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Pinealocyte
Objective To investigate the effect of amputating the tail on the circadian rhythm of serum melatonin level in mice.Methods The distal 2.5 cm length of the tails in female mice were removed.72 normal and 72 tail-amputated female mice were divided into 6 groups randomly,with 12 mice in each group.All the mice were feeded under a standard light-dark rhythm(light phase 6:00-18:00;light:dark=12:12 h) for two weeks.Then they were decollated at 4:00,8:00,12:00,16:00,20:00 and 24:00,respectively,and the blood was drawn quickly to study the circadian rhythm of serum melatonin level by ELISA.Results Significant circadian rhythm of normal mice′s serum melatonin level was found.The serum melatonin level was lower in the day-time and higher at night.The melatonin level at night is about 2.5 times as that in the day-time.Similar circadian rhythm of serum melatonin level in tail-amputated mice was found.The serum melatonin level at night was about 1.8 times as that in the day-time.Conclusion Both normal and tail-amputated mice had significant circadian rhythms of serum melatonin level.Compared with normal mice,serum melatonin level of tail-amputated mice in the day-time was significantly increased and fluctuated obviously.
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OBJECTIVES Pineal gland hormone, melatonin, is a current issue of interest for accumulating data concerning its diverse physiological functions. The disturbances in melatonin secretion are observed in different pathological conditions involving pineal regions, but it is not ascertained if those disturbances present any clinical implications. The aim of this work was to examine whether pineal gland compression changes melatonin secretion. SETTING AND DESIGN The experiment was carried out on adult rats, divided into four equal groups: (i) control (no surgery was performed), (ii) sham-operated, (iii) with sham pineal gland compression and (iv) with pineal gland compression performed by cotton piece application. METHODS The profile of melatonin secretion was assessed in blood samples collected five times daily, every second day, starting from 8 to 14 day following surgery. RESULTS We found that surgery itself significantly increased night melatonin secretion in comparison to controls. By contrast, in pineal-gland compressed rats, melatonin secretion was lower than in control group, suggesting that the influence of pineal compression overcame that induced by operation stress. CONCLUSIONS In conclusion, we presume that pineal gland compression (like in case of some tumors) results in decrease of the concentration of blood melatonin, that may possibly result in decreased protective action of the indoleamine.
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The morphological and biochemical aspects of the pineal gland of pregnant and non-pregnant female vizcachas were investigated to examine whether there is a relationship between the pregnancy and this gland.Pregnant and non-pregnant adult female vizcachas were used. The ultrastructure of type I cell (dark and light pinealocytes) was studied. Pineal and serum melatonin were investigated by radioimmunoassay. Radiometric methods were applied to investigate the arylalkylamine-N-acetyltransferase (AA-NAT) and hydroxyindole-O-methyltransferase (HIOMT) activities.The morphological study showed the existence of dark and light pinealocytes. The differences between both cells are slight. However, the appearance of dark pinealocytes suggests that they have a high activity. These cells were more abundant in the pineal gland of pregnant females. The pineal melatonin levels and the AA-NAT activity were higher in the pregnant females. Serum melatonin and HIOMT activity did not show significant differences.Our results suggest that the morphological and biochemical changes in the pineal gland of pregnant vizcachas are associated with the gestation. However, the relation between the pineal gland and the pregnancy is complex and further studies are necessaries to clearly establish it.
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Endocrine gland
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Both qualitative and quantitative comparative studies of "dark" and "light" pinealocytes of the porcine pineal gland have been carried out. These cells differ from each other in their electronic density of cytoplasm, shape of nucleus, the structure of membrane bound dense bodies and the number of microtubules and smooth endoplasmic reticulum. The membrane bound dense bodies--characteristic structures of pig pinealocytes as well dense core vesicles occur in both types of cells. The relative volume of the majority of the cells' organellae apart from the Golgi apparatus, also do not show any significant difference. The results obtained support a functional basis for pinealocyte differentiation in the porcine pineal gland.
