| 1. |
- Kurasov, Pavel
(författare)
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Distribution theory for discontinuous test functions and differential operators with generalized coefficients
- 1996
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Ingår i: Banach Journal of Mathematical Analysis. - : Elsevier BV. - 1735-8787 .- 0022-247X. ; 201:1, s. 297-323
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Tidskriftsartikel (refereegranskat)abstract
- Investigation of the differential operators with the generalized coefficients having singular support on a disjoint set of points requires the consideration of the distribution theory with the set of discontinuous test functions. Such a distribution theory for test functions having discontinuity at one point is developed. A four-parameter family of Schrödinger operators, formed by the operators with singular potential, singular metrics and singular gauge field, is considered. It is proved that this family of singular interactions describes all possible selfadjoint extensions of the second derivative operator defined on the functions vanishing in a neighbourhood of the point. Approximation by operators with smooth coefficients is discussed.
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| 2. |
- Holmberg, Hans, et al.
(författare)
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Developmental adaptation of withdrawal reflexes to early alteration of peripheral innervation in the rat
- 1996
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Ingår i: Journal of Physiology. - : Wiley. - 1469-7793 .- 0022-3751. ; 495:2, s. 399-409
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Tidskriftsartikel (refereegranskat)abstract
- 1. In adult decerebrate spinal rats whose plantar nerves (PLN) had been transected at either postnatal day 1. (P1) or P21 the nociceptive withdrawal reflexes (NWR) of musculi extensor digitorum longus (EDL), peroneus longus (PER) and semitendinosus (ST) were characterized with respect to receptive field (RF) organization, magnitude and time course, using electromyography. Thermal (short CO2 laser pulses) and mechanical (calibrated pinch) stimulation were used. The innervation patterns in normal and lesioned adult rats mrere assessed by acute nerve lesions. 2. The spatial organization of the mean mechano- and thermonociceptive RFs of all the muscles studied was similar to normal in both P1- and P21-lesioned rats, although in some P21-lesioned rats atypical EDL RFs were encountered. 3. In P1-lesioned rats thermo-NWR of PER and EDL had normal magnitudes, while mechano-NWR were reduced. In P21-lesioned rats both thermo- and mechano-NWR of these muscles had reduced magnitudes. Except for thermo-NWR of ST in P1-lesioned rats, which were increased, NWR of ST had normal magnitudes in both P1- and P21-lesioned rats. The time course of thermonociceptive NWR of the muscles studied were near normal in both P1- and P21-lesioned rats. 4. Acute nerve lesions in adult P1-lesioned rats revealed an essentially abolished contribution to NWR from the PLN. Instead, the contribution to NWR from other hindpaw nerves, such as the superficial and deep peroneal nerves, was dramatically increased. By contrast, in P21 lesioned rats, the regenerated PLN contributed significantly to the NWR. 5. It is concluded that despite profound alterations of plantar hindpaw innervation induced by early PLN transection the cutaneous nociceptive input to NWR attained an essentially normal spatial organization. An experience-dependent mechanism is suggested to be instrumental in adapting the reflex connectivity to the peripheral innervation.
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| 3. |
- Hansbrough, John F., et al.
