Rhythmic secretion of melatonin by the superfused pike pineal organ: thermo- and photoperiod interaction.
In the pineal organ of the pike (Esox lucius, teleost), the rhythmic production of melatonin by the photoreceptor cells is governed by a population of endogenous circadian oscillators, synchronized and entrained by the light/dark (L/D) cycle. Production of melatonin is inhibited by light and highly increased in the dark. In the present study, isolated and superfused pike pineals were exposed to a 24-hour temperature cycle of high (10 degrees C) or low (4 degrees C) amplitude, either under L/D, or under constant darkness. Under L/D, photoperiod is the dominant entraining stimulus for the melatonin secretion rhythm. It was high during the dark phase and low during the light phase, either under cold light/warm dark or under warm light/cold dark conditions. Under a warm light/cold dark cycle, the amplitude of the melatonin rhythm was reduced. In pineals cultured at 10 degrees C, a 20 degrees C temperature pulse potentiated or reduced the night-induced rise in melatonin production when applied, during the dark or during the preceding light phase, respectively. Under constant darkness, high- or low-amplitude temperature cycles could synchronize the rhythmic production of melatonin, which peaked with the high temperature. However, the shape of the oscillation could appear modified under warm subjective-L/cold subjective-D, depending on the experimental conditions. Finally, the rhythmic release of melatonin synchronized by a temperature cycle under constant darkness was no longer observed after removal of the external zeitgeber. The present study provides direct evidence that the pineal acts as a photothermotransducer.
Falcón
J
J
Laboratoire de Neurobiologie et Neuroendocrinologie Cellulaires, URA CNRS 1869, Université de Poitiers, France.
Bolliet
V
V
Ravault
J P
JP
Chesneau
D
D
Ali
M A
MA
Collin
J P
JP
D000818:Animals; D017859:Esocidae / Q000502:physiology*; D006358:Hot Temperature; D008550:Melatonin / Q000378:metabolism*; D010507:Periodicity; D017440:Photoperiod; D010870:Pineal Gland / Q000378:metabolism*
D008550:Melatonin