Tinnitus is associated with increased extracellular matrix density in the auditory cortex

Most scientist agree that subjective tinnitus is the pathological result of an interaction of damage to the peripheral auditory system and central neuroplastic adaptations. Here we investigate such tinnitus related adaptations in the primary auditory cortex (AC) 13 days after noise trauma induction of tinnitus by quantifying the density of the extracellular matrix (ECM) in the AC of Mongolian gerbils (Meriones unguiculatus). The ECM density has been shown to be relevant for neuroplastic processes and synaptic stability within the cortex. We utilized a mild monaural acoustic noise trauma in 9 gerbils to induce tinnitus and a sham exposure in 3 control animals. Tinnitus was assessed by a behavioral response paradigm. Four of the trauma animals did show tinnitus 13 days after trauma (T), the remaining 5 trauma (NT) and the 3 control animals (C) did not show the percept. The ECM density 13 days after trauma was quantified using immunofluorescence luminance of Wisteria floribunda lectin-fluoresceine-5-isothiocyanate (WFA-FITC) on histological slices of the primary AC, relative to the non-auditory brainstem as a reference area. We found that the WFA-FITC luminance of the AC of NT animals was not significantly different from that of C animals. However, we found a significant increase of luminance in T animals’ ACs compared to NT or C animals’ cortices. This effect was found exclusively on the AC side contralateral to the trauma ear. These results point to a process of stabilization of synaptic connections in primary AC, which may be involved in the chronic manifestation of tinnitus.