The suprachiasmatic nucleus participates in food entrainment: a lesion study.

Daily feeding schedules entrain temporal patterns of behavior, metabolism, neuronal activity and clock gene expression in several brain areas and periphery while the suprachiasmatic nucleus (SCN), the biological clock, remains coupled to the light/dark cycle. Because bilateral lesions of the SCN do not abolish food entrained behavioral and hormonal rhythms it is suggested that food entrained and light entrained systems are independent of each other. Special circumstances indicate a possible interaction between the light and the food entrained systems and indicate modulation of SCN activity by restricted feeding. This study explores the influence of the SCN on food entrained rhythms. Food entrained temporal profiles of behavior, core temperature, corticosterone and glucose, as well as Fos and PER1 immunoreactivity in the hypothalamus and corticolimbic structures were explored in rats bearing bilateral SCN lesions (SCNX). In SCNX rats food anticipatory activity and the food entrained temperature and corticosterone increase were expressed with earlier onset and higher values than in intact controls. Glucose levels were lower in SCNX rats in all time points and SCNX rats anticipation to a meal induced higher c-Fos positive neurons in the hypothalamus, while a decreased c-Fos response was observed in corticolimbic structures. SCNX rats also exhibited an upregulation of the PER1 peak in hypothalamic structures, especially in the dorsomedial hypothalamic nucleus (DMH), while in some limbic structures PER1 rhythmicity was dampened. The present results indicate that the SCN participates actively during food entrainment modulating the response of hypothalamic and corticolimbic structures, resulting in an increased anticipatory response.