The orexin component of fasting triggers memory processes underlying conditioned food selection in the rat

.To test the selectivity of the orexin A (OXA) system in olfactory sensitivity, the present study compared the effects of fasting and of central infusion of OXA on the memory processes underlying odor–malaise association during the conditioned odor aversion (COA) paradigm. Animals implanted with a cannula in the left ventricle received ICV infusion of OXA or artificial cerebrospinal fluid (ACSF) 1 h before COA acquisition. An additional group of intact rats were food-deprived for 24 h before acquisition. Results showed that the increased olfactory sensitivity induced by fasting and by OXA infusion was accompanied by enhanced COA performance. The present results suggest that fasting-induced central OXA release influenced COA learning by increasing not only olfactory sensitivity, but also the memory processes underlying the odor–malaise association. A large variety of behaviors that are essential for animal survival depend onthesensoryperceptionandprocessing of odorspresent in the natural environment. Food-search behavior, which is conditioned by hunger, is directly driven by the perception of odors associated with food (Le Magnen 1959). Several studies have demonstrated that nutritional status influences odor processing by modulating olfactory sensitivity. In particular, fasting has been shown to enhance odor detection in rats, whereas satiety reduced