Multimodal cues displayed by submissive rats promote prosocial choices by dominants.

Animals often display prosocial behaviors, performing actions that benefit others. Although prosociality is essential for social bonding and cooperation, we still know little about how animals integrate behavioral cues from those in need to make decisions that increase their well-being. To address this question, we used a two-choice task where rats can provide rewards to a conspecific in the absence of self-benefit and investigated which conditions promote prosociality by manipulating the social context of the interacting animals. Although sex or degree of familiarity did not affect prosocial choices in rats, social hierarchy revealed to be a potent modulator, with dominant decision-makers showing faster emergence and higher levels of prosocial choices toward their submissive cage mates. Leveraging quantitative analysis of multimodal social dynamics prior to choice, we identified that pairs with dominant decision-makers exhibited more proximal interactions. Interestingly, these closer interactions were driven by submissive animals that modulated their position and movement following their dominants and whose 50-kHz vocalization rate correlated with dominants' prosociality. Moreover, Granger causality revealed stronger bidirectional influences in pairs with dominant focals and submissive recipients, indicating increased behavioral coordination. Finally, multivariate analysis highlighted body language as the main information dominants use on a trial-by-trial basis to learn that their actions have effects on others. Our results provide a refined understanding of the behavioral dynamics that rats use for action-selection upon perception of socially relevant cues and navigate social decision-making.

Stimuli predicting high-calorie reward increase dopamine release and drive approach to food in the absence of homeostatic need.

Animals and humans are motivated to consume high-fat, high-calorie foods by cues predicting such foods. The neural mechanisms underlying this effect are not well understood.Objective: We tested the hypothesis that cues paired with a food reward, as compared to explicitly unpaired cues, increase rats' food-seeking behavior by potentiating dopamine release in the nucleus accumbens, and that this effect would be less evident under satiety.Methods: We used a simple discriminative stimulus task and electrochemical recordings of dopamine release in freely moving rats.Results: We found that both food-predictive cue and hunger increased conditioned approaches to the receptacle (food-seeking behavior indicated by movement to the food receptacle). In addition, we observed dopamine release when the food-predictive cue (but not the unpaired cue) was presented, independent of hunger or satiety. Finally, we found a positive correlation between dopamine release amplitude and the number of conditioned approaches to the food receptacle in the sated condition, but not in the hungry condition.Discussion: Our results suggest that dopamine could drive seeking behavior for calorie-dense food in absence of homeostatic need, a core aspect of binge eating disorders.

Endogenous opioids in the nucleus accumbens promote approach to high-fat food in the absence of caloric need.

When relatively sated, people (and rodents) are still easily tempted to consume calorie-dense foods, particularly those containing fat and sugar. Consumption of such foods while calorically replete likely contributes to obesity. The nucleus accumbens (NAc) opioid system has long been viewed as a critical substrate for this behavior, mainly via contributions to the neural control of consumption and palatability. Here, we test the hypothesis that endogenous NAc opioids also promote appetitive approach to calorie-dense food in states of relatively high satiety. We simultaneously recorded NAc neuronal firing and infused a µ-opioid receptor antagonist into the NAc while rats performed a cued approach task in which appetitive and consummatory phases were well separated. The results reveal elements of a neural mechanism by which NAc opioids promote approach to high-fat food despite the lack of caloric need, demonstrating a potential means by which the brain is biased towards overconsumption of palatable food.