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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: Immunohistochemical staining of rat pineal gland with the antibody demonstrated the presence of D-Asp in the cytoplasm of pinealocytes, the predominant cell type in this gland, and this may indicate some yet unknown role in the regulation of melatonin secretion.

77 citations

Journal ArticleDOI
TL;DR: Avian pineal gland and mammalian SCN seem to share a fundamental molecular framework of the clock oscillator composed of a transcription/translation-based autoregulatory feedback loop.
Abstract: The pineal gland is a neuroendocrine organ that functions as a central circadian oscillator in a variety of nonmammalian vertebrates. In many cases, the pineal gland retains photic input and endocrinal-output pathways both linked tightly to the oscillator. This contrasts well with the mammalian pineal gland equipped only with the output of melatonin production that is subject to neuronal regulation by central circadian oscillator located in the suprachiasmatic nucleus (SCN) of the hypothalamus. Molecular studies on animal clock genes were performed first in Drosophila and later developed in rodents. More recently, clock genes such as Per, Cry, Clock, and Bmal have been found in a variety of vertebrate clock structures including the avian pineal gland. The profiles of the temporal change of the clock gene expression in the avian pineal gland are more similar to those in the mammalian SCN rather than to those in the mammalian pineal gland. Avian pineal gland and mammalian SCN seem to share a fundamental molecular framework of the clock oscillator composed of a transcription/translation-based autoregulatory feedback loop. The circadian time-keeping mechanism also requires several post-translational events, such as protein translocation and degradation processes, in which protein phosphorylation plays a very important role for the stable 24-h cycling of the oscillator and/or the photic-input pathway for entrainment of the clock.

76 citations

Journal ArticleDOI
TL;DR: Melatonin binding sites in the nucleus of many cell types and its potent intracellular anti‐oxidant action suggest mechanisms of action other than through the G‐protein coupled receptor.
Abstract: The pineal gland of poikilothermic vertebrates originates as an evagination from the diencephalic roof between the habenular and the posterior commissures, and associates with a parapineal organ to form the so-called pineal complex. The pinealocytes may be photosensitive, secretory or intermediate cells between both. Melatonin, the indoleamine secreted by the pineal, exhibits a circadian secretory rhythm that conveys environmental information to the organism. The peak melatonin secretion occurs during the night, although there are a few examples of an increase in indoleamine secretion during the day. Melatonin is also synthesized in other sites such as the retina, and it has been found in many invertebrates and unicellular organisms. The rhythmic secretory pattern of melatonin is responsible for many biological rhythms exhibited by lower vertebrates. These rhythms are abolished by pinealectomy in some species, but not in others, suggesting the existence of an extra-pineal pacemaker. The photoperiod and the temperature (especially in reptiles) are the main environmental factors affecting the secretory rhythm of melatonin. Poikilothermic vertebrates exhibit a circadian rhythmic color change, with nocturnal blanching, usually related to melatonin secretion. In amphibians, melatonin exhibits a potent skin lightening activity. However, in fishes and reptiles the melatonin effects vary with the species, the developmental stage, and the pigment cell location. Melatonin also exerts inhibitory or excitatory activity on the amphibian reproductive system, regulation of circadian locomotory activity in reptiles, and modulation of the amphibian metamorphosis. Melatonin has also a modulatory effect on the response of target cells to different hormones and high concentrations or prolonged exposure to the indoleamine may cause autodesensitization in various tissues. Binding sites of melatonin have been detected in the central nervous system and peripheral tissues of various vertebrates. The relative potencies of melatonin analogues demonstrated two subtypes of melatonin receptors (ML-1 and ML-2). A transmembrane melatonin receptor has been cloned from Xenopus laevis melanophores; it belongs to the family of the G protein-coupled receptors and exhibits 85% homology with the mammalian nervous system receptor. Melatonin binding sites in the nucleus of many cell types and its potent intracellular anti-oxidant action suggest mechanisms of action other than through the G-protein coupled receptor.

76 citations

Journal ArticleDOI
TL;DR: How the photic environment and the circadian clock interact in determining melatonin levels is discussed, in addition to the role that melatonin plays in retinal physiology.
Abstract: Several studies have established that melatonin synthesis occurs in the retina of vertebrates, including mammals. In mammals, a subpopulation of photoreceptors (probably the cones) synthesize melatonin. Melatonin synthesis in the retina is elevated at night and reduced during the day in a fashion similar to events in the pineal gland. Both the MT1 and MT2 melatonin receptors are present in the retina and retinal melatonin does not contribute to circulating levels, suggesting that retinal melatonin acts locally as a neurohormone and/or neuromodulator. Melatonin synthesis in the retina of mammals is under the control of a circadian oscillator, and circadian rhythms in melatonin synthesis and/or release have been described for several species of mammals. These rhythms are present in vivo, persist in vitro, are entrained by light and are temperature compensated. The cloning of the gene responsible for the synthesis of the enzyme arylalkylamine N-acetyltransferase (the key enzyme in the melatonin biosynthetic pathway) has allowed studies of the molecular mechanisms responsible for the generation of retinal melatonin rhythmicity. The present review focuses on the cellular and molecular mechanisms that regulate melatonin synthesis. In particular, we discuss how the photic environment and the circadian clock interact in determining melatonin levels, in addition to the role that melatonin plays in retinal physiology.

76 citations

Journal Article
TL;DR: The intact sympathetic innervation, the functional beta-adrenergic receptors, and the appropriate level of norepinephrine are all essential prerequisites for the circadian pattern of melatonin synthesis.
Abstract: In addition to its sympathetic innervation, a mammalian pineal gland also receives a distinct central pinealopetal innervation. Earlier studies in rat have established that the photic signals originating in the retina pass via the retinohypothalamic tract to the suprachiasmatic nucleus, to the tuberal hypothalamus, over medial forebrain bundle, reticular formation, and upper thoracic interomediolateral cell column to the superior cervical ganglion, whose postganglionic sympathetic fibers, traveling along the tentorium cerebelli, enter the pineal gland via the conarian nerve. Recent electron microscopic analyses of the pineal gland of several mammalian species have revealed intrapineal nerve terminals different from the sympathetic ones. In addition, lesion experiments performed in the habenular nuclei or the posterior commissure support the central origin of these terminals. The intact sympathetic innervation, the functional beta-adrenergic receptors, and the appropriate level of norepinephrine are all essential prerequisites for the circadian pattern of melatonin synthesis. However, other receptors such as alpha-adrenergic, D2-dopaminergic, GABAergic, benzodiazepinergic, and glutamatergic receptors and their agonists are also able to modulate the synthesis of melatonin, and this function depicts dramatic species variation. The impact of pinealopetal projections and intrapineal neurons on the physiological and biochemical aspects of pineal functions awaits clarification.

76 citations


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