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Biomedical subjects

W Berger

Publications and source records attributed to W Berger.

At least 19 recordsLinked to original sources
PubMed1996

Biceps femoris tendon jerk reflexes are enhanced at the end of the swing phase in humans.

The phase-dependent modulation of the biceps femoris (BF) tendon jerk reflexes was investigated in a reduced form of walking. All subjects (12) investigated showed tendon reflexes throughout the whole step cycle but the amplitude was largest in the middle and late swing phase of the ipsilateral leg. It is concluded that the normally occurring BF burst at end swing could be due to stretch-induced activity.

Electromyography↗
PubMed1996

Medial gastrocnemius is more activated than lateral gastrocnemius in sural nerve induced reflexes during human gait.

In humans the sural nerve was stimulated at one of 16 phases of the step cycle. In MG (medial gastrocnemius) the amplitude of the P2 responses (latency 80-93 ms) was on average 1.3 times larger than the corresponding background activity while this was 0.9 for LG (lateral gastrocnemius; predominantly suppressive responses). It is speculated that such differences contribute to an exorotation moment during gait.

Adult↗
PubMed1996

Specific genetic deficiencies of the A and B isoenzymes of monoamine oxidase are characterized by distinct neurochemical and clinical phenotypes.

Monoamine oxidase (MAO) exists as two isoenzymes and plays a central role in the metabolism of monoamine neurotransmitters. In this study we compared the neurochemical phenotypes of previously described subjects with genetically determined selective lack of MAO-A or a lack of both MAO-A and MAO-B with those of two subjects with a previously described X chromosome microdeletion in whom we now demonstrate selective MAO-B deficiency. Mapping of the distal deletion breakpoint demonstrates its location in intron 5 of the MAO-B gene, with the deletion extending proximally into the Norrie disease gene. In contrast to the borderline mental retardation and abnormal behavioral phenotype in subjects with selective MAO-A deficiency and the severe mental retardation in patients with combined MAO-A/MAO-B deficiency and Norrie disease, the MAO-B-deficient subjects exhibit neither abnormal behavior nor mental retardation. Distinct neurochemical profiles characterize the three groups of MAO-deficient patients. In MAO-A-deficient subjects, there is a marked decrease in deaminated catecholamine metabolites and a concomitant marked elevation of O-methylated amine metabolites. These neurochemical changes are only slightly exaggerated in patients with combined lack of MAO-A and MAO-B. In contrast, the only biochemical abnormalities detected in subjects with the MAO-B gene deletion are a complete absence of platelet MAO-B activity and an increased urinary excretion of phenylethylamine. The differences in neurochemical profiles indicate that, under normal conditions, MAO-A is considerably more important than MAO-B in the metabolism of biogenic amines, a factor likely to contribute to the different clinical phenotypes.

Adult↗
PubMed1996

Dissection of the vertebral artery with cervical nerve root lesions.

Vertebral artery dissection may cause upper limb peripheral motor deficit. We report three young patients presenting with nuchal pain followed by a nearly painless proximal paresis of the arm several days later. The cause, as detected by colour-coded Duplex sonography and MRI, was an extracranial dissection of the vertebral artery. The proximity of the intervertebral segment to the vertebral artery and the nerve roots indicated that compression by an intramural haematoma was the likely cause of the disorder. Subsequent examinations during anticoagulation treatment showed almost complete disappearance of the intramural haematoma and of the neurological deficits within a few weeks. We believe that the occurrence of an upper limb peripheral motor deficit should be added to the spectrum of potentially misleading signs of vertebral artery dissection.

Adult↗
PubMed1996

A comparative study of unsedated transnasal esophagogastroduodenoscopy and conventional EGD.

