When food is restricted to a few hours daily, animals increase their locomotor activity 2-3 hours preceding food access, which has been termed food anticipatory activity (FAA). Food entrainment has been linked to the expression of a circadian food entrained oscillator (FEO) and the anatomical substrate of this oscillator seems to depend on diverse neural systems and peripheral organs. Previously we have described a differential involvement of hypothalamic nuclei in the food entrained process. For the food-entrainment pathway the communication between the gastrointestinal system and central nervous system is essential. The visceral synaptic input to the brain stem arrives to the dorsal vagal complex and is transmitted directly from the nucleus of the solitary tract (NST) or via to the parabrachial nucleus (PBN) to hypothalamic nuclei and other areas of the forebrain. The present study was aimed to characterize the response of brain stem structures in food entrainment. The expression of c-Fos immunoreactivity (c-Fos-IR) was used to identify neuronal activation. Present data show an increased c-Fos-IR following mealtime in all brain stem nuclei studied. Food entrained temporal patterns did not persist under fasting conditions indicating a direct dependence of feeding elicited signals for this activation. Because NST and PBN exhibited a different and increased response from that expected after a regular meal, we suggest that food-entrainment promotes ingestive adaptations that lead to a modified activation in these brain stem nuclei, e.g. stomach distension. Neural information provided by these nuclei to the brain, may provide the essential entraining signal for FEO.