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Biomedical subjects

M Hammer

Publications and source records attributed to M Hammer.

At least 55 records · Page 3Linked to original sources
PubMed1999

Optimised sample preparation of synovial fluid for detection of Chlamydia trachomatis DNA by polymerase chain reaction.

OBJECTIVE: To optimise sample preparation of synovial fluid for Chlamydia trachomatis (CT) specific polymerase chain reaction (PCR). METHODS: Serial dilutions of purified CT elementary bodies in synovial fluid were prepared. The synovial fluid pellet was processed by eight different methods of sample preparation. Then samples were analysed by CT specific PCR. The sensitivity of PCR was the basis of ranking of the eight different methods. RESULTS: Highest sensitivity was achieved by methods including an additional step of DNA isolation. Additional extraction of protein and polysaccharides by cetyltrimethylammonium bromide (CTAB) increased sensitivity. Addition of hyaluronidase did not increase sensitivity of QIAEX-DNA extraction but was necessary, however, before phenol-chloroform-DNA extraction. CONCLUSIONS: The method of synovial fluid sample preparation significantly influences the sensitivity of subsequent PCR. Additional DNA isolation and extraction of PCR inhibitors by CTAB led to higher sensitivity.

Cetrimonium↗
PubMed1999

IA in Kenyon cells of the mushroom body of honeybees resembles shaker currents: kinetics, modulation by K+, and simulation.

Cultured Kenyon cells from the mushroom body of the honeybee, Apis mellifera, show a voltage-gated, fast transient K+ current that is sensitive to 4-aminopyridine, an A current. The kinetic properties of this A current and its modulation by extracellular K+ ions were investigated in vitro with the whole cell patch-clamp technique. The A current was isolated from other voltage-gated currents either pharmacologically or with suitable voltage-clamp protocols. Hodgkin- and Huxley-style mathematical equations were used for the description of this current and for the simulation of action potentials in a Kenyon cell model. Activation and inactivation of the A current are fast and voltage dependent with time constants of 0.4 +/- 0.1 ms (means +/- SE) at +45 mV and 3.0 +/- 1.6 ms at +45 mV, respectively. The pronounced voltage dependence of the inactivation kinetics indicates that at least a part of this current of the honeybee Kenyon cells is a shaker-like current. Deactivation and recovery from inactivation also show voltage dependency. The time constant of deactivation has a value of 0.4 +/- 0.1 ms at -75 mV. Recovery from inactivation needs a double-exponential function to be fitted adequately; the resulting time constants are 18 +/- 3.1 ms for the fast and 745 +/- 107 ms for the slow process at -75 mV. Half-maximal activation of the A current occurs at -0.7 +/- 2.9 mV, and half-maximal inactivation occurs at -54.7 +/- 2.4 mV. An increase in the extracellular K+ concentration increases the conductance and accelerates the recovery from inactivation of the A current, affecting the slow but not the fast time constant. With respect to these modulations the current under investigation resembles some of the shaker-like currents. The data of the A current were incorporated into a reduced computational model of the voltage-gated currents of Kenyon cells. In addition, the model contained a delayed rectifier K+ current, a Na+ current, and a leakage current. The model is able to generate an action potential on current injection. The model predicts that the A current causes repolarization of the action potential but not a delay in the initiation of the action potential. It further predicts that the activation of the delayed rectifier K+ current is too slow to contribute markedly to repolarization during a single action potential. Because of its fast activation, the A current reduces the amplitude of the net depolarizing current and thus reduces the peak amplitude and the duration of the action potential.

Action Potentials↗
PubMed1999

Acute airway effects of formaldehyde and ozone in BALB/c mice.

