Gunn rats, a mutant strain of rats, suffer from autosomal recessive hyperbilirubinemia. The homozygotes (j/j) develop jaundice soon after birth and often exhibit kernicterus and cerebellar hypoplasia that are due to bilirubin. Therefore, j/j Gunn rats have been used as an animal model of bilirubin encephalopathy, as well as of neonatal hyperbilirubinemia. In this review, we discuss morphologica...