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Biomedical subjects

K M Donovan

Publications and source records attributed to K M Donovan.

6 recordsLinked to original sources
PubMed1986

Otoconia as test masses in biological accelerometers: what can we learn about their formation from evolutionary studies and from work in microgravity?

This paper reviews previous findings and introduces new material about otolith end organs that help us to understand their functioning and development. In particular, we consider the end organs as biological accelerometers. The otoconia are dealt with as test masses whose substructure and evolutionary trend toward calcite may prove significant in understanding formation requirements. Space-flight helps illuminate the influence of gravity, while right-left asymmetry is suggested by study of certain rat strains.

Aging↗
PubMed1977

Antarctic environment and nail growth.

Nail growth of all fingers was measured on 13 men wintering in Antarctica. A mean rate of 109-5 micrometer/day was found with the longer digits having faster growth. No significant difference was demonstrated between the warmer and colder months of the study period. Monthly variations suggested that subjects had an individual rate irrespective of environmental influences. Comparison with previous studies both in polar and temperature conditions showed growth rates in Antarctica have increased progressively; present values being comparable with observations in temperate climates.

Antarctic Regions↗
PubMedDate not supplied

Innervation patterns in rat saccular macula. A structural basis for complex sensory processing.

Serial sections through the anterior part of rat saccular macula were reconstructed as montages. Findings are that type II hair cells are integrated into the neural circuitry of type I cells, chiefly by synapses with neighboring calyces and their collaterals; and that complex interactions between afferent- and efferent-type nerve elements take place. Three basic types of nerve/calyx pattern are present: U-type nerves lose their myelin before they enter the macula and have complex calyces with several collaterals; M-type nerves are myelinated up to the calyx, which lacks collaterals; and M/U-type nerves have short, unmyelinated segments proximal to their calyces, which have few collaterals. Both afferent- and efferent-type collaterals spring from calyces, chiefly from those of U-type nerves. Type II cells are presynaptic both to electron-lucent and to vesiculated terminals; some synapses are reciprocal. Electron-lucent boutons sometimes are presynaptic to calyces and to type II hair cells; and morphologically afferent-to-afferent kinds of synapses occur in the neuroepithelium. The anatomical findings indicate that complex information processing must occur in mammalian gravity receptors.

Animals↗
PubMedDate not supplied

Macular suprastructure, stereociliary bonding and kinociliary/stereociliary coupling in rat utricular macula.

This report considers rat utricular macular suprastructure after chemical treatment with the sodium salt of N,N-Naphthaloylhydroxylamine (NHA), used alone or in combination with tannic acid (TA). NHA and TA preserve calcium and complex carbohydrate-protein molecules, respectively. Macromolecules of supramacular substance appear comparable morphologically to material of the external lamina of glycocalyx. Similar material crosslinks stereocilia with approximately equal to 58 nm periodicity and couples parts of kinocilia with specific stereocilia. Particles which occur within kinocilia at certain attachment sites connect to dynein arms of the kinocilia. Interstereociliary connections are aligned with internal linkers to actin. Thus, a basis for dynamic communication between kinocilia and stereociliary actin has been shown. The mechanism would appear to be calcium dependent. The findings support the concept that kinocilia are motile and lead to the stereociliary tuft in vestibular hair cells.

Animals↗
PubMedDate not supplied

The suprastructure of the saccular macula.

Inclusion of tannic acid in the primary fixative fortuitously preserved the macular suprastructure, from the macular surface to the otoconia, in rat. Results demonstrate that fluid-filled channels around the stereociliary tufts and a slit-like space immediately above the macula are artefacts of tissue preparation. Filaments fill the area between, and show linkage to, the macular surface and the more peripheral, closely knit layer identified here as the true otoconial membrane. The material also passes through the otoconial membrane at various sites to surround the otoconia and extends well beyond the maculas in all directions. Although it may prove later to be endolymph, it is referred to here as supramacular substance. Kinocilia and the tallest stereocilia as well as the otoconia are tethered to the otoconial membrane. Findings were confirmed in decalcified material. Results are discussed in terms of functional and biochemical implications, and by analogy to man-made acceleration sensing devices.

Animals↗