Background

Anorexia nervosa (AN) is a severe psychiatric disorder characterized by extreme hypophagia, severe body weight loss, distorted self-image, and maladaptive food choices (Mitchell and Peterson, 2020). The onset of AN usually occurs in adolescence or young adulthood (Favaro et al., 2009) and it mainly affects females (roughly 92%) (Udo and Grilo, 2018). It has the highest mortality rate among psychiatric disorders (Treasure et al., 2015), 12 times higher than the death rate associated with all causes of death for females 15–24 years old (Smink et al., 2013; Fichter and Quadflieg, 2016). Currently, there are no effective pharmacological cures for AN (Crow, 2019). To inform new therapies and to identify individuals at risk for the disorder, a deeper understanding of the neurobiology underlying AN is urgently needed. The etiology of AN is complex since it involves interactions between genetic, environmental, social, and cultural factors. Such complexity has made it difficult to develop an appropriate animal model so far (Siegfried et al., 2003). Previous studies have used approaches involving genetic, environmental, and/or dietary manipulations to study AN in animal models. Genetically modified mouse models have been used to ablate or activate specific neuronal populations, with immediate reduction of food intake (Luquet et al., 2005; Calvez et al., 2011). While most of these studies might provide insights into neural circuits causing anorexia (simply seen as the loss of appetite for food), their translatability to humans is minimal since the nature and timing of the stressors are different from those that increase the risk of developing AN in humans (François et al., 2022).

The best characterized animal model of AN is the activity-based anorexia model (ABA) (Klenotich and Dulawa, 2012). This is a bio-behavioral phenomenon described in rodents that models the key symptoms of AN (self-induced starvation and compulsive running, to list a few of them) and is based on the principle that mice will prefer to run instead of eating even when food is available, if previously exposed to food restriction. The ABA, however, cannot capture the sociocultural factors that might promote AN.

Here, we propose a method to couple a genetically modified mouse model to a specific ABA protocol designed for adolescent female and male mice. We chose to investigate the involvement of the hypothalamic agouti-related peptide and neuropeptide Y (AgRP/NPY)-expressing neurons. These neurons are physiologically active during fasting, but also modulate complex non-feeding behaviors (Dietrich et al., 2015). To impair AgRP neuron function, we studied AgRP neuron-specific diphtheria toxin receptor-expressing mice (AgRP-DTR), which allow ablation of AgRP neurons early postnatally by administering diphtheria toxin at P5 (Luquet et al., 2005). By combining ABA with a transgenic mouse model and further choosing a critical time window (adolescence), it is feasible to get insights into genetic × environmental factors (such as early life stress) that contribute to the onset or propagation of AN. This protocol will be useful for future studies that aim to identify the contribution of specific neuronal populations to AN symptomatology. Combining the two approaches in adolescent mice will also allow the unraveling of mechanisms that contribute to resilience or vulnerability to AN.