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Biomedical subjects

G Frei

Publications and source records attributed to G Frei.

6 recordsLinked to original sources
PubMed2006

Neutron phase imaging and tomography.

We report how a setup consisting of three gratings yields quantitative two- and three-dimensional images depicting the quantum-mechanical phase shifts of neutron de Broglie wave packets induced by the influence of macroscopic objects. Since our approach requires only a little spatial and chromatic coherence it provides a more than 2 orders of magnitude higher efficiency than existing techniques. This dramatically reduces the required measurement time for computed phase tomography and opens up the way for three-dimensional investigations of previously inaccessible quantum-mechanical phase interactions of neutrons with matter.

Journal Article↗
PubMed1999

Cryptic female choice: frogs reduce clutch size when amplexed by undesired males.

In species with internal fertilization, females can 'cryptically' choose (e.g. through sperm selection) which individuals sire their offspring, even when their overt preferences for copulatory partners are overrun by male-male competition and sexual coercion. The experiment presented here reveals that control of paternity after copulation has begun is also possible in species with external fertilization. Females of the hybridogenetic Rana essonae-Rana esculenta (LL-LR) waterfrog complex adjust their clutch size in response to mate type: they release fewer eggs when amplexed by hybrid LR males who--jeopardize successful reproduction--than when amplexed by parental LL males. This reduction in the number of eggs laid can increase a female's residual reproductive value through a second mating in the same breeding season or a larger clutch size in the next year. We argue that cryptic female choice through clutch size adjustment (i) may have evolved more often than previously assumed, and (ii) can arise even where females mate only once during a reproductive period.

Animals↗
PubMed1999

Genetic linkage of the dentinogenesis imperfecta type III locus to chromosome 4q.

Dentinogenesis imperfecta type III (DGI-III) is an autosomal-dominant disorder of dentin formation which appears in a tri-racial southern Maryland population known as the "Brandywine isolate". This disease has suggestive evidence of linkage to the long arm of human chromosome 4 (LOD score of 2.0) in a family presenting with both juvenile periodontitis and DGI-III. The purpose of this study was to screen a family presenting with only DGI-III to determine if this locus was indeed on chromosome 4q. Furthermore, we wanted to determine if DGI-III co-localized with dentinogenesis imperfecta type II (DGI-II), which has been localized to 4q21-q23. Therefore, a large kindred from the Brandywine isolate was identified, oral examination performed, and blood samples collected from 21 family members. DNA from this family was genotyped with 6 highly polymorphic markers that span the DGI-II critical region of chromosome 4q. Analysis of the data yielded a maximum two-point LOD score of 4.87 with a marker for the dentin matrix protein 1 (DMP1) locus, a gene contained in the critical region for DGI-II. Our results demonstrated that the DGI-III locus is on human chromosome 4q21 within a 6.6 cM region that overlaps the DGI-II critical region. These results are consistent with the hypothesis that DGI-II is either an allelic variant of DGI-III or the result of mutations in two tightly linked genes.

Aggressive Periodontitis↗
PubMed1990

[The effect of rejection crises and immunosuppressive therapy on the lymphocyte subpopulations of patients after kidney transplantation].

The lymphocyte subsets in the peripheral blood were examined 3 times a week in 17 patients receiving a cadaveric renal allograft using 2-color flow cytometry and several combinations of monoclonal antibodies. Patients who experienced a rejection crisis (n = 12) had a significantly higher CD4/CD8-ratio (2.72 +/- 1.26 mean +/- SD) than patients with stable graft function (1.76 +/- 1.33, p less than 0.05). 9/12 patients showed 0-3 days prior to the rejection episode an increase of the CD4/CD8- ratio (greater than or equal to 0.5) and/or a high ratio (greater than or equal to 2.5) with a decrease following antirejection therapy. The activation markers HLA-DR and IL-2 receptor on T cells were increased only during 3/12 rejection episodes. Patients with rejections resistant to prednisone pulse therapy (n = 6) had significantly more lymphocytes/mm3 in the peripheral blood (1111.7 +/- 597.5) than successfully treated patients (n = 6, 336.7 +/- 196.0, p less than 0.02). Antirejection therapy with prednisone pulses and/or antithymocyte globuline resulted in a significant decrease of T lymphocytes (CD3+) with a selective reduction of T helper/inducer cells (CD4+). 6 months after renal transplantation the patients had a higher percentage of suppressor/cytotoxic cells (CD8+) compared to the pretransplant values (26.3 +/- 10.9% vs 17.7 +/- 6.2%, p less than 0.02) and blood donors (16.3 +/- 6.2%, p less than 0.01). Furthermore the percentage of T helper cells (CD4+/CD28-) was significantly higher and the T suppressor-inducer cells (CD4+/CD28+) were significantly lower compared to the controls. Serial flow cytometric determinations of lymphocyte subsets in renal allograft recipients may be helpful in some cases although rejection episodes could not be predicted in the individual patient.

Adult↗