A quantitative analysis of the nerve fibers in the VIIIth nerve of BelgianWaterslager canaries with a hereditary sensorineural hearing loss

The number of auditory nerve fibers was determined for non-Belgian Watersla ger canaries (non-BWS) and Belgian Waterslager canaries (BWS) that are affe cted by a sensorineural high frequency hearing loss and a 30% reduction in the number of auditory hair cells. Counts were obtained from semithin cross sections of the Durcupan-embedded auditory nerve at the level of the inter nal auditory meatus. In addition, the number of lagenar fibers was determin ed from cross sections near the apical end of the cochlear duct in order to separate them from the total number of auditory nerve fibers. The mean num ber of auditory nerve fibers was 6076 in non-BWS and 5363 in BWS canaries, representing a 12% reduction in BWS. This small reduction in the number of auditory nerve fibers? as compared to the larger reduction in hair cell num ber, might be explained by a predominant loss of abneural hair cells in BWS , since it has been shown for other species that a large proportion of abne ural hair cells are devoid of afferent innervation. In addition, we observe d that despite the prominent hair cell pathologies documented for BWS canar ies, the mean diameter of auditory nerve fibers from non-BWS canaries (2.22 +/- 0.81 mum) did not differ from those of BWS canaries (2.21 +/- 0.96 mum ). (C) 2001 Elsevier Science B.V. All rights reserved.