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Biomedical subjects

M D Ross

Publications and source records attributed to M D Ross.

At least 55 records · Page 3Linked to original sources
PubMed1984

Some properties of otoconia.

Otoconia are dynamic mineral deposits present in the gravity receptors of most vertebrates; fishes often have a single large mass called an otolith instead. Otoconia generally have the appearance of single crystals but contain organic and inorganic components, the mineral being almost exclusively a polymorph of calcium carbonate. The two phases are closely interrelated structurally. Ultra-high resolution transmission electron microscopy of rat otoconia showed them to be mosaic biominerals. The crystallites were 50-100 nm in diameter, had some rounded edges, and were highly ordered into laminae. This suggests that crystallite seeding and growth is organic matrix mediated. Crystallite asymmetry may also indicate piezoelectricity. A further finding of similarities in electron beam diffraction patterns obtained from some frog and rat otoconia could mean that the calcite of mammalian units mimics aragonite. A comparative study showed that turtles, which are close to the stem line for mammals, had calcite-type otoconia in the utricle. Alligators, which share a common ancestry with birds, had this type otoconium in all three gravity receptors, although saccular otoconia had a variety of forms. The nature of the mineral is unknown. The biochemical composition of the organic otoconial material is under study, to learn how mineral deposition is regulated. Proteins of rat otoconial complexes ranged between ca. 16500 and over 100000 Da in molecular mass and were similar in saccular and utricular otoconial complexes. Our new analysis of the amino acid composition of the complexes by high performance liquid chromatography showed the complexes to be high in the acidic and low in the basic amino acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Alligators and Crocodiles↗
PubMed1984

Development of reproductive tract lesions in male F344 rats after treatment with dimethyl methylphosphonate.

Dimethyl methylphosphonate (DMMP) is an organophosphorous compound that impairs fertility in male rodents. In previous studies, male rats treated with DMMP had decreased sperm motility and count, and sired fewer litters with fewer pups per litter. The following studies examined the development of the reproductive lesions by light and electron microscopy after treatment with DMMP. Adult male F344 rats were treated po with DMMP, 1750 mg/kg, for up to 12 weeks. Tissues were perfused in situ with Karnovsky's fixative and embedded in glycol methacrylate. After 5 weeks of treatment there were occasional PAS-positive bodies in lumina of tubules in stages XII-III. These were ultrastructurally similar to cytoplasm of step 12-17 spermatids. After 7 weeks of treatment, there was an increase in the number of tubules exhibiting these bodies, as well as an increase in the number of tubules showing delayed or early spermiation, or focal exfoliation of nonnecrotic cap-phase spermatids and some spermatocytes. No multinucleated giant cells were seen. Focal loss of germ cells occurred more frequently as duration of exposure increased, and occupied 5-100% of an affected tubule. Frequently, an area of germ cell exfoliation occurred adjacent to areas of normal tubular epithelium. These lesions were not specific to any particular stages of spermatogenesis. Occasionally, elongating spermatids were without rib elements of the fibrous sheath in the tail; these were not seen in epididymal sections. Animals left to recover for 14 weeks after treatment showed approximately 80% normal tubules; affected tubules varied in their degree of recovery, but all showed the loss of normal epithelial organization, a characteristic of DMMP treatment. Epididymal epithelium was not visibly affected by treatment with DMMP. DMMP produced morphologic alterations in Sertoli cells and elongating spermatids, as well as producing functional defects in spermatozoa.

Animals↗
PubMed1984

The influence of gravity on structure and function of animals.

Gravity is the only environmental parameter that has remained constant during the period of evolution of living matter on Earth. Thus, it must have been a major force in shaping living things. The influence of gravitational loading in evolution of the vertebrate skeleton is well recognized, and scale effects have been studied. This paper, however, considers in addition four pivotal events in early evolution that would seem to have been significant for the later success and diversification of animal life. These are evolution of the cytoskeleton, cell motility (flagellae and cilia), gravity detecting devices (accelerometers), and biomineralization. All are functionally calcium dependent in eukaryotes and all occurred or were foreshadowed in prokaryotes. A major question is why calcium was selected as an ion of great importance to the structure and function of living matter; another is whether gravity played a role in its selection.

Animals↗
PubMed1984

Immersion fixation methods for glycol methacrylate-embedded testes.

Routine processing of testicular tissue through 10% neutral buffered formalin (NBF) into paraffin produces severe cellular shrinkage which obscures most of the morphologic detail. The following studies were performed to compare different combinations of immersion fixatives and embedding media for optimal cellular detail in the final histologic sections. We examined sections of testes from rats, mice, and rabbits fixed in either NBF, Bouin's, Zenker's, or Helly's fixatives, and embedded in either standard paraffin or glycol methacrylate. The results were similar in all 3 species. In paraffin, Bouin's or Helly's fixatives produced the fewest artifacts, while in glycol methacrylate, NBF-fixed tissue showed the greatest intracellular detail and preservation. The merits and limitations of each method are discussed for the rat, with exceptions for the other species noted where appropriate. The use of glycol methacrylate as the support medium for sectioning makes high-quality tissue sections available from formalin-fixed testes.

Acrylates↗
PubMed1984

Gravity receptors: an ultrastructural basis for peripheral sensory processing.

Our ultrastructural study of serial sections has shown that type II hair cells of the anterior part of the utricular macula are integrated into the afferent neural circuitry of type I cells, which are arranged in clusters. Additionally, there exists a complex system of intramacularly originating efferent-type nerve fibers and terminals. The findings taken together suggest that, on morphological grounds, complex processing of sensory information occurs in gravity receptors. Asymmetry of such a complex system may contribute to motion and Space-motion sickness.

