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Biomedical subjects

B Kramer

Publications and source records attributed to B Kramer.

At least 37 records · Page 2Linked 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↗
PubMed1982

Cancer chemotherapy associated symptomatic stomatitis: role of Herpes simplex virus (HSV).

The relationship between oral shedding of Herpes simplex virus (HSV) and cytotoxic cancer chemotherapy was studied. HSV seropositive outpatients receiving cytotoxic chemotherapy had HSV recovered from throat washings in eight of 114 patients (7.0%), significantly more often than HSV seropositive outpatients with malignancy who were not receiving cytotoxic chemotherapy (one of 91 patients; 1.1%; P = 0.04). Twenty-eight HSV seropositive chemotherapy patients and 11 HSV seropositive healthy hospital personnel were studied serially 2-3 times per week over a 3-4 week period for oral HSV shedding. Although a comparable percentage of each group shed HSV at least once (57.1% of chemotherapy patients versus 36.4% of controls), chemotherapy patients had a strikingly higher incidence of multiple positive cultures: 40/218 attempts (18.7%) versus 4/156 attempts (2.6%) for controls (P less than 10(-5)). Among chemotherapy patients who developed clinically evident stomatitis, 12 of 14 (85.7%) had HSV recovered compared to four of 14 (28.6%) without lesions (P = 0.004). We conclude that while oral mucosal HSV infection is associated with symptomatic stomatitis following chemotherapy, HSV does not account for all mucosal lesions in chemotherapy patients.

Antibodies, Viral↗
PubMed1982

Acute and long-term effects of captopril on exercise cardiac performance and exercise capacity in congestive heart failure.

Although many studies have shown that captopril (CPT) provides acute hemodynamic improvement in patients with severe congestive heart failure (CHF) at rest, little information is available concerning exercise hemodynamic responses to CPT or the effect of this drug on exercise tolerance in CHF. Therefore, we evaluated the hemodynamic effects of CPT at rest and during upright bicycle exercise in 15 patients with stable CHF. CPT (25 to 50 mg) reduces both resting heart rate and mean arterial pressure (84 +/- 11 to 78 +/- 7 bpm, p less than 0.025 and 85 +/- 9 to 64 +/- mm Hg, p less than 0.001). Concomitantly, left ventricular filling pressure dropped dramatically (26 +/- 9 to 15 +/- 7 mm Hg, p less than 0.001), while cardiac and stroke indices rose (2.0 +/- 0.5 to 2.5 +/- 0.6 L/min/m2, p less than 0.001, and 25 +/- 8 to 33 +/- 7 ml/m2, p less than 0.001). Similar directional changes occurred during exercise, with heart rate, mean arterial pressure, and left ventricular filling pressure at maximum exercise being less (123 +/- 15 to 115 +/- 16 bpm, p less than 0.01; 93 +/- 17 to 86 +/- 14 mm Hg, p less than 0.05; and 35 +/- 10 to 30 11 mm Hg, p less than 0.001, respectively) after CPT ingestion. Peak exercise cardiac index rose slightly (3.6 +/- 0.7 to 3.9 +/- 0.6 L/min/m2) but not significantly. Six patients followed long term on CPT underwent elective recatheterization after 3 months. In these, the beneficial hemodynamic changes seen acutely persisted or further improvement was noted, both at rest and during exercise. Most impressively, peak exercise cardiac index rose from 3.6 +/- 0.7 to 4.6 +/- 1.0 L/min/m2 (p less than 0.05), and this was associated with an increase in exercise duration (8.0 +/- 2.2 to 11.5 +/- 1.4 minutes, p less than 0.05) and exercise work load (332 +/- 32 to 468 +/- 52 kp-m/min, p less than 0.05). These findings indicate that in patients with severe CHF, oral CPT provides markedly beneficial augmentation of cardiac function during activity as well as at rest; moreover, chronic CPT therapy substantially increases exercise capacity in this setting.

Aged↗
PubMed1980

Is there a ventral neural ridge in chick embryos? Implications for the origin of adenohypophyseal and other APUD cells.

Two- to ten-somite chick embryos were studied in order to ascertain whether, as has been proposed, there exists a 'ventral neural ridge' which gives rise to the hypophyseal (Rathke's) pouch. Serial sections and stereo-microscopy were used. The neural ridges arch around the rostral end of the embryo onto the ventral surface of the head, but no evidence was found for their extension to form a 'ventral neural ridge' reaching the stomodaeum: in fact a considerable expanse of non-thickened surface ectoderm was seen to separate the ventral portions of the neural ridges from the stomodaeum. The thickening of neural ectoderm which does appear on the ventral surface of the head results from apposition and fusion of the opposite neural ridges flanking the neural plate and thus the tip of the anterior neuropore--the classically accepted mode of closure of the neuropore. These findings are in accord with the generally accepted concept of the origin of the hypophyseal pouch rather than with its derivation from a 'ventral neural ridge'. No sign of neural crest formation was encountered ventrally; this observation excludes the possibility that endocrine cells of the APUD series could originate from neural crest in this region.

APUD Cells↗