Influence of constant light and darkness, light intensity, and light spectrum on plasma melatonin rhythms in senegal sole.
Light is the most important synchronizer of melatonin rhythms in fish. This paper studies the influence of the characteristics of light on plasma melatonin rhythms in sole. The results revealed that under long-term exposure to constant light conditions (LL or DD), the total 24 h melatonin production was significantly higher than under LD, but LL and DD conditions influenced the rhythms differently. Under LL, melatonin remained at around 224 pg/ml throughout the 24 h, while under DD a significant elevation (363.6 pg/ml) was observed around the subjective evening. Exposure to 1 h light pulses at MD (mid-dark) inhibited melatonin production depending on light intensity (3.3, 5.3, 10.3, and 51.9 microW/cm(2)). The light threshold required to reduce nocturnal plasma melatonin to ML (mid-light) values was 5.3 microW/cm(2). Melatonin inhibition by light also depended on the wavelength of the light pulses: while a deep red light (lambda>600 nm) failed to reduce plasma melatonin significantly, far violet light (lambda(max)=368 nm) decreased indoleamine's concentration to ML values. These results suggest that dim light at night (e.g., moonlight) may be perceived and hence affect melatonin rhythms, encouraging synchronization to the lunar cycle. On the other hand, deep red light does not seem to inhibit nocturnal melatonin production, and so it may be used safely during sampling at night.
Oliveira
Catarina
C
Faculty of Biology, Department of Physiology, University of Murcia, Campus Espinardo, 30.100 Murcia, Spain.
Ortega
Aurelio
A
López-Olmeda
José Fernando
JF
Vera
Luisa María
LM
Sánchez-Vázquez
Francisco Javier
FJ
D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology*; D003624:Darkness; D005412:Flatfishes / Q000502:physiology*; D008027:Light; D008550:Melatonin / Q000097:blood* / Q000378:metabolism; D017440:Photoperiod; D011863:Radioimmunoassay
D008550:Melatonin