Low dopamine and serotonin levels in anorexia nervosa

Pharmacological manipulations in animal models of anorexia and binge eating in relation to humans

Eating disorders, such as anorexia nervosa (AN), bulimia nervosa (BN) and binge eating disorders (BED), are described as abnormal eating habits that usually involve insufficient or excessive food intake. Animal models have been developed that provide insight into certain aspects of eating disorders. Several drugs have been found efficacious in these animal models and some of them have eventually proven useful in the treatment of eating disorders. This review will cover the role of monoaminergic neurotransmitters in eating disorders and their pharmacological manipulations in animal models and humans. Dopamine, 5-HT (serotonin) and noradrenaline in hypothalamic and striatal regions regulate food intake by affecting hunger and satiety and by affecting rewarding and motivational aspects of feeding. Reduced neurotransmission by dopamine, 5-HT and noradrenaline and compensatory changes, at least in dopamine D2 and 5-HT(2C/2A) receptors, have been related to the pathophysiology of AN in humans and animal models. Also, in disorders and animal models of BN and BED, monoaminergic neurotransmission is down-regulated but receptor level changes are different from those seen in AN. A hypofunctional dopamine system or overactive α2-adrenoceptors may contribute to an attenuated response to (palatable) food and result in hedonic binge eating. Evidence for the efficacy of monoaminergic treatments for AN is limited, while more support exists for the treatment of BN or BED with monoaminergic drugs.

Impaired visual discrimination learning in anorexia nervosa

The primate dopamine system is involved in appetitively motivated behaviours, including certain forms of learning, for example, visual discrimination learning. Furthermore, food restriction in animals and anorexia in humans is associated with impaired dopamine signaling. Based on this, we hypothesized that patients with anorexia nervosa (AN) would show a deficit in visual discrimination learning. In a dynamic categorization task involving the learning of a series of two-alternative forced-choice visual discriminations, conceptually identical to one shown to activate dopamine neurons in primates, and sensitive to dopaminergic manipulations in humans, patients with AN showed a deficit in learning that was most pronounced in the early stages of acquisition. In contrast, AN showed spared performance on a pattern recognition memory test sensitive to medial temporal lobe lesions, but insensitive to dopaminergic manipulations. We conclude that impaired appetitive function in patients with AN extends to include deficits in visual discrimination learning, and that this deficit represents indirect evidence for altered dopaminergic neurotransmission in AN.

Etiologia dos transtornos alimentares: aspectos biológicos, psicológicos e sócio-culturais

Os transtornos alimentares possuem uma etiologia multifatorial, composta de predisposições genéticas, socioculturais e vulnerabilidades biológicas e psicológicas. Entre os fatores predisponentes, destacam-se a história de transtorno alimentar e (ou) transtorno do humor na família, os padrões de interação presentes no ambiente familiar, o contexto sociocultural, caracterizado pela extrema valorização do corpo magro, disfunções no metabolismo das monoaminas centrais e traços de personalidade. A dieta é o comportamento precursor que geralmente antecede a instalação de um transtorno alimentar. Contudo, a presença isolada da dieta não é suficiente para desencadear o transtorno alimentar, tornando-se necessária uma interação entre os fatores de risco e outros eventos precipitantes. Por último, o curso transitório ou crônico de um transtorno alimentar está relacionado à persistência de distorções cognitivas, à ocorrência de eventos vitais significativos e a alterações secundárias ao estado de desnutrição.

A review of endocrine changes in anorexia nervosa

Anorexia nervosa is a syndrome of unknown etiology. It is associated with multiple endocrine abnormalities. Hypothalamic monoamines (especially serotonin), neuropeptides (especially neuropeptide Y and cholecystokinin) and leptin are involved in the regulation of human appetite, and in several ways they are changed in anorexia nervosa. However, it remains to be clarified whether the altered appetite regulation is secondary or etiologic. Increased secretion of corticotropin-releasing hormone and proopiomelanocortin seems to be secondary to starvation, however, there is evidence that it may maintain and intensify anorexia, excessive physical activity and amenorrhea. Hypothalamic amenorrhea, which is a diagnostic criterion in anorexia nervosa, is not solely related to the low body weight and exercise. Growth hormone resistance with low production of insulin-like growth factor I and high growth hormone secretion reflect the nutritional deprivation. The nutritional therapy of patients with anorexia nervosa might be improved by administering an anabolic agent such as growth hormone or insulin-like growth factor I. So far none of the endocrine abnormalities have proved to be primary, however, there is increasing evidence that some of these might participate in a vicious circle.

Whole blood serotonin content, tryptophan concentrations, and impulsivity in anorexia nervosa

BACKGROUND

We hypothesized that anorectics with or without bulimic features would differ on impulsivity and indices of central serotoninergic function (high impulsivity being correlated with reduced serotoninergic function).

METHODS

For all patients impulsivity rating scales and questionnaires detailing severity of eating disorder were assessed, and whole blood serotonin concentration (5-HT), free and total tryptophan (TT) concentrations, and large neutral amino acids (LNAA) were assayed.

