Melatonin rhythms in quail: regulation by photoperiod and circadian pacemakers.
The profile of melatonin in the eyes, pineal, and blood of Japanese quail was assessed in birds held under LD 16:8 and LD 6:18 photoperiods. Melatonin levels in all three tissues showed a robust daily rhythm with higher levels occurring at night. The amplitude of the rhythm was depressed and its duration lengthened on LD 6:18 relative to LD 16:8. The blood melatonin rhythm precisely reflected the rhythms shown by the pineal and eyes, supporting the idea that the blood rhythm is a result of melatonin secretion by both the eyes and pineal. The ocular melatonin rhythm continued after sectioning of the optic nerve, was reentrainable to a shift in the phase of the LD cycle, and persisted for at least 2 days in constant darkness. It was concluded that either an intraocular circadian clock drives the ocular melatonin rhythm, or an extraocular clock drives the ocular melatonin rhythm via a route other than the efferent innervation (which enters the eye via the optic tract).
D000818:Animals; D001921:Brain / Q000502:physiology; D002940:Circadian Rhythm; D003370:Coturnix / Q000378:metabolism*; D005123:Eye / Q000032:analysis*; D005260:Female; D008027:Light; D008297:Male; D008550:Melatonin / Q000032:analysis* / Q000097:blood; D009900:Optic Nerve / Q000502:physiology; D010507:Periodicity; D010870:Pineal Gland / Q000032:analysis*; D011784:Quail / Q000378:metabolism*; D014981:Xenopus
D008550:Melatonin