Effects of restricted feeding cycle on the locomotor activity rhythm in the mouse Mus booduga

The effect of restricted feeding (RF) cycles on the circadian locomotor act ivity rhythm was studied in the nocturnal field mouse Mus booduga. Mice wer e presented with a 2-h meal schedule every 24 h in continuous darkness (DD) , in continuous light (LL), and in a light-dark (LD) cycle. Additionally, i n DD, two groups of mice were subjected to RF cycles of periodicities 22 (T 22) and 26 h (T26), respectively, in order to assess the limits of entrainm ent. The T22 and T26 RF cycles failed to produce any entrainment of the loc omotor activity rhythm, whereas some of the animals that had a free-running period (tau) close to 24 h showed stable entrainment or "relative coordina tion" to daily (T24) RF cycle. In LD, the locomotor activity rhythm phase a dvanced under the influence of the daily RF cycle when the food presentatio n preceded the light to dark (L to D) transition by 5-6 h. However, when th e timing of food presented in the RF cycle coincided with the L to D transi tion, locomotor activity rhythm dissociated into two components. Some of th e mice whose locomotor activity rhythm disappeared in LL showed prominent m eal-AA. These results suggest that RF modifies the expression of the light- entrainable pacemaker (LEP) directly and also that in the absence of the ex pression of the LEP, RF can induce meal-AA. (C) 2000 Elsevier Science Inc. All rights reserved.