Auditory brainstem response after electrolytic lesions in the unilateral medial geniculate body of tree shrews.

Objectives: This study aimed to assess the processing of clicks and tone pips in the auditory brainstem of tree shrews and analyze the long-term evolution of postlesion plasticity in the auditory system and its ability to self-repair.

Methods: The auditory brainstem response (ABR) was measured in the normal control group (n=10) and the electrolytic damage group (n=10) before and 0 h, 24 h, 48 h, 72 h, and 25 d after electrolytic damage. Recordings were performed under closed-field conditions using clicks and tone pips, followed by statistical analysis of the ABR threshold, amplitude and latency.

Results: The results were as follows: (1) After electrolytic damage to the tree shrew medial geniculate body (MGB), the latency and amplitude of ABR waveforms from the left ear changed from 0 h to 25 d. All parameters were lower at 25 d than they were preoperatively. The amplitude of ABR wave VI (using click sound stimulation) decreased or disappeared in both ears. (2) The ABR threshold was significantly different in both ears at 72 h postoperatively compared with preoperatively (0 h) (P < 0.05) but recovered by 25 d.

Conclusion: Based on these results, we conclude the following: (1) The origin of wave VI in tree shrews may be associated with the MGB. After electrolytic damage to the MGB, the changes in the ABR waveforms at different frequencies indicated that the MGB nucleus had a certain characteristic frequency. (2) Unilateral injury to the MGB can lead to similar levels of hearing impairment in both ears.