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Biomedical subjects

T B Clark

Publications and source records attributed to T B Clark.

At least 19 recordsLinked to original sources
PubMed1998

Phase II trial of docetaxel (Taxotere) for untreated advanced colorectal carcinoma.

The antimicrotubule agent docetaxel (Taxotere), a semisynthetic taxoid, has demonstrated antitumor activity against colorectal cancer cell lines in vitro, and in murine tumor models. We sought to characterize its activity in a group of previously untreated patients with colorectal carcinoma. Eighteen previously untreated patients with advanced, measurable colorectal carcinoma were treated with a 60-min intravenous infusion of docetaxel with a dose of 100 mg/m2 administered every 21 days. Routine premedication with diphenhydramine was given. Patients were required to have normal organ function and a Karnofsky performance status (KPS) > or = 60%. No complete response (CR) or partial responses (PR) were observed. Median survival was 13 months, despite a median time to progression of only 1.3 months. Neutropenia was the most common dose-limiting toxicity, resulting in 5 episodes of febrile neutropenia requiring hospitalization and intravenous antibiotics. One patient experienced a grade 4 hypersensitivity reaction (HSR) requiring treatment termination. No toxic deaths occurred. Despite encouraging preclinical data, docetaxel is an inactive drug in advanced colorectal cancer when given in the dose and on the schedule examined in the present study, and has significant, although reversible, toxicities.

Adult↗
PubMed1997

Lack of pineal beta-adrenergic receptor alterations in suicide victims with major depression.

Noradrenergic function may be altered in depressive illness and thereby contribute to decreased pineal production of melatonin levels, as previously described in some depressed subjects. In the present study, the hypothesis was tested that pineal beta-adrenergic binding would be increased in persons committing suicide with evidence of depressive disorders, reflecting diminished noradrenergic input. Initially, post-mortem human pineal glands were obtained at autopsy. Diagnostic and symptomatic information was then systematically collected from family members using standardized interview techniques. Seven subjects who committed suicide and suffered from major depression, and without exposure to treatment for depressive symptoms were age- and sex-matched with control subjects. Pineal beta-adrenergic binding was assessed by quantitative autoradiography employing four concentrations of [125I]pindolol. Because of possibly complex adrenergic regulation of the pineal, beta-adrenergic receptor binding were subtyped using the selective blocker ICI 89406. No differences in beta-adrenergic receptors were detected between subjects with major depression compared to the matched controls.

Adult↗
PubMed1996

Spiroplasma syrphidicola sp. nov., from a syrphid fly (Diptera: Syrphidae).

Spiroplasma sp. strain EA-1(T) (T = type strain) (subgroup VIII-1), which was isolated from the syrphid fly Eristalis arbustorum, was serologically distinct from other spiroplasma species, groups, and subgroups, The cells of this strain, as revealed by dark-field light microscopy, were short, helical, and motile. An electron microscopic examination revealed wall-less cells delimited by a single membrane. The unusually short cells passed through 220-nm filter pores with no reduction in titer. The organisms grew well in SM-1, M1D, and SP-4 liquid media. Growth also occurred in conventional horse serum medium and 1% serum fraction medium. Strain EA-1(T) grew at temperatures between 10 and 41 degrees C, and optimum growth occurred at 32 degrees C. The doubling time at the optimal temperature was 1.0 h. The strain catabolized glucose and hydrolyzed arginine but did not hydrolyze urea. The guanine-plus-cytosine content of the DNA was 30 +/- 1 mol%. The genome size was about 1,230 kbp. Strain Ea-1 (= ATCC 33826), which represents subgroup VIII-1, is designated the type strain of a new species, Spiroplasma syrphidicola.

Animals↗
PubMed1996

Spiroplasma corruscae sp. nov., from a firefly beetle (Coleoptera: Lampyridae) and tabanid flies (Diptera: Tabanidae).

