Biomedical subjects

H Schnyder

Publications and source records attributed to H Schnyder.

At least 19 recordsLinked to original sources

PubMed2005

Partitioning respiration of C3-C4 mixed communities using the natural abundance 13C approach--testing assumptions in a controlled environment.

Contributions of C3 and C4 plants to respiration of C3-C4 ecosystems can be estimated on the basis of their contrasting 13C discrimination. But accurate partitioning requires accurate measurements of the isotope signature of whole system respiratory CO2 (deltaR), and of its members (delta3 and delta4). Unfortunately, experimental determination of representative delta3 and delta4 values is virtually impossible in nature, generating a need for proxies (surrogates) of delta3 and delta4 values (e.g., the delta of leaf biomass). However, recent evidence indicates that there may be systematic differences among the delta of respiratory and biomass components. Thus, partitioning may be biased depending on the proxy. We tested a wide range of biomass- and respiration-based delta proxies for the partitioning of respiration of mixed Lolium perenne (C3) - Paspalum dilatatum (C4) stands growing at two temperatures inside large 13CO2/ 12CO2 gas exchange chambers. Proxy-based partitioning was compared with results of reference methods, including (i) the delta of whole plant respiratory CO2 (delta3 and delta4) or (ii) respiration rate of intact C3 and C4 plants. Results of the reference methods agreed near perfectly. Conversely, some proxies yielded erroneous partitioning results. Partitioning based on either the delta of shoot or root respiratory CO2 produced the worst bias, because shoot respiratory CO2 was enriched in 13C by several per thousand and root respiratory CO2 was depleted by several per thousand relative to whole plant respiratory CO2. Use of whole plant or whole shoot biomass delta gave satisfactory partitioning results under the constant conditions of the experiments, but their use in natural settings is cautioned if environmental conditions are variable and the time scales of respiration partitioning differ strongly from the residence time of C in biomass. Other biomass-based proxies with faster turnover (e.g., leaf growth zones) may be more useful in changing conditions.

Carbon↗

PubMed2005

The plant's capacity in regulating resource demand.

Regulation of resource allocation in plants is the key to integrate understanding of metabolism and resource flux across the whole plant. The challenge is to understand trade-offs as plants balance allocation between different and conflicting demands, e.g., for staying competitive with neighbours and ensuring defence against parasites. Related hypothesis evaluation can, however, produce equivocal results. Overcoming deficits in understanding underlying mechanisms is achieved through integrated experimentation and modelling the various spatio-temporal scaling levels, from genetic control and cell metabolism towards resource flux at the stand level. An integrated, interdisciplinary research concept on herbaceous and woody plants and its outcome to date are used, while drawing attention to currently available knowledge. This assessment is based on resource allocation as driven through plant-pathogen and plant-mycorrhizosphere interaction, as well as competition with neighbouring plants in stands, conceiving such biotic interactions as a "unity" in the control of allocation. Biotic interaction may diminish or foster effects of abiotic stress on allocation, as changes in allocation do not necessarily result from metabolic re-adjustment but may obey allometric rules during ontogeny. Focus is required on host-pathogen interaction under variable resource supply and disturbance, including effects of competition and mycorrhization. Cost/benefit relationships in balancing resource investments versus gains turned out to be fundamental in quantifying competitiveness when related to the space, which is subject to competitive resource exploitation. A space-related view of defence as a form of prevention of decline in competitiveness may promote conversion of resource turnover across the different kinds of biotic interaction, given their capacity in jointly controlling whole plant resource allocation.

Energy Metabolism↗

PubMed1999

[Effective treatment of a large muscle hernia by local botulinum toxin administration].

