Resting neural activity patterns in auditory brainstem and midbrain in conductive hearing loss

Abstract

Conclusions: Conductive hearing loss (CHL) lowers resting neural activity patterns in the auditory periphery. Such reductions of peripheral auditory activity may influence the developing central brain during early postnatal years when the system is still highly plastic. Objectives: A common cause of CHL in young children is otitis media; if chronic and/or episodic there may be a risk to speech and language development. In this clinical context we have investigated changes in neural activity patterns in the brainstem and midbrain in an animal model of CHL. Methods: In a mouse model, a 50–60 dB CHL was produced by blocking the ear canals. We quantified resting neural activity patterns in the cochlear nucleus and inferior colliculus using c-fos immuno-labelling. This experimental group was compared with normal-hearing controls and with animals with bilateral cochlear ablation. Results: Subjects with CHL had a statistically significant reduction in c-fos-labelled cells in the cochlear nucleus and central nucleus of the inferior colliculus compared with normal controls. This decreased c-fos expression suggests a change in resting neural activity generated at the inner hair cell synapse, leading to a reduction in activity levels in the ascending auditory pathways.

Keywords::

• otitis media
• cochlear nucleus
• inferior colliculus
• spontaneous activity
• inner hair cell
• c-fos
• NeuN
• auditory brainstem response
• ABR
• developmental plasticity

Acknowledgments

This research was funded by the Canadian Institutes of Health Research (CIHR; grant VIH-105441) and by the Masonic Foundation of Ontario.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.