Mitochondrial and endoplasmic reticulum pathways involved in microcystin-LR-induced apoptosis of the testes of male frog (Rana nigromaculata) in vivo

•MCLR can induce apoptosis on testes of Rana nigromaculata.•1μg/L MCLR (the drinking water standard level) has ecological risks on frogs.•MCLR induces frog testes apoptosis via oxidative stress.•MCLR-induced apoptosis on frog testes is associated with mitochondrial pathway.•Endoplasmic reticulum pathway is involved in MCLR-induced apoptosis on frog testes. Previous studies have shown that toxins produced by toxic cyanobacterial blooms are hazardous materials. In the present study, 1μg/L microcystin-LR (MC-LR) was observed to induce apoptosis in the testes of male Rana nigromaculata via the mitochondrial and endoplasmic reticulum (ER) pathways at exposure times ranging from 7 d to 14 d. The results showed that reactive oxygen species production and malondialdehyde content were positively correlated with exposure time. Antioxidant enzyme contents, such as reduced glutathione and glutathione peroxidase rapidly decreased, implying that the defense system of the testes induces oxidative damage. MC-LR significantly stimulated the release of cytochrome c in the testes, thereby improving the protein expressions of Bax and caspases-3, 8, and 9 (p