Somatostatin and somatostatin receptors in the pig pineal gland during postnatal development: An immunocytochemical study

An immunohistochemical study of the pineal gland of the domestic pig was ca rried 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 supplemen ted by immunohistochemical staining with rabbit antisera raised against fiv e 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 somat ostatin and prosomatostatin. The nerve fibers were located throughout the p ineal gland-in the capsule, connective septa, and parenchyma-with the highe st density in proximo-ventral part of the gland. The somatostatin positive fibers were also found in the habenular and posterior commissurae areas. So matostatin-immunoreactive cell bodies were observed mostly in the central p art of the gland. These results point to the existence of two somatostatin sources in the pig pineal gland: 1) nerve fibers, probably of central origi n; and 2) cells that may represent intrapineal neurons or specialised pinea locytes. A clear difference in the immunoreactivity between newborn, 21-day -old, and 7-month-old pigs was found. Generally, the density of nerve fiber s was lower in adult than young animals. The number of the cells also decre ased with age. By using the antisera against the five somatostatin receptor s, only sst3-receptor immunoreactivity could be detected. The receptor;immu noreactivity 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. ( C) 2000 Wiley-Liss, Inc.