RESULTS

Nineteen patients with anorexia nervosa were included, 10 presented associated bulimic features and nine did not. Twelve healthy matched controls were also included. Our hypothesis was not verified. However, tryptophan concentration and the ratio of tryptophan concentration to LNAA allow us to separate controls from anorectics, whereas 5-HT concentration does not. Two significant and positive correlations were found: between impulsivity and anxiety in the total anorectic population, and between anxiety and serotonin in the impulsive group.

CONCLUSIONS

All measured peripheral biologic indices except 5-HT concentration may be of interest in this pathology. Impulsivity and anxiety seem to be two personality components involved in anorexia nervosa. This study lead us to the necessity of redefining impulsivity in anorexia nervosa.

Toward a unified theory of serotonin dysregulation in eating and related disorders

Patients with eating disorders (EDs) exhibit several clinical features and biologic findings indicative of serotonin (5-hydroxytryptamine, 5-HT) dysregulation. These include feeding disturbances, depression and suicide, impulsivity and violence, anxiety and harm avoidance, obsessive-compulsive features, seasonal variation of symptoms, as well as disturbances in neuroendocrine and vascular tissues, as well as other neurochemical systems linked to 5-HT, such as temperature. This review attempts to integrate available results from controlled studies in humans, with particular focus on cerebrospinal fluid (CSF), platelet and plasma studies, as well as pharmacologic challenge strategies using a variety of serotonergic agents. Taken together, these findings support the concept of altered post-synaptic, hypothalamic 5-HT receptor sensitivity in bulimia nervosa (BN), regardless of the presence of anorexia nervosa (AN) or major depression (MD), although these conditions may be associated with other disturbances in 5-HT function, perhaps pre-synaptic ones. The observation that different response measures of 5-HT function in the same subjects may be simultaneously increased, decreased and no different in patients compared to controls is consistent with a 5-HT dysregulation hypothesis. It may be that a variety of psychobiological stressors, such as dieting, binge-eating, purging, drug abuse, photoperiodic changes, as well as psychosocial-interpersonal stressors, perturb and interact with an already vulnerable 5-HT system.

Peripheral opioid secretory pattern in anorexia nervosa

The peripheral secretion of endogenous opioids was studied in 10 women with restrictive anorexia nervosa and 10 age- and sex-matched healthy controls. The circadian rhythm of beta-endorphin (beta-EP) and beta-lipotropin (beta-LPH), and their responses to the administration of corticotropin releasing hormone (CRH, 1 micrograms/kg body weight, i.v.), clonidine (150 microgram, i.v.), domperidone (10 mg, i.v.), and 5-hydroxytryptophan (5-HTP, 200 mg, p.o.) were examined in patients and controls. The results revealed increased nocturnal secretion of beta-EP and diurnal-nocturnal secretion of beta-LPH with loss of circadian rhythmicity of both peptides, normal response to CRH stimulation, blunted response to clonidine and domperidine, and normal beta-EP and blunted beta-LPH response to 5-HTP stimulation. The data suggest a complex alteration of peripheral opioids and of central aminergic mechanisms that regulate proopiomelanocortin-derived peptide secretion and eating behavior.

Eating disorders and depression: is there a serotonin connection?

Central serotonin pathways modulate eating patterns, and may also participate in the regulation of behavioral impulsivity and mood. Recent studies lend support to the hypothesis that impaired postingestive satiety in bulimia nervosa is associated with reduced hypothalamic serotonergic responsiveness. Serotonin dysregulation has been implicated in major depression, and may play a role in the increased prevalence of depressive episodes in patients with eating disorders. This review compares evidence for alterations in central serotonin regulation in patients with anorexia nervosa, bulimia nervosa, and depression. It is proposed that impaired synaptic transmission in functionally distinct serotonin pathways may result in concurrent or sequential periods of binge eating, behavioral impulsivity, and depression in patients with eating disorders.

Tyrosine hydroxylase, tryptophan hydroxylase, biopterin, and neopterin in the brain of anorexia nervosa

The activities of tyrosine hydroxylase and tryptophan hydroxylase and contents of biopterin and neopterin were measured for the first time in various regions of human brain from a patient with anorexia nervosa (AN). In AN as compared with controls, tyrosine hydroxylase activity was markedly reduced in all brain regions analyzed, while tryptophan hydroxylase activity and biopterin content had a tendency to increase. Neopterin content did not change dramatically. The opposite changes of tyrosine hydroxylase and tryptophan hydroxylase suggest an imbalance between the activity of catecholaminergic neurons and that of serotonergic neurons, and may be related to pathogenesis of AN.

Reversible anorexia and rapid weight loss associated with neuroleptic administration in Alzheimer's disease

Weight loss and malnutrition despite adequate dietary intake has been reported to be part of the clinical course in advanced dementia of the Alzheimer type. We present a case of reversible weight loss associated with neuroleptic use in a patient with Alzheimer's disease and discuss a possible pathophysiological basis for the weight loss.