A 53-year-old patient developed an impairing muscle hernia when a fascia lata graft was harvested as a substitute for a cruciate ligament of the knee and closure of the defect was not possible. The fascial defect enlarged with time, extending along the whole upper leg. The large muscle protrusion and incarceration in the distal fascial slit was extremely painful during walking and getting up from a chair. Since autologous grafts were disregarded because of the high tissue pressure and alloplastic substitutes seemed problematic, the large hernia was successfully reduced by local muscle denervation with injections of botulinum-A toxin into the protruding vastus lateralis muscle. This procedure achieved relief of pain and enabled the patient to walk without complaints. Side effects were not observed.

Botulinum Toxins, Type A↗

PubMed1999

Fluxes of reserve-derived and currently assimilated carbon and nitrogen in perennial ryegrass recovering from defoliation. The regrowing tiller and its component functionally distinct zones

The quantitative significance of reserves and current assimilates in regrowing tillers of severely defoliated plants of perennial ryegrass (Lolium perenne L.) was assessed by a new approach, comprising 13C/12C and 15N/14N steady-state labeling and separation of sink and source zones. The functionally distinct zones showed large differences in the kinetics of currently assimilated C and N. These are interpreted in terms of "substrate" and "tissue" flux among zones and C and N turnover within zones. Tillers refoliated rapidly, although C and N supply was initially decreased. Rapid refoliation was associated with (a) transient depletion of water-soluble carbohydrates and dilution of structural biomass in the immature zone of expanding leaves, (b) rapid transition to current assimilation-derived growth, and (c) rapid reestablishment of a balanced C:N ratio in growth substrate. This balance (C:N, approximately 8.9 [w/w] in new biomass) indicated coregulation of growth by C and N supply and resulted from complementary fluxes of reserve- and current assimilation-derived C and N. Reserves were the dominant N source until approximately 3 d after defoliation. Amino-C constituted approximately 60% of the net influx of reserve C during the first 2 d. Carbohydrate reserves were an insignificant source of C for tiller growth after d 1. We discuss the physiological mechanisms contributing to defoliation tolerance.

Journal Article↗

PubMed1999

Pre-Anthesis Reserve Utilization for Protein and Carbohydrate Synthesis in Grains of Wheat.

We assessed the contribution of pre-anthesis reserve C to protein and carbohydrate deposition in grains of wheat (Triticum aestivum L.) using a new approach comprised of steady-state (13)C/(12)C labeling and separation of the protein and carbohydrate fractions of mature grains. Experiments were performed with two spring wheat cultivars (Kadett and Star) grown with differential N fertilizer supply over 2 years. Pre-anthesis reserves contributed between 30% and 47% of the C in protein and 8% to 27% of the C in carbohydrates of grains. Partitioning of pre-anthesis C among the grain fractions was strongly dependent on the C/N (w/w) ratio in mobilized pre-anthesis biomass (r(2) = 0.92). There appeared to be no significant exchange of pre-anthesis C between amino acids and carbohydrates during redistribution. The mean apparent efficiency of mobilized carbohydrate-C use in grain filling (ME(CHO), estimated as the mass of pre-anthesis C deposited in grain carbohydrates per gram of pre-anthesis C mobilized from carbohydrates in vegetative plant parts) was 0.72, whereas that of protein-C (ME(P)) was 0.56. However, ME(P) and ME(CHO) varied among treatments. ME(CHO) increased with increasing contributions of water-soluble carbohydrates to total pre-anthesis carbohydrate mobilization. ME(P) decreased with increasing residence time of protein in vegetative biomass. Possible causes for variability of ME(P) and ME(CHO) are discussed.

Journal Article↗

PubMed1998

Corticosteroid-responsive postmalaria encephalopathy characterized by motor aphasia, myoclonus, and postural tremor.

