Abstract
This study presents the varying ultrastructural characteristics of the principal cell along the different zones of the epididymis of the greater cane rat. Ten sexually mature male cane rats with known medical and reproductive history were perfusion-fixed using Karnovsky fixative (phosphate buffered 2% paraformaldehyde – 2.5% glutaraldehyde fixative at pH 7.4). Epididymal samples were then obtained, processed for ultrastructural analysis and examined under the transmission electron microscope. Our findings showed that the cane rat epididymis has four distinct regions – initial segment, caput, corpus and cauda epididymides. These regions are further subdivided into discrete subregional zones based on the cytological characteristics of the principal cell in each region. The principal cell in the proximal initial segment showed abundant rough endoplasmic reticulum and extensive Golgi apparatus arranged in a peculiar whorl shape predominantly in the apical cytoplasm with small vesicles, dense granules and multivesicular bodies scattered in and around the whorls. The principal cell of the distal initial segment is characterized by multivesicular bodies, small and coated vesicles as well as numerous flat and whorl-shaped cisternae of rough endoplasmic reticulum and dense-core mitochondria. In the caput epididymis, the principal cell contains more of lipid vacuoles, while in the corpus, it has prominent dense bodies of various sizes at its supranuclear area. These dense bodies tend to increase in the principal cells of the cauda epididymis. The transition between regions was however observed to be gradual with overlapping of morphological characteristics between two adjacent regions. These ultrastructural diversities exhibited by the epididymis along its length point to a corresponding functional diversity and do dictate the overall intra-luminal environment necessary for sperm maturation in the cane rat.

Key words: Epididymis, Ultrastructure, Greater cane rat, Principal cell