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Related Experiment Videos

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
PubMed
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.

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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.

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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.