Graeme Clark Collection

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Start date: 2000 × End date: 2009 × Author: Clark, Graeme × Author: Shepherd, Robert × Subject: otolaryngology × Type: Conference Item ×

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    Effects of sensorineural hearing loss on the refractory properties of auditory nerve fibers
    Roberts, L. A. ; Shepherd, R. K. ; Paolini, A. G. ; Clark, Graeme M. ; Burkitt, A. N. ( 2000)
    We hypothesised that the loss of the peripheral processes and the partial demyelination of auditory nerve fibres (ANFs) following a sensorineural hearing loss would increase their refractory properties. Normal control, and long-term (2.5 months) systemically deafened rats were anaesthetised (urethane, 1.3 g/kg i.p.), a bipolar stimulating electrode was implanted into the scala tympani and glass microelectrodes (30-80 MΩ) used to record single ANF activity. Stimuli (pairs of 100 µs/phase charge balanced biphasic pulses with interpulse intervals (IPIs) of 0.34-10 ms) were presented at 6 dB above threshold using a repetition interval of 250 ms. Absolute refractory period (ARP) was defined as the IPI at which the probability of eliciting a spike to the second stimulus was 0.1. In the present results, based on recordings from 62 fibres, ANFs were distinguished from cochlear nucleus (CN) neurones by their significantly shorter median latencies (AN: 0.575ms vs CN: 1.137ms; Whitney-Mann Rank Sum, p<0.0001). There were no significant differences between minimum ANF latencies from normal and deafened animals. Although the median ARP was greater in deafened versus normal animals, this difference was not statistically significant (normals: median0.658ms, interquartile range 0.554-0.913ms; deafened: 0.772ms and 0.616-1.073ms; p=0.16). Finally, the spike latency associated with the second pulse of a pair systematically increased with decreasing IPI, contrasting with the stable latency of the response to the leading pulse. Although pathological changes to ANFs may increase their refractory properties, at this duration of deafness these changes were not significant.