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Pinealocyte
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Darkness
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It has been known for many years that the pineal gland is involved in regulating tumor growth. In order to evaluate the functional activity of the pineal gland in neoplastic diseases, melatonin serum levels and its light/dark rhythm have been determined with the RIA method in patients affected by various forms of tumor. Irrespectively of the type of the tumor and of its localization, existence of two subpopulations has been observed within the oncologic patients, the former with normal levels of melatonin, and the latter with high ones. The light/dark rhythm of melatonin was anomalous in some cases. An evident decrease of serum melatonin values was seen after chemotherapy. It might be interesting to establish whether melatonin levels may conditionate the prognosis of patients with cancer.
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Abstract The zebrafish pineal gland plays a fundamental role in the regulation of the circadian rhythm through the melatonin secretion. The pinealocytes, also called photoreceptive cells, are considered the morphofunctional unit of pineal gland. In literature, the anatomical features, the cellular characteristics, and the pinealocytes morphology of zebrafish pineal gland have not been previously described in detail. Therefore, this study was undertaken to analyze the structure and ultrastructure, as well as the immunohistochemical profile of the zebrafish pineal gland with particular reference to the pinealocytes. Here, we demonstrated, using RT‐PCR, immunohistochemistry and transmission electron microscopy, the expression of the mRNA for rhodopsin in the pineal gland of zebrafish, as well as its cellular localization exclusively in the pinealocytes of adult zebrafish. Moreover, the ultrastructural observations demonstrated that the pinealocytes were constituted by an outer segment with numerous lamellar membranes, an inner segment with many mitochondria, and a basal pole with the synapses. Our results taken together demonstrated a central role of zebrafish pinealocytes in the control of pineal gland functions. Microsc. Res. Tech., 2011. © 2011 Wiley Periodicals, Inc.
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Danio
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Endocrine gland
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Melatonin,N-acetyl-5-methoxytryptamine, is a hormonal product of the pineal gland. Its synthesis is higher at night than during the day in all vertebrates including man. Once melatonin is produced in the pineal gland it is quickly released into the vascular system. The rapid release of melatonin is generally believed to relate to its high lipophilicity which allows it to readily pass through the membrane of the pinealocytes and the endothelial cells which line the capillaries. The result of the nocturnal synthesis and secretion of melatonin is high blood levels at night. Also because of its highly lipophilic nature, melatonin from the blood readily escapes into every other bodily fluid and all cells in the body. Until recently it was generally thought that melatonin's action in the organism depended on its exclusive interaction with specific receptors on cells located in discrete locations. Certainly, the interactions of melatonin with these membrane-bound receptors are believed to mediate the endocrine and circadian rhythm effects of melatonin. It was recently discovered, however, that melatonin's primary action may not depend on the previously described membrane receptors. We have found that melatonin is a very potent hydroxyl radical scavenger; free radicals and the hydroxyl radical in particular, because of its very high reactivity, can be extremely damaging to macromolecules in cells. Compared to glutathione and mannitol, two well known free radical scavengers, melatonin is a more powerful scavenger and affords protection of molecules, especially DNA, from oxidative damage. Melatonin's extremely high diffusibility is important for its scavenging action because this feature allows it to enter all cells and every subcellular compartment. Whereas the free radical quenching activity of melatonin does not require a receptor, we also have evidence that it may be bound in the nucleus thereby providing on-site protection to DNA. Besides scavenging the highly toxic hydroxyl radical, melatonin also stimulates glutathione peroxidase activity which metabolizes the precursor of the hydroxyl radical, hydrogen peroxide, to water. Thus, melatonin has at least two means to protect the cell from oxidative damage, i.e., it breaks down hydrogen peroxide to harmless water and, in the event any hydroxyl radicals are formed, melatonin scavenges them. Melatonin may be the premier molecule to protect the organism from oxidative damage.
Free radical scavenger
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