Socialization, and its modulation by sex, on the development and recovery of activity-based anorexia in rats.

The activity-based anorexia (ABA) animal model has been used in the laboratory to study the role of excessive physical activity in the manifestation of anorexia nervosa (AN) in humans. Factors of social context are crucial in human health and the emergence of many psychological disorders, which have also been observed in studies using different mammal species that, like human beings, set their lives in groups. In the present study, the animals' social condition was manipulated to observe the effect of socialization in ABA development, and the possible different influence of the variable sex on the phenomenon. Eighty Wistar Han rats were distributed into four male and four female groups with 10 subjects each, manipulating social conditions (group housing or social isolation) and physical activity (access or not to a running wheel). Throughout the procedure, all groups had food restricted to 1 h/day during the light period. Furthermore, ABA experimental groups with access to the running wheel had two periods of access to the wheel of 2 h each, one before and the other after the food period. In this experiment, socialized rats were less vulnerable to weight loss during the procedure, although there were no differences between the ABA groups. Moreover, social enrichment was shown to be an enabling variable of the animals' recovery after their withdrawal from the procedure, with this effect being more pronounced in females. The results in this study suggest the need to further in the analysis of the role of socialization in the development of ABA.

Activity-based anorexia alters hypothalamic POMC and orexin populations in male rats.

The objective of this study was to investigate the orexin and POMC populations in the hypothalamic nuclei of male Wistar rats after the activity-based anorexia (ABA) procedure. Four groups were established based on food restriction and activity: activity (A), ABA, diet (D) and control (C). The ABA protocol consisted of free access to a running wheel for a period of 22 h and access to food for 1 h. When the animals in the ABA group reached the ABA criterion, were sacrificed, and their brains were collected and serially sectioned. The free-floating sections were processed for orexin and POMC immunostaining. The number of orexin A-ir cells in the perifornical-dorsomedial-hypothalamus continuum (PFD) and lateral hypothalamus (LH) and the number of POMC-ir cells in the arcuate nucleus (Arc) were estimated. Data on food intake, body weight and wheel turns were also analyzed. The ABA procedure caused a significant decrease in body weight along with a significant increase in activity. Moreover, at the end of the ABA procedure, the number of POMC-ir cells decreased in the Arc in the A group, and significantly more in the ABA group, and the number of orexin A-ir positive cells decreased in the LH in D and ABA groups. The differential decrease in POMC in the ABA group emphasizes the importance of the melanocortin system in the maintenance of ABA, but more research is needed to elucidate the involvement of this peptide in the mechanism that promotes and maintains anorexia nervosa and how increased activity may interact with all these processes.

The effects of combined intravenous cocaine and ethanol self-administration on the behavioral and amino acid profile of young adult rats.

Under paradigms of combined intravenous cocaine and ethanol self-administration, the effects on behavior have been poorly explored. Numerous studies have found sex differences in amino acids profile and behavioral responses to each drug, yet few have focused on the interactions between cocaine and ethanol. The main objective of this work was to explore the acquisition and maintenance of intravenous self-administration behavior with a combination of cocaine and ethanol in male and female young adult rats. Likewise, the amino acids profile in blood plasma was quantified 48 hours after the last self-administration session. Male and female 52 days old Wistar rats were randomly assigned to one of 3 groups: i) saline control, ii) cocaine (1 mg/kg bodyweight/injection) and iii) cocaine and ethanol (1 mg + 133 mg/kg bodyweight/ injection). After 24 self-administration sessions carried out on a fixed-ratio-1 schedule, with a limit of 15 doses per session, 14 plasma amino acids were quantified by mean Capillary Electrophoresis technique. The curve of cocaine and ethanol combined self-administration was similar to that associated with cocaine administration alone, with females acquiring self-administration criterion before males. The self-administration of cocaine and ethanol altered the plasma concentration and relative ratios of the amino acid L-Tyrosine. In our intravenous self-administration model, females appeared more vulnerable to acquire abusive consumption of the cocaine and ethanol combination, which altered plasma L-Tyrosine levels.

Exercise, diet, and the reinforcing value of food in an animal model of anorexia nervosa.

Activity-based anorexia (ABA) develops when laboratory rats are subjected to a single meal per day and have access to an activity wheel for the remaining time. Here, we studied the contribution of exercise and diet to the reinforcing value of food during ABA development. Three groups of eight adult male Wistar rats were used: an ABA group with 21.5 hr (then 22 hr) of wheel access and 1 hr (then 30 min) of food access, a control group with the same time exposure to food but without exercise, and a yoked group to the ABA in terms of weight loss. Rats were daily tested on a progressive-ratio schedule to measure their motivation for food. ABA rats gradually reduced their body weight more than the food control group. Animals steadily increased their breaking points in parallel to losses in body weight, but no significant differences were found between groups. Adult rats can develop ABA, but their loss in weight neither resulted in a decrease of food intake nor in the motivation to obtain it.