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Research on age-dependent changes in pineal activity has been limited almost exclusively to melatonin (MLT). This study determined, for the first time, the alterations occurring in the metabolic profile of MLT synthesis-related indoles during the post-embryonic development period in birds. Turkeys reared under a 12 h light/dark cycle were euthanized at 2 h intervals for 24 h at the ages of 2, 7, 14, and 28 days and 10, 20, 30, and 45 weeks. The results showed prominent changes in the metabolic profile of indoles during development and could be distinguished in four stages. The first stage, from hatching to the age of 2 weeks, was characterized by a decrease in the 5-hydroxytryptophan concentration and an increase in the concentrations of serotonin (5-HT), MLT, 5-methoxyindoleacetic acid, and 5-methoxytryptamine (5-MTAM). During the second stage, around the age of 1 month, the concentrations of N-acetylserotonin (NAS) and MLT reached a maximum. The synthesis and degradation of 5-HT were also the highest. The third stage, around the age of 10 weeks, was characterized by decreased levels of 5-HT (approximately 50%) and 5-hydroxyindoleacetic acid and a high level of 5-MTAM. The last stage, covering the age of 20 to 45 weeks, was characterized by a large decrease in the synthesis, content, and degradation of 5-HT. Despite these changes, there were no prominent differences in the nocturnal levels of NAS and MLT between the third and fourth stages. The concentrations of all tryptophan derivatives showed daily fluctuations until the age of 45 weeks. [ABSTRACT FROM AUTHOR]

This study characterizes the diurnal profiles of ten melatonin synthesis-related indoles, the quantitative relations between these compounds, and daily variations in the contents of catecholamines and their metabolites in the domestic duck pineal organ. Fourteen-week-old birds, which were reared under a 12L:12D cycle, were killed at two-hour intervals. The indole contents were measured using HPLC with fluorescence detection, whereas the levels of catecholamines and their metabolites were measured using HPLC with electrochemical detection. All indole contents, except for tryptophan, showed significant diurnal variations. The 5-hydroxytryptophan level was approximately two-fold higher during the scotophase than during the photophase. The serotonin content increased during the first half of the photophase, remained elevated for approximately 10 h and then rapidly decreased in the middle of the scotophase. N-acetylserotonin showed the most prominent changes, with a more than 15-fold increase at night. The melatonin cycle demonstrated only an approximately 5-fold difference between the peak and nadir. The 5-methoxytryptamine content was markedly elevated during the scotophase. The 5-hydroxyindole acetic acid, 5-hydroxytryptophol, 5-methoxyindole acetic acid and 5-methoxytryptophol profiles were analogous to the serotonin rhythm. The norepinephrine and dopamine contents showed no significant changes. The DOPA, DOPAC and homovanillic acid levels were higher during the scotophase than during the photophase. Vanillylmandelic acid showed the opposite rhythm, with an elevated level during the daytime. [ABSTRACT FROM AUTHOR]

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The embryonic ontogeny of pineal secretory activity in birds has been investigated almost exclusively in chickens. This study aimed to characterize this process in domestic geese. The pineal organs of embryos aged 18–28 days were incubated in superfusion culture under different light conditions for 4–5 days and treated with norepinephrine (NE). Melatonin (MLT) was measured by radioimmunoassay and other indoles by HPLC with fluorescence detection. Additionally, pineal organs were collected from embryos at 14–28 days of age and used to measure catecholamines by HPLC with electrochemical detection. MLT secretion increased with embryo age, most intensively between the 22nd and 24th days of life. The daily changes in MLT secretion under the 12 L:12D cycle occurred on the first day of culture, starting from an embryonic age of 24 days. MLT secretion was controlled by the light-dark cycle in all age groups studied. However, exposure to light during the scotophase did not alter the secretion of MLT. The endogenous oscillator expressed its activity in regulating MLT secretion in the pineal organs of embryos aged 24 days and older but could not generate a rhythm after one cycle. The rhythm of 5-hydroxytryptophan release during the first day of culture was found in the pineal organs of all embryos, while the rhythmic release of N-acetylserotonin and 5-methoxyindole acetic acid started at the age of 24 days. The proportion of released indoles changed with embryo age. NE caused a decrease in MLT secretion and provoked an increase in serotonin release. Incubation of the pineal organs induced the development of MLT secretory machinery and its diurnal rhythmicity. The pineal content of catecholamines increased prominently at the end of embryonic development. [ABSTRACT FROM AUTHOR]

