Age-related decreases in endocochlear potential are associated with vascular abnormalities in the stria vascularis

The density and diameter of strial capillaries were assessed in whole-mount preparations of the cochlear lateral wall from 18 gerbils aged in quiet for at least 36 months. Following morphometric analysis, histopathologic changes in selected regions of the lateral wall were examined by light and transmission electron microscopy. Alterations in strial vasculature were compared with the endocochlear potential (EP) measurements from the same ear. Vascular degeneration occurred in a segmental fashion in that regions of atrophic capillaries were found throughout the cochlea but primarily in the apical and lower basal turns and in the hook. The amount of stria with normal capillaries varied greatly among the aged ears, ranging from 19 to 87%. The resting EP also varied markedly, ranging from 23 to 83 mV. Little correlation was found between vascular alterations and the corresponding EP value from individual cochlear turns. However, significant correlations were found between the total strial area with normal vasculature and both the mean EP value and that recorded at either the round window or first turn in that ear.