Age-Related Changes of the Cochlear Lateral Wall (Stria Vascularis) in the Guinea Pigs: An Ultrastructural Study

Background: It is current opinion that the morphological changes in the stria vascularis and acquired hearing impairment appear to be the most prominent anatomic characteristic of aged human cochlea. The stria vascularis generates positive endocochlear potential and secretes endolymph which contains high concentration of potassium. Both of them are essential for normal sound transduction carried out by hair cells. Aim of the Work: Is to compare between the structure of stria vascularis in adult and senile guinea pigs, in an attempt to explain impairment of transduction of sound in old age (presbyacusis). Materials and Methods: Cochleae of guinea pigs were extracted and processed to semithin and ultrathin sections, stained, examined and photographed. Results: The senile stria vascularis showed herniations or protrusions from the luminal surface with blebs formation. Some marginal cells were vacuolated with pyknotic nuclei. The majority of mitochondria appeared fragmented, or swollen with disrupted cristae. However, the tight junctions between these cells were preserved. The most apparent ultrastructure alteration with age was loss of basolateral infolding with reduction of interdigitation between the marginal and intermediate cells. Dramatic decrease of the amount of melanin pigments with abundant myelin like figure was clearly noticed. The basal lamina of the strial blood capillaries was thickened and folded in some areas. The endothelial cells remained intact; however pericytes were not observed. Conclusion: The present findings proved that there were marked structural changes in the stria vascularis of senile guinea pigs, suggesting that these might be one of the causes of acquired hearing impairment in old age.