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Biomedical subjects

G Jacobs

Publications and source records attributed to G Jacobs.

At least 19 recordsLinked to original sources
PubMed2001

Dust-acoustic modes in self-gravitating plasmas with dust size distributions.

Using a kinetic description, dust-acoustic waves are considered for dusty plasmas containing, besides the electrons and ions, dust particles with continuous mass (size) distributions. For broad size spectra, self-gravitational effects cannot be neglected anymore because in the competition between electromagnetic and gravitational forces, the scale tips over towards gravitation for the heavier dust grains. Self-gravitational effects are clearly interwoven with the grain size distribution and here the effects of different power-law size distributions on the propagation, damping, and instability of low-frequency waves are discussed.

Journal Article↗
PubMed2001

Kinetic approach to low-frequency waves in dusty self-gravitating plasmas.

A kinetic model is derived for the propagation of low-frequency waves in a dusty plasma containing very heavy dust particles, when the self-gravitational interaction due to these grains is included in the analysis. Analytical expressions for the dispersion function are used to examine the instability and damping of the modes. The stability regions of low-frequency waves are compared in the kinetic and the analogous hydrodynamic models, showing that there are only slight differences. However, the kinetic analysis modifies the growth rates of the Jeans instability and can considerably alter the conditions for the propagation of stable dust modes.

Journal Article↗
PubMed2001

The association of Western flower thrips, Frankliniella occidentalis, with a near Erwinia species gut bacteria: transient or permanent?

Associations between insects and gut bacteria are ubiquitous. It is possible to make a distinction between permanent associations (called symbiosis), in which the same type of bacteria is present in more than one generation of the insect, and transient associations. Transient bacteria are ingested together with food but do not settle in the insect gut in such a way that they will be passed on to the next generation. In this study, we describe the permanent association between Western flower thrips (Frankliniella occidentalis), a polyphagous insect species that is a major pest worldwide, and one type of gut bacteria. On the basis of direct microscopic observations and counts of bacteria, it was found that thrips from the populations studied contained large numbers of bacteria in their hindgut. Bacteria were isolated from their host and grown on 10 different agar media. The number of bacteria isolated on agar media equaled the number of direct counts. All isolates had the same colony morphology. On the basis of their 16S rDNA sequence these bacteria were identified as Enterobacteriaceae, closely related to Escherichia coli. Isolates tested with API 20E biochemical tests were Erwinia species. This was the only type of bacteria found in all thrips individuals on any of the 10 different agar media. Universal primers, which would potentially pick up DNA from any bacterium present in the insect, were applied on crude DNA extracts from thrips with bacteria. We only found 16S rDNA sequences similar to those of the isolated thrips gut bacteria. The same type of bacteria was present in all life stages of the thrips and was found to persist in the thrips populations for at least 2 years (more than 50 generations).

Animals↗
PubMed2001

Growth and transmission of gut bacteria in the Western flower thrips, Frankliniella occidentalis.

The Western flower thrips (Frankliniella occidentalis), a polyphagous insect with global distribution, has a permanent association with a near Erwinia species TAC bacterium in its hindgut. Since this bacterium is able to grow outside the thrips, it is a facultative symbiont that is not completely dependent on the host. In this study we address the question of how the association is maintained and how bacteria are transmitted to newly hatched thrips larvae. Bacteria are passed on to new thrips via the food source. No evidence was found for vertical transmission from mother to offspring via the egg. Gut bacteria show unlimited growth during the larval (feeding) stages, and in the second instar stage 100% of the larvae become infected with high numbers of bacteria. In the prepupal and pupal stage, the number of bacteria declines, but increases again during the adult phase. A method to rear aposymbiotic (bacteria-free) thrips is described which enables studies on the impact of bacteria on the fitness of thrips.

Animals↗
PubMed2001

An early lesion in hepatic carcinogenesis: loss of heterozygosity in human cirrhotic livers and dysplastic nodules at the 1p36-p34 region.

