Reversible Conductive Hearing Loss: Restored Activity in the Central Auditory System

Abstract

The effect of a reversible, unilateral hearing loss on 2-deoxyglucose (2-DG) uptake in the central auditory system was studied using young gerbils. All animals had a unilateral conductive hearing loss (CHL), induced by atresia, on postnatal day 21 (P21). One week later, on P28, animals had their atresia repaired (CHL/R), or not repaired (CHL/NR), and CHL/NR animals entered the 2-DG experiments. CHL/R animals were allowed a 1-week period of restored binaural hearing experience prior to entering 2-DG experiments on P35. Animals in each group were injected with 2-DG and exposed to ambient sounds for 45 min prior to sacrifice. Uptake of 2-DG was measured in the anteroventral cochlear nucleus (AVCN), the medial superior olive (MSO), and the inferior colliculus (IC) on both sides of the brain. In CHL/NR animals, there were significant differences in uptake between the AVCN, MSO, and IC ipsilateral versus contralateral to the manipulated ear, indicating an imbalance in ascending afferent activity. In CHL/R animals, there were no significant differences, suggesting that 1 week after CHL repair, the appearance of balanced afferent activity had been restored.

Developmental Hearing Loss Disrupts Synaptic Inhibition: Implications for Auditory Processing

“…As compared with most SNHL models, CHL can be induced reversibly by ear plugs or atresia. These studies suggest that some of the neural effects of unilateral CHL are reversed when normal hearing is restored, although this depends on the age at which hearing is restored [173,174]. This is consistent with the effects observed after reversible unilateral SNHL was induced by tetrodotoxin application to the round window.…”

Unilateral Conductive Hearing Loss Disrupts the Developmental Refinement of Binaural Processing in the Rat Primary Auditory Cortex

“…Moreover, UCHL in young rats induced a significant shift of the aural dominance from contralateral preference to ipsilateral preference in AI but not in the inferior colliculus (Popescu and Polley, 2010), and this result suggests that the effect of RUCHL exerts stronger plasticity in the auditory cortex than in the inferior colliculus. Consistently, a 2-deoxyglucose uptake study in gerbils demonstrated that RUCHL at young age could restore balanced afferent activity on both sides of the anteroventral cochlear nucleus, the medial superior olive, and the inferior colliculus 1 week after restoring binaural hearing from P28 (Hutson et al, 2009). Based on these findings, we postulate that the observed RUCHL effects in the present study most likely occurred above the inferior colliculus.…”

Auditory temporal abilities in children with history of recurrent otitis media in the first years of life and persistent in preschool and school ages

“…The prolongation of I-V and I-III interpeak latencies were also related to ROME in early life in children aged 3, but not those aged 4 and 5 years (13) . In fact, the changes found in the brainstem auditory evoked potential may be justified, as experimental studies identified structural changes in the cochlear nuclei, medial olivary complex, and inferior colliculus, that is, from the low trunk to the high trunk (18) . These neural structures are responsible, respectively, for waves III and for the IV-V complex (32) .…”

“…Another assumption concerns the critical period of maturation of the ANCS, because it is well documented that a greater likelihood of recurrence of OME is related to how early its first episode occurs, such as in the first years of life (17) . Special attention to periods referred as key on the maturation process of the ANCS is required, because experimental studies show structural and functional changes in synaptic relays that are important for sound processing, resulting from sensory deprivation due to middle ear disorders, such as in the cochlear nucleus, superior olive, and inferior colliculus (13,18) . However, these studies show evidence of the ability of the ANCS to establish new neural networks after periods of deprivation.…”