A preliminary report on pain thresholds in bulimia nervosa during a bulimic episode

Perceptual Dysfunction in Eating Disorders

Eating disorders (EDs) are characterized by abnormal responses to food and weight-related stimuli and are associated with significant distress, impairment, and poor outcomes. Because many of the cardinal symptoms of EDs involve disturbances in perception of one's body or abnormal affective or cognitive reactions to food intake and how that affects one's size, there has been longstanding interest in characterizing alterations in sensory perception among differing ED diagnostic groups. Within the current review, we aimed to critically assess the existing research on exteroceptive and interoceptive perception and how sensory perception may influence ED behavior. Overall, existing research is most consistent regarding alterations in taste, visual, tactile, and gastric-specific interoceptive processing in EDs, with emerging work indicating elevated respiratory and cardiovascular sensitivity. However, this work is far from conclusive, with most studies unable to speak to the precise etiology of observed perceptual differences in these domains and disentangle these effects from affective and cognitive processes observed within EDs. Further, existing knowledge regarding perceptual disturbances in EDs is limited by heterogeneity in methodology, lack of multimodal assessment protocols, and inconsistent attention to different ED diagnoses. We propose several new avenues for improving neurobiology-informed research on sensory processing to generate actionable knowledge that can inform the development of innovative interventions for these serious disorders.

Reduced Sensory-Evoked Locus Coeruleus-Norepinephrine Neural Activity in Female Rats With a History of Dietary-Induced Binge Eating

Noradrenergic pathways have been implicated in eating pathologies. These experiments sought to examine how dietary-induced binge eating influences the neuronal activity of the locus coeruleus (LC)-norepinephrine (NE) system. Young adult female Sprague Dawley rats (7-8 weeks old) were exposed to a repeated intermittent (twice weekly) cycle of 30-min access to a highly palatable sweetened fat (i.e., vegetable shortening with 10% sucrose) with or without intermittent (24 h) calorie restriction (Restrict Binge or Binge groups, respectively). Age- and weight-matched female control rats were exposed to standard chow feeding (Naive group) or intermittent chow feeding (Restrict group). The Binge and Restrict Binge groups demonstrated an escalation in sweet-fat food intake after 2.5 weeks. On week 3, in vivo single-unit LC electrophysiological activity was recorded under isoflurane anesthesia. Restrict Binge (20 cells from six rats) and Binge (27 cells from six rats) had significantly reduced (approximate 20% and 26%, respectively) evoked LC discharge rates compared with naive rats (22 cells, seven rats). Spontaneous and tonic discharge rates were not different among the groups. Signal-to-noise ratio was reduced in the groups with intermittent sweetened fat exposure. In order to investigate the neuropeptide alterations as a consequence of dietary binge eating, relative gene expression of neuropeptide Y (NPY), glucagon-like peptide 1 receptor (GLP-1r), prodynorphin, and related genes were measured in LC and hypothalamic arcuate (Arc) regions. Glp-1r, Npy2r, and Pdyn in LC region were reduced with repeated intermittent restriction. Npy1r was reduced by approximately 27% in ARC of Restrict compared with Naive group. Such data indicate that dietary-induced binge eating alters the neural response of LC neurons to sensory stimuli and dampens the neural stress response.

Fasting and acquired capability for suicide: a test of the interpersonal-psychological theory of suicide in an undergraduate sample

Though some preliminary research within the framework of the interpersonal-psychological theory of suicide (IPTS; Joiner, 2005) has postulated that restrictive eating may contribute to increased risk for suicide through its effect on the acquired capability for suicide (ACS; i.e., increased fearlessness about death and heightened physical pain tolerance), existing studies have not conducted direct tests of this relationship. To enhance understanding of this relationship, we compared undergraduates who endorsed one form of restrictive eating, fasting, (n = 99) to controls endorsing no forms of eating pathology over the lifetime (n = 94). We hypothesized that the fasting group would have higher ACS and higher likelihood of suicide attempt history. Contrary to hypotheses, no differences emerged between groups on ACS, and frequency of fasting within the fasting group was not significantly associated with ACS. Consistent with hypotheses, the fasting group was more likely to have suicide attempt history. Though results were not entirely consistent with hypotheses, the current study represents the first attempt at isolating and examining one form of restrictive eating (i.e., fasting) within the context of the IPTS. Results suggest that, in isolation, fasting may not be directly contributing to increases in ACS.

