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Selective interruption of cochlear blood flow is possible without operative manipulations in the middle or inner ear. By fitting a magnet into the external auditory canal and injecting iron filings into the cephalic vein is it possible to obtain an impaired inner ear in otherwise healthy experimental animals that can be kept alive for any length of time. The hearing loss induced by the ischemia normally remains unchanged over a period of weeks. The highly vascularised areas of the cochlea, namely the spiral ligament, the vascular stria, the spiral prominence and the root cells in the external spiral sulcus, as well as the spiral limbus were all clearly degenerated, but to different degrees. Pronounced vacuolisation of cells, degeneration of tissue, reduction of cellular elements, stasis in large and small blood vessels and morphological disorganisation were observed. The organ of Corti showed no changes worthy of note. On revascularisation of the spiral ligament and the spiral limbus with resumption of function, the organ of Corti can return to normal activity again. Repeat blood flow disturbances can also lead to recurrent sudden hearing loss and intermittent loss of hearing.

The structure of the internal and external tissue of the cochlear opening of the cochlear aquaeduct was examined by light microscopy on semithin sections and by scanning electron microscopy. The whole area is filled with a net of mesenchymal cells. The cell axes are randomly orientated inside the aquaeduct. On the outside of the cochlear aquaeduct fibrocytic tissue fills a space which is triangular in cross-section between the basal part of the cochlea wall of the tympanic scala and the middle portion of the round window membrane. In this area the direction of the net is uniform and it gives the impression of anchorage of the round window membrane on the perilymphatic side. The rim bordering the perilymphatic space is a dense net but not fully closed. The scanning electron microscopic pictures taken perpendicular to this border structure show clearly a texture of mesenchymal cells with open spaces. No closed "membrana limitans" was found. The possible function of the fixation of the round window membrane to the perilymphatic space giving rise to an asymmetric perilymph movement is discussed with regard to the physiology of sound transmission.

The ultrastructure of the area of the external spiral sulcus of the cochlea was studied in 15 hamsters. Intravital fixation with glutaraldehyde was followed by osmium citrate fixation and embedding in araldite. The endolymphatic surface of the external spiral sulcus is nearly completely covered by Claudius cells under which the root cells are situated. These epithelial cells are composed of bundles (roots), which protrude into the connective tissue of the spiral ligament in a tree-like fashion, forming primary, secondary, and tertiary branches. The basement membrane is a reliable landmark in this complex region, serving as a differentiating zone between the root cells and the mesenchymal tissue. Two different types of root cells are found. There are organelle rich "dark" cells and "light" cells which contain only a few cell organelles. All types of transitional forms between these two cell types are found, which can be interpreted as an expression of different metabolic activity of the same cell type. Between the root cells are seen extracellular clefts into which the "dark" cells, with their high synthetic and secretory activity, expel their secretions. These clefts lead to the endolymphatic space. A continuous production and secretion of part of the endolymph by the root cells is very likely. The anchoring of fibrils at the basement membrane of the root cell bundles, and their continuity with the basilar membrane leads to the assumption that this whole system may act as a mechanical pump. At high sound pressure levels, the strong vibration of the basilar membrane may lead to a locally and temporarily enhanced secretion of substances from the root cells into the cochlear duct.

The ultrastructure of the external sulcus of the cochlea of young healthy guinea pigs and hamsters was investigated as well as the distribution of lactate dehydrogenase (LDH) in this region. The demonstration of LDH activity was carried out as follows. The unfixed and undecalcified cochlea was cut in 80 micron thick frozen sections, which were incubated immediately in the reaction mixture for LDH and subsequently fixed with paraformaldehyde. For electron microscopy the usual procedure was applied. The epithelial cells of the external sulcus show deep reaching extensions into the vessel-rich connective tissue of the basal part of the spiral ligament. These roots are bound together into root bundles surrounded by the basement membrane and fibrills. The root cells differ in their ultrastructure. The light cells, which have been described previously, contain a number of stretched mitochondria and only few other cell organels. Beside these, dark cells can be found (Fig. 2). Their cytoplasm shows high contrast and contains many mitochondria, ribosomes, rough endoplasmatic reticulum and Golgi apparatus. In the dark cells big vasuoles can be seen. All these structures indicate a high rate of synthesis in the dark cells. The root cells are linked together by membranous foldings, which diverge in some parts, forming intercellular spaces in which small cell protrusions are found. Other intercellular gaps can also be detected building a system of small channels. It is possible that these structures serve for extracellular transport. The LDH activity, which is demonstrated by formazan deposits can be exclusively found in the root cells. This could be demonstrated in light microscopic semithin sections (Fig. 3) and with electron microscopy (Fig 4). The possible role of LDH in the root cells is discussed.

The ultrastructure of the external sulcus of the cochlea of young healthy guinea pigs and hamsters was investigated as well as the distribution of lactate dehydrogenase (LDH) in this region. The demonstration of LDH activity was carried out as follows. The unfixed and undecalcified cochlea was cut in 80 μm thick frozen sections, which were incubated immediately in the reaction mixture for LDH and subsequently fixed with paraformaldehyde. For electron microscopy the usual procedure was applied. The epithelial cells of the external sulcus show deep reaching extensions into the vessel-rich connective tissue of the basal part of the spiral ligament. These roots are bound together into root bundles surrounded by the basement membrane and fibrills. The root cells differ in their ultrastructure. The light cells, which have been described previously, contain a number of stretched mitochondria and only few other cell organels. Beside these, dark cells can be found (Fig. 2). Their cytoplasm shows high contrast and contains many mitochondria, ribosomes, rough endoplasmatic reticulum and Golgi apparatus. In the dark cells big vascuoles can be seen. All these structures indicate a high rate of synthesis in the dark cells. The root cells are linked together by membranous foldings, which diverge in some parts, forming intercellular spaces in which small cell protrusions are found. Other intercellular gaps can also be detected building a system of small channels. It is possible that these structures serve for extracellular transport. The LDH activity, which is demonstrated by formazan deposits can be exclusively found in the root cells. This could be demonstrated in light microscopic semithin sections (Fig. 3) and with electron microscopy (Fig. 4). The possible role of LDH in the root cells is discussed. [ABSTRACT FROM AUTHOR]