Anatomical volume change of the Cochlear Nucleus depending on the hearing experience of the rat

Introduction Deafness leads to different degrees of changes along the auditory pathway depending on the time and duration of deafness. Here we investigate the effect of neonatal deafness (ND; unilateral and bilateral) compared to bilateral adult deafness (AD) on the volume of the cochlear nucleus (CN).

Methods Unilateral ND in rats (n=5) was induced on postnatal (P) day 10 by intracochlear injection of neomycin. Bilateral ND (n=5) was induced by intraperitoneal injection of kanamycin (P10-20). Bilateral young and old AD (n=5 each) was induced by the combined injection of ethacrynic acid and kanamycin in 3- and 12-months old rats. Deafness was verified by ABR measurements with hearing thresholds>90 dB. Perfusion of the animals was performed at 4 and 13 months of age. This was followed by the preparation of brain sections, their light microscopic examination with the taking of photographs and the evaluation of the CN sections. Finally, length, width, area, and volume of the CN were determined.

Results The CNs of ND rats was significantly reduced in volume. Compared to normal hearing rats, bilateral deafness resulted in a 31.41% smaller CN volume, unilateral deafness resulted in a 36.93% smaller CN volume on the deaf compared to the hearing side. In both cases, the ventral part was most affected by the volume reduction. In young and old AD rats, the CN volume was reduced by 10.43% and 1.37%, respectively, and did not reach significance.

Conclusion Our histological data show that both unilateral and bilateral ND leads to severe anatomical changes in the CNS compared to AD. This confirms the importance of diagnosing deafness in patients as early as possible to prevent reduced or impaired development of the central auditory system using hearing prostheses.

Publication History

Article published online:
19 April 2024