Disrupted light–dark cycle abolishes circadian expression of peripheral clock genes without inducing behavioral arrhythmicity in mice

Drinking behavior in mice exhibited a free-running period of 26.03 h under an ultradian light-dark cycle (LD 3:3).

• Core body temperature lost its robust daily rhythm and instead showed a 6-hour rhythm with low amplitude under LD 3:3.
• Circadian expression of key clock genes (Per1, Per2, Clock, Bmal1) was flattened to intermediate levels in the liver, heart, and white adipose tissue under LD 3:3.
• The expression of Rev-erbα mRNA was completely damped in these tissues under the disrupted light cycle.
• Rhythmic pre-mRNA expression of clock-controlled genes was abolished under LD 3:3, indicating a disruption at the transcription level.
• Abolished systemic time cues, such as plasma corticosterone and body temperature, may be involved in the disrupted expression of circadian genes.

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