Measurement of CSF dynorphin A 1-8 immunoreactivity in anorexia nervosa and normal-weight bulimia

Endogenous opioid receptors and the feast or famine of maladaptive feeding

Maladaptive feeding comprises unhealthy eating patterns that jeopardize survival, including over- and underconsumption. These behaviors are often coordinated by endogenous opioid receptors (EORs). Here, we explore the involvement of EORs in obesity and anorexia nervosa (AN), two disorders associated with dysregulated feeding behavior and relevant animal models. While seemingly opposing metabo-psychiatric states, our goal is to highlight common circuit and synaptic mechanisms underlying obesity and AN with a focus on EOR functionality. We examine the neural substrates underlying maladaptive feeding and comorbid conditions including pain, suggesting a role for EOR-driven plasticity in the pathogenesis of both obesity and AN.

Backstage of Eating Disorder-About the Biological Mechanisms behind the Symptoms of Anorexia Nervosa

Anorexia nervosa (AN) represents a disorder with the highest mortality rate among all psychiatric diseases, yet our understanding of its pathophysiological components continues to be fragmentary. This article reviews the current concepts regarding AN pathomechanisms that focus on the main biological aspects involving central and peripheral neurohormonal pathways, endocrine function, as well as the microbiome-gut-brain axis. It emerged from the unique complexity of constantly accumulating new discoveries, which hamper the ability to look at the disease in a more comprehensive way. The emphasis is placed on the mechanisms underlying the main symptoms and potential new directions that require further investigation in clinical settings.

Decreased cerebral opioid receptors availability related to hormonal and psychometric profile in restrictive-type anorexia nervosa

PURPOSE

The opioid system role in anorexia nervosa (AN) pathophysiology is still unclear since conflicting results were reported on peripheral and cerebrospinal fluid opioids levels. The study main aim was to evaluate cerebral AN opiate receptor availability by using [¹¹C] diprenorphine, a ligand with non-selective binding.

METHODS

In vivo [¹¹C]diprenorphine cerebral non-displaceable binding potential (BP_ND) evaluated by PET imaging was compared between three groups : 17 undernourished restrictive-type AN patients (LeanAN), 15 AN patients having regained normal weight (RecAN) and 15 controls. A lower BP_ND may account for an increased opioid tone and vice versa. Serum hormones and endogenous opioids levels, eating-related and unspecific psychological traits were also evaluated.

RESULTS

Compared to controls, LeanAN and RecAN patients had decreased [¹¹C]diprenorphine BP_ND in middle frontal gyrus, temporo-parietal cortices, anterior cingulate cortex and in left accumbens nucleus. Hypothalamo-pituitary (H-P), left amygdala and insula BP_ND was found decreased only in LeanAN and that of putamen only in RecAN. LeanAN presented higher dynorphin A and enkephalin serum levels than in controls or RecAN. Inverse correlations were found in total group between : 24 h mean serum cortisol levels and anterior cingulate gyrus or insula BP_ND; eating concern score and left amygdala BP_ND. Positive correlation were found between leptin and hypothamus BP_ND; LH and pituitary BP_ND.

CONCLUSIONS

Low opiate receptor availability may be interpreted as an increased opioid tone in areas associated with both reward/aversive system in both AN groups. The relationship between the opioid receptors activity and hypercorticism or specific psychometric scores in some of these regions suggests adaptive mechanisms facing anxiety but also may play a role in the disease perpetuation.

Central and peripheral peptides regulating eating behaviour and energy homeostasis in anorexia nervosa and bulimia nervosa: a literature review

A large body of literature suggests the occurrence of a dysregulation in both central and peripheral modulators of appetite in patients with anorexia nervosa (AN) and bulimia nervosa (BN), but at the moment, the state or trait-dependent nature of those changes is far from being clear. It has been proposed, although not definitively proved, that peptide alterations, even when secondary to malnutrition and/or to aberrant eating behaviours, might contribute to the genesis and the maintenance of some symptomatic aspects of AN and BN, thus affecting the course and the prognosis of these disorders. This review focuses on the most significant literature studies that explored the physiology of those central and peripheral peptides, which have prominent effects on eating behaviour, body weight and energy homeostasis in patients with AN and BN. The relevance of peptide dysfunctions for the pathophysiology of eating disorders is critically discussed.

