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Biomedical subjects

L Green

Publications and source records attributed to L Green.

At least 217 records · Page 12Linked to original sources
PubMed1987

Consumption-leisure tradeoffs in pigeons: Effects of changing marginal wage rates by varying amount of reinforcement.

Pigeons' rates of responding and food reinforcement under simple random-ratio schedules were compared with those obtained under comparable ratio schedules in which free food deliveries were added, but the duration of each food delivery was halved. These ratio-with-free-food schedules were constructed so that, were the pigeon to maintain the same rate of responding as it had under the simple ratio schedule, total food obtained (earned plus free) would remain unchanged. However, any reduction in responding would reduce total food consumption below that under the simple ratio schedule. These "compensated wage decreases" led to decreases in responding and decreases in food consumption, as predicted by an economic model of labor supply. Moreover, the reductions in responding increased as the ratio value increased (i.e., as wage rates decreased). Pigeons, therefore, substituted leisure for consumption. The relationship between these procedures and negative-income-tax programs is noted.

Journal Article↗
PubMed1987

Qualities and locations of stimuli and responses affecting discrimination learning of chinchillas (Chinchilla laniger) and pigeons (Columba livia).

Chinchillas and pigeons were used as subjects in separate experiments to study interactions among stimulus and response characteristics in discrimination learning. Both the stimuli and the responses could differ with respect to their "quality" and their "location." Bright versus dim lights and upper versus lower lights served as the stimulus qualities and stimulus locations for the chinchillas, respectively. Red versus green lights and upper versus lower lights served as the stimulus qualities and stimulus locations for the pigeons, respectively. Respond versus no-respond and respond-left versus respond-right served as the response qualities and response locations, for both species, respectively. In both experiments, response-quality performance was superior when the discriminative stimuli differed in quality than when they differed in location, whereas response-location performance was superior when the discriminative stimuli differed in location than when they differed in quality. These results were interpreted within the framework provided by a general law of learning, that is, the "quality-location hypothesis."

Animals↗
PubMed1986

Histone gene stability during cellular senescence.

The extent to which human histone gene organization is conserved during the in vitro lifespan of human diploid fibroblast-like cells was determined by comparing the restriction patterns of a human H4 and an H3 histone gene from cells of various in vitro ages. No age related change in the organization of these two genes was detected.

Aging↗
PubMed1986

Opiate withdrawal: inpatient versus outpatient programmes and preferred versus random assignment to treatment.

The relative effectiveness of an inpatient and an outpatient withdrawal programme for opiate addicts was studied. Forty five men and 15 women (mean age 26.13 (SD 5.12) years) took part in the study, all of whom were voluntary patients at the drug dependence clinic of the Maudsley Hospital in London between 1984 and 1985. Subjects were asked if they were prepared to accept either inpatient or outpatient withdrawal, and those who were willing to do so were assigned randomly to the randomised outpatient group or the randomised inpatient group. Those who expressed a strong preference were assigned, as appropriate, to the preferred outpatient group or the preferred inpatient group. Addicts in the inpatient group were more likely to achieve complete withdrawal (25 out of 31, 81%) than those in the outpatient group (five out of 29, 17%). This difference could not be attributed to pretreatment factors related to drugs or to social or psychological differences between the groups. These results have clinical and policy implications for the treatment of opiate addicts.

Adult↗
PubMed1986

The evolution of DNA sequences in Escherichia coli.

It is proposed that certain families of transposable elements originally evolved in plasmids and functioned in forming replicon fusions to aid in the horizontal transmission of non-conjugational plasmids. This hypothesis is supported by the finding that the transposable elements Tn3 and gamma delta are found almost exclusively in plasmids, and also by the distribution of the unrelated insertion sequences IS4 and IS5 among a reference collection of 67 natural isolates of Escherichia coli. Each insertion sequence was found to be present in only about one-third of the strains. Among the ten strains found to contain both insertion sequences, the number of copies of the elements was negatively correlated. With respect to IS5, approximately half of the strains containing a chromosomal copy of the insertion element also contained copies within the plasmid complement of the strain.

Base Sequence↗
PubMed1986

Structural determinants of electroencephalographic findings in acute hemispheric lesions.

