Morphological changes of the endolymphatic sac induced by microinjection of artificial endolymph into the cochlea

 

Helga Rask-Andersen,  Alec N. Salt, John E. DeMott, Dan Bagger-Sjöbäck

 

Abstract

Morphological changes of the endolymphatic sac were analysed in guinea pigs following microinjection of artificial endolymph into the cochlea, or withdrawal of a quantity of native endolymph. Injections were performed into the second turn of scala media with a micro-pump at a rate of 60-100 nanolitres/minute, lasting for a period of 4, 7.5, 15 or 18 minutes. In withdrawal experiments, endolymph was aspirated from the second cochlear turn over a period of 8 minutes. For each procedure the contralateral (non-treated) ear served as a histological control. Following artificial endolymph injections of 7.5 minutes or more there was an almost total absence of the normal intraluminal homogenous substance (HS) on the injected side. Our observations suggest that the disappearance of the HS occurs by both enzymatic and macrophagic activity. After endolymphatic withdrawals the ES was found to contain increased amounts of HS. The results could suggest that the volume of fluid in the ES, and hence the volume of the entire membranous labyrinth, may be regulated by a dynamic relationship between active secretion and enzymatic degradation of a lumen-expanding substance that is intimately related to the intraluminal macrophages. The exact mechanism governing these regulatory systems, and their relationship to ion and water movements across the epithelium of the sac, remain to be elucidated.
 

This study was supported by the National Institutes of Health through the National Institute on Deafness and other Communication Disorders, Grant number DC01368


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