Olfactory dysfunction in anorexia and bulimia nervosa

The olfactory bulb: A neuroendocrine spotlight on feeding and metabolism

Olfaction is the most ancient sense and is needed for food-seeking, danger protection, mating and survival. It is often the first sensory modality to perceive changes in the external environment, before sight, taste or sound. Odour molecules activate olfactory sensory neurons that reside on the olfactory epithelium in the nasal cavity, which transmits this odour-specific information to the olfactory bulb (OB), where it is relayed to higher brain regions involved in olfactory perception and behaviour. Besides odour processing, recent studies suggest that the OB extends its function into the regulation of food intake and energy balance. Furthermore, numerous hormone receptors associated with appetite and metabolism are expressed within the OB, suggesting a neuroendocrine role outside the hypothalamus. Olfactory cues are important to promote food preparatory behaviours and consumption, such as enhancing appetite and salivation. In addition, altered metabolism or energy state (fasting, satiety and overnutrition) can change olfactory processing and perception. Similarly, various animal models and human pathologies indicate a strong link between olfactory impairment and metabolic dysfunction. Therefore, understanding the nature of this reciprocal relationship is critical to understand how olfactory or metabolic disorders arise. This present review elaborates on the connection between olfaction, feeding behaviour and metabolism and will shed light on the neuroendocrine role of the OB as an interface between the external and internal environments. Elucidating the specific mechanisms by which olfactory signals are integrated and translated into metabolic responses holds promise for the development of targeted therapeutic strategies and interventions aimed at modulating appetite and promoting metabolic health.

Investigating the Link between Eating Attitudes, Taste and Odour Preferences and the Chemical Senses

OBJECTIVES

To examine if higher degrees of pathological eating attitudes in a non-clinical sample are associated with odour and taste perception and preferences based on psychophysical ratings.

PARTICIPANTS AND METHODS

A total of 80 female university students completed the eating attitudes test (EAT-26), followed by four chemosensory measures including olfactory and gustatory perception plus perceptual ratings and preferences for food odours and tastes.

RESULTS

There were no significant correlations between EAT-26 scores and measures of olfactory and gustatory perception. However, a significant interaction effect indicated higher degrees of pathological eating attitudes may be associated with differential sensitivity to sweet and fatty food odours compared to those with lower levels of pathological eating attitudes.

CONCLUSIONS

This was the first study to examine pathological eating attitudes using food stimuli with a non-clinical sample. The results remain preliminary until replication. However, the findings highlight the need for development of measures of disordered eating attitudes and behaviours that go beyond caloric restriction.

High prevalence of olfactory dysfunction detected in treatment-naive patients with head and neck cancer

BACKGROUND

Previous studies demonstrated the difficulty of patients with Head and Neck Cancer (HNC) in sensing food taste, a function in which olfaction has a significant role. However, neither study employed psychophysical tests or control groups to establish the veracity of such complaints.

AIMS/OBJECTIVES

In this study, we quantitatively tested the olfactory function of HNC individuals and compared their function to that of healthy controls.

METHODS

Thirty-one HNC naïve treatment patients and thirty-one controls, matched for sex, age, schooling, and smoking, were tested with the University of Pennsylvania Smell Identification Test (UPSIT).

RESULTS

The olfactory function was significantly worse among the patients diagnosed with head and neck cancer [UPSIT cancer = 22.9(CI 95%: 20.5-25.4) vs. UPSIT controls = 29.1(CI 95%: 26.9-31.3); p < .001]. Most patients with HNC had olfactory disorders (n = 29, 93.5%). The risk of olfactory loss was higher in the cancer group [OR: 10.5(CI 95%: 2.1-51.9; p = .001)].

CONCLUSION AND SIGNIFICANCE

Olfactory disorders can be detected in more than 90% of patients with head and neck cancer when evaluated using a well-validated olfactory test. Smell disorders may be a potential marker for early diagnosis of HNC.

International consensus statement on allergy and rhinology: Olfaction

BACKGROUND

The literature regarding clinical olfaction, olfactory loss, and olfactory dysfunction has expanded rapidly over the past two decades, with an exponential rise in the past year. There is substantial variability in the quality of this literature and a need to consolidate and critically review the evidence. It is with that aim that we have gathered experts from around the world to produce this International Consensus on Allergy and Rhinology: Olfaction (ICAR:O).

METHODS

Using previously described methodology, specific topics were developed relating to olfaction. Each topic was assigned a literature review, evidence-based review, or evidence-based review with recommendations format as dictated by available evidence and scope within the ICAR:O document. Following iterative reviews of each topic, the ICAR:O document was integrated and reviewed by all authors for final consensus.

RESULTS

The ICAR:O document reviews nearly 100 separate topics within the realm of olfaction, including diagnosis, epidemiology, disease burden, diagnosis, testing, etiology, treatment, and associated pathologies.

CONCLUSION

This critical review of the existing clinical olfaction literature provides much needed insight and clarity into the evaluation, diagnosis, and treatment of patients with olfactory dysfunction, while also clearly delineating gaps in our knowledge and evidence base that we should investigate further.

Olfactory capacity in anorexia nervosa: correlations with set-shifting ability

PURPOSE

The purpose of this study is to examine olfactory capacity in adults with anorexia nervosa (AN), in terms of odor identification and odor threshold and search for possible correlations between odor identification and cognitive flexibility in this population.

