Binge-Eating Behavior in Socially-Insolated Female Mice

Abstract

gia, during which individuals quickly consume excessive amounts of food (Perello, Valdivia, Romero, & Raingo, 2014), often including palatable, high-fat food. Rodents provided with intermittent (as opposed to continuous or daily) access to high-fat food have served an important role in modeling and investigating the pathophysiology of this disorder (Corwin, Avena, & Boggiano, 2011). Mice and rats provided with palatable food rapidly consume upwards to 80% of their daily caloric intake within a 2-hour period of limited access (Bake, Morgan, & Mercer, 2014; Bake, Murphy, Morgan, & Mercer, 2014). This resembles feeding behaviors observed in humans with BED. Animal studies have also used social isolation to model the depressive-like behaviors observed in humans. This is important because real or perceived social isolation and loneliness are major precipitants of depression (Matthews et al., 2016). Housing mice alone, for example, increase immobility during the tail suspension test (Ieraci, Mallei, & Popoli, 2016), a popular method for assessing behavioral despair and for screening anti-depressant drugs (Castagné, Moser, Roux, & Porsolt, 2010). Consistent with the comorbidity that depression shares with eating disorders in humans, prolonged social isolation has also been shown to increase total food intake in rodents (Perez et al., 1997; Sun et al., 2014; Yamada et al., 2015). Only one study assessed the effects of social isolation on food intake in female mice (Yamada et al., 2015). Importantly though, the effects of social isolation on binge-eating of palatable food in female mice have not yet been investigated. We used social isolation as a model for depression and investigated its impact on feeding behavior during a test of binge-eating in female mice. Mice were individually housed (social isolation) or pair-housed (control) and provided with intermittent access to high-fat food. After 4 weeks, the tail suspension test was used to measure isolation-induced despair. To examine co-occurring binge-eating behavior in detail, we measured food intake at 5 time INTRODUCTION Depression is a highly prevalent mental disorder affecting 6.7% of adults (16.1 million) in the United States annually (Center for Behavioral Health Statistics and Quality, 2016; Centers for Disease Control and Prevention (CDC), 2010). Eating disorders including binge-eating, anorexia nervosa, and bulimia nervosa affect an estimated 4.6% of the population each year (Le Grange, Swanson, Crow, & Merikangas, 2012). Depression and eating disorders are significantly comorbid conditions (Hudson, Hiripi, Pope, Kessler, & Kessler, 2007). For example, approximately 32.3% of patients with the binge-eating disorder (BED) also meet criteria for major depressive disorder (Hudson, Hiripi, Pope, Kessler, & Kessler, 2007). Women are nearly twice as likely than men to be diagnosed with depression (Noble, 2005). Women are also more susceptible to developing BED than men (Hudson et al., 2007). In fact, 20 million women in the United States alone suffer from BED, compared to only 10 million men (Striegel-Moore et al., 2009). Still, females are understudied in biomedical research (Beery & Zucker, 2011). These data support an unmet need to study the pathophysiology of BED in females. Binge-eating is defined as a period of uncontrolled hyperphaBinge-Eating Behavior in Socially-Isolated Female Mice