Developmental morphology of the turkey pineal gland in histological images and 3D models.

The histological structure of the avian pineal gland during embryonic life has so far only been studied in chickens. It is known that the pineal organs of hatched chickens and turkeys differ significantly from each other based on their morphology and physiology. The aim of the present study was to investigate the histological structure of the embryonic pineal gland of domestic turkeys. The study was performed on turkey embryos aged 4-28 days. Along with histological analyses, three-dimensional (3D) images of the pineal glands from embryos aged 6-28 days were also obtained. In four-day-old embryos [embryonic day (ED) 4], primary evagination of the pineal gland from the neuroectoderm of the diencephalon was observed. On ED 6, the evagination formed a pineal recess with a thick and folded wall. In the next embryonic stages, the pineal recess was lengthened to the pineal canal, with the lumen opening to the third ventricle. The connection of the pineal lumen with the ventricular lumen was observed in all studied embryos. The first cellular rosettes without the lumen separated from the wall of the pineal recess occurred on ED 6. Several small and round follicles containing their own lumens were visible on ED 8. On ED 10, the pineal parenchyma was composed mainly of small, round follicles. The first oval follicles appeared on ED 12 and branched follicles appeared on ED 16. In some embryos at different stages, follicles formed from secondary evaginations of the diencephalon epithelium were observed. The turkey pineal organ maintained the follicular type of parenchyma without solid cellular aggregates throughout embryonic life. The pineal follicles originated from: 1) rosettes arising from the wall of the pineal canal (from ED 6); 2) an accessory evagination occurring in the neuroectoderm anteriorly and posteriorly to the pineal canal end (from ED 6); 3) direct development in the walls of larger follicles and detaching from them in a manner similar to the budding process (from ED 14); and 4) fusion of smaller follicles into branched ones. The pineal capsule started to develop on ED 6, first as a vascularization and later as a thin mesenchymal outline around the apical part, then at the dorsal and at the end the ventral part of the pineal gland. The pineal stroma was composed of mesenchymal tissue consisting of abundant in cells and blood vessels. The first evagination of the choroid plexus in the diencephalon was observed on ED 8. The attachment of the pineal gland to the dura mater first occurred on ED 16. Finally, the pineal gland of ED 28 embryos consisted of a wide proximal part attached to the dura mater and a narrow distal part that extended into the pineal stalk, which extended to the intercommissural region of the diencephalon. The present study revealed the occurrence of significant morphological differences in the developing embryonic pineal gland of turkeys compared with chickens.

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

The aim of this study was to characterize the diurnal rhythm of plasma melatonin (MLT) concentration and its regulation by light and endogenous oscillators in 10-week-old domestic turkeys. Three experiments were performed to examine (i) the course of daily changes in plasma MLT concentration in turkeys kept under a 12 h light: 12 h dark (12L:12D) cycle; (ii) the influence of night-time light exposure lasting 0.5, 1, 2, or 3 h on the plasma MLT level; and (iii) the occurrence of circadian fluctuations in plasma MLT levels in birds kept under continuous dim red light and the ability of turkeys to adapt their pineal secretory activity to a reversed light-dark cycle (12D:12L). The plasma MLT concentration was measured with a direct radioimmunoassay. The plasma MLT concentration in turkeys kept under a 12L:12D cycle changed significantly in a daily rhythm. It was low during the photophase and increased stepwise after the onset of darkness to achieve the maximal level in the middle of the scotophase. Next, it decreased during the second half of the night. The difference between the lowest level of MLT and the highest level was approximately 18-fold. The exposure of turkeys to light during the scotophase caused a rapid, large decrease in plasma MLT concentration. The plasma MLT concentration decreased approximately 3- and 10-fold after 0.5 and 1 h of light exposure, respectively, and reached the day-time level after 2 h of exposure. In turkeys kept under continuous darkness, the plasma MLT level was approximately 2.5-fold higher at 02:00 h than at 14:00 h. In birds kept under 12D:12L, the plasma MLT level was significantly higher at 14:00 h than at 02:00 h. The results showed that plasma MLT concentrations in 10-week-old turkeys have a prominent diurnal rhythm, which is endogenously generated and strongly influenced by environmental light.

Pinopsin and photoreception in the pineal organ of the domestic turkey during post-hatching development.

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.

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.

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.

Embryonic Ontogeny of 5-Hydroxyindoles and 5-Methoxyindoles Synthesis Pathways in the Goose Pineal Organ.

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.

Effects of Streptozotocin-Induced Diabetes on the Pineal Gland in the Domestic Pig.

