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  • 1
    ISSN: 1365-2761
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1420-9071
    Keywords: Melatonin ; receptors ; in vitro ; autoradiography ; brain ; pituitary
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The influence of melatonin on circadian and photoperiodic functions in numerous species is well documented. It is known that the effect of melatonin on circadian rhythmicity is mediated via the suprachiasmatic nucleus (SCN), the biological clock of the brain. It is not known however where the photoperiodic effects of melatonin are mediated. Evidence from brain lesioning and melatonin implant studies point to a site in or near the medial hypothalamus. In contrast to these studies, melatonin receptors have been reported in widespread areas of the brain, the pituitary and in peripheral tissues. The characteristics of the reported melatonin receptors vary widely between studies and consequently no definitive description of a physiologically relevant melatonin receptor has received universal recognition. This review marshals recent evidence for the localization and characterization of the melatonin receptor and discusses these findings in the context of the known effects of the hormone in different species.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 113 (1982), S. 189-192 
    ISSN: 1615-6102
    Keywords: Brassica napus ; Membrane ; Nucleolus ; Nucleus ; Ultrastructure ; Vacuole
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Vacuole-like structures were found in the nuclei of root tip cells ofBrassica napus. The cells containing the unusual nuclear inclusions were found to be adjacent to zones of degenerating cells. Such groups of cells occurred irregularly in the meristematic regions of the young root tips. The possibility that they represent changes which have occurred in old seeds is discussed. The “vacuole-like” structures seen in the cells adjacent to the degenerating zones were bounded by a membranous layer 12 nm thick. This is thicker than most cellular membranes. The “vacuoles” frequently contained inclusions and showed similarities to protein bodies reported elsewhere. The structures are thought to represent rearrangements of cell products which may have accumulated through an imbalance of metabolism in consequence of the imminent cell degeneration.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of pineal research 26 (1999), S. 0 
    ISSN: 1600-079X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Summer infertility remains a major problem in domestic pigs. It has been proposed that sows which display this trait are inherent seasonal breeders. The influence of photoperiod on domestic pigs has been difficult to ascertain as significant diurnal fluctuations in blood levels of the pineal hormone, melatonin, which provide a direct neuroendocrine transduction of the ambient photoperiod in other species, remain questionable in adult pigs. To investigate whether the pig is potentially receptive to melatonin, central sites of action for this hormone were localized and characterized within the brain and pituitary of the neonatal pig by in vitro autoradiography using 2-(125I)iodomelatonin. Specific binding was distributed over a number of discrete regions of the brain including the cerebral cortex, hypothalamus, thalamus, brainstem, and cerebellum. The choroid plexus, and the pars tuberalis and pars distalis of the pituitary were also specifically labeled. Specific binding was completely abolished in the presence of 10−7 M melatonin, and inhibited in the presence of 10 −4 M GTPγS (guanosine-5-0-(3-thiotriphosphate)), a non-hydrolysable analogue of GTP, in all regions examined, indicating that binding is representative of a G-protein coupled receptor.Characterization studies showed that 2-(125I)iodomelatonin binding was saturable with a dissociation constant (Kd) in the low picomolar range (∼ 30 pM). Competition studies with iodomelatonin, melatonin, N-acetylserotonin and serotonin (5-HT) gave IC50 values similar to those previously characterized for the melatonin receptor in the ovine pars tuberalis.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report properties of device quality Hg1−xCdxTe grown by a precracking metalorganic chemical vapor deposition technique. The refinement of the low-temperature growth process and a higher purity metalorganic mercury source enable us to obtain material which has a carrier concentration of 2×1015 cm−3 and mobility as high as 330 000 cm2/V s. Infrared transmission spectra and the photoluminescence measurements obtained from this material will be presented. With further development in the synthetic route of the metalorganic mercury source, further improvement in the purity of the Hg1−xCdxTe is possible.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have fabricated high-sensitivity Hg1−xCdxTe detectors from low-temperature metalorganic vapor deposition samples. Responsivities of R=2000 V/W and detectivities of D*=2×1010 cm Hz1/2/W have been achieved.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 1329-1331 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For the first time, small-period epitaxial superlattices were grown using plasma-enhanced chemical vapor deposition. The superlattices were periods of HgTe-CdTe grown on CdTe substrates at 150 °C using dimethylcadmium, dimethylmercury, and dimethyltelluride. Cross-section transmission electron microscopy shows that layers as thin as 80 A(ring) were obtained.