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Journal Article 2005; 26(5): 503-510 PubMed PMID: 16264410 Citation  Keywords:  Aging:physiology, Animals, Chickens:metabolism, Darkness, Female, Light, Male, Melatonin:metabolism, Organ Culture Techniques, Perfusion, Pineal Gland:metabolism, Temperature,.   

: The melatonin rhythm of cultured chicken pineal cells can be synchronized by cyclic environmental effects. Unlike the effects of light on the melatonin secretion, those of the temperature changes are much less known. Similarly, only a few data are available on the interactions between environmental illumination and periodic temperature changes and on the sensitivity of the pineal gland to temperature changes in different ages of animals. We monitored the effects of temperature on chicken pineals for several days in vitro, in a perifusion system under different illumination patterns. The effects of temperature on pineals from chicken of different age were also compared. The phase of the melatonin rhythm was controlled by periodic elevations of temperature under both constant darkness and continuous illumination. These results show that rhythmic changes of temperature prevent desynchronization induced by constant light. Following elevation of the temperature, the melatonin rhythm of pineals of young chickens (less, than 14 weeks old) was altered for 16 - 18 hours. Similar changes in melatonin rhythm were not found in older animals. It is concluded that the sensitivity for temperature changes of the pineal cells is varying with age....

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Comparative Study 2004; 25(1-2): 102-108 PubMed PMID: 15159692 Citation  Keywords:  Adaptation, Physiological, Animals, Circadian Rhythm:radiation effects, Darkness, Light, Male, Photoperiod, Photoreceptor Cells:radiation effects, Pineal Gland:radiation effects, Rats, Rats, Wistar,.   

OBJECTIVE: This study was aimed to examine the pineal gland of rats exposed to constant light and darkness at light and electron microscopic level.

DESIGN: For this purpose 18 male Wistar rats were used. Animals were divided into three groups. Rats in group I (Control) were kept under 12 hrs light: 12 hrs dark conditions. Rats in group II were exposed to constant darkness, while rats in group III were exposed to constant light for 6 weeks. At the end of the experiment, all animals were killed by decapitation. The pineal glands of rats were removed, then processed for light and electron microscopy.

RESULTS: In our study, extensive number of pinealocytes was observed in the structure of pineal gland of rats exposed to constant darkness and some of the observed pinealocytes were determined to contain double nucleoli. Furthermore, mitochondria and lipid droplets in the cytoplasm of pinealocytes were increased and rough endoplasmic reticulum sacs were enlarged in this group. Whereas, in rats those exposed to the constant light, a decrease in pinealocyte intensity was associated with increase in the connective tissue between parenchymal cells. Additionally, mitochondria and lipid droplets in the cytoplasm of cells were decreased.

CONCLUSIONS: It was observed that the pinealocyte cell activity of rats exposed to constant darkness was increased but decreased in rats exposed to constant light....

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Comparative Study 2002; 23(4): 345-350 PubMed PMID: 12195239 Citation  Keywords:  Aging:metabolism, Animals, Antioxidants:metabolism, Darkness, Hippocampus:enzymology, Lighting, Lipid Peroxidation:physiology, Male, Pineal Gland:physiology, Rats, Rats, Wistar, Receptors, N-Methyl-D-Aspartate:metabolism, Superoxide Dismutase:metabolism,.   

OBJECTIVES: To investigate the effects of pinealectomy on lipid peroxidation, antioxidant status and NMDA receptor subunits 2A and 2B concentrations in hippocampus.

DESIGN: Forty-eight male Wistar-albino rats were used.

SETTINGS: Animals were divided into three groups: 24 h dark throughout the study (highest melatonin release), 24 h light exposure (light-induced functional pinealectomy) and 12 h light/12 h dark exposure (control group). Thereafter, each group was divided into two groups as young and old animals.

