Eur J Anat, 5 (2): 55-66 (2001)

Embryonic development of the rabbit pineal gland (Oryctolagus Cuniculus) (Lagomorpha)

Garcia-Maurino J.E., Sicilia C., Boya J., Calvo J.L.

Dept. Biología Celular, Facultad de Medicina, Universidad Complutense, 28040 Madrid, Spain

ABSTRACT The embryonic development of the rabbit pineal gland was studied from day 12 post conception (E-12) until day 30 (E-30, the end of gestation). The pineal anlage appears on E-12 as a thickening of the neuroepithelium lining the roof of the diencephalon. By E-14, a rostrally-orientated evagination appears in this area. From E-18 the pineal gland grows caudally, acquiring an elongated shape with a distal thickening. Although still small (1.469 mm in length), it shows its final form and anatomical relationships by E-22. On E-30 it is 2.99 mm long and has a volume of 0.123 mm³. Characteristic of the embryonic pineal parenchyma are rosette-like structures formed by type II pinealoblasts with ovoid, heterochromatic nuclei, located around a narrow lumen. These rosettes originate through the intense mitotic activity of the neuroepithelium lining the pineal recess. As development proceeds, the rosettes begin to lose their structure and separate from one another due to the proliferation of cell cords between them. These cords are composed of type I pinealoblasts, which have rounded nuclei and loose chromatin. Melanin granules are first seen on E-16 in type II pinealoblasts. Therefore, the greatest amount of pigmentation is seen in the rosettes, mainly in those located at the enlarged, distal end of the gland. The connective tissue septa, which carry blood vessels, invade the pineal gland from the thin capsule. From E-18 they develop throughout the rest of embryonic life, contributing to the gradual separation of the rosettes. From the beginning of its development, the pineal gland is associated with large cerebral veins. A large part of the gland ends up occupying an "intravascular" position. We suggest that during embryonic development, the pineal gland may act, at least in the rabbit, as a reference for the location and organisation of large cerebral veins.

Keywords: melanin, animal cell, animal tissue, article, brain vein, cellular distribution, chromatin, connective tissue, diencephalon, embryo development, functional anatomy, gestational age, microscopic anatomy, mitosis, neuroanatomy, neuroepithelium, nonhuman, pigmentation, pineal body, rabbit, stem cell