METHODS

Thirty-nine patients diagnosed with AN and 60 healthy participants, participated. Odor identification was assessed using the University Pennsylvania Smell Identification Test and a two alternative forced choice, ascending method with n-butanol was used to assess odor threshold. Cognitive flexibility was determined using the Intra/Extra-Dimensional Set-Shift test (IED), a subtest of the Cambridge Neuropsychological Test Automated Battery (CANTAB).

RESULTS

Patients with AN presented a poorer performance in odor identification compared with controls (p = 0.001). No differences were found in odor threshold, between the two groups. Patients with AN exhibited poor cognitive flexibility compared with controls (p = 0.003). A significant correlation between odor identification and cognitive flexibility was documented in AN (p = 0.01), but not in controls.

CONCLUSION

Our findings suggest that olfactory capacity is altered in AN: Qualitative characteristics of olfaction were affected in patients with AN (lower odor identification), while there was no difference in quantitative characteristics (odor threshold) compared with controls. Furthermore, odor identification in AN was correlated to cognitive flexibility.

LEVEL OF EVIDENCE

Level III: case-control analytic study.

Psychophysical chemosensory dysfunction in eating disorders: a qualitative systematic review

PURPOSE

Patients with chemosensory dysfunction experience significant quality of life disruptions, including reduced enjoyment of eating. While chemosensory dysfunction has been associated with eating disorders, the relationship is poorly understood. This systematic review aims to characterize psychophysical gustation and olfaction in patients with eating disorders.

METHODS

Systematic review of investigations assessing psychophysical chemosensory function in patients with organic eating disorders.

RESULTS

26 studies were included. Five studies assessed both chemosenses, while 12 and 9 assessed exclusively gustation or olfaction, respectively. In total, 779 patients were included [72.4% anorexia nervosa (AN), 26.7% bulimia nervosa (BN), 0.8% combined AN/BN]. Patients with eating disorders experienced rates of hypogeusia up to 87% in AN and 84.6% in BN. There was evidence for alterations in psychophysical olfaction, but orientation of trends were less clear. Chemosensory dysfunction was more evident in AN patients. Treatment correlated with improved chemosensory function.

CONCLUSIONS

Despite heterogeneity in study methodology and results, this review demonstrates that patients with eating disorders experience some degree of chemosensory dysfunction, particularly in gustation. This symptomatology overlaps with those experienced by patients with other causes of chemosensory impairment. These findings suggest potential broad psychosocial, dietary, and mental health implications in patient populations experiencing chemosensory dysfunction.

LEVEL OF EVIDENCE

Level II.

Caloric restriction reduces basal cell proliferation and results in the deterioration of neuroepithelial regeneration following olfactotoxic mucosal damage in mouse olfactory mucosa

The effects of caloric restriction (CR) on cell dynamics and gene expression in the mouse olfactory neuroepithelium are evaluated. Eight-week-old male C57BL/6 mice were fed either control pellets (104 kcal/week) or CR pellets (67 kcal/week). The cytoarchitecture of the olfactory neuroepithelium in the uninjured condition and its regeneration after injury by an olfactotoxic chemical, methimazole, were compared between mice fed with the control and CR diets. In the uninjured condition, there were significantly fewer olfactory marker protein (OMP)-positive olfactory receptor neurons and Ki67-positive proliferating basal cells at 3 months in the CR group than in the control group. The number of Ki67-positive basal cells increased after methimazole-induced mucosal injury in both the control and the CR groups, but the increase was less robust in the CR group. The recovery of the neuroepithelium at 2 months after methimazole administration was less complete in the CR group than in the control group. These histological changes were region-specific. The decrease in the OMP-positive neurons was prominent in the anterior region of the olfactory mucosa. Gene expression analysis using a DNA microarray and quantitative real-time polymerase chain reaction demonstrated that the expression levels of two inflammatory cytokines, interleukin-6 and chemokine ligand 1, were elevated in the olfactory mucosa of the CR group compared with the control group. These findings suggest that CR may be disadvantageous to the maintenance of the olfactory neuroepithelium, especially when it is injured.

Dysfunction of the to in Anorexia and Bulimia Nervosa: A fMRI

Brain reward dysfunction in eating disorders has been widely reported. However, whether the neural correlates of hedonic and motivational experiences related to food cues are differentially affected in anorexia nervosa of restrictive type (ANr), bulimia nervosa (BN), and healthy control (HC) participants remains unknown. Here, 39 women (14 ANr, 13 BN, and 12 HC) underwent fMRI while smelling food or non-food odors in hunger and satiety states during liking and wanting tasks. ANr and BN patients reported less desire to eat odor-cued food and odor-cued high energy-density food (EDF), respectively. ANr patients exhibited lower ventral tegmental area (VTA) activation than BN patients to food odors when rating their desire to eat, suggesting altered incentive salience attribution to food odors. Compared with HC participants, BN patients exhibited decreased activation of the caudate nucleus to food odors in the hunger state during the wanting task. Both patient groups also showed reduced activation of the anterior ventral pallidum and insula in response to high EDF odors in the hunger state during the wanting task. These findings indicate that brain activation within the food reward-regulating circuit differentiates the three groups. ANr patients further exhibited lower activation of the precuneus than other participants, suggesting a possible role of body image distortion in ANr. Our study highlights that food odors are relevant sensory probes to gain better insight into the dysfunction of the mesolimbic and striatal circuitry involved in food reward processing in patients with EDs.