1. Concentration and time-effect relationships of formaldehyde and ozone on the airways were investigated in BALB/c mice. The effects were obtained by continuous monitoring of the respiratory rate, tidal volume, expiratory flow rate, time of inspiration, time of expiration, and respiratory patterns. 2. With concentrations up to 4 p.p.m., formaldehyde showed mainly sensory irritation effects of the upper airways that decrease the respiratory rate from a trigeminal reflex. The no-effect level (NOEL) was about 0.3 p.p.m. This value is close to the human NOEL, which is about 0.08 p.p.m. 3. Ozone caused rapid, shallow breathing in BALB/c mice. Later on, the respiratory rate decreased due to another vagal response that indicated an incipient lung oedema. The NOEL in mice was about 1 p.p.m. during 30 min of ozone exposure. No major effect occurs in resting humans at about 0.4 p.p.m. 4. Thus, the upper airway irritant, formaldehyde, and the deep lung irritant, ozone, showed the same types of respiratory effects in humans and in BALB/c mice. Also, the sensitivity was nearly identical. Continuous monitoring of respiratory effects in BALB/c mice, therefore, may be a valuable method for the study of effects of other environmental pollutants, which, however, should be confirmed in further studies.

Animals↗
PubMed1998

[Detection of Borrelia DNA in urine using polymerase chain reaction in rheumatologic laboratory diagnosis of Lyme borreliosis].

Borrelia burgdorferi specific DNA has been detected by polymerase chain reaction (PCR) in different specimens of patients with Lyme disease (LD). The aim of the present study is to evaluate PCR-diagnostic of urine specimens regarding rheumatologic diagnosis of Lyme disease. Urine specimens of 77 patients (LD, n = 34; undifferentiated arthritis (UA), n = 25; arthralgia/myalgia (AM), n = 18) and 15 controls were investigated. Flagellin gene (60 specimens) or OspA-plasmid (32 specimens) were used as targets. Sensitivity of the flagellin-nested-PCR was 27%, by OspA-nested-PCR only one positive PCR result was found. Despite of low sensitivity PCR enabled the correct diagnosis of LD in two patients classified as UA. Therefore, PCR can give valuable hints in single cases if LD is clinically suspected.

Adult↗
PubMed1998

Different genetic components in the Ethiopian population, identified by mtDNA and Y-chromosome polymorphisms.

Seventy-seven Ethiopians were investigated for mtDNA and Y chromosome-specific variations, in order to (1) define the different maternal and paternal components of the Ethiopian gene pool, (2) infer the origins of these maternal and paternal lineages and estimate their relative contributions, and (3) obtain information about ancient populations living in Ethiopia. The mtDNA was studied for the RFLPs relative to the six classical enzymes (HpaI, BamHI, HaeII, MspI, AvaII, and HincII) that identify the African haplogroup L and the Caucasoid haplogroups I and T. The sample was also examined at restriction sites that define the other Caucasoid haplogroups (H, U, V, W, X, J, and K) and for the simultaneous presence of the DdeI10394 and AluI10397 sites, which defines the Asian haplogroup M. Four polymorphic systems were examined on the Y chromosome: the TaqI/12f2 and the 49a,f RFLPs, the Y Alu polymorphic element (DYS287), and the sY81-A/G (DYS271) polymorphism. For comparison, the last two Y polymorphisms were also examined in 87 Senegalese previously classified for the two TaqI RFLPs. Results from these markers led to the hypothesis that the Ethiopian population (1) experienced Caucasoid gene flow mainly through males, (2) contains African components ascribable to Bantu migrations and to an in situ differentiation process from an ancestral African gene pool, and (3) exhibits some Y-chromosome affinities with the Tsumkwe San (a very ancient African group). Our finding of a high (20%) frequency of the "Asian" DdeI10394AluI10397 (++) mtDNA haplotype in Ethiopia is discussed in terms of the "out of Africa" model.

Black People↗
PubMed1998

A data reduction scheme for improving the accuracy of oxygen saturation calculations from spectrometric in vivo measurements.

A developing tool in ophthalmological research and practice is the study of the oxygen saturation in retinal vessels because this measurement contains important diagnostic information about the metabolism at the human ocular fundus. Imaging spectrometry enables locally resolved measurements of the oxygen saturation simultaneously in arteries and veins. The vessel reflex, imaging errors of the detection system and the noise of the signal result in substantial uncertainties in the calculated data. We present a data processing method for the improvement of the primary information leading to a reduction of the uncertainties of the derived oxygen saturation.

Biometry↗
PubMed1998

Respiratory effects in mice exposed to airborne emissions from Stachybotrys chartarum and implications for risk assessment.

