Morphological reproductive characteristics of testes and fertilization capacity of cryopreserved sperm after the Fukushima accident in raccoon (Procyon lotor)

Abstract

Since the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, we have established an archive system of livestock and wild animals from the surrounding ex‐evacuation zone. Wildlife within the alert zone have been exposed to low‐dose‐rate (LDR) radiation for a long continuous time. In this study, we analysed the morphological characteristics of the testes and in vitro fertilization (IVF) capacity of cryopreserved sperm of racoons from the ex‐evacuation zone of the FDNPP accident. The radioactivity of caesium‐137 (137Cs) was measured by gamma‐ray spectrometry, and the measured radioactivity concentration was 300–6,630 Bq/kg in the Fukushima raccoons. Notably, normal spermatogenesis was observed in the seminiferous tubules of the testes, with the germinal epithelium composed of a spermatogenic cell lineage with no evident ultrastructural alterations; freeze‐thawing sperm penetration ability was confirmed using the interspecific zona pellucida‐free mouse oocytes IVF assays. This study revealed that the chronic and LDR radiation exposure associated with the FDNPP accident had no adverse effect on the reproductive characteristics and functions of male raccoons.

Ultrastructural Analysis of Large Japanese Field Mouse (Apodemus speciosus) Testes Exposed to Low-Dose-Rate (LDR) Radiation after the Fukushima Nuclear Power Plant Accident

“…Data obtained in this work are in agreement with previous studies demonstrating no significant differences in the male reproductive system of wild animals exposed to LDR radiation after the Fukushima accident [19,26,27].…”

“…Particularly, Takino and colleagues [19] (2017) investigated the effect of chronic LDR radiation on spermatogenic cells in A. speciosus, finding enhanced spermatogenesis. In contrast, significant changes were not observed in raccoon testes after long-term exposure to ionizing radiation [26], or in the in vitro fertilizing capacity of cryopreserved sperm of A. speciosus after chronic LDR radiation exposure [27].…”

Low‐dose radiation‐induced demethylation of 3β‐HSD participated in the regulation of testosterone content

“…Legendre et al (2016) also identified that low‐dose depleted uranium could affect the production of these sex steroid hormone levels in adult rats. Interestingly, we did not detect acute physiological damages/changes in the male reproductive organ, including testis and epididymis, consistent with the latest finding that chronic LDR exposure associated with the Fukushima plant accident did not affect the characteristics and functions of male raccoons' reproductive system (Ashoub et al, 2021; Komatsu et al, 2020). Nevertheless, the current study found that LDR indeed increased the content of testosterone without the remarkable detectable damages in radiosensitive organs.…”

Evaluation of Global DNA Methylation and Gene Expression of Izumo1 and Izumo1r in Gonads after High- and Low-Dose Radiation in Neonatal Mice

“…In another study focusing on raccoon testes, although the total amount of radiation was unknown, chronic LDR exposure associated with the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident had no adverse effect on their reproductive characteristics and functions. [ 50 ]. Moreover, enhanced spermatogenesis occurred in large Japanese field mice ( Apodemus speciosus ) living in and around the FDNPP ex-evacuation zone (407–447 μGy/day) [ 43 ].…”