Autistic traits impact on olfactory processing in adolescent girls with Anorexia Nervosa restricting type

The correct functioning of the chemosensory pathway is pivotal for the attitude towards feeding. In some neuropsychiatric disorders, abnormalities of the sensory processing dramatically affect feeding behavior; however, evidences for an olfactory involvement in Anorexia Nervosa (AN) are still controversial. We administered a complete olfactory testing battery, the Sniffin' Sticks Extended Test, to a cohort of 19 girls with Restrictive Anorexia Nervosa (AN-R) and 19 healthy controls. A battery of questionnaires aiming to evaluate eating attitude, psychopathologic disorders and autistic traits was also administered. No difference was found between the two groups in any of the olfactory tasks. Despite the lack of correlation between olfaction and disease severity, however, olfactory performances were related to autistic traits in anorectic girls (r = -0.489, p = 0.039). Girls with AN-R do not appear to have an impaired olfactory function with respect to controls. However, a possible correlation between olfactory ability and autistic traits was discovered. In light of such findings, the role of possible relations between social functioning-related features and olfactory processing in AN-R is discussed.

Neuroimaging of smell and taste

The senses of taste and smell developed early in evolution and are of high ecological and clinical relevance in humans. Chemosensory systems function, in large part, as hazard avoidance systems, thereby ensuring survival. Moreover, they play a critical role in nutrition and in determining the flavor of foods and beverages. Their dysfunction has been shown to be a key element of early stages of a number of diseases, including Alzheimer's and Parkinson's diseases. Advanced neuroimaging methods provide a unique means for understanding, in vivo, neural and psychological processing of smell, taste, and flavor, and how diseases can impact such processing. This chapter provides, from a neuroimaging perspective, a comprehensive overview of the anatomy and physiology involved in the odor and taste processing in the central nervous system. Some methodological challenges associated with chemosensory neuroimaging research are discussed. Multisensory integration, the mechanisms that enable holistic sensory experiences, is emphasized.

Taste and Smell Disturbances in Patients with Gastroparesis and Gastroesophageal Reflux Disease

Background/Aims

Patients with gastroparesis and gastroesophageal reflux disease (GERD) often report decreased enjoyment when eating. Some patients remark that food does not smell or taste the same. To determine if taste and/or smell disturbances are present in patients with gastroparesis and/or GERD and relate these to gastrointestinal symptom severity.

Methods

Patients with gastroparesis and/or GERD completed questionnaires evaluating taste and smell (Taste and Smell Survey [TSS]), Patient Assessment of Upper Gastrointestinal Symptom Severity Index (PAGI-SYM), and Demographics. TSS questioned the nature of taste/smell changes and the impact on quality of life. PAGI-SYM was used to calculate Gastroparesis Cardinal Symptom Index (GCSI) and Heartburn and Regurgitation Score (HB/RG).

Results

Seventy-six subjects were enrolled: healthy controls (n = 13), gastroparesis alone (n = 30), GERD alone (n = 10), and both gastroparesis and GERD (n = 23). Taste and smell disturbances were higher in patients with gastroparesis, GERD, and both gastroparesis and GERD compared to healthy controls. Taste and smell abnormalities were significantly correlated (r = 0.530, P < 0.001). Taste score was strongly correlated with HB/RG (r = 0.637, P < 0.001) and with GCSI (r = 0.536, P < 0.001). Smell score was also strongly correlated to HB/RG (r = 0.513, P < 0.001) and GCSI (r = 0.495, P < 0.001).

Conclusions

Taste and smell abnormalities are prominent in gastroparesis and GERD patients. Abnormalities in taste and smell are significantly correlated with both gastroparesis and GERD symptom severity. Awareness of this high prevalence of taste and smell dysfunction among patients with gastroparesis and GERD may help to better understand the food intolerances these patients often have.

Heightened Olfactory Sensitivity in Young Females with Recent-Onset Anorexia Nervosa and Recovered Individuals

Introduction

Olfaction may be related to food restriction and weight loss. However, reports regarding olfactory function in individuals with anorexia nervosa (AN) have been inconclusive.

Objective

Characterize olfactory sensitivity and identification in female adolescents and young adults with first-episode AN and young females recovered from AN.

Methods

We used the Sniffin’ Sticks Odor Threshold Test and Odor Identification Test to assess 43 participants with first-episode AN, 27 recovered participants, and 39 control participants. Participants completed the Importance of Olfaction questionnaire, the Beck Youth Inventory and the Eating Disorder Inventory. We also conducted a psychiatric diagnostic interview and the Autism Diagnostic Observation Schedule with participants.

Results

Both clinical groups showed heightened olfactory sensitivity. After excluding participants with depression, participants with first-episode AN identified more odors than recovered participants.

Conclusion

Heightened olfactory sensitivity in AN may be independent of clinical status, whereas only individuals with current AN and without depression show more accurate odor identification.

The association between smoking prevalence and eating disorders: a systematic review and meta-analysis

BACKGROUND AND AIMS

Cigarette smoking is associated with severe mental illness, including schizophrenia and bipolar disorder, and with morbidity and mortality, but the association with anorexia (AN), bulimia nervosa (BN) and binge eating disorder (BED) is unclear. This meta-analysis compared the odds of smoking in eating disorders (ED) (ED = AN or BN or BED) versus healthy controls (HC) and calculated the prevalence of smokers in people with ED.

