STARGAZER (STG), NEW DEAFNESS MUTANT IN THE ZUCKER RAT

We describe a new deafness mutant found in the Zucker rat. The mutant phenotype appears to be caused by an autosomal recessive gene, tentati vely named stargazer, gene symbol stg. The phenotype is characterized by stargazing, head tossing, drawing back, circling, and hyperactivity , all of which are apparent by the third week of life. Although the af fected animals sire or bear normal-sized litters, mortality is high fo r litters of affected dams, apparently due to trampling or neglect by the hyperactive dams. Affected animals are unable to swim and, when li fted by the tail, they are likely to curl ventrally, rather than exten ding their paws downward. These behaviors are consistent with a disord er of the vestibular system. Auditory evoked potential recordings were attempted as a hearing test. The failure of audible clicks up to 90 d ecibels to stimulate the auditory tract indicates that stargazers are profoundly deaf. These disruptions of vestibular and auditory systems suggest that the stargazer phenotype may be caused by disordered devel opment of the inner ear. Histologic examination of the inner ear revea led progressive degeneration of cells in the acoustic ganglion and of hair cells. The stargazer rat may be useful as a model for hereditary deafness or hyperactivity.