Loss of heterozygosity (LOH) of chromosome 1 has been suggested, by karyotyping, to be an initial episode in human hepatocarcinogenesis. However, this alteration has not yet been investigated in cirrhotic nodules (CNs) or dysplastic nodules (DNs). In an initial study from explanted or resected cirrhotic livers, LOH in 1p36-p32 was examined in 31 hepatocellular carcinomas (HCCs), 25 low-grade dysplastic nodules (LGDNs), and 24 high-grade dysplastic nodules (HGDNs). In HCCs, LOH was detected most frequently at loci D1S2843 (1p36.1) (28.6%), D1S513 (1p34.3) (29.2%), and MYCL1 (1p34.1) (28.6%). In HGDN and LGDN, LOH incidences at D1S513 were 11.1% and 13.6%, respectively. To further refine those results and to determine sequential relationships among CN, DN, and HCC, LOH was next studied in an additional 53 HCCs, 56 HGDNs, 30 LGDNs, and 215 CNs from 11 explanted human cirrhotic livers, including 30 "nodule-in-nodule" lesions. Seven markers between D1S2843 (1p36.12) and MYCL1 (1p34.1), and 1 each at D1S484 (1q24.1), IGF2R-3 (6q26), and TP53 (17p13.1) were used. LOH at D1S2843 and D1S513 was detected in HCCs (20.4% and 23.5%, respectively), HGDNs (7.7% and 18.5%), LGDNs (13.6% and 6.9%), and CNs surrounding either HCCs or DNs (7.4% and 8.3%). These results demonstrate that LOH at D1S2843 and D1S513 are early events in human liver carcinogenesis. Data from CN surrounding either HCCs or DN, and also nodule-in-nodule lesions, provide evidence supporting a CN-->DN-->HCC progression. Different deletion patterns from multiple HCCs and DNs suggest independent origins for carcinogenesis in the same individual.

Chromosomes, Human, Pair 1↗
PubMed2001

Effects of dietary fat and L-carnitine on plasma and whole blood taurine concentrations and cardiac function in healthy dogs fed protein-restricted diets.

OBJECTIVE: To evaluate plasma taurine concentrations (PTC), whole blood taurine concentrations (WBTC), and echocardiographic findings in dogs fed 1 of 3 protein-restricted diets that varied in fat and L-carnitine content. ANIMALS: 17 healthy Beagles. DESIGN: Baseline PTC and WBTC were determined, and echocardiography was performed in all dogs consuming a maintenance diet. Dogs were then fed 1 of 3 protein-restricted diets for 48 months: a low-fat (LF) diet, a high-fat and L-carnitine supplemented (HF + C) diet, or a high-fat (HF) diet. All diets contained methionine and cystine concentrations at or above recommended Association of American Feed Control Officials (AAFCO) minimum requirements. Echocardiographic findings, PTC, and WBTC were evaluated every 6 months. RESULTS: The PTC and WBTC were not significantly different among the 3 groups after 12 months. All groups had significant decreases in WBTC from baseline concentrations, and the HF group also had a significant decrease in PTC. One dog with PT and WBT deficiency developed dilated cardiomyopathy (DCM). Taurine supplementation resulted in significant improvement in cardiac function. Another dog with decreased WBTC developed changes compatible with early DCM. CONCLUSIONS AND CLINICAL RELEVANCE: Results revealed that dogs fed protein-restricted diets can develop decreased taurine concentrations; therefore, protein-restricted diets should be supplemented with taurine. Dietary methionine and cystine concentrations at or above AAFCO recommended minimum requirements did not prevent decreased taurine concentrations. The possibility exists that AAFCO recommended minimum requirements are not adequate for dogs consuming protein-restricted diets. Our results also revealed that, similar to cats, dogs can develop DCM secondary to taurine deficiency, and taurine supplementation can result in substantial improvement in cardiac function.

