Considerations in building a low-noise reflection absorption infrared spectrometer.

The design and performance of several dispersive spectrometers for reflection absorption infrared spectroscopy are presented. Sources of noise and their control are discussed in detail. Individual component selection for the spectrometers is discussed with particular attention paid to optimizing sensitivity for surface measurements. These efforts culminated in an ellipsometric spectrometer with a sensitivity of <0.01% absorption and capable of following transients with a temporal resolution of 10 ms.

Streptomycin-induced defects of the otoconial membrane.

Damage to the neuro-epithelium caused by the vestibulotoxic drugs has been well described in previous reports; however, little is known about the effect of such drugs on the otoconia. In this investigation, streptomycin sulfate was found to create a circumscribed defect in the crystalline layer of the otoconial membrane in the utricle of the guinea pig. The defect was secondary to a sharply outlined lesion of the neuroepithelium which corresponded in size and location to the otoconial defect. Many of the otoconia along the margin of the defect showed signs of degeneration and appeared similar to those observed in the saccule of man during aging. In advanced stages of decay, the otoconia were reduced to hollow shells consisting of longitudinal interconnecting strands. All the epithelial lesions occurred with remarkable consistency in the same region of the macula utriculi at the posterior end of the striola.

Defects of the otoconial membranes in normal guinea pigs.

Otoconial membranes from a large number of normal albino and pigmented guinea pigs were examined by light microscopy. In more than 20% of the animals, microdissection revealed that the crystalline layer of the otoconial membrane was incomplete, leaving large areas of the underlying gelatinous layer uncovered by crystals. These defects were bilateral, more or less symmetrical, and invariably more extensive in the saccule than in the utricle. In two animals, huge single conglomerates of crystals were found on both the saccular and utricular maculae. None of the animals displayed abnormal behavior or posture and no obvious cause for the otoconial defects was found. The presence of a hereditary congenital condition is postulated. The high incidence of otoconial defects in guinea pigs makes them poorly suited for most investigations of experimentally induced pathology. Therefore, previous reports of otoconial pathology in guinea pigs should be viewed in the light of these findings.

Incorporation of radioactive calcium into otolithic membranes of the guinea pig after aminoglycoside treatment.

The influence of neomycin and streptomycin on the calcium metabolism of the otolithic membranes was investigated in the guinea pig. After chronic treatment with either drug, animals were injected intraperitoneally with radioactive calcium. Retention of calcium in the serum was unaffected by drug treatment, as was the incorporation of radioactivity into bone (femur and otic capsule). Both drugs inhibited the calcium uptake into saccular and utricular otolithic membranes by 30 to 40%.

Efferent nerve fibers associated with the outermost supporting cells of the organ of Corti in the guinea pig.

In whold-mount preparations of the organ of Corti nerve fibers are sometimes seen peripheral to the third-row outer hair cells where they appear to wander among the Hensen cells. These fibers were studied in the guinea pig by both light and electron microscopy. In the upper second, third and fourth cochlear turns nerve fibers were seen between and on the peripheral side of the third-row Deiters cells as well as in the floor of the outer tunnel space. They were not found in the intercellular spaces between the Hensen cells. These nerve fibers are continuous with the spiral efferent fibers beneath the outer hair cells. Also their ultrastructural and histochemical characteristics indicate that they are efferent neural elements. This identification was confirmed by the finding that they degenerate following interruption of the olivo-cochlear bundle in the brain stem.

Cochlear innervation in the guinea pig. II. The spiral tunnel bundle.

The organization of nerve fibers in the spiral tunnel bundle (STB) of the guinea pig organ of Corti has been studied by light and electron microscopy. In the basal turn STB fibers were found to run toward the base or apex in about equal numbers while in the upper turns they ran predominantly in an apical direction. Long spiral fascicles of 100 microns or more in length were abundant in the third and fourth turns, but were rarely seen in the lower turns. No synaptic contacts between tunnel bundle fibers could be found and no afferent nerve fibers were seen in the bundle. Furthermore, interruption of the efferent nerve supply resulted in complete degeneration of the STB. The tunnel bundle does not, therefore, appear to be a site of synaptic interaction between afferent and efferent neutral elements.

Incorporation of radioactive calcium into otolithic membranes and middle ear ossicles of the gerbil.

45CaCl2 was injected into gerbils in single or multiple doses, and the resulting radioactivity in serum, otoconial CaCO3, bone samples, and selected labyrinthine epithelium was determined by liquid scintillation spectrometry. Incorporation into both utricular and saccular otoconia occurred at the rate of 0.06-0.07 nmole Ca++ per day, corresponding to a fractional rate of uptake of 0.1%. The retention of radioactivity had a half-life of approximately 11 days. The rate of incorporation of calcium for the middle ear ossicles was 5-7 times that for otoconia and was similar to that for otic capsule and skeletal bone. The level of 45Ca++ was higher in the pigmented regions of the utricular membranous wall than in the non-pigmented areas of the utricular and ampullary wall and in the stria vascularis.