BACKGROUND: A significant portion of the cost and complications associated with conventional esophagogastroduodenoscopy (EGD) is attributed to conscious intravenous sedation, which usually results in loss of work on the day of the endoscopy. Earlier studies have described the feasibility and safety of unsedated transnasal EGD in normal volunteers. METHODS: We compared the diagnostic yield and patient acceptability of this new technique performed first, with conventional EGD performed second in 24 outpatients. RESULTS: The sensitivity of transnasal EGD was 89% and its specificity was 97%. Transnasal EGD was more acceptable and less stressful to the patients than conventional EGD (p < 0.05). Oxygen saturation and blood pressure did not change during transnasal EGD. CONCLUSION: Transnasal EGD is feasible, safe, and well tolerated by patients. Specificity of transnasal EGD is similar to, but its sensitivity is lower than, conventional EGD. By eliminating the need for sedation-related work loss and postprocedural monitoring, transnasal EGD potentially is more cost-effective than conventional EGD.

Adult↗
PubMed1996

An animal model for Norrie disease (ND): gene targeting of the mouse ND gene.

In order to elucidate the cellular and molecular processes which are involved in Norrie disease (ND), we have used gene targeting technology to generate ND mutant mice. The murine homologue of the ND gene was cloned and shown to encode a polypeptide that shares 94% of the amino acid sequence with its human counterpart. RNA in situ hybridization revealed expression in retina, brain and the olfactory bulb and epithelium of 2 week old mice. Hemizygous mice carrying a replacement mutation in exon 2 of the ND gene developed retrolental structures in the vitreous body and showed an overall disorganization of the retinal ganglion cell layer. The outer plexiform layer disappears occasionally, resulting in a juxtaposed inner and outer nuclear layer. At the same regions, the outer segments of the photoreceptor cell layer are no longer present. These ocular findings are consistent with observations in ND patients and the generated mouse line provides a faithful model for study of early pathogenic events in this severe X-linked recessive neurological disorder.

Amino Acid Sequence↗
PubMed1996

Identification of a gene disrupted by a microdeletion in a patient with X-linked retinitis pigmentosa (XLRP).

The gene for the most frequent from of X-linked retinitis pigmentosa (XLRP), RP3, has been assigned by genetic and physical mapping to a segment of less than 1000 kbp, which is flanked by the marker DXS1110 and the ornithine transcarbamylase (OTC) gene. In search of microdeletions, we have screened the DNA of 30 unrelated patients with XLRP by employing a representative set of YAC-derived DNA fragments that were generated by restriction enzyme digestion and PCR amplification. In one of these patients, a 6.4 kbp microdeletion was detected which was not present in the DNA of 444 male controls. A cosmid contig spanning the deletion was constructed and used to isolate cDNAs from retina-specific libraries. Exons corresponding to these expressed sequences as well as other putative exons were identified by sequencing more than 30 kbp of the critical region. So far, no point mutations in these putative exon sequences have been identified.

Cell Line↗
PubMed1996

Positional cloning of the gene for X-linked retinitis pigmentosa 3: homology with the guanine-nucleotide-exchange factor RCC1.

The gene for retinitis pigmentosa 3 (RP3), the most frequent form of X-linked RP (XLRP), has been mapped previously to a chromosome interval of less than 1000 kbp between the DXS1110 marker and the OTC locus at Xp21.1-p11.4. Employing a novel technique, YAC Representation Hybridization (YRH)', we have recently identified a small XLRP associated microdeletion in this interval, as well as several putative exons including the 3' end of a gene that was truncated by the deletion. cDNA library screening and sequencing of a cosmid centromeric to the deletion has now enabled us to identify numerous additional exons and to detect several point mutations in patients with XLRP. The predicted gene product shows homology to RCC1, the guanine-nucleotide-exchange factor (GEF) of the Ras-like GTPase Ran. Our findings suggest that we have cloned the long-sought RP3 gene, and that it may encode the GEF of a retina-specific GTP-binding protein.

Amino Acid Sequence↗
PubMed1996

[Experimental studies of the biomechanics of scaphoid screws].

