Orexin A in the ventral tegmental area enhances saccharin-induced conditioned flavor preference: The role of D1 receptors in central nucleus of amygdala.

In industrialized societies, food intake is largely determined by its hedonic characteristics, which can be modified by our experience via taste learning. In this learning, the hedonic value of a neutral flavor changes after its association with a motivationally significant stimulus. Experiment 1 analyzes the effect of orexin administration (53 and 107 ng) in the ventral tegmental area (VTA) on hedonic intake through acquisition of a flavor-taste preference and a flavor-taste aversion. Accordingly, animals underwent four one-bottle acquisition sessions with unilateral application of orexin-A or saline in the VTA at 10 min before a 15-min flavor intake period. Preference and aversion were tested by a two-bottle test containing the flavors used for CS+ and CS-. Results indicate that intra-VTA orexin strengthens flavor-taste conditioned flavor preference (CFP) by saccharin but does not facilitate flavor-taste aversion induced by association of a neutral flavor with the unpalatable taste of quinine. Experiment 2 examines the acquisition of a flavor-taste preference after co-administration of an effective dose of orexin-A in the VTA and of D1-like dopamine receptor antagonist SCH23390 (6 and 12 nmol) in the central nucleus of the amygdala (CeA). SCH23390 impedes the CFP strengthening observed after intra-VTA orexin administration, indicating that this effect may be mediated by dopaminergic receptors in the CeA. These data suggest that the simultaneous presentation of a flavor and a hedonically positive taste may be detected by orexinergic neurons that activate dopamine-releasing neurons of the VTA, thereby reinforcing the positive signals required to develop a taste preference.