4,905 research outputs found
Significant familial differences in the frequency of abortion and Toxoplasma gondii infection within a flock of Charollais sheep
A study was carried out to investigate the frequencies of abortion and congenital Toxoplasma gondii infection within 27
families (765 individuals) of a pedigree Charollais sheep flock maintained on a working farm in Worcestershire, UK, since
1992. Pedigree lambing records were analysed to establish the frequency of abortion for each family. The frequency of
congenital infection was determined for each family by PCR analysis of tissue samples taken from newborn lambs. Atotal of
155 lambs were tested for congenital T. gondii infection, which were all born during the study period 2000–2003. Significant
differences in the frequency of abortion between sheep families within this flock were observed with frequencies ranging
between 0% and 48% (P<0.01). Significantly different infection frequencies with T. gondii were also observed for different
families and ranged between 0% and 100% (P<0.01). Although the actual cause of each abortion was not verified, a highly
significant positive correlation was found to exist between the frequency of abortion and the frequency of T. gondii infection
in the same families (P<0.01). The data presented here raise further questions regarding the significance of congenital
transmission of T. gondii within sheep populations, the possible successive vertical transmission of T. gondii within families
of sheep, and the potential role of inherited genetic susceptibility to abortion with respect to T. gondii infection. This work
invites further study into the epidemiology of ovine toxoplasmosis and may have implications for sheep husbandry methods
in the future.
Key words: Toxoplasma gondii, ovine, toxoplasmosis, congenital, transmission, pedigree, sheep
High levels of congenital transmission of toxoplasma gondii in longitudinal and cross-sectional studies on sheep farms provides evidence of vertical transmission in ovine hosts
Recent research suggests that vertical transmission may play an important role in sustaining Toxoplasma gondii infection in some species. We report here that congenital transmission occurs at consistently high levels in pedigree Charollais and outbred sheep flocks sampled over a 3-year period. Overall rates of transmission per pregnancy determined by PCR based diagnosis, were consistent over time in a commercial sheep flock (69%) and in sympatric (60%) and allopatric (41%) populations of Charollais sheep. The result of this was that 53·7% of lambs were acquiring an infection prior to birth: 46·4% of live lambs and 90·0% of dead lambs (in agreement with the association made between T. gondii and abortion). No significant differences were observed between lamb sexes. Although we cannot distinguish between congenital transmission occurring due to primary infection at pregnancy or reactivation of chronic infection during pregnancy, our observations of consistently high levels of congenital transmission over successive lambings favour the latter
The prevalence of Neospora caninum and co-infection with Toxoplasma gondii by PCR analysis in naturally occurring mammal populations
Neospora caninum and Toxoplasma gondii are closely related intracellular protozoan parasites associated with bovine and ovine abortion respectively. Little is known about the extent of Neospora/Toxoplasma co-infection in naturally infected populations of animals. Using nested PCR techniques, based on primers from the Nc5 region of N. caninum and SAG1 for T. gondii, the prevalence of N. caninum and its co-infection with T. gondii were investigated in populations of Mus domesticus, Rattus norvegicus and aborted lambs (Ovis aries). A low frequency of infection with N. caninum was detected in the Mus domesticus (3%) and Rattus norvegicus (4·4%) populations. A relatively high frequency of infection with N. caninum was detected in the brains of aborted lambs (18·9%). There was no significant relationship between N. caninum and T. gondii co-infection. Investigation of the tissue distribution of Neospora, in aborted lambs, showed that Neospora could not be detected in tissues other than brain and this was in contrast to Toxoplasma where the parasite could be frequently detected in a range of tissues
Tumor response to radiotherapy is dependent on genotype-associated mechanisms in vitro and in vivo
