Endolymphatic sac is involved in the regulation of hydrostatic pressure of cochlear endolymph

To clarify the role of the endolymphatic sac (ES) in the regulation of endolymphatic pressure, the effects of isoproterenol, a β-adrenergic receptor agonist, and acetazolamide, a potent carbonic anhydrase inhibitor, both of which decrease ES direct current potential on cochlear hydrostatic pressure, were examined in guinea pigs. When isoproterenol was applied intravenously, hydrostatic pressures of cochlear endolymph and perilymph were significantly increased with no change in endocochlear potential or the hydrostatic pressure of cerebrospinal fluid. Acetazolamide produced no marked change in the hydrostatic pressure of cochlear endolymph. In ears with an obstructed ES, the action of isoproterenol on the hydrostatic pressure of cochlear endolymph and perilymph was suppressed. These results suggest that the ES may regulate the hydrostatic pressure of the endolymphatic system via the action of the agents such as catecholamines on the ES.

Finite element modeling of the 3D otolith structure

A 3D finite element model (FEM) of the mammalian utricular otolith corresponding to spatial structure, shape and size of the otolith from the guinea pig was developed. The otolithic membrane (OM) was considered as consisting of gel and otoconial layers. The macular surface was approximated as a plane. The deformation of the OM under static loads such as gravity and the change of endolymphatic pressure was analyzed using the FEM for different mechanical parameters of the OM and for different gravity vector orientations. The analytical dependence of OM displacements caused by the acceleration parallel to the macular plane was obtained. By comparison of the results of calculations with the known experimental data Young’s modulus of the gel layer was estimated to be of order of 10 N/m 2 . It was shown that static loads result in 3D local otolith displacements inhomogeneously distributed along the macular surface and across otolith thickness. Their distribution depends on the geometrical and mechanical parameters of the otolith components. The influences of the finite size of the OM, the Young’s modulus, Poisson’s ratio and thickness of the gel layer on the local displacements distribution of the OM were analyzed. The results of simulation suggest that: a) the Young’s modulus of the thin lowest part of the gel layer adjacent to the macular surface is much smaller than that of the rest of the OM; b) the structure of the border is designed to reduce the spatial inhomogeneity of the gel layer displacement; c) a change of the endolymphatic pressure may result in significant deformation of the OM.