Impact of hunger state on palatable food-cue associative learning and consumption in adult and adolescent male and female rats

Abstract

Hunger and palatability modulate food intake through homeostatic and hedonic mechanisms that can work either independently, or in tandem. Both also influence food-seeking and learning about cues for food. Our prior work suggested that hunger and satiety impact motivation for palatable food differently in males and females. Sensitivity to food rewards also differs between adolescence and adulthood. Adolescents exhibit heightened motivation to consume and work for palatable food compared to adults. However, sex and age differences in palatable food motivation under sated and hungry conditions have not been explored. Here, we examined how rats consume and learn about palatable food. To assess cue-food associative learning and memory, rats underwent Pavlovian conditioning, extinction, and testing to assess the renewal of conditioned behavior. Male and female adult and adolescent Sprague Dawley rats were either food restricted (85% ad libitum body weight) or had ad libitum access to regular chow (n=8 per group). Rats learned palatable food-cue associations across 8 acquisition sessions, followed by cue-only presentations for 4 extinction sessions in a different context. They were then tested for renewal of conditioned responding (time spent at the food cup) to the food cue in the acquisition compared to extinction context. Before learning and after renewal testing, rats were tested for consumption of palatable food and chow in their home cage (1hr test/day per food). We found that adults and adolescents of both sexes were able to learn, extinguish, and renew conditioned responding regardless of hunger. Adolescents consistently had higher responding than adults across the learning and memory protocol. During consumption testing, females of both ages ate more palatable food than males, particularly when sated. Adolescent consumption was dependent on hunger state. Sated adolescents ate more palatable food than adults, and both sated adults and adolescents showed a preference for palatable food over chow. Food-deprived adolescents and adults ate similar amounts of chow, but only adults showed a preference for palatable food over chow. Palatable food consumption and conditioned responding during early acquisition training for that same food were positively correlated, indicating that hunger and satiety similarly impact palatable food-cue learning and consumption. Overall, these findings suggest that physiological hunger is not a prerequisite for successful associative learning and memory during adolescence or adulthood, and that female sensitivity to palatable food is present during adolescence.