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Biomedical subjects

A Keller

Publications and source records attributed to A Keller.

At least 37 records · Page 2Linked to original sources
PubMed2001

Membrane bistability in olfactory bulb mitral cells.

Whole-cell patch-clamp recordings were used to investigate the electrophysiological properties of mitral cells in rat main olfactory bulb brain slice preparations. The majority of mitral cells are bistable. These cells spontaneously alternate between two membrane potentials, separated by approximately 10 mV: a relatively depolarized potential (upstate), which is perithreshold for spike generation, and a relatively hyperpolarized potential (downstate), in which spikes do not occur. Bistability occurs spontaneously in the absence of ionotropic excitatory or inhibitory synaptic inputs. Bistability is voltage dependent; transition from the downstate to the upstate is a regenerative event activated by brief depolarization. A brief hyperpolarization can switch the membrane potential from the upstate to the downstate. In response to olfactory nerve (ON) stimulation, mitral cells in the upstate are more likely to fire an action potential than are those in the downstate. ON stimulation can switch the membrane potential from the downstate to the upstate, producing a prolonged and amplified depolarization in response to a brief synaptic input. We conclude that bistability is an intrinsic property of mitral cells that is a major determinant of their responses to ON input.

Action Potentials↗
PubMed2001

Reliability of the isokinetic trunk extensor test, Biering-Sørensen test, and Astrand bicycle test: assessment of intraclass correlation coefficient and critical difference in patients with chronic low back pain and healthy individuals.

STUDY DESIGN: A reliability study was performed. OBJECTIVE: To determine the intersession reproducibility of the isokinetic trunk extensor strength test, the Biering-Sørensen test, and the Astrand test by calculation of the intraclass correlation coefficient and the critical difference. SUMMARY OF BACKGROUND DATA: Several physical measurements have been used in clinical evaluation of patients with chronic low back pain. Reliability can be evaluated by calculation of either intraclass correlation coefficient or critical difference, but interpretation of the results may vary depending on which method is used. METHODS: For this study, 31 patients with chronic low back pain carried out the isokinetic trunk extensor test, the Biering-Sørensen test, and the Astrand test as also did age- and gender-matched healthy individuals. Measurements were performed in three separate sessions at the same time of the day and by the same experienced examiner. The intervals between the sessions were 5 to 10 days. RESULTS: The isokinetic tests showed a learning effect between Tests 1 and 2. For the isokinetic test, the critical difference increased with increased angular velocities from 28% to 63% in the patients and from 27% to 39% in the healthy subjects. The critical differences for the patients and the healthy individuals were 57% vs 54% for the Biering-Sørensen test and 21% vs 23% for the Astrand test, respectively. The intraclass correlation coefficient ranged from 93% to 98% in the patients and 80%-98% in the healthy individuals. CONCLUSIONS: The reliability was found to be acceptable for the Astrand test and the isokinetic test at 60 degrees per second, as evaluated by the critical difference. All the tests were highly reliable according to the intraclass correlation coefficient, except for Biering-Sørensen test for healthy individuals. The critical difference is the preferable measure because calculation of the intraclass correlation coefficient may give a misleading high estimate of reliability.

Adult↗
PubMed2001

Beta-enolase deficiency, a new metabolic myopathy of distal glycolysis.

A severe muscle enolase deficiency, with 5% of residual activity, was detected in a 47-year-old man affected with exercise intolerance and myalgias. No rise of serum lactate was observed with the ischemic forearm exercise. Ultrastructural analysis showed focal sarcoplasmic accumulation of glycogen beta particles. The enzyme enolase catalyzes the interconversion of 2-phosphoglycerate and phosphoenolpyruvate. In adult human muscle, over 90% of enolase activity is accounted for by the beta-enolase subunit, the protein product of the ENO3 gene. The beta-enolase protein was dramatically reduced in the muscle of our patient, by both immunohistochemistry and immunoblotting, while alpha-enolase was normally represented. The ENO3 gene of our patient carries two heterozygous missense mutations affecting highly conserved amino acid residues; a G467A transition changing a glycine residue at position 156 to aspartate, in close proximity to the catalytic site, and a G1121A transition changing a glycine to glutamate at position 374. These mutations were probably inherited as autosomal recessive traits since the mother was heterozygous for the G467A and a sister was heterozygous for the G1121A transition. Our data suggest that ENO3 mutations result in decreased stability of mutant beta-enolase. Muscle beta-enolase deficiency should be considered in the differential diagnosis of metabolic myopathies due to inherited defects of distal glycolysis.

