Figure 2.

Changes in the auditory cortex expression of Arg3.1/Arc and cochlear ribbon synapse density related to the degree of acoustic trauma. (A) Following exposure to acoustic trauma that renders non-permanent threshold elevation (100 dB SPL, 2 h), reverse-transcriptase polymerase chain reaction (RT-PCR) analysis reveals Arg3.1/Arc expression is significantly upregulated in the auditory cortex; (B) by contrast, animals overexposed at 115–119 dB SPL for 2 h displayed marked downregulation of Arg3.1/Arc transcipts. Modified with permission from Tan et al. (2007). ^*p ≤ 0.05. (C,D) This relative downregulation is illustrated by immunohistochemical labeling of Arg3.1/Arc mRNA in the auditory cortex of animals exposed to a similar trauma (120 dB SPL, 2 h). Glutamate decarboxylase puncta are also indicated. Modified with permission from Singer et al. (2013). When animals were acoustically overexposed for either (E) 1 h or (F) 1.5 h, staining in the cochlea for IHC ribbon synapses (CtBP2, green, open arrows) indicated a subset of animals with marked reduction in ribbon synapse density, illustrated here for the mid-basal turn of the cochlea. IHC nuclei are labeled with DAPI (blue, circled); glutamate receptor subunit GluR4 protein labeled (red, open arrowheads). Scale bars 10 μm. (G,H) For each exposure protocol, a subset of animals could be categorized according to significant proportional reductions in midbasal and basal cochlear IHC ribbon synapse densities, relative to exposed animals without this pathology. Open bars = controls; filled bars = exposed. Numbers in each bar correspond to respective n. Modified with permission from Rüttiger et al. (2013). ^*p ≤ 0.05; ^**p ≤ 0.01; ^***p ≤ 0.001.