INDUCTION OF ENDOLYMPHATIC HYDROPS IN THE GUINEA-PIG BY PERISACCULAR DEPOSITION OF SEPHAROSE BEADS CARRYING AND NOT CARRYING IMMUNE-COMPLEXES

We tried to induce endolymphatic hydrops in guinea pig cochleas by uni lateral, perisaccular-deposition of sepharose beads carrying immune co mplexes. Controls consisted of the deposition of sepharose beads witho ut immune complexes and the contralateral, untreated ear. The effects of the treatment were studied by light microscopy and electrophysiolog ical recordings of the gross cochlear potentials 1, 2, and 6 weeks aft er treatment. Each condition included six animals. Analysis of varianc e of the morphometric data concerning the ears treated with deposition of the beads showed a statistically significant difference (P = 0.04) between the degree of hydrops found for the beads with immune complex es and for those without. The difference between the treated ears and the contralateral untreated ears was significant (P = 0.01) for the be ads with immune complexes and not significant (P = 0.8) for those with out immune complexes while there was no significant effect of post-tre atment time interval. Analysis of variance of the electrophysiological data, collected in response to tone bursts al the apex of the cochlea , showed no significant differences between the results for the beads with and without immune complexes. Therefore these results were pooled . One week after treatment the pooled results for the compound action potential showed a small decrease in amplitude, just significant at 2 kHz, but not at 4 and 8 kHz. This decrease disappeared completely afte r 6 weeks. The pooled results for the negative summating potential (SP ) showed a significant increase in magnitude at all frequencies decrea sing with post-treatment interval. The cochlear microphonics did not d emonstrate any change in amplitude after treatment. The results indica te that deposition of sepharose beads with immune complexes induces en dolymphatic hydrops. Also, deposition of the sepharose beads itself ma y have induced hydrops together with enhancement of the SP. SP enhance ment may be related to the development of endolymphatic hydrops rather than to the presence of hydrops as such. This may be based on pressur e build-up while hydrops develops. (C) 1998 Elsevier Science B.V.