Forced dissociation of food- and light-entrainable circadian rhythms of rats in a skeleton photoperiod

To investigate the control over drinking and feeding behavior by the light- entrainable circadian pacemaker, rats were maintained in a 12 h:12 h skelet on photoperiod for 36 days with both food and water restricted to the subje ctive day. During the restriction period most of the food and water intake was concentrated during the first 4 h of the subjective day. The subsequent release into ad lib conditions under the skeleton photoperiod or continuou s dark showed that this increased ingestion during the subjective day persi sted for up to 6-10 days. This may indicate the entrainment of a food-entra inable oscillator, which has hitherto been investigated solely in anticipat ory activity. The daily activity rhythm returned to its original phase posi tion. Thus the phase of the overt daily rhythm is eventually only determine d by the phase of the light-entrainable oscillator (LEO) but can temporaril y be influenced by the restriction of food and water access. This restricti on apparently stimulated a food-entrainable oscillator in antiphase with th e light-entrainable oscillator but failed to phase shift or entrain the lig ht-entrainable oscillator. (C) 1998 Elsevier Science Inc.