Pain sensitivity is reduced in borderline personality disorder, but not in posttraumatic stress disorder and bulimia nervosa

BACKGROUND

Several studies revealed reduced pain sensitivity in patients suffering from borderline personality disorder (BPD) under baseline and stress conditions. To establish whether these findings are specific for BPD, we compared pain thresholds in patients with BPD, posttraumatic stress disorder (PTSD), bulimia nervosa, and healthy controls.

METHODS

The study included 76 female subjects: 16 patients with BPD, 16 patients with PTSD, 20 patients with bulimia nervosa and 24 healthy controls. Heat and cold pain thresholds were assessed under baseline and stress conditions, using a contact thermode. Mental stress was induced by the Paced Auditory Serial Addition Task.

RESULTS

Under baseline conditions, pain thresholds in patients with BPD were significantly higher compared to healthy controls. Patients with PTSD and bulimia nervosa did not show significant differences in pain thresholds compared to healthy controls. Under stress conditions, the difference between BPD patients and healthy controls became even more prominent, whereas the results in the other patient groups remained insignificant.

CONCLUSIONS

Our results support the hypothesis that reduced pain sensitivity is a prominent feature of BPD, which may differentiate this disorder from other stress-related psychiatric conditions.

Pediatric obesity: parallels with addiction and treatment recommendations

Rates of pediatric obesity have increased dramatically over the past decade. This trend is especially alarming because obesity is associated with significant medical and psychosocial consequences. It may contribute to cardiovascular, metabolic, and hepatic complications, as well as to psychiatric difficulties. The development of obesity appears to be influenced by a complex array of genetic, metabolic, and neural frameworks, along with behavior, eating habits, and physical activity. Numerous parallels exist between obesity and addictive behaviors, including genetic predisposition, personality, environmental risk factors, and common neurobiological pathways in the brain. Typical treatments for pediatric obesity include behavioral interventions targeting diet or exercise. These treatments have yielded mixed results and typically have been examined in specialty clinic populations, limiting their generalizability. There are limited medication options for overweight children and adolescents, and no approved medical intervention in children younger than 16 years old. Bariatric surgery may be an option for some adolescents, but due to the risks of surgery, it is often seen as a last resort. The parallels between addiction and obesity aid in developing novel interventions for pediatric obesity. Motivational enhancement and cognitive-behavioral strategies used in addiction treatment may prove to be beneficial.

A genetic approach for investigating vagal sensory roles in regulation of gastrointestinal function and food intake

Sensory innervation of the gastrointestinal (GI) tract by the vagus nerve plays important roles in regulation of GI function and feeding behavior. This innervation is composed of a large number of sensory pathways, each arising from a different population of sensory receptors. Progress in understanding the functions of these pathways has been impeded by their close association with vagal efferent, sympathetic, and enteric systems, which makes it difficult to selectively label or manipulate them. We suggest that a genetic approach may overcome these barriers. To illustrate the potential value of this strategy, as well as to gain insights into its application, investigations of CNS pathways and peripheral tissues involved in energy balance that benefited from the use of gene manipulations are reviewed. Next, our studies examining the feasibility of using mutations of developmental genes for manipulating individual vagal afferent pathways are reviewed. These experiments characterized mechanoreceptor morphology, density and distribution, and feeding patterns in four viable mutant mouse strains. In each strain a single population of vagal mechanoreceptors innervating the muscle wall of the GI tract was altered, and was associated with selective effects on feeding patterns, thus supporting the feasibility of this strategy. However, two limitations of this approach must be addressed for it to achieve its full potential. First, mutation effects in tissues outside the GI tract can contribute to changes in GI function or feeding. Additionally, knockouts of developmental genes are often lethal, preventing analysis of mature innervation and ingestive behavior. To address these issues, we propose to develop conditional gene knockouts restricted to specific GI tract tissues. Two genes of interest are brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), which are essential for vagal afferent development. Creating conditional knockouts of these genes requires knowledge of their GI tract expression during development, which little is known about. Preliminary investigation revealed that during development BDNF and NT-3 are each expressed in several GI tract regions, and that their expression patterns overlap in some tissues, but are distinct in others. Importantly, GI tissues that express BDNF or NT-3 are innervated by vagal afferents, and expression of these neurotrophins occurs during the periods of axon invasion and receptor formation, consistent with roles for BDNF or NT-3 in these processes and in receptor survival. These results provide a basis for targeting BDNF or NT-3 knockouts to specific GI tract tissues, and potentially altering vagal afferent innervation only in that tissue (e.g., smooth muscle vs. mucosa). Conditional BDNF or NT-3 knockouts that are successful in selectively altering a vagal GI afferent pathway will be valuable for developing an understanding of that pathway's roles in GI function and food intake.

