Pineal gland calcification under hypoxic conditions

Abstract

The pineal gland (glandula pinealis) is neuroendocrine gland located at the epithalamus of the brain secreting melatonin. The aim of this study was to explore effects of prenatal hypoxia in rats at the age of 33 weeks on the occurrence of pineal gland calcification. Distribution and chemical composition of calcerous material by light, scanning and transmission electron microscopy was investigated. Melatonin concentrations in blood plasma by direct radioimmunoassay were measured. Rats were exposed to prenatal hypoxia for 12 h at day 20 of development and second group to prenatal hypoxia for 2x8 h at days 19 and 20 of development. Vacuoles of intracellular edema in the pineal samples after 12 h hypoxia were found. Their size ranges up to 30 µm. Some of them were filled with the flocculent and fibrous material. Samples of pineal glands after 2 x 8 h hypoxia revealed the pericellular edema of pinealocytes. The amount of calcium rich particles in 2 x 8 h hypoxia group was lower than in 12 h hypoxia group. Plasma melatonin levels did not differ between control and both hypoxia groups. We concluded that calcification is a process induced by osteoblasts and osteocytes with melatonin as a promotor and it is favored under hypoxic conditions.

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“…In the center of the concentrical "corpora arenacea", exophytic membrane debris was found; this could represent a byproduct of pineal neuronal and glial polypeptide exocytosis [197]. There is also the possibility of osteoblast-like and osteocytes-like transformation of local, or vascular migrated mesenchymal stem cells (MSCs), under pathological conditions [174,203,210]; thus, the high melatonin levels promote calcification by stimulating mesenchymal cell differentiation in bone cells [174,211,212].…”

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“…Calcifications in the PG are located within the pineal parenchyma or connective tissue septa (intrapineal corpora arenacea) or in the pial capsule or arachnoid cover (meningeal corpora arenacea) [108,111]. They mainly contain hydroxyapatite [Ca 10 (PO 4 ) 6 (OH) 2 ] and may exhibit different growth patterns [103,108,111,116,118]. Some of the acervuli are small (up to 2-3 μm), regular in shape, round or globular (globular pattern), and others are larger (up to 1 mm), irregular in shape, with concentric, lamellar pattern (mulberry-like structures), which can form large aggregates [108,111,116].…”

“…Some of these techniques reveal the presence of Ca 2+ ions in the pinealocyte cytoplasm, as well as in the cell membrane [108]. Ca 2+ -dependent adenosine triphosphatase (ATPase) plays an important role in maintaining calcium homeostasis within the pinealocytes, eliminating calcium in the extracellular space; any dysfunction of this enzyme may lead to pinealocytes lesions and low melatonin levels [111,118].…”

“…In addition, it is suggested that melatonin stimulates the synthesis of type I collagen fibers and activates the gene expression of some bone proteins (e.g., BMP2, alkaline phosphatase, osteocalcin, osteopontin, etc. ), which eventually form the bone matrix [103,118,120,121]. Several physiological or pathological factors may contribute to MSCs migration in the PG, such as PG rich blood supply, inflammation, hypoxia [103,118,121], sunlight exposure [105,117], etc.…”

“…), which eventually form the bone matrix [103,118,120,121]. Several physiological or pathological factors may contribute to MSCs migration in the PG, such as PG rich blood supply, inflammation, hypoxia [103,118,121], sunlight exposure [105,117], etc. (Figure 3).…”