CONSIDERING SEX IN LEARNED APPETITIVE CONTROL BY DEPRIVATION STATES

Decisions about when to eat in response to food cues in the environment are based on interoceptive energy states (i.e., hunger and fullness) and learning and remembering prior eating experiences. Experiment 1 examines how rats learn about interoceptive deprivation states and external cues as discriminative cues for sucrose reinforcement, and how consuming a high-fat, high sugar Western-style diet (WD) might alter this discriminative control. Group Dep+ was trained with both deprivation states and discrete external cues predicting reinforcement, while for Group Deprivation Noncontingent (DepN), only external cues predicted sucrose, while deprivation states did not (i.e., sucrose delivered half of the time under each deprivation state). Subsequent tests confirmed stimulus control by deprivation states for Group Dep+, and external cues for both groups. When half of the rats were switched to WD, discriminative control by deprivation states was re-assessed. Group Dep+ Chow maintained discriminative control by deprivation states, while Group Dep+ WD, showing similar performance to DepN groups trained without a deprivation state reward contingency. When external cues were again available, Group Dep+ WD recovered discriminative control, and all groups could discriminate with the compound cue. These findings indicate that WD impairs the ability to use deprivation states, but not external cues, to predict appetitive outcomes. Within our associative framework for food intake control, a diminished ability to use interoceptive state cues leads confers a weakened ability to suppress appetitive responding to food cues in the environment. These findings support our lab’s model linking Western diet, deficits in inhibition, and damage to neural substrate underlying these processes. However, this research has exclusively used male rodents. Women are more susceptible to obesity and Alzheimer’s disease. Experiment 2 begins an investigation into associative learning mechanisms involved in food intake control in female rats. As in Experiment 1, males and females were trained with deprivation state / external cue compound, and external cues were removed to assess deprivation state learning. Females exhibited higher levels of appetitive responding than males. Females outperformed males in discriminative control by deprivation states, particularly on the contingency rewarded under satiation and not deprivation. To investigate the role of hormonal status in these sex differences, Experiment 3 examined how another environmental factor, the massive use of hormonal contraceptives (i.e., 80% of women have taken), might affect these associative learning processes in food-seeking behavior. These hormonal manipulations necessitated a more time-sensitive paradigm in which we examined how deprivation states would function as contexts in the conditioning, extinction, and renewal of operant appetitive behavior. Female groups showed less contextual control by deprivation states than males. This work begins an investigation into the role of sex and hormonal status in basic learning processes involved in food intake control, but much future work is needed to understand these learning mechanisms to develop more effective strategies to treat and prevent obesity and its associated cognitive decline.