Differential effects of dark pulses on the two components of split circadian activity rhythms in golden hamsters

Different free-running periods in split components of the circatidal rhythm in the shore crab Carcinus maenas

“…These oscillators may themselves be composed of a large number of oscillatory components, but may be regarded functionally as discrete units. The splitting of circadian clocks into 2 separate components is well documented, particularly for the circadian rhythm of the golden hamster Mesocncetus aura tus (Pittendrigh & Daan 1976, Shibuya et al 1980, Boulos & Morin 1982, Lees et al 1983, Mrosovsky & Hallonquist 1986) but also in other species (Lees et al 1983). As in the present study, this splitting usually occurs only under abnormal circumstances, such as in constant light (Pittendrigh 1974, Pittendngh & Daan 1976), or after induced changes in hormone levels (Morin & Cummings 1981).…”

“…It is not clear from the work to date whether these components could be considered as separate oscillators, as is the case with the separate components of circadian rhythrnicity in Mesocncetussp. (Pittendrigh & Daan 1976, Lees et al 1983, Mrosovsky & Hallonquist 1986 or whether they are both controlled by a single oscillator. If there were 2 oscillators controlling the 2 split components it would be expected that they would, occasionally, free-run with different periods, as was observed with the multiple circalunadian oscillators controlling circatidal rhythmicity in Helice sp.…”

The Two-Oscillator Circadian System of Tree Shrews (Tupaia belangeri) and Its Response to Light and Dark Pulses

“…At the same time, two new components arose, which finally made up the components of the split rhythm (see also Hoffmann, 1969Hoffmann, , 1971. In hamsters, Pittendrigh and Daan ( 1976b) (Boulos and Rusak, 1982b;Lees et al, 1983), light pulses (Earnest and Turek, 1986), and carbachol injections (Meijer et al, 1988 (Underwood, 1981) and in the elegant pacemaker transplantation experiments in cockroaches by Page (1983). However, there appears to be a short time zone of a few hours following each of the two activity bands where the other component does not express itself in activity (see blow-up in Fig.…”

“…This phenomenon of &dquo;splitting&dquo; typically occurs in bright continuous illumination (LL) in nocturnal species (Syrian hamster- Pittendrigh, 1974;rat-Boulos and Terman, 1979) and in dim LL in diurnal species (ground squirrels -Pittendrigh, 1960; Swade and Pittendrigh, 1967;Pohl, 1972;tree shrew-Hoffmann, 1969). Splitting has been most intensively investigated in the Syrian hamster Earnest and Turek, 1982;Ellis et al , 1982;Turek et al, 1982;Lees et al, 1983;Boulos and Morin, 1986). At the onset of splitting, two components of the circadian activity rhythm often run temporarily with different frequencies, until they reach about 180° antiphase, and a new stable phase relationship is established.…”

c-Fos Expression in the Brains of Behaviorally “Split” Hamsters in Constant Light: Calling Attention to a Dorsolateral Region of the Suprachiasmatic Nucleus and the Medial Division of the Lateral Habenula

“…Pittendrigh and Daan (1976) were the first to systematically describe this phenomenon in hamsters and called it "splitting," citing it as evidence that the rodent circadian clock must be a complex pacemaker consisting of 2 mutually coupled oscillators. Further experimental analyses revealed that circadian rhythms of drinking (Shibuya et al, 1980), body temperature (Pickard et al, 1984), and luteinizing hormone secretion (Swann and Turek, 1985) could also split and that the 2 oscillators underlying the split state appeared to be functionally equivalent (Lees et al, 1983;Boulos and Morin, 1985;Meijer et al, 1988;Meijer et al, 1990). Pickard and Turek (1982) suggested that the split oscillators might correspond to the left and right sides of the bilaterally paired SCN, based on their observation that unilateral SCN lesions in split hamsters abolished behavioral splitting and produced a single bout of locomotion.…”