Dynamics of noradrenergic circadian input to the chicken pineal gland

Abstract

To analyze the dynamics of sympathetic input to the chicken pineal the concentrations of catecholamines, indoleamines and some of their metabolites were determined by high performance liquid chromatography with electrochemical detection (HPLC-EC) in the pineal glands of young chickens killed at different times of day. Rhythmic variations over 24 h were observed in tissue levels of dopamine (DA), 5-hydroxytryptamine (5-HT), N-acetylserotonin (NAS) and 5-hydroxyindoleacetic acid (5-HIAA), while norepinephrine (NE) concentrations exhibited no significant change. DA content peaked 2 h after onset of darkness and NAS was detectable only during the night. A bimodal pattern of 5-HT and 5-HIAA levels was observed with peak tissue levels occurring at dawn and dusk. To determine the possible differential effects of light on these biogenic amines, birds were sacrificed at midday, midnight and at midnight following a 1 h exposure to light, and their pineals processed for HPLC-EC. NE, DA and 5-HT levels were similar at midday and midnight, while 5-HIAA and NAS were elevated during the night. Midnight illumination decreased NE and NAS levels, increased 5-HT and 5-HIAA levels and had no effect on DA levels. Temporal variations in NE turnover were determined by pretreating young chickens with α-methyl- p-tyrosine, a tyrosine hydroxylase inhibitor, and measuring the rates of decline in NE content over 2 h at midday and midnight in birds held on light cycles at mid-subjective day in birds held in constant darkness (DD). NE declined slowly at midday and mid-subjective day but did not decline at all at midnight, indicating NE turnover, release and/or metabolism is highest during the day. Together, these data suggest that the chicken pineal receives circadian input from sympathetic fibers which mediates pineal indole metabolism.