Effects of Renal Insufficiency on the Cochlear Absorptive-secretory Areas: A Morphological Study in the Mongolian Gerbil

Abstract

In order to evaluate the effects of experimental renal insufficiency (RI) on the labyrinthine absorptive-secretory areas (ASA), 54 adult Mongolian gerbils were submitted to bilateral nephrectomy or to sham procedure. At different intervals (3, 6, 9, 12, 15, 18, 21, 24 hours) after the surgical procedures, or during the terminal stage (28 h) the animals were decapitated and both temporal bones were dissected to obtain selected specimens of the cochlear ASA. The specimens were processed and analysed by light and electron microscopy. Structurally, RI induced progressive thickening of the epithelial components (stria, prominentia, sulcus); separation by fluid accumulation between stria and mesodermal layer; and frequent dilatation of intraepithelial vessels. Ultrastructurally, diverse signs were observed parallel to the evolution of the RI. After 12 h a progressive enlargement of the intercellular spaces, which was particularly evident in the stria surrounding the vessels and in the other sulcus, was observed. Its latest expression was a marked widening of the basolateral spaces containing a granular substance. After 12 h the formation of large cytoplasmic perinuclear spaces containing small rounded vesicles, probably secondary to fluid accumulation, could be observed in the marginal cells. After 24 h diverse signs of organellar damage became evident (schedule: mitochondrial swelling, lysosome like figures, myelin like figures). In the terminal stage, a general homogenization of the cytosol was common. The findings suggest a definite re-distribution of fluids in the inner ear. A close relationship between renal dysfunction and labyrinthine microhomeostasis is therefore proposed.