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Melatonin is rhythmic in newborn seals exposed to continuous light
J J Aarseth1, T J Van't Hof, K-A Stokkan
1Department of Arctic Biology and Institute of Medical Biology, University of Tromsø, Norway. jojorem@fagmed.uit.no
Summary
Newborn seals exhibit high plasma melatonin levels with pronounced daily rhythms, suggesting maternal influence and circadian control. This may be a fetal strategy to impact maternal blood flow during diving.
Area of Science:
- Marine Mammal Physiology
- Endocrinology
- Circadian Biology
Background:
- Newborn seals possess unusually large and active pineal glands.
- Melatonin, a hormone regulated by light, plays a crucial role in circadian rhythms.
Purpose of the Study:
- To investigate the effect of light and darkness on plasma melatonin levels in newborn seals.
- To understand the relationship between melatonin rhythmicity and the large pineal gland in seals.
- To explore the potential maternal influence on fetal melatonin levels.
Main Methods:
- Measuring plasma melatonin concentrations in captive newborn harp and hooded seals under varying light conditions (continuous light, darkness, natural light-dark cycle).
- Analyzing melatonin rhythmicity in relation to environmental light cycles.
- Measuring daytime plasma melatonin in fetal hooded seals and their mothers.
Main Results:
- Newborn seals displayed extremely high plasma melatonin levels (0.8-62.3 ng/ml) with pronounced rhythmicity.
- Melatonin rhythms persisted under continuous light, continuous darkness, and natural light-dark cycles, closely following the light-dark cycle.
- Fetal melatonin levels were higher than maternal levels, indicating a transfer of melatonin from fetus to mother.
Conclusions:
- Melatonin rhythmicity in newborn seals is primarily under circadian control, potentially influenced by maternal factors during gestation.
- The high melatonin levels and large pineal gland in newborn seals might be a temporary fetal adaptation to influence maternal blood supply for diving.
- This study highlights a unique endocrine strategy in marine mammals during early development.