The Influence of Various Irradiances of Artificial Light, Twilight, and Moonlight on the Suppression of Pineal Melatonin Content in the Syrian Hamster

Abstract

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 microW/cm2 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 microW/cm2 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 microW/cm2 was capable of always suppressing melatonin. Furthermore, increasing the duration of 0.019-microW/cm2 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 microW/cm2 or less did not suppress nocturnal melatonin whereas twilight irradiances of 3.0 microW/cm2 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 microW/cm2) or January (0.240 microW/cm2). However, pineal melatonin levels remained high in the majority of animals exposed to full moonlight.

Illuminance Threshold for Maintenance of Testes in Syrian Hamsters (Mesocricetus auratus) Is Higher in Continuous Light than in Long Photoperiods

“…4). Brainard et al (1982Brainard et al ( , 1984 exposed Syrian hamsters to cool white fluorescent light during the peak of the hamster's nocturnal production of melatonin (7-10 hr after lightsoff). They found that within 8 min after experimental light exposure began, an illuminance of 1.08 lux significantly decreased pineal melatonin content, whereas 0.11 lux did not.…”

Melatonin: Receptor-mediated events that may affect breast and other steroid hormone–dependent cancers

“…It has been demonstrated for animals and suggested for humans that EMFs and light at night inhibit melatonin production [32][33][34]. Does this affect cancer risk and how?…”

Exposure to Different Spectra of Light, Continuous Light and Treatment with Melatonin Affect Reproduction in the Indian Desert Gerbil Meriones hurrianae (Jerdon)

“…The entraining effects of different spectra of light and their influence on reproduction are in need of investigation. Although the effect of exposure, during night, to various light irradiances and spectra on pineal metabolism are documented [11,22,23], studies pertaining to exposure during day (light phase) to the light spectra are rare. The present results underline the need for such studies.…”

“…Both artificial and natural light cycles influence the daily and annual rhythms of melatonin production [6][7][8][9] in a number of vertebrates. In Syrian hamsters, both the light irradiance and wavelengths are important in regulating the nocturnal rise in melatonin levels [10,11]. Clearly, light influences pineal gland activity, and the latter, in turn, has a regulatory role in reproduction [2].…”