RESULTS: There was an increase in NR2A and NR2B concentration in DY group compared to all other treatments. CuZn and Mn SOD activities were found to be increased in CO compared to CY group. Continual light exposure for 4 weeks did not change neural CuZn and Mn SOD activities. In old rats, light exposure reduced the activities of both CuZn and Mn SOD relative to those in the young animals. In addition, CuZn and Mn SOD activities were higher in dark exposed rats than in those in the continual light exposed or LD 12:12 rats. GSH-Px activity was found elevated in the DY rats compared to the CY groups. MDA levels were significantly higher in the CO than in the CY group.

CONCLUSIONS: NR2A and NR2B receptor concentrations in hippocampus of the rats maintained in dark showed significant increases compared to the control and functional pinealectomy groups but there was no significant increase in lipid peroxidation....

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Editorial 2002; 23(Suppl 2): 71-78 PubMed PMID: 12163852 Citation  Keywords:  Darkness, Decision Making, Humans, Light:adverse effects, Neoplasms:epidemiology, Neurosecretory Systems:physiology, Risk Factors,.   

: Research on light at night and cancer is evolving at an accelerating pace, fueled largely by exciting results in rodent toxicology and basic human biology. Epidemiologic research is at a relatively early stage of development in which the exposure surrogates such as shift work and blindness predominate. Causal graphs for shift work, light at night and breast cancer illustrate some of the subtleties that can arise in the use of exposure surrogates of different kinds. Baseline data on circadian rhythms and melatonin cycles among human populations living at different latitudes are needed. Epidemiologic study of this topic is expected to mature soon as studies begin to incorporate quantitative and semiquantitative measurements and personal histories of exposure to light at night. The current emphasis on breast cancer should widen to include other cancers and intermediate outcomes. An advance in epidemiologic studies of blind persons would be to compare cancer rates between the "cortically blind" and the "retinally blind" within levels of visual impairment. Without a proposed intervention to reduce exposure to light at night, attributable fraction and attributable caseload estimates are meaningless. In the near future, both epidemiologic and laboratory research in this area are expected to grow appreciably in scope and scale....

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Journal Article 2002; 23(Suppl 2): 52-56 PubMed PMID: 12163849 Citation  Keywords:  Animals, Darkness, Humans, Light:adverse effects, Melatonin:physiology, Neoplasms:physiopathology, Photoperiod, Pineal Gland:physiology,.   

: Over the past few years, we have shown that the surge of melatonin in the circulation during darkness represents a potent oncostatic signal to tissue-isolated rat hepatoma 7288CTC, which is an ER+ adenocarcinoma of the liver. This oncostatic effect occurs via a melatonin receptor-mediated suppression of tumor cAMP production that leads to a suppression of the tumor uptake of linoleic acid (LA), an essential fatty acid with substantial oncogenic properties. The ability of LA to promote cancer progression is accomplished by its intracellular metabolism to 13-hydroxyoctadecadienoic acid (13-HODE) which amplifies the activity of the epidermal growth factor receptor/mitogen-activated protein kinase pathway leading to cell proliferation. By blocking tumor LA uptake, melatonin effectively blocks the production of 13-HODE and thus, markedly attenuates tumor growth. A similar effect of melatonin is observed in tissue-isolated, ER+ MCF-7 human breast cancer xenografts and nitrosomethylurea (NMU)-induced rat mammary cancers. When male rats bearing tissue-isolated hepatomas are exposed either to constant bright light (300 lux) or dim light (0.25 lux) during the dark phase of a 12L:12D photoperiod, the latency to onset was significantly reduced while the growth of tumors was markedly increased over a 4 wk period as compared with control tumors in 12L:12D-exposed rats. In constant light- and dim light during darkness-exposed rats, melatonin levels were completely suppressed while tumor growth, LA uptake and 13-HODE production were markedly increased. Similar results were obtained in constant bright light-exposed female rats bearing tissue-isolated NMU-induced mammary cancers or MCF-7 human breast cancer xenografts. To date, these studies provide the most definitive experimental evidence that light exposure during darkness increases the risk of cancer progression via elimination of the nocturnal melatonin signal and its suppression of tumor LA uptake and metabolism to 13-HODE....

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