Hydrops in the cochlea can be induced by sound as well as by static pressure

The Reissner's membrane (RM) was visualised by confocal microscopy in the i solated temporal bone of the guinea pig. The function of the organ was foll owed by measuring its physiological response. Static pressure applied in th e basal coil caused a distention of the RM in the apical coil into the scal a vestibuli. The sensitivity to a test tone was reduced. When the pressure was relieved, the RM returned to its original position and the response rec overed. If the increased pressure was maintained, the RM would bulge furthe r. The RM could then be reversibly stretched and return gradually, with a d elay, to its original position. Alternatively, it could be over-stretched a nd return with an over-shoot past its original position toward the organ of Corti. In response to repetitive tone pulses of above 80 dB, hydrops of th e RM also developed. This was accompanied by a reduced sensitivity. A slow recovery to the original position, or over-shoot, and return of responsiven ess could be seen. Above 106 dB sustained loss was generally seen. It is co ncluded that the RM can accommodate increased scala media pressure by diste ntion. This will relieve the organ of Corti from part of the pressure and m ay protect the organ from trauma. (C) 2000 Elsevier Science B.V. All rights reserved.