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Djungarian Hamsters: A Species with a Labile Circadian Pacemaker? Arrhythmicity under a Light-Dark Cycle Induced by Short Light PulsesDepartment of Zoology, School of Veterinary Medicine, Bünteweg 17, D-30559 Hannover, Germany; e-mail: stephan.steinlechner{at}tiho-hannover.de
Department of Zoology, School of Veterinary Medicine, D-30559 Hannover, Germany
Research Institute of Wildlife Ecology, University of Veterinary Medicine, Vienna, Austria In most cases, phase-shifting effects of light pulses are studied in animals kept in constant darkness (DD) or in animals released into DD following the stimulus. In this study, the authors exposed Djungarian hamsters (Phodopus sungorus) to short light pulses during the dark phase of a 16:8 light-dark (LD) cycle and thus obtained a type VI phase response curve. Light pulses early in the night caused phase delays of the activity onset as well as phase advances of the activity offset, whereas light pulses later in the night resulted in phase advances of the activity offset only. Acombination of two 15-min light pulses—the first one given late in the scotophase and the second given early in the dark phase of the following night—led to a strong compression of the activity phase [.alpha]. In 75% of all animals, daily rhythms were no longer visible after complete [.alpha] compression, and long-term arrhythmicity (up to 145 days) persisted despite continued exposure to an LD cycle. Because three independent output rhythms of the clock (i.e., activity, body temperature, and melatonin rhythms) were equally affected, the authors conclude that overt arrhythmicity was due not merely to disrupted output pathways but to an altered state of the central pacemaker. The authors suggest a qualitative two-oscillator model to explain this phenomenon. Their hypothesis assumes that, due to loose coupling, the pacemaker of Djungarian hamsters can be driven to a state of zero phase difference between the two oscillators, with zero amplitude of their outputs.
Key Words: arrhythmicity • Phodopus sungorus • light pulse • phase response curve • evening/morning oscillators • coupling
Journal of Biological Rhythms, Vol. 17, No. 3,
248-258 (2002) This article has been cited by other articles:
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