A. Fridberger et al., PRESSURE-INDUCED BASILAR-MEMBRANE POSITION SHIFTS AND THE STIMULUS-EVOKED POTENTIALS IN THE LOW-FREQUENCY REGION OF THE GUINEA-PIG COCHLEA, Acta Physiologica Scandinavica, 161(2), 1997, pp. 239-252
We have used the guinea pig isolated temporal bone preparation to inve
stigate changes in the nonlinear properties of the tone-evoked cochlea
r potentials during reversible step displacements of the basilar membr
ane towards either the scala tympani or the scala vestibuli. The posit
ion shifts were produced by changing the hydrostatic pressure in the s
cala tympani. The pressures involved were calculated from measurements
of the fluid flow through the system, and the cochlear DC impedance c
alculated (1.5 x 10(11) kg m(-4) s(-1), n = 10). Confocal microscopic
visualization of the organ of Corti showed that pressure increases in
the scala tympani caused alterations oi the position of the reticular
lamina and stereocilia bundles. For low pressures, there was a sigmoid
al relation between the DC pressure applied to the scala tympani (and
thus the position shift of the organ of Corti) and the amplitude of th
e summating potential. The cochlear microphonic potential also showed
a pronounced dependence on the applied pressure: pressure changes alte
red the amplitude of the fundamental as well as its harmonics. In addi
tion, the sound pressure level at which the responses began to saturat
e was increased, implying a transition towards a linear behaviour. An
increase of the phase lag of the cochlear microphonic potential was se
en when the basilar membrane was shifted towards the scala vestibuli.
We have also measured the intracochlear DC pressure using piezoresisti
ve pressure transducers. The results are discussed in terms of changes
in the non-linear properties of cochlear transduction. In addition, t
he implications of these results for the pathophysiology and diagnosis
of Meniere's disease are discussed.