Outbred Sprague-Dawley rats from two breeders exhibit different incidences of neuroanatomical abnormalities affecting the primary cerebellar fissure.

A significant variation in the incidence of alterations in the cellular organization along the primary fissure of the cerebellum is observed in outbred Sprague-Dawley rats obtained from Hilltop Animal Labs (89.9%) and Charles River Canada (34.1%). In this abnormality, there are areas in the depths of the primary fissure which lack pial cells, exhibit fusion of the apposing molecular layers, and contain ectopic granule cells, often with an associated disorganization of the cortical laminae. The extent and incidence of the abnormality can vary between individuals and litters, but the general incidence rate for a given breeder appears to be consistent over extended breeding cycles. This finding has serious implications for the use of outbred animals from different breeders when collecting data during the course of an experiment and when comparing and replicating data from different laboratories.