The metabolism of pineal indoles is closely related to alterations in the light and dark phases of a daily cycle. Recent research showed important interspecies differences in the pineal biochemistry, and a strong impact of monochromatic light on many physiological processes in birds. Therefore, the aims of study were to characterize the metabolism of melatonin-synthesis indoles in the pineal organ of the domestic turkey, and to determine the changes occurring in this metabolism under the influence of different wavelengths and intensities of light. For this purpose, 3-week-old turkeys were kept under 16 lx white light, or under blue, green, and red light with intensities of 16, 32, and 64 lx during the photophase, and after 7 d were sacrificed at 4 h intervals. The activities of melatonin-synthesizing enzymes and the contents of indoles were measured in the same pineal organ. The results revealed that the activities of tryptophan hydroxylase and arylalkylamine N-acetyltransferase, and the levels of all tryptophan derivatives had significant daily changes in birds kept under each light condition used. The profile of pineal indole metabolism in 4-week-old turkeys was characterized by high-amplitude rhythms in the activity of arylalkylamine N-acetyltransferase and the contents of N-acetylserotonin and melatonin, equal relative amounts of serotonin and 5-hydroxyindoleacetic acid, and higher content of melatonin than N-acetylserotonin. The monochromatic light significantly modified the pineal indole metabolism, and its effects were dependent on the color and intensity of light. Pronounced changes occurred in the level of serotonin synthesis and the daily rhythm course of melatonin synthesis. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The aim of this study was to characterize the embryonic ontogeny of 5-hydroxyindoles and 5-methoxyindoles synthesis pathways in the goose pineal organ. The study was performed on embryos aged 14–28 days, which have been incubated under a 12L:12D cycle. The pineal organs were collected for measurements of indole content by HPLC every 6 h on embryonic day (ED) 14, ED 16, ED 18 and ED 22 or every 2 h on ED 24, ED 26 and ED 28. The level of tryptophan showed no significant changes during development and no day-night variations. The content of 5-hydroxytryptophan increased between ED 14 and ED 26. It was significantly higher during scotophase than during photophase starting from ED 14. The serotonin content was low during the early stages of development (ED 14–ED 18) and prominently increased from ED 20. The serotonin levels also showed day-night differences; however, they were less conspicuous than those of 5-hydroxytryptophan. The changes in the level of 5-hydroxyindole acetic acid were similar to those of serotonin. 5-Hydroxytryptophol was measurable from ED 18. Levels of N-acetylserotonin, which were detectable for the first time on ED 16, prominently increased between ED 22 and ED 28 and showed significant day–night differences from ED 20. Melatonin was detectable from ED 18. Like N-acetylserotonin, its content increased rapidly between ED 22 and ED 28, and from ED 20 showed diurnal variations. 5-Methoxyindole acetic acid and 5-methoxytryptophol occurred at measurable levels from ED 18 and ED 26, respectively. The obtained results showed that embryonic development of indole metabolism in the goose pineal organ starts with the beginning of serotonin synthesis. The processes of serotonin acetylation and 5-hydroxyindoles methylation were turned on later. Diurnal rhythmicity develops very early in the embryonic pineal organ of the goose when the eggs are incubated under a 12 h light: 12 h dark schedule. Two processes are responsible for generation of the diurnal rhythms of 5-hydroxyindoles and 5-methoxyindoles: (i) hydroxylation of tryptophan and (ii) acetylation of serotonin. [ABSTRACT FROM AUTHOR]