Several observations from experiments in rodents and human patients suggest that diabetes affects pineal gland function, including melatonin secretion; however, the accumulated data are not consistent. The aim of the present study was to determine the effects of streptozotocin-induced diabetes on the pineal gland in the domestic pig, a species widely used as a model in various biomedical studies. The study was performed on 10 juvenile pigs, which were divided into two groups: control and diabetic. Diabetes was evoked by administration of streptozotocin (150 mg/kg of body weight). After six weeks, the animals were euthanized between 12.00 and 14.00, and the pineal glands were removed and divided into two equal parts, which were used for biochemical analyses and for preparation of explants for the superfusion culture. The pineal contents (per 100 µg protein) of serotonin, 5-hydroxyindole acetic acid, 5-hydroxytryptophol, 5-methoxyindole acetic acid, 5-methoxytryptophol, and 5-methoxytryptamine were significantly lower in diabetic pigs than in control pigs. In contrast, the level of N-acetylserotonin was significantly higher in diabetic animals. No significant differences were found in the level of melatonin between control and experimental pigs. The amounts of 3,4-dihydroxyphenylalanine, dopamine, norepinephrine, and 3,4-dihydroxyphenylacetic acid were significantly lower in the pineal glands of diabetic animals. The level of vanillylmandelic acid was higher in diabetic pigs. No differences were observed in the level of basal and NE-stimulated release of N-acetylserotonin or melatonin between the pineal explants prepared from control and experimental animals. In vitro treatment with insulin was ineffective. In conclusion, streptozotocin-induced diabetes affects both indole metabolism and adrenergic neurotransmission in the pig pineal gland.

The Effects of Deoxynivalenol and Zearalenone on the Pig Large Intestine. A Light and Electron Microscopy Study.

The contamination of feed with mycotoxins results in reduced growth, feed refusal, immunosuppression, and health problems. Deoxynivalenol (DON) and zearalenone (ZEN) are among the most important mycotoxins. The aim of the study was to examine the effects of low doses of these mycotoxins on the histological structure and ultrastructure of the large intestine in the pig. The study was performed on 36 immature gilts of mixed breed (White Polish Big × Polish White Earhanging), which were divided into four groups administrated per os with ZEN at 40 µg/kg BW, DON at 12 µg/kg BW, a mixture of ZEN (40 µg/kg BW) and DON (12 µg/kg BW) or a placebo. The pigs were killed by intravenous overdose of pentobarbital after one, three, and six weeks of treatment. The cecum, ascending and descending colon samples were prepared for light and electron microscopy. Administration of toxins did not influence the architecture of the mucosa and submucosa in the large intestine. ZEN and ZEN + DON significantly decreased the number of goblet cells in the cecum and descending colon. The mycotoxins changed the number of lymphocytes and plasma cells in the large intestine, which usually increased in number. However, this effect differed between the intestine segments and toxins. Mycotoxins induced some changes in the ultrastructure of the mucosal epithelium. They did not affect the expression of proliferative cell nuclear antigen and the intestinal barrier permeability. The obtained results indicate that mycotoxins especially ZEN may influence the defense mechanisms of the large intestine.

Adrenergic regulation of cytoplasmic structures related to secretory processes in pig pinealocytes-an ultrastructural, quantitative study.

Two structures, considered as secretory in nature, are present in the pinealocytes in of the domestic pig show the presence of two structures, which are considered as secretory in nature - the dense core vesicles (DCV) and the membrane bounded (dense) bodies (MBB). The latter are extremely numerous in pig pinealocytes (they occupy 6-20% of the cytoplasm), and the number of MBB changes under different physiological and experimental conditions. Norepinephrine is the main neurotransmitter that regulates the secretion of pineal melatonin. The present study was carried out to 1) clarify whether the DCV and their source - the Golgi apparatus (GA) - as well as the MBB are controlled by norepinephrine, 2) determine the effect of adrenergic stimulation on these structures, and 3) identify the receptors involved in the regulation of these structures. The studies were performed using a static organ culture of pig pineal explants. The explants were incubated in a control medium between 08:00 and 20:00 and in a medium with 10µM norepinephrine or alpha- or beta-adrenoceptor agonists between 20:00 and 08:00 on five consecutive days. The tissues were subsequently prepared for ultrastructural analysis. The results distinctly showed that the DCV, GA and MBB in pig pinealocytes are under adrenergic control. The stimulation of the beta-adrenoceptors resulted in an increase in the numerical density of the DCV and a decrease in the relative volume of the GA in the perikarya, while the incubation with agonists of the alpha1-adrenoceptors was ineffective. The relative volume of the MBB in the perikarya significantly decreased after treatment with both beta-agonists and alpha1-agonists, which suggested the involvement of two types of adrenoceptors in the regulation of these structures.

