Ultrastructural organization and histochemical profile of adult fowl choroid plexus epithelium

The choroid plexus epithelial cell of adult fowl is columnar with an irregular apical border of smooth‐surfaced microvilli and cilia. Bi‐nucleate cells occur frequently. Coated plasmalemma pits and vesicles (∼ 1000 Å) are present at all margins of the cell. Smaller coated vesicles (600–700 Å), found in variable numbers throughout the apical zone, tend to be concentrated in the Golgi region. Sparse to profuse amounts of granular endoplasmic reticulum (RER) are found throughout the cell with tubular whorled configurations occasionally noted in the subnuclear cytoplasm. Parallel arrays of RER extend from the cell base, around the nucleus, to the Golgi zone. Oval, fine granular masses occur in the subnuclear area. Free ribosomes are distributed throughout the cell. An array of diverse dense bodies and a few multi‐vesicular bodies lie near the Golgi complex. Variable amounts of smooth ER are present in the supra‐nuclear region. Toluidine blue, pH 4.0, demonstrates a heavy subnuclear condensation of cytoplasmic RNA. After sulfation, the apical margin and basement membrane are made metachromatic by Toluidine blue. A diastase‐resistant, strong PAS positive reaction occurs in the apical border and basement membrane. Lateral cell margins are lightly stained with PAS. Alcian blue and colloidal iron intensely color the microvillous border. Bromphenol blue and bromsulfalein heavily stain the apical and basal zones of all cells.