Signaling through the ghrelin receptor modulates hippocampal function and meal anticipation in mice

The ability to predict a particular meal is achieved in part by learned associations with stimuli that predict nutrient availability. Ghrelin is an orexigenic peptide produced by both the gut and brain that rises before anticipated meals and it has been suggested that pre-prandial ghrelin increases may act as a signal to predict meal delivery. Here, we used wild type and ghrelin receptor deficient mice to test the hypothesis that ghrelin signaling is necessary for the processing of emotionally relevant stimuli, spatial learning and habituated feeding responses. We tested spatial and fear-related memory with the Morris water maze and step through passive avoidance tests, respectively and utilized food anticipatory activity to monitor habituated feeding responses following two weeks of a meal feeding paradigm. Our results indicate that ghrelin signaling modulates spatial memory performance and is necessary for the development of food anticipatory activity. Collectively, these results suggest that ghrelin receptor signaling is necessary for adaptations in the anticipatory responses that accompany restricted feeding.