Dysfunctions of leptin, ghrelin, BDNF and endocannabinoids in eating disorders: beyond the homeostatic control of food intake

A large body of literature documents the occurrence of alterations in the physiology of both central and peripheral modulators of appetite in acute patients with anorexia nervosa (AN) and bulimia nervosa (BN). Until more recently the role of most of the appetite modulators in the control of eating behavior was conceptualized solely in terms of their influence on homeostatic control of energy balance. However, it is becoming more and more evident that appetite modulators also affect the non-homeostatic cognitive, emotional and rewarding component of food intake as well as non food-related reward, and, recently, AN and BN have been pathophysiologically linked to dysfunctions of reward mechanisms. Therefore, the possibility exists that observed changes in appetite modulators in acute AN and BN may represent not only homeostatic adaptations to malnutrition, but also contribute to the development and/or the maintenance of aberrant non-homeostatic behaviors, such as self-starvation and binge eating. In the present review, the evidences supporting a role of leptin, ghrelin, brain-derived neurotrophic factor and endocannabinoids in the homeostatic and non-homeostatic dysregulations of patients with AN and BN will be presented. The reviewed literature is highly suggestive that changes in the physiology of these modulators may play a pivotal role in the pathophysiology of eating disorders by providing a possible link between motivated behaviors, reward processes, cognitive functions and energy balance.

Ghrelin: central and peripheral implications in anorexia nervosa

Increasing clinical and therapeutic interest in the neurobiology of eating disorders reflects their dramatic impact on health. Chronic food restriction resulting in severe weight loss is a major symptom described in restrictive anorexia nervosa (AN) patients, and they also suffer from metabolic disturbances, infertility, osteopenia, and osteoporosis. Restrictive AN, mostly observed in young women, is the third largest cause of chronic illness in teenagers of industrialized countries. From a neurobiological perspective, AN-linked behaviors can be considered an adaptation that permits the endurance of reduced energy supply, involving central and/or peripheral reprograming. The severe weight loss observed in AN patients is accompanied by significant changes in hormones involved in energy balance, feeding behavior, and bone formation, all of which can be replicated in animals models. Increasing evidence suggests that AN could be an addictive behavior disorder, potentially linking defects in the reward mechanism with suppressed food intake, heightened physical activity, and mood disorder. Surprisingly, the plasma levels of ghrelin, an orexigenic hormone that drives food-motivated behavior, are increased. This increase in plasma ghrelin levels seems paradoxical in light of the restrained eating adopted by AN patients, and may rather result from an adaptation to the disease. The aim of this review is to describe the role played by ghrelin in AN focusing on its central vs. peripheral actions. In AN patients and in rodent AN models, chronic food restriction induces profound alterations in the « ghrelin » signaling that leads to the development of inappropriate behaviors like hyperactivity or addiction to food starvation and therefore a greater depletion in energy reserves. The question of a transient insensitivity to ghrelin and/or a potential metabolic reprograming is discussed in regard of new clinical treatments currently investigated.

Non-suicidal self-injurious behavior, endogenous opioids and monoamine neurotransmitters

BACKGROUND

Self-inflicted injury, including cutting or burning, is the most frequent reason for psychiatric visits to medical emergency departments. This behavior, particularly when there is no apparent suicidal intent, is poorly understood from both biological and clinical perspectives.

OBJECTIVE

To examine the role of endogenous opioids and monoamine neurotransmitters in non-suicidal self-injury (NSSI).

METHODS

We compared cerebrospinal fluid (CSF) levels of endogenous opioids, 5 hydroxyindolacetic acid (5-HIAA) and homovanillic acid (HVA) in individuals with a history of repetitive non-suicidal self-injury with a diagnostically-matched group of individuals who had never engaged in non-suicidal self-injury. History of suicidal behavior, demographic background and psychopathology was assessed. All patients were diagnosed with a Cluster B personality disorder (i.e. borderline, antisocial, narcissistic or histrionic) (N=29) and had a history of at least one suicide attempt. Fourteen participants had a history of repeated non-suicidal self-injurious behavior (NSSI) in adulthood and 15 did not (no NSSI).

