Experimental lipidosis of the inner ear. Morphological and functional results

Otic pathology of caprine beta-mannosidosis

Caprine beta-mannosidosis is an autosomal recessive defect of glycoprotein catabolism with a deficiency of tissue and plasma beta-mannosidase activity and tissue accumulation of oligosaccharides within lysosomes. This rapidly fatal genetic disorder of Nubian goats is expressed at birth by a variety of clinical signs including deafness. Affected goats had folded pinnas, and the tympanic cavity was decreased due to multiple, polypoid projections of bone covered by middle ear mucosa which obstructed the view of the cochlear promontory. Numerous cells of the cochlear duct including mesothelial and epithelial cells of Reissner's membrane, mesothelial cells lining the scala tympani, cells of the stria vascularis, numerous supportive cells of the organ of Corti, cochlear hair cells, endothelial cells, perithelial cells, fibroblasts, macrophages, and neurons of the spiral ganglion contained numerous nonstaining intracytoplasmic vacuoles which resulted in distention of affected cells and caused thickening of involved structures. Ultrastructurally, the vacuoles were membrane-bound and consistent with lysosomes. Vacuolated cells were desquamated into the scala vestibuli and scala tympani. This is one of few reports describing light and electron microscopic otic alterations of a storage disease. Goats with beta-mannosidosis appear to be good models of hearing loss in patients with storage disease.

Vacuolar degeneration of the cochlea in young rats

In the course of investigations of the post-natal development of the ear in Sprague-Dawley rats, a hitherto unrecorded degenerative process was seen in two animals (7-and-8-days old). The process was characterized by vacuolization of almost all the cellular elements of the cochlear tissues. The overall shape and size of the cochlear structures remained well preserved. The organ of Corti did not atrophy but its components were vacuolized, as well as the cells of other inner ear tissues, except for nuclei in the lower part of the modiolus.

Chlorphentermine-induced changes of the peripheral vestibular sense organ of the rat

Chronic feeding of chlorphentermine to young rats induces an accumulation of electron dense conglomerates and vacuoles in intraepithelial afferent nerve fibres of maculae and cristae in the vestibular part of the inner ear. In spite of the fact that preterminal parts of axons are severely swollen due to this accumulation, the nerve terminals maintain their normal size but can sometimes contain inclusions. Efferent fibres always remain free of these changes. Sensory cells, vestibular ganglion cells and occasionally supporting cells contain lamellar and crystalloid-like inclusions which disappear when the treatment is interrupted. After a long-term feeding break the nerve fibre inclusions disappear. A few swollen distended morphologically empty preterminals remain. The preference of inclusion body accumulation in afferent neurons may indicate an especially high lipid turnover in this part of the hair cell innervation.