The purpose of this study was to determine the anchoring forces of four commonly used scaphoid screws in synthetic polyurethane foam. A linear relation was found between the length of the probe and the anchoring forces. The leading thread of the Herbert screw showed a anchoring force of 54 N/mm, the trailing thread 80 N/mm, and the Ulrich screw 75 N/mm. This linear relation of the shaft screws was only relevant upto a border probe length no longer that of the thread. Furthermore, it is valid for screws with continuous threads up to a probe length of 12 mm respectively. The cortical screw developed an anchoring force of 59 N/mm and the cancellous screw, 63 N/mm. With short probes of 4 and 6 mm, the trailing threads of the Herbert and Ulrich screws have the best anchoring forces, with values of 319 N/399 N and 307 N/435 N, respectively. The forces necessary for extraction of the tested scapoid bone screws placed in 8 mm polyurethane cubes were between 404 N and 527 N and were narrowly distributed. An additional conclusion of this study was that the application of screws with flat ends (Herbert and Ulrich screws) which were placed perpendicular to the dense material layer, significantly increased the anchoring forces.

Bone Screws↗
PubMed1996

A mathematical model of temperature distribution in frozen tissue.

A computer simulation for a frozen region expansion around a cryoprobe in liver tissue is presented and compared with experimental measurements in liver tissue. Both the analytical solution under simplifying assumptions and the numerical solution of the heat equation were tested. No analytical solution is possible when studying the freezing process in the time scope of minutes. The problem is that the solution needs spherical coordinate transformation, which is singular in the origin. For the frozen region, the analytical solution is not constrained, and conclusions are unrealistic. Neither does it account for the cryoprobe diameter. The numeric solution to the same problem is much more informative. It adopts the natural boundary conditions that are the constant temperatures of both the cooling medium and the bath. Comparisons between the numerical solution and experimental measurements show good approximation of the problem by the model of temperature distribution in a homogeneous medium which freezes around a cryoprobe. Differences were smaller than the apparent measurement errors. Our approach allows relevant results to be obtained within the time period available during the surgery.

Animals↗
PubMed1995

Benzothiazepine binding domain of purified L-type calcium channels: direct labeling using a novel fluorescent diltiazem analogue.

We have synthesized a series of N-propylamino-substituted benzazepinones (NPSBs) as specific probes for the benzothiazepinone (BTZ) binding domain of muscle L-type calcium channels (LTCCs). NPSBs were identified which possess high affinity for the channel after purification. We synthesized a fluorescent NPSB, DMBODIPY-BAZ, as the first benz(othi)azepinone derivative known to reversibly label partially purified LTCCs. DMBODIPY-BAZ binds to the partially purified channel with high affinity (Kd = 25 nM, Bmax = 580 pmol/mg of protein). Fluorescence resonance energy transfer (FRET) occurred between tryptophan residues of the channel protein and the DMBODIPY fluorophore upon specific drug binding. FRET was exploited to allow highly time-resolved detection of specific drug binding kinetics. We found that the dissociation half-life (t1/2) of DMBODIPY-BAZ decreased with the concentration of an unlabeled competitor, which indicates ligand-induced accelerated dissociation. In contrast, t1/2 was concentration-dependently increased by the dihydropyridine (DHP) (+)-isradipine. These kinetic properties of DMBODIPY-BAZ indicate that a high-affinity BTZ binding domain also exists on purified LTCCs. NPSBs represent novel tools to provide further insight into the molecular pharmacology of the BTZ binding domain on LTCCs.

Animals↗
PubMed1995

Linkage analysis in a Dutch family with X-linked recessive congenital stationary night blindness (XL-CSNB).

Linkage analysis has been performed in a large Dutch pedigree with X-linked recessive congenital stationary night blindness (CSNB) by utilizing 16 DNA markers from the proximal short arm of the human X chromosome (Xp21.1-11.2). Thirteen polymorphic markers are at least partially informative and have enabled pairwise and multipoint linkage analysis. For three loci, i.e. DXS228, the monoamine oxidase B gene and the Norrie disease gene (NDG), multipoint linkage studies have yielded maximum lod scores of > 3.0 at a recombination fraction of zero. Analysis of recombination events has enabled us to rule out the possibility that the underlying defect in this family is allelic to RP3; the gene defect could also be excluded from the proximal part of the region known to carry RP2. Linkage data are consistent with a possible involvement of the NDG but mutations in the open reading frame of this gene have not been found.

Chromosome Mapping↗
PubMed1995

Gating of sensation and evoked potentials following foot stimulation during human gait.