METHODS

Three independent authors searched PubMed, MEDLINE and Scopus from database inception until 31 December 2015 for studies reporting data on life-time or current smoking prevalence in BED, BN and AN with or without control group. Meta-analyses were undertaken, calculating odds ratios (ORs) of life-time smoking in BED, BN, AN versus healthy controls (HCs) or prevalence of smoking in BED, BN and AN with 95% confidence intervals (CI).

RESULTS

Thirty-one studies (ED = 8517, controls = 68 335) were meta-analysed. Compared with HCs, there were significantly more smokers among people with BN (life-time OR = 2.165) and BED (life-time OR = 1.792) but not AN (life-time OR = 0.927). BED was associated with smoking the most (life-time prevalence = 47.73%) followed by BN (life-time prevalence = 39.4%) and AN (life-time prevalence = 30.8%). In BN, life-time smoking prevalence was highest in Europe. In AN, higher age moderated both life-time and current smoking prevalence, and body mass index moderated higher life-time smoking prevalence. In BN, female sex moderated higher life-time smoking prevalence.

CONCLUSIONS

People with binge eating disorder and bulimia nervosa are significantly more likely to be life-time smokers than healthy controls, which is not the case for anorexia nervosa.

Cell migration in the developing rodent olfactory system

The components of the nervous system are assembled in development by the process of cell migration. Although the principles of cell migration are conserved throughout the brain, different subsystems may predominantly utilize specific migratory mechanisms, or may display unusual features during migration. Examining these subsystems offers not only the potential for insights into the development of the system, but may also help in understanding disorders arising from aberrant cell migration. The olfactory system is an ancient sensory circuit that is essential for the survival and reproduction of a species. The organization of this circuit displays many evolutionarily conserved features in vertebrates, including molecular mechanisms and complex migratory pathways. In this review, we describe the elaborate migrations that populate each component of the olfactory system in rodents and compare them with those described in the well-studied neocortex. Understanding how the components of the olfactory system are assembled will not only shed light on the etiology of olfactory and sexual disorders, but will also offer insights into how conserved migratory mechanisms may have shaped the evolution of the brain.

Smell-taste dysfunctions in extreme weight/eating conditions: analysis of hormonal and psychological interactions

(1) The objective of this study is to analyze differences in smell-taste capacity between females in extreme weight/eating conditions (EWC) and (2) to explore the interaction between smell/taste capacity, gastric hormones, eating behavior and body mass index (BMI). The sample comprised 239 females in EWC [64 Anorexia nervosa (AN) and 80 age-matched healthy-weight controls, and 59 obese and 36 age-matched healthy-weight controls]. Smell and taste assessments were performed through "Sniffin' Sticks" and "Taste Strips," respectively. The assessment measures included the eating disorders inventory-2, the symptom check list 90-revised, and The Dutch Eating Behavior Questionnaire, as well as peptides from the gastrointestinal tract [Ghrelin, peptide YY, cholecystokinin]. Smell capacity was differentially associated across EWC groups. Smell was clearly impaired in obese participants and increased in AN (hyposmia in Obesity was 54.3 and 6.4 % in AN), but taste capacity did not vary across EWC. Ghrelin levels were significantly decreased in obese subjects and were related to smell impairment. EWC individuals showed a distinct smell profile and circulating ghrelin levels compared to controls. Smell capacity and ghrelin may act as moderators of emotional eating and BMI.

Olfaction in eating disorders and abnormal eating behavior: a systematic review

The study provides a systematic review that explores the current literature on olfactory capacity in abnormal eating behavior. The objective is to present a basis for discussion on whether research in olfaction in eating disorders may offer additional insight with regard to the complex etiopathology of eating disorders (ED) and abnormal eating behaviors. Electronic databases (Medline, PsycINFO, PubMed, Science Direct, and Web of Science) were searched using the components in relation to olfaction and combining them with the components related to abnormal eating behavior. Out of 1352 articles, titles were first excluded by title (n = 64) and then by abstract and fulltext resulting in a final selection of 14 articles (820 patients and 385 control participants) for this review. The highest number of existing literature on olfaction in ED were carried out with AN patients (78.6%) followed by BN patients (35.7%) and obese individuals (14.3%). Most studies were only conducted on females. The general findings support that olfaction is altered in AN and in obesity and indicates toward there being little to no difference in olfactory capacity between BN patients and the general population. Due to the limited number of studies and heterogeneity this review stresses on the importance of more research on olfaction and abnormal eating behavior.

Chemosensory rehabilitation and malnutrition in the newborn: how far, how close?

Olfaction is critical to the hedonic appreciation of foods, caloric regulation of food intake, quality of life and taste preferences since birth. However, malnutrition in newborns down-regulates chemosensory function. Thus, olfactory measures might be used as early markers of chemosensory dysfunction in malnutrition, and may also be useful in assessing feeding adjustments during nutritional rehabilitation. Olfactory anomalies originated by malnutrition would be reversed by nutritional rehabilitation following flavor-enhancing odorants.

