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  • Pineal gland  (1)
  • SCN neurons  (1)
  • iontophoresis  (1)
  • melatonin synthesis  (1)
  • rat  (1)
  • receptorautoradiography  (1)
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  • 1
    ISSN: 1432-1106
    Keywords: Pineal gland ; Circadian rhythm ; Golden hamster ; Electrophysiology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In one of the most-widely used species in pineal gland research, the strongly photoperiodic golden hamster, Mesocricetus auratus, no electrophysiological data on pinealocytes are currently available. To fill this gap, in the present study 185 spontaneously active pinealocytes from male golden hamsters were recorded extracellularly, both during day- and night-time (light: dark cycle 12 ∶ 12, lights on at 07.00 h). As in other species, pinealocytes exhibited action potentials of 1–2 ms duration. An irregular firing pattern was observed in 95% of the pinealocytes, the remainder fired more regularly or showed a phasic discharge pattern. The firing frequencies ranged from 0.2 to 25 Hz and showed clear time-dependent differences. From 07.00 h to 22.00 h the mean firing frequencies were identical, i.e. in the range of 2 Hz; between 22.00 h and 01.00 h mean discharge rate increased to 5 Hz and exhibited a peak of 7 Hz between 01.00 h and 04.00 h, followed by a decrease to 4 Hz between 04.00 h and 07.00 h. Electrical stimulation of the superior cervical ganglion during day-time resulted in an augmentation of firing frequency in some pinealocytes and a decrease in others; during night-time, inhibitory responses only were observed. Photic stimulation, or electrical stimulation of either the optic chiasm or the habenular nuclei mostly decreased the firing rate of pinealocytes. Compared to other mammalian species, the electrophysiological properties of golden hamster pinealocytes appear to be basically similar.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1420-9071
    Keywords: Central innervation ; melatonin synthesis ; pineal gland ; rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary To investigate a possible central neural influence on nocturnal pineal metabolic activity, frontal transsections of the stria medullaris thalami were conducted. Enzymes involved in melatonin synthesis, i.e. N-acetyltransferase and hydroxyindole-O-methyl-transferase, exhibited reduced activities in operated animals when compared to controls. These results indicate a modulatory role of central structures on noctural pineal indole metabolism.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1435-1463
    Keywords: SCN neurons ; circadian rhythm ; iontophoresis ; melatonin receptors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Circadian rhythms, endogenously generated in suprachiasmatic nuclei (SCN), seem to be under the direct influence of melatonin. Therefore, the effect of iontophoretically applied melatonin on electrical activity of SCN neurons was investigated in vitro. Usually, melatonin had an inhibitory effect. In the 3-h periods before (2.00–5.00 p.m.) or after (5.00–8.00 p.m.) the light-dark transition the percentage of SCN neurons sensitive to melatonin was very high (80% and 100%, respectively). However, efficacy of melatonin was low in the periods preceeding (20%) and following (33%) this 6-h time interval.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1435-1463
    Keywords: Melatonin receptors ; chicken brain ; visual suprachiasmatic nucleus ; 125I-melatonin ; receptorautoradiography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Melatonin, released in a circadian manner from the avian pineal gland into the circulation, is concentrated in distinct brain areas, possibly by receptor-mediated uptake mechanisms. For anatomical localisation of putative melatonin receptors in birds, cryostat-cut, coronal 15 Μm brain sections of 2-day-old chicken were investigated by means of in vitro receptorautoradiography, using125I-melatonin as a ligand. Binding occurred in brain structures receiving or mediating visual or auditory sensory input. Binding characteristics were investigated in homogenates of a brain region labelled by125I-melatonin and showed to be specific and saturable (Kd: 87.2 pM; Bmax: 16.1 fmol/mg protein). Results confirm that a wealth of structures in chicken brain are equipped with putative melatonin receptors, including the visual suprachiasmatic nucleus. However, as results show that fewer structures were labelled in the brain of 2-day-old chicken as compared to a similar investigation conducted with 12-day-old chicken, developmental changes in distribution and/or density of putative melatonin receptors might be present.
    Type of Medium: Electronic Resource
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