Humans↗
PubMed2001

Differential stable isotope labeling of peptides for quantitation and de novo sequence derivation.

We have demonstrated the use of per-methyl esterification of peptides for relative quantification of proteins between two mixtures of proteins and automated de novo sequence derivation on the same dataset. Protein mixtures for comparison were digested to peptides and resultant peptides methylated using either d0- or d3-methanol. Methyl esterification of peptides converted carboxylic acids, such as are present on the side chains of aspartic and glutamic acid as well as the carboxyl terminus, to their corresponding methyl esters. The separate d0- and d3-methylated peptide mixtures were combined and the mixture subjected to microcapillary high performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS). Parent proteins of methylated peptides were identified by correlative database searching of peptide tandem mass spectra. Ratios of proteins in the two original mixtures could be calculated by normalization of the area under the curve for identical charge states of d0- to d3-methylated peptides. An algorithm was developed that derived, without intervention, peptide sequence de novo by comparison of tandem mass spectra of d0- and d3-peptide methyl esters.

Algorithms↗
PubMed2001

The muscle-specific enolase is an early marker of human myogenesis.

In higher vertebrates, the glycolytic enzyme enolase (2-phospho-D-glycerate hydrolase; EC 4.2.1.11) is active as a dimer formed from three different subunits, alpha, beta and gamma, encoded by separate genes. The expression of these genes is developmentally regulated in a tissue-specific manner. A shift occurs during development, from the unique embryonic isoform alphaalpha, towards specific isoforms in two tissues with high energy demands: alphagamma and gammagamma in the nervous system, alphabeta and betabeta in striated muscles. The alphaalpha remains widely distributed in adult tissues. Here we report the results of the first extensive study of beta enolase expression during human development. Indeed, the beta subunit is specifically expressed at early stages of human myogenesis. Immunocytochemical analyses demonstrated that it is first detected in the heart of 3-week-old embryos and in the myotomal compartment of somites from 4-week-old embryos. At this stage, the muscle-specific sarcomeric protein titin is expressed in this structure, which will give rise to all body skeletal muscles, but embryonic myosin heavy chain is not yet present. Analyses at the protein level show that, during human ontogenesis, myogenesis is accompanied by an increase in beta enolase expression and by a decrease in the expression of the two other alpha and gamma subunits. Furthermore, beta enolase subunit is expressed in proliferating myoblasts from both embryonic and post-natal muscles. In addition, clonal analysis of primary cell cultures, obtained from the leg muscle of a 7-week-old human embryo, revealed that the beta subunit is present in the dividing myoblasts of all four types, according to the classification of Edom-Vovard et al. [(1999) J Cell Sci 112: 191-199], but not in cells of the non-myogenic lineage. Myoblast fusion is accompanied by a large increase in beta enolase expression. Our results demonstrate that this muscle-specific isoform of a glycolytic enzyme (beta enolase) is among the earliest markers of myogenic differentiation in humans.

Adult↗
PubMed2001

Low-dose theophylline does not exert its anti-inflammatory effects in mild asthma through upregulation of interleukin-10 in alveolar macrophages.

BACKGROUND: There is accumulating evidence that theophylline has anti-inflammatory or immunomodulatory effects. This may be, in part, mediated via an upregulation in the production of the anti-inflammatory cytokine interleukin (IL)-10. We determined whether low-dose theophylline (LDT) would increase the production of IL-10, and attenuate the production of proinflammatory cytokines by alveolar macrophages. METHODS: In a double-blind, placebo-controlled, crossover study involving 15 steroid-free patients with mild asthma, fiberoptic bronchoscopy and bronchoalveolar lavage (BAL) were performed at the end of the treatment and placebo periods. Alveolar macrophages were cultured in vitro, and we measured their release of IL-10, GM-CSF, and TNF-alpha. We also measured IL-10 production in whole blood together with the number of monocytes and T cells expressing intracellular IL-10 by flow cytometry. RESULTS: LDT did not increase the production of IL-10, or attenuate the production of GM-CSF or TNF-alpha by alveolar macrophages. However, after theophylline treatment, there was a significant reduction in mean (SD) (95% CI) BAL eosinophil number from 3.4 (1.7)% (95% CI 2.4-4.4) to 1.7 (1.0)% (95% CI 1.1-2.3) compared with placebo (P<0.05). Similarly, there was no increase in whole-blood IL-10 release or in the number of monocytes and T cells expressing intracellular IL-10 after treatment. CONCLUSIONS: LDT has an anti-inflammatory effect in asthma; however, this effect is not mediated via the production of IL-10 or the attenuation of GM-CSF or TNF-alpha. The mechanisms of theophylline activity remain to be determined.