<p>Abstract</p> <p>Background</p> <p>We have previously shown that in vitro radiosensitivity of human tumor cells segregate non-randomly into a limited number of groups. Each group associates with a specific genotype. However we have also shown that abrogation of a single gene (p21) in a human tumor cell unexpectedly sensitized xenograft tumors comprised of these cells to radiotherapy while not affecting in vitro cellular radiosensitivity. Therefore in vitro assays alone cannot predict tumor response to radiotherapy.</p> <p>In the current work, we measure in vitro radiosensitivity and in vivo response of their xenograft tumors in a series of human tumor lines that represent the range of radiosensitivity observed in human tumor cells. We also measure response of their xenograft tumors to different radiotherapy protocols. We reduce these data into a simple analytical structure that defines the relationship between tumor response and total dose based on two coefficients that are specific to tumor cell genotype, fraction size and total dose.</p> <p>Methods</p> <p>We assayed in vitro survival patterns in eight tumor cell lines that vary in cellular radiosensitivity and genotype. We also measured response of their xenograft tumors to four radiotherapy protocols: 8 Ă— 2 Gy; 2 Ă— 5Gy, 1 Ă— 7.5 Gy and 1 Ă— 15 Gy. We analyze these data to derive coefficients that describe both in vitro and in vivo responses.</p> <p>Results</p> <p>Response of xenografts comprised of human tumor cells to different radiotherapy protocols can be reduced to only two coefficients that represent 1) total cells killed as measured in vitro 2) additional response in vivo not predicted by cell killing. These coefficients segregate with specific genotypes including those most frequently observed in human tumors in the clinic. Coefficients that describe in vitro and in vivo mechanisms can predict tumor response to any radiation protocol based on tumor cell genotype, fraction-size and total dose.</p> <p>Conclusions</p> <p>We establish an analytical structure that predicts tumor response to radiotherapy based on coefficients that represent in vitro and in vivo responses. Both coefficients are dependent on tumor cell genotype and fraction-size. We identify a novel previously unreported mechanism that sensitizes tumors in vivo; this sensitization varies with tumor cell genotype and fraction size.</p
Area Regge Calculus and Discontinuous Metrics
Taking the triangle areas as independent variables in the theory of Regge
calculus can lead to ambiguities in the edge lengths, which can be interpreted
as discontinuities in the metric. We construct solutions to area Regge calculus
using a triangulated lattice and find that on a spacelike hypersurface no such
discontinuity can arise. On a null hypersurface however, we can have such a
situation and the resulting metric can be interpreted as a so-called refractive
wave.Comment: 18 pages, 1 figur
An action principle for the quantization of parametric theories and nonlinear quantum cosmology
By parametrizing the action integral for the standard Schrodinger equation we
present a derivation of the recently proposed method for quantizing a
parametrized theory. The reformulation suggests a natural extension from
conventional to nonlinear quantum mechanics. This generalization enables a
unitary description of the quantum evolution for a broad class of constrained
Hamiltonian systems with a nonlinear kinematic structure. In particular, the
new theory is applicable to the quantization of cosmological models where a
chosen gravitational degree of freedom acts as geometric time. This is
demonstrated explicitly using three cosmological models: the Friedmann universe
with a massless scalar field and Bianchi type I and IX models. Based on these
investigations, the prospect of further developing the proposed quantization
scheme in the context of quantum gravity is discussed.Comment: 14 page
Spatial modulation of dark versus bright stimulus responses in the mouse visual system
A fundamental task of the visual system is to respond to both increases and decreases of luminance with action potentials (ON and OFF responses1–4). OFF responses are stronger, faster, and more salient than ON responses in primary visual cortex (V1) of both cats5,6 and primates,7,8 but in ferrets9 and mice,10 ON responses can be stronger, weaker,11 or balanced12 in comparison to OFF responses. These discrepancies could arise from differences in species, experimental techniques, or stimulus properties, particularly retinotopic location in the visual field, as has been speculated;9 however, the role of retinotopy for ON/OFF dominance has not been systematically tested across multiple scales of neural activity within species. Here, we measured OFF versus ON responses across large portions of visual space with silicon probe and whole-cell patch-clamp recordings in mouse V1 and lateral geniculate nucleus (LGN). We found that OFF responses dominated in the central visual field, whereas ON and OFF responses were more balanced in the periphery. These findings were consistent across local field potential (LFP), spikes, and subthreshold membrane potential in V1, and were aligned with spatial biases in ON and OFF responses in LGN. Our findings reveal that retinotopy may provide a common organizing principle for spatial modulation of OFF versus ON processing in mammalian visual systems
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