Immunohistochemical studies on the peptidergic nerve fibers in the pineal organ of the dog.

The distribution of vasopressin-, oxytocin- and LHRH-containing nerve fibers in the pineal organ of the dog was demonstrated by use of the peroxidase-antiperoxidase immunohistochemical technique. These neuropeptide-containing fibers penetrated through the pineal stalk from the brain, mainly from the posterior commissural region, into the pineal organ. The vasopressin fibers were the most prominent in number, oxytocin fibers and LHRH fibers were the least. Most of these fibers were found in the proximal part of the pineal organ, but some of them were also observed in the distal part. These peptidergic fibers were distributed not only in the perivascular spaces but among the parenchymal cells.