Adult↗
PubMed2001

[Effect of retinal coagulation status on oxidative metabolite and VEGF in 208 patients with proliferative diabetic retinopathy].

BACKGROUND: Oxidative metabolites and different cytokines are believed to be involved in the pathogenesis of (proliferative) diabetic retinopathy. It was the aim of this study to analyze vitreous body and proliferations of diabetic patients for oxidative metabolites and VEGF und to correlate these values to the retinal coagulation status. PATIENTS AND METHODS: The study was performed in 208 patients vitrectomized for diabetic retinopathy (Type I: n = 114, Type II: n = 94). Grouping of patients was performed according to retinal coagulations status: (1) no or minimal preoperative coagulation [mean coagulation area, CA: 156 mm2], (2) coagulation (scatter laser coagulation und/oder cryopexy) < 3 months before surgery [CA: 589 mm2]. (3) coagulation > 3 months before surgery [CA: 546 mm2]. In the vitreous body and, if present, in the fibrovascular proliferations (Type I: n = 83; Type II: n = 73) the level of lipid peroxides (LPO, measured with two methods) and VEGF was determined. RESULTS: In the vitreous body LPO in group 1 were significantly (P < 0.01 (Type I und II)) higher as compared to other groups. In group 3 LPO were significantly lower as compared to group 2 (P < 0.01 (Typ I) and P < 0.05 (Typ II)). Similar results were observed in the proliferations. In Type I patients VEGF values were significantly (P < 0.01 for group 1 vs. 2 and groups 1/2 vs. 3) reduced following coagulation and coagulation + 3 months. In Type II patients only group 3 was significantly (P < 0.01) different from group 1. In proliferations groups 2 and 3 were significantly different from group 1 (P < 0.05 for Typ I and Type II patients). CONCLUSIONS: The time course of the values leads to the conclusion that oxidative metabolites are able to directly modulate growth activity and to exert this effect via induction of VEGF. This hypothesis has to be confirmed in vitro and by means of a prospective study.

Diabetes Mellitus↗
PubMed2001

Patent foramen ovale presenting as platypnea-orthodeoxia: diagnosis by transesophageal echocardiography.

Platypnea-orthodeoxia is a rare syndrome that is often associated with interatrial shunting through a patent foramen ovale or atrial septal defect. We describe the case of a 65-year-old woman with progressive dyspnea and hypoxia when standing and walking, which was relieved by assuming the recumbent position. The diagnosis was confirmed by tilt-table transesophageal echocardiography demonstrating a large right-to-left shunt through a patent foramen ovale while the patient was in a semiupright position and no significant shunt while in a recumbent position. This case demonstrates that platypnea-orthodeoxia caused by a patent foramen ovale can be clearly demonstrated by the technique of contrast transesophageal echocardiography performed on a tilt table.

Aged↗
PubMed2001

Gap junction proteins in inhibitory neurons of the adult barrel neocortex.

Recent studies indicate that electrical coupling among cortical neurons may persist throughout development; electrophysiological recordings made in cortical slices from young rats reveal that numerous GABAergic neurons are electrically coupled. To determine whether these in vitro findings reflect an inhibitory neural circuit that could be functionally relevant in vivo in adult rodents, we sought to identify whether inhibitory, parvalbumin-containing neurons of the mature cortex express gap junction proteins. Immunohistochemistry was used to examine the laminar distribution of the gap junction-forming proteins connexin 32 (Cx32), connexin 36 (Cx36) and connexin 43 (Cx43) in the somatosensory cortex of the adult mouse. Double labeling immunofluorescence identified Cx32, Cx36 and Cx43 in cortical neurons that were immunoreactive (-ir) for the neuronal markers neurofilament 145 kDa and neuronal nuclei (NeuN). Parvalbumin-ir neurons throughout the cortical laminae were labeled with Cx32-ir, Cx36-ir and Cx43-ir. Stereological methods were used to quantify the extent of parvalbumin colocalization with connexins. Analysis indicated that approximately 40% of parvalbumin-ir neurons were double labeled with either Cx32-ir or Cx43-ir, and approximately 50% of parvalbumin-ir neurons were double labeled with Cx36. These findings establish an anatomical substrate for widespread electrical coupling of neurons in somatosensory cortex and suggest that gap junctions among inhibitory interneurons may persist into adulthood, providing an important mechanism for neuronal communication.

