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C G Thomas

Publications and source records attributed to C G Thomas.

100 records · Page 6Linked to original sources
PubMedDate not supplied

Investigation of BOLD contrast in fMRI using multi-shot EPI.

High resolution volume coverage of the brain in fMRI studies can be accomplished using multi-slice, multi-shot EPI. We demonstrate that the optimum contrast sensitivity in BOLD based fMRI experiments using multi-shot EPI is achieved by using the shortest possible TR values between segments and the longest tolerable echo train length. For a fixed paradigm time, acquiring the largest number of images under these conditions yields the best statistical detection thresholds. For a multi-slice multi-shot EPI fMRI study, the best approach is to perform the acquisition of all the segments in a single slice before continuing on to each of the slices in turn. Our results regarding the number of shots and TR are also applicable to other multi-shot techniques such as interleaved spirals.

Brain↗
PubMedDate not supplied

Role of thyroid stimulating hormone suppression in the management of thyroid cancer.

Well-differentiated thyroid cancers (papillary, follicular, and some Hurthle cell tumors) contain membrane receptors for TSH. Responsiveness of these tumors to TSH stimuli is documented by increased radioactive iodine uptake, secretion of thyroglobulin, increase in thyroid size, and potential progression to an anaplastic type. Although TSH suppression has a variable effect on the growth of existing tumors and the incidence of recurrent disease, there is a sound rationale for long-term TSH suppression in all patients with differentiated tumors of the thyroid. The ultrasensitive TSH test permits ready monitoring of the adequacy of thyroxine dosage. The cost is minimal (approximately $.10/day) and the risks are negligible if one assumes the avoidance of hyperthyroxinemia.

Carcinoma↗
PubMedDate not supplied

Resolution of radioiodinated thyrotropin into receptor active and inactive components by column chromatography.

Following radioiodination by the lactoperoxidase method and subsequent purification on Sephadex G100, it was found that [125I]TSH exhibited varying degrees of binding activities to the thyrotropin receptor. In order to further purify the radiolabeled hormone, the [125I]TSH preparation was chromatographed on Sepharose 6B. Two peaks of radioactive material (Peaks I and II) were recovered, containing approx. 60% of the applied radioactivity. Upon elution with Mg2+, the remainder of the radiolabeled material was recovered as a single peak (Peak III). Characterization of these 3 peaks by radioimmunoassay demonstrated that all 3 were immunocompetent, although Peaks I and III were 3-4-fold more immunoreactive than Peak II. Analysis by radioreceptor assay indicated that Peak III showed an increase in receptor-binding capacity (in comparison with the [125I]TSH preparation purified by Sephadex G100 alone), while both Peaks I and II exhibited significantly reduced binding activity. In contrast, human TSH (NIH) chromatographed mainly as a receptor inactive peak, although it was fully immunocompetent. Scatchard analysis of receptor binding to bovine [125I]TSH from Peak III yielded a curvilinear plot with affinities similar to those we have previously reported for [125I]TSH purified by Sephadex G100 chromatography. The total number of binding sites, however, increased proportionally with the active fraction of the [125I]TSH preparation. Since the mass of bound hormone is calculated from the percent bound of total radioactivity and only a fraction of the measured total participates in the binding, it is therefore necessary to correct for the inactive fraction when calculating the total receptor number.

Chromatography, Affinity↗
PubMedDate not supplied

Thyrotropin binding to porcine thyroid plasma membranes: kinetic and thermodynamic analyses.

Evaluation of TSH binding to plasma membranes of porcine thyroid revealed unique sensitivity to pH and temperature. Analysis of apparent equilibrium binding yielded a linear Scatchard plot at the optimal pH of 6.0, indicating one class of binding sites. At physiological pH 7.4 a curvilinear Scatchard plot was obtained, resolved by computer analysis into two classes of binding sites of different affinities and capacities. Treatment of membranes with phospholipase C resulted in a 20% decrease in the number of high affinity sites, but no change occurred in binding affinity. In contrast, low affinity sites were not altered. To evaluate the significance of the curvilinear Scatchard plot, the kinetics of association were examined. The intrinsic Kd (kd/ka) was 0.20 nM, a value essentially equivalent to that of the high affinity binding component. The 'negative cooperativity' model of hormone binding was evaluated by examining the effect of excess unlabeled TSH on dissociation rate. Dissociation of bound 125I-labeled TSH was biphasic, and was enhanced by unlabeled hormone, regardless of whether the membranes were prelabeled at pH 6.0 or 7.4. This effect was not correlated with curvilinear Scatchard plots, and therefore not proof of negative cooperativity. Binding sites for TSH were further distinguished by their sensitivity to temperature. A van't Hoff plot of temperature dependence of the apparent Kd of the high affinity site was linear from 4 to 37 degrees C. In contrast, the apparent Kd of low affinity binding did not vary with respect to temperature. These results demonstrate that there are at least two independent binding sites for TSH on porcine thyroid plasma membranes, distinguishable by their equilibrium binding properties.

Animals↗
PubMedDate not supplied

Quantitative neuronal c-fos and c-jun expression in Alzheimer's disease.

Apoptosis, or programmed cell death, has been proposed as a mechanism of neuropathology in Alzheimer's disease (AD). Activation of immediate early genes (IEG) c-jun and c-fos appears to be required for the initiation of apoptosis. Furthermore, the expression of c-jun is induced in cultured neurons that undergo beta-amyloid-mediated apoptosis suggesting a direct role for c-jun in the apoptosis of AD neurons. Using immunohistochemical methods, we calculated the average number of neuronal profiles per unit area expressing c-Jun and c-Fos within hippocampal regions CA1, CA2/3, and CA4 in postmortem brain samples from AD patients and age-matched non-AD patients. There was an increase in c-Jun-positive and c-Fos-positive neuronal profile density in nearly all AD hippocampal regions examined. In cerebellum there was no evidence of apoptosis as determined by using TUNEL technique, and negligible c-Jun labeling.

Aged↗