To investigate how gait influences the perceived intensity of cutaneous input from the skin of the foot, the tibial or sural nerves were stimulated at the ankle during walking or running on a treadmill. As compared to standing, the detection threshold for these stimuli was raised by more than 30% during the locomotion tasks. During walking, there was a phase-dependent modulation in perceived intensity of suprathreshold stimuli (1.5, 2, or 2.5 x PT). Stimuli given just prior to footfall were perceived as significantly above average (Wilcoxon signed-rank test). In contrast there was a significant phasic decrease in sensitivity for shocks delivered immediately after ipsi- and contralateral footfall. The amplitude of somatosensory evoked potentials (P50-N80 complex), simultaneously evoked from pulse trains to the sural nerve and recorded at scalp level, was, on average, 62% of the level during standing. During gait, the amplitude of this complex was significantly smaller just after footfall than the amplitude during late swing (MANOVA). It is suggested that the reduced sensation and the decreased evoked potentials after touchdown may be due to occlusion or masking by concomitant afferent input from the feet. On the other hand, the phasic increase in sensitivity at the end of swing is thought to result from a centrally generated facilitation of sensory transmission of signals in anticipation of foot-placing.

Adult↗
PubMed1995

Modulation of sural nerve somatosensory evoked potentials during stance and different phases of the step-cycle.

In order to investigate the modulation of somatosensory processing during stance and locomotion, sural nerve somatosensory evoked potentials were recorded during both stance and different phases of the step-cycle. Characteristic sequences of negative-positive waves were elicited, consisting of an early component, N40, presumably of subcortical origin, followed by a P50-N80-P220 complex of cortical origin. The N40 and N40-P50 components had similar amplitudes in both gait and stance. However, the P50-N80 component was attenuated whereas the N80-P220 complex became biphasic during gait. Within the step-cycle, amplitudes of the cortical components P50-N80 and N80-P110 were larger prior to footfall and smaller at the beginning of the support phase. The results demonstrate that locomotion produces a modulatory effect on somatosensory input at a cortical level. Within the step-cycle, excitability of the somatosensory cortex is increased during the middle and late swing phases and decreased during the support phase. Such modulation may contribute to an improved detection of foot contact at touchdown.

Adult↗
PubMed1995

Leg muscle activation during gait in Parkinson's disease: adaptation and interlimb coordination.

Adaptation in leg muscle activity and coordination between lower limbs were studied during walking on a treadmill with split belts in one group of parkinsonian patients and one of age-matched healthy subjects. Four different belt speeds (0.25/0.5/0.75/1.0 m/sec) were applied in selected combinations to the left and right leg. While these walking conditions were easily tolerated by the healthy subjects, the parkinsonian patients usually reached the limits of their walking capabilities. Both groups adapted automatically to a change in belt speed within approximately 20 stride cycles. Healthy subjects adapted by reorganizing their stride cycle with a relative shortening of duration of support and lengthening of the swing phase of the "fast" leg and vice versa on the "slow" leg. The patients showed a restricted range of stride frequencies for the various belt speeds during normal and split-belt walking with consequent deviations in the reorganization of the stride cycle. In both healthy subjects and patients, ipsilateral gastrocnemius and contralateral tibialis anterior electromyographic (EMG) activity increased predominantly with an ipsilateral increase in belt speed. Two main differences were observed in the EMG patterns: (1) In the patients leg muscle EMG activity was less modulated and gastrocnemius EMG amplitude was small during normal and split-belt walking. However, there was no significant difference between the two groups in respect to the reorganization of the EMG pattern required for the various split-belt walking conditions. (2) The amount of co-activation of antagonistic leg muscles during the support phase of the stride cycle was greater in the patients compared to the healthy subjects during normal and split-belt walking. It is suggested that reduced EMG modulation and recruitment in the leg extensors may contribute to the impaired walking of the patients. This in turn is a result of an impaired proprioceptive feedback from extensor load receptors. This defective control is partially compensated for in parkinsonian patients by a greater amount of leg flexor activation which leads to a higher degree of co-activation. Visual input plays a role in the control of this increased activation.

Adaptation, Physiological↗