We studied electroencephalograms and computed tomographic scans of 54 patients with acute hemispheric strokes. Electrographic parameters evaluated included field, amplitude, frequency, persistence, and reactivity of focal or lateralized slow-wave activity. Ipsilateral and contralateral background activity were also assessed. Structural and clinical features studied were lesion size, density, mass effect, location, tissue involvement, deep structure involvement, level of consciousness, and outcome. The data were analyzed using computer sorting and the chi 2 test. The field, amplitude, and frequency of focal slow-wave abnormalities generally failed to show a specific association with structural details. Continuous focal abnormalities correlated with large lesions (p less than 0.05), mass effect (p less than 0.05), and altered state of consciousness (p less than 0.05). Reactive focal abnormalities were associated with small lesions (p less than 0.05) and the absence of mass effect (p less than 0.02). Ipsilateral background activity abnormalities correlated with lesion size (p less than 0.001) and mass effect (p less than 0.01). Attenuation of ipsilateral background activity was more important than irregularity. Abnormal background activity contralateral to the lesion side was associated with alteration of consciousness (p less than 0.05).

Adult↗
PubMed1986

Progressive sacro-iliac obliteration in Forestier disease.

In 11 patients with Forestier disease 4 were shown to have obliteration of the sacroiliac joints. We suggest that if patients with this disease are observed for a long period ossification of the sacro-iliac joints will be seen, as in ankylosing spondylitis, with loss of sacro-iliac pain when present.

Humans↗
PubMed1986

Empiric use of vancomycin during prolonged treatment-induced granulocytopenia. Randomized, double-blind, placebo-controlled clinical trial in patients with acute leukemia.

Because gram-positive infections cause morbidity following intensive antileukemic chemotherapy, the effects of vancomycin versus placebo were evaluated in a randomized, double-blind, placebo-controlled trial in 60 adult patients with acute leukemia and first infectious fever during prolonged (mean of 32 days) granulocytopenia. Gram-positive sepsis was associated with first fever in 17 (28 percent) of the 60 patients. None of 31 patients randomly assigned to receive vancomycin demonstrated gram-positive infection, whereas 16 of 22 patients randomly assigned to receive placebo subsequently had gram-positive infection (seven had sepsis, and nine had local infections; p less than 0.005). All patients with gram-positive infection were then given vancomycin, and all showed prompt clinical responses. The predominant gram-positive organism causing infection was beta-lactam-resistant Staphylococcus epidermis (19 of 44 isolates). Patients randomly assigned to receive vancomycin had more rapid resolution of first infectious fever and fewer total febrile days during the granulocytopenic course than did patients randomly assigned to receive placebo. Although vancomycin had no effect on the presence or absence of documented fungal infection, patients treated with vancomycin received empiric amphotericin B for recurrent or persistent fever later (mean of 14 days after initial antibiotic coverage was begun) than did patients receiving placebo (mean of 9.9 days; p less than 0.005), and thus received fewer total days of empiric amphotericin B therapy (mean of 16.3 days) than did patients given placebo (mean of 24.6 days; p less than 0.01). These data demonstrate that empiric use of vancomycin reduces the morbidity of gram-positive infections following intensive antileukemic therapy and decreases the need for empiric use of toxic amphotericin B.

Adult↗
PubMed1986

Human histone gene organization. Identification of a histone gene polymorphism prevalent in a black population.

Analysis of the restriction enzyme digests of total genomic DNAs from a broad spectrum of human cell lines and from individuals with different genetic backgrounds, by hybridization with a series of cloned human histone sequences, indicated restriction site polymorphisms (RSPs) for two adjacent human histone genes which reside on chromosome 1. In most cell lines and individuals examined we observed a single 2.05 kb H4 histone HindIII fragment and a 7.0 kb H3 histone HindIII fragment. In contrast, the polymorphisms were manifested as a 2.15 kb H4 HindIII fragment and a 9.1 kb H3 HindIII fragment. From population studies, we were able to show that there is no linkage disequilibrium between these two polymorphic restriction sites. Nor was there any apparent correlation between the presence of the H3/H4 histone polymorphisms and maintenance of the transformed karyotype, passage in culture, transformation or tumor progression. These chromosome 1 H3 and H4 histone gene polymorphisms are common in the American Black population and, in our survey of individuals, were not found in the American Caucasian population. Among the American Blacks studied, the frequency of the H3 HindIII(-) allele is 43% and of the H4 HindIII(-) allele 30%. In limited family studies, we were unable to detect recombination between these two physically linked alleles.

Black People↗
PubMed1986

Severe early malnutrition and DRL performance in the rat.

