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  • 1
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Dead reckoning, a form of navigation used to locate a present position and to return to a starting position, is used by rats to return to their home base. The present experiment examined whether dead reckoning is displayed by rats during their first exploratory excursions in a novel environment and also examined whether the behaviour requires the integrity of the cells of the hippocampus. Experimental rats, those with NMDA (N-methly d-aspartate) lesions of Ammon's horn and the dentate gyrus, and control rats could leave a cage to explore a large circular table under light and dark conditions. Home base behaviour, use of olfactory cues, and thigmotaxic- based navigation were evaluated. Temporal, topographical and kinematic analyses were conducted on the first three exploratory excursions that extended at least halfway across the table. Groups did not differ in numbers of exits from the home base, lingering near the home base, distance travelled, or the use of surface cues as might be exemplified by thigmotaxic and olfactory behaviour. Temporal, topographical and kinematic reconstructions of homing behaviour, however, indicated that control rats, but not hippocampal rats, made direct high velocity return trips to the home base in both the light and the dark. Peak velocity of the trips occurred at the trip midpoint, independent of trip distance, suggesting the movements were preplanned. These results are discussed in relation to the ideas that dead reckoning is used in the homing of exploring rats and that this form of navigation involves the hippocampus.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: L-type Ca2+ currents (ICa) in rod photoreceptors exhibit Ca2+-dependent inactivation. Perforated-patch whole-cell recordings were obtained from isolated rods of the tiger salamander using 1.8 mm Ca2+ in the bathing medium to determine the extent of Ca2+-dependent inactivation of ICa with physiological [Ca2+] and endogenous buffering. ICa was measured with voltage ramps applied before and after 5-s steps to −40, −30, −20, or −10 mV. Long depolarizing steps in isolated rods produced inactivation of ICa ranging from 15% at −40 mV to 〉 80% at −10 mV. Because, in addition to Ca2+-dependent inactivation, depletion of synaptic cleft Ca2+ accompanying activation of ICa can reduce presynaptic ICa at calycal synapses, we investigated whether a similar mechanism worked at the invaginating rod synapse. Rods from retinal slices with intact synapses were compared with isolated rods in which synaptic cleft depletion is absent. ICa was more strongly depressed by depolarization of rods in retinal slices, with ICa reduced by 47% following voltage steps to −40 mV. The depression of currents by depolarization was also greater for rods from retinal slices than isolated rods when Ca2+ was replaced with Ba2+ to reduce Ca2+-dependent inactivation. The stronger depolarization-evoked inhibition of ICa in retinal slices compared to isolated rods probably reflects depletion of synaptic cleft Ca2+ arising from sustained Ca2+ influx. Inactivation of ICa exhibited slow onset and recovery. These findings suggest that Ca2+-dependent inactivation and depletion of synaptic cleft Ca2+ may combine to regulate ICa in response to light-evoked changes in rod membrane potential.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1442-1984
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Species that have become rare or endangered due to human disturbance are at increased risk of extinction as a result of environmental, demographic, and genetic stochasticity. Smaller populations, which can be typical of endangered species, are especially vulnerable to loss of variation through stochastic events. For 10 populations of Platanthera leucophaea (Nuttall) Lindley (Orchidaceae), a threatened species, genetic variation at allozyme and random amplified polymorphic DNA (RAPD) loci was measured to assess the potential effects of fragmentation and reduced population size on the future viability of populations. Allozymes revealed very low levels of diversity (AP = 1.18; PP = 12%; HO = 0.008) and high levels of population differentiation (FST = 0.75). Additionally, inbreeding coefficients were very high in five of the 10 populations surveyed, due largely to the fixation of alternative alleles at two loci in different populations. In contrast, every individual displayed a unique RAPD fingerprint, yielding higher levels of polymorphism (PP = 45%) and gene diversity (Nei's H = 0.159). Estimates of population differentiation based on RAPD are moderate as measured by amova (ΦST = 0.21), Wright's F-statistics (GST = 0.26), or Shannon's information index (Hamong = 0.30). However, genetic and geographic distances are not significantly correlated, suggesting a lack of interpopulation gene flow and/or genetic drift within populations. Population size is not a good predictor of genetic variation in the present study, and it is hypothesized that plant dormancy patterns and chaotic fluctuations in population size from year to year may buffer against stochastic events, especially in small populations.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1442-9993
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract  Monitoring biodiversity presents the challenge of informing complex aspects of biological systems with consistent, repeatable, data-based indicators. The present paper does not address directly the selection of indicators for rangeland biodiversity, but rather presents essential aspects and examples of monitoring systems that address natural resource questions at comparable scales. In general, concepts of landscape quality, such as range condition, conservation value, health and biodiversity, are descriptive rather than quantitative and are either ill-defined or multiply defined. Assessment of the status of such indicators involves value systems, as well as process understanding at a range of scales for which data are often unavailable. Effective monitoring systems, in contrast, require repeated quantitative data at suitable temporal density and spatial scale, as well as appropriate methods and a conceptual framework to simplify and interpret these data. In recent years, broad-scale operational monitoring systems for land and vegetation have been developed in Australia based on sequences of satellite data, digital elevation models, ground information and appropriate statistical methods. These same datasets have been used to inform landscape qualities over broad areas; examples are given of the production of salinity risk maps and conservation management zones based on fragmentation patterns. These results have been achieved as a partnership between ecologists, resource scientists and statisticians and illustrate how surrogates for integrated concepts such as biodiversity can be derived from available data.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1365-2133
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background Advances in telemedicine permit consultations where the doctor and patient are at different sites. Objectives To determine whether this technology could be used to triage referrals of pigmented lesions to a dermatology out-patient clinic, and thereby assist in managing the ever increasing number of lesions being referred. Methods When patients attended clinic, a clinical diagnosis of their pigmented lesion was made and recorded. A still image of each lesion was subsequently taken from a video camera using a PC card, and stored. These images were subsequently viewed in conjunction with the general practitioner's referral information and designated as ‘warrants referral’ or ‘does not warrant referral’. For each lesion this decision was compared with the clinical diagnosis made during the live consultation in the clinic (the ‘gold standard’). Clinical diagnoses designated as warranting referral were malignant melanoma, basal cell carcinoma, keratoacanthoma, atypical naevus and pyogenic granuloma (due to the potential clinical confusion with amelanotic melanoma). Lesions that were not considered to warrant referral included benign melanocytic naevus, seborrhoeic keratosis, dermatofibroma, congenital naevus, solar lentigo, actinic keratosis and various other benign conditions. Results In total, 819 lesions were evaluated, resulting in a mean sensitivity of 81% and specificity of 73% for the technique. Conclusions We feel that the overall sensitivity of 81% is encouraging as regards the use of such a technique as a triage tool, but that the inability to examine the whole patient or palpate the lesions is a major drawback in the safe triage of patients with pigmented lesions.
    Type of Medium: Electronic Resource
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