KANGAROO RATS EXHIBIT SPONGIFORM DEGENERATION OF THE CENTRAL AUDITORY-SYSTEM SIMILAR TO THAT FOUND IN GERBILS

Kangaroo rats develop spongiform degeneration of the central auditory system similar to that seen in the gerbil. Light microscopic and trans mission electron microscopic study of the cochlear nucleus and auditor y nerve root (ANR) of Dipodomys deserti and D. merriami show that spon giform lesions develop in dendrites and oligodendrocytes of the cochle ar nucleus and in oligodendrocytes of the ANR that are morphologically indistinguishable from those extensively described in the Mongolian g erbil, Meriones unguiculatus. As in Mongolian gerbils, the spongiform degeneration in Dipodomys were much more numerous in animals continual ly exposed to modest levels of low-frequency noise (<75 dB SPL). The k angaroo rats with extensive spongiform degeneration also show slightly , but significantly, elevated auditory brainstem evoked response (ABR) thresholds to low-frequency stimuli, a result also found in Mongolian gerbils. These results suggest that the elevated ABR thresholds may b e the result of spongiform degeneration. Because low-frequency noise-i nduced spongiform degeneration has now been shown in the cochlear nucl eus of animals from separate families of Rodentia (Heteromyidae and Mu ridae), the possibility should be investigated that similar noise-indu ced degenerative changes occur in the central auditory system of other mammals with good low-frequency hearing.