One hundred and ten chinchillas were exposed to a 700–2800 Hz noise at 123 dB for 15 minutes. A consistent pattern of ultrastructural pathology within the lateral cochlear wall was found. Significant damage to the stria vascularis was first observed one hour postexposure, reached a peak at 24 hours, and had recovered almost completely by 28 days. Spiral prominence damage was permanent. The pathology included stria widening, temporary disappearance of intermediate cells, alterations of the internal membrane system and abnormal vessel transport. Horseradish peroxidase (HRP) was employed as an indicator of transport from vessels. Transport from the stria vessels was absent when stria ultrastructural abnormality was at a maximum; at other postexposure times, however, abnormally rapid exodus of HRP from the vessels of the stria was observed in animals who had received intravenous injections of HRP 30 seconds prior to sacrifice. On the other hand, no leakage was observed in the animals injected one minute before sacrifice. Theories to explain this transport dichotomy are proposed.
