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Abstract
Adult hens were chronically cannulated and held in light-dark (LD) 12:12 h lighting
regimes or in constant darknesS (DD). Periodic blood sampling for 5-9 days revealed
circadian rhythms in plasma melatonin titres. Superior cervical ganglionectomy (SCG-X)
performed 1 week after hatching had little or no effect on these rhythms in LD, but
unlike normals. SCG-X birds did not sustain persistent rhythms in DD. In SCG-X birds,
norepinephrine (NE) infusion for 12 h of each 24 h in DD significantly reduced plasma
melatonin titres during the infusion and re-established a rhythm. After each experiment,
hens were killed, their pineals were removed and assayed by HPLC-EC for NE, dopamine
(DA), serotonin (5-HT) and 5-hydroxy-3-indole-acetic acid (5-HIAA). SCG-X resulted
in a 90% depletion of pineal NE: DA content was reduced to undetectable levels. Pineal
5-HT and 5-HIAA were also reduced by SCG-X. The chicken pineal contains circadian
oscillators which persist in vitro8.19.29. The results reported here suggest that
noradrenergic fibres from the SCG regulate the pineal's inherent rhythmicity. NE normally
released from sympathetic terminals during the bird's day may synchronize oscillators
within the pineal by inhibiting melatonin synthesis.