Monstrosity - The Atomic Brain (1963)

Mrs. March, a sadistic, selfish and rich old woman, uses her aging gigolo boyfriend, the renegade scientist Otto Frank whose illegal experiments she is subsidizing in her Gothic mansion, in a plan to transplant her brain into the body of a young woman. Three foreign female domestics, the Mexican Anita, the British Bea and the Austrian Nina, are hired. Frank's mysterious and unexplained use of atomic radiation can inexplicably transplant brains without surgery. After he puts a cat's brain into Anita and she scratches out Bea's eye, Nina becomes the prospective receptacle for Mrs. March's aging but still active libido.