Acoustic Maculae↗
PubMed1983

The ultrastructure of the calcium carbonate balance organs of the inner ear: an ultra-high resolution electron microscopy study.

The balance organs of the inner ear of vertebrates, found as single, large growths of aragonite ('otoliths') in fish and small clumped masses ('otoconia') of either aragonite (amphibians) or calcite (mammals), have long been regarded as polycrystalline and single crystals respectively. The use of ultra-high resolution electron microscopy and electron diffraction to study comparatively crushed samples of these biominerals and samples of geological calcium carbonates, as examples of pure inorganic crystals, reveals that the biological structures are composed of microcrystals joined together by organic matrices to form composite crystals. Such structures either grow to a finite, controlled size (otoconia) or have daily growth patterns (otoliths). Mechanisms of growth are proposed to link these seemingly different patterns varying only in the number of nucleation sites and the degree of biological as against chemical control over the growth.

Animals↗
PubMed1983

Interrelated striated elements in vestibular hair cells of the rat.

Unusual fixation procedures revealed a series of interrelated striated organelles in type I and type II vestibular hair cells of the rat; these organelles seemed to be less well developed in cochlear hair cells. The findings suggest that contractile elements may play a role in sensory transduction in the inner ear, particularly in the vestibular system.

Actins↗
PubMed1983

Gravity and the cells of gravity receptors in mammals.

Two new findings, that crystals located in the inner ear gravity receptors of mammals have the internal organization requisite for the piezoelectric property, and that sensory hair cells of these same receptors possess contractile-appearing striated organelles, have prompted the author to model mammalian gravity receptors in the ear on the principles of piezoelectricity and bioenergetics. This model is presented and a brief discussion of its implications for the possible effects of weightlessness follows.

Acceleration↗
PubMed1982

Distribution and significance of norepinephrine in the lateral cochlear wall of pigmented and albino rats.

Picogram quantities of norepinephrine were found in cochlear regions of pigmented and non-pigmented rats. These regions of the cochlea were the modiolus, organ of Corti--osseous spiral lamina and the lateral cochlear wall. The content of norepinephrine in the modiolus and lateral cochlear wall of the pigmented rat was significantly greater than that in areas of the non-pigmented rat. In contrast, there was no statistical difference between the norepinephrine content of the organ of Corti--osseous spiral lamina region of the pigmented rat and that of the albino rat. Since a major difference between the pigmented and albino rats is the presence of melanin-containing melanocytes in the modiolus and lateral cochlear wall region of the pigmented animals, it is possible that norepinephrine is stored in cochlear melanocytes.

Animals↗
PubMed1981

Quantitative evidence for cochlear, non-neuronal norepinephrine.

Endogenous norepinephrine was quantitatively measured in cochlear tissues of pigmented and nonpigmented animals by high-performance liquid chromatography and electrochemical detection. Epinephrine, dopamine and serotonin were not detected. The cochlear norepinephrine content of the pigmented animals was found to be more than double that present in corresponding albinos. Cochlear norepinephrine was only minimally depleted 48 h after surgical removal of the superior cervical ganglion. 12 h after administration of reserpine (5 mg/kg), cochlear norepinephrine was partially depleted. These results indicate that the norepinephrine located in the cochlea is probably not confined entirely to noradrenergic nerve terminals.

Adrenergic Agents↗
PubMed1980

Critique of "an electron microscope study of crystal calcium carbonate formation in the mouse otolith".

Electron micrographs of otoconia of fetal mice, as obtained by Nakahara and Bevelander, provide morphological evidence that the otoconia consist of both organic material and calcium carbonate (calcite), contrary to their own conclusions. Calcite is an integral component of otoconia, apparently from their inception. The concept of mineralization by calcite of an already developed organic template ("preotolith") is shown to be in error.

Animals↗
PubMed1980

The sensitivity of cochlear albino melanocytes to horseradish peroxidase.

The effects of low concentrations (0.5%--0.0005%) of HRP and varying postperfusion survival times (5.5 hours--15 seconds) on cochlear albino melanocytes were studied by light and electron microscopy. Approximately 50 microliter of differing concentrations of HRP dissolved in artificial perilymph were perfused through the perilymphatic space in 32 albino guinea pigs. Tissues were subsequently treated histochemically to demonstrate HRP reaction product. The results indicate that concentrations of HRP > 0.0005% in combination with postperfusion survival times > 1 hour bring about acute and selective injury to the albino melanocytes; cytoplasmic vacuolization and rupture of cell membranes occurred. The structural integrity of the albino melanocytes appeared unaltered when exposed to 0.0005% concentrations of HRP for less than or equal to 1 hour. An apparently non-toxic 0.0005% concentration of HRP may provide a means of labeling cochlear melanocytes when the effects of other substances on the cells are investigated.

Animals↗
PubMed1979

Calcium ion uptake and exchange in otoconia.

Calcium ion uptake into otoconia and bone mineral of the young adult rat was studied by use of 45Ca and liquid scintillation spectrometry. Results showed that saccular and utricular otoconia take up 45Ca in a time course generally comparable to bone but on a much lower scale. Saccular otoconia showed greater uptake than utricular. The results are interpreted to indicate the dynamic nature of saccular and utricular otoconia and their possible importance in preserving ionic homeostasis of the inferior and superior parts of the labyrinth, respectively.

Animals↗