Ultrastructural analysis on raccoon testis after the Fukushima Daichi Nuclear Power Plant accident

BACKGROUND: Ionizing radiation affects biological systems, resulting in an increased risk of cancer and mutagenesis. Male reproductive function is sensitive to ionizing radiation, with implications connected to infertility. After the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, the wildlife within the alert zone was exposed to low-dose-rate (LDR) radiation fora 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. These radioactive substances were released in the environment, 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. METHODS: We performed an ultrastructural study by Light and Transmission Electron Microscopy to better assess the reproductive function of raccoon (Procyon lotor) testis collected from adult animals recovered from the Fukushima area at different time schedule after the FDNPP accident. RESULTS: The ultrastructural analysis showed no remarkable changes in spermatogonia, spermatocytes, spermatids and elongated spermatids. However, during the reproductive season, radiation-exposed testes had increased cellularity in spermatogonium, spermatocyte, and spermatid number, compared to control testes. The presence of cytoplasmic holes in the spermatogenic cell lineage and detachment of germ cells from adjacent cells were the occasionally evident signs of ultrastructural alterations. 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. CONCLUSIONS: Sperm ultrastructure and morphology is an important parameter, which can indicate the potential male fertility. Results from this study revealed that, 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.