Alternative Frameworks for Advancing the Study of Eating Disorders

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.

Taking better advantage of the activity-based anorexia model

The lack of specific treatments for anorexia nervosa (AN) is partly driven by an inadequate understanding of the neurobiological drivers of the condition. The activity-based anorexia (ABA) model recapitulates key characteristics of AN in rats and mice, and can be used to understand factors that predispose, maintain, and rescue anorectic behaviour. With the rapidly evolving suite of technologies to manipulate and record neural activity during the development of ABA, we are better placed than ever before to take advantage of this unique biobehavioural model in order to develop and refine novel treatments for AN. This will require a collective effort to bridge research disciplines in order to capitalise on knowledge gains from genetics, neurobiology, metabolism, and cognition.

AgRP neurons coordinate the mitigation of activity-based anorexia

Anorexia nervosa (AN) is a debilitating and deadly disease characterized by low body mass index due to diminished food intake, and oftentimes concurrent hyperactivity. A high percentage of AN behavioral and metabolic phenotypes can be replicated in rodents given access to a voluntary running wheel and subject to food restriction, termed activity-based anorexia (ABA). Despite the well-documented bodyweight loss observed in AN human patients and ABA rodents, much less is understood regarding the neurobiological underpinnings of these maladaptive behaviors. Hunger-promoting hypothalamic agouti-related peptide (AgRP) neurons have been well characterized in their ability to regulate appetite, yet much less is known regarding their activity and function in the mediation of food intake during ABA. Here, feeding microstructure analysis revealed ABA mice decreased food intake due to increased interpellet interval retrieval and diminished meal number. Longitudinal activity recordings of AgRP neurons in ABA animals exhibited a maladaptive inhibitory response to food, independent of basal activity changes. We then demonstrated that ABA development or progression can be mitigated by chemogenetic AgRP activation through the reprioritization of food intake (increased meal number) over hyperactivity, but only during periods of food availability. These results elucidate a potential neural target for the amelioration of behavioral maladaptations present in AN patients.

Adolescent female rats prone to the activity based anorexia (ABA) paradigm have altered hedonic responses and cortical astrocyte density compared to resistant animals

OBJECTIVE

Anhedonia, which in part involves the lack of pleasure in consuming palatable food, is a long-lasting symptom observed in patients both when acutely ill and when long term recovered from Anorexia Nervosa. The neurocircuitry underlying this phenomenon is not well understood. Here we use the preclinical activity-based anorexia (ABA) model in adolescent female rats to assess the impact of excessive exercise, limited food intake and acute weight loss, on adolescent female rat orofacial responding to intraoral sucrose, as measured by the taste reactivity test (TRT). Animals were identified as either prone or resistant to this paradigm based on a weight loss criterion. Measures of food intake, running wheel activity, taste reactivity and medial prefrontal cortex astrocyte expression were compared across groups.

METHODS

Adolescent female rats implanted with an intraoral catheter were given a TRT using 1 M (M) sucrose at baseline, max weight loss (25% weight loss from start of ABA or 7 full days on the paradigm) or 10 days recovered from the ABA paradigm. Animals were sacrificed after the final TRT and astrocyte density was measured via immunohistochemistry.

RESULTS

Animals resistant to the ABA paradigm ran less than prone animals during the ABA period. Additionally, we found that resistant animals displayed more cumulative 'liking' responses to sucrose compared to prone animals at maximum weight loss. Finally, we found prone animals 10-days recovered from ABA had reduced medial prefrontal cortex astrocyte density compared to levels in resistant animals.

DISCUSSION

Rats presented with the physiological challenge of the ABA paradigm either adapt their behavior to stabilize their body weight (i.e. resistant), or rapidly lose weight (i.e. prone). Furthermore, we found that prone animals have reduced orofacial responding to 1 M sucrose at maximum weight loss compared to responses in resistant animals, and this anhedonia-like behavior may be a result of reduced astrocyte density that affects cortical function.

The Utility of Animal Models for Studying the Metabo-Psychiatric Origins of Anorexia Nervosa

Anorexia nervosa (AN) is a severe eating disorder that primarily affects young women and girls, and is characterized by abnormal restrictive feeding and a dangerously low body-mass index. AN has one of the highest mortality rates of any psychiatric disorder, and no approved pharmacological treatments exist. Current psychological and behavioral treatments are largely ineffective, and relapse is common. Relatively little basic research has examined biological mechanisms that underlie AN compared to other major neuropsychiatric disorders. A recent large-scale genome-wide association study (GWAS) revealed that the genetic architecture of AN has strong metabolic as well as psychiatric origins, suggesting that AN should be reconceptualized as a metabo-psychiatric disorder. Therefore, identifying the metabo-psychiatric mechanisms that contribute to AN may be essential for developing effective treatments. This review focuses on animal models for studying the metabo-psychiatric mechanisms that may contribute to AN, with a focus on the activity-based anorexia (ABA) paradigm. We also highlight recent work using modern circuit-dissecting neuroscience techniques to uncover metabolic mechanisms that regulate ABA, and encourage further work to ultimately identify novel treatment strategies for AN.