Assessment of gene expression in peripheral blood using RNAseq before and after weight restoration in anorexia nervosa

We examined gene expression in the blood of six females with anorexia nervosa (AN) before and after weight restoration using RNAseq. AN cases (aged 19-39) completed clinical assessments and had blood drawn for RNA at hospital admission (T1,<~75% ideal body weight, IBW) and again at discharge (T2,≥ ~ 85% IBW). To examine the relationship between weight restoration and differential gene expression, normalized gene expression levels were analyzed using a paired design. We found 564 genes whose expression was nominally significantly different following weight restoration (p<0.01, 231 increased and 333 decreased). With a more stringent significance threshold (false discovery rate q<0.05), 67 genes met criteria for differential expression. Of the top 20 genes, CYP11A1, C16orf11, LINC00235, and CPA3 were down-regulated more than two-fold after weight restoration while multiple olfactory receptor genes (OR52J3, OR51L1, OR51A4, and OR51A2) were up-regulated more than two-fold after weight restoration. Pathway analysis revealed up-regulation of two broad pathways with largely overlapping genes, one related to protein secretion and signaling and the other associated with defense response to bacterial regulation. Although results are preliminary secondary to a small sample size, these data provide initial evidence of transcriptional alterations during weight restoration in AN.

Olfaction under metabolic influences

Recently published work and emerging research efforts have suggested that the olfactory system is intimately linked with the endocrine systems that regulate or modify energy balance. Although much attention has been focused on the parallels between taste transduction and neuroendocrine controls of digestion due to the novel discovery of taste receptors and molecular components shared by the tongue and gut, the equivalent body of knowledge that has accumulated for the olfactory system, has largely been overlooked. During regular cycles of food intake or disorders of endocrine function, olfaction is modulated in response to changing levels of various molecules, such as ghrelin, orexins, neuropeptide Y, insulin, leptin, and cholecystokinin. In view of the worldwide health concern regarding the rising incidence of diabetes, obesity, and related metabolic disorders, we present a comprehensive review that addresses the current knowledge of hormonal modulation of olfactory perception and how disruption of hormonal signaling in the olfactory system can affect energy homeostasis.

Olfactory function and alternation learning in eating disorders

Orbitofrontal dysfunction is a prominent feature of obsessive compulsive disorder (OCD). In the present study we assessed orbitofrontal functioning in eating disorders (EDs) which share many features with OCD. For this purpose we studied female adolescent inpatients with anorexia nervosa restricting type (n=40), anorexia nervosa binge/purge type (n=23), a normal weight group including patients with either bulimia nervosa or eating disorder not otherwise specified-purging type (n=33), and 20 non-ED control females. Patients were assessed at admission, and when achieving weight restoration and symptom stabilization at discharge, for depression, non-ED, and ED-related OC symptoms. Orbitofrontal functioning was assessed with an alternation learning task, and with a battery assessing olfactory threshold and discrimination. Control females were assessed once. ED patients of all subtypes performed better on olfactory threshold and discrimination, but not on alternation learning, in comparison to healthy controls. More favorable orbitofrontal functioning was associated with greater ED-related obsessionality. No changes were found in olfactory threshold and discrimination between acutely-ill and symptomatically-stabilized patients. The improvement shown in alternation learning from admission to discharge was suggested to reflect a learning effect rather than being an actual change. Our findings suggest that the better orbitofrontal functioning of ED patients in comparison to healthy controls may represent a core feature of the ED that is independent of malnutrition and deranged eating behaviors, but is associated with ED-related obsessionality.

Intact sensory function in anorexia nervosa

BACKGROUND

In anorexia nervosa (AN), taste and smell are believed to be anhedonic, hunger and pain are muted, and body-image distortion obscures wasting, which together facilitate self-starvation. However, the emphasis on these deficits may be biased because other sensory systems have been sparsely investigated.

OBJECTIVES

Objectives of the study were to clarify whether these dysfunctions are specific or part of a pattern of sensory-perceptual deficits in AN patients and to test the gustatory senses dissociated from ingestion to clarify whether any deficit is sensory or affective.

DESIGN

In 15 adolescent, first-episode, hospitalized, restrictive AN patients and 15 matched healthy controls who responded to gustatory stimuli (intensity and hedonics of 5 basic tastes and tastes and odors of foods and nonfoods), size estimation (manual and oral judgment of size and shape, kinesthesia, and body size and esthetics), cold pain, and auditory and visual processing were compared.

RESULTS

AN patients did not differ on most tests, were better at odor recognition, were less successful in central auditory processing and oral assessment of size and shape, and may have been more sensitive to cold. Body-image dissatisfaction in AN patients was not related to dysfunctional size estimation.

CONCLUSIONS

There is no systematic sensory-perceptual deficit in AN patients, and specifically, not in gustatory function. The few differences shown might be due to fear of food-related stimuli or comorbidity.

Role of the evolutionarily conserved starvation response in anorexia nervosa

This review will summarize recent findings concerning the biological regulation of starvation as it relates to anorexia nervosa (AN), a serious eating disorder that mainly affects female adolescents and young adults. AN is generally viewed as a psychosomatic disorder mediated by obsessive concerns about weight, perfectionism and an overwhelming desire to be thin. By contrast, the thesis that will be developed here is that, AN is primarily a metabolic disorder caused by defective regulation of the starvation response, which leads to ambivalence towards food, decreased food consumption and characteristic psychopathology. We will trace the starvation response from yeast to man and describe the central role of insulin (and insulin-like growth factor-1 (IGF-1))/Akt/ F-box transcription factor (FOXO) signaling in this response. Akt is a serine/threonine kinase downstream of the insulin and IGF-1 receptors, whereas FOXO refers to the subfamily of Forkhead box O transcription factors, which are regulated by Akt. We will also discuss how initial bouts of caloric restriction may alter the production of neurotransmitters that regulate appetite and food-seeking behavior and thus, set in motion a vicious cycle. Finally, an integrated approach to treatment will be outlined that addresses the biological aspects of AN.

