PubMed Health⌕ Search

Biomedical subjects

B Kramer

Publications and source records attributed to B Kramer.

At least 127 records · Page 7Linked to original sources
PubMed1987

A microprocessor system for the digital synthesis of pulsed and continuous discharges of electric fish (or animal vocalizations).

Traditionally, the sensitivity of electric fish to electric stimuli has been investigated using a variety of electronically generated signal functions, for example sine, square, and sawtooth waves (both continuous and pulsed). None of these resemble the species- or sex-specific electric organ discharges (EODs) of fish. Therefore, EODs recorded on magnetic tape were used in open-loop playback experiments. However, as shown in the present paper, the waveforms of EODs reproduced from magnetic tape are distorted, and cannot be manipulated with speed and accuracy as to frequency or pulse repetition rate by feedback from the experiment. Good EOD imitations are generated by our microprocessor-based system for the digital synthesis of EODs which is controlled by a small 'personal computer'. Digitized EOD samples edited by computer are output by the fast digital-to-analogue converter of the microprocessor system. This system was devised for the synthesis of pulse-type (discontinuous) and wave type (continuous) EODs with continuous, on-line frequency and amplitude control. The rate of digital synthesis is 500 kHz in pulse-type EODs, and 250-500 kHz in wave type EODs at 0.06-0.24 Hz frequency resolution, depending on the repetition frequency of the synthesized wave EOD. The present paper describes the steps in EOD synthesis, and indicates some applications which benefit from the playback of high-fidelity imitations of natural EODs at amplitudes and frequencies selected by the experimenter, or automatically controlled by feedback from the experiment in closed-loop applications.

Analog-Digital Conversion↗
PubMed1987

The effect of pancreatic mesenchyme on the differentiation of endocrine cells from gastric endoderm.

To determine whether mesenchyme plays a part in the differentiation of gut endocrine cells, proventricular endoderm from 4- to 5-day chick or quail embryos was associated with mesenchyme from the dorsal pancreatic bud of chick embryos of the same age. The combinations were grown on the chorioallantoic membranes of host chick embryos until they reached a total incubation age of 21 days. Proventricular or pancreatic endoderm of the appropriate age and species reassociated with its own mesenchyme provided the controls. Morphogenesis in the experimental grafts corresponded closely to that in proventricular controls, i.e. the pancreatic mesenchyme supported the development of proventricular glands from proventricular endoderm. Insulin, glucagon and somatostatin cells and cells with pancreatic polypeptide-like immunoreactivity differentiated in the pancreatic controls. The latter three endocrine cell types, together with neurotensin and bombesin/gastrin-releasing polypeptide (GRP) cells, developed in proventricular controls and experimental grafts. The proportions of the major types common to proventriculus and pancreas (somatostatin and glucagon cells) were in general similar when experimental grafts were compared with proventricular controls but different when experimental and pancreatic control grafts were compared. Hence pancreatic mesenchyme did not materially affect the proportions of these three cell types in experimental grafts, induced no specific pancreatic (insulin) cell type and allowed the differentiation of the characteristic proventricular endocrine cell types, neurotensin and bombesin/GRP cells. However, an important finding was a significant reduction in the proportion of bombesin/GRP cells, attributable in part to a decrease in their number and in part to an increase in the numbers of endocrine cells of the other types. This indicates that mesenchyme may well play a part in determining the regional specificity of populations of gut endocrine cells.

Animals↗
PubMed1986

Phase II evaluation of diaziquone in gastric and pancreatic cancers. A Southeastern Cancer Study Group Trial.

Seventeen patients with pancreatic carcinoma and 30 patients with gastric carcinoma were treated with diaziquone on days 1 and 8 of repeated 4-week courses. No objective responses were seen. Toxicity was primarily myelosuppression, nausea, and vomiting. Since only 10 chemotherapy-naive patients were treated in each disease category, we do not regard this as a definitive trial, but our experience suggests that this dose schedule is not likely to be useful in these types of cancer.

Aged↗
PubMed1985

Short course prophylactic cranial irradiation for small cell lung cancer.