Histological structure of duodenum in gilts receiving low doses of zearalenone and deoxynivalenol in feed.

Deoxynivalenol (DON) and zearalenone (ZEN), produced by microfungi of the Fusarium family, are among the most commonly occurring mycotoxins. They are considered important factors affecting human and animal health as well as livestock productivity. The aim of this study was to determine the effect of low doses of these mycotoxins on the histological structure of the pig duodenum. The study was performed on 72 gilts, with initial weights of approximately 25kg, divided into 4 equal groups. Group I received per os ZEN (40µg/kg BW), group II-DON (12µg/kg BW), group III-ZEN (40µg/kg BW) and DON (12µg/kg BW), and group IV-vehicle. The pigs were killed after 1, 2, 3, 4, 5 and 6 weeks of the treatment, and the duodenum samples were prepared for histological investigations. The slides were digitalized and subjected to morphometrical analysis. The treatment with DON and ZEN did not change the architecture of the mucosa or the ratio between goblet and adsorptive cells in the epithelium. The administration of DON induced an increase in the number of lymphocytes in the mucosal epithelium. Both mycotoxins, administered alone or together, increased the quantity of lymphocytes, plasma cells and macrophages with black-brown granules in the lamina propria. The time-courses of changes in the number of defense system cells evoked by DON and ZEN were different. In conclusion, dietary exposure to low doses of Fusarium mycotoxins should be considered an important risk factor for subclinical inflammation in the small intestine.

The effects of low doses of two Fusarium toxins, zearalenone and deoxynivalenol, on the pig jejunum. A light and electron microscopic study.

Immature gilts were administered per os with zearalenone (ZEN) at 40 µg/kg BW (group Z, n = 9), deoxynivalenol (DON) at 12 µg/kg BW (group D, n = 9), a mixture of ZEN and DON (group M, n = 9) or a placebo (group C, n = 9) over a period of six weeks. The pigs were sacrificed after one, three, or six weeks of the treatment (12 pigs per each time-point). Histological investigations revealed an increase in the mucosal thickness and the crypt depth as well as a decrease in the ratio of the villus height to the crypt depth in groups D and M after six weeks of exposure to the mycotoxins. The number of goblet cells in the villus epithelium was elevated in groups Z and M after one week and in group D after three weeks. The administration of ZEN increased the lymphocyte number in the villus epithelium after 1 week and the plasma cell quantity in the lamina propria after one, three, and six weeks of the experiment. DON treatment resulted in an increase in the lymphocyte number in the villus epithelium and the lamina propria after six weeks, and in the plasma cell quantity in the lamina propria after one, three, and six weeks of exposure. In group M, lymphocyte counts in the epithelium and the lamina propria increased significantly after six weeks. Neither mycotoxin induced significant adverse changes in the ultrastructure of the mucosal epithelium and the lamina propria or in the intestinal barrier permeability. Our results indicate that immune cells are the principal target of low doses of ZEN and DON.

Adrenergic activation of melatonin secretion in ovine pineal explants in short-term superfusion culture occurs via protein synthesis independent and dependent phenomena.

The ovine pineal is generally considered as an interesting model for the study on adrenergic regulation of melatonin secretion due to some functional similarities with this gland in the human. The present investigations, performed in the superfusion culture of pineal explants, demonstrated that the norepinephrine-induced elevation of melatonin secretion in ovine pinealocytes comprised of two subsequent periods: a rapid increase phase and a slow increase phase. The first one included the quick rise in release of N-acetylserotonin and melatonin, occurring parallel to elevation of NE concentration in the medium surrounding explants. This rapid increase phase was not affected by inhibition of translation. The second, slow increase phase began after NE level had reached the maximum concentration in the culture medium and lasted about two hours. It was completely abolished by the treatment with translation inhibitors. The obtained results showed for the first time that the regulation of N-acetylserotonin synthesis in pinealocytes of some species like the sheep involves the on/off mechanism, which is completely independent of protein synthesis and works very fast. They provided strong evidence pointing to the need of revision of the current opinion that arylalkylamines N-acetyltransferase activity in pinealocytes is controlled exclusively by changes in enzyme abundance.

Diurnal profiles of melatonin synthesis-related indoles, catecholamines and their metabolites in the duck pineal organ.

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.

Light and electron microscopy of the European beaver (Castor fiber) stomach reveal unique morphological features with possible general biological significance.

