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Light-induced changes in pineal gland N-acetyltransferase activity: developmental aspects
D M Bronstein1, K A Haak, G Torres
1Department of Psychology, University of California, Santa Barbara.
Neuroendocrinology
|February 1, 1990
Summary
Light exposure suppresses melatonin production in neonatal rats starting at 6 days of age. This effect is mediated by the eyes and involves the beta-noradrenoceptor pathway.
Area of Science:
- Neuroendocrinology
- Chronobiology
- Developmental Biology
Background:
- Light influences pineal gland biochemistry in adult rats by entraining circadian rhythms and suppressing nocturnal melatonin.
- N-acetyltransferase (NAT) is the rate-limiting enzyme in melatonin biosynthesis.
Purpose of the Study:
- To determine the age at which photic stimulation first affects pineal gland NAT activity in neonatal rats.
- To investigate cellular mechanisms mediating light-induced effects on melatonin production in neonates.
Main Methods:
- Rats of varying ages were exposed to brief light or darkness during the night.
- Pineal gland NAT activity was measured after light exposure.
- Experiments included enucleation and beta-noradrenoceptor agonist pretreatment.
Main Results:
- Nocturnal light exposure suppressed NAT activity in rats 6 days of age and older.
- Suppression was not observed in 3- to 5-day-old rats, despite existing light:dark differences.
- Enucleation prevented light-induced suppression, indicating retinal mediation.
- Isoproterenol pretreatment blocked the suppressive effect of nocturnal light.
Conclusions:
- Photic suppression of melatonin biosynthesis begins around 6 days of age in rats.
- The retino-pineal pathway, involving beta-noradrenoceptors, mediates light's effect on nocturnal melatonin production in neonatal rats.