Season-Related Differences in the Biosynthetic Activity of the NeonatalChicken Pineal Gland

摘要

Influence of the season of hatch on the functional characteristics of the pineal gland was examined in neonatalHi-Line male chickens. The pineal glands from 2-day-old birds hatched in summer and winter, and kept from the day ofhatch in artificial lighting conditions (12L:12D), were isolated under dim red light in the middle of the day or night. Thepineal glands were analyzed to characterize their melatonin biosynthetic activity: (1) expression of the Arylalkylamine–N–acetyltransferase and Hydroxyindole-O-methyltransferase genes, encoding the final two enzymes of the melatoninbiosynthesis pathway; (2) the activity of AA-NAT and HIOMT; and (3) the content of the main substrates of thispathway, tryptophan (TRY) and serotonin (5-HT). Daily changes in pineal AA-NAT activity were observed in chickenshatched in both seasons, with a more pronounced nocturnal increase in summer. In contrast, the level of Aa-nat geneexpression, although exhibited the same nocturnal/diurnal pattern in both seasons, was much lower in the summer. Theactivity of HIOMT was season- and daytime-independent. In “winter” chickens the pineal content of 5-HT was low andstable, while in “summer” birds it was correlated with levels of AA-NAT activity and Aa-nat gene expression. TRYcontent was very high and exhibited neither daily nor seasonal changes. The pineal gland of newly hatched chickens keptin controlled 12L:12D conditions exhibits daily variations in melatonin biosynthetic activity influenced by the season.This suggests a maternal effect on the perinatal/postnatal development of the circadian clock residing in the chicken pinealgland.