Ultrastructure of crystalloid inclusions in the dog and rat epididymis

Fine structural studies of the epididymis of mature mongrel dogs and of Sprague-Dawley rats were undertaken in conjunction with research dealing with the effects of vasectomy upon this organ. This paper reports the observation of crystalloid and lamellar inclusions present in these species following fixation of the epididymis in 5 % glutaraldehyde, post-fixation in osmium, and routine processing for electron microscopy. In the dog, crystalloid inclusions were observed within the cauda epididymidis of unoperated and vasectomized animals. They were found within the apical cytoplasm of principal cells in association with the Golgi apparatus and endoplasmic reticulum, and in some instances, in close proximity to the nucleus. These crystalloids exhibited a 12 nm periodicity and often measured over 3 μm in length. In the rat, two types of inclusions were found, one within mitochondria of clear cells from unoperated animals and another within membrane-bound bodies of principal cells from the caput epididymidis of unoperated and vasectomized animals. The mitochondria which contained inclusions were basally located and were observed in stacks of up to eight elongate mitochondria each. The mitochondrial inclusions exhibited a complex lamellar structure with an approximate periodicity of 36 nm. In contrast, the crystalloid inclusions found within principal cells were sequestered within supranuclear cytoplasmic bodies which increased in number with age. Such crystalloids exhibited a linear periodicity of 11–13.5 nm, but the precise lattice structure remains to be determined. Although certain aspects of the morphology of these bodies suggests a relationship to microbodies, we have been unable to demonstrate catalase activity within them. At present, neither the origin of crystalloid structures described, nor their relationship to epididymal physiology is clear.