Abstract
The regulation of melatonin secretion in the avian pineal organ is highly complex and shows prominent interspecies differences. The aim of this study was to determine the roles of direct photoreception and the internal oscillator in the regulation of melatonin secretion in the pineal organ of the domestic turkey. The pineal organs were collected from 12-, 13- and 14-week-old female turkeys reared under a 12 L:12 D cycle with the photophase from 07.00 to 19.00, and were incubated in superfusion culture for 3–6 days. The cultures were subjected to different light conditions including 12 L:12 D cycles with photophases between 07.00 and 19.00, 13.00 and 01.00 or 01.00 and 13.00, a reversed cycle 12 D:12 L, cycles with long (16 L:8 D) and short (8 L:16 D) photophases, and continuous darkness or illumination. The pineal organs were also exposed to light pulses of variable duration during incubation in darkness or to periods of darkness during the photophase. The secretion of melatonin was determined by direct radioimmunoassay. The turkey pineal organs secreted melatonin in a well-entrained diurnal rhythm with a very high amplitude. Direct photoreception as an independently acting mechanism was able to ensure quick and precise adaptation of the melatonin secretion rhythm to changes in light-dark conditions. The pineal organs secreted melatonin in circadian rhythms during incubation in continuous darkness or illumination. The endogenous oscillator of turkey pinealocytes was able to acquire and store information about the light-dark cycle and then to generate the circadian rhythm of melatonin secretion in continuous darkness according to the stored data. The obtained data suggest that the turkey pineal gland is highly autonomous in the generation and regulation of the melatonin secretion rhythm. They also demonstrate that the turkey pineal organ in superfusion culture is a valuable model for chronobiological studies, providing a highly precise clock and calendar. This system has several features which make it an attractive alternative to other avian pineal glands for circadian studies.
Highlights
And seasonal changes in the environmental photoperiod are reflected in the rhythmicity of many physiological processes and behaviors in vertebrates
Pineal organs incubated under a 12 L:12 D cycle with the light phase from 07.00 to 19.00, which was the same light-dark cycle used at the time of turkey rearing, secreted MLT in a regular diurnal rhythm throughout the experiment (Figure 1)
The turkey pineal organ in superfusion culture is characterized by an extremely well-entrained diurnal rhythm of MLT secretion with a very high amplitude compared to the pineal organs of other examined domesticated birds
Summary
And seasonal changes in the environmental photoperiod are reflected in the rhythmicity of many physiological processes and behaviors in vertebrates. Throughout the year, duration of the elevated MLT concentration in the general circulation changes parallel to the seasonal alternations in the night length, which enables MLT to be a calendar molecule [2,6,8,9,10,11]. It is well-documented that the environmental light is received directly by avian pinealocytes, which possess own photoreceptive structures and phototransduction molecules [12,13,14,15,16,17]. Three oscillators cooperate with each other in birds and form a centralized system keeping daily time
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