Animals↗
PubMed2001

The deep inferior epigastric perforator free flap for breast reconstruction.

Deep inferior epigastric perforator (DIEP) flap breast reconstruction is an improved method of autologous tissue breast reconstruction with minimal insult to the abdominal wall. This study summarizes the data collected on 148 consecutive DIEP flaps used for breast reconstruction in 109 patients. Of the patients, 90.7% had immediate breast reconstruction after mastectomy, 6.5% had secondary reconstruction, and 2.8% had bilateral reconstruction after having had a mastectomy and having a new primary cancer diagnosed in the remaining breast. A total of 78.7% patients underwent unilateral reconstruction, 21.3% underwent bilateral reconstruction, and 15.7% needed two flaps to make a single larger breast. There was one flap failure. Incidence of fat necrosis was 6.8% and incidence of incisional hernia was 1.4%. The advantages of a free transverse rectus abdominis musculocutaneous flap breast reconstruction are inherent in DIEP flap breast reconstruction. The increased technical effort for DIEP flap reconstruction is offset by the lesser insult to the abdominal wall with maintenance of the entire rectus abdominis muscle.

Adult↗
PubMed2001

Computer-guided, population-based screening system for growth disorders (CrescNet) and on-line generation of normative data for growth and development.

The mean age at which the diagnosis of growth disorders such as Turner's syndrome, growth hormone (GH) deficiency or true GH-dependent gigantism is established is still rather late in many countries around the world. In addition, the question of secular trends in a given population and the rate at which childhood obesity is increasing in industrialized countries make it mandatory to establish a time-adapted system to develop percentiles for body height, weight and body mass index (BMI) and also to develop a screening system for growth disorders. In 1998 we established a network, now involving more than 160 paediatric practices in Germany and seven paediatric endocrinology departments. Paediatricians record heights, weights and growth velocities of all children in their care and systematically feed the data into the database at our centre usually by mailing formatted, structured data tickets. Data are then continuously analysed at the centre and the paediatricians in the network are informed immediately about their individual patients' growth situations via phone or E-mail (feedback system). Regular annual conferences including structured reports, scientific presentations and discussion groups are organized for all participants at our centre. By May 2001, the data of 83,721 children and adolescents had been analysed. The mean values for height were 1-1.5 cm higher than the mean values in the German Synthetic Growth Curve, which serves as an internal standard. However, and most importantly, in comparison with the internal standard and historical normative data from Germany and Switzerland, there is a continuous increase in the 97th percentile for weight and BMI, while the third percentile remains unchanged. In addition, many children with short stature and tall stature due to a variety of endocrine disorders and genetic diseases which had not been diagnosed previously are now being identified. In conclusion, the databank allows for a continuous adaptation of normative curves based on a large number of children in a given population, i.e. eastern Germany. Secondly, the system allows for detection of pathological growth curves and is already serving to diagnose growth disorders in a defined population in a systematic way.

Adolescent↗
PubMed2000

The SM19 gene, required for duplication of basal bodies in Paramecium, encodes a novel tubulin, eta-tubulin.

The discovery of delta-tubulin, the fourth member of the tubulin superfamily, in Chlamydomonas [1] has led to the identification in the genomes of vertebrates and protozoa of putative delta homologues and of additional tubulins, epsilon and zeta [2-4]. These discoveries raise questions concerning the functions of these novel tubulins, their interactions with microtubule arrays and microtubule-organising centres, and their evolutionary status. The sm19-1 mutation of Paramecium specifically inhibits basal body duplication [5] and causes delocalisation of gamma-tubulin, which is also required for basal body duplication [6]. We have cloned the SM19 gene by functional complementation and found that it encodes another new member of the tubulin superfamily. SM19p, provisionally called eta-tubulin (eta-tubulin), shows low sequence identity with the tubulins previously identified in Paramecium, namely, alpha [7], beta [8], gamma [6], delta (this work) and epsilon (P. Dupuis-Williams, personal communication). Phylogenetic analysis indicated that SM19p is not consistently grouped with any phylogenetic entity.

Amino Acid Sequence↗
PubMed2000

[Effects of written intervention on the number of laboratory studies per patient].

