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  • 1
    Unknown
    Oxford : Oxford University Press
    Call number: 05-MET-15:55 ; 05-MET-15:55a
    Keywords: Nuclear magnetic resonance spectroscopy
    Notes: Cataloging based on CIP data.
    Pages: p.
    ISBN: 0198551916
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    05-MET-15:55 departmental collection or stack – please contact the library
    05-MET-15:55a departmental collection or stack – please contact the library
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  • 2
    ISSN: 1432-0703
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
    Notes: Abstract Copper and cadmium concentrations were monitored in a population of the grasshopperChorthippus brunneus in grasslands in and around a copper refinery. Total body copper and cadmium concentrations increased with site contamination levels from control to highly contaminated refinery site environments. Refinery site grasshoppers accumulated both metals throughout the summer and autumn reaching a peak concentration of 1,600 μg/g for copper. The seasonal pattern of accumulation of copper and cadmium closely followed seasonal trends in metal contamination levels in the indigenous vegetation, particularlyAgrostis stolonifera. Copper accumulated progressively through the developmental instars ofC. brunneus. However, there was evidence of copper exclusion during the final moult. This may be linked to copper compartmentalization in the integument of the later instars. Metals were not evenly distributed within the grasshopper body; 85% of total body copper and cadmium is associated with the integument.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-1106
    Keywords: Human ankle joint ; Stretch reflex dynamics ; Mean joint position ; Tibialis anterior ; Triceps surae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The purpose of this study was to examine the effect of ankle position on the human ankle stretch reflexes during tonically-maintained contractions over most of the range of motion. The ankle was placed at randomly selected mean positions. Target levels of triceps surae (TS) or tibialis anterior (TA) tonic contractions were generated while the ankle was displaced by small amplitude, stochastic perturbations. System identification techniques were used to identify the stretch reflex dynamics at each combination of tonic level and ankle angle. As shown previously, the TS stretch reflex was characterized by an unidirectional, velocity-sensitive impulse response function whereas the TA stretch reflex was characterized by a linear impulse response function between ankle velocity and TA EMG. TS stretch reflexes showed a strong dependence on ankle position while TA stretch reflexes did not. Thus the TS stretch reflex magnitude increased greatly as the ankle was progressively dorsiflexed. In contrast, ankle mean position had only a minor effect on the TA stretch reflex magnitude. Our results indicate that the position-dependent facilitation of the TS stretch reflex is not due to changes in the level of skeletal motoneuron excitability. Rather, this effect may be accounted for by mechanisms that modulate the efficacy of the stochastic ankle perturbation. Such mechanisms could include position-induced: (1) modulation of monosynaptic and polysynaptic afferent inputs to skeletal motoneurons, (2) alterations in the extent of fusimotor drive and (3) changes in the transmission of the joint perturbation to spindle receptors. Such mechanisms are discussed in terms of the differences between TS and TA stretch reflexes. Finally, the functional significance of position-dependent reflex responses are considered.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-1106
    Keywords: Spinal reflexes ; Monosynaptic reflex ; Muscle afferent ; Presynaptic inhibition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Stimulation of low threshold afferents in the peroneal nerve causes a short latency facilitation of individual tibialis anterior motor units considered to be due to the composite Ia EPSP. This facilitation is depressed by vibration 20 to 128 Hz applied over the tibialis anterior. The depression occurs without any change in the firing rate of the motor unit or in the facilitation from cutaneous afferents and so is unlikely to be due to postsynaptic inhibition. The depression can occur with vibration frequencies as low as 40 Hz and is therefore unlikely to be due to occlusion in Ia afferents. There is no evidence that vibration alters the electrical threshold of large afferents. A similar facilitation of soleus motor units resulting from stimulation of low threshold afferents in the tibial nerve is depressed for up to 75 ms following a 40 ms burst of 50 Hz vibration applied to the tendon of the tibialis anterior. The burst of vibration itself did not facilitate soleus motor units so there is no evidence to suggest that the vibration spread to soleus spindles. Homosynaptic depression is, therefore, unlikely. These findings provide further evidence that pesynaptic inhibition of Ia afferents occurs in man.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-1106