(författare)
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Neutrophil activation and tissue neutrophil sequestration in a rat model of thermal injury
- 1996
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Ingår i: Journal of Surgical Research. - : Elsevier BV. - 1095-8673 .- 0022-4804. ; 61:1, s. 17-22
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Tidskriftsartikel (refereegranskat)abstract
- Neutrophil (PMN) deposition in tissues (leukosequestration) after shock may produce local tissue injury from proteases and oxygen intermediaries which are released from sequestered PMNs. We quantified leukosequestration in tissues in burned rats using two methods of analysis: 1), measurement of lung myeloperoxidase (MPO); 2), measurement of radiolabeled PMNs and erythrocytes deposited in multiple tissues. After tracheostomy and venous cannulation, rats received 17% TBSA full-thickness contact burns and were resuscitated with 20 cc intraperitoneal saline. Lung PMNs were estimated by measuring MPO in lung tissue. PMN influx into lung, liver, spleen, gut, skin, muscle, kidney, and brain was determined by removing (preburn) and differentially radiolabeling PMNs (111In) and erythrocytes (51Cr), reinfusing cells 4.5 hr postburn, and measuring tissue radioactivity 5 hr postburn. Tissue edema was measured by determining extravasation of 125I-labeled albumin in tissues. Peripheral blood PMNs were analyzed for intracellular H2O2 content utilizing a fluorescent dye which reacts with H2O2 coupled with analysis of cell fluorescence by flow cytometry. MPO was elevated in lungs 8 hr postburn (P < 0.05). PMN influx into lung tissues was confirmed by histologic examination. Radioisotope studies demonstrated significant (P < 0.05) leukosequestration into lung, gut, kidney, skin, and brain tissues at 5 hr postburn. Respiratory burst activity of peripheral blood PMNs was increased 5 hr postburn (P < 0.05). Flow cytometric analysis indicated that peripheral blood PMNs were capable of producing markedly increased H2O2 levels 5 hr postburn. Tissue edema, manifested by radiolabeled albumin influx, was not seen in any tissues. Since others have shown that sequestration of metabolically active PMNs may induce remote tissue injury, therapies which block postburn leukosequestration may be able to improve clinical outcomes by limiting remote tissue injury.
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| 4. |
- Holmberg, Hans, et al.
(författare)
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Postnatal development of the nociceptive withdrawal reflexes in the rat : A behavioural and electromyographic study
- 1996
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Ingår i: Journal of Physiology. - : Wiley. - 1469-7793 .- 0022-3751. ; 493:1, s. 239-252
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Tidskriftsartikel (refereegranskat)abstract
- 1. The postnatal development of nociceptive withdrawal reflexes was studied. In awake intact rats, forelimb, hindlimb and tail reflexes were recorded on videotape. In decerebrate spinal rats, electromyography (EMG) was used to record nociceptive withdrawal reflexes in musculi extensor digitorum longus (EDL), peronei, gastrocnemius-soleus (G-S) and biceps posterior-semitendinosus (BP-ST). Thermal (short-lasting CO2 laser pulses) and mechanical stimulation were used. 2. In adults, nociceptive withdrawal reflexes were typically well directed and reflex pathways to single hindlimb muscles had functionally adapted receptive fields. By contrast, at postnatal day (P) 1-7, the nociceptive withdrawal reflexes were often inappropriate, sometimes producing movements towards the stimulation, and EMG recordings revealed unadapted variable receptive fields. With increasing age, the nociceptive withdrawal reflexes progressively became well directed, thus producing localized withdrawal. Both withdrawal movements and spatial organization of the receptive fields were adult-like at P20-25. 3. Up to P25, reflex thresholds were more or less constant in both intact awake rats and spinal decerebrate rats, except in G-S in which no nociceptive withdrawal reflexes were evoked from P20 on. After P25, mechanical, but not thermal, thresholds increased dramatically. 4. EMG recordings revealed that during the first three postnatal weeks, the latency of the CO2 laser-evoked nociceptive withdrawal reflexes decreased significantly in peronei and BP-ST, but not in EDL, and thereafter increased significantly in peronei, BP-ST and EDL. The magnitude of the nociceptive withdrawal reflexes in these muscles increased markedly between P7 and P20 and showed little change thereafter. 5. Possible mechanisms underlying the postnatal tuning of the nociceptive withdrawal reflexes are discussed.
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| 5. |
- Johanson, U, et al.