Gastric compliance in bulimia nervosa

Bulimia nervosa (BN) is a psychiatric illness characterized by eating binges followed by inappropriate behavioral attempts to compensate for the binges, usually vomiting or laxative abuse. Patients with BN have disturbances in the development of satiety during a meal as well as disturbances in functions of the upper gastrointestinal tract such as slowed gastric emptying, impaired gastric accommodation reflex and blunted cholecystokinin release. The present study examined gastric compliance and sensory responses to gastric distention in women with BN and controls. Sixteen women with BN and 13 healthy control subjects swallowed an inflatable bag that was placed in the proximal stomach. The bag was inflated to produce increasing steps of pressure against the stomach wall, before and after consumption of a 200 ml (200 Kcal) liquid meal. Pressure and volume were recorded for 2-min periods, beginning at 0 mm Hg pressure and increasing in steps of 2 mm Hg until subjects reported discomfort, gastric volume reached 600 ml, or pressure reached 20 mm Hg. At each pressure step subjects made sensory ratings. Gastric compliance was calculated as the slope of the best-fit straight line of each subject's gastric volume vs. gastric pressure. There was a significant postmeal increase in gastric compliance in both groups of subjects but there was no difference in compliance between patients with BN and controls. Patients with BN appeared to have diminished sensitivity to gastric distention. In conclusion, although other studies have described gastrointestinal abnormalities associated with BN, the current study found gastric compliance of patients with BN to be normal.

Elevated pain threshold in eating disorders: physiological and psychological factors

Several studies have found decreased pain sensitivity in patients with eating disorders but it is unclear what physiological and psychological factors are associated with this abnormality. In the present investigation, thermal pain threshold latency, somatoform dissociation, body image disturbance and physiological indices of autonomic neural system activity were measured in 39 female patients with eating disorders (21 with anorexia nervosa and 18 with bulimia nervosa) and 17 healthy women. Pain threshold was elevated in patients with eating disorders, especially those with binge-purging symptomatology. A regression analysis indicated that increased pain threshold is moderately associated with decreased peripheral skin temperature and weakly associated with lack of familiarity with one's own body. However, the between group differences in pain perception remained significant after controlling for peripheral skin temperature. Hence, elevation of pain threshold in eating disorders is a replicable finding, which is not explicable by peripheral indices of autonomic system activity or by somatoform dissociation. In future research it may be evaluated as a potential marker of broader phenotype of decreased interoceptive awareness, which may be associated with vulnerability to the development of eating disorders.

Eating disorders: clinical features and pathophysiology

Anorexia nervosa (AN) and bulimia nervosa (BN) are disorders of eating and weight-related behavior that together afflict some 1-3% of women in the United States. One of the remarkable features about each of the eating disorders is how persistent the disordered eating behavior becomes once it has begun. Substantial psychological, social, and physiological disturbances are associated with eating disorders, and it has been very difficult to disentangle those factors that may result from the disturbed behavior from the factors that may have predisposed individuals to, or precipitated the development of, the disorder. This article will briefly review the definitions, phenomenology, and identified risk factors for development of each of the major eating disorders. Pathophysiology will be discussed, with a particular focus on candidate factors that might sustain disordered eating behavior, as informed by clinical and basic science research. Future research directions will be suggested.

