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The Influence of Various Irradiances of Artificial Light, Twilight, and Moonlight on the Suppression of Pineal Melatonin Content in the Syrian Hamster
Author(s) -
Brainard George C.,
Richardson Bruce A.,
Hurlbut Edward C.,
Steinlechner Stephan,
Matthews Susan A.,
Reiter Rüssel J.
Publication year - 1984
Publication title -
journal of pineal research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.881
H-Index - 131
eISSN - 1600-079X
pISSN - 0742-3098
DOI - 10.1111/j.1600-079x.1984.tb00202.x
Subject(s) - melatonin , moonlight , photoperiodism , darkness , pineal gland , nocturnal , endocrinology , medicine , biology , zoology , botany , ecology
The purpose of the present studies using artificial light was to determine how the timing and duration of exposure influence the light‐induced suppression of pineal melatonin levels in hamsters. An 8‐min exposure to 0.186 μW/cm 2 of cool white fluorescent light caused a continued depression of pineal melatonin even when animals were returned to darkness. In addition, the pineal gland does not appear to change its sensitivity to light throughout the night. A 20‐min exposure to 0.019 μW/cm 2 of cool white fluorescent light did not significantly suppress pineal melatonin during any time of the melatonin peak, whereas a 20‐min exposure to 0.186 μW/cm 2 was capable of always suppressing melatonin. Furthermore, increasing the duration of 0.019‐μW/cm 2 exposure to 30, 60, 120, or 180 min does not increase the capacity of this irradiance to depress melatonin. Similar to artifical light, natural light has a variable capacity for suppressing nocturnal levels of pineal melatonin. Twilight irradiances of 0.138 μW/cm 2 or less did not suppress nocturnal melatonin whereas twilight irradiances of 3.0 μW/cm 2 or greater did suppress pineal melatonin. A few animals did have lower melatonin after a 40‐min exposure to full moonlight during July (0.045 μW/cm 2 ) or January (0.240 μW/cm 2 ). However, pineal melatonin levels remained high in the majority of animals exposed to full moonlight.