Epididymal spermatozoa: a hidden treasure with great potential

An azoospermic ejaculate or a “dry ejaculate”, as it is called in case of aspermia, might not be the end of the hopes of procreation. When a donor male accidentally dies or undergoes orchiectomy for medical reasons can still generate offspring. In both cases, the precious germplasm can be hidden in the epididymides as a treasure with great potential. Epididymal spermatozoa can be retrieved from ex vivo or in vivo testicles, can be cryopreserved and used in assisted reproductive technologies (ARTs). This review intends to shed light on these topics providing a critical analysis on recent results obtained in carnivores. From ex vivo testicles, spermatozoa can be collected by mincing the epididymal cauda in a Petri dish containing medium, or by flushing or squeezing epididymides and deferential ducts. Different techniques have been tested in humans to retrieve epididymal spermatozoa from in vivo testicles. We previously investigated the feasibility in dogs of one of these methods: the percutaneous epididymal sperm aspiration (PESA). The quality of gametes was similar to that of those collected from ex vivo testicles, although a wide variation in concentration amongst animals was observed1. During epididymal transit, functional and structural modifications leading to full maturation enable male gametes to reach, recognize and fertilize the oocytes. An extensive analysis has been conducted in cats and characteristics of the spermatozoa collected from six different epididymal regions have been described in detail2. We demonstrated that DNA integrity of feline epididymal spermatozoa seems to be independent from all the measured variables of sperm head morphology and morphometry3. In dogs, we showed that an acrosomal reshaping occurs during maturation from the proximal to the distal epididymal tract and that the migration of the cytoplasmic droplet occurs in the epididymal corpus. Thus, the highest sperm motility, acrosomal integrity and normal morphology is found in the cauda4. The fertilizing ability of fresh and frozen epididymal spermatozoa has been demonstrated in several mammalian species including carnivores. In vitro embryo production in cats have been successfully obtained with epididymal spermatozoa. In dogs, intravaginal and intrauterine artificial insemination with fresh and frozen epididymal spermatozoa resulted in pregnancies and in viable puppies. We found that DNA fragmentation is not affected by the freezing procedure further demonstrating that epididymal spermatozoa can be successfully cryopreserved5. The hidden treasure represented by epididymal spermatozoa deserves special attention and serious consideration for its potential use in the current reproductive technologies. [1] Varesi S, Vernocchi V, Faustini M, et al. Quality of canine spermatozoa retrieved by Percutaneous Epididymal Sperm Aspiration. J Small Anim Pract 2013;54:87-91. [2] Axnér E, Linde-Forsberg C, Einarsson S: Morphology and motility of spermatozoa from different regions of the epididymal duct in the domestic cat. Theriogenology 1999;52:767-778. [3] Vernocchi V, Morselli MG, Lange Consiglio A et al. DNA fragmentation and sperm head morphometry in cat epididymal spermatozoa. Theriogenology 2014;82:982-987. [4] Varesi S, Vernocchi V, Faustini M, et al. Morphological and acrosomal changes of canine spermatozoa during epididymal transit. Acta Vet Scand 2013;55:17. [5] Varesi S, Vernocchi V, Morselli MG, et al. DNA integrity of fresh and frozen canine epididymal spermatozoa. Reprod Biol 2014;14:257-261.