Browsing by Author "Siebert, Ursula"

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    Effect of photoperiod on the development of wheel-running activity rhythms in LEW/Ztm rats
    (1993) Siebert, Ursula; Wollnik, Franziska
    Wheel-running activity of LEW/Ztm rats is characterized by a multimodal pattern consisting of two activity bouts about 3-5 h apart. In this study we investigated the development of activity rhythms in LEW rats born and raised under three different photoperiods (LD 18:6, LD 12:12, and LD 6:18). Wheel-running activity was measured for 6 weeks in LD and for another 6 weeks in constant darkness (DD). The length of the photoperiod influenced the phase relationship between the two activity bouts only during the first week after weaning. Then, the characteristic activity pattern was established independently of the length of the photoperiod. However, development under long photoperiods (LD 18:6) resulted in a temporary increase in the level of activity and a significant shortening of the free-running period under DD. These results indicate that the multimodal activity pattern displayed by LEW rats is controlled by separate activity oscillators that establish their unique phase relationship early during development.
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    Wheel-running activity rhythms in two inbred strains of laboratory rats under different photoperiods
    (1991) Siebert, Ursula; Wollnik, Franziska
    Wheel-running activity patterns were studied in two inbred rat strains (ACI/Ztm and LEW/Ztm) under 24-h light-dark cycles with various photoperiods. The ACI strain was characterized by a unimodal activity pattern, whereas the LEW strain exhibited a multimodal activity pattern consisting of two activity bouts about 3-5 h apart. Harmonic spectral analyses and chi square periodograms revealed strain-specific differences in the characteristic rhythmic components of the activity pattern. The ACI strain showed only a strong 24-h rhythm, whereas the LEW strain showed additional rhythmic components with periods of 6, 4.8, and 4 h. Except in very young rats, these strain specific patterns were not affected by an experimental lengthening of the dark period. However, differences between the two strains were found in the free-running period and in the mode of entrainment. Our results indicate that the multimodal activity pattern of the LEW strain is not due to an ultradian bout oscillator, instead it may be the result of a unique coupling of multiple circadian oscillators.