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

Abstract

The effect of restrictedfeeding (RF) cycles on the circadian locomotoractivityrhythm was studied in the nocturnalfieldmouseMusbooduga. Mice were 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, in DD, two groups of mice were subjected to RF cycles of periodicities 22 (T22) and 26 h (T26), respectively, in order to assess the limits of entrainment. The T22 and T26 RF cycles failed to produce any entrainment of the locomotoractivityrhythm, whereas some of the animals that had a free-running period (τ) close to 24 h showed stable entrainment or “relative coordination” to daily (T24) RF cycle. In LD, the locomotoractivityrhythm phase advanced under the influence of the daily RF cycle when the food presentation preceded the light to dark (L to D) transition by 5–6 h. However, when the timing of food presented in the RF cycle coincided with the L to D transition, locomotoractivityrhythm dissociated into two components. Some of the mice whose locomotoractivityrhythm disappeared in LL showed prominent meal-AA. These results suggest that RF modifies the expression of the light-entrainable pacemaker (LEP) directly and also that in the absence of the expression of the LEP, RF can induce meal-AA.