The environmental light-dark (LD) cycle entrains the central circadian clock 
located in the suprachiasmatic nucleus (SCN) of mammals. The present study 
examined the effects of disrupted LD cycles on peripheral clocks in mice housed 
under a normal 12 h light-12 h dark cycle (LD 12:12) or an ultradian LD 3:3 
cycle. Drinking behavior seemed to be free-running with a long period (26.03 h) 
under ultradian LD 3:3 cycles, in addition to light-induced direct suppression 
(masking effect). Core body temperature completely lost robust circadian rhythm 
and acquired a 6-h rhythm with a low amplitude under LD 3:3. Robust circadian 
expression of Per1, Per2, Clock and Bmal1 mRNAs was similarly flattened to 
intermediate levels in the liver, heart and white adipose tissue under LD 3:3. 
Robust circadian expression of Rev-erbα mRNA was completely damped in these 
tissues. Circadian expression of Dbp, a clock-controlled gene, was also 
disrupted in these tissues from mice housed under LD 3:3. The aberrant LD cycle 
seemed to induce the loss of circadian gene expression at the level of 
transcription, because rhythmic pre-mRNA expression of these genes was also 
abolished under LD 3:3. In addition to the direct effect of the aberrant LD 
cycle, abolished systemic time cues such as those of plasma corticosterone and 
body temperature might be involved in the disrupted expression of these 
circadian genes under LD 3:3. Our findings suggest that disrupted environmental 
LD cycles abolish the normal oscillation of peripheral clocks and induce 
internal desynchrony in mammals.