Animals↗
PubMed2001

Effects of the angiotensin converting enzyme inhibitor benazepril in cats with induced renal insufficiency.

OBJECTIVE: To determine effects of the angiotensin converting enzyme inhibitor benazepril in cats with induced renal insufficiency. ANIMALS: 32 cats. PROCEDURE: Renal mass was surgically reduced, and cats were assigned to 1 of 4 eight-cat groups. Group 1 received placebo, whereas groups 2, 3, and 4 received benazepril hydrochloride orally once daily for approximately 6.5 months at the following doses: group 2, 0.25 to 0.50 mg/kg of body weight; group 3, 0.50 to 1.00 mg/kg; and group 4, 1.00 to 2.00 mg/kg. Arterial blood pressures, glomerular filtration rate (GFR), and renal plasma flow were determined before treatment and during the treatment period. Other determinants of renal hemodynamics were measured by use of micropuncture techniques. Renal biopsy specimens were examined microscopically. RESULTS: Compared with cats that received placebo, mean systolic arterial blood pressure was significantly less and GFR significantly greater in cats that received benazepril. Glomerular capillary pressure and the ratio of efferent to afferent arteriolar vascular resistance were also significantly less in treated cats. However, histologic differences in renal specimens were not detected. CONCLUSIONS AND CLINICAL RELEVANCE: Treatment with benazepril sustained single nephron GFR in remnant nephrons of cats with induced renal insufficiency. Administration of benazepril was also associated with a small but significant reduction in degree of systemic hypertension and an increase in whole kidney GFR. Benazepril may be an effective treatment to slow the rate of progression of renal failure in cats with renal disease.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed2001

Cytosine arabinoside, idarubicin and divided dose etoposide for the treatment of acute myeloid leukemia in elderly patients.

Elderly patients with acute myeloid leukemia (AML) have an unfavourable prognoses due to low remission rates, short remission durations, and a high treatment related toxicity. Therefore, new chemotherapy regimens with curative potential, decreased toxicity, and applicability to the majority of these patients are still needed. For remission induction, AML patients > or = 61 years of age received one to three induction courses of the DIVA regimen (idarubicin 10 mg/m2/d days 1 and 3, etoposide 2 x 60 mg/m2/d every 12 hrs. days 2 to 5, and cytarabine 100 mg/m2/d as continuous i.v. infusion days 1 to 5). After achieving CR, patients received two additional courses of DIVA as consolidation therapy. Forty-two consecutive patients with de novo and secondary AML with a median age of 68 years were entered into this trial while six patients were judged ineligible for medical reasons. 62% of the patients achieved a CR, lasting for a median of 26 weeks. Toxicity was mainly hematologic with an early death rate of 12%. The median overall survival for all patients was 38 weeks, and 51 weeks for the 26 patients who achieved CR. Outcome was not significantly different for patients with de novo compared to secondary AML. In conclusion, DIVA showed a promising antileukemic activity and acceptable toxicity as remission induction therapy for de novo and secondary AML in this negligible selected group of elderly patients. However, relapse rate was high, indicating the need for novel approaches for consolidation and maintenance therapy.

Age Factors↗
PubMed2001

Localization of constitutive nitric oxide synthase isoforms and the nitric oxide target enzyme soluble guanylyl cyclase in the human bladder.