Eating without a nose: olfactory dysfunction and sensory-specific satiety

Odor stimuli play an important role in the perception of food flavor. Olfactory dysfunction is thus likely to affect eating behavior. In the present study, we hypothesized that dysfunctional olfactory perception promotes sensory-specific satiety, a decrease in pleasure derived from a certain test food during and shortly after its consumption relative to other unconsumed control foods. A total of 34 hyposmic/anosmic participants were compared with 29 normosmic control participants. All participants repeatedly consumed a fixed portion of one and the same food item, a procedure known to induce sensory satiation. We found evidence for sensory-specific satiety (SSS) regardless of olfactory function. It thus appears that olfactory deficits have no major effect on SSS.

The endocannabinoid 2-arachidonoyl-glycerol controls odor sensitivity in larvae of Xenopus laevis

Cannabinoids modulate the activity of many neuronal cells, among them sensory neurons in the olfactory epithelium. Here we show that the endocannabinoid 2-arachidonoyl-glycerol (2-AG) is synthesized in both olfactory receptor neurons and glia-like sustentacular cells in larval Xenopus laevis. Its production in the latter depends on the hunger state of the animal. The essential effect of 2-AG in olfactory receptor neurons is the control of odorant detection thresholds via cannabinoid CB(1) receptor activation. Hunger renders olfactory neurons more sensitive. Endocannabinoid modulation in the nose may therefore substantially influence food-seeking behavior.

The endocannabinoid 2-arachidonoyl-glycerol controls odor sensitivity in larvae of Xenopus laevis

Cannabinoids modulate the activity of many neuronal cells, among them sensory neurons in the olfactory epithelium. Here we show that the endocannabinoid 2-arachidonoyl-glycerol (2-AG) is synthesized in both olfactory receptor neurons and glia-like sustentacular cells in larval Xenopus laevis. Its production in the latter depends on the hunger state of the animal. The essential effect of 2-AG in olfactory receptor neurons is the control of odorant detection thresholds via cannabinoid CB(1) receptor activation. Hunger renders olfactory neurons more sensitive. Endocannabinoid modulation in the nose may therefore substantially influence food-seeking behavior.

Odor perception in alexithymic patients

Alexithymia is characterized by a marked inability to identify feelings and emotional states and some studies have documented sensorial perception in response to visual or auditory cues in this disease. Although olfaction is well known for its emotional correlates, the perception of olfactory stimulations has not been previously investigated. This study compares with standard psychophysical methods the olfactory sensitivity and the self-ratings of intensity and hedonic valence of a panel of odorants in alexithymic patients, non-alexithymic patients and control subjects. Results show that alexithymics over-evaluate intensity and pleasantness of odorants compared to non-alexithymics or control subjects. This could be interpreted in the framework of a lack of inhibitory control including this particular sense.

Computational Biology of Olfactory Receptors

Olfactory receptors, in addition to being involved in first step of the physiological processes that leads to olfaction, occupy an important place in mammalian genomes. ORs constitute super families in these genomes. Elucidating ol-factory receptor function at a molecular level can be aided by a computationally derived structure and an understanding of its interactions with odor molecules. Experimental functional analyses of olfactory receptors in conjunction with computational studies serve to validate findings and generate hypotheses. We present here a review of the research efforts in: creating computational models of olfactory receptors, identifying binding strategies for these receptors with odorant molecules, performing medium to long range simulation studies of odor ligands in the receptor binding region, and identifying amino acid positions within the receptor that are responsible for ligand-binding and olfactory receptor activation. Written as a primer and a teaching tool, this review will help researchers extend the methodologies described herein to other GPCRs.

Gustatory and olfactory sensitivity in patients with anorexia and bulimia in the course of treatment

BACKGROUND

The majority of studies on taste and smell in eating disorders have revealed several alterations of olfactory or gustatory functions. Aim of this prospective study was to employ detailed olfactory and gustatory testing in female subjects of three homogenous groups - anorexia nervosa, bulimia nervosa and healthy controls - and to look at the effects of treatment on these measures.

METHODS

Sixteen hospitalized female patients with anorexia (restricting type, mean age [M]=24.5 years), 24 female patients with bulimia (purging type, M=24.3 years) as well as 23 healthy controls (M=24.5 years) received olfactory ("Sniffin' Sticks") and gustatory testing ("Taste Strips"). Group differences in olfactory and gustatory sensitivity, body mass index (BMI), the Beck depression inventory, the eating attitudes test (EAT), and the influence of therapy on gustatory and olfactory function were investigated.

RESULTS

(1) Group differences were present for odor discrimination and overall olfactory function with anorexic patients having the lowest scores. (2) Regarding taste function, controls scored higher than patients with anorexia. (3) At admission small but significant correlations were found between overall olfactory function and body weight (r(63)=0.35), BMI (r(63) = 0.37), and EAT score (r(63) = -0.27). Similarly, (4) the taste test score correlated significantly with body weight (r(63)= 0.48), and BMI (r(63) = 0.45). Finally, (5) at discharge overall olfactory and gustatory function were significantly higher compared to admission in anorexic patients.

CONCLUSIONS

As compared to healthy controls and bulimic patients our results show lowered olfactory and gustatory sensitivities in anorexic patients that improved with increasing BMI and decreasing eating pathology in the course of treatment.

