ENTRAINMENT OF AGED, DYSRHYTHMIC RATS TO A RESTRICTED FEEDING SCHEDULE

Aged rats often display abnormal circadian activity rhythms; the rhyth m amplitude is low and entrainment to light-dark cycles is irregular. The activity rhythm of young rats can be entrained by both light and n onphotic cues, specifically food availability. In young rats, entrainm ent to restricted feeding cycles does not depend on intact suprachiasm atic nuclei, the presumed anatomical location of the light-entrainable oscillator. In this study, aged rats that displayed disrupted entrain ment to light were assessed for their ability to entrain to restricted feeding schedules. Aged rats, young controls, and young suprachiasmat ic nuclei-lesioned (SCN) rats were placed on a food restriction schedu le (FR) for 14 days. Food was available for 2 h during the light phase of a 12-h light-dark cycle. Despite the absence of entrainment to lig ht/dark cycles, both SCN-lesioned and aged groups showed entrainment t o FR, with clear bouts of anticipatory activity during a period of com plete food deprivation following 2 weeks of FR. The results suggest th at the dysrhythmia of aged rats is a result of natural deterioration o f a central circadian light-entrainable pacemaker, but that a secondar y oscillator entrainable to food cycles is spared. Copyright (C) 1996 Elsevier Science Inc.