Combined electrophysiological and autoradiographic delimitation of retrocochlear dysfunction in a mouse mutant

The hereditary retrocochlear dysfunction in the quivering (qv) mouse was investigated with autoradiography and single unit recordings. Whilst the cochlea appears to function normally, earlier studies had indicated some single unit dysfunction detectable at the level of the cochlear nucleus (CN) and abnormality of auditory evoked potentials recorded at the inferior colliculus (IC). The present study investigated the possibility of progressive deterioration of function at successive higher levels in the auditory system. The 2-deoxyglucose technique illustrated auditory activity in the CN of quivering mice similar to that seen in normally-hearing control animals. There was only a slight increment in metabolic activity detectable at the level of the IC. Electrophysiology demonstrated that this minimal IC activity was the result of abnormally raised thresholds associated with all single units recorded, rather than of activity in a few normally responding cells. There was no evidence from autoradiography for any enhanced auditorily evoked metabolic activity in either the superior olivary complex or the lateral lemniscus. This study suggests that the retrocochlear dysfunction in quivering mice is due to a specific abnormality at a low stage in the auditory pathway rather than being non-specific and cumulative over stages.