Effect of Ageing on the Organisation of Lateral Wall Tissues

Abstract

Hair cell loss and nerve degeneration have long been suggested as the primary pathology and cause of age-related hearing loss. However recent research has challenged previous theories and has suggested that in some cases the primary pathology may be degenerative changes in cochlear supporting tissues particularly the cochlear lateral wall comprised of epithelial cells and fibrocytes. Cells within the supporting tissue are inter-connected via gap junctions to form electrical and metabolic communication pathways to provide the correct electrochemical environment for sensory cells which is crucial for hearing. As part of a larger investigation into how disturbances in cochlear fluid ion homeostasis, particularly potassium, contribute to age-related and noise-induced cochlear degeneration and hearing loss, this study looked at the structural changes in the supporting tissues in the ageing mouse. Cochlear tissues were extracted and examined histologically in the 1, 3, 6, and 12 month old mouse. The organisation of the different supporting cells was described and the pattern of changes was assessed with age. With increasing age degenerate changes were seen in the region of type I and IV fibrocytes. Age-related changes also occurred in other regions of the cochlea including the spiral limbus and spiral ganglion. These changes were accompanied by sensory hair cell loss progressing from the basal turn. Further data from our laboratory, however, showed no change in the endocochlear potential in these mice implying that fibrocytes affected by age do not play an essential role in potassium ion homeostasis. Further investigation is required to explain the function of these cells.