Stachybotrys chartarum, a mycotoxin producing mould found in some damp buildings, was grown in aluminum dishes in closed exposure chambers. The loading factor, 5.12 m2/m3, corresponded to 2.8 times the loading in a normal room with all surfaces covered by mould. Sensory irritation, bronchoconstriction and pulmonary irritation effects were investigated using a sensitive mouse bioassay in which the airway reactions were measured plethysmographically. Little effect was seen from the vapours in agreement with the predicted effects of the low concentrations of volatile organic compounds measured. Even under the influence of an airflow about four times that measured in normal buildings, the concentration of liberated spores and other particles was very low, corresponding to the biological effects observed, and probably reflecting the high water content of the substrate. These results demonstrate that many factors are important for the transport of biologically active mould metabolites from building material to occupants and that no direct relationship may exist between immediate biological effects and surface area covered with mould. Therefore, risk assessments should be based on estimated effects of emitted vapours, effects of liberated particles, e.g. sensitization potentials of the mould spores and effects of the generated metabolites (mycotoxins).

Air Microbiology↗
PubMed1997

The mouse calretinin gene promoter region: structural and functional components.

The 5' flanking region of the mouse calretinin gene was cloned and a 1.8 kbp region adjacent to exon 1 was sequenced. Putative upstream promoter and enhancer elements were identified, including appropriately positioned TATA and CAAT boxes (positions -50 and -68, respectively). There was considerable sequence and structural homology between mouse and human upstream elements. Neuron-restrictive activity was demonstrated via transfection of calretinin promoter-reporter constructs into primary embryonic mouse brain cultures expressing calretinin. In promoterless reporter constructs, the proximal upstream 1.5 kbp of the mouse calretinin gene boosted luciferase activity (up to 100-fold) exclusively in the neuronal population. Deletion analysis revealed the minimal promoter to be within the 95-bp proximal to the transcription start site. Transfections with SV40 promoter constructs in these cultures resulted in reporter gene expression predominantly in non-neuronal cells. Inserting the proximal 1.5 kbp of mouse calretinin upstream in SV40 promoter-reporter constructs reduced luciferase activity. Thus, calretinin upstream sequences increased reporter expression in cultured neurons and decreased expression from the SV40 promoter in non-neuronal cultured brain cells. The calretinin promoter contained relevant regulatory element consensus motifs and demonstrated in vitro neuron-restrictive bioactivity.

3T3 Cells↗
PubMed1997

The neural basis of associative reward learning in honeybees.

Appetitive learning of food-predicting stimuli, an essential part of foraging behavior in honeybees, follows the rules of associative learning. In the learning of odors as reward-predicting stimuli, an individual neuron, one of a small group of large ascending neurons that serve principal brain neuropiles, mediates the reward and has experience-dependent response properties. This implies that this neuron functions as an integral part of associative memory, might underlie more complex features of learning, and could participate in the implementation of learning rules. Moreover, its structural properties suggest that it organizes the interaction of functionally different neural nets during learning and experience-dependent behavior.

Animals↗
PubMed1997

[An experimental study on the use of the Hilbert operator as a method of signal preprocessing for the determination of oxygen saturation in retinal vessels].

For the non-invasive measurement of the oxygen saturation in human retinal vessels, the light reflected by a vessel and its surroundings is evaluated. Differences in the absorption and scattering properties of the optical media provide so-called vessel profiles, but the central vessel section is often disturbed by a regular reflex. In order to eliminate this reflex, a method based on the Hilbert transform is presented, which can be used for the determination of logarithmic differences between the reflected light on and that beside the vessel. The data for our investigations were produced by simulation of the radiation transport in multi-layered tissue. A linear regression between expected and measured values based on 40 pairs was used for the evaluation of the proposed method. A linear relationship was shown to exist.

Anisotropy↗
PubMed1997

Complex retinal detachment treated with silicone oil or sulfur hexafluoride gas: a randomized clinical trial.

BACKGROUND AND OBJECTIVE: To determine if either silicone oil or sulfur hexafluoride gas (SF6) is superior to the other in the treatment of complex retinal detachment after previously failed vitreous surgery. PATIENTS AND METHODS: In this randomized clinical trial, 18 patients received treatment with silicone oil and 16 patients received SF6. The primary outcome was defined as successful anatomic attachment of the retina. Secondary outcomes included the time to retinal detachment, visual acuity, anatomic macular attachment, and any complications of surgery. RESULTS: The odds of successful reattachment with silicone oil were 50% greater than they were with SF6, but this difference was not statistically significant. There were no differences between the two groups in any of the secondary outcomes. CONCLUSIONS: This study did not have enough statistical power to detect a small but clinically important difference between the two treatment groups. Physicians must use their clinical judgment to select a vitreal substitute for complex retinal detachment when clinical trials are inconclusive. Data pooling is one method of overcoming the limitation of clinical trials with small sample sizes.