[Changed taste perception in patients with eating disorders]

OBJECTIVE

Taste is a hereditary trait and affects eating and dietary behavior. The tongue's papillae represent the first line of the gustatory apparatus to provide information about taste. The aim of the present investigation was to evaluate the number of fungiform papillae (fPap) in relationship with 6-n-propylthiouracil (PROP) sensitivity and body mass index (BMI) in patients with eating disorders.

METHODS

18 female patients with eating disorders (anorexia or bulimia nervosa; age 14-20 yrs.) and 15 age-matched female controls were included. The number of fPap was quantified. Bitter taste was probed with PROP. Different BMIs (e.g. minimal BMI, maximal BMI) were calculated.

RESULTS

As regards non-tasters (PROP negative), anorectic patients showed a significant reduction in the number of fPap compared to both PROP negative healthy controls and also bulimic patients. The number of fPap did not differ significantly between tasters and non-tasters within controls and eating disorder groups. There was a trend of higher BMI's in bulimic and healthy non-tasters.

CONCLUSIONS

In anorectic patients a reduced number of fPap was associated with a decreased PROP sensitivity, which is a new finding. The data of the present study support the notion that the variation of fPap number and PROP sensitivity influences the pathophysiology of eating behavior and taste perception, and following this are involved in the development of eating disorders.

Olfaction: a potential cognitive marker of psychiatric disorders

Cognitive deficits are well documented in psychiatric disorders, particularly in schizophrenia and depression. Cognitive activity roots in perceptions. However, research on sensorial alterations in psychiatric conditions has mainly focused on visual or auditory processes and less on olfaction. Here, we examine data on olfactory deficits in psychiatric patients using a systematic review of recent publications. Schizophrenic patients are mainly characterized by no reliable change in odour sensitivity and by a deficit in odour identification, recognition and discrimination. Depressed patients principally exhibit a deficit in the hedonic aspects of this perception, even if, in some case, alterations in sensitivity or identification are also found. Changes in odour perception are also found in dementia and in some neurodegenerative disease, but in this case alterations concern all aspects of the sensorial experience (detection threshold, identification and recognition). Taken together, these data indicate that olfactory abnormalities might be a marker of psychiatric conditions, with a specific pattern for each disease.

Effects of anti-depressants on olfactory sensitivity in mice

RATIONALE AND OBJECTIVES

Some studies have underlined a decrease in olfactory sensitivity in patients suffering from depression. The present study aims to evaluate the effects of current anti-depressant drugs on the olfactory sensitivity in mice. METHODS MICE: (N degrees =22) were tested in a Y-maze with a choice between an odorant (butanol) or distilled water before and during 3 weeks of daily intra-peritoneal injection of either citalopram or clomipramine. Their performance was compared with those of a control group (N degrees =11) injected with a saline solution.

RESULTS

The results showed a significant decrease in olfactory sensitivity with both anti-depressants during the three weeks of treatment.

CONCLUSION

The antidepressant induced alteration in serotonin and/or noradrenaline transmission in the olfactory bulb may account for the altered olfactory sensitivity observed in this study.

OdorMapComparer: An Application for Quantitative Analyses and Comparisons of fMRI Brain Odor Maps

Brain odor maps are reconstructed flat images that describe the spatial activity patterns in the glomerular layer of the olfactory bulbs in animals exposed to different odor stimuli. We have developed a software application, OdorMapComparer, to carry out quantitative analyses and comparisons of the fMRI odor maps. This application is an open-source window program that first loads two odor map images being compared. It allows image transformations including scaling, flipping, rotating, and warping so that the two images can be appropriately aligned to each other. It performs simple subtraction, addition, and average of signals in the two images. It also provides comparative statistics including the normalized correlation (NC) and spatial correlation coefficient. Experimental studies showed that the rodent fMRI odor maps for aliphatic aldehydes displayed spatial activity patterns that are similar in gross outlines but somewhat different in specific subregions. Analyses with OdorMapComparer indicate that the similarity between odor maps decreases with increasing difference in the length of carbon chains. For example, the map of butanal is more closely related to that of pentanal (with a NC = 0.617) than to that of octanal (NC = 0.082), which is consistent with animal behavioral studies. The study also indicates that fMRI odor maps are statistically odor-specific and repeatable across both the intra- and intersubject trials. OdorMapComparer thus provides a tool for quantitative, statistical analyses and comparisons of fMRI odor maps in a fashion that is integrated with the overall odor mapping techniques.

Odor perception in patients with mood disorders

BACKGROUND

Olfaction has obvious correlates with emotional processes but little is known about the several aspects of olfaction in psychiatric disorders characterized by mood disturbance. This research aims at pointing out the specificities of olfactory perception in patients in order to identify the specific cerebral impairments involved in these disorders.

METHODS

Olfactory sensitivity, detection, identification, self-evaluation of intensity and pleasantness have been recorded in a control group of healthy subjects (N = 58) and in three sample populations admitted to a Psychiatry Department: depressive patients (N = 49), anorectic patients (N = 17), and patients suffering from addiction to alcohol or drugs (N = 21).

RESULTS

Depressive patients have a poor sensitivity, poor detection abilities but over-evaluate the pleasantness of odors. Anorectic patients have a high sensitivity, over-evaluate the intensities of the odors but under-evaluate their pleasantness. Alcoholic/drug addicted patients showed impairments in identification.

