Extraretinal mechanisms mediate light-induced changes in neonatal rat pineal gland N-acetyltransferase activity

Nocturnal light-induced changes in pineal gland N-acetyltransferase activity were investigated in intact or enucleated 4-, 6-, or 8-day-old maternally isolated rats maintained at different ambient temperatures. Nighttime enzyme activity was increased markedly in rats maintained in 23 degrees C compared to 35 degrees C environments. Four hours of nocturnal light significantly reduced N-acetyltransferase activity in intact rats at all ages studied when the animals were maintained at 35 degrees C. Shorter duration (1 min) nocturnal light reduced N-acetyltransferase activity in intact rats 6 days of age. However, the enzyme activity suppression observed after the 4 hr of nocturnal light was still present in 4-day-old rats (but not older animals) even when the younger animals had been made blind by bilateral orbital enucleation. Taken together, these data suggest that an extraretinal mechanism may mediate light-induced changes in some aspects of pineal gland indoleamine biochemistry in newborn rats.