The mole rat (Spalax ehrenbergi) burrows throughout its life in subterranean tunnels. Several structural and functional features which adapt the mole rat to its habitat have been discerned. The goal of this study was to elucidate the structural basis for adaptation of the auditory end-organ to an environment where low-frequency acoustical signals prevail. For this purpose, cochleae of adult mole rats were studied with light and electron microscopy. Inner hair cells throughout the cochlea, and outer hair cells in the basal (high-frequency) portion of the cochlea, were similar in structure to those seen in other mammals. In contrast, outer hair cells in the apical (low-frequency) portion displayed unique structural features. These features resembled the structure of inner hair cells or immature outer hair cells. The innervation of outer hair cells was most uncommon, in that classical medial efferent innervation was not found throughout the cochlear spiral.
The elemental composition of human muscle fibres have been determined by electron probe microanalysis. In order to distinguish between different types of fibres, two approaches were used. In one approach individual fibres were isolated, portions of them used for a typing by histochemical methods and the main part used for X-ray microanalysis. In the other approach the muscle biopsy was serial-sectioned, some sections used for a histochemical typing and the others (16 micrometer thick cryosections) used for X-ray microanalysis in th eelectron microscopy. The comparison of the ratios between P, S and K in Study No. 1 and 2 indicates different concentrations of sulphur in the subsarcolemmal zone and in the interior of the fibre. Both routes give information on all elements (except the ten lightest ones) contained in the fibres or in sections of them, provided the concentration is high enough. In order to obtain quantitative data, expressed as mmol/kgw, the spectra of the specimens were compared to those of standards of known composition and the data subjected to a so called ZAF-correction (corrections for the atomic number effect, absorption of X-rays in the specimen and secondary fluorescence). Quantitative data concerning phosphorus, sulphur, chlorine and potassium were obtained in Study No. 2. A significantly higher sulphur concentration was found in type IIA muscle fibres as compared to those of type I.
Methodological aspects of quantitative X-ray microanalysis of semi-thick cryosections (2--6 micrometers) of biological soft tissue were investigated. The preparation of a low background specimen holder is described. Scanning and scanning transmission images of the sections could be obtained, allowing identification and separate analysis of nuclei and cytoplasm. Parallel observations of histochemically stained adjacent sections in the light microscope allowed correlation of the microanalytical data with tissue morphology and histochemistry. Quantitative analysis could be carried out with the help of a standard: a gelatin/glycerol matrix containing mineral salts in known quantities, frozen and sectioned in the same way as the specimen. Mass loss under the electron beam was found to be comparable in specimen and standard. Comparison of various theoretical models for quantitative analysis showed that the 'P/B-method' (determination of the background intensity under the characteristic peak) is the most suitable for semi-thick sections. Factor determining the choice of accelerating voltage were analyzed. The usefulness of this specimen type is illustrated in some biological applications (human oral mucosa, rat salivary gland).
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