The Development of Mouse Ovaries after Low-dose Irradiation at Birth

Abstract

A single dose of 20 r of X-rays given to mice at birth influences the development of their ovaries considerably. The effect becomes evident a few hours after radiation, and the damage can be traced in the infantile and pre-pubertal ovaries and in the organs of young mature animals. The immediate damage seems to be due to the marked radiation sensitivity of oocytes in pachytene, i.e. the pre-stationary stage of meiotic prophase, in which many of the oocytes still are on the day of birth in the "Street" mouse. Oocytes in pachytene disappear quickly after radiation, whereas oocytes already in the stationary phase of meiosis at the time of radiation seem more resistant to immediate damage. Although irradiated animals start to ovulate at about the same age as normal animals and produce morphologically normal ova soon after they reach maturity, histological analysis reveals already marked degeneration and destruction of parts of the ovary at that time.