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Biomedical subjects

N Shannon

Publications and source records attributed to N Shannon.

13 recordsLinked to original sources
PubMed2006

Determination of the androgenic potency of whole effluents using mosquitofish and trout bioassays.

This study combined bioassay-derived and direct chemical analysis of steroidal compounds in pulp and paper and municipal sewage effluent in order to determine the cause of masculinization of female mosquitofish. The bioassays used in this study consisted of androgen and estrogen receptor binding, and aromatase inhibition using tissues from rainbow trout. This study observed no masculinization of female mosquitofish from a pulp and paper mill effluent that was previously observed to cause this effect. Mosquitofish sampled from the receiving environment of the same mill verified that masculinization was not occurring in the wild. The municipal sewage effluent also had no masculinizing effect. In vitro bioassays indicated significant sources of both androgens and estrogens in the effluents tested with sewage effluent having both the highest estradiol (41 ng/L) and testosterone (182 ng/L) equivalent concentration. These results could not be attributed to any particular compounds measured in the effluents. Two compounds implicated in the masculinization of mosquitofish by pulp and paper effluent, androstenedione and androstadienedione required relatively large (10-100 microg/L) waterborne concentrations to elicit a masculinizing effect and neither of these compounds are likely to occur at levels this high in the natural environment. The potent aromatase inhibitor, 4-hydroxyandrostenedione also did not cause masculinization at 100 microg/L indicating that masculinization did not occur through this mechanism. The mammalian anti-androgen, cyproterone acetate was only partially effective in mosquitofish and reduced the severity of masculinization in the presence of methyl testosterone. While neither effluent masculinized mosquitofish, there was a significant reduction of in vitro ovarian steroid production with the most severe effects observed with the sewage effluent. Overall, this study found the disappearance of a masculinizing effect that had been previously observed; concluded that based on 21 days aqueous exposures androstenedione and androstadienedione are not likely candidates for mosquitofish masculinization, and showed that masculinization and in vitro steroid production are unrelated biological endpoints.

Androgens↗
PubMed2005

Spin correlations in the paramagnetic phase and ring exchange in La2CuO4.

Spin correlations in the paramagnetic phase of La(2)CuO(4) have been studied using polarized neutron scattering, with two important results. First, the temperature dependence of the characteristic energy scale of the fluctuations and the amplitude of the neutron structure factor are shown to be in quantitative agreement with the predictions of the quantum nonlinear sigma model. Second, a comparison of a high-temperature series expansion of the equal-time spin correlations with the diffuse neutron intensity provides definitive experimental evidence for ring exchange.

Journal Article↗
PubMed2002

Intrinsic inhomogeneities in manganite thin films investigated with scanning tunneling spectroscopy.

Thin films of La0.7Sr0.3MnO3 on MgO show a metal insulator transition and colossal magnetoresistance. The shape of this transition can be explained by intrinsic spatial inhomogeneities, which give rise to a domain structure of conducting and insulating domains at the submicrometer scale. These domains then undergo a percolation transition. The tunneling conductance and tunneling gap measured by scanning tunneling spectroscopy were used to distinguish and visualize these domains.

Journal Article↗
PubMed2000

DNA flow cytometry does not predict 5- or 10-year recurrence rates for T1-2 node-negative breast cancer.

BACKGROUND: A small proportion of T1 or T2 node-negative breast cancer tumors will recur in patients by 5 years, and more by 10 years. Results of recent studies have suggested improvement in overall survival with administration of adjuvant chemotherapy to all patients. More sensitive and specific methods are needed to identify patients at highest risk for recurrence who might benefit most from adjuvant therapy, saving others from unnecessary treatment. Some investigators have suggested DNA flow cytometry as a method to discriminate patients at greatest risk for recurrence. HYPOTHESIS: DNA flow cytometry has predictive value for breast cancer recurrence in node-negative patients. METHODS: The cancer registry of a medium-sized university-affiliated hospital was used to identify patients with T1-2 N0 M0 breast cancer treated with a uniform surgical approach and no adjuvant therapy who had completed at least 5 years of follow-up or had recurrence. Flow cytometric analysis was performed on paraffin-embedded specimens. RESULTS: Of 115 patients, 92 (80%) had disease-free survival without recurrence and 23 (20%) had recurrence. Comparison of diploid and nondiploid tumors for likelihood of recurrence revealed no association (P = .79). Furthermore, the DNA index and S-phase fraction were not significantly different between recurrent and nonrecurrent groups. CONCLUSIONS: The likelihood of recurrence of small node-negative breast cancers after mastectomy cannot be accurately predicted on the basis of DNA flow cytometric analysis. Traditional methods for determining risks-such as nuclear and histological grade, lymph node status, and tumor size-seem to be more useful. Sentinel lymph node biopsy techniques may increase the detection of micrometastases.

