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  • 1
    Electronic Resource
    Electronic Resource
    Inverse behaviour of “synaptic” ribbon and spherule numbers in the pineal gland of male guinea-pigs exposed to continous illumination (1986)
    Springer
    Anatomy and embryology 173 (1986), S. 349-354 
    Details
    ISSN: 1432-0568
    Keywords: Pineal gland ; “Synaptic” ribbons ; “Synaptic” spherules ; Cominuous illumination ; Guinea-pig
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary There is increasing evidence that pineal “synaptic” ribbons are a heterogeneous population of organelles. In addition to “synaptic” ribbons (SR) sensu stricto, which consist of an electron-dense rod surrounded by electronlucent vesicles, “synaptic” spherules (SS) exist, the electrondense core of which is round and much wider than that of the SR. In the guinea-pig SR and SS numbers exhibit an inverse day/night rhythmicity. To gain more insight into the functional significance of SR and SS, guinea-pigs were exposed to continuous illumination for approximately 4 months (LL) and the respective structures in the pineal gland were quantitated under the electron microscope and compared with control animals kept under a lighting regiment of 12 h light and 12 h dark. It was found that SR numbers increase following LL whereas SS numbers decrease. The proximal, intermediate and distal parts of the dumbbell-shaped organ respond differently. The increase in SR numbers is significant in the distal and intermediate regions only, whereas the decrease in SS numbers is significant in the proximal and the intermediate regions only. Within each pineal region analyses of parenchymal subareas measuring 65 μm by 65 μm exhibit an inverse correlation of SR and SS numbers indicating that there are parenchymal domains in which either SR or SS predominate. Morphometric analyses of a number of pinealocytic parameters reveal minor differences between different pineal regions and that exposure to LL does not strikingly affect the pinealocyte perikarya. By contrast, the numbers of pinealocyte processes increase significantly after LL in the distal and intermediate, but not the proximal region of the pineal gland. These observations suggest structural and functional differences between different parts of the guinea-pig pineal gland.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00318918
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of electrical stimulation of the superior cervical ganglia on the number of “synaptic” ribbons and the activity of melatonin-forming enzymes in the rat pineal gland (1989)
    Springer
    Anatomy and embryology 179 (1989), S. 341-345 
    Details
    ISSN: 1432-0568
    Keywords: Melatonin synthesis ; Pineal gland ; Rat ; “Synaptic” ribbons ; Sympathetic stimulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Melatonin metabolism in the mammalian pineal gland is under the clear influence of sympathetic fibers originating in the superior cervical ganglia (SCG). Previous studies suggested that pineal “synaptic” ribbons (SR) as well are regulated by the gland's sympathetic innervation. To gain more insight into the mechanisms involved, we examined the effects of sympathetic stimulation on SR number and on the activity of melatonin forming enzymes, serotonin N-acetyltransferase (NAT) and hydoxyindole-O-methyltransferase (HIOMT). The SCG in adult male rats were stimulated electrically during daytime for either 15 or 120 min. Immediately following stimulation, the glands were removed and processed for electron microscopy and for the determination of NAT and HIOMT activities. No differences in pineal SR number, size or location were found in rats stimulated with either parameters when compared with sham-stimulated or control animals. While the activity of HIOMT remained unchanged, the activity of NAT was also unaltered following 15 min of stimulation, but was augmented approximately three-fold in animals stimulated for 120 min. It is concluded that if SR in the rat pineal gland are under sympathetic control, the regulation is different from that involved in melatonin formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00305060
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  • 3
    Electronic Resource
    Electronic Resource
    Dual Neurosecretory Innervation of the Adenohypophysis of Hippocampus , the Sea-horse (1967)
    [s.l.] : Nature Publishing Group
    Nature 214 (1967), S. 309-309 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] We investigated independently two species of Hippocampus, but our findings were sufficiently consistent to be presented together in one communication. The pituitaries of Hippocampus guttulatus prepared at Naples were investigated at Birmingham, and those of Hippocampus cuda at Wurzburg. Two kinds ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/214309a0
