Cold exposure or norepinephrine injections altered melatonin levels in the quail retina

The possible involvement of ambient temperature and norepinephrine on daytime levels of retinal melatonin were investigated in quails. For a minimum of 1 week, experimental animals were housed under constant room temperature of 23 +/- 2 degrees C and a daily 12:12 h light-dark cycle with light on at 06.00-18.00 h. The quails were then transferred to a cold room of 4 degrees C and cold-exposed for 0, 30, 60, 90 and 120 min. Retina samples were subsequently collected at mid-light for melatonin radioimmunoassay. An initial decline of melatonin was detected in the cold treated birds after 30 min of exposure. Thereafter prolongation of cold stimulation produced significant increases in the levels of retinal melatonin. In the second experiment, intra-peritoneal norepinephrine injections (0, 1, 10 and 100 micrograms/bird) at mid-light were found to increase the levels of retinal melatonin in quails. We postulate the cold-induced increase of retinal melatonin may be attributed to an augmented level of catecholamines released as a general neuroendocrine response to temperature decrements.