Palatable Food and Synaptic Plasticity

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DESCRIPTION (provided by applicant): Food intake and energy balance are profoundly influenced by stress, and vice versa. However, the neural mechanisms underlying these effects are largely unknown. The long-term objective of this project is to pursue the mechanisms by which stress and food/energy balance interact. More specifically, this proposal seeks to understand how highly palatable foods provide stress relief. These mechanisms are studied using a model of limited palatable food intake in which rats with free access to food and water are given additional twice-daily access to a small amount of sucrose solution or water as a control. In this model, sucrose rats have attenuated hypothalamic-pituitary-adrenal (HPA) axis responses to stress and diminished stress-induced neuronal activation in brain reward regions. Moreover, the calories and other post-ingestive consequences of sucrose are neither sufficient nor necessary for the HPA dampening, suggesting that brain reward regions may mediate the response. The basolateral amygdala (BLA) is a key brain reward region that is also implicated in driving stress responses. Moreover, neural activity in the BLA is necessary for stress-dampening by sucrose, and genes related to synaptic plasticity are up-regulated in the BLA following a history of sucrose intake. Collectively, this suggests that palatable foods may dampen stress responses via synaptic remodeling in the BLA. Thus, the current proposal addresses the hypothesis palatable food causes synaptic reorganization in the BLA. We predict that sucrose intake increases BLA inhibitory tone, leading to less stress-excitatory output. Furthermore, we hypothesize that enhanced inhibitory tone in the BLA is due to increased drive to the intra-BLA inhibitory interneurons. The proposal tests this hypothesis in two specific aims. The first specific aim will test the hypothesis that sucrose intake increases synaptic appositions in a manner consistent with enhanced inhibition of BLA output. This aim will use anatomical approaches to identify and quantify synaptic appositions onto BLA neurons following sucrose intake. The second specific aim will test that hypothesis that sucrose-induced BLA synaptic reorganization is mediated by AMPA receptor activation of pCREB. This aim will use intra-BLA blockade of AMPA receptor activity and CREB/pCREB expression to determine whether this signaling pathway mediates sucrose-induced synaptic reorganization. PUBLIC HEALTH RELEVANCE: When under stress, many people increase their intake of highly palatable (e.g., tasty, high-sugar or high-fat) foods, presumably to help calm or comfort themselves. However, this behavior can increase body weight and contribute to the development of obesity. This project seeks to understand how palatable foods act to decrease the response to stress, thereby providing insight into the motivation to consume these foods and potentially offering new strategies for the prevention and treatment of obesity.