Spiroplasma strain EC-1T (T = type strain), which was isolated from the gut of a lampyrid beetle (Ellychnia corrusca) in Maryland, was serologically distinct from other spiroplasma species and groups. Similar strains were obtained from other E. corrusca specimens, and, later, numerous isolates of similar or partially related strains were obtained from several species of tabanid files. Cells of strain EC-1T were helical, motile filaments that were bound by a single cytoplasmic membrane, and there was no evidence of a cell wall. The cells were filterable through 220-nm-pore-size membrane filters but not through 100-nm-pore-size membrane filters. The organism was absolutely resistant to penicillin (1,000 U/ml) and required sterol for growth. Strain EC-1T grew well in M1D and SP-4 liquid media and could be cultivated in the Edward formulation of conventional mycoplasma medium and in 1% serum fraction medium. Optimal growth occurred at 32 degrees C (doubling time, 1.5 h). Strain EC-1T multiplied at 10 to 41 degrees C, but not at 5 or 43 degrees C. This organism produced acid from glucose, but did not hydrolyze arginine or utilize urea. The guanine-plus-cytosine content of the DNA was determined to be 26.3 mol% by the melting temperature method and 27.0 mol% by the buoyant density method. As a result of our studies, strain EC-1 (= ATCC 43212) is designated the type strain of a new species, Spiroplasma corruscae.

Animals↗
PubMed1996

Alteration of brain dopamine and serotonin levels in cocaine users: a preliminary report.

OBJECTIVE: This study tested the hypothesis that cocaine depletes dopamine levels in the brain. METHOD: Levels of dopamine, serotonin, and their metabolites in the frontal cortex and striatum of nine cocaine users and nine matched control subjects who had never used cocaine were determined from postmortem autopsy material. RESULTS: The cocaine users had significantly lower dopamine levels and higher serotonin levels in the frontal cortex than the control subjects. Levels in other brain areas did not differ between the two groups. CONCLUSIONS: Alterations of dopamine and serotonin levels might contribute to symptoms of cocaine withdrawal and craving.

Adult↗
PubMed1995

Spiroplasma velocicrescens sp. nov., from the vespid wasp Monobia quadridens.

Spiroplasma strain MQ-4T (T = type strain), which was isolated from the hemolymph of the vespid wasp Monobia quadridens, was serologically distinct from other spiroplasma species, groups, putative groups, and subgroups. Each strain MQ-4T cell was helical and motile and was surrounded by a single cytoplasmic membrane; there was no evidence of a cell wall. The strain grew well in 1% serum fraction medium, as well as in SM-1, M1D, and SP-4 liquid media, under both aerobic and anaerobic conditions. Strain MQ-4T grew at temperatures ranging from 10 to 41 degrees C but did not grow at 43 degrees C. The strain grew optimally at 37 degrees C with a doubling time of 0.6 h, the shortest doubling time recorded for any spiroplasma. Strain MQ-4T catabolized glucose and arginine but did not hydrolyze urea. The guanine-plus-cytosine content of the DNA was about 27.5 +/- 1 mol%. The genome size was 1,480 kbp (940 MDa). Strain MQ-4 (= ATCC 35262) is designated the type strain of a new species, Spiroplasma velocicrescens.

Animals↗
PubMed1994

Taxonomic descriptions of eight new non-sterol-requiring mollicutes assigned to the genus Mesoplasma.

Twenty mollicute strains isolated primarily from insect hosts were characterized and arranged into eight new species in the genus Mesoplasma. Morphological examination of the organisms by electron and dark-field microscopic techniques revealed that the cells of each strain were small, nonhelical, nonmotile, pleomorphic, and coccoid and that each cell was surrounded by a single cytoplasmic membrane with no evidence of a cell wall. Although the new mollicutes grew well in media containing horse or fetal bovine serum, growth in serum-free or cholesterol-free medium occurred only when the medium contained 0.04% polyoxyethylene sorbitan (Tween 80). The optimum temperature for growth was usually 30 degrees C, but multiplication generally occurred over a temperature range of 10 to 32 degrees C. All strains catabolized glucose. Most strains did not hydrolyze arginine or urea, although three related strains isolated from fireflies (the strain PUPA-2T [T = type strain] group) did hydrolyze arginine. The genome sizes ranged from 825 to 930 kbp, and the DNA base compositions (guanine-plus-cytosine contents) ranged from 26.5 to 31.6 mol%. The proposed type strains of the eight new species were not serologically related to the type strains of four other Mesoplasma species, five Entomoplasma species, 11 Acholeplasma species, and 100 Mycoplasma species and subspecies. Strain PS-1 (= ATCC 49582) is the type strain of Mesoplasma pleciae sp. nov., strain PUPA-2 (= ATCC 49581) is the type strain of Mesoplasma photuris sp. nov., strain YJS (= ATCC 51578) [corrected] is the type strain of Mesoplasma syrphidae sp. nov., strain CHPA-2 (= ATCC 49578) is the type strain of Mesoplasma chauliocola sp. nov., strain ELCA-2 (= ATCC 49579) is the type strain of Mesoplasma corruscae sp. nov., strain GRUA-1 (= ATCC 49580) is the type strain of Mesoplasma grammopterae sp. nov., strain BARC 779 (= ATCC 49583) is the type strain of Mesoplasma coleopterae sp. nov., and strain BARC 857 (= ATCC 49584) is the type strain of Mesoplasma tabanidae sp. nov.

