Progressive anticipation in behavior and brain activation of rats exposed to scheduled daily palatable food.

Scheduled and restricted access to a palatable snack, i.e. chocolate, elicits a brief and strong anticipatory activation and entrains brain areas related with reward and motivation. This behavioral and neuronal activation persists for more than 7days when this protocol is interrupted, suggesting the participation of a time-keeping system. The process that initiates this anticipation may provide a further understanding of the time-keeping system underlying palatable food entrainment. The aim of this study was to analyze how this entraining protocol starts and to dissect neuronal structures that initiate a chocolate-entrained activation. We assessed the development of anticipation of 5g of chocolate during the first 8days of the entrainment protocol. General activity of control and chocolate-entrained rats was continuously monitored with movement sensors. Moreover, motivation to obtain the chocolate was assessed by measuring approaches and interaction responses toward a wire-mesh box containing chocolate. Neuronal activation was determined with c-Fos in reward-related brain areas. We report a progressive increase in the interaction with a box to obtain chocolate parallel to a progressive neuronal activation. A significant anticipatory activation was observed in the prefrontal cortex on day 3 of entrainment and in the nucleus accumbens on day 5, while the arcuate nucleus and pyriform cortex reached significant activation on day 8. The gradual response observed with this protocol indicates that anticipation of a rewarding food requires repetitive and predictable experiences in order to acquire a temporal estimation. We also confirm that anticipation of palatable food involves diverse brain regions.