Immunohistochemical Investigation of Nerve Fibers among the Cochlear Supporting Cells with the Combination of Antigen Retrieval and Signal Amplification Method

We examined the nerve fibers among the cochlear supporting cells (NFSCs) in paraffin- and celloidin-embedded sections stained by the use of sodium retrieval immunoperoxidase technique (SRT) and/or tyramine amplification immunoperoxidase technique (TAT). SRT or TAT showed clear immunostaining of the radial nerve fibers and spiral ganglions, but a combination of the both techniques resulted in a higher density of the immunostained components at an amplification of 300-1,000 fold compared with the conventional immunoperoxidase technique (CIT). The presence of NFSCs was also clear with the combined use. This innervation was seen in the apical turns but not in the basal turns, similar to the location of lipid droplets among the Hensen cells, which are proposed to provide a high-energy source. Although the physiological significance and role of these nerve fibers has not yet been clearly defined, the coexistence of NFSCs and lipid droplets suggests that NFSCs may relate to energy metabolism. Our study also showed that SRT and/or TAT markedly enhanced the signal strength. These methods should allow the detection of very weak immunohistochemical signals under the use of stronger fixation or harder embedding.