Attachment of the tectorial membrane revealed by scanning electron microscope.

Our present-day descriptions of the causes of many forms of sensorineural deafness are based on what is known about the morphology of the organ of Corti. Unfortunately, this information is still woefully inadequate for a complete interpretation of normal events within this structure. Nevertheless there has been no shortage of theories based, in part at least, on assumptins of what the unknown morphology might be. One of the least understood structures is the tectorial membrane, for which the extent and position have had many descriptions. A review of these reveals that the observations vary with the techniques used, and different techniques have various effects on the sticky gel of the tectorial membrane which is reported to be 90% water. Here is described a technique whereby the bulk frozen-hydrated tectorial membrane is viewed by scanning microscopy. In its natural living state the tectorial membrane is sealed to the Hensen's cells, protecting the reticular lamina from endolymph.

Cochlear potentials and oxygen associated with hypoxia.

In the guinea pig, during general hypoxia produced by shutoff of respiratory air, oxygen-sensitive microelectrodes detect a decrease in oxygen concentration in the fluids of the tunnel of Corti before detecting a decrease in scala media oxygen concentration. The present experiments were designed to measure the cochlear microphonic (CM) potential generated by the organ of Corti when vibrated by a microprobe on the basilar membrane along with the oxygen decline in both tunnel and scala media to see upon which source of oxygen CM is dependent. Because oxygen concentration in both areas can decrease considerably before CM is affected, the recovery following a brief period of hypoxia is a more accurate measure. Because CM starts a recovery before scala media oxygen, the positive endolymphatic potential (EP) was also measured to determine its role in the generation of CM. Our interpretation of the course of events is that CM is partially dependent upon oxygen supplied to the extracellular spaces of the organ of Corti by the spiral vessels and upon EP that, itself, is dependent upon several factors. The data indicate that EP plays a more complex role than that of providing a current flow for modulation by a resistance varying with vibration.

Safety considerations of cochlear implantation.

This article reviews past research on the safety of surgical techniques, cell response to implants, and electrode design. New information obtained from animal studies and from in vitro observations of human temporal bones is also presented.

Oxygen reserve and autoregulation in the cochlea.

Endolymphatic O2-concentration was measured in the guinea pig cochlea with a microelectrode inserted through the zona pectinata of the basilar membrane and the cells of Claudius, so as not to interfere with the blood supply to the organ of Corti. The O2-level and the amplitude of the cochlear potentials were followed during hypoxia produced by lowering the pO2 of the inspired air. Persistence of a normal endolymphatic O2-level following the fall in arterial pO2 indicated an O2-reserve and au autoregulation of the cochlear circulation.

Identification and analysis of bacterial protein secretion inhibitors utilizing a SecA-LacZ reporter fusion system.

Protein secretion is an essential process for bacterial growth, yet there are few if any antimicrobial agents which inhibit secretion. An in vivo, high-throughput screen to detect secretion inhibitors was developed based on the translational autoregulation of one of the central protein components, SecA. The assay makes use of a SecA-LacZ fusion reporter construct in Escherichia coli which is induced when secretion is perturbed. Several compounds, including two natural product extracts, which had the ability to induce the reporter fusion were identified and the MICs of these compounds for Staphylococcus aureus strain MN8 were found to be < or =128 microg/ml. Enzyme-linked immunosorbent assay, Western blotting, and immunoprecipitation techniques were used to analyze the affects of these compounds on protein secretion. Six representative compounds presented here appear to be bona fide secretion inhibitors but were found to have deleterious effects on membranes. It was concluded that, while the method described here for identifying inhibitors of secretion is valid, screens such as this, which are directed against the membrane-bound portion of a pathway, may preferentially identify compounds which affect membrane integrity.