ANATOMICAL AND PHYSIOLOGICAL MEASURES OF AUDITORY-SYSTEM IN MICE WITHPERIPHERAL MYELIN DEFICIENCY

Animal models with genetic abnormalities have been increasingly used i n auditory research. Both Tr(J) mice and P-o-DT-A mice are animals wit h peripheral myelin deficiency. In Tr(J) mice, the defect is due to a mutated PMP-22 gene. In P-o-DT-A mice, the defect is produced by a tra nsgene using the rat P-o promotor to direct the expression of gene enc oding for the bacterial diphtherial toxin A chain (DT-A). This study e valuates the auditory system both physiologically and histologically i n these two strains of mice. Histological examination revealed that th ere was myelin deficiency of the auditory nerve fibers, accompanied by a loss of dendrites and a loss of spiral ganglion cell bodies in both strains of mice. In general, histological deficits in Tr(J) mice were greater than those in P-o-DT-A mice. There was a strong correlation b etween the degree of myelin deficiency and the survival of spiral gang lion neurons. ABR measurements exhibited differences in threshold, lat ency and slope of the ABR growth function between myelin-deficient mic e and their respective controls. These results suggest that the integr ity of the myelin in the auditory nerve is important both for neural s urvival and for normal electrophysiological function of spiral ganglio n neurons.