A new inbred rat strain (TS) with suprainguinal ectopic testes: a model for human cryptorchidism

Abstract

A mutant rat (TS) has been described with so-called ectopic scrotum, but the published photograph suggested that only the testes were ectopic. We established a colony of these inbred rats as a possible model for cryptorchidism. Five breeding pairs were obtained from the Imamichi Institute, Japan. Immature male offspring (0–21 days) were examined macro- and microscopically to document inguinoscrotal anatomy and gubernacular development. Uni- or bilateral, suprainguinal ectopic testes occurred in 39/46 males. Abnormal gubernacular position was visible microscopically by 3 days and macroscopically by 3–7 days of age. The processus vaginalis, cremaster muscle, and epididymis developed normally. The scrotum was hypoplastic but in the normal position. The TS rat is a new animal model for superficial inguinal ectopic testes, and will be invaluable for elucidating the cause of cryptorchidism and studying the effects of treatment. Our preliminary morphological studies suggest that the gubernaculum develops properly, but appears to migrate in the wrong direction.