Pain perception in recovered bulimia nervosa patients

OBJECTIVE

Decreased pain sensitivity is found in individuals who are ill with bulimia nervosa (BN). The purpose of this study is to determine whether altered pain perception persists after recovery from bulimia nervosa (RBN).

METHODS

Eleven women who were recovered from BN for more than 1 year were compared with 15 healthy volunteer women. The participants received two pain evaluations--thermal pain stimulation (TPS), which evaluates threshold and tolerance to heat, and the submaximal effort tourniquet test (SETT), which assesses threshold and tolerance to ischemic pain induced by inflation of a blood pressure cuff.

RESULTS

Compared with the controls, the RBN women showed elevated pain threshold as measured with the SETT and a tendency to elevated pain threshold on the TPS.

DISCUSSION

Decreased pain sensitivity persists after recovery from BN and may reflect altered modulatory function in this illness.

The brain decade in debate: VIII. Peptide hormones and behavior: cholecystokinin and prolactin

This article is a transcription of an electronic symposium held on November 28, 2000 in which active researchers were invited by the Brazilian Society of Neuroscience and Behavior (SBNeC) to discuss the advances of the last decade in the peptide field with particular focus on central actions of prolactin and cholecystokinin. The comments in this symposium reflect the diversity of prolactin and cholecystokinin research and demonstrate how the field has matured. Since both peptides play a role in reproductive behaviors, particularly mother-infant interactions, this was the starting point of the discussion. Recent findings on the role of the receptor subtypes as well as interaction with other peptides in this context were also discussed. Another issue discussed was the possible role of these peptides in dopamine-mediated rewarding systems. Both prolactin and cholecystokinin are involved in mechanisms controlling food intake and somatic pain thresholds. The role of peripheral inputs through vagal afferents modulating behavior was stressed. The advent of knockout animals as potential generators of new knowledge in this field was also addressed. Finally, interactions with other neuropeptides and investigation of the role of these peptides in other fields such as immunology were mentioned. Knowledge about the central functions of prolactin and cholecystokinin has shown important advances. The role of these peptides in neurological and psychiatric syndromes such as anorexia, drug abuse and physiological disturbances that lead to a compromised maternal behavior seems relevant.

Vagotomy decreases excitability in primary vagal afferent somata

Standard patch-clamp and intracellular recording techniques were used to monitor membrane excitability changes in adult inferior vagal ganglion neurons (nodose ganglion neurons, NGNs) 5 days following section of the vagus nerve (vagotomy). NGNs were maintained in vivo for 5 days following vagotomy, and then in vitro for 2-9 h prior to recording. Vagotomy increased action potential (AP) threshold by over 200% (264 +/- 19 pA, mean +/- SE, n = 66) compared with control values (81 +/- 20 pA, n = 68; P < 0.001). The number of APs evoked by a 3 times threshold 750-ms depolarizing current decreased by >70% (from 8.3 to 2.3 APs, P < 0.001) and the number of APs evoked by a standardized series of (0.1-0.9 nA, 750 ms) depolarizing current steps decreased by over 80% (from 16.9 APs to 2.6 APs, P < 0.001) in vagotomized NGNs. Similar decreases in excitability were observed in vagotomized NGNs in intact ganglia in vitro studied with "sharp" microelectrode techniques. Baseline electrophysiological properties and changes following vagotomy were similar in right and left NGNs. A "sham" vagotomy procedure had no effect on NGN properties at 5 days, indicating that changes were due to severing the vagus nerve itself, not surrounding tissue damage. NGNs isolated after being maintained 17 h in vivo following vagotomy revealed no differences in excitability, suggesting that vagotomy-induced changes occur some time from 1-5 days after injury. Decreased excitability was still observed in NGNs isolated after 20-21 days in vivo following vagotomy. These data indicate that, in contrast to many primary sensory neurons that are thought to become hyperexcitable following section of their axons, NGNs undergo a marked decrease in electrical excitability following vagotomy.