LIMITATION

This study does not identify inter-individual differences in olfactory perception.

CONCLUSION

The psychiatric diseases, here at hand although every one of them may be characterized by depressive components, show diverging impairments in olfactory perception. When variations in sensitivity are usually attributed to peripheral cues, impairments in emotional and cognitive aspects of olfaction are typically related to specific brain structures and processes which could be particularly involved in these diseases.

Restrained eaters show altered brain response to food odor

Do restrained and unrestrained eaters differ in their brain response to food odor? We addressed this question by examining restrained eaters' brain response to food (chocolate) and non-food (geraniol, floral) odors, both when odor was attended to and when ignored. Using olfactory event-related potentials (OERPs), we found that restrained eaters and controls responded similarly to the non-food odor; however, unlike controls, restrained eaters showed no increase in brain response to the food odor when they focused attention on it. Rather, restrained eaters showed attenuated OERP amplitudes to the food odor in both attended and ignored conditions, suggesting that the brain's response to attended food odor was abnormally suppressed.

Olfactory deficits in anorexia nervosa

OBJECTIVE

Young patients admitted to the hospital due to anorexia nervosa report reduced pleasure and impaired perception of smell while eating. So far, two studies on odour identification ability in eating disorders did not suggest any significant deficits. Therefore a new and more detailed method of olfactory testing may be needed, in order to determine the subjective impairment of olfaction.

METHOD

By using all three subtests of the recently developed smell test called "Sniffin'Sticks", the olfactory deficits were assessed in more detail and the results of female anorectic patients (n = 17) were compared with those of healthy females (n = 15).

RESULTS

By examining the anorectic patients no deficits in the subtest odour identification were found. On the contrary, in the subtests odour discrimination and odour threshold deficits of the anorectic patients were detected.

CONCLUSION

Reduced olfactory perception might be considered as a common deficit in anorexia nervosa with possible influences and consequences for therapy.

Causes of eating disorders

Anorexia nervosa and bulimia nervosa have emerged as the predominant eating disorders. We review the recent research evidence pertaining to the development of these disorders, including sociocultural factors (e.g., media and peer influences), family factors (e.g., enmeshment and criticism), negative affect, low self-esteem, and body dissatisfaction. Also reviewed are cognitive and biological aspects of eating disorders. Some contributory factors appear to be necessary for the appearance of eating disorders, but none is sufficient. Eating disorders may represent a way of coping with problems of identity and personal control.

Odor identification impairments in schizophrenia: relationship with demographic measures, clinical variables, and diagnostic subtypes

Smell identification deficits are consistently found in schizophrenia (SZ), but little is known about the nature and characterization of this deficit or its relationship to the phenomenology of the illness. This study aims to further delineate smell identification errors in SZ by examining the relationship of patient demographic differences with smell-identification performance. Our results showed that a patient's gender and education were related to odor-identification scores, with better performance seen in female patients and in those with greater educational attainment. However, there was no effect related to age, ethnicity, or socioeconomic status on odor identification. A smell identification deficit was also unrelated to clinical characteristics of the patients, including age at first hospitalization, number of psychiatric hospitalizations, and duration of illness. Odor identification also did not differ by SZ subtype, nor between SZ and schizoaffective disorder patients. These findings emphasize that odor identification deficits in SZ are unrelated to clinical illness features, cannot be explained by other confounds related to olfaction in the general population, and may be core features related to the SZ disease process.

Olfaction

The main and accessory olfactory systems have received considerable attention on the part of scientists and clinicians during the last decade, largely because of (a) quantum advances in understanding their genetically expressed receptor mechanisms, (b) evidence that their receptor cells undergo neurogenesis and both programmed and induced cell death, and (c) important technical and practical developments in psychophysical measurement. The latter developments have led to the proliferation of standardized olfactory testing in laboratories and clinics, and to the discovery that smell loss is among the first signs of a number of neurodegenerative diseases, including Alzheimer's disease and idiopathic Parkinson's disease. Recent controversial claims that humans possess a functioning vomeronasal system responsive to "pheromones" has added further interest in intranasal chemoreception. This review focuses on recent progress made in understanding olfactory function, emphasizing transduction, measurement, and clinical findings.

Olfaction and its alteration by nasal obstruction, rhinitis, and rhinosinusitis

The sense of smell has been largely ignored by otorhinolaryngologists, even though 1) its medical stewardship falls within their specialty's purview, 2) olfactory dysfunction is not uncommon in the general population, and 3) disorders of olfaction have significant quality of life, nutritional, and safety consequences. This report provides a succinct overview of the major intranasal neural systems present in humans (namely, cranial nerves O, I, and V, and the nonfunctional accessory [vomeronasal] organ system), along with a summary of notable findings resulting from the application of modern olfactory tests to patient populations, emphasizing diseases of the nose. Such tests have led to the discovery of significant influences of age, gender, smoking, toxic exposure, and genetics on the ability to smell. Within the field of otorhinolaryngology, they have revealed that 1) surgical and medical interventions in patients with rhinosinusitis do not, on average, lead to complete recovery of olfactory function, despite common beliefs to the contrary, and 2) associations are generally lacking between measures of airway patency and olfactory function in such cases. These findings have thrown into question the dogma that olfactory loss in rhinosinusitis is attributable primarily to blockage of airflow to the receptors and have led to histopathological studies demonstrating significant olfactory epithelial compromise in sinonasal syndromes.