(författare)
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The dynamic structure of EF-G studied by fusidic acid resistance and internal revertants
- 1996
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Ingår i: Journal of Molecular Biology. - : Elsevier BV. - 0022-2836. ; 258:3, s. 32-420
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Tidskriftsartikel (refereegranskat)abstract
- We have previously identified 20 different fusidic acid-resistant alleles of fusA, encoding mutant forms of the ribosomal translocase EF-G. One of these, P413L, is used here as the starting point in selections for internal revertants, identifying 20 different pseudo-wild-type forms of EF-G. We have also identified two alleles of fusA previously isolated as suppressors of 4.5 S RNA deficiency. All of these mutants are analysed in terms of their effects on the structural dynamics of EF-G. Most mutation conferring fusidic acid-resistance interfere with conformational changes of EF-G, but some may be located at a possible fusidic acid binding site. Revertants of the P413L mutations restore the function of EF-G with or without affecting the level of resistance to fusidic acid. The revertant mutations probably restore the balance between the GDP and GTP conformations of EF-G off the ribosome, and most of them are located close to the interface between the G domain and domain II. The procedure for the isolation of pseudo-wild-type forms of EF-G can be used to direct evolution progressively away from the wild-type while still maintaining the essential functions of EF-G.
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| 6. |
- Klaassen, Marcel, et al.
(författare)
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Departure fuel loads in time-minimizing migrating birds can be explained by the energy costs of being heavy
- 1996
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Ingår i: Journal of Theoretical Biology. - : Elsevier BV. - 1095-8541 .- 0022-5193. ; 183:1, s. 29-34
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Tidskriftsartikel (refereegranskat)abstract
- Lindström & Alerstam (1992Am. Nat.140,477–491) presented a model that predicts optimal departure fuel loads as a function of the rate of fuel deposition in time-minimizing migrants. The basis of the model is that the coverable distance per unit of fuel deposited, diminishes with increasing fuel load. This is an effect of the increasing flight costs associated with increasing body mass. Lindström & Alerstam (1992) found that birds left at lower fuel loads than their model predicted for which they considered various ecological explanations. Alternatively, we hypothesize that the difference between prediction and empirical data might be a result of extra resting metabolic and transport costs associated with an increase in fuel load during stopover. We develop a new version of the Lindström & Alerstam (1992) model taking fuel load associated costs during stopover into account. We fit empirical data from rufous hummingbirdsSelasphorus rufus(Carpenteret al., 1983Proc. Natl. Acad. Sci. U.S.A.80,7259–7263) and bluethroatsLuscinia svecica(Lindström & Alerstam, 1992) to this new model. Estimated fuel-load costs are discussed in relation to knowledge presently available on variations in basal metabolic costs and transport costs with body mass. We show that fuel-load costs within a reasonable range can explain the observed departure fuel loads when migrating birds are time minimizers.
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| 7. |
- Pettersson, Gösta
(författare)
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A New Approach for Determination of the Selectively Favoured Kinetic Design of Enzyme Reactions
- 1996
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Ingår i: Journal of Theoretical Biology. - : Elsevier BV. - 1095-8541 .- 0022-5193. ; 183:2, s. 179-183
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Tidskriftsartikel (refereegranskat)abstract
- A new criterion is applied for characterization of the kinetic design of enzymes that should be favoured by a selective pressure in the direction of increased metabolic reaction flux. According to this criterion, the selectively favoured state of a metabolic sequence of enzyme reactions conforming to Michaelis-Menten kinetics is identical with the uniform one which is known to optimize reaction flux for a given average magnitude of enzyme concentrations and of true and apparent first-order rate constants in the reaction system. It is argued that presently observed values of on-velocity constants for metabolite binding to enzymes are unlikely to represent the upper limit for a diffusion-controlled association process and are more likely to represent those corresponding to the selectively favoured kinetic design at the present stage of the evolutionary development of enzyme function.
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| 8. |
- Pettersson, Gösta
(författare)
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Errors Associated with Experimental Determinations of Enzyme Flux Control Coefficients
- 1996
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Ingår i: Journal of Theoretical Biology. - : Elsevier BV. - 1095-8541 .- 0022-5193. ; 179:3, s. 191-197
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Tidskriftsartikel (refereegranskat)abstract
- An analysis is presented of the likely statistical error and mathematical bias of experimental enzyme flux control coefficient estimates, calculated from observations of the flux changes caused by finite changes of the concentration of an enzyme in a metabolic pathway. The results indicate that such control coefficients are not likely to be determined with satisfactory precision unless the experimental data are evaluated by hyperbolic regression