Anatomical, histological, and ultrastructural studies of the European beaver stomach revealed several unique morphological features. The prominent attribute of its gross morphology was the cardiogastric gland (CGG), located near the oesophageal entrance. Light microscopy showed that the CGG was formed by invaginations of the mucosa into the submucosa, which contained densely packed proper gastric glands comprised primarily of parietal and chief cells. Mucous neck cells represented <0.1% of cells in the CGG gastric glands and 22-32% of cells in the proper gastric glands of the mucosa lining the stomach lumen. These data suggest that chief cells in the CGG develop from undifferentiated cells that migrate through the gastric gland neck rather than from mucous neck cells. Classical chief cell formation (i.e., arising from mucous neck cells) occurred in the mucosa lining the stomach lumen, however. The muscularis around the CGG consisted primarily of skeletal muscle tissue. The cardiac region was rudimentary while the fundus/corpus and pyloric regions were equally developed. Another unusual feature of the beaver stomach was the presence of specific mucus with a thickness up to 950 µm (in frozen, unfixed sections) that coated the mucosa. Our observations suggest that the formation of this mucus is complex and includes the secretory granule accumulation in the cytoplasm of pit cells, the granule aggregation inside cells, and the incorporation of degenerating cells into the mucus.

The foetal pig pineal gland is richly innervated by nerve fibres containing catecholamine-synthesizing enzymes, neuropeptide Y (NPY) and C-terminal flanking peptide of NPY, but it does not secrete melatonin.

Innervation of the mammalian pineal gland during prenatal development is poorly recognized. Therefore, immunofluorescence studies of the pineals of 70- and 90-day-old foetuses of the domestic pig were performed using antibodies against tyrosine hydroxylase (TH), dopamine-ß-hydroxylase (DßH), neuropeptide Y (NPY) and C-terminal flanking peptide of NPY (CPON). The investigated glands were supplied by numerous nerve fibres containing TH and DßH. The density of these fibres was higher in the distal and middle parts of the gland than in the proximal one. NPY and CPON were identified in the majority of DßH-positive fibres as well as in a small population of DßH-negative fibres localized mainly in the proximal part of the pineal. The immunoreactive fibres were more numerous in 90-day-old foetuses than in 70-day-old ones. The effect of norepinephrine on melatonin secretion by the foetal pineals in the short-term organ culture was studied to determine the role of DßH-positive fibres during prenatal life. For the same purpose melatonin was measured in the blood in the umbilical cords and in the jugular vein of the mother. The pineals of both groups of foetuses did not secrete melatonin in the organ culture, independently of the presence or absence of norepinephrine in the medium. Melatonin concentrations in the blood in the umbilical cords of foetuses from the same litter and in the jugular vein of their mother were similar. The presence of adrenergic nerve fibres in the pig pineal during gestation does not seem to be associated with the control of melatonin secretion.

Morphological studies of the pineal gland in the common gull (Larus canus) reveal uncommon features of pinealocytes.

The avian pineal is a directly photosensory organ taking part in the organization of the circadian and seasonal rhythms. It plays an important role in regulation of many behavior and physiological phenomena including migration. The aim of the study was to investigate morphology of the pineal organ in the common gull (Larus canus). The light and electron microscopic studies were performed on the pineals of juvenile birds living in natural conditions of the Baltic Sea coast, which have been untreatably injured during strong storms in autumn and qualified for euthanasia. The investigated pineals consisted of a wide, triangular, superficially localized distal part and a narrow, elongated proximal part, attached via the choroid plexus to the intercommissural region of the diencephalon. The accessory pineal tissue was localized caudally to the choroid plexus. Based on the histological criteria, the organ was classified as the solid-follicular type. Two types of cells of fotoreceptory line were distinguished: rudimentary-receptor pinealocytes and secretory pinealocytes. Both types of cells were characterized by unusual features, which have been not previously described in avian pinealocytes: the presence of paracrystalline structures in the basal processes and their endings, the storage of glycogen in the form of large accumulations and the arrangement of mitochondria in clusters. Further studies on other species of wild water birds dwelling in condition of cold seas are necessary to explain if the described features of pinealocytes are specific for genus Larus, family Laridae or a larger group of water birds living in similar environmental conditions.

N-bromoacetyltryptamine strongly and reversibly inhibits in vitro melatonin secretion from mammalian pinealocytes.

