Ultrastructural study on raccoon (Procyon lotor) testis after the Fukushima Daiichi nuclear power plant accident

After the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, the wildlife within the alert zone have been exposed to low-dose-rate (LDR) radiation for a long and continuous time. Since raccoons invaded human residential areas and damaged non-residential buildings, the Fukushima Prefecture is attempting to control the population of raccoons exposed to chronic and low-dose-rate (LDR) radiation attributed to the FDNPP accident, that released in the environment radioactive substances, particularly volatile elements such as radioactive iodine, caesium and tellurium. Due to bias risks in germ cell and early developmental processes, the effects of radiation on reproduction and development remain unclear. Therefore, we performed an ultrastructural study by Light and Transmission Electron Microscopy to better assess the reproductive function of raccoon testis. Results showed no remarkable changes in spermatogonia, spermatocytes, spermatids and elongated spermatids. However, radiation-exposed testes tended to have an increased cellularity in terms of the number of spermatogonia, spermatocytes, and spermatids as compared to control testes during the reproductive season. Signs of ultrastructural alterations, as the presence of cytoplasmic holes in the spermatogenic cell lineage and detachment of germ cells from adjacent cells, were occasionally evidenced. No signs of tubular atrophy or cellular undifferentiation were detected. The interstitial spaces appeared dilated and with a spongy aspect, probably indicative of fluid accumulation and, therefore, interstitial oedema. In conclusion, although the reproductive organs are hypersensitive to radiation, long-term LDR radiation exposure associated with the FDNPP accident seems to not induce evident ultrastructural alterations on raccoon testis and spermatogenesis.