OBJECTIVES: To study the clinical spectrum of an acute severe encephalopathy occurring in 2 patients after recovery from falciparum malaria infection and to compare it with the reported clinical features of the postmalaria neurological syndrome. DESIGN: Case report. SETTING: Tertiary care hospital. PATIENTS: Two patients presented with acute onset of fluctuating motor aphasia, severe generalized myoclonus, and postural tremor. Additional signs were cerebellar ataxia, and in 1 patient, generalized epileptic seizures. Magnetic resonance imaging of the brain revealed patchy white matter lesions in 1 patient. Clinically, the patients' conditions continued to worsen until corticosteroids were introduced, the use of which induced a rapid, albeit incomplete, recovery. CONCLUSIONS: We describe a new, severe variant of the still poorly defined postmalaria neurological syndrome. We propose a preliminary classification of this syndrome, according to its clinical characteristics, as follows: a mild or localized form, characterized by isolated cerebellar ataxia or postural tremor; a diffuse, but relatively mild encephalopathic form, characterized by acute confusion or epileptic seizures; and a severe, corticosteroid-responsive encephalopathy that is characterized by motor aphasia, generalized myoclonus, postural tremor, and cerebellar ataxia.

Adrenal Cortex Hormones↗

PubMed1995

[Creutzfeldt-Jakob disease].

Creutzfeldt-Jakob's disease is a transmissible encephalopathy manifesting with dementia and motor disturbances, which usually progresses rapidly and is lethal within months. It occurs mainly sporadically, but it can also be transmitted by proteinaceous infective particles called prions. The diagnosis has to rely on clinical symptoms, EEG and brain biopsy being the most suitable additional examinations. No therapy is yet known. "Naturally" occurring transmission has not been observed: all transmitted cases reported so far have been iatrogenic and followed administration of cadaveric hypophyseal hormones, transplantation of tissue from CNS or related organs, or brain surgery with contaminated instruments. Remarkable discoveries in the past decades with respect to the molecular and genetic characterization of the transmissible pathogen have led to a new understanding of the disease. The infective agent appears to be an abnormal isoform of a physiologically occurring protein: the cellular prion (PrPc). The crucial pathogenetic event is the conformational conversion of PrPc into its pathological isoform (PrPsc), an event thought to be triggered autocatalytically by the infectious agent itself. The disease can be elicited in experimental animals by inoculation of PrPsc. In the sporadic cases of Creutzfeldt-Jakob's disease, PrPsc is thought to arise through spontaneous conversion of PrPc. A growing body of evidence indicates that specific alleles of the prion gene confer a genetic predisposition to Creutzfeldt-Jakob's disease and to related pathologies.

Adult↗

PubMed1994

[The diagnostic significance of additional electrophysiological studies in suspected neurogenic thoracic outlet syndrome].

The neurogenic thoracic outlet syndrome (TOS) is a controversial clinical entity, since unambiguous diagnostic criteria are lacking and abnormal findings are absent in many patients. To evaluate electrodiagnostic methods a retrospective analysis was done comprising all 75 patients with suspected TOS who had been examined electrophysiologically in our laboratory in the last 5 years. 35 of the 75 patients were finally diagnosed as having TOS, but only 10 of them had a corresponding electrophysiological pathology. 6 had "classic" TOS with clinically obvious sensorimotor deficits, whereas in 4 the electrophysiologic findings were the only abnormalities (in 3 of 4, only minor neurographic anomalies were found). Proximal motor stimulation techniques did not improve the diagnostic yield. We conclude that electrodiagnostic methods are of little value in the diagnosis of TOS if there are no clinical abnormalities. The electrophysiological examinations did however reveal distal entrapment neuropathies in 15 of 75 patients (12 carpal tunnel syndromes). The frequent detection of such neuropathies in our patients is interesting and it justifies per se electrodiagnostic examination of the patient with suspected TOS.

Adolescent↗

PubMed1992

[The treatment of hemifacial spasm using botulinum toxin].

Hemifacial spasm is a disagreeable disturbance with involuntary unilateral twitching of the facial muscles. Its most common form is supposedly due to an irritation of the facial nerve at its proximal intracranial segment by vascular structures. Various forms of treatment including surgical procedures are employed, very often without satisfactory results but frequently involving the risk for severe complications. For a few years a new method has been using injection of botulinum toxin into the affected muscles, which in the majority of patients relieves the abnormal movements for about half a year; therefore, this very effective and secure procedure is recommended as first-line treatment of hemifacial spasm.