Animals↗
PubMed1993

Cocaine use increases [3H]WIN 35428 binding sites in human striatum.

Animal studies suggest that chronic cocaine exposure may increase the function and/or synthesis of the dopamine transporter (DAT) under certain conditions, but the literature is complex. In order to test the hypothesis that cocaine exposure alters the DAT in humans, preliminary studies were done characterizing [3H]WIN 35428 binding in human striatum from normal controls. Following these experiments, the effects of chronic cocaine were examined in post mortem striatal specimens from 7 cocaine users and 7 controls matched for age and post mortem interval, employing quantitative autoradiography. Initial saturation experiments indicated that a one-site model was preferred with a Kd of 11 +/- 4 nM. [3H]WIN 35420 binding was then examined in cocaine users and controls at 0.5, 5, 10, and 50 nM radioligand concentrations. At each concentration of [3H]WIN 35420, optical densities for cocaine-exposed subjects were increased in caudate, putamen, and accumbens. The results suggest that total numbers of binding sites were increased in cocaine users. Based on the present and previous results, it appears that the regulation of the DAT is fairly plastic, and is highly sensitive to cocaine dosing regimes and withdrawal intervals. Chronic adaptations induced by cocaine in the DAT could contribute to the symptoms of binging, withdrawal depression, and/or craving.

Adult↗
PubMed1993

Beta-adrenergic receptor binding in frontal cortex from suicide victims.

Beta-adrenergic binding in frontal cortex samples from suicide victims has been reported to be increased, unaltered, and decreased compared to matched controls. Subject's diagnoses and drug exposures in these studies were not equivalently documented and were possibly different. In the present study, diagnostic and symptomatic information was systematically collected from family members of 15 subjects committing suicide and 15 matched controls using standardized interview techniques. The goal was to test the hypothesis that alterations in beta-adrenergic binding were more likely to be found in subjects with evidence of depressive disorders. [125I]pindolol binding in frontal cortex was found to be significantly lower in the group committing suicide compared to the matched controls (21.1 +/- 1.1 fmol/mg protein vs. 24.8 +/- 0.8 fmol/mg protein, p < .02). However, no diagnostic subgroup among the suicide victims appeared distinct.

Adolescent↗
PubMed1987

New spiroplasmas from insects and flowers: isolation, ecology, and host association.

Eight spiroplasma strains from insects and one from spring flowers failed to react with antisera specific for any of the 11 described spiroplasma groups, with sera directed against spiroplasma Group I subgroups, or with sera directed against two unnumbered groups previously reported to occur in tabanid flies. Strains, all from Maryland, were isolated from the hemolymph of the spotted cucumber beetle Diabrotica undecimpunctata and the lampyrid beetle Ellychnia corrusca, and the guts of the cantharid beetles Cantharis bilineatus and C. carolinus. Other strains were obtained from a tabanid fly, Tabanus gladiator and from the firefly Photuris pennsylvanica in Maryland and from the mosquito Culex tritaeniorhynchus in Taiwan. An isolate from pooled Cicadulina bipunctella leafhoppers in Syria apparently represented a unique group. A single isolate from spring flowers in Oklahoma also appeared to be unrelated to existing groups or subgroups. One-way deformation tests using sera prepared against known beetle and tabanid spiroplasmas showed each of the above strains to be unique. Although these results strongly indicate that the nine strains studied are representatives of unique new spiroplasma groups, the formal designation of new groups awaits fulfillment of recently proposed criteria.

Animals↗
PubMed1987

Characterization of some new insect-derived acholeplasmas.

