Sex differences in habituation to novel food and novel context

Abstract

Novel foods and novel environments both impact consumption, but their interaction is poorly understood, especially how this interaction varies across habituation and by sex. Prior studies found that placement in a novel context suppressed consumption of a novel food across habituation in a two-choice paradigm with familiar food, and there were neural correlates in the amygdala of consumption under novelty during the first exposure. The current study extended these findings using a paradigm with only a novel food. We placed adult male and female rats in a novel or familiar environment and measured their consumption of a novel, palatable food across four habituation sessions and a final test session. We collected brain tissue after the test session to measure Fos induction with immunohistochemistry during the final exposure to novelty. Fos induction was measured in the central nucleus of the amygdala and the nuclei of the basolateral complex. We found that placement in a novel context suppressed consumption of a novel food at every time point. During the test, Fos induction was elevated in groups tested in the novel context in the medial part of the central nucleus and all nuclei of the basolateral complex except the anterior part of the basolateral nucleus despite the test being the fifth exposure to the novel stimuli. Parts of the central nucleus and nuclei of the basolateral complex showed sex-specific elevations in Fos induction in females regardless of the testing context. Correlations of Fos induction across regions showed that novel context tested groups had similarly elevated Fos induction throughout the central nucleus and basolateral complex, unlike their familiar context tested counterparts. Females had more correlations of Fos induction than males regardless of testing context. These results demonstrated that habituation to eating a novel food is prolonged in a novel environment compared to a familiar environment. Notably, Fos induction remained high in the novel context groups after multiple exposures to novelty. These behavioral and neural findings demonstrate that unfamiliar environments remain salient throughout the process of habituation.