In the context of economic measures in health care we followed over a period of nine months the consequences of a written intervention on the attitude of house staff to prescribe laboratory tests. Since it is well known that these tests have a major impact on health costs several studies have been conducted to test whether costs can be reduced without sacrifice of treatment quality. The study was undertaken in 1997. It had three phases of three months duration each: one for observation, one with the intervention and a follow-up phase. The laboratory tests requested by eleven physicians for their patients during the first month after the initial visit were analyzed. During the intervention--phase six physicians chosen at random were informed about their own average as well as that of the entire group (mean of the entire observation period of all physicians). Unexpectedly the hypothesis that the number of laboratory tests requested per patient would drop only in the group of informed physicians and should stay the same for the physicians without this intervention did not materialize. The number of performed tests dropped in both groups.

Attitude of Health Personnel↗
PubMed2000

Long-lasting depolarizations in mitral cells of the rat olfactory bulb.

We investigated the mechanisms of long-lasting depolarizing potentials (LLDs) generated in mitral cells with whole-cell patch recordings in the rat olfactory bulb slice. LLDs occur spontaneously and are evoked by either orthodromic stimulation of the olfactory nerve or antidromic stimulation of mitral and tufted (M/T) cells. LLDs are followed by a long refractory period, limiting LLD generation to approximately 1 Hz. LLD production does not appear to involve either intrinsic voltage-activated or metabotropic mechanisms. The initiation of LLDs requires activation of non-NMDA but not NMDA receptors. Dual recordings from the apical dendrites and somata of mitral cells show that LLDs are generated in the distal portion of the apical dendrite, most likely in the glomerulus. The rising phase of LLDs shows characteristics of polyneuronal input, including a high variability and sensitivity to charge screening. Paired recordings from adjacent mitral cells suggest that LLDs occur synchronously only in cells whose apical dendrites ramify in the same glomerulus. These findings suggest that LLDs involve recurrent, intraglomerular dendrodendritic interactions among M/T cells.

2-Amino-5-phosphonovalerate↗
PubMed2000

Thalamic-evoked synaptic interactions in barrel cortex revealed by optical imaging.

We used optical imaging of voltage-sensitive dye signals to study the spatiotemporal spread of activity in the mouse barrel cortex, evoked by stimulation of thalamocortical afferents in an in vitro slice preparation. Stimulation of the thalamus, at low current intensity, results in activity largely restricted to a single barrel, and to the border between layers Vb and VI. Low concentrations of the GABA(A) receptor antagonist bicuculline increase the amplitude of the optical signals, without affecting their spatiotemporal propagation. Higher concentrations of bicuculline result in paroxysmal activity, which propagates via intracolumnar and intercolumnar excitatory pathways. Enhancing the activity of NMDA receptors, by removing Mg(2+) from the extracellular solution, dramatically alters the spatiotemporal pattern of excitation: activity spreads to supragranular and infragranular layers and adjacent barrel columns. This enhanced propagation is suppressed by the NMDA receptor antagonist AP5. A similar enhancement of activity propagation can be produced by stimulating the thalamus with a short, high-frequency pulse train. Application of AP5 suppresses the frequency-dependent spread of activity. These findings indicate that the spatiotemporal spread of activity in the barrel cortex is altered by varying the temporal patterns of thalamic inputs, via an NMDA receptor-mediated mechanism, and suggest that a similar process occurs during repetitive whisking activity.

2-Amino-5-phosphonovalerate↗
PubMed2000

Psychosocial morbidity: the economic burden in a pediatric health maintenance organization sample.

OBJECTIVES: To evaluate psychosocial morbidity in pediatric primary care and to determine displaced health care utilization. DESIGN AND SETTING: A cross-sectional sample of parent-child dyads was screened using the Pediatric Symptom Checklist (PSC) at 6 pediatric sites of a health maintenance organization (HMO). Cost and utilization data were retrieved from regional databases for this sample. PARTICIPANTS: Parent-child dyads from an HMO in northern California (N = 1840). The children ranged in age from 2 to 18 years. RESULTS: In all, 13.0% of children exhibited psychosocial dysfunction. The rate of children's chronic illness was 18.4%. Multiple regression analyses measured utilization and cost of health and psychiatric care for the selected population for the previous year; the average log cost of health care per child was $393. The average health care cost for children with anxious, depressed symptoms was $805. Chronically ill children were the highest utilizers of health care, with an average log cost of $1138. When psychosocial dysfunction was present, regression models showed that health care spending was highest for young children. CONCLUSIONS: Health care utilization was higher for children with psychosocial morbidity, was higher among younger children, and decreased with age as psychiatric costs progressively increased.

Adolescent↗