Effect of Long-Term Exposure to Constant Dim Light on the Circadian System of Rats

Aug 10, 2005Neuro-Signals

Long-term exposure to constant dim light changes rats' internal body clocks

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Abstract

Exposure to constant red dim light for 60 days did not change Period 1 mRNA expression in the hypothalamus.

Arylalkylamine N-acetyltransferase (Aa-nat) mRNA levels in the retina and pineal gland were significantly altered in 20-30% of animals during the subjective day.
All tested animals maintained a circadian rhythm of serum melatonin and locomotor activity.
In 4 animals, serum melatonin levels were elevated during the subjective day.
Long-term exposure to constant red dim light may lead to desynchronization between locomotor activity and serum melatonin rhythms.

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The newly discovered multi-oscillatory nature of the mammalian circadian clock system and the cloning of the genes involved in the molecular mechanism that generates circadian rhythmicity have opened new approaches for understanding how mammals are temporally organized and how the mammalian circadian system reacts to the lack of normal synchronization cues. In the present study we investigated the effects of long-term exposure to constant red dim light on the pattern of the expression of Period 1 in the suprachiasmatic nuclei of the hypothalamus and of Arylalkylamine N-acetyltransferase(Aa-nat) in the retina and pineal gland. Our data demonstrate that Period 1 mRNA expression in the suprachiasmatic nuclei of the hypothalamus was not affected by exposure to constant red dim light for 60 days, whereas Aa-nat mRNA expression in the retina and in the pineal gland was significantly affected, since in some animals (20-30%) Aa-nat mRNA levels were found to be higher during the subjective day. A circadian rhythm of serum melatonin and locomotor activity was present in all the animals tested. In 4 animals serum melatonin levels were high during the subjective day. Our data suggest that long-term exposure to constant red dim light may induce desynchronization between the circadian rhythm of locomotor activity and serum melatonin levels.

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Effect of Long-Term Exposure to Constant Dim Light on the Circadian System of Rats

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