Characteristics and Variability in Entrainment of Circadian Rhythms to Light in Diurnal Rodents

Abstract

Entrainment of circadian systems of vertebrates to light cycles has been studied most thoroughly in rodents. A model of non-parametric entrainment, proposed by Pittendrigh (1966) for the pupal eclosion rhythm of Drosophila, has been found adequate to explain to a certain extent entrainment of circadian pacemakers in night-active (nocturnal) rodents (Daan and Pittendrigh 1976a, b, Pittendrigh and Daan 1976a, b). In a comparative analysis of functional aspects of circadian pacemakers in four species of nocturnal rodents, Pittendrigh and Daan have shown that various pacemaker properties, such as the stability of the period (τ), the shape of the phase response curve (PRC) for light pulses, the light-dependence of τ, and the ranges of entrainment to light cycles, vary interdependently. Empirical regularities of these characteristics on an interspecific, inter- and intra-individual basis indirectly support the usefulness of the non-parametric entrainment model.