ELECTRICALLY-EVOKED AUDITORY BRAIN-STEM RESPONSE IN PERIPHERALLY MYELIN-DEFICIENT MICE

The integrity of the myelin sheath is important for normal electrophys iological function and survival of neurons that make up the auditory n erve. It is hypothesized that myelin deficiency of the auditory nerve may change the electrophysiologic characteristics of the auditory syst em, especially the temporal properties. In this study, the electricall y evoked auditory brainstem response (EABR) was systematically evaluat ed in Tr(J) and P-o-DT-A mice. Both of these mice have a deficit of th eir peripheral myelin. Correlation between the EABR and degree of myel in deficiency was also evaluated. The EABR in both strains of poorly m yelinated mice exhibited prolonged latency, decreased amplitude, eleva ted threshold of wave I evoked by short-duration stimuli (20 mu s/phas e). A 2-pulse stimulation paradigm was used to evaluate refractory pro perties. Myelin-deficient mice exhibited slower recovery from the refr actory state than controls. Long-duration stimuli (4 ms/phase) were us ed to assess integration properties. Myelin-deficient mice demonstrate d prolonged wave I latency and more gradual latency changes with curre nt level. Myelin thickness showed a strong correlation with EABR thres hold for short-duration stimulation (r=-0.784), maximum wave I latency (r=-0.778) and the time constant of the wave I latency-current level function (r=-0.736) for long-duration stimulation and normalized wave I recovery functions (r=-0.718). These findings suggest that EABR meas urement may be a promising tool to assess the electrically stimulated properties of auditory neurons, particularly related to the status of myelin sheath.