Macrophagic ameboid cells in the brain ventricles of the neonatal rat.

Scanning electron microscopy revealed numerous macrophagic ameboid cells on the ependymal surface of all brain ventricles in neonatal rats. Macrophagic ameboid cells aggregated in the sulcus medianus of the fossa rhomboidea, the recessus of the cerebral aqueduct and the recessus infundibuli, i.e. the ventromedial floor of the ventricular cavity covered mainly with non-ciliated ependyma. Macrophagic ameboid cells were numerous in the first few days after birth, often intermingling with extravasated erythrocytes. Subsequently, these cells decreased in number until 10 days after birth. Thus, it was rather difficult to find such ameboid cells in the brain ventricles of 21-day-old rats. Intravenous injection of primuline, a fluorescence dye used as a cytoplasmic marker in the previous study, enhanced the appearance of the ameboid cells and caused them to remain longer on the ventricular surface.