AVIAN MELATONIN SYNTHESIS - PHOTIC AND CIRCADIAN REGULATION OF SEROTONIN N-ACETYLTRANSFERASE MESSENGER-RNA IN THE CHICKEN PINEAL-GLAND AND RETINA

The circadian rhythms in melatonin production in the chicken pineal gl and and retina reflect changes in the activity of serotonin N-acetyltr ansferase (arylalkylamine N-acetyltransferase; AA-NAT; EC 2.3.1.87). H ere we determined that the chicken AA-NAT mRNA is detectable in follic ular pineal cells and retinal photoreceptors and that it exhibits a ci rcadian rhythm, with peak levels at night. AA-NAT mRNA was not detecte d in other tissues. The AA-NAT mRNA rhythm in the pineal gland and ret ina persists in constant darkness (DD) and constant lighting (LL). The amplitude of the pineal mRNA rhythm is not decreased in LL. Light app ears to influence the phase of the clock driving the rhythm in pineal AA-NAT mRNA in two ways: The peak is delayed by similar to 6 h in LL, and it is advanced by >4 h by a 6-h light pulse late in subjective nig ht in DD. Nocturnal AA-NAT mRNA levels do not change during a 20-min e xposure to light, whereas this treatment dramatically decreases AA-NAT activity. These observations suggest that the rhythmic changes in chi cken pineal AA-NAT activity reflect, at least in part, clock-generated changes in mRNA levels. In contrast, changes in mRNA content are not involved in the rapid light-induced decrease in AA-NAT activity.