Peculiarities of psammoma bodies distribution in the human pineal gland: a new approach to determining the functional significance of pineal gland calcifications

The pineal gland is a neuroendocrine gland that synchronizes the functional activity of body organs with the light regime using the hormone melatonin, which is actively released into the bloodstream at night. Melatonin is synthesized by pinealocytes, the main cell population of the pineal gland, in addition to which there are also astroglia, microglia, and mast cells. Besides, the pineal gland contains psammoma bodies (calcifications), the functional significance of which and the mechanisms of formation have not been determined. The aim of this study was to investigate the occurrence of calcifications in different parts of the human pineal gland (parenchyma, connective tissue trabeculae and capsule) and to describe the relationship of calcifications with astroglial cells and their processes, microgliocytes, mast cells, as well as blood vessels and nerve fibers using appropriate immunohistochemical reactions. Material and methods. For immunohistochemical examination, antibodies to glial fibrillary acidic protein (GFAP), vimentin, two microglia markers (Iba-1 and TMEM119), mast cell tryptase, tyrosine hydroxylase and von Willebrand factor were used. Results. Our study revealed calcifications mainly in the central part of the pineal gland, in the lobules among pinealocytes, with their number and size being increased from young to middle age. Processes of astroglial (mainly GFAP-, but not vimentin-containing) cells tightly envelop psammoma bodies. No relationship was found between the location of calcium deposits and blood vessels, tyrosine hydroxylase-immunoreactive nerve fibers, microgliocytes or mast cells. Prevalence of activated microglia and degranulating mast cells was not observed. Tyrosine hydroxylase-immunoreactive nerve fibers were identified for the first time in the human pineal gland. Conclusions. The obtained data indicate that psammoma bodies are normal and, apparently, obligatory components of the adult human pineal gland, the formation of which is associated with pinealocytes and/or astrocytes, but not with blood vessels, nerve fibers, microglia or mast cells. The possible functional role of calcifications in the human pineal gland may be associated with the functional activity of pinealocytes.