Selective Synaptic Remodeling in Rat Auditory and Visual Cortices Following Noise-Induced Permanent Hearing Loss in Adulthood.

Abstract

In adults with acquired hearing loss, cortical reorganization and cross-modal plasticity critically influence the timing and outcomes of cochlear implantation. This study examined the effects of 2 weeks of bilateral auditory deprivation-induced by intense broadband noise-on the structure and gene expression in the primary auditory (A1) and visual (V1) cortices of adult rats. The results revealed that the total neuronal counts in both the A1 and V1 remained unchanged compared to controls. Morphological analysis showed no significant change in mature dendritic spine density in either region, but immature spine density was significantly reduced in the V1 cortex. Ultrastructural examination demonstrated notable synaptic alterations in the A1 cortex, including significant reductions in postsynaptic density (PSD) length, thickness, area, and synaptic vesicle number-changes that were not observed in the V1 cortex. Transcriptomic profiling indicated a region-specific response, with 197 differentially expressed genes (DEGs) in the A1 cortex, compared to a broader alteration of 545 DEGs in the V1 cortex, which were significantly involved in neuronal signaling and synaptic transmission. These findings demonstrate that auditory deprivation induces distinct molecular and synaptic remodeling in the A1 and V1 cortices, identifying neuronal plasticity and synaptic regulation as central mechanisms for cross-modal reorganization in the adult brain.