Dark pulses affect the circadian rhythm of activity in hamsters kept in constant light

Abstract

We compared the effects of light pulses in constant darkness (DD) and dark pulses in constant light (LL) on the free-running rhythm of locomotor activity in male golden hamsters. Light pulses yielded advances, delays, or no change in the rhythm of activity. These data conform to a typical phase-response curve; this curve was unaffected by pinealectomy. Dark pulses occurring either late in the subjective night or early in the subjective day had little effect. In contrast, dark pulses occurring either late in the subjective day or early in the subjective night altered the rhythm in one of three ways: advance of the rhythm; splitting into two components; or induction of a new component, in phase with the pulse. Because dark pulses in LL perturb the circadian system in a different manner than do light pulses in DD, they may have value in identifying heretofore unknown aspects of circadian systems. As such, the use of dark pulses to perturb circadian rhythmicity will be a useful tool in examining the formal properties of circadian systems.

Resetting of the hamster circadian system by dark pulses

“…Our PRC for the 3-h dark pulse is in general agreement with the previous findings of other laboratories that used 2-or 3-h dark pulses (5,16,23,29,30). We observed slightly larger phase advances, which occurred slightly earlier (CT 4 -8) than in the above-mentioned studies (CT 9 -12).…”

“…For example, exposure of bats, mice, and hamsters kept in constant light (LL) to pulses of darkness for 2-6 h phase-dependently phase resets their behavioral activity rhythms in a characteristic pattern of temporal sensitivity that differs markedly from photic PRCs (4,5,10,16,34). In hamsters, dark pulses evoke phase advances during the middle to late subjective day and phase delays when given at late subjective night and early subjective day (5,16). Consequently, dark-pulse PRCs were originally hypothesized to be the mirror image of photic PRCs (5,34).…”

Exercise elicits phase shifts and acute alterations of melatonin that vary with circadian phase

“…analyses of the circadian locomotor rhythms of nocturnal rodents revealed that exposure to single nonphotic stimuli, such as pulses of induced activity during constant darkness (25,26,28,31) or pulses of darkness during constant light, which also induce increased activity (7,16), results in phase shifts that are dependent on the timing of stimulus presentation. Detailed studies of the nonphotic component of the rodent circadian system have led to an understanding of the types of stimuli that lead to phase shifts and/or alterations of photic entrainment, as well as model systems for examining the neural pathways and genes involved in these processes.…”

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

“…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.…”