The orexigenic force of olfactory palatable food cues in sated rats

Background: Environmental cues recalling palatable foods are ubiquitous and motivate eating beyond metabolic need, yet the timing of this response and whether it can develop towards a non-palatable readily available food remain elusive. Although there is increasing evidence indicating that external stimuli in the olfactory modality can communicate with the major hub in the feeding neurocircuitry, the hypothalamic arcuate nucleus (Arc), the identity of hypothalamic substrates has been only partially uncovered. Methods: Using a palatable home-cage hidden-food paradigm, we investigate the ability of olfactory food cues to promote chow overconsumption in sated male rats, together with their impact on meal pattern. We likewise explore, by means of an immediate early gene marker, the neural mechanisms involved, including the possible engagement of the orexigenic ghrelin system. Results: Olfactory detection of a familiar palatable food shifts diurnal patterns towards an increase in meal frequency to cause persistent overconsumption of chow in sated conditions. In line with the orexigenic response observed, sensing the palatable food in the environment stimulates food-seeking and risk-taking behavior, and also triggers release of active ghrelin. Olfactory food cues recruit intermingled populations of cells embedded within the feeding circuitry within the Arc, including, notably, those containing the ghrelin receptor, even when food is not available for consumption. Conclusions: These data demonstrate leverage of ubiquitous food cues, not only for palatable food-searching, but also to powerfully drive food consumption in ways that resonate with heightened hunger, for which the orexigenic ghrelin system is implicated.