The circadian rhythm of rabbits in light-dark alternation, in the absence of time indicators and in time-restricted feeding
Jilge, B.
Deutsche Tierärztliche Wochenschrift 94(1): 18-23
1987
ISSN/ISBN: 0341-6593 PMID: 3545757 Document Number: 297858
During a regular 12-h light:dark schedule (LD 12:12) rabbits have a clear nycthermal rhythm of locomotor activity, food intake, water intake, hard faeces excretion and urine excretion. While some have an unimodal rhythm with a nocturnal percentage of 60 to 85%, other rabbits have a biomodal rhythm. In the absence of any external synchronizer the endogenous circadian period becomes apparent. Period length may be affected by previous environmental conditions for 10 to 75 days. After the decay of "after-effects" the circadian rhythm during continuous light conditions free-runs with a "constant" period length of more than 24 h. The internal synchronization of the 5 functions within an animal continues even in the absence of environmental time cues. Restrictive food access for 4/24 h entrains the circadian rhythms. The process of entrainment is detectable in spite of masking.