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Pinealocyte

About: Pinealocyte is a research topic. Over the lifetime, 1605 publications have been published within this topic receiving 55609 citations.


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Journal ArticleDOI
TL;DR: A role for intracellular calcium fluxes in entrainment of the circadian pacemaker is pointed toward.
Abstract: Chick pineal cells in dispersed cell culture display a persistent, photosensitive, circadian rhythm of melatonin production and release. Light pulses have at least two distinguishable effects on these cells, i.e., acute suppression of melatonin output and phase shifts (entrainment) of the underlying circadian pacemaker. Previous results linked calcium influx through voltage-sensitive calcium channels in the plasma membrane to acute regulation of melatonin synthesis but denied a role for such influx in entrainment. Those experiments did not, however, address the role of intracellular calcium metabolism. Here we describe the effects of pulses of caffeine, thapsigargin, and EGTA on the melatonin rhythm, and their interactions with the effects of light pulses. Caffeine had two distinguishable effects on these cells, acute enhancement of melatonin output (attributable to phosphodiesterase inhibition) and phase shifts of the circadian pacemaker with a light-like pattern (attributable to effects on intracellular calcium). Phase shifts induced by light and caffeine were not additive. Thapsigargin (which specifically blocks the pump that replenishes intracellular calcium stores, thereby increasing cytoplasmic calcium and depleting intracellular stores) had no phase-shifting effects by itself but reduced the size of the phase advances induced by caffeine or light. Low calcium solution acutely suppressed melatonin output without inducing phase shifts or affecting those induced by caffeine or light. However, addition of EGTA (which specifically chelates calcium, thereby lowering cytoplasmic calcium and depleting intracellular stores) did reduce the size of phase advances induced by caffeine or light, in normal medium or in low calcium solution, without inducing a phase shift by itself at that phase. Taken together, these results point toward a role for intracellular calcium fluxes in entrainment of the circadian pacemaker.

29 citations

Journal ArticleDOI
TL;DR: Monitoring of the numbers of SR and SS in male guinea pigs showed that the rhythms of SR numbers and SS numbers are out of phase by 180°, and it is suggested that they characterize different types of pinealocytes with differing rhythmicities.
Abstract: Previous studies have shown that the “synaptic” bodies of mammalian pinealocytes are a heterogeneous group of organelles. Whereas “synaptic” ribbons (SR) exhibit a day/night rhythm with small numbers during daytime and high numbers at night, the so-called “synaptic” spherules (SS) show species-specific differences in their rhythmicity. In the present study the numbers of SR and SS were monitored in male guinea pigs over a full 24-h period at 4-hourly intervals (LD 12:12, lights on at 7:00). The results obtained show that the rhythms of SR numbers and SS numbers are out of phase by 180°. SR numbers are small during daytime and high at night, whereas SS numbers are high during daytime and low at night. As there are no indications that SR are transformed into SS and vice versa and as SR and SS lie in different parenchymal areas it is suggested that they characterize different types of pinealocytes with differing rhythmicities. — Serum melatonin levels were low during daytime (30 pg/ml) and increased at night to reach a peak (84 pg/ml) at 24:00 h.

29 citations

Journal ArticleDOI
TL;DR: Cat pinealocytes showed a nucleus with prominent nucleoli, a well developed Golgi apparatus, centrioles, granular endoplasmic reticulum, ribosomes, abundant microtubuli and enlarged mitochondria and their processes were characterized by the presence of abundant filaments.
Abstract: The ultrastructure of the pineal gland in the adult cat is described and compared with that of other mammals. Connective tissue spaces showed capillaries with nonfenestrated endothelia and numerous unmyelinated nerve fibers. In the proximal region of the gland, myelinated nerve fibers coming from the anterior commissure were also found. Cat pinealocytes showed a nucleus with prominent nucleoli, a well developed Golgi apparatus, centrioles, granular endoplasmic reticulum, ribosomes, abundant microtubuli and enlarged mitochondria. Pinealocytes showed several long processes with bulbous endings filled with clear vesicles and scarce "synaptic" ribbons. Pineal astrocytes and their processes were characterized by the presence of abundant filaments.

29 citations

Journal ArticleDOI
TL;DR: In two experiments carried out on two alternate days, the 24-hrhythmicity of pineal gland volume, pinealocyte nuclear size in cortex and medulla and mitotic actty were studied in male Sprague-Dawley rats to assess to what extent morphological parameters reflect the pronounced day/night differences in pineal melatonin formation.
Abstract: In two experiments carried out on two alternate days, the 24-hrhythmicity of pineal gland volume, pinealocyte nuclear size in cortex and medulla and mitotic actty were studied in male Sprague-Dawley rats, to assess to what extent morphological parameters reflect the pronounced day/night differences in pineal melatonin formation. Pineal volume exhibited statistically significant changes in the second experiment only, with a distinct trough at 6 p.m. Karyometry revealed highly variable patterns. In the first experiment, pinealocyte nuclear changes lacked parallelism in cortex and medulla. The cortex exhibited a bimodal curve with peaks at noon of the first day and at 6 a.m. of the second day, and two troughs at 6 a.m. and midnight respectively of the first day. The medulla showed no clear-cut rhythmicity. In the second experiment, cortex and medulla reacted similarly, nuclear size decreasing from 6 a.m. to 6 p.m., remaining low thereafter. Mitotic activity of pinealocytes is low (on average 23 mitotic figures/gland). In both experiments statistically significant differences existed between certain times, pointing in the direction of 24-hrhythmicity, but whereas the curve exhibited a peak at midnight in the first experiment, mitotic activity in the second experiment showed a trough at midnight. It is concluded that for as yet unexplained reasons morphological parameters do not appear to accurately reflect circadian rhythmicity of pineal melatonin formation.

29 citations

Journal ArticleDOI
TL;DR: Pinealmelatonin release was unaffected by either dopamine or SKF38393, a D1 receptor agonist, suggesting that the effects of quinpirole were not mediated by dopamine receptors, and the regulatory mechanisms underlying pineal melatonin rhythms appear to differ among teleosts.

29 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202310
202219
202116
202011
201915
201817