PURPOSE: Nitric oxide is a free radical gas synthesized from L-arginine by a family of isoenzymes called nitric oxide synthase that has an important role in smooth muscle relaxation. L-arginine, the substrate for nitric oxide synthase, may be beneficial under pathophysiological conditions in the bladder, as in interstitial cystitis. We determined the localization of nitric oxide synthase and the target enzyme of NO, soluble guanylyl cyclase, in the human bladder. MATERIALS AND METHODS: Benign bladder tissues were obtained from 18 patients with localized superficial bladder tumors undergoing transurethral bladder resection. Histochemical nicotinamide adenine dinucleotide phosphate-diaphorase staining, nitric oxide synthase immunohistochemical testing and soluble guanylyl cyclase immunoreactivity studies were performed in all benign tissue specimens. RESULTS: A different pattern of nitric oxide synthase expression was confirmed by nicotinamide adenine dinucleotide phosphate-diaphorase staining and immunohistochemical testing for endothelial and neuronal nitric oxide synthase. In addition to endothelial nitric oxide synthase expression, detrusor smooth muscle was recognized as an important location of endothelial nitric oxide synthase, while the urothelium had only small endothelial nitric oxide synthase positive cell clusters. Neuronal nitric oxide synthase expression was only found in nitrinergic fibers of the submucosal surface and between muscle cells. Detrusor and vascular smooth muscle as well as interstitial cells, nerve fibers and transitional epithelium were recognized as targets of nitric oxide, as shown by soluble guanylyl cyclase expression. CONCLUSIONS: The distribution of constitutive nitric oxide synthase isoforms and soluble guanylyl cyclase provides evidence of nitric oxide-cyclic guanosine monophosphate mediated regulation of detrusor smooth muscle relaxation, neurotransmission and blood flow. Furthermore, the urothelium may also be a target of nitric oxide.

Aged↗
PubMed2000

Results of ambulatory electrocardiography in overtly healthy Doberman Pinschers with echocardiographic abnormalities.

OBJECTIVE: To identify, by means of 24-hour ambulatory electrocardiography, electrocardiographic abnormalities in overtly healthy Doberman Pinschers in which results of echocardiography were abnormal. DESIGN: Clinical case series. ANIMALS: 56 (35 male, 21 female) overtly healthy Doberman Pinschers with echocardiographic evidence of cardiomyopathy on initial examination that subsequently died of cardiomyopathy. PROCEDURE: Twenty-four-hour ambulatory electrocardiographic (Holter) recordings obtained at the time of initial examination were reviewed. For all dogs, scan quality was > 90%. RESULTS: Initial Holter recordings of all 56 dogs contained ventricular premature contractions (VPC). Thirty-six (65%) dogs had > 1,000 VPC/24 h, 17 (31%) had > 5,000 VPC/24 h, and 11 (19%) had > 10,000 VPC/24 h. Fifty-four (96%) dogs had couplets of VPC, 37 (66%) had triplets of VPC, and 36 (64%) had episodes of nonsustained (< 30 seconds) ventricular tachycardia. Number of VPC/24 h during the initial Holter recordings was positively correlated with numbers of couplets and triplets of VPC and number of ventricular escape beats and negatively correlated with left ventricular fractional shortening. Twenty-eight dogs died suddenly prior to the putative onset of congestive heart failure. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that along with echocardiography, 24-hour ambulatory electrocardiography can be used to help identify overtly healthy Doberman Pinschers with cardiomyopathy.

Animals↗
PubMed2000

How predatory mites learn to cope with variability in volatile plant signals in the environment of their herbivorous prey.

When the chemical cues co-occurring with prey vary in time and space, foraging predators profit from an ability to repeatedly associate chemical cues with the presence of their prey. We demonstrate the ability of a predatory arthropod (the plant-inhabiting mite, Phytoseiulus persimilis) to learn the association of a positive stimulus (herbivorous prey, Tetranychus urticae) or a negative stimulus (hunger) with a chemical cue (herbivore-induced plant volatiles or green leaf volatiles). It has been suggested that the rate at which the integration of information becomes manifest as a change in behaviour, differs between categories of natural enemies (parasitoids versus insect predators: specialist versus generalist predators). We argue that these differences do not necessarily reflect differential learning ability, but rather relate to the ecologically relevant time scale at which the biotic environment changes.

Animals↗
PubMed1999

Enrichment polymerase chain reaction for the detection of Ki-ras mutations: relevance of Taq polymerase error rate, initial DNA copy number, and reaction conditions on the emergence of false-positive mutant bands.

