Novel competition test for food rewards reveals stable dominance status in adult male rats

Abstract

Social hierarchy is a potent modulator of behavior, that is typically established through overt agonistic interactions between individuals in the group. Once established, social ranks are maintained through subtler interactions allowing the redirection of energy away from agonistic interactions towards other needs. The available tasks for assessing social rank in rats allow the study of the mechanisms by which social hierarches are formed in early phases but fail to assess the maintenance of established hierarchies between stable pairs of animals, which might rely on distinct neurobiological mechanisms. Here we present and validate a novel trial-based dominancy assay, the modified Food Competition test, where established social hierarchies can be identified in the home cage of non-food deprived pairs of male rats. In this task, we introduce a small conflict in the home cage, where access to a new feeder containing palatable pellets can only be gained by one animal at a time. We found that this subtle conflict triggered asymmetric social interactions and resulted in higher consumption of food by one of the animals in the pair, which reliably predicted hierarchy in other tests. Our findings reveal stable dominance status in pair-housed rats and provide a novel tool for the evaluation of established social hierarchies, the modified Food Competition test, that is robust and easy to implement.

Multimodal cues displayed by submissive rats promote prosocial choices by dominants

“…To understand how social dominance may modulate prosocial choice, we first identified the social status within pairs of cage mate rats. For this, we used the modified food competition test, 30 a novel trial-based dominance assay, where established social hierarchies can be identified in the home cage of nonfood-deprived pairs of male rats. It has the added advantage of not inducing aggressive interactions during testing that could influence later prosocial tendencies.…”

Multimodal cues displayed by submissive rats promote prosocial choices by dominants

“…See also To understand how social dominance may modulate prosocial choice, we first identified the social status within pairs of cage mate rats. For this, we used the modified Food Competition Test 30 , a novel trial-based dominance assay, where established social hierarchies can be identified in the home cage of non-food deprived pairs of male rats. It has the added advantage of not inducing aggressive interactions during testing which could influence later prosocial tendencies.…”

“…After acclimation to the vivarium and handling by the experimenter, 23 pairs of male cage-mates rats were tested in the Food Competition Test (mFC) 30 , to identify the stable social hierarchies. This tests reliably measures already established social hierarchies by introducing a subtle conflict for the access to palatable pellets in the homecage of non food-deprived pairs of animals.…”

“…Statistics evaluating differences between dominant and submissive animals were performed in the average consumption of all days. To have a quantitative measure of the strength of the differences in hierarchy across dyads we computed a Dominance Index (DI), as previously proposed 30 . Briefly, the pellets eaten by the recipient are substracted from those of the focal and normalized by the total number of pellets eaten:…”

Involvement of prelimbic cortex neurons and related circuits in the acquisition of cooperative learning by pairs of rats

“…To have a deeper insight of the hierarchical dynamics taking place, we summed the number of successful displacements and aggressions to the social dominance index based on the work of Costa, et al, (2021). We found that follower rats showed a significantly higher level of social dominance (Fig.…”