Dexamethasone modifies the effect of Pseudomonas aeruginosa exotoxin A on hearing

In the present study, the protective effect of dexamethasone was analysed f ollowing exposure of the cochlea to Pseudomonas aeruginosa Exotoxin A (PaEx oA). Four groups of albino Sprague-Dawley rats were used. 20 mu l saline wa s instilled through the tympanic membrane into the round window niche (grou p A, n = 4); 1 mu g/20 mu l dexamethasone sodium 21-phosphate (dexamethason e) solution was instilled (group B, n = 4); 1 mu g/20 mu l PaExoA solution was initiaily instilled followed 1 h later by 20 mu l saline (group C, n = 6); and 1 mu g/20 mu l PaExoA solution was initially instilled followed 1 h later by 1 mu g/20 mu l dexamethasone solution (group D, n = 6). Frequency -specific (4, 8, 10, 12, 16 and 20 kHz) auditory brainstem responses (ABR) were used to ascertain the threshold prior to exposure and 1, 2, 3, and 5 d ays and 1 and 2 weeks afterwards. No threshold change was observed in group s A and B, whereas the animals in groups C and D showed some threshold elev ation, that in D bring smaller than that in C. There was a significant diff erence at the frequencies 12, 16 and 20 kHz, 2 and 5 days after exposure. T he intensity-latency (I-L) curve showed that in group D the cochlear compon ent almost disappeared at high frequency one week after exposure. Our resul ts indicate that dexamethasone can modify the effect of PaExoA caused bq no n-specific inflammation.