Screening for oncogene mutations as a marker for malignancy can be a powerful tool for the early diagnosis of cancer. The enrichment polymerase chain reaction (PCR) is a sensitive method for the detection of low-frequency mutations in small samples. However, false-positive results, caused by methodological errors, may have severe clinical implications. When applied to the detection of Ki-ras mutations in pancreatic secretions, the assay sensitivity is limited to approximately 1:1400. Our investigation of Ki-ras mutations in blood samples from patients with pancreatic carcinoma revealed PCR bands presumably derived from mutant Ki-ras in samples from healthy volunteers, while all blood samples of the patients with pancreatic carcinomas showed a wild-type band pattern. Mathematical modeling of the PCR reaction reveals that the rate of false positive PCR results depends on the initial amount of DNA, the Taq polymerase error rate, the number of PCR reaction cycles, reaction efficiency and the restriction endonuclease chosen. The overall error rate of false positive results of the enrichment PCR can be reduced to the square of the rate of a single-step analysis if repeated amplifications of the same DNA specimen show an identical result.

False Positive Reactions↗
PubMed1999

Immunolocalization of inducible and constitutive nitric oxide synthases in human bladder cancer.

OBJECTIVES: Nitric oxide (NO) is synthesized by the enzyme family of NO synthases (NOS) and plays an important role in tumor growth and angiogenesis. NO generation by inducible NOS (iNOS) also influences the cytotoxicity of macrophages and tumor-induced immunosuppression. Before now, the expression of iNOS and constitutive NOS in bladder carcinoma tissue had not been determined. METHODS: Bladder carcinoma tissue specimens were procured from 18 patients (mean age 69.7 years) undergoing transurethral resection. In every patient, tumor biopsies were compared with biopsies of benign bladder regions. Histochemical NADPH-diaphorase staining and NOS immunohistochemistry were performed on all tissue specimens. RESULTS: Positive NADPH-diaphorase staining was detected in all sections from bladder carcinoma tissue. NOS immunohistochemistry showed a different pattern. The malignant epithelial cells were highly iNOS positive. Specimens of bladder mucosa outside of the malignant regions showed only a weak positive iNOS immunostaining. The endothelial cells of abundant precapillary vessels in the stroma of bladder tumors showed a highly positive endothelial NOS (eNOS) immunostaining compared with the stroma of nonmalignant bladder tissue. Neuronal NOS immunoreactivity was only found in nitrinergic fibers in the fibromuscular stroma. CONCLUSIONS: Bladder carcinoma tissue had a high iNOS content; benign tissue did not. NO generation from iNOS in the malignant epithelium and from eNOS in tumor stroma may play different roles in tumor angiogenesis and tumor-induced immunosuppression.

Aged↗
PubMed1999

Neuromuscular function of the latissimus dorsi muscle in goats after dynamic cardiomyoplasty.

Skeletal muscle deterioration is emerging as a limitation to long-term cardiac assist by dynamic cardiomyoplasty. Chronic electrical stimulation of in situ skeletal muscle showed that ischemia, decreased muscle preload, muscle overuse, and chronic electrical stimulation are factors for muscle deterioration. Transposition around the heart has been associated with signs of muscle denervation after chronic electrical stimulation. To evaluate latissimus dorsi muscle neuromuscular function after longterm dynamic cardiomyoplasty, we performed neuromuscular functional analysis and histology on the latissimus dorsi muscle and thoracodorsal nerve of six normal goats and six goats after 6 months of dynamic cardiomyoplasty. Electromyographic analysis showed positive sharp waves and fibrillation potentials in the latissimus dorsi of three goats from the dynamic cardiomyoplasty group. Conduction velocity of the thoracodorsal nerve of goats from the dynamic cardiomyoplasty group (58.32+/-9.80 m/s) was reduced compared to the goats from the control group (71.48+/-5.71 m/s, P = 0.02). Histologic changes in skeletal muscle were compatible with denervation. Loss of myelin sheaths, collapse of endoneurial connective tissue, and solitary foci of axonophagia and myelinophagia further documented severe injury to the thoracodorsal nerve in goats from the dynamic cardiomyoplasty group. The latissimus dorsi muscle wrap was denervated after long-term dynamic cardiomyoplasty. Traction on the neurovascular pedicle at each contraction of the transposed muscle may induce afferent axonal injury of the thoracodorsal nerve resulting in diminished muscular function.