OBJECTIVES: Cell-permeable and specific inhibitors of melatonin secretion are sill lacking among tools of the pineal research. Recently, a large effort has been made in the development of arylalkylamine N-acetyltransferase inhibitors, but in most cases the new drugs were tested exclusively using cell-free assays or non-pineal cells. The aim of the present study was to characterize the effect of N-bromoacetyltryptamine (BAT), the first synthesized cell-permeable inhibitor of arylalkylamine N - acetyltransferase, on melatonin secretion from rat and pig pineal glands. METHODS: The studies were performed in the superfusion cultures of rat and pig pineal explants. Melatonin secretion was determined by radioimmunoassay (RIA). RESULTS: BAT strongly inhibited the non-stimulated and norepinephrine - stimulated melatonin secretion from the pig and rat pineal explants, with ED50 0.3 - 0.7 microM. The adrenergic stimulation did not modify significantly the inhibitory potency of BAT on the melatonin release. The decline in melatonin secretion induced by the BAT - treatment was biphasic in both rat and pig pinealocytes, with an initial rapid phase followed by a slow one. The half-time of BAT-induced decline in the non - stimulated and norepinephrine-stimulated melatonin secretion was ca. 25 - 35 minutes. The inhibitory effect of BAT was reversible in pinealocytes of both investigated mammals. CONCLUSIONS: The results show that BAT is a potent and reversible inhibitor of the melatonin secretion in the mammalian pineal gland and open the way for the use of this inhibitor in investigations on the pinealocyte physiology performed in vitro.

Post-hatching development of the turkey pineal organ: histological and immunohistochemical studies.

OBJECTIVE: The study was performed to analyze structural changes of the turkey pineal during the post-hatching development. MATERIAL AND METHODS: The pineals were collected from male turkeys at the age of 1 day, 2, 8, 22, 56 weeks and subjected to histological investigations including morphometrical analyses. The pinealocytes were identified immunohistochemically using antiserum against hydroxyinolo-O-methyltransferase (HIOMT). RESULTS AND CONCLUSIONS: Independently of age, the pineal consisted of a narrow proximal part and a club-shaped top. The narrow part extended into the stalk attached to the diencephalon. The pineal parenchyma was formed by the follicles, surrounded by the connective tissue. The caudal part of the organ contained the pineal lumen, which prolonged into the stalk lumen. Up to the age of two weeks the stalk lumen was open to the third ventricle, later--closed. The proximal part of the stalk showed age-dependent reduction. During the investigated period of life, the pineal increased in size due to creation of new follicles, enlargement of the follicles and development of the stroma. In immature turkeys, the follicular wall was formed by elongated cells bordering the lumen and sparse, peripherally localized, round cells. This pseudostratified organization was transformed during ontogenesis into thick, multilayer structure (characteristic for 22- and 56-week-old turkeys) composed by the layer of elongated cells and several layers of round cells, located peripherally. The rudimentary-receptor and secretory pinealocytes were demonstrated based on HIOMT-immunoreactivity. The secretory pinealocytes were sparse in young birds and predominated in mature turkeys. Intra-pineal calcified concrements occurred in 56-week-old turkeys.

Diurnal rhythms of pinealocyte ultrastructure, pineal serotonin content and plasma melatonin level in the domestic pig.

The study was conducted to investigate diurnal changes in pinealocyte ultrastructure, pineal serotonin content and plasma melatonin concentration in the domestic pig. The immature pigs (n=24) were kept under a cycle of 12 h light : 12 h dark, with a photophase between 0800 and 2000. During the photophase the animals were exposed to direct sunlight. After four weeks the gilts were slaughtered at 0900, 1400, 2100 and 0200. The pineals were removed and divided into two parts - one for quantitative ultrastructural study (by a point count method) and one for serotonin assay. Simultaneously, blood samples were taken for melatonin assay. The relative volume of mitochondria in pinealocyte perikarya was significantly higher at 1400 than at 0200 and 0900 as well as at 2100 than at 0200. The relative volume of Golgi apparatus was higher at 0900 and 1400 than at 0200. The relative volume of dense bodies of the MBB-1 type in pinealocyte perikarya was significantly lower at 1400 and 2100 than at 0900. In contrast, the relative volume of MBB-2 was higher at 1400 than at 0900 and 0200. The numerical density of DCV in perikarya was significantly higher at 0200 than at 1400. No significant differences were found in rough endoplasmic reticulum, lysosomes and multivesicular bodies. The pineal serotonin content showed a prominent rhythm with the maximum at 1400. The plasma melatonin concentration was significantly higher at 0200 than at 0900, 1400 and 2100. The obtained results demonstrate that both pinealocyte ultrastructure and pineal biochemistry in the pig undergo significant changes in the course of the diurnal rhythm.