Age-dependent morphological changes in the seminal colliculus in male mice. Light and scanning electron microscopic study.

The developmental changes in the seminal colliculus of male mice were studied by light and scanning electron microscopy. The epithelium of the mouse seminal colliculus is transformed to the mature epithelium between 20 and 25 days of age, while the transformation of the remaining urethral wall occurred from 5 to 10 days of age. During the process of this epithelial transformation at the seminal colliculus unusual structures, including prominent epithelial proliferations and protrusions, were observed in the area adjacent to the ejaculatory duct openings and the ventral area of the upper medial region of the seminal colliculus in 15-day-old mice. In these unusual structures, three types of cells were recognized by their surface characteristics: cells which had distinct borders and ruffled cell surfaces with microridges; cells which had distinct borders and flat or slightly ruffled cell surfaces with many short microvilli, and small cells which had rounded cell surfaces with many long microvilli. In the remaining area of the seminal colliculus, two types of cells were distinguished: those which had flat or slightly rounded cell surfaces with many short microvilli and those cells with many long microvilli similar to the ones in the previously described area. In 25-day-old mice, the unusual protruding structures were not observed, but some cells with ruffled surfaces were still seen.