Ghrelin but not nesfatin-1 affects certain forms of learning and memory in both rats and mice

• We revised our manuscript according to the reviewers' comments.
• We provided a diagram for locations of all cannula tips in Fig. 5.
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Ghrelin and nesfatin-1 are two recently discovered peptide hormones that play opposite roles in the food intake, body-weight control and energy homeostasis in both human and rodents. Beyond its appetite-control function, increasing evidence has shown that ghrelin affects multiple advanced activities in the central nervous system, including memory and emotion. Nesfatin-1 was also widely expressed in extra-hypothalamic brain regions including hippocampus and amygdala. However, the possible actions of nesfatin-1 in those important brain regions are largely unknown. In this study, we micro-infused ghrelin or nesfatin-1 into the lateral amygdala (LA) or area CA1 of the dorsal hippocampus (CA1) and investigated the immediate effects of those two peptide hormones on cognitive and affective behaviors. We found that the micro infusion of ghrelin into the LA or the CA1 interfered with certain types of learning and memory in both rats and mice, while nesfatin-1 had no effect. Our data thus suggested that although nesfatin-1 works as a functional antagonist of ghrelin in the feeding control, only ghrelin affects learning and memory.