Distribution in the Macaque Pineal of Nerve Fibers Containing Immunoreactive Substance P, Vasopressin, Oxytocin, and Neurophysins

The distribution of nerve fibers containing immunoreactive substance P (SP), estrogen‐stimulated neurophysin (ESN), nicotine‐stimulated neurophysin (NSN), oxytocin (OT), and vasopressin (VP) was examined in the epithalamic area of adult male and female macaques. Perfused or immersion‐fixed epithalamic tissues, sectioned, and mounted on glass slides were processed through the avidin–biotin immunofluorescence method. Fibers containing immunoreactive SP were observed in the pineal organ along the periphery, in the perivascular space, and dispersed between the pinealocytes. Fibers were often observed in the pineal stalk region, and the habenular nuclei had high concentration of immunoreactive SP. Immunoreactive ESN fibers were observed in the stria medullaris, in the lateral habenula, in the pineal stalk, and in the pineal organ. Within the pineal, fibers containing ESN were present in the perivascular space, often concentrated in the walls of blood vessels, but also dispersed between pineal cells. Fibers containing OT, NSN, and VP were also present in the macaque pineal, but in lower quantities compared with fibers containing ESN. These studies show that the pineal of subhuman primates contain nerve fibers (ESN, NSN, VP, OT) of possibly hypothalamic origin. It also has a rich supply of SP fibers, which might be of habenula origin, peripheral parasympathetic ganglia origin, or both. The functional significance of these peptidergic nerve fibers remains to be determined. However, there are indications that they might be involved in regulation of blood flow and release of secretory products from the pinealocytes.