Ninety-one patients with small cell carcinoma of the lung were given a shortened, intensive course of prophylactic cranial irradiation consisting of 2,000 rad in five fractions. The CNS relapse rate was 21%, but in only one of 91 patients was the brain the first and only site of relapse. Acute toxicities consisting of headache (16%) and nausea and vomiting (15%) were observed. Results are compared with previous results from other studies of cranial irradiation.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1985

Long-term effects of cancer chemotherapy.

As the management of advanced malignancy with multimodality therapy becomes more successful, the practicing general physician will see more chronic and late sequelae of therapy in the cured cancer patient. Chronic or late toxicities may occur in nearly every organ system. This article has briefly described the most common late toxicities that the practicing internist, pediatrician, family physician, and obstetrician/gynecologist should be prepared to recognize.

Adolescent↗
PubMed1984

The gapped duplex DNA approach to oligonucleotide-directed mutation construction.

A simple and efficient method is described to introduce structurally pre-determined mutations into recombinant genomes of filamentous phage M13. The method rests on gapped duplex DNA (gdDNA) molecules of the phage M13 genome as the key intermediate. In this gdDNA, the (+) and the (shorter) (-) strand carry different genetic markers in such a way, that a rigorous selection can be applied for phage carrying the markers of the (-) strand. For introduction of the mutation, a synthetic oligonucleotide with partial homology to a target site within the single stranded DNA region is annealed to the gdDNA. The oligonucleotide subsequently becomes part of the (-) strand by enzymatic DNA gap filling and sealing. This physical linkage is preserved at the genetic level after transfection of a recipient E.coli strain deficient in DNA mismatch correction, so that the synthetic marker can be selected from the phage progeny independent from its potential phenotype. It is demonstrated that by this method mutants can be constructed with marker yields in excess of 70%.

Coliphages↗
PubMed1984

Different base/base mismatches are corrected with different efficiencies by the methyl-directed DNA mismatch-repair system of E. coli.

The efficiency of methyl-directed DNA mismatch-repair of E. coli acting in vivo on heteroduplex genomes of phage M13 was found to be strongly dependent on the nature of the base/base mismatch to be corrected. Three efficiency classes were characterized:high (T/G, C/A and G/G); intermediate (A/A); and low (G/A, A/G, T/T, C/C, C/T and T/C). Methyl-directed DNA mismatch repair was lost completely for any type of mismatch in strains carrying either mutL or mutS mutations. Data obtained with a mutH mutant suggest that this locus is involved in methyl-dependent DNA strand discrimination. A functional correlation is suggested between the differential repair efficiencies and the frequencies of the corresponding replication errors.

Base Composition↗
PubMed1984

The distribution of endocrine cell progenitors in the gut of chick embryos.

The aim of this experiment was to find out whether or not, at early stages of development, progenitors of the various types of gut endocrine cells are localized to one or more specific regions of the gastrointestinal tract. Transverse strips of blastoderm two to four somites in length were excised between the levels of somites 5 and 27 in chick embryos at 5- to 24-somite stages and were cultured as chorioallantoic grafts. The distribution of endocrine cells in the grafts revealed confined localization of progenitor cells only in the case of insulin-immunoreactive cells. The progenitors of cells with somatostatin-, pancreatic polypeptide-, glucagon-, secretin-, gastrin/CCK-, motilin-, neurotensin- and serotonin-like immunoreactivity were distributed along the length of the presumptive gut at the time of explantation; indeed, in many cases they were more widespread than are their differentiated progeny in normal gut of the same age. This finding indicates that conditions in grafts must differ from those that operate in the intact embryo. Also it may explain the occurrence of ectopic gut or pancreatic endocrine cells in tumours of the digestive tract.

Animals↗
PubMed1983

The histological appearance of carbon fibre implants and neo-ligament in man.

The results of this study indicate that a fibrous ingrowth occurs in man after surgical replacement of a tendon or ligament with carbon fibre. This ingrowth resembles normal tendon or ligament very closely, with parallel orientation of collagen fibres and fibroblasts. A multinucleate foreign-body giant-cell response was seen, but it was not possible to ascertain whether the fragmented carbon lay within or on these cells and other macrophagic components. Numerous intact carbon fibres were still present 2 and 3 years after implantation.

Carbon↗