Abnormal tonotopic organization in the ventral cochlear nucleus of the hearing-impaired DBA/2 mouse

The representation of sound frequency by auditory neurons (tonotopic organization) was evaluated in the ventral cochlear nucleus (VCN) of DBA/2 mice, a strain with impaired sensitivity to the highest and lowest frequencies heard by normal mice. Tuning curves were obtained from multiple-unit activity (MUA) and compared with those of C57 mice, which do not have severe hearing loss. Tuning curves in the C57 VCN displayed the dorsoventral progression from high- to low-frequency sensitivity that is typical of mammals. By contrast, tuning curves of DBA mice varied little as a function of dorsoventral location, and most MUA thresholds were lowest for frequencies within a narrow range (about 12-16 kHz). Thus, normal tonotopic organization is absent in the DBA mouse's VCN. In addition, because of the consistently low thresholds for 12-16 kHz tones in DBA MUA, mean thresholds for these frequencies are lower than those of C57 MUA in the dorsal and ventral portions of the VCN.