Synchronization of PER1 protein in parabrachial nucleus in a natural model of food anticipatory activity.

Rabbit pups represent a natural model of food anticipatory activity (FAA). FAA is the behavioral output of a putative food entrainable oscillator (FEO). It had been suggested that the FEO is comprised of a distributed system of clocks that work in concert in response to gastrointestinal input by food. Scheduled food intake synchronizes several nuclei in the brain, and the hypothalamus has received particular attention. On the contrary, brainstem nuclei, despite being among the brain structures to first receive food cues, have been scarcely studied. Here we analysed by immunohistochemistry possible oscillation of FOS and PER1 proteins through a complete 24-h cycle in the dorsal vagal complex (DVC) and parabrachial nucleus (PBN) of 7-8-day-old rabbit pups scheduled to nurse during the night (02:00 h) or day (10:00 h), and also in fasted subjects to explore the possible persistence of oscillations. We found a clear induction of FOS that peaks 1.5 h after nursing in all nuclei studied. PER1 was only synchronized in the PBN, reaching highest values 12 h after nursing. Only PER1 oscillations persisted, with a shift, in fasted subjects. We conclude that the DVC nuclei are probably more related to the transmission of food cues to other brain regions, but that the PBN participates in the integration of information essential for FAA. Our results support previous findings suggesting that the DVC nuclei, but not PBN, are not essential for FAA. We suggest that PBN is a key component of the proposed distributed system of clocks involved in FAA.