. Molecular genetic techniques offer complementary approaches for studying the behavioral roles of individual 5-HT receptor subtypes through the generation of gene-targeted and transgenic lines of mice with altered expression of 5-HT receptor genes. This review will examine insights into the serotonergic regulation of behavior that have been produced by the study of these lines, as well as discuss important caveats to the interpretation of these studies.

The eating disorders as addiction: a psychobiological perspective

A number of theories have been proposed to explain the substantial comorbidity between the eating disorders and the substance-related disorders. Among them is the claim that self-starvation--exacerbated by excessive exercising--is itself an addiction to the body's endogenous opioids. While efforts have also been made to identify an "addictive personality," attempts to establish whether eating-disordered patients share these characteristics have met with mixed success. The present study was designed to determine the degree to which anorexic and bulimic patients display addictive personality characteristics, and whether these traits are useful in predicting the severity of the patient's weight preoccupation and their degree of excessive exercising. Results confirmed that both anorexic and bulimic patients had high scores on the Addiction Scale of the Eysenck Personality Questionnaire, and that addictiveness and obsessive-compulsiveness were related simultaneously to weight preoccupation and excessive exercising in both patient groups. Findings are discussed within the framework of the auto-addiction opioid theory, and they highlight the similarities and differences in the personality structure of the eating-disorder subtypes.

D4 dopamine receptor gene exon III polymorphism and obesity risk

Many genes have been identified that may play a role in increasing individual susceptibility to obesity. Reduced dopamine function appears to play a role in dysfunctional eating patterns and may predispose some individuals to obesity. The long version of the D4 dopamine receptor gene (D4DR) has been shown to alter receptor function and reduce intracellular response to dopamine. It also has been associated with novelty-seeking-related personality traits that are found with greater frequency in obese individuals. We examined the association between the long alleles of the D4DR and obesity in a sample of 115 obese patients participating in a weight management program. No direct relationship was found between the D4DR and body mass or novelty-seeking-related personality traits. We constructed four models of increased obesity risk that included combinations of traditional risk factors (i.e., long-term history of obesity, parental obesity, a body mass index > 40) and elevations on the novelty-seeking-related scales of the Karolinska Scales of Personality. There was a significant increase in the frequency of the D4DR long alleles in individuals defined as high risk using the combination of novelty-seeking-related personality traits, severe obesity (i.e., BMI > 40), and any other traditional risk factor, but not with the traditional risk factors alone. These preliminary data suggest a potential role for the D4DR gene in increasing obesity susceptibility.