Pinealocyte

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

Clock-Controlled Regulation of the Acute Effects of Norepinephrine on Chick Pineal Melatonin Rhythms

Abstract: The chicken pineal gland synthesizes and releases melatonin rhythmically in light/dark (LD) cycles, with high melatonin levels during the dark phase, and in constant darkness (DD) for several cycles before it gradually damps to arrhythmicity in DD. Daily administration of norepinephrine (NE) in vivo and in vitro prevents the damping and restores the melatonin rhythm. To investigate the role of the circadian clock on melatonin rhythm damping and of its restoration by NE, the effects of NE administration at different phases of the melatonin cycle revealed a robust rhythm in NE sensitivity in which NE efficacy in increasing melatonin amplitude peaked in late subjective night and early subjective day, suggesting a clock underlying NE sensitivity. However, NE itself had no effect on circadian phase or period of the melatonin rhythms. Transcriptional analyses indicated that even though the rhythm of melatonin output damped to arrhythmicity, messenger RNA (mRNA) encoding clock genes gper2, gper3, gBmal1, gclock, gcry1, and gcry2; enzymes associated with melatonin biosynthesis; and enzymes involved in cyclic nucleotide signaling remained robustly rhythmic. Of these, only gADCY1 (adenylate cyclase 1) and gPDE4D (cAMP-specific 3',5'-cyclic phosphodiesterase 4D) were affected by NE administration at the mRNA levels, and only ADCY1 was affected at the protein level. The data strongly suggest that damping of the melatonin rhythm in the chick pineal gland occurs at the posttranscriptional level and that a major role of the clock is to regulate pinealocytes' sensitivity to neuronal input from the brain.

Dense accumulations of synaptic-like microvesicles in 'dark' pinealocytes of the gerbil pineal gland.

Abstract: In an electron-microscopical study the occurrence and ultrastructural features of electron-dense ‘dark’ variants of pinealocytes were evaluated in the gerbil pineal gland. A few ‘dark’ pinealocytes, which tended to form small clusters of contiguous cells, could consistently be detected in pineals fixed and embedded by various procedures. Apart from the different degree of electron density, the only conspicuous difference between ‘dark’ and electron-lucent ‘light’ pinealocytes concerned their compartment of synaptic-like microvesicles. Thus, both variants of pinealocytes contained abundant clear microvesicles of variable size which accumulated in dilated process terminals. However, the vesicles within the process endings of ‘dark’ pinealocytes showed an unusually dense arrangement throughout the cytoplasm. As was demonstrated by immunogold staining, the accumulations of vesicles in the ‘dark’ terminals contained synaptophysin, a major synaptic vesicle-associated protein. This protein is present in small clear vesicles with putative secretory functions in a wide variety of neuroendocrine cells and has previously been shown to be a common constituent of microvesicles in mammalian pinealocytes. Since gerbil pinealocytes displayed distinct gradations of electron density, their ultrastructural heterogeneity may be the expression of different states of secretory activity of one pinealocyte cell type. On the other hand, differences in the content of synaptic-like microvesicles in the process terminals of ‘light’ and ‘dark’ cells could also indicate a principal functional heterogeneity of the microvesicular compartment among pinealocytes, pointing to the existence of different types of pinealocytes.

On the presence of conspicuous electron dense bodies in the pinealocytes of the pig

Abstract: The pinealocytes of the pig contain a large number of aldehydefuchsin positive granules In order to determine their nature an ultrastructural study was carried out Numerous bodies having a maximal diameter of about 1,600 nm were found These elements showed a great variety of internal structure, ranging from a “homogeneous” content and amorphous dense aggregates to lamellate bodies Although only a few of them displayed a positive reaction for acid phosphatase, their morphological appearance strongly suggests that they belong to the lysosomal system

Quantitative differences in the pineal ultrastructure of perinatal and adult harp (Phoca groenlandica) and hooded seals (Cystophora cristata).

Abstract: Seals are unique among mammals in that newborns have a large pineal gland and extremely high plasma levels of melatonin at birth. Melatonin levels are also high in the seal fetus but decline rapidly during the first few days of life. The aim of the present study was to provide quantitative information about the ultrastructure of the seal pineal gland using fetal, newborn, and adult hooded seals (Cystophora cristata), and newborn and adult harp seals (Phoca groenlandica). The relative and absolute volumes of pinealocytes (Pi), arteries and veins, nerves, connective tissue, capillaries and glial cells, as well as mitocondria and lipid droplets in Pi, were calculated by use of point count analysis. Whereas the pineal ultrastructure was similar in fetuses and newborns, both seal species showed a pronounced and particular reduction in the volume of Pi and a similar reduction in pinealocyte mitochondria. There was also a shift from unmyelinated to myelinated pineal nerves in adults compared with fetal/newborns. The selective and marked reduction of Pi may explain the zonated pineal structure typical of the adult seal. The results demonstrate that the fetal gland is as large and active as that of the newborn seal and support the notion that the large size and high activity of the pineal gland in the newborn seal is a fading consequence of its prenatal condition.