The distribution of nerve fibers immunoreactive (IR) to catecholamine-synthesizing enzymes, tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (D beta H), and phenylethanolamine-N-methyltransferase (PNMT) as well as neuropeptide Y (NPY), in the pineal gland of adult sows was investigated by the use of double-labeling immunohistochemistry. The porcine pineal gland was found to be supplied by TH-IR nerve fibers, the vast majority of which were also D beta H-positive. TH- and TH/D beta H-IR nerves were located mostly in the capsula and connective septa of the pineal gland, and their fine varicose branches terminated in the adherent parenchyma. NPY-IR fibers formed a loose network overlapping that was observed in the case of TH- and D beta H-IR fibers. Most of NPY-IR fibers were also positive for TH. The density of the fiber networks depended on the region of the gland. No PNMT-IR structures were observed.
The pineal glands of pregnant and nursing sows were studied by light and electron microscopy. Similar structural changes in the pineal gland during pregnancy and lactation were noted as follows: a proliferation of glial cells concurrent with a decrease in the number of pinealocytes, a relative increase in the number of pinealocytes with cytoplasmic accumulation of dense bodies, and an increase in number of presumptive microglia. It appears that pregnancy and lactation exert a complex influence on pineal function, with a predominantly stimulating effect.
The pinealocytes of the pig contain conspicuous dense bodies, the nature and role of which are not yet fully elucidated. The aim of this study was to demonstrate whether or not these structures are involved in the secretion process. The tannic acid-Ringer incubation (TARI)-method, which allows a clear-cut ultrastructural study of secretory discharge by exocytosis, has been used. The results indicate that pig pinealocytes release the content of the dense bodies with an amorphous inner structure into the extracellular space via exocytosis and that this secretion is quantitatively important. The secreted material is proteinaceous in nature; this indicates that polypeptides are released by the pineal.
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