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1.
A model of a myelinated nerve axon is developed on the basis of FitzHugh-Nagumo dynamics under the assumption that the nodes of Ranvier are of small but finite width. It is shown that a periodic excited state may not exist if the width of the nodes is too small and the leakage across the myelin sheath is too great. The propagation of a super threshold pulse is prevented in the absence of nodes. Global stability of the resting equilibrium state is investigated as well as the propagation of wave front, type solutions. 相似文献
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D. P. Sleeman J. Davenport S. J. More T. A. Clegg J. M. Griffin I. O’Boyle 《European Journal of Wildlife Research》2009,55(3):267-278
This study’s objective was to estimate the permeability of barriers to badger immigration during the Irish Four Area project.
These barriers were at the boundaries of removal areas, where there was proactive culling of badgers. Data from the last 3 years
of the study were used. Each length of barrier was allocated a space within the removal area. These were further sub-divided
into spaces of 0–2, 2–5 km and sometimes of more than 5 km from the edge of the removal area. It is assumed that all, or some,
of the badgers caught within these spaces came across the barriers. The barriers were one of the following: external buffers,
sea, rivers and political boundaries. The total lengths of the barriers in all areas were: external buffer 128.5 km; sea 70.9 km;
river 78.6 km; political 32.2 km. We assume three scenarios: (1) all badgers caught in the final 3 years were immigrants,
(2) 75% were immigrants or (3) 50% were immigrants. We test these scenarios using chi-square tests, applying internal buffers
of 1 km to counter movements of badgers across zones. Using this approach and multivariate analysis, we found that the permeability
of barrier types varied, with sea and external buffers being the most effective barriers. The combined capture data are further
examined by the sex ratio in each range, and then the sex ratio in total. Equal numbers of males and females were found, but
the source populations were probably predominantly female. If badger management options are to achieve maximum benefits, then
the field effectiveness of such barriers needs to be understood. 相似文献
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Litman GW; Rast JP; Shamblott MJ; Haire RN; Hulst M; Roess W; Litman RT; Hinds- Frey KR; Zilch A; Amemiya CT 《Molecular biology and evolution》1993,10(1):60-72
Immunoglobulins are encoded by a large multigene system that undergoes
somatic rearrangement and additional genetic change during the development
of immunoglobulin-producing cells. Inducible antibody and antibody-like
responses are found in all vertebrates. However, immunoglobulin possessing
disulfide-bonded heavy and light chains and domain-type organization has
been described only in representatives of the jawed vertebrates. High
degrees of nucleotide and predicted amino acid sequence identity are
evident when the segmental elements that constitute the immunoglobulin gene
loci in phylogenetically divergent vertebrates are compared. However, the
organization of gene loci and the manner in which the independent elements
recombine (and diversify) vary markedly among different taxa. One striking
pattern of gene organization is the "cluster type" that appears to be
restricted to the chondrichthyes (cartilaginous fishes) and limits
segmental rearrangement to closely linked elements. This type of gene
organization is associated with both heavy- and light-chain gene loci. In
some cases, the clusters are "joined" or "partially joined" in the germ
line, in effect predetermining or partially predetermining, respectively,
the encoded specificities (the assumption being that these are expressed)
of the individual loci. By relating the sequences of transcribed gene
products to their respective germ-line genes, it is evident that, in some
cases, joined-type genes are expressed. This raises a question about the
existence and/or nature of allelic exclusion in these species. The
extensive variation in gene organization found throughout the vertebrate
species may relate directly to the role of intersegmental
(V<==>D<==>J) distances in the commitment of the individual
antibody-producing cell to a particular genetic specificity. Thus, the
evolution of this locus, perhaps more so than that of others, may reflect
the interrelationships between genetic organization and function.
相似文献
8.
An 11-mo-old captive-bred male neutered bobcat (Felis rufus) presented with lethargy, anorexia, leukopenia, neutropenia, lymphopenia, and nonregenerative anemia. The animal was diagnosed as feline leukemia virus (FeLV) positive by immunofluorescent antibody and enzyme-linked immunosorbant assay (ELISA) testing. It died despite supportive care. Pathologic examination revealed multifocal non-suppurative encephalitis, diffuse interstitial pneumonia, multifocal hepatocellular necrosis, non-suppurative peritonitis, and lymphoid depletion. FeLV was isolated from peripheral blood mononuclear cells, bone marrow, spleen, and lymph node. FeLV-specific gag sequences were amplified by DNA polymerase chain reaction (PCR) and aligned with known domestic cat FeLV's. The source of the virus was speculated to be a domestic cat that was a surrogate nurse. Case reports of FeLV in nondomestic felids are few, and FeLV does not appear to be enzootic in wild felids, except European wildcats (Felis silvestris) in France and Scotland. Introduction of FeLV into free-living and captive nondomestic felid populations could have serious consequences for their health and survival. Measures to prevent the introduction of this virus to nondomestic felids are warranted. 相似文献
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A retrospective study was conducted to identify causes of morbidity and mortality of free-living raptors in northeast Colorado and the surrounding areas of Nebraska and Wyoming. The study included 409 raptors, representing 23 species, admitted to the Colorado State University Veterinary Teaching Hospital, Fort Collins, Colorado, USA, from 1995 to 1998. Causes of morbidity and mortality were identified as trauma (66.3%), orphaned young (15.6%), unknown (9.0%), infectious disease (4.4%), metabolic and nutritional disease (2.2%), toxicosis (2.0%), and degenerative disease (0.5%). Trauma was the most frequent cause of morbidity and mortality for all species and during all seasons. 相似文献
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A field study was carried out on Little Island (County Waterford, Ireland) in June 2000 to evaluate the potential of a bait-marking system for use in European badgers (Meles meles). Two oral biomarkers, sulfadimethoxine (SDM) and rhodamine B, were incorporated into fishmeal baits and distributed by hand at main sets in five test territories for 3 consecutive days. In parallel, non-biomarked baits were distributed at a single control territory. The objectives of the study were to: (1) assess the effects of SDM and rhodamine B on palatability and thus bait acceptance, and (2) investigate the marking capacity of SDM and rhodamine B in serum and hair samples taken from badgers. Trapping was carried out in each territory for 5 consecutive days immediately after bait distribution. Analysis of data revealed that 90-100% of baits were removed in four of the test territories and from the control territory. In the fifth test territory, 61% of baits were removed. Of the badgers (n = 26) trapped in the test territories, 18 (69%) were positive when tested for both biomarkers. In contrast, the remaining eight animals and those captured in the control territory (n = 6 badgers) were negative. In the marked animals, the highest levels of SDM were recorded in serum samples taken soon after bait distribution. Thereafter, the levels declined in each badger over the course of the study. In contrast, rhodamine B was readily detectable by fluorescence microscopy of hair samples throughout the period of study. The results indicate that SDM and rhodamine B act as systemic markers in badgers and have potential future applications for monitoring of oral vaccine uptake. 相似文献