Structure of the ovine pineal gland during prenatal development

The structure of the pineal gland of 32 clinically healthy ovine embryos at different stages of development was studied. Embryos were arranged in four age groups, each containing eight embryos (four males and four females), d efined in terms of the most relevant histological feature!;: group 1 (27 to 69 days of prenatal development), group 2 (70 to 97 days), group 3 (98 to 116 days), and group 4(117 to 150 days). At around 30 days of prenatal life , according to topographic criteria, the pineal outline begins to different iate into a dorsal evagination of the diencephalic medium line, close to th e anterior and posterior commissures. The growth of the pineal is biphasic. The ontogenic-proliferative phase begins at 30 days and includes the invas ion of ependymal cells and the proliferation of the pineal parenchyma cells . The hypertrophic-differentiation phase includes the volume increment of t he pinealoblasts and their differentiation into pinealocytes; this occurs a t around 118 days. Ar around 98 days, the gland acquires its definitive com pact appearance due to I) glandular growth in constant volume and 2) the ob literation of pineal recess. The glandular structure displays a parenchyma made up of pinealoblasts, interstitial cells, and cells containing pigment. The pineal stroma is structured in pseudolobes formed by reticular and col lagen fiber septae, which constitute together the interstitial cell prolong ation net, which is the support structure of the whole glandular cytology. Capillaries are detected all over the glandular surface, being more abundan t in the medullary zone. At around 98 days of prenatal development, VIP (Va soactive Intestinal Peptide) positive fibers, distributed around blood vess els and among pinealoblasts were detected.