Exposure to low frequency noise during rearing induces spongiform lesions in gerbil cochlear nucleus: high frequency exposure does not.

Spongiform lesions of the gerbil cochlear nucleus are reduced in number and extent by rearing in acoustic isolation compared with rearing while exposed to normal colony low-frequency background noise. This study tested whether rearing under exposure to noise bands of moderate intensity would increase the number and extent of cochlear nucleus spongiform lesions. Gerbils were reared from weaning to young adulthood in acoustic isolation chambers while continually exposed to moderately intense bands of either high frequency or low frequency noise. Exposure to low frequency noise resulted in lesion number and area densities that were more than twice those seen in gerbils exposed to high frequency noise. Lesion extent in the low frequency group was similar to that in colony-reared gerbils; lesion extent in the high frequency group was similar to gerbils reared in acoustic isolation. Comparisons within the posterior ventral cochlear nucleus revealed that the differences in lesion extent were most pronounced in the middle and dorsal-medial portions, the regions that are most responsive to middle and high frequencies. These finding suggest that the regional restriction of spongiform lesions within the cochlear nucleus does not have a tonotopic basis.