Rats with a history of severe early malnutrition (6% casein) were compared to well-fed control animals on an ascending series of DRL values ranging from 5 to 60 seconds. The 6% rats who were dietarily-rehabilitated at weaning did not differ from control animals in efficiency, responses per reinforcement or response rate. In contrast, rats chronically exposed to 6% diets performed so poorly during training with continuous reinforcement that they did not advance to even the first DRL (5-sec) condition. These findings show that severely-undernourished rats can perform within normal limits on even high DRL values, provided they are well trained and that they have adequate nutritional rehabilitation.

Animals↗
PubMed1986

Cell cycle-dependent expression of a stable episomal human histone gene in a mouse cell.

We have constructed a recombinant plasmid that includes a cell cycle-dependent human H4 histone gene with 650 base pairs of 5' and 900 base pairs of 3' flanking sequences and the 69% transforming fragment of bovine papilloma virus. When transfected into C127 mouse cells, this plasmid is maintained as a stable episome with approximately 20 copies per cell. Micrococcal nuclease digestion indicates that the episomal human histone gene is packaged as chromatin. The human H4 histone transcript is initiated at the correct 5' start site and undergoes selective destabilization when DNA synthesis is inhibited. When C127 cells containing the episomal H4 histone gene are synchronized, the human H4 histone mRNA levels are regulated coordinately with DNA replication and parallel those of transcripts from the murine chromosomal H4 histone genes. Our results suggest that the regulatory sequences and/or regulatory molecules associated with murine and human histone genes are compatible. The human histone gene-bovine papillomavirus episome is therefore a viable system for studying cell cycle-regulated histone gene expression under conditions where control is not influenced at the site of chromosomal integration by cis-acting elements of genes normally not contiguous.

Animals↗
PubMed1986

Resistance to mercury and to cadmium in chromosomally resistant Staphylococcus aureus.

Apparently chromosomally located mercury resistance determinants in five methicillin-resistant Staphylococcus aureus strains of different geographical origin were structurally homologous to plasmid-located mercury resistance determinants in S. aureus. These were all located on a 6.3-kilobase (kb) Bg/II fragment, as evident from Southern hybridization experiments with the 6.3-kb Bg/II fragment of plasmid pI258 as the probe. These methicillin-resistant S. aureus strains exhibited similar phage susceptibility patterns and biochemical reactions. They differed, however, in the DNA location of the mercury resistance determinants, as evidenced by neighboring cleavage sites for restriction endonucleases EcoRI, HindIII, and PstI. In an environmental (nonhospital) strain in which mercury resistance was also apparently chromosomally conferred, these determinants were also homologous to pI258 DNA, but they were located on a 6.6-kb Bg/II fragment. Cadmium resistance determinants in the five methicillin-resistant S. aureus strains and the environmental S. aureus strain were not similar to the known plasmid-located determinants cadA and cadB. Cd2+ resistance was based on an efflux mechanism for Cd2+. However, no parallel resistance to zinc was conferred. The 3.2-kb XbaI-Bg/II fragment obtained from plasmid pI258 and used as a cadA-specific probe did not hybridize to total DNA digests of the strains with apparently chromosomally determined cadmium resistance.

Cadmium↗
PubMed1985

Joint distribution of insertion elements IS4 and IS5 in natural isolates of Escherichia coli.

A reference collection of natural isolates of Escherichia coli has been studied in order to determine the distribution, abundance and joint occurrence of DNA insertion elements IS4 and IS5. Among these isolates, 36% were found to contain IS4 and 30% were found to contain IS5. Among strains containing IS4 the mean number of copies per strain was 4.4 +/- 0.8; the comparable figure for IS5 was 3.7 +/- 1.0. Although the presence of the elements among the isolates was independent, among those isolates containing both IS4 and IS5, there was a significant negative correlation in the number of copies of the elements. The reference collection was also studied for the presence of the DNA sequences flanking the single copy of IS4 in the chromosome of E. coli K12. Homologous sequences were found in only 26% of the isolates. The sequences flanking the IS4 invariably occur together, and their presence is significantly correlated with the presence of IS4. In eight of the strains that carry these flanking sequences, an IS4 is located between them, and the sequences are present at the homologous position as in the K12 strain. We suggest that IS4 and its flanking sequences share a common mechanism of dissemination, such as plasmids, and we present evidence that they are included in a much larger transposable element.

Base Composition↗