Distribution of substance P neurons in the epithalamus of the rat: an immunohistochemical investigation.

Substance P (SP) immunoreactivity was studied in the epithalamus of intact and superior cervical ganglionectomized female rats by using the peroxidase-antiperoxidase immunocytochemical technique. Cells containing immunoreactive SP were located in the medial habenula, and SP fibers were observed in the lateral habenula, habenular commissure, pineal stalk, and the pineal organ. Bilateral removal of the superior cervical ganglia did not affect the immunocytochemical staining of SP-containing cells and fibers 15-30 days later. It is suggested that habenular neurons containing SP send projections into the pineal organ of the rat.