| Research Abstract |
The levels of melatonin in pineal gland and retina show a circadian rhythm in phase with a light-dark cycle.; levels of melatonin increase notably at night and, inversely, are low in the daytime.
At 0 day of age, White Leghorn chicks were either pinealectomized (PX), sham-pinealectomized (SP), blinded by complete bilateral orbital enucleation (BL), pinealectomized and blinded (PX-BL), or left intact (I). All birds were held in a chick brooder with a common 12L:12D light/dark cycle, lights on from 06:00 to 18:00. Lighting was provided by ceiling 40-W fluorescent bulbs, with an average intensity of 200-300 lux at the chick blooder. Blood sample were obtained from l-, 7-, 16-, 29-, 65- and 100-day-old cockrels at 8, 12, 16, 20, 24, 4 and 8 o'clock each day. Melatonin concentrations in the plasma were determined by a radioimmunoassay. The plasma melatonin,concentrations of control (I and SP) birds showed a prominent daily rhythm with a peak at mid scotophase. A small plasma melatonin rhythm
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(about 30% of the control levels at mid-scotophase) was detected in the PX birds at each day of age. In BL bij:-ds, plasma melatonin showed a small daily rhythm ( 30% of the control levels at mid-scotophase ) on day 1. Although the melatonin level at mid- scotophase increased with advancing age, the level was same as the control (I and SP) after 16 days. PX-BL birds showed little daily rhythm.
White Leghorn chicks were.incubated under DD. After hatching some were kept under DD in continuous White noise to counteract the influence of noise and the other were kept under DD with 12h (6:00-18:00) White noise. Pineal glands and blood samples were obtained from l-, 7-, 13- and 24-day-old chickens at 8, 12, 16, 20, 24, 4 and 8 o'clock of each day. melatonin contents in pineal glands and melatonin concentrations in the plasma were determined by a radioimmunbassay. Both melatonin content of pineal glands and melatonin concentrations in plasma did not, however, peak under DD and continuous white noise conditions at any time during the experiment. In the birds kept under DD in 12h White noise, melatonin content of pineal glands peaked at the multime during 6:00-18:00 at each day of age. So this result indicated the signal of noise was a potential Zeitgeber for forming the rhythm. Less
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