Turkey retina and pineal gland differentially respond to constant environment

Abstract

Dynamics of rhythmic oscillations in the activity of arylalkylamine N-acetyltransferase (AA-NAT, the penultimate and key regulatory enzyme in melatonin biosynthesis) were examined in the retina and pineal gland of turkeys maintained for 7 days in the environment without daily light-dark (LD) changes, namely constant darkness (DD) or continuous light (LL). The two tissues differentially responded to constant environment. In the retina, a circadian AA-NAT activity rhythm disappeared after 5 days of DD, while in the pineal gland it persisted for the whole experiment. No circadian rhythm was observed in the retinas of turkeys exposed to LL, although rhythmic oscillations in both AA-NAT and melatonin content were found in the pineal glands. Both tissues required one or two cycles of the re-installed LD for the full recovery of the high-amplitude AA-NAT rhythm suppressed under constant conditions. It is suggested that the retina of turkey is less able to maintain rhythmicity in constant environment and is more sensitive to changes in the environmental lighting conditions than the pineal gland. Our results indicate that, in contrast to mammals, pineal glands of light-exposed galliformes maintain the limited capacity to rhythmically produce melatonin.

Diurnal Rhythm of Plasma Melatonin Concentration in the Domestic Turkey and Its Regulation by Light and Endogenous Oscillators

“…The lower amplitude of circadian fluctuations of plasma MLT concentrations resulted both from higher levels during the day-time and lower levels during the night-time. Similar data were obtained from younger turkeys, in which the circadian rhythm of MLT secretion persisted for 7 days under continuous dim red light and had an amplitude that was 50-80% lower than the rhythm in the 12L:12D cycle [27,41]. The circadian rhythm of MLT secretion with gradually decreasing amplitude was also observed in the superfusion culture of the turkey pineal organs for 5 days in continuous darkness [33].…”

Roles of Direct Photoreception and the Internal Circadian Oscillator in the Regulation of Melatonin Secretion in the Pineal Organ of the Domestic Turkey: A Novel In Vitro Clock and Calendar Model

“…These data suggest that extrapineal oscillators play a crucial role in the generation of the MLT synthesis rhythm in this species. The circadian rhythm of plasma MLT in young turkeys maintained in continuous darkness persisted for seven days [4,60]. A longer-lasting in vivo MLT rhythm may result from the influence of oscillators located outside the pineal gland.…”

“…All light pulses caused a significant decrease in MLT secretion, but it should be emphasized that it was only the 6-hour exposure decreased the MLT level to the daytime level. The in vivo inhibitory effect of light in the turkey was stronger than that in vitro, which suggests the involvement of retina photoreception in the regulation of the secretory activity of the turkey pineal gland; however, the possibility of age-dependent differences cannot be excluded [4,5,60]. Light exposure influenced the activity of the turkey pineal oscillator and induced a phase-shift in the circadian MLT rhythm.…”

Characterization of the relations between morphology and physiological status of the pineal gland in connection with the somatic development level in turkeys reared in Romania

“…During the night 5-HT is N-terminal acetylation by means of N-acetyltransferase to form Nacetylserotonin (NAS), a substrate of the final transfer enzyme, which is hydroxyindole-omethyltransferase (HIOMT). NAT and HIOMT activity is intensified at dark due to the increased released of noradrenaline from the sympathetic nerve endings located at the level of cellular membrane of pinealocites (Arendt et al 1991;Lorenc-Duda 2008;Pryzbylska et al 2009;Skene et al 1991).…”