Neural circuitries for the control of feeding during novelty in male and female rats

Abstract

The influence of novelty on feeding behavior is significant and can override both homeostatic and hedonic drives due to the uncertainty of danger. The potential risks associated with consuming novel foods or consuming foods in a novel environment can lead to avoidance. While it is established that both novel foods and novel feeding environments can reduce or suppress feeding, it remains unclear how these two factors interact with each other to impact consumption and whether there are sex differences. Additionally, the neural mechanisms that underlie the impact of novelty on consumption are not well understood. This dissertation aimed to investigate the behavioral and neural mechanisms of the impact of novelty during food consumption in male and female rats. We first examined the consumption of novel and familiar foods in novel or familiar contexts for male and female rats (Chapter 2). Acutely food deprived rats were tested in either their familiar or novel context and were given two foods, one familiar and one novel. They underwent repeated consumption tests to allow us to track habituation to novelty overtime. Results indicated a robust behavioral sex difference in consumption during habituation. Males habituated to novel foods faster than females who showed suppressed consumption throughout testing. Next, we aimed to determine the neural circuitry mediating consumption of novel foods and feeding in novel environments (Chapter 3). Male and female rats were tested for consumption in either a familiar or in a novel context and were given either a familiar or novel food. Rats were perfused after testing to determine Fos induction. Results revealed increased activation in the novel context condition within several key areas: the central (CEA) and basolateral complex nuclei of the amygdala, the thalamic paraventricular (PVT) and reuniens nuclei, the nucleus accumbens (ACB), and the medial prefrontal cortex prelimbic and infralimbic areas. Additionally, novel food condition increased activation within the CEA, anterior basomedial nucleus of the amygdala, and anterior PVT. Sex differences in activation patterns were also observed within specific regions. The capsular and lateral CEA had greater activation for male groups and the anterior PVT, ACBv core, and ACB ventral shell had greater activation for female groups. We also investigated different patterns of related regions and the nature of those relationships and found that the CEA is a pivotal hub in our network. Therefore, we investigated the recruitment of specific inputs to the CEA in male and female rats during consumption of a novel food in a novel context (Chapter 4). We used a combination of retrograde tract tracing and Fos induction to determine whether PVTp, ILA, and AId neurons that send direct projections to the CEA were specifically recruited during the consumption test under novelty and whether that activation was sex specific. Results indicated that during consumption of a novel food in a novel context, connections from the PVTp to the CEA were recruited more heavily compared to rats that were consuming familiar food in a familiar context. These results suggest that projections from the PVTp to CEA may be driving the inhibition of feeding during novelty processing. Overall, this dissertation provides valuable insights into the behavioral and neural mechanisms of consumption under novelty and allows us to begin building the circuitry that underlies feeding inhibition during novelty processing.