Genetic analysis of circadian and ultradian locomotor activity rhythms in laboratory rats.

Obvious differences exist in the daily activity patterns of the LEW/Ztm and ACI/Ztm inbred strains of Laboratory rats. The inbred strain ACII Ztm shows a clear 24-h rhythm of locomotor activity. The activity pattern of the LEW/Ztm strain, however, is characterized by ultradian rhythms of 4and 4.8-h periods. Genetic analysis of crosses between the two strains was used to examine the relative amounts of additive genetic and dominance effects for traits associated with circadian and ultradian rhythms of locomotor activity. The measured variables of the timing mechanism (amplitude c; acrophase I(); 24-, 4.8-, and 4-h spectral estimates) exhibited substantial heritability, with general dominant-recessive modes of inheritance and the associated dominance variance.