Immunohistochemical studies on the coexistence of catecholamine-synthesizing enzymes and neuropeptide Y in nerve fibers of the porcine pineal gland.

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.