ELECTROPHYSIOLOGICAL EFFECTS OF MULTIPLE INSTILLATION OF HAEMOPHILUS-INFLUENZAE TYPE-B ENDOTOXIN ON THE INNER-EAR

An analysis of auditory brainstem response (ABR) thresholds and APR-ba sed frequency tuning curves was performed in 15 Sprague-Dawley rats ex posed to Haemophilus influenzae type b endotoxin; 5 mu g/50 mu l toxin was instilled every second day, altogether five times, into the middl e 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 confi guration were observed. It is concluded that Haemophilus influenzae ty pe b endotoxin, instilled repeatedly through the tympanic membrane int o the middle ear, does not affect cochlear electrophysiology.