Specializations of the ependyma in the third ventricle of the developing hamster

Ependymal cells in the region of the hypothalamic sulcus, hypothalamus, infundibular recess and supraoptic recess exhibit large apical protrusions between day 12 and day 14 post coitus. The ependyma was examined using light microscopy and transmission and scanning electron microscopy. The protrusions contain ribosomes and cytoplasmic matrix. Occasionally other cytoplasmic organelles were found within the protrusions. The protrusions range in shape from a rounded elevation of the apical surface of the ependymal cell to spherical bodies attached to cell surface by a slender stalk. The unique transitory specialization of the ependyma may represent either a neurosecretory or mechanical folding mechanism.