Adult↗

PubMed1991

[Benign, focal amyotrophy].

Benign focal amyotrophy is a usually asymmetrical motor neuron disease affecting young people. Its favourable prognosis differentiates it from progressive motor neuron diseases such as the much more frequent and most severe form, amyotrophic lateral sclerosis (ALS). We report on one patient with "juvenile muscular atrophy of unilateral upper extremity" of the Hirayama type and two patients with selective amyotrophy of one calf ("wasted leg-syndrome"). In addition, we have observed three young women with selective muscle atrophy in the scapula region which has appeared stable for many years and might represent another entity of so-called benign focal amyotrophy.

Adult↗

PubMed1989

Growth rates and assimilate partitioning in the elongation zone of tall fescue leaf blades at high and low irradiance.

Tall fescue (Festuca arundinacea Schreb.) leaf blades elongated 33% faster at continuous low than at continuous high irradiance (60 versus 300 micromoles per second per square meter photosynthetic photon flux density) when temperature of the leaf elongation zone was held constant at 21 degrees C. Increased rate of elongation was associated with a near proportional increase in length of the elongation zone (+38%). In contrast, growth in width and thickness was decreased at low irradiance, resulting in only a 12% increase in leaf area production and 5% less total growth-associated water deposition than at high irradiance. At low irradiance dry matter (DM) import into the elongation zone was 28% less, and 55% less DM was used per unit leaf area produced. DM use in synthesis of structural components (i.e. DM less water-soluble carbohydrates) was only 13% less at low irradiance, whereas water-soluble carbohydrates (WSC) deposition was 43% less. The lower rate of WSC deposition at low irradiance was associated with a higher net rate of monosaccharide deposition (+39%), whereas net deposition rates for sucrose (-27%) and fructan (-56%) were less than at high irradiance. Still, at low irradiance, net fructan accumulation accounted for 64% of WSC deposition, i.e. 25% of DM import, demonstrating the high sink strength of the leaf elongation zone.

Journal Article↗

PubMed1988

Diurnal growth of tall fescue leaf blades : I. Spatial distribution of growth, deposition of water, and assimilate import in the elongation zone.

Tall fescue leaf blades elongate at near constant rates during most of the light and dark periods of the diurnal cycle, with the dark rate being higher by 60 to 65%. Our objective was to determine relationships among diurnal rates of leaf elongation, deposition of water and deposition of dry matter (DM) into the elongation zone. Two separate experiments were conducted, both with a 15-hour photoperiod and constant 21 degrees C at the growth zone. Increased rates of leaf elongation in darkness were due to proportionally increased rates of elongation of 4-millimeter segments of the elongation zone. Length of the total elongation zone was 30 millimeters in both light and darkness. The spatial distribution of water contents in the elongation zone varied little during the diurnal cycle. Thus, dark stimulation of leaf elongation rate (+65%) and of water deposition (+77%) into elongation zones were similar. Water content per unit leaf length increased by 50% between the basal and distal limits of the elongation zone, indicating that tissue also grew in the lateral and vertical dimensions. Longitudinal growth of tissue, however, allowed 5 to 7 times more water deposition into the elongation zone than growth in cross-sectional area. This relationship was similar in light and darkness. In both light and darkness net rates of DM deposition (microgram per millimeter leaf length per hour) increased from the zone of cell division towards the region of most active elongation, 10 to 15 millimeters from the ligule, then decreased towards the distal end of the elongation zone. Net DM deposition rates (microgram per hour) integrated over the 30-millimeter elongation zone were similar during light and darkness. Thus, DM in the elongation zone was diluted during darkness as a result of increased water deposition. Net DM deposition rates at and above the distal end of the elongation zone were clearly positive during the light, but were close to zero or negative in darkness. Thus, DM deposition into the elongation zone and the adjacent recently expanded tissue was differentially affected in the diurnal cycle, DM deposition occurred in both tissues in light, but was restricted to the elongation zone in darkness.

