This mutation occurred in the laboratory of Dr. Simon Koletsky in 1969 at Case Western Reserve University School of Medicine. It was developed from a cross between a hypertensive female rat and a normotensive male Sprague Dawley rat. The colony was maintained as brother x sister matings in a closed colony at Case Western Reserve University School of Medicine since 1971. To Genetic Models, Inc. in 2000. To Charles River in 2001.