Neural damage in the Guinea pig cochlea after noise exposure a light microscopic study

Neural damage produced by exposure to 8 kHz octave-band noise was studied by light microscopy in guinea pigs. Abnormal nerve endings were found beneath both inner and outer hair cells within 24 hours after exposure at either 118 or 120 dB SPL. In areas where the organ of Corti was destroyed degeneration of myelinated nerve fibers was seen immediately after 24-hour exposures. Nerve degeneration secondary to hair cell loss was observed. However, degeneration of myelinated fibers occurred in some cases without significant hair cell loss. At survival times as long as two months nerve fibers coursing near capillaries were still present in extensively damaged areas. In three animals nerve fibers which had apparently regenerated into regions where the sensory epithelium was destroyed were found distal to the habenula perforata. Evidence of regenerative activity was also noted in the osseous spiral lamina.