Permeability of the implanted round window membrane in the cat: an investigation using horseradish peroxidase

Abstract

The round window membrane of seven cats was implanted with a Silastic® prosthesis 5 mm long. The membrane's permeability to horseradish peroxidase was investigated at different stages after implantation. All cats were treated with amoxycillin for a period of one week after the operation. Results showed an increased permeability over a period of approximately two weeks following implantation. Thereafter the round window barrier to horseradish peroxidase returned to normal. In all cases cochlear hair cells and auditory nerve fibres were preserved. In cases of spontaneous infection in the bulla the membrane responded with a proliferation of the subepithelial connective tissue, and the formation of protuberances. In these round windows although the permeability was increased the penetration of horseradish peroxidase into the scala tympani was limited. Horseradish peroxidase always passed through the gap between the membrane and the prosthesis. Particles were taken up, however, by the connective tissue envelope that formed around the prosthesis after one week.