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  • 4
    Electronic Resource
    Electronic Resource
    A Functional Relationship between Neurosecretory Fibres and Pituicytes in the Eel (1965)
    [s.l.] : Nature Publishing Group
    Nature 208 (1965), S. 1343-1343 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Fifty eels were kept in darkness for 35 weeks and then transferred to illuminated white or black backgrounds for 4 h. The pituitaries of the white background animals showed the following features in contrast to those of eels kept on a black background: (1) Many synapses between neurosecretory ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/2081343a0
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  • 5
    Electronic Resource
    Electronic Resource
    A Dual Neurosecretory Innervation of the Pars Distalis of the Pituitary of the Eel (1965)
    [s.l.] : Nature Publishing Group
    Nature 208 (1965), S. 1343-1344 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Under the electron microscope, however, an extensive neurosecretory innervation of the pars distalis can be demonstrated. Most of the fibres which invade the anterior lobes of the pituitary (proximal and rostral pars distalis) are seen to contain vesicles, irregular in outline, each with a central ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/2081343b0
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  • 6
    Electronic Resource
    Electronic Resource
    Biphasic 24-Hour Variations in Cyclic GMP Accumulation in the Rat Pineal Gland Are Due to Corresponding Changes in the Activity of Cytosolic and Particulate Guanylate Cyclase (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 59 (1992), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Various parameters of the rat pineal gland display a 24-h rhythm. However, nothing is known about possible 24-h variations in cyclic GMP (cGMP) metabolism. In the present study, 24-h variations in pineal gland cGMP accumulation were investigated by determining the increase in cGMP level with and without inhibitors of phosphodiesterase at different time points over a light/dark cycle (12/12 h). Furthermore, the activity of guanylate cyclase (GC) was determined under substrate-saturated conditions regarding the cytosolic and particulate forms of the enzyme. It has been found that cGMP accumulation and GC activity display biphasic 24-h variations with two peaks—one ∼7 h after lights “on” and the other ∼7 h after lights “off.” The activity of cytosolic GC remains unchanged in the presence of the nitric oxide (NO) synthesis inhibitor N-monomethyl-L-arginine, indicating that 24-h variations in the activity do not reflect changes in the synthesis of the GC stimulator NO.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1992.tb10098.x
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  • 7
    Electronic Resource
    Electronic Resource
    Adrenergic Stimulation of Cyclic GMP Formation Requires NO-Dependent Activation of Cytosolic Guanylate Cyclase in Rat Pinealocytes (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 61 (1993), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Cyclic GMP (cGMP) formation in rat pinealocytes is regulated through a synergistic dual receptor mechanism involving β-and α1-adrenergic receptors. The effects of N-monomethyl-l-arginine (NMMA), which inhibits nitric oxide (NO) synthase and NO-mediated activation of cytosolic guanylate cyclase, and methylene blue (MB), which inhibits cytosolic guanylate cyclase, were investigated in an attempt to understand the role of NO in adrenergic cGMP formation. Both NMMA and MB inhibited β-adrenergic stimulation of cGMP formation as well as α1-adrenergic potentiation of β-adrenergic stimulation of cGMP formation, whereas they had no effect in unstimulated pinealocytes. The inhibitory action of NMMA was antagonized by addition of l-arginine. On the basis of these findings it can be concluded that the adrenergic stimulation of cGMP formation involves NO synthesis followed by activation of cytosolic guanylate cyclase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1993.tb03548.x
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  • 8
    Electronic Resource
    Electronic Resource
