Auditory deprivation of the central auditory system resulting from selective inner hair cell loss: animal model of auditory neuropathy.
Auditory neuropathy is often characterized by normal thresholds, present otoacoustic emissions, poor speech discrimination, absent acoustic reflexes, absent or abnormal auditory brainstem response waveform, but normal late cortical potential. This paper describes an animal model that has many characteristics of auditory neuropathy. Chinchillas can be deprived of a significant portion of the neural inputs to the central auditory system by administering carboplatin, an antineoplastic agent that selectively destroys inner hair cells (IHCs) and type I auditory nerve fibers. Selective IHC loss has no effect on distortion product otoacoustic emissions or the cochlear microphonic potential, implying normal outer hair cell function. However, selective IHC loss causes the amplitude of the compound action potential to decrease in proportion to the degree of IHC loss. However, the threshold of the CAP shows little increase with mild to moderate IHC loss. Acoustically responsive auditory nerve fibers in ears with mild to moderate IHC loss have normal thresholds and tuning curves with narrowly tuned tips. Although the central auditory pathway is deprived of much of its sensory inputs, the amplitude of the local field potential in the auditory cortex was normal or enhanced, while those from the inferior colliculus were slightly reduced. The results are related to those of a patient with auditory neuropathy.