Objective: To study the long-term effect of cochlear ablation on cochlear nucleus (CN).
Methods: A total of 40 BALB/c adult mice were used in the present study. Mice were divided into experimental group and control group at random. In experimental group, the cochlea was destroyed with stainless steel needle under the anatomy microscopy. Mice were tested for ABR thresholds at second day and 4 months after operation to assess hearing sensitivity. Animals were allowed to survive for four months. Histological sections of the cochlear nucleus were evaluated with serial sections stained with Nissl staining and silver staining alternatively. Morphological change in anteroventral cochlear nucleus (AVCN), posteroventral cochlear nucleus (PVCN), dorsal cochlear nucleus (DCN) and octopus cell area (OCA) was observed evaluated four month later after the cochlear ablation.
Results: In the experimental group, after operation, early components of ABR couldn't be recognized. The volume of CN was decreased dramatically and the cells were less comparing to the control group. The volume of AVCN after cochlear ablation showed a decline to 22% less than the control group, and the number of neurons also dropped by 25%. In PVCN, the decreased volume by 40% with significant neuronal loss of 47% was observed four month later after the cochlear ablation. And in DCN, the volume shrinking to 24% and the loss of neurons reached to 39%. The most significant change was observed in OCA (octopus cell area), with the neuron numbers, the area and the volume of OCA decreased by 60%, 19%, and 47% respectively. There was a statistically significant difference (P<0.05, Mann-Whitney U test) in the morphological changes between the two groups.
Conclusion: Neuronal degeneration was observed in cochlear nucleus after four months cochlear ablation.