Journal Article↗

PubMed1988

Diurnal Growth of Tall Fescue Leaf Blades : II. Dry Matter Partitioning and Carbohydrate Metabolism in the Elongation Zone and Adjacent Expanded Tissue.

The spatial distributions of net deposition rates of water soluble carbohydrate-free dry matter (WSC-free DM) and WSC were evaluated within and above the elongation zone of tall fescue (Festuca arundinacea Schreb.) leaf blades during light and darkness. Imported DM used for WSC-free DM synthesis during darkness (67% of the total in experiment I and 59% in experiment II) was greater than during light (47% in both experiments), suggesting that the 65% higher leaf elongation rate during darkness was accompanied by higher rates of synthesis of cellular structural components. Deposition rates of WSC in the basal and central part of the elongation zone (0-20 mm from the ligule) were similar during light and darkness, but above 20 millimeters WSC deposition occurred during light and WSC loss occurred during darkness. WSC deposition and loss throughout the elongation zone and the recently expanded tissue were mostly due to net synthesis and degradation of fructan. Fructan was predominantly low molecular weight and contributed about 50% of the total osmotic partial pressure of WSC. In the most actively growing region, where fructan synthesis was most rapid, no diurnal change occurred in molecular weight distribution of fructan. WSC solute concentrations were diluted in the most actively growing tissue during darkness because net monosaccharide and fructan deposition were unaltered and sucrose deposition was decreased, but growth-associated water deposition was increased by 77%. Net rates of fructan synthesis and degradation were not related to tissue sucrose concentration, but appeared to respond to the balance between assimilate import and assimilate use in synthesis of cellular structural components (i.e. WSC-free DM) and deposition of monosaccharides. Fructan synthesized in tissue during most active elongation was degraded when the respective tissue reached the distal limit of the elongation zone where assimilate import in darkness was insufficient to maintain synthetic processes associated with further differentiation of cells.

Journal Article↗

PubMed1987

Assessment of spatial distribution of growth in the elongation zone of grass leaf blades.

Knowledge about the spatial distribution of growth is essential for understanding the leaf growth process. In grasses the elongation zone is located at the base of the leaf blade and is enclosed by sheaths of older leaves. Assessment of spatial growth distribution, therefore, necessitates use of a destructive method. We used a fine needle to make holes through bases of tillers at the location of the leaf elongation zone of tall fescue (Festuca arundinacea Schreb.), then measured the displacement of the holes after a 6 or 24 h interval. Needle holes caused a 22 to 41% decrease in daily leaf elongation so experiments were conducted to investigate if the spatial distribution of growth in the elongation zone was altered. Leaf elongation rate was reduced similarly when needle holes were made within or above the zone where cell elongation occurs. Distribution of elongation within the zone was the same when estimated by displacement of needle holes or ink marks placed on the epidermis of the elongation zone after surrounding tissue had been removed. Making holes at different locations within the elongation zone did not differentially affect the relative contribution of the damaged or undamaged parts to leaf elongation. These findings demonstrate that needle holes or ink marks in paired leaves can be used to estimate the relative distribution of growth in the elongation zone of undamaged tall fescue leaf blades.

Journal Article↗

PubMed1987

Growth Rates and Carbohydrate Fluxes within the Elongation Zone of Tall Fescue Leaf Blades.

