Immunohistochemical and ultrastructural study of interstitial cells during postnatal development of the sheep pineal gland

*Address correspondence to: Sergio Regodón. Departments of Embryology and Histology, Faculty of Veterinary Medicine, University of Extremadura, 10071 Cáceres, Spain. e-mail: [email protected] The pineal originates as an outgrowth of the roof of the diencephalon in all vertebrate species. This evagination arises between the habenular commissure anteriorly (or rostrally) and the posterior commissure and subcommisural organ posteriorly (or caudally). Three cell types have been defined in mammal pineal gland parenchyma: pinealocytes or principal cells, supportive or interstitial cells and pigmented cells. Numerous terms have been used to designate the second cell type, including interstitial cells, type II pinealocytes, glial cells and astrocytes.