EFFECTS OF LIGHT ON THE CIRCADIAN ACTIVITY RHYTHM OF DJUNGARIAN HAMSTERS (PHODOPUS SUNGORUS) WITH DELAYED ACTIVITY ONSET

Mar 9, 2010Chronobiology international

Light's effects on daily activity patterns in Djungarian hamsters with late activity start times

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Abstract

Djungarian hamsters with delayed activity onset (DAO) exhibit a significantly longer free-running period of their circadian rhythm compared to wild-type hamsters in constant darkness.

DAO hamsters showed a free-running period that was longer in constant darkness than that of wild-type hamsters.
Increasing light intensity lengthened the free-running period in both hamsters, but not at the same rate.
In constant light, the free-running period did not differ between DAO and wild-type hamsters.
The robustness of the circadian activity rhythm was highest in constant darkness and decreased in constant light, with no phenotype differences.
Arrhythmicity was low in constant darkness but significantly higher in constant light, particularly in wild-type hamsters.
Light pulses induced phase delays at CT14 and phase advances at CT22, with advances being stronger than delays.

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A number of Djungarian hamsters (Phodopus sungorus) of our institute show activity patterns that seem incompatible with proper adjustment to a periodic environment. The activity onset of those animals is continuously delayed, whereas the activity offset is stably coupled to "lights-on", leading to compression of activity time. A series of experiments was conducted to evaluate the possible causes of the deteriorated ability of DAO (delayed activity onset) hamsters to synchronize. Thus, we investigated the properties of the endogenous circadian rhythm plus parametric and non-parametric light effects on hamsters of DAO and Wild type (WT) phenotypes. Free-running rhythms were studied in constant darkness (DD) or constant light (LL) of different intensities (1, 10, 100 lux). To investigate photic phase responses, hamsters were kept in DD and exposed to light pulses (100 lux, 15 min), at circadian time (CT) CT14 and CT22. Differences were verified statistically by ANOVA. Light intensity exerted significant effect on the free-running period (tau). In DD, tau was significantly longer in DAO than WT hamsters. With increasing light intensity, tau lengthened in both phenotypes, though not at a similar rate. In 10 and 100 lux LL, however, tau did not differ between the two phenotypes. The robustness of the circadian activity rhythm was highest in DD and decreased in LL. No differences between phenotypes were noted. The percentage of arrhythmic animals was low in DD, but remarkably high in LL, and always higher in WT hamsters. The total amount of activity/day was highest in DD; DAO hamsters were less active than WT hamsters under each lighting condition. Light pulses induced phase delays when applied at CT14 and phase advances at CT22, with advances being stronger than delays. Also at CT14, the response of the activity onset was stronger than the activity offset. The opposite was observed at CT22. At CT14, the phase response did not differ between the phenotypes. However, at CT22 the phase advance was significantly weaker in DAO than WT hamsters despite their longer tau. The results provide further evidence that the distinct activity pattern of DAO hamsters is due to an altered interaction between the circadian clock and photic zeitgeber.

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EFFECTS OF LIGHT ON THE CIRCADIAN ACTIVITY RHYTHM OF DJUNGARIAN HAMSTERS (PHODOPUS SUNGORUS) WITH DELAYED ACTIVITY ONSET

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