Scheduled meal accelerates entrainment to a 6‐h phase advance by shifting central and peripheral oscillations in rats

Travelling across several time zones requires a fast adjustment of the circadian system and the differential adjustment speeds of organs and systems results in what is commonly referred as jet lag. During this transitory state of circadian disruption, individuals feel discomfort, appetite loss, fatigue, disturbed sleep and deficient performance of multiple tasks. We have demonstrated that after a 6‐h phase advance of the light–dark cycle (LD) scheduled food in phase with the new night onset can speed up re‐entrainment. In this study, we explored the possible mechanisms underlying the fast re‐entrainment due to the feeding schedule. We focused on first‐ and second‐order structures that provide metabolic information to the suprachiasmatic nucleus (SCN). We compared (i) control rats without change in LD cycle; (ii) rats exposed to a 6‐h phase advance of the LD cycle with food ad libitum; and (iii) rats exposed to the 6‐h phase advance combined with food access in phase with the new night. We found an immediate synchronizing effect of food on stomach distention and on c‐Fos expression in the nucleus of the solitary tract, arcuate nucleus of the hypothalamus, dorsomedial hypothalamic nucleus and paraventricular nucleus. These observations indicate that in a model of jet lag, scheduled feeding can favour an immediate shift in first‐ and second‐order relays to the SCN and that by keeping feeding schedules coupled to the new night, a fast re‐entrainment may be achieved by shifting peripheral and extra‐SCN oscillations. Individual exposed to a sudden shift of the light cycle requires 7–10 cycles for re‐entrainment. Scheduled food coinciding with the new night onset speeds up re‐entrainment. Here, we show that scheduled food in phase with the new night produced an immediate shift in brain areas that receive and process food‐elicited signals (red symbols), contrasting with brain regions that receive direct light input from the retina (IGL and SCN). These observations indicate that effects of scheduled feeding are mediated by first and second‐order relays to the SCN.