Investigations were performed to better understand the carbon economy in the elongation zone of tall fescue leaf blades. Plants were grown at constant 21 degrees C and continuous 300 micromoles per square meter per second photosynthetic photon flux density where leaf elongation was steady for several days. Elongation occurred in the basal 20 mm of the blade (0-20 millimeters above the ligule) and was maximum at 9 to 12 millimeters. Eight 3-millimeter long segments were sampled along the length of the elongation zone and analyzed for water-soluble carbohydrates. Sucrose concentration was high in the zone of cell division (0-6 millimeters) whereas monosaccharide concentration was high at and distal to the location where cell elongation terminated (20 millimeters). Fructan concentration increased in the basal part, then remained constant at about 85% of the total mass of water-soluble carbohydrates through the remainder of the elongation zone. Data on spatial distribution of growth velocities and substance contents (e.g. microgram fructan per millimeter leaf length) were used to calculate local net rates of substance deposition (i.e. excess rates of substance synthesis and/or import over substance degradation and/or export) and local rates of sucrose import. Rates of sucrose import and net deposition of fructan were positively associated with local elongation rate, whereas net rates of sucrose deposition were high in the zone of cell division and those of monosaccharide were high near the termination of elongation. At the location of most active elongation imported sucrose (29.5 milligrams per square decimeter per hour) was used largely for synthesis of structural components (52%) and fructan (41%).

Journal Article↗

PubMed1985

Frontal eye field projection to the paramedian pontine reticular formation traced with wheat germ agglutinin in the monkey.

Injections of the retrograde tracer [125I]wheat germ agglutinin have been placed in different areas of the paramedian pontine reticular formation (PPRF), a well known premotor center for gaze control. Experiments in 5 monkeys revealed 3 major sources of input: (1) bilateral projections from the so-called frontal eye field (FEF), which is situated in the frontal cortex around the arcuate sulcus; (2) the intermediate and deep layers of mainly the contralateral superior colliculus; and (3) ipsilateral projections from brainstem structures such as the accessory oculomotor nuclei (nucleus interstitialis of Cajal, nucleus of Darkschewitsch, and nucleus of the posterior commissure), the mesencephalic reticular formation, the vestibular nuclei, the nucleus prepositus hypoglossi, and the cerebellar fastigial nucleus. The results are compared with previous anatomical investigations and confirm the electrophysiologically demonstrated FEF-PPRF-abducens disynaptic pathway.

Animals↗

PubMed1984

The innervation of the monkey accessory lateral rectus muscle.

The source and pattern of innervation of the accessory lateral rectus muscle has been re-investigated in 3 Macaca fascicularis monkeys by means of a tracing method employing [125I] wheat germ agglutinin and a morphological analysis of the myo-neuronal junctions. The present findings suggest that this muscle is composed of exclusively singly innervated fibers and that its motoneurons are situated in the accessory abducens nucleus. This is in contrast to a previous study, where the monkey accessory lateral rectus was found to be composed of singly and multiply innervated fibers and to be innervated by a group of motoneurons lying within principle and accessory abducens nucleus. It is concluded that the monkey accessory lateral rectus reflects in principle the organization of the retractor bulbi of other vertebrates, although this muscle is gradually vanishing in primate evolution and remains vestigial in the macaque monkey. The absence of comparable motor units in man is more likely to mean an actual loss of structure and function than their integration into the lateral rectus system.

Animals↗

PubMed1984

Is there a retinopetal system in the rat?

The centrifugal innervation of the retina was reinvestigated in albino and pigmented rats with intraocular injections of horseradish peroxidase (HRP), radioactive wheat germ agglutinin (WGA) and proline. No labeled cells were found in the brains injected with HRP and proline, except some eye muscle motoneurons in one case apparently involving orbital contamination from the injection. In the cases injected with WGA and having a survival time of at least two days cells were labeled in the lateral mesencephalic tegmentum, ventral to the parabigeminal nucleus and in the periaqueductal gray. Both these findings are most likely due to transneuronal anterograde-retrograde transport of the tracer through the superior colliculus. The results yielded no compelling evidence for the existence of a direct retinopetal pathway in the rat, which is in contrast to a recently claimed retinal projection originating from the pretectum. Special attention was paid to the labeling in the lateral mesencephalic tegmentum, an area giving rise to retinal projections in various submammalian species. This finding is discussed with regard to the possibility that also in the rat the lateral tegmentum exerts an early influence on visual input, but at the "higher" collicular level and not at the "original" retinal one.

Animals↗