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 50 (1988), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Static and superfused pineal slices (750 μm) have been used to study the control of melatonin synthesis by ovine pineals. Static incubates show a time-dependent accumulation of melatonin in the medium; this is significantly increased by stimulation with norepinephrine (NE) (10−5M), reaching 300% above control levels after 4 h. Perifused pineal slices show a rapid rise in melatonin release within 12–18 min in response to NE stimulation. This reaches a 3.5–4.5-fold increase in melatonin released within 30 min. Withdrawal of NE is associated with a rapid return to prestimulated levels within 12–18 min. These time-course characteristics compare favorably to those changes seen in vivo. The formation of [14C]melatonin from [14C]-tryptophan shows a linear increase with time. In the presence of NE (10−5M), the rate of synthesis is increased, albeit after an initial time lag of at least 30 min. The latter may reflect an N-acetyltransferase-independent mechanism of synthesis and release. In static incubations, propranolol (10−5M) inhibited NE-induced melatonin production by about 60%. but prazosin (10−5M) had no effect. As dibutyryl cyclic AMP (10−3M) stimulated melatonin production, it is concluded that β-receptors are of primary importance to the control of melatonin production, as in the rat. The role of α1-receptors is less clear, but the stimulatory action of phorbol 12-myristate 13-acetate on melatonin release implicates a receptor linked to phosphatidylinositol turnover.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Photoperiodic control of the neuroendocrine axis is mediated by changes in the duration of the nocturnal melatonin signal. This study tested the hypothesis that reading of the signal depends upon the presence of a period free of melatonin between successive signals. Adult male Syrian hamsters were pinealectomized and received chronic subcutaneous infusions of melatonin or saline for 6 weeks. Animals which received saline had large testes. Those which received a single daily infusion which lasted for 10 h (50 ng/h) followed by 14 h without infusion underwent gonadal atrophy. Other animals received a compound melatonin signal in which the melatonin-free interval was occluded by a continuous infusion (25 ng/h). Superimposed upon this was a 10 h phasic increase in infusion rate such that the maximum rate of infusion was equivalent to that observed in controls (25 ng/h increase, 50 ng/h peak rate), or the increase in rate over the baseline was the same as in controls (50 ng/h increase, 75 ng/h peak rate). In neither group did the animals undergo gonadal regression. Analysis of iodomelatonin binding sites by in vitro autoradiography failed to reveal any systematic difference between animals which did and did not respond to melatonin and so the absence of a response could not be attributed to loss of receptors. These data demonstrate that the photoperiodic system cannot identify the melatonin signal solely upon the features of nocturnal peak height or amplitude of the peak over baseline. They are consistent with the hypothesis that the melatonin-free interval plays a significant role in photoperiodic time measurement.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Melatonin acts via high affinity, G-protein coupled, seven transmembrane domain receptors. To precisely localize these receptors, antibodies were raised in chickens against a 15 amino acid fragment at the intracellular C-terminal region of the human melatonin receptor subtype mt1 (DSSNDVADRVKWKPS, mt1338−352). A chimeric form of the receptor with a hydrophilic Flag peptide (DYKDDDDK) in sequence with the extracellular N-terminus (Flag-mt1) was generated by polymerase chain reaction and expressed in mammalian cell lines. An IgY antibody (Y31), which gave high antibody titres by enzyme-linked immunosorbent assay, was used to localize Flag-mt1 in stably transfected cells by immunofluoresence. Flag-mt1 localization with Y31 was identical to that obtained with the M5 antibody directed against the Flag epitope and was mainly localized to the Golgi apparatus with some staining at the cell surface. No staining was seen in untransfected cells with either antibody. Y31 staining was abolished using antibody preabsorbed with peptide antigen. Y31 immunofluorescence in fetal human kidney sections was restricted to nephrogenic regions and matched that of 2-(125I)iodomelatonin binding and mt1 gene expression by in situ hybridization. Y31 was used to immunoprecipitate biotinylated membrane proteins from Flag-mt1 stably transfected and untransfected CHO cells. Western blotting of immunoprecipitated proteins revealed two major bands specific to stably transfected cells, one at 63 kDa and one at 86 kDa. The first band almost certainly corresponds to the glycosylated form of Flag-mt1 and the second band to receptor dimers. Thus, Y31 antibody is suitable for use in detecting the human mt1 receptor subtype in tissues and in transfected cells.
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