In pursuit of biomarkers for predicting susceptibility to activity‐based anorexia in adolescent female rats

Abstract

Objective Identifying risk factors that contribute to the development of anorexia nervosa (AN) is critical for the implementation of early intervention strategies. Anxiety, obsessive–compulsive behavior, and immune dysfunction may be involved in the development of AN; however, their direct influence on susceptibility to the condition remains unclear. Here, we used the activity‐based anorexia (ABA) model to examine whether activity, anxiety‐like behavior, compulsive behavior, and circulating immune markers predict the subsequent development of pathological weight loss. Method Female Sprague–Dawley rats (n = 44) underwent behavioral testing before exposure to ABA conditions after which they were separated into susceptible and resistant subpopulations. Blood was sampled before behavioral testing and after recovery from ABA to screen for proinflammatory cytokines. Results Rats that were vulnerable to pathological weight loss differed significantly from resistant rats on all key ABA parameters. While the primary measures of anxiety‐like or compulsive behavior were not shown to predict vulnerability to ABA, increased locomotion and anxiety‐like behavior were both associated with the extent of weight loss in susceptible but not resistant animals. Moreover, the change in expression of proinflammatory markers IL‐4 and IL‐6 evoked by ABA was associated with discrete vulnerability factors. Intriguingly, behavior related to risk assessment was shown to predict vulnerability to ABA. Discussion We did not find undisputable behavioral or immune predictors of susceptibility to pathological weight loss in the ABA rat model. Future research should examine the role of cognition in the development of ABA, dysfunction of which may represent an endophenotype linking anorectic, anxiety‐like and compulsive behavior. Public Significance Anorexia nervosa (AN) has among the highest mortality rates of all psychiatric disorders and treatment options remain limited in their efficacy. Understanding what types of risk factors contribute to the development of AN is essential for implementing early intervention strategies. This study describes how some of the most common psychological features of AN could be used to predict susceptibility to pathological weight loss in a well‐established animal model.

Rapid, automated, and experimenter-free touchscreen testing reveals reciprocal interactions between cognitive flexibility and activity-based anorexia in female rats

“…Susceptible and resistant rats differed on all key ABA parameters (i.e. body weight loss trajectory, food intake, running activity) as we have previously published ( Milton et al, 2018 ; Milton et al, 2022 ) (see Figure 3—figure supplement 1 ), and resistant rats also spent less time moving than susceptible rats during touchscreen sessions (see Figure 3—figure supplement 3 ). Rats that went on to be susceptible to ABA were able to learn pairwise discrimination at the same rate as rats that went on to be resistant to ABA, as demonstrated by a similar number of sessions and trials to reach the performance criterion (all p s> 0.8214; Figure 3B–D ).…”

“…Although running activity overall was significantly reduced in animals that had previously undergone cognitive testing both at baseline and during ABA (overall p=0.0002; baseline p=0.0160; ABA p<0.0001; Figure 5G ), these rats showed elevated running specifically in the hour preceding food access, known as food anticipatory activity, which is an adaptive response to scheduled feeding (overall p<0.0001; baseline p=0.0010; ABA p<0.0001; Figure 5H ). While our previous work has shown elevated food anticipatory activity to be consistently associated with resistance to ABA ( Milton et al, 2021 ; Milton et al, 2018 ; Milton et al, 2022 ), the increased food anticipatory activity at baseline for these animals suggests that an anticipatory response was carried over from the scheduled feeding conducted during touchscreen testing. Considering that exposure to cognitive training significantly increased the percentage of rats that were resistant to ABA, it was important to also examine the effects of cognitive training on ABA outcomes in only those rats susceptible to weight loss.…”

Rapid, automated and experimenter-free assessment of cognitive flexibility reveals learning impairments following recovery from activity-based anorexia in female rats

“…Susceptible and resistant rats differed on all key ABA parameters (i.e. body weight loss trajectory, food intake, RWA) as we have previously published [51, 52] and resistant rats also spent less time moving than susceptible rats during touchscreen sessions ( see Supp Fig 7 ). Rats that went on to be susceptible to ABA were able to learn PD at the same rate as rats that went on to be resistant to ABA, as demonstrated by a similar number of days, sessions and trials to reach performance criterion ( Fig 2B-G ).…”

“…Although running activity overall was significantly reduced in animals that had previously undergone cognitive testing both at baseline and during ABA (baseline p= .0160; ABA p <.0001; Fig 5G ), these rats showed elevated running specifically in the hour preceding food access, known as food anticipatory activity (FAA), which is an adaptive response to scheduled feeding (baseline p= .0010; ABA p <.0001; Fig 5H ). While our previous work has shown elevated FAA to be consistently associated with resistance to ABA [17, 51, 52], the increased FAA at baseline for these animals suggests that an anticipatory response was carried over from the scheduled feeding conducted during touchscreen testing. Considering that exposure to cognitive training significantly increased the percentage of rats that were resistant to ABA, it was important to also examine the effects of cognitive training on ABA outcomes in only those rats susceptible to weight loss.…”

Psilocybin prevents activity-based anorexia in female rats by enhancing cognitive flexibility: contributions from 5-HT1A and 5-HT2A receptor mechanisms

“…Similarly, food intake increased over successive days of ABA exposure regardless of treatment ( I ) and psilocybin did not change the average amount of food consumed across the ABA period ( p =.3290; Fig 1J ). When comparing psilocybin treated rats that were susceptible versus resistant to weight loss, it appeared that psilocybin-induced resistance was not qualitatively distinct from previous work 58, 73 , but was similarly defined by both reduced food-restriction evoked hyperactivity ( Fig 1K ) that was specific to running during the first ABA (baseline p =.7415, ABA p <.0001; Fig 1L ), increased running in anticipation of food ( p <.0001; Fig 1M ) and increased food intake across days ( Fig 1N ) and the overall ABA period ( p <.0001; Fig 1O ). Notably, the only behavioural feature that preceded improved body weight maintenance after psilocybin treatment was wheel running on the day prior to administration (Baseline Day 7; Fig 1K ).…”