Adolescent↗
PubMed1996

[Long-term outcome of managing medial femoral neck fractures with ceramic head endoprostheses].

Total hip replacement is often recommended for the treatment of femoral neck fractures in elderly patients. A less invasive approach with shorter operating time is the replacement of the femoral head only, leaving the acetabular cartilage in situ. Hemiarthroplastic hip replacement using a metallic head prosthesis was not successful in the past, because the majority of patients developed protrusio acetabuli after surgery. In the present study hemiarthroplastic hip replacement using an Al2O3-ceramic head was shown to be a useful method for the treatment of femoral neck fractures in elderly patients. From 1985 to 1990 277 patients were treated with hemiarthroplasty. The average age at the time of accident and operation was 81.7 years. At the time of follow-up in 1993 only 77 survivors were available for examination. A standardized score was calculated assessing activity, gait, hip pain, etc., with the patients obtaining an average score of 58 out of possible 78 points. Only three patients had hip pain, and in four cases the roentgenographic examination revealed protrusio acetabuli. Two of these four patients underwent revision surgery for replacement of the cup, leaving the stem in situ. In view of the small number of approach-related complications, hemiarthroplastic hip replacement using an Al2O3-ceramic head is the recommended surgical treatment for femoral neck fractures in elderly patients. In the rare patient with protrusio acetabuli, revision surgery can be performed to replace the cup, leaving the stem in situ.

Activities of Daily Living↗
PubMed1996

Sensory irritation mechanisms investigated from model compounds: trifluoroethanol, hexafluoroisopropanol and methyl hexafluoroisopropyl ether.

Quantitative structure-activity relationships (QSAR) have suggested the importance of hydrogen bonding in relation to activation of the sensory irritant receptor by nonreactive volatile organic chemicals. To investigate this possibility further, three model compounds with different hydrogen bond acidity, trifluoroethanol, hexafluoroisopropanol and methyl hexafluoroisopropyl ether, were selected for study. The potency of each chemical is obtained from the concentration necessary to reduce respiratory rate in mice by 50% (RD50). The RD50 values obtained were: methyl hexafluoroisopropyl ether (> or = 160,000 ppm), trifluoroethanol (11,400-23,300 ppm), and hexafluoroisopropanol (165 ppm). QSAR showed that trifluoroethanol and methyl hexafluoroisopropyl ether behaved as predicted as nonreactive sensory irritants, whereas hexafluoroisopropanol was much more potent than predicted. The higher than predicted potency of hexafluoroisopropanol could be due to a coupled reaction, involving both strong hydrogen bonding and weak Brönsted acidity. A concerted reaction could thus be more efficient in activation of the receptor. Hydrogen bonding properties and concerted reactions may be important in the activation of the sensory irritant receptor by nonreactive volatile organic chemicals.

1-Propanol↗
PubMed1996

Behavioral, neural and cellular components underlying olfactory learning in the honeybee.

A top-down approach as applied to learning and memory in honeybees provides the opportunity of relating different levels of complexity to each other, and of analyzing the rules and mechanisms from the viewpoint of the respective next higher level. Olfactory conditioning of harnessed bees exemplifies essential elements of associative learning and, in general, forms a bridge between the systems and the cellular levels of analysis. Intracellular recordings of identified neurons during olfactory conditioning play a key role in this effort. They allow testing of the assumptions made by modern behavioral theories of associative learning and provide access to cellular and molecular studies, owing to the identification of their transmitters and the peculiarities of the connectivities. Analysis at this intermediate level of complexity is particularly profitable in the bee, because essential neural elements of the associative network are known and can be tested during ongoing learning behavior. In this respect, the honeybee offers unique properties for the building of bridges between the molecular, cellular, neuronal, network and behavioral levels of associative learning.

Animals↗