Limits of maternal entrainment of the activity rhythm in the field mouse Mus booduga

Abstract

Cycles of 12 h presence and 12 h absence of mother Mus booduga entrain the circadian rhythm in the locomotor activity of her pups such that the pups rest in her presence and are active in her absence. We wanted to determine whether this maternal entrainment arises because activity is inhibited by the mother's presence and enhanced by her absence (masking). We performed experiments with the period of the presence/absence cycles ranging from 20 to 28 h and find that only periods of 23-25 h allow entrainment while periods below 23 h and above 25 h do not allow entrainment. Our results speak against the involvement of masking and in favour of the involvement of a genuine circadian organization.