Further analysis of three sterol-nonrequiring Mollicutes (strains PS-1, TAC, and YJS) isolated from gut fluids of insects confirms their similarity to Acholeplasma. They are serologically distinct from acholeplasmas of vertebrates and several other sterol nonrequiring Mollicutes isolated from plant surfaces. The PS-1 strain had a DNA G + C content of 31 mol % and a genome size of 1,030 megadaltons (MDa). Optimum temperature is in the range of 23 to 30 C. Thirty-two new nonhelical Mollicutes isolated from a much wider range of insect hosts were examined for acholeplasmas. Twenty-five of the insect isolates were grown consistently in serum-free broth, with or without Tween 80 supplements. Two of the acholeplasmas were serologically related to Acholeplasma florum, 13 strains were serologically identical to the TAC isolate reported earlier, and 10 of the putative acholeplasmas could not be identified with current reference antisera. Seven of the new nonhelical insect isolates appeared to be sterol-requiring Mollicutes. One sterol-requiring isolate (ELCN-1) was recovered from the hemolymph of a firefly, and is the first report of nonhelical Mollicutes in the insect hemocoel. Two of the seven sterol-requiring Mollicutes, which were nonhelical in earlier passages in broth, later reverted to typically helical spiroplasmas. Confirmation of sterol-requiring, nonhelical Mollicutes in insects would provide an important ecological finding that insects constitute an important reservoir for both acholeplasmas and mycoplasmas.

Acholeplasma↗
PubMed1984

Diversity of spiroplasma host-parasite relationships.

Studies of many new mollicutes isolates from insects collected over the last 2 years have suggested a tentative grouping of host-parasite relationships. Those that have been partially studied to date include: 1) temporary gut infection or gut contamination in which the spiroplasmas may survive gut passage with little or no multiplication and with very limited persistence; 2) permanent gut infection in which the host gut is the year-round reservoir; 3) gut infection with hemolymph invasion in which spiroplasmas occur commonly in insect guts but with ability to invade the hemolymph of certain species to which they are pathogenic; and 4) hemolymph infection with noncultivable spiroplasmas in which spiroplasmas occurring in hemolymph or other host tissues are noncultivable.

Animals↗
PubMed1984

Spiroplasmas in the Tabanidae.

Spiroplasmas were observed in seven species of the family Tabanidae (horse flies and deer flies). This is the fifth family of the order Diptera now known to harbor spiroplasmas. Noncultivable spiroplasmas were seen in the hemolymph of three species of the genus Tabanus, and cultivable forms were isolated from the guts of six species in three genera. Isolates from T. calens and T. sulcifrons were serologically similar and closely related to a spiroplasma in the lampyrid beetle, Ellychnia corrusca. These three isolates represent a new serogroup. Isolates from Hybomitra lasiophthalma were related to Group IV strains, while those from T. nigrovittatus and Chrysops sp. both represented new serogroups. At least some tabanids probably acquire spiroplasmas from contaminated flower surfaces. The possibility of vertebrate reservoirs for some tabanid spiroplasmas remains an open question.

Animals↗
PubMed1984

Occurrence and frequency of subgroup I-6 spiroplasma in arthropods associated with old fields in Maryland and Virginia.

The Subgroup I-6 spiroplasma, "Maryland Flower Spiroplasma," originally discovered on fall flowers and subsequently recovered from a syrphid fly and a beetle triungulin, was isolated from two new fall flower hosts and from the guts of nine nectar-imbibing insect species. These data, together with lack of recovery of I-6 spiroplasma from foliage-feeding, plant-sucking, or flightless flower-associated insects, suggest that I-6 spiroplasma may infect and be disseminated by nectar- or pollen-foraging insects, and that the dynamics of maintenance will prove to be complex.

Animals↗
PubMed1982

Influence of chirality of amino acids on the growth of perceived taste intensity with concentration.

Amino acids have markedly different taste properties depending upon their chirality and the structure of their side chains. They can modify the taste quality of foods in which they are found naturally or to which they are added depending on their concentrations. In this study, the influence of chirality of amino acids on the growth in perceived taste intensity with concentration was examined. Serial dilutions of 19 D-amino acids were presented to young subjects who indicated the relative intensities of the dilutions using the magnitude estimation procedure. The slopes of the psychophysical functions for 13 of the 19 D-amino acids which related log concentration and log perceived intensity were greater than the slopes for L-amino acids that have been reported in a previous study. The ratio (average slope D-amino acids)/(average slope L-amino acids) was found to be 1.21. The ratio of the slopes for individual enantiomers bears some relationship to taste quality. No conclusive relationships between the slopes of the psychophysical functions were found with chemical structure of thresholds, however. Implications for receptor mechanisms and nutrition are discussed.

Adolescent↗