• Organization and ultrastructure of the turkey pineal organ change during development. • Rudimentary photoreceptor pinealocytes dominate in young and young adult birds. • Rudimentary photoreceptor cells regress with age, while the secretory cells develop. • Photoreceptor cells do not transform into secretory ones. • Glial-like cells are an important component of the parenchyma. Our previous study showed that the turkey pineal organ, in contrast to that of the chicken, is characterized by a follicular structure throughout the entire period of post-hatching life. Despite the preservation of the follicular organization, the histological structure of the pineal follicles in turkeys changes prominently with age. The present research was performed to investigate the cellular composition and organization of the follicle wall as well as the ultrastructure of parenchymal cells in the turkey pineal organ during the period of post-hatching development. Pineal organs were collected from female turkeys at 2 days, 2 weeks, 4 weeks, 10 weeks, 20 weeks, 30 weeks, 40 weeks, and 56 weeks post-hatching. The organs were prepared for immunocytochemical studies using antibodies against N -acetylserotonin O -methyltransferase (ASMT), glial fibrillary acidic protein (GFAP) and proliferating cell nuclear antigen (PCNA) and for ultrastructural examination. The results showed that regardless of age, the pineal follicle was formed by ASMT-immunopositive cells, among which rudimentary photoreceptor and secretory pinealocytes were identified. The second component of the follicle wall consisted of GFAP-immunopositive cells, as represented by ependymal-like and astrocyte-like cells. Rudimentary photoreceptor pinealocytes and ependymal-like cells formed the inner part of the follicle wall, while secretory pinealocytes and astrocyte-like cells created the outer part. Three forms of the pineal follicle structure characteristic of young (two days to ten weeks), young adult (20–30 weeks) and adult (40–56 weeks) turkeys were distinguished. These forms primarily differed in the relative dimensions of the inner and outer parts of the follicle wall. Ultrastructural studies showed prominent changes in the organization of rudimentary receptor pinealocytes during the investigated period of life. These cells developed until the age of 20 weeks, at which time they appeared as strongly elongated cells with a stratified, highly regular distribution of organelles. In adult turkeys, rudimentary receptor pinealocytes showed pronounced regressive changes; however, we never observed their transformation into cells of the secretory type. Secretory pinealocytes increased in number and size during the post-hatching period, which was especially pronounced after 20 weeks of age. The most prominent changes in the supporting cells included the intensification of GFAP-immunoreactivity due to the accumulation of filaments in the cytoplasm and the development of astrocyte-like cells. The increase in the number of secretory pinealocytes and astrocyte-like supporting cells resulted in the formation of two distinct parts of the follicle wall in the pineal organs of young adult and adult turkeys. [ABSTRACT FROM AUTHOR]

• The turkey pineal organ shows presence of pinopsin during entire period of posthatching development. • Pinopsin distribution changes with age. • Both rudimentary photoreceptor and secretory pinealocytes are photoreceptive. • Secretory pinealocytes are less light sensitive. • The autonomus regulatory mechanism work well regardless of the age of birds. The avian pineal organ is photosensitive because of the presence of photopigments, of which pinopsin seems to be one of the most important. This organ is subject to far-reaching changes during post-hatching development, but evidence regarding pinopsin presence and direct photoreception during this time is lacking. This study was carried out to demonstrate the following: 1) the structures showing immunoreactivity to pinopsin in the turkey pineal organ, 2) the changes of these structures during development, 3) the pinopsin localization in pinealocytes in monolayer cultures, and 4) the role of direct photoreception in the regulation of melatonin secretion in pineal organs in adult turkeys. Pinopsin immunoreactivity was localized in the apical extensions of columnar cells limiting the follicular lumen, in fiber-like structures located between columnar cells in the inner part of follicle wall, in string-shapes or small spherical structures distributed in the outer part of follicle wall and in amorphous material inside the follicle lumen. In young birds, immunoreactivity was also sporadically noted in cell bodies of rudimentary receptor pinealocytes. The distribution of pinopsin showed prominent age-dependent changes, including a subsequent increase in pinopsin-positive structures in the outer part of the follicle wall and a prominent reduction in the number and size of positive apical extensions in 40- and 56-week-old turkeys. These data demonstrate that the role of secretory pinealocytes in pineal photoreception increases with age. In monolayer cultures, all pinealocytes showed strong reactions in club- or bulbous-shaped prolongations. The pineal organs of adult birds were less sensitive to light exposition at night than those of young turkeys, which points to differences in light sensitivity between rudimentary receptor and secretory pinealocytes. However, direct photoreception could play an important role in the regulation of melatonin secretion in adult turkeys. [ABSTRACT FROM AUTHOR]