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The ability to remember contexts associated with aversive and rewarding experiences provides a clear adaptive advantage to animals foraging in the wild. The present experiments investigated whether hormonal signals released during feeding might enhance memory of recently experienced contextual information. Oleoylethanolamide (OEA) is an endogenous lipid mediator that is released when dietary fat enters the small intestine. OEA mediates fat-induced satiety by engaging type-alpha peroxisome proliferator-activated receptors (PPAR-alpha) in the gut and recruiting local afferents of the vagus nerve. Here we show that post-training administration of OEA in rats improves retention in the inhibitory avoidance and Morris water maze tasks. These effects are blocked by infusions of lidocaine into the nucleus tractus solitarii (NTS) and by propranolol infused into the basolateral complex of the amygdala (BLA). These findings suggest that the memory-enhancing signal generated by OEA activates the brain via afferent autonomic fibers and stimulates noradrenergic transmission in the BLA. The actions of OEA are mimicked by PPAR-alpha agonists and abolished in mutant mice lacking PPAR-alpha. The results indicate that OEA, acting as a PPAR-alpha agonist, facilitates memory consolidation through noradrenergic activation of the BLA, a mechanism that is also critically involved in memory enhancement induced by emotional arousal.
Campolongo et al. (Mon,) studied this question.