Electron Microscopic and Histochemical Identification of Lipofuscin in the Human Inner Ear

Abstract

Normal inner ears of 14 individuals ranging from 2 days to 91 years of age were studied with electron microscopic and histochemical techniques for the distribution of lipofuscin and lysosomal enzymes (acid phosphatase, beta-glucuronidase and N-acetyl-beta-glucosaminidase). The electron microscope revealed in the cochlea large membrane-limited inclusions in the apical cytoplasm of all epithelial cells lining the endolymphatic space. Similar inclusions were also seen in the vestibular apparatus; the apical zone of the sensory and supporting cells, as well as the transitional epithelium and dark cells contained numerous lipofuscin granules. In the same locations where these structures occurred, we have observed intracytoplasmic granules with the histochemical characteristics of lipofuscin, including yellow to green autofluorescence. The sites of lipofuscin accumulation also displayed strong acid phosphatase activity. Lipofuscin could not be demonstrated histochemically in the newborn and was only sparse in children, but with age it gradually increased in quantity. On the other hand, acid phosphatase activity was practically the same in individuals of all ages. The age-dependent increase of lipofuscin in the human inner ear is apparently associated with lysosomal activity.