History-Dependent Changes in Entrainment of the Activity Rhythm in the Syrian Hamster (Mesocricetus auratus)

Abstract

The authors have studied the activity rhythm of Syrian hamsters exposed to square LD cycles with a 22-h period (T22) with the aim of testing the effects of the previous history on the rhythmic pattern. To do so, sequential changes of different lighting environments were established, followed by the same LD condition. Also, the protocol included T22 cycles with varying lighting contrasts to test the extent to which a computational model predicts experimental outcomes. At the beginning of the experiment, exposure to T22 with 300 lux and dim red light occurring respectively at photophase and scotophase (LD300/dim red) mainly generated relative coordination. Subsequent transfer to cycles with approximately 0.1-lux dim light during the scotophase (LD300/0.1) promoted entrainment to T22. However, a further reduction in light intensity to 10 lux during the photophase (LD10/0.1) generated weak and unstable T22 rhythms. When, after that, animals were transferred again to the initial LD300/dim red cycles, the amplitude of the rhythm still remained very low, and the phases were very unstable. Exposure to constant darkness partially restored the activity rhythm, and when, afterwards, the animals were submitted again to LD300/dim red cycles, a robust T22 rhythm appeared. The results demonstrate history-dependent changes in the hamster circadian system because the locomotor activity pattern under the same T22 cycle can show relative coordination or unstable or robust entrainment depending on the prior lighting condition. This suggests that the circadian system responds to environmental stimuli depending on its previous history. Moreover, computer simulations allow the authors to predict entrainment under LD300/0.1 cycles and indicate that most of the patterns observed in the animals due to the light in the scotophase can be explained by different degrees of coupling among the oscillators of the circadian system.

Isochron-Based Phase Response Analysis of Circadian Rhythms

“…This hypothesis was partly supported by the observations called ''aftereffects'' in which the circadian periods between preand post-entrainment differ (41). Such a phenomenon has been observed in many organisms, for example in fruit flies (42), cockroaches (43), Bulla gouldiana (44), and hamster (45). As noted above, light input increases the TIM degradation rate in Drosophila, and thus, exerts comparable phase and period response (parameter n dT in quadrant II).…”

A Review of Human Physiological Responses to Light: Implications for the Development of Integrative Lighting Solutions

“…For example, animal studies examining phase resetting by light have found that the magnitude of a phase shift is significantly reduced after pre-exposure to a non-saturating stimulus (Nelson and Takahashi 1999). Stability of entrainment to 22 h light-dark (LD) cycles in Syrian hamsters also appears to depend on prior lighting conditions (Chiesa et al 2006). Some of these results could be explained by strong early effects of light on the circadian system leading to a reduction in photic sensitivity due to light adaptation, as proposed in a methodological examination of phase sensitivity to 12 light pulses of different durations (Comas et al 2006).…”

Circadian and Metabolic Effects of Light: Implications in Weight Homeostasis and Health

“…Chronic exposure to light (LL) is a typical strategy to induce circadian arrhythmicity in nocturnal rodents or to study the circadian free-running period in diurnal species. LL gradually increases the circadian period of motor activity rhythm (in proportion to irradiance) in nocturnal rodents (Aschoff), resulting in arrhythmicity in rat and mice ( 112 , 115 , 135 ). Besides behavioral activity, the circadian feeding and drinking rhythm are also lost under LL ( 136 , 137 ), and SCN-physiological outputs such as heart rate and CBT also exhibit arrhythmicity ( 138 ).…”