Abstract

Introduction

Materials & Methods

Results

Discussion & Conclusion

References

Discussion
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Circadian rhythms of rats are known to be entrained by daily administration of melatonin (MEL). We questionned the importance of the duration of administration on entrainment, using timed infusion. Body temperature, wheel-running, and general activity were recorded on-line. Animals in constant dim red light showed a classical free-run, and vehicle infusion did not interfere with the circadian patterns. MEL (100 µg/h) infused 1h daily entrained the circadian rhythms to 24 h. A lower dose (50 µg/h) was less effective. Infusions of 8h of MEL entrained the rhythms. With a 16h infusion, MEL entrained the rhythms only in a part of the animals. With two infusions of 1h per cycle (seperated by 8h), entrainment occured when the active phase was within the shorter interval. The phase angle between onset of infusions and the rhythms varied with the infusions duration. Body temperature acrophase and running-wheel onset were delayed as the duration of infusions increased. These results suggest that chronobiotic properties of MEL are independent of the infusion duration (up to a certain range, since a 16h infusion was less effective), while the phase angle difference was affected by the infusion duration. Entrainment was also dependent of the temporal succession of short signals.

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Presentation Number SApitrosky0141
Keywords: Melatonin, Circadian rhythms, Entrainment, Rat