Restricted feeding schedules phase shift daily rhythms of c-Fos and protein Per1 immunoreactivity in corticolimbic regions in rats

Entrainment by daily restricted feeding schedules (RFS) produces food anticipatory activity (FAA) which involves motivational processes which may be regulated by corticolimbic structures and the nucleus accumbens. The present study aimed first to determine whether corticolimbic structures participate in the expression of FAA, therefore c-Fos immunoreactivity (Fos-IR) was employed as marker of neuronal activity. The second goal was to characterize diurnal rhythms of the clock protein protein Per1 (PER1) in corticolimbic structures and to determine the influence of RFS on the diurnal temporal pattern. Rats were maintained under RFS with food access for 2 h daily, a control group was fed ad libitum. Food entrainment produced a pattern of increased Fos-IR during FAA and after mealtime in the two sub-regions of the nucleus accumbens (ACC), in the basolateral and central amygdala, in the bed nucleus of the stria terminalis (BNST), in the lateral septum (LS), in the prefrontal cortex (PFC), and in the paraventricular thalamic nucleus (PVT). No increased Fos-IR was observed in the hippocampus. Under ad libitum conditions all structures studied showed daily oscillations of PER1, excluding both amygdalar nuclei and the PFC. RFS shifted and set the daily peaks at zeitgeber time (ZT) 12 for both sub-regions in the accumbens, the hippocampus, lateral septum and PFC. RFS enhanced the amplitude at ZT12 of the BNST and shifted the peak of the PVT to ZT6. No changes were observed in the amygdalar nuclei. Present data indicate that cellular activation of corticolimbic structures is associated with behavioral events related to food anticipatory activity and that mealtime is a relevant signal that shifts daily oscillations of PER1 in corticolimbic structures. Data suggest a relevant role of corticolimbic structures as oscillators for FAA.