Disparities in auditory physiology and pathology between C57BL/6J and C57BL/6N substrains

C57BL/6 inbred mice are frequently used as models in auditory research, mostly the C57BL/6J and C57BL/6N substrains. Genetic variation and phenotypic disparities between these two substrains have been extensively investigated, but conflicting information exists about differences in their auditory and vestibular phenotypes. Literature-based comparisons are rendered difficult or impossible because most auditory publications do not designate the substrain used. We therefore evaluated commercial C57BL/6N and C57BL/6J mice for their baseline auditory brainstem response (ABR) thresholds at 3 months of age as well as their susceptibility to noise exposure and aminoglycoside antibiotics. Both substrains have similar thresholds at 4 and 12 kHz, but C57BL/6N show significantly higher baseline thresholds at 24 and 32 kHz. Because of these elevated thresholds, the N substrain is unsuitable as a model for drug ototoxicity, which primarily affects high frequencies. Exposure to 2-20 kHz broadband noise for 2 h at 110 dB produced significantly higher threshold shifts in the J substrain. These results suggest caution in the selection of C57BL/6 substrains for auditory research and indicate the need to specify substrains, age and the breeding source in all publications.