RESULTS

The NSSI group had significantly lower levels of CSF beta-endorphin and met-enkephalin when compared with the non-NSSI group. CSF dynorphin, HVA and 5-HIAA levels did not differ. Severity of depression, hopelessness and overall psychopathology was greater in the NSSI group.

CONCLUSION

beta-endorphin and met-enkephalin, opioids acting upon receptors involved in mediating stress-induced and physical pain analgesia respectively, are implicated in NSSI. Serotonergic and dopaminergic dysfunctions do not appear to be related to NSSI. Based on our findings, we propose a model of non-suicidal self-injury. Our results suggest that drugs acting on the opioid system warrant exploration as pharmacological treatments for NSSI.

New frontiers in endocrinology of eating disorders

Alterations of both central and peripheral feeding regulatory substances occur in the acute phases of anorexia nervosa (AN) and bulimia nervosa (BN) and, generally, reverse after recovery. Some of these alterations are believed not only to sustain the altered eating behavior but also to contribute to certain psychopathological aspects and/or etiopathogenetic processes of eating disorders (EDs). It has been suggested that EDs are clinical conditions linked to reward-related mechanisms leading to a kind of addiction to self-starvation and/or overeating. Most of the feeding regulatory substances, which are dysregulated in EDs, are also implicated in the modulation of reward, emotional, and cognitive functions, thus representing possible links between altered nutritional regulation, motivated behaviors and reward processes. In this chapter, the ED literature dealing with ghrelin, brain-derived neurotrophic factor, opioid peptides, and endocannabinoids, which have prominent effects on eating behavior, body weight, reward, emotional, and cognitive functions, is reviewed in view of the above suggested links. Moreover, the potential therapeutics of new medications developed on the basis of neuroendocrine aberrations found in EDs is also presented.

New targets in the treatment of anorexia nervosa

The pathophysiology of anorexia nervosa (AN) is complex and involves alterations of serotonin, dopamine and histamine neurotransmitters. In addition, receptor activity is disturbed, presumably in response to the neurotransmitter changes. These alterations are reviewed in relation to symptomatology and outcome of AN. Neuropeptide and peripheral orexigenic and satiety peptide research is in its infancy but holds much promise to shed light on the pathophysiological mechanisms involved in this illness. Current drug therapies have not demonstrated the efficacy desired in the treatment of AN. Current therapies are reviewed and new drug targets are explored. Compounds that interact with serotonin, histamine and dopamine receptors may offer unique treatment opportunities. In the future, the manipulation of peptides may add to the therapeutic potential of pharmacotherapy.

Neuropeptides in eating disorders

The past decade has witnessed a dramatic acceleration in research on the role of the neuropeptides in the regulation of eating behavior and body weight homeostasis. This expanding research focus has been driven in part by increasing public health concerns related to obesity and the eating disorders anorexia nervosa (AN) and bulimia nervosa (BN). Preclinical advances have been facilitated by the development of new molecular and behavioral research methodologies. With a focus on clinical investigations in AN and BN, this article reviews research on selected hypothalamic and gut-related peptide systems with prominent effects on eating behavior. Studies of the orexigenic peptides neuropeptide Y and the opioid peptides have shown state-related abnormalities in patients with eating disorders. With respect to gut-related peptides, there appears to be substantial evidence for blunting in the meal-related release of the satiety promoting peptide cholecystokinin in BN. Fasting plasma levels of the orexigenic peptide ghrelin have been found to be elevated in patients with AN. As discussed in this review, additional studies will be needed to assess the role of nutritional and body weight changes in neuropeptide alterations observed in symptomatic eating disorder patients, and to identify stable trait-related abnormalities in neuropeptide regulation that persist in individuals who have recovered from an eating disorder.

Elevated pain threshold in anorexia nervosa subjects

BACKGROUND

Conflicting data have been published regarding pain threshold in subjects with anorexia nervosa (AN), with some studies indicating elevated pain threshold and others indicating normal thresholds. Previous research has indicated the presence of elevated pain threshold in eating disorder subjects with binge-eating behavior.

METHODS

In this study pressure pain detection thresholds (PDT) (assessed by a pressure analgesiometer) in binge-eating/purging and restricting subtypes of AN subjects were compared to control subjects.

