Electrophysiological effects of multiple instillation of Haemophilus influenzae type b endotoxin on the inner ear.

An analysis of auditory brainstem response (ABR) thresholds and ABR-based frequency tuning curves was performed in 15 Sprague-Dawley rats exposed to Haemophilus influenzae type b endotoxin; 5 microg/50 microl toxin was instilled every second day, altogether five times, into the middle ear cavity through a small perforation in the tympanic membrane. ABR was measured 48 h after the second application and 24 h, 48 h, 5 days and 10 days after the fifth instillation. Five applications of toxin had no statistical effect on ABR thresholds and no changes in TC configuration were observed. It is concluded that Haemophilus influenzae type b endotoxin, instilled repeatedly through the tympanic membrane into the middle ear, does not affect cochlear electrophysiology.