    In Vitro Synthesis of Dopamine and Noradrenaline in the Isolated Rat Pineal Gland: Day-Night Variations and Effects of Electrical Stimulation (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 53 (1989), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Isolated rat pineal glands were incubated in vitro in a medium containing [I4C]dopamine or [14C]tyrosine, and the tissue contents of l4C-labelled and total dopamine and noradrenaline were determined by HPLC followed by electrochemical detection and scintillation spectrometry. During incubation with [l4C]dopamine, the labelled amine accumulated in pineal glands and was partially converted into [l4C]noradrenaline. Nomifensine, a neuronal amine uptake blocker, largely inhibited the accumulation of [l4C]dopamine and the formation of [14C]noradrenaline. These experiments demonstrated dopamine β-hydroxylase activity in the sympathetic nerves of the pineal gland. During incubation with [14C]tyrosine, formation of [l4C]dopamine and [14C]noradrenaline was observed in the pineal tissue, indicating that noradrenaline can also be synthesized from dopamine, endogenously formed in the gland. Electrical stimulation of the stalk region of the pineal gland during incubation with [l4C]dopamine enhanced the accumulation of [l4C]dopamine and synthesis of [14C]noradrenaline. Electrical stimulation also enhanced the formation of [l4C]dopamine during incubation with [l4C]tyrosine. Compared to that at midday, the tissue content of endogenous noradrenaline at midnight was enhanced by 50% and that of dopamine by 450%. The in vitro accumulation of [14C]dopamine, as well as the synthesis of [14C]dopamine and [14C]noradrenaline, was also increased at midnight. In conclusion, sympathetic nerves in the rat pineal gland contain tyrosine hydroxylase and dopamine β-hydroxylase, the two enzymes required for the synthesis of noradrenaline. The capacity of the pineal gland to synthesize dopamine and noradrenaline is enhanced during the night.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1989.tb07342.x
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  • 9
    Electronic Resource
    Electronic Resource
    Mouse photoreceptor synaptic ribbons lose and regain material in response to illumination changes (2004)
    Oxford, UK : Blackwell Science, Ltd
    European journal of neuroscience 19 (2004), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Chemical synapses equipped with ribbons are tonically active, high-output synapses. The ribbons may play a role in the trafficking of synaptic vesicles. Recent findings in retinal rod cells of BALB/c mice indicate that ribbons are large and smooth in the dark phase, and, due to the formation and release of protrusions, small during the light phase. As a consequence of these changes, ribbons may traffick fewer vesicles in the light than in the dark phases. The aim of the present study was to find out whether the above ribbon changes in this mouse strain are strictly illumination-dependent and which signalling processes may be involved. Here, we show that ribbons form protrusions and release them into the cytoplasm within 30–60 min after lights on, the reverse occurring within 30 min after lights off. Under constant light or constant dark, no circadian rhythm of synaptic ribbon changes is observed. The illumination-dependence of ribbon structure is supported by in vitro experiments showing that in dark-adapted retinas, light induces the same morphological changes as in vivo. In vitro, the effect of light on the ribbons can be counteracted by cyclic guanosine monophosphate and melatonin. In dark-adapted retinas, light effects can be produced by decreasing the calcium ion concentrations in the incubation media. These results suggest that in retinal rod cells, the well known phototransduction signalling mechanisms may be responsible for the ribbon changes presently and previously reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-9568.2004.03198.x
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  • 10
    Electronic Resource
    Electronic Resource
    No Correlation of Pineal “Synaptic” Ribbon Numbers and Melatonin Formation in Individual Rat Pineal Glands (1984)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of pineal research 1 (1984), S. 0 
    Details
    ISSN: 1600-079X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: As previous circadian studies of pineal “synaptic” ribbon numbers and melatonin formation suggested that a positive correlation of the two variables exists, in the present investigation this problem was examined in individual pineal glands of rats killed at 1200 h and 2400 h, respectively. For this purpose, one half of the gland was processed for electron microscopy and the ribbons were counted in an area of 20,000 μm2 tissue; in the other half serotonin N-acetyltransferase (NAT) activity and melatonin content were determined. No correlation was found to exist between ribbon numbers and pineal NAT activity, pineal melatonin levels and serum melatonin levels, either at day- or at nighttime. It is concluded that the ribbons may perhaps be more closely related to the innervation of the pineal gland than to melatonin formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1600-079X.1984.tb00210.x
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