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An immunohistochemical study of the pineal gland of the domestic pig was carried out using rabbit antisera raised against synthetic peptide fragments corresponding to different amino acid sequences of the prosomatostatin, the somatostatin-14, and the somatostatin-28 molecule. The study was supplemented by immunohistochemical staining with rabbit antisera raised against five subtypes of somatostatin receptors. The pineal glands were taken from the newborn, 21-day-old and 7-month-old pigs. Immunoreactive nerve fibers and cells were observed in the pineal gland with all the antisera against somatostatin and prosomatostatin. The nerve fibers were located throughout the pineal gland—in the capsule, connective septa, and parenchyma—with the highest density in proximo-ventral part of the gland. The somatostatin positive fibers were also found in the habenular and posterior commissurae areas. Somatostatin-immunoreactive cell bodies were observed mostly in the central part of the gland. These results point to the existence of two somatostatin sources in the pig pineal gland: 1) nerve fibers, probably of central origin; and 2) cells that may represent intrapineal neurons or specialised pinealocytes. A clear difference in the immunoreactivity between newborn, 21-day-old, and 7-month-old pigs was found. Generally, the density of nerve fibers was lower in adult than young animals. The number of the cells also decreased with age. By using the antisera against the five somatostatin receptors, only sst3 - receptor immunoreactivity could be detected. The receptor-immunoreactivity was confined to varicose and smooth fibers and some cells. The sst3-receptor positive structures were localised in all parts of the gland and their number was higher in younger pigs. Anat Rec 259:141–149, 2000. © 2000 Wiley-Liss, Inc.

An immunohistochemical study of the pineal gland of the domestic pig was carried out using rabbit antisera raised against synthetic peptide fragments corresponding to different amino acid sequences of the prosomatostatin, the somatostatin‐14, and the somatostatin‐28 molecule. The study was supplemented by immunohistochemical staining with rabbit antisera raised against five subtypes of somatostatin receptors. The pineal glands were taken from the newborn, 21‐day‐old and 7‐month‐old pigs. Immunoreactive nerve fibers and cells were observed in the pineal gland with all the antisera against somatostatin and prosomatostatin. The nerve fibers were located throughout the pineal gland—in the capsule, connective septa, and parenchyma—with the highest density in proximo‐ventral part of the gland. The somatostatin positive fibers were also found in the habenular and posterior commissurae areas. Somatostatin‐immunoreactive cell bodies were observed mostly in the central part of the gland. These results point to the existence of two somatostatin sources in the pig pineal gland: 1) nerve fibers, probably of central origin; and 2) cells that may represent intrapineal neurons or specialised pinealocytes. A clear difference in the immunoreactivity between newborn, 21‐day‐old, and 7‐month‐old pigs was found. Generally, the density of nerve fibers was lower in adult than young animals. The number of the cells also decreased with age. By using the antisera against the five somatostatin receptors, only sst3 ‐ receptor immunoreactivity could be detected. The receptor‐immunoreactivity was confined to varicose and smooth fibers and some cells. The sst3‐receptor positive structures were localised in all parts of the gland and their number was higher in younger pigs. Anat Rec 259:141–149, 2000. © 2000 Wiley‐Liss, Inc.

The pineal gland is richly innervated by the neuropeptide Y (NPY)-positive nerves that mostly exibit immunoreactivity for the enzyme tyrosine hydroxylase, a marker of sympathetic nerve fibers. NPY is synthesized as a part of larger prepromolecule. The present study was undertaken to demonstrate that the posttranslational processing of preproNPY resulted in the presence of C-terminal flanking peptide of NPY (CPON) in nerve fibers of the pig pineal gland. An immunohistochemical anti-CPON technique was done over mounted sections of perfusion-paraformaldehyde-fixed material. An immunocytochemical preembedding technique was done to study the CPON-positive nerve terminals under electron microscopy. The pig pineal gland is densely innervated by CPON-immunoreactive nerve fibers. These nerve fibers follow from the pineal capsule into the connective tissue septa and farther into the pineal parenchyma, where the varicose branches terminate between the pinealocytes. The fiber density was the highest in the peripheral and ventral parts of the gland. At the ultrastructural level, the CPON-immunoreactive nerve terminals were found in the perivascular spaces and in the parenchyma. The terminals contained small vesicles (30-40 nm in diameter), some of which showed an eccentrically located dense core. In addition, large clear vesicles (80-100 nm in diameter) were present. Some of the CPON-immunoreactive nerve terminals were found in close apposition to the pinealocyte cell membrane, making a synapticlike contact with the pinealocytes. Our results show the presence of dense CPON-IR innervation in the pig pineal gland. The ultrastructural localization of CPON-IR nerve terminals shows that the peptide can be released to both perivascular and intercellular spaces. The functional role for this peptide in pig pineal gland is still an open question. Anat. Rec. 248:576-582, 1997. © 1997 Wiley-Liss, Inc.