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6-Sulphatoxymelatonin secretion in different locomotor activity types of the blind mole rat Spalax ehrenbergi
R Ben-Shlomo1, E Nevo, U Ritte
1Institute of Evolution, University of Haifa, Israel.
Abstract:
6-Sulphatoxymelatonin (aMT6S) excretion was examined in the urine of rhythmic and arrhythmic blind subterranean mole rats (Spalax ehrenbergi) to test the correlation between melatonin secretion (as represented by aMT6S) and variability in circadian locomotor activity. Activity pattern was tested in four males, first for a week under short photoperiod [light:dark (LD) 10:14], followed by 10 days in constant darkness (DD). After several months the experiment was repeated under long photoperiod (LD 14:10), followed by DD conditions. Under LD conditions all animals exhibited aMT6S excretion during the dark phase, with a decline just before the onset of light. No correlation was found between activity pattern and melatonin secretion. The animal with the highest melatonin secretion both under LD and DD had an arrhythmic locomotor pattern. The results suggest that in mole rats melatonin secretion and circadian locomotor activity are controlled by two different mechanisms. There were large differences in the aMT6S levels among individuals, suggesting the importance of duration of melatonin secretion over amplitude for gonadal development and thermoregulatory changes. During summer, i.e., before the breeding season, the animals keep a more stable aMT6S secretion than in winter, and the amplitude of secretion is higher under DD vs. LD conditions.
Insights
Melatonin secretion (aMT6S) and circadian activity in blind mole rats are independently controlled. High melatonin excretion did not correlate with rhythmic activity, suggesting separate regulatory mechanisms in this species.
Area of Science:
- Chronobiology
- Animal Physiology
- Endocrinology
Background:
- Circadian rhythms are crucial for physiological regulation.
- Melatonin is a key hormone in synchronizing circadian rhythms.
- The relationship between melatonin secretion and activity patterns in subterranean mammals is not well understood.
Purpose of the Study:
- To investigate the correlation between 6-Sulphatoxymelatonin (aMT6S) excretion and circadian locomotor activity in blind subterranean mole rats (Spalax ehrenbergi).
- To determine if melatonin secretion influences activity patterns or if they are independently regulated.
Main Methods:
- Urine samples were collected from four male mole rats under varying light:dark (LD) and constant darkness (DD) conditions.
- Urinary 6-Sulphatoxymelatonin (aMT6S) levels were measured as an indicator of melatonin secretion.
- Locomotor activity patterns were monitored to assess rhythmicity and variability.
Main Results:
- All animals exhibited aMT6S excretion during the dark phase under LD conditions.
- No significant correlation was found between activity pattern (rhythmic vs. arrhythmic) and melatonin secretion levels.
- The mole rat with the highest melatonin secretion displayed an arrhythmic locomotor pattern.
Conclusions:
- Melatonin secretion and circadian locomotor activity in mole rats appear to be regulated by distinct mechanisms.
- Individual variations in aMT6S levels suggest duration, rather than amplitude, may be critical for physiological functions.
- Melatonin secretion stability varies seasonally, with higher amplitude under constant darkness compared to light-dark cycles.