Animals↗
PubMed1998

Neutropenia and thrombocytopenia in three dogs treated with anticonvulsants.

Three dogs became lethargic and had poor appetites within 2 months after anticonvulsant treatment was initiated to control seizures. Dogs were neutropenic, thrombocytopenic, and anemic and had splenomegaly. Sensitivity to phenobarbital and related anticonvulsants may induce life-threatening leukopenia, thrombocytopenia, and anemia in dogs. Phenobarbital-induced neutropenia in these 3 dogs may have posed a risk for developing bacteremia. It is important for clinicians to be aware of adverse effects so that adequate precautions can be taken. A baseline hemogram should always be obtained before starting anticonvulsant treatment, and periodic hemograms should be obtained to monitor animals. Furthermore, client education should include instructions on recognizing signs of bacteremia, thrombocytopenia, and anemia.

Anemia↗
PubMed1998

Fluoroscopic determination of latissimus dorsi muscle shortening fraction after dynamic cardiomyoplasty.

Optimization of the skeletal muscle contraction during cardiac assist is important to achieve maximal cardiac assist and yet avoid overstimulation that may injure skeletal muscle. Dynamic cardiomyoplasty suffers from lack of an objective, reproducible, and accurate technique to measure skeletal muscle shortening fraction after wrap and training of the muscle. A recruitment curve is considered the best way to select the proper stimulation level to achieve supramaximal contraction without overstimulating the muscle. A fluoroscopic technique of determining latissimus dorsi recruitment curve was evaluated in five goats undergoing dynamic cardiomyoplasty with an anterior cardio-subcutaneous wrap. Two pairs of stainless steel targets (0.5 and 1 cm of diameter) were implanted on each side of the muscle wrap. One pair of sonomicrometer crystals was also implanted. Displacement of the targets was measured under fluoroscopy at five different stimulation levels. Correlation coefficients between targets on the inside surface of the wrap and the sonomicrometer crystals, and targets on the outside surface of the wrap and the sonomicrometer crystals were 0.71 (P < 0.05) and 0.60 (P < 0.05), respectively. Targets on the inside surface of the wrap were more accurate than targets on the outside surface of the wrap for measurement of skeletal muscle shortening fraction and establishment of a recruitment curve. Adverse effects from the targets were not observed.

Animals↗
PubMed1997

Comparison of thoracic radiographs with images transmitted via advanced telecommunications equipment.

OBJECTIVE: To compare thoracic radiographs of clinically normal dogs and dogs with mild clinical heartworm disease with images transmitted by a desk-top, two-way audiovisual teleconferencing system. DESIGN: Prospective, matched-set study. STUDY POPULATION: 50 thoracic radiographs from clinically normal and heartworm-infected dogs and the digitally transmitted images of those radiographs. PROCEDURE: Thoracic radiographs from 25 clinically normal dogs and 25 dogs infected with 1 to 24 heartworms were evaluated by 3 clinicians. Using classic criteria for heartworm disease, evaluations of radiographs and images transmitted digitally over 2 high-speed data-transfer telephone lines (56 kilobits/s/line) were performed. Clinicians were asked to determine whether dogs had radiographic signs of heartworm disease. RESULTS: Clinicians' ability to detect heartworm disease did not differ between interpretations of radiographs and those of transmitted images. CLINICAL IMPLICATIONS: Radiographic images transmitted via a teleconference system can be used to provide reliable diagnostic information. Thoracic radiographs can be interpreted at a remote site permitting rapid consultation and immediate advice on clinical management.

Animals↗