Purpose. Transcription and translation inhibitors cause circadian phase shifts in some circadian systems, suggesting that synthesis of one or more central clock proteins is critical in clock function. We have shown previously that a circadian clock in Xenopus laevis photoreceptors controls the rhythm of melatonin release. We have now tested the hypothesis that pulse treatment with the protein synthesis inhibitors, cycloheximide (CYC) or anisomycin (ANI), causes phase-dependent shifts in the melatonin release rhythm. Methods. Left-right pairs of Xenopus eye cups were maintained in individual flow-through culture chambers for five days in constant darkness and temperature (21°C). One member of each pair served as a control. Melatonin was measured by RIA as an index of circadian phase in two hour fractions throughout each experiment. Results. Both CYC and ANI delivered as three hour pulses (50 μg/ml) during the first circadian cycle in vitro caused consistent and stable phase delays that were maintained throughout the five days of culture. The magnitude of the phase delays varied as a function of circadian time with maximum effects (12 hour delays) in the subjective morning and minimum effects (2 hour delays) in subjective afternoon; night-time treatments gave intermediate effects. Conclusions. Our results demonstrate that protein synthesis inhibitors are strong phase shifting agents; a "morning" pulse can cause a complete phase reversal. Furthermore, sensitivity of the underlying clock mechanism to protein synthesis inhibition varies according to circadian time. These results are consistent with clock models in which synthesis of one or more "clock" proteins is critical in determination of circadian phase.
|Original language||English (US)|
|Journal||Investigative Ophthalmology and Visual Science|
|State||Published - Feb 15 1996|
ASJC Scopus subject areas
- Sensory Systems
- Cellular and Molecular Neuroscience