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How does melatonin control seasonal reproductive cycles?
J Arendt1, A M Symons, J English
1Department of Biochemistry, University of Surrey, Guildford, U.K.
Reproduction, Nutrition, Developpement
|January 1, 1988
Summary
The duration of melatonin secretion signals photoperiod length to the pineal gland. Seasonal variations in sensitivity and lack of circadian influence are key factors in these photoperiodic responses.
Area of Science:
- Endocrinology
- Chronobiology
- Animal Reproduction
Background:
- The pineal gland mediates photoperiod perception in many species.
- Melatonin, a pineal hormone, conveys information about day length.
- Melatonin administration can mimic artificial photoperiod effects.
Purpose of the Study:
- To investigate the role of melatonin secretion duration in photoperiodic signaling.
- To explore seasonal variations in sensitivity to melatonin.
- To determine if circadian rhythms influence melatonin's photoperiodic effects.
Main Methods:
- Experimental administration of melatonin via continuous release implants and daily feeding.
- Observation of photoperiodic responses in ewes, including oestrus induction.
- Manipulation of melatonin secretion patterns and timing.
Main Results:
- The duration of high nighttime melatonin secretion, not just its presence, signals photoperiod length.
- Continuous melatonin release or short photoperiods induce comparable short-day effects in ewes.
- A minimum duration of melatonin secretion appears critical for short-day responses.
- Seasonal variations in sensitivity to melatonin exist, affecting oestrus timing.
- Melatonin secreted with short periodicity (22 hours) is perceived as long-day, indicating a lack of circadian sensitivity variation.
Conclusions:
- Melatonin secretion duration is the primary signal for photoperiod perception.
- Photoperiodic responses are influenced by seasonal changes in sensitivity.
- Circadian variations in sensitivity to melatonin are unlikely to play a significant role.