    Keywords: Avian forebrain ; Synapses ; Stereology ; Disector ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The lobus parolfactorius (LPO) of the chick has been shown to undergo an increase in the mean synaptic numerical density (Nv syn) in response to one-trial passive avoidance learning (Stewart et al. 1987). The present study was undertaken in order to describe the pattern of normal development of synapses in the LPO, to further investigate the significance of this plastic response. The LPO's from each hemisphere of pre-hatch (16 days), and post-hatch (1 day, 9 day and 22 day old) chicks were processed for electron microscopy. Synapses were classified into asymmetric spine, asymmetric shaft, symmetric spine, and symmetric shaft synapses, on the basis of the density of the post-synaptic thickening and the nature of the post-synaptic target. A 3-dimensional stereological probe was used (the ‘disector’) to calculate Nv syp, and mean projected height (H syp) of the post-synaptic density (PSD). Mean values for each age and hemisphere were compared with a 2-way analysis of variance test using paired samples. A six-fold increase in Nv syp was seen between 16 days in ovo, and 9 days post-hatch. There was a hemispheric asymmetry at 9 days post-hatch, with the left hemisphere LPO containing 1.6 times as many synapses per μm-3. There was a subsequent period of reduction in synaptic density in the left hemisphere LPO between 9 and 22 days post-hatch. The Nv of all classes of synapse increased with age, but the proportions of the symmetrical synapses with respect to the total number of synapses, decreased with age. This decrease was of a similar magnitude for each hemisphere. A hemispheric difference was seen in post-hatch asymmetric synapses, with a greater proportion of asymmetric spine synapses in the left hemisphere. The magnitude of the hemispheric asymmetry was constant throughout the 3 week period of post-hatch development, but was not present in pre-hatch chicks. The PSD increased in length in each hemisphere by approximately 40% between post-hatch day 1 and post-hatch day 9. These data show that the LPO contains a synaptic population which undergoes substantial modification during the first week post-hatch. An asymmetry exists at post-hatch day 9 which is not present at the earlier ages investigated, nor indeed after 22 days post-hatch. This may have significance with regard to studies of passive avoidance learning in the one-day old chick, where an increase in both the size and number of synapses in the LPO has been demonstrated (Stewart et al. 1987). It is possible that ‘training’, in this situation, may simply enhance the timing of synaptic events that result as a consequence of normal development.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Skin fibroblasts from a patient with mild osteogenesis imperfecta (OI) type IV synthesize two populations of type I procollagen molecules. One population contains proα1(I) and proα2(I) chains that migrate normally in sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and a second population contains only slower migrating proα1(I) and proα2(I) chains. The total amount of type I procollagen made by OI cells and the ratio of proα1(I): proα2(I) is normal. When labeled under conditions that inhibit post-translational modification of proα chains, the OI cells produce only single populations of proα1(I) and proα2(I) chains indicating that the apparent increased molecular weight of some OI proα chains is due to excessive post-translational modification rather than peptidyl insertions. Peptide maps indicate that excessive post-translational modification occurs along the entire triple helical segment of some α1(I) and α2(I) chains produced by OI cells. The effect of the mutation is to lower the melting temperature of the molecules containing slow migrating α1(I) and α2(I) chains to 39.5°C (compared to 41.5°C for control), and to delay secretion of the overmodified type I procollagen from OI cells. These data are consistent with a mutation near the carboxyl-terminal end of the triple helical domain which delays triple helical formation and renders all chains available for further post-translational modification amino-terminal to the mutation. Such alterations in triple helical structure, thermal stability, and secretion previously associated only with the lethal OI type II phenotype are thus also seen in the mild OI type IV phenotype.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary An inherited genetic disorder causes XY embryos of the horse to develop as mares. On the basis of our study of 38 such mares, we have identified four grades or classes of XY sex reversal according to this scheme: class I, nearly normal female, of which some are fertile; class II, female with gonadal dysgenesis, normal mullerian development; calss III, intersex mare with gonadal dysgenesis, abnormal mullerian development, enlarged clitoris; class IV, virilized intersex characterized by high levels of testosterone. In general, class I and calss II mares were typed H-Y antigen-negative whereas class III and class IV mares were typed H-Y antigen-positive.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Choroideremia is a distinct blinding condtion with an X-linked pattern of inheritance. We have analyzed two RFLPs, DXS3 and DXYS1, for linkage with the choroideremia locus (TCD) within three kindreds. A maximum LOD score of 3.98 was obtained at $$\hat \theta = 0.14$$ . Contrary to previous reports, the present data demonstrate that these two RFLPs are not tightly linked to the choroideremia gene locus.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1432-1246
    Keywords: Children ; Blood lead level ; Attainment ; Intelligence ; Behaviour
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary This study replicates an earlier one carried out in London in which an association was found between lead and intelligence, reading and spelling. In the present study 194 children living near an urban motorway were given the same battery of tests as well as an extensive family interview to determine background variables. Before social factors were taken into account there were no significant associations between lead and outcome variable. Possible reasons for the negative results from this study are discussed.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1432-8798
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A slowly growing subgroup 2 bovine adenovirus (BAV) strain designated Ruakura 78-5371 was isolated from a yearling heifer with systemic adenovirus infection. Cross neutralization tests and restriction endonuclease analysis of the viral DNA showed the virus to be distinct from the other 9 recognised types of BAV. It is proposed that this strain should be regarded as the prototype strain of the new type BAV-10.
    Type of Medium: Electronic Resource
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