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 numbe r and extent by rearing in acoustic isolation compared with rearing wh ile exposed to normal colony low-frequency background noise. This stud y tested whether rearing under exposure to noise bands of moderate int ensity would increase the number and extent of cochlear nucleus spongi form lesions. Gerbils were reared from weaning to young adulthood in a coustic isolation chambers while continually exposed to moderately int ense bands of either high frequency or low frequency noise. Exposure t o low frequency noise resulted in lesion number and area densities tha t were more than twice those seen in gerbils exposed to high frequency noise. Lesion extent in the low frequency group was similar to that i n colony-reared gerbils; lesion extent in the high frequency group was similar to gerbils reared in acoustic isolation. Comparisons within t he posterior ventral cochlear nucleus revealed that the differences in lesion extent were most pronounced in the middle and dorsal-medial po rtions, the regions that are most responsive to middle and high freque ncies. These finding suggest that the regional restriction of spongifo rm lesions within the cochlear nucleus does not have a tonotopic basis .