An immunohistochemical study of vasoactive intestinal peptide and neuropeptide Y in the sheep pineal gland during prenatal development

In this immunohistochemical study we investigate the presence of vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) during embryonic development in the sheep pineal gland. We use ten ovine embryos at different stages of development (117 to 150 days of prenatal development). The VIP positive fibers were observed along the blood vessels, entering the pineal gland through the pineal capsule. We also observe isolated VIP positive nerve fibers between the pinealocytes. The presence of VIP-immunoreactive fibers in the pineal capsule supports a possible origin from a peripheral ganglion. The NPY fibers enter the gland through the pineal capsule occupying a perivascular localization. Some NPY nerve fibers leave the lobular septae and are localized intraparenchymally between the pinealocytes. Moreover, we believe that the majority of the NPY immunoreactive fibers originate, during the prenatal development of the sheep pineal gland, in the superior cervical ganglion ; however, some fibers probably originate from the brain itself.