RESULTS

PDT was elevated in AN compared to control subjects at baseline. There was no difference in PDT between the subgroups of AN subjects.

CONCLUSIONS

The etiology of elevated PDT in AN subjects is most likely different from the etiology of elevated PDT in bulimia nervosa subjects.

The role of the central nervous system in the psychoneuroendocrine disturbances of anorexia and bulimia nervosa

It has been well-recognized that starvation in anorexia and bulimia nervosa causes endocrine disturbances. Such disturbances may help understand why many people with eating disorders cannot easily reverse their illness since people with eating disorders often enter a downward spiraling circle with malnutrition sustaining and perpetuating the desire for more weight loss and dieting. Symptoms, such as obsessions and dysphoric mood, and altered appetitive behavior, may be exaggerated by neuropeptide alterations and thus contribute to this downward spiral. While neuropeptide disturbances do not appear to be a permanent feature or cause or anorexia nervosa, these disturbances are strongly entrenched, and are not easily corrected by improved nutrition or short-term weight normalization. This suggests that therapy should be sustained for months after nutritional normalization.

Neuropeptide abnormalities in anorexia nervosa

Starvation-induced alterations of neuropeptide activity probably contribute to neuroendocrine dysfunctions in anorexia nervosa. For example, CRH alterations contribute to hypercortisolemia and NPY alterations may contribute to amenorrhea. Alterations of these peptides as well as opioids, vasopressin, and oxytocin activity could contribute to other characteristic psychophysiological disturbances, such as reduced feeding, in acutely ill anorexics. Such neuropeptide disturbances could contribute to the vicious cycle that has been hypothesized to occur in anorexia nervosa. That is, the consequences of malnutrition perpetuate pathological behavior.

T-lymphocyte concentrations of cholecystokinin-8 and beta-endorphin in eating disorders: II. Bulimia nervosa

Concentrations of cholecystokinin-8 (CCK-8) and beta-endorphin (beta-EP) in T-lymphocytes of 26 women with bulimia nervosa (BN) and in 26 age- and sex-matched healthy comparison subjects were measured. Ten patients were then treated with 300 mg/day of fluvoxamine, p.o., and five patients were treated with 300 mg/day of amineptine, p.o., for 4 months. Concentrations of the two peptides were measured again after 1, 2, and 4 months of therapy. Basal CCK-8 values were significantly lower in patients than in healthy subjects. During fluvoxamine therapy, CCK-8 values increased, reaching normal levels by month 4 of treatment. No such increase occurred during amineptine therapy. Baseline beta-EP values were normal in the bulimic patients but had declined by month 4 of fluvoxamine therapy.

T-lymphocyte cholecystokinin-8 and beta-endorphin concentrations in eating disorders: I. Anorexia nervosa

Baseline concentrations of cholecystokinin-8 (CCK-8) and beta-endorphin (beta-EP) were measured in T-lymphocytes from 33 restricting patients with anorexia nervosa (AN-R), 23 binging/purging patients with anorexia nervosa (AN-BP), and 24 healthy volunteers. CCK-8 basal values were significantly lower and beta-EP values significantly higher in AN-R and AN-BP patients than in normal volunteers. Levels of the peptides were measured three more times during a 4-month combined cognitive-behavioral/psychopharmacological treatment (nortriptyline or fluoxetine in AN-R, fluoxetine or amineptine in AN-BP). CCK-8 values fluctuated (nonsignificantly) during each treatment, while beta-EP values decreased (to a significant degree only in fluoxetine-treated AN-R patients).

Pain perception in psychiatric disorders: a review of the literature

Aberrations of pain experience occur frequently in psychiatric disorders and hence pathological alterations in the basic mechanisms underlying pain experience can be expected. Nevertheless, pain perception, as one of the most important basic mechanisms of pain experience, has rarely been assessed experimentally in psychiatric disorders. The authors review the relevant experimental studies on pain perception in patients with anxiety disorders, schizophrenia, depression, eating disorders and personality disorders and suggest lines for future research. Finally, they point out that the experimental study of pain perception is useful not only in understanding aberrant pain experiences in psychiatric disorders but also in elucidating pathophysiological mechanisms because pain perception is controlled by neurochemical and neurohormonal functions known to be affected by psychiatric disease processes.

The effects of continuous morphine infusion on diet selection and body weight

The administration of morphine causes a short-term increase in food intake, and repeated administration of morphine has been shown to cause progressively larger increases in intake and/or the relative intake of dietary fat. In this experiment, we measured the effects of continuous morphine infusions on diet choice and total intake. Male rats were given ad lib access to two diets: a high-carbohydrate diet (80% carbohydrate, 20% protein) and a high-fat diet (80% fat, 20% protein). Diet intakes were measured daily for 21 days. Via the implantation of osmotic minipumps, one group received continuous infusions of morphine sulfate (approx. 2.8 mg/kg/h) for days 1-7 and of saline for days 8-14. A second group was infused with saline for days 1-7 and with morphine for days 8-14. A third group received sham surgery but no minipumps. Total caloric intake was significantly decreased on the final 6 days of morphine infusions. The percentage of total caloric intake consumed from the high-fat diet was significantly increased for the first 2-3 days of morphine treatment; this effect was due to an initial reduction in carbohydrate intake and an increase in fat intake. Over the course of the infusion period, fat intake gradually decreased and carbohydrate intake increased. The effects of morphine when infused on days 1-7 were similar to those observed when the drug was infused during days 8-14.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-endorphin and dynorphin abnormalities in rats subjected to exercise and restricted feeding: relationship to anorexia nervosa?

Exercise and the endogenous opioids have been linked to anorexia nervosa. This investigation determined the effects of the weight-loss syndrome induced by voluntary exercise (22.5 h/day) in food-restricted rats (1.5 h/day food access) on the endogenous opioids. The animals were tested under resting-fed and 2-deoxy-D-glucose (2DG) stimulated conditions. Weight-matched, freely fed exercised and ad libitum fed unexercised groups served as controls. Specific opioid abnormalities were found in the syndrome. These included a basal elevation in plasma beta-endorphin, which was abnormally suppressed by 2DG, and 2DG-induced elevations in arcuate hypothalamic beta-endorphin content and supraoptic hypothalamic dynorphin-A content. None of these changes occurred in controls. Finally, it was found that short-term moderate exercise itself chronically reduced adenohypophysial beta-endorphin content and elevated supraoptic dynorphin-A content. The relationship of the syndrome's hyperendorphinism to the hypothalamo-pituitary-adrenal axis and the auto-addiction hypothesis of anorexia nervosa was considered, as was the significance of the supraoptic dynorphin-A abnormality to the hypothalamo-neurohypophysial system. The differential sensitivity of the supraoptic dynorphin-A system compared to the arcuate hypothalamic beta-endorphin system to moderate exercise was also discussed.

Fluoxetine induces vasopressin and oxytocin abnormalities in food-restricted rats given voluntary exercise: relationship to anorexia nervosa

Anorexia nervosa is associated with vasopressin, oxytocin and serotonin abnormalities. Because of the relationship between exercise and anorexia nervosa, we explored the weight-loss syndrome produced by wheel running in food-deprived rats. Its effects on regional vasopressin and oxytocin concentrations were determined under basal conditions and following systemic fluoxetine. Weight-matched, exercised and unexercised rats served as controls. Fluoxetine caused abnormalities in suprachiasmatic vasopressin and dynorphin A content and in thymus oxytocin content that did not occur in weight-matched or exercised controls. No syndrome-specific anomalies occurred in the hypothalamo-neurohypophysial system or dorsal vagal complex (DVC). However, weight reduction and fluoxetine increased circulating vasopressin; moderate exercise caused fluoxetine-induced elevations in posterior pituitary vasopressin and oxytocin; and, unlike the other groups, fluoxetine increased DVC oxytocin in freely fed unexercised rats. It was concluded that syndrome-specific vasopressin and oxytocin abnormalities occur that are not secondary to weight loss or moderate exercise; that weight loss or fluoxetine increases circulating vasopressin; that moderate exercise alters neurohypophysial vasopressin and oxytocin content; and that weight loss or exercise inhibits a fluoxetine-stimulated increase in DVC oxytocin. Finally, it was argued that the fluoxetine abnormalities indicate possible serotonin dysfunction in the syndrome.