A morphometric analysis of the development of the fourth ventricle choroid plexus in the rat.

The choroid plexus from the rat fourth ventricle was investigated at ages from 16 days of gestation to 30 days after birth. Choroid plexus weights were measured and light and electron micrographs were analysed by quantitative stereological techniques at 4 levels of magnification. There was a 10-fold increase in plexus weight between 19 days of gestation and 30 days after birth which was largely due to an increase in epithelial weight, with little change occurring in the connective tissue core. Before birth, epithelial cell height decreased whereas between 10 and 30 days after birth cross-sectional area increased, both events being accompanied by corresponding changes in cell volume. Large intracellular stores of glycogen were present around birth, when they occupied up to 20% of the cell volume. After birth there were significant increases in apical microvillus height, the number of microvilli per cell and in the size of the mitochondria, suggesting that a large increase in choroid plexus secretory function, or the commencement of a new function, occurs after birth in the rat.