Mouse model for morningness/eveningness.

Human morning/evening preferences has recently been reported to be associated with polymorphism of the 3' flanking region of the Clock gene, which was the first identified mammalian circadian clock gene. We recorded body temperature, spontaneous activity, electroencephalogram and electromyogram for 48 h in mice with Jcl:ICR genetic background and homozygous for the Clock mutation (Cl/Cl on Jcl:ICR). In both wild-type and Cl/Cl on Jcl:ICR, body temperature, activity, wake and sleep were completely entrained to LD cycle. However, phases of the rhythm for body temperature, activity and wake duration in the Cl/Cl on Jcl:ICR were about 2 h delayed in comparison with the wild-type. This study has provided further evidence on the close relationship between human morning/evening preference and the molecular basis of circadian clock system, and has suggested that Cl/Cl on Jcl:ICR is useful for an animal model for human morning/evening preference.