[Cochlear morphological changes over time after the introduction of bacterial endotoxin into the middle ear]

Guinea pigs weighing 350 g each were used in this experiment. A small piece of Gelform containing 0.04 mg of E. coli derived endotoxin was set on the round window 24 hours after intraperitoneal injection of 0.02 mg endotoxin. Morphological changes in the cochlea were observed at 24 hours (previous report), 48 hours, 72 hours and 7 days after the introduction of the endotoxin into the middle ear. As the results of the morphological changes of cochlea at 24 hours after the introduction of the endotoxin were reported in previous paper we present only an outline of these. Inflammatory cell infiltration and bleeding were observed in both endolymphatic and perilymphatic spaces. Inflammatory cells also infiltrated the stria vascularis, spiral ligament, spiral prominence and organ of Corti. Almost all of the inflammatory cells were neutrophils. Blood sludge was observed in all of the strial capillaries of the upper three turns. The hair cells were intact in every turn except for having small vacuoles. Intermediate cells and marginal cells of the stria vascularis were shrunken. At 48 hours after the introduction of the endotoxin into the middle ear, the changes in the stria vascularis were almost the same as at 24 hours. However the infiltrated inflammatory cells changed from neutrophils to macrophages. Macrophages had phagocytosed many neutrophils. The hair cells had many large vacuoles. At 72 hours, the enlargement of the intercellular space in the stria vascularis disappeared and damage to the hair cells decreased although many macrophages were still observed. At 7 days, the cochlea was morphologically normal.