This transgene expresses a mouse Gabrb3 gene under the control of the rat neural-specific enolase promoter. Expression was detected in the brain. This line exhibited behavioral defects not seen in other lines, suggesting that insertional inactivation of an endogenous gene was responsible for the phenotype. A non-complementation test demonstrated that the insertional mutation is allelic to pirouette. Further molecular analysis showed that the insertion is located in intron 2, 25 kb downstream of exon 2.