Breast Neoplasms↗
PubMed1998

Costello syndrome: two cases with embryonal rhabdomyosarcoma.

Costello syndrome is a well delineated mental retardation syndrome of unknown aetiology in which the occurrence of benign tumours, especially papillomata, is recognised. We report two children in whom the diagnosis of Costello syndrome was made in the first months of life, who both developed a retroperitoneal embryonal rhabdomyosarcoma. Although not previously reported, the occurrence of this relatively uncommon childhood tumour in two girls with Costello syndrome suggests that an increased risk of malignancy may be part of this condition. The genetic basis of this susceptibility requires further clarification.

Child, Preschool↗
PubMed1996

Kitchen notes, 'the grapevine', and other writing in childhood.

In semistructured interviews, 20 men and 20 women (10 deaf and 10 hearing) between the ages of 18 and 28 recalled instances of instrumental, social, and expressive writing from their childhood. In contrast to earlier research, we found that instrumental writing occurred as frequently between deaf children and their hearing parents as between deaf children and their deaf parents and that all homes with a deaf family member had telecommunication devices for the deaf(TTYs). Whereas all respondents engaged in some form of social writing, deaf respondents did less personal or expressive writing than their hearing peers. Implications for literacy instruction and further research are that (a) teachers should take advantage of the writing experience that students bring to the classroom, (b) writing should be used as a tool for learning and classroom communication, and (c) the effects of experience, genre, school setting, and technology on the writing of deaf students should be examined.

Journal Article↗
PubMed1984

Determination of free thyroxin in serum by ultrafiltration: validation of a method and preliminary results.

We describe the determination of concentrations of free thyroxin in serum by ultrafiltration based on the Amicon micropartition system. The assay is straightforward and requires about 4 h for 25 samples. Our results demonstrate a correlation coefficient of 0.81 compared with equilibrium dialysis, and of 0.88 compared with radioimmunoassay. For sera from 49 normal, 25 hyperthyroid, 24 hypothyroid, 50 euthyroid sick, and 13 pregnant subjects, the means (and SD) were respectively: 19.3 (4.9), 40.1 (13.6), 5.0 (2.9), 25.9 (10.5), and 16.1 (3.2) ng/L. The interassay CV was 9.9% and the intra-assay CV 7.2%. We conclude that this procedure is useful in the diagnosis of thyroid disease and offers advantages of simplicity, rapidity, and economy.

Dialysis↗
PubMed1981

Clinical features, investigation and treatment of post-traumatic syringomyelia.

Thirteen patients who sustained spinal cord trauma causing persisting disability, developed new symptoms, the chief one of which was severe pain unrelieved by analgesics. The clinical diagnosis of post traumatic syringomyelia was confirmed in each case by means of myelography, as well as endomyelography in seven patients. In every case exploration of the spinal cord syrinx was performed. Ten patients were troubled by severe pain while three patients were mainly subject to altered sensation in the upper limbs. Of the six patients who had initially sustained complete cord transections, three were treated by cord transection and three were treated by syringostomy. The seven patients who sustained incomplete cord lesions were all treated by syringostomy. The patients who initially sustained incomplete sensory motor spinal cord damage had a better symptomatic response to surgery than hose who had sustained a complete spinal cord lesion. The ten patients whose main symptom was severe pain were completely relieved of their symptoms by surgery.

Adult↗
PubMed1979

L4/5 and L5/S1 disc protrusions: analysis of 323 cases operated on over 12 years.

A retrospective study of the results of excision of L4/5 and L5/S1 intervertebral discs in 323 patients operated on between January 1965 and January 1977 was undertaken. In every case the amount of disc excised was weighed immediately after operation. The patients had been followed up at the hospital for periods of between one and 14 years. As assessment was made of the clinical state of each patient at the end of follow-up. There was no evidence that the weight of disc excised affected the prognosis with respect either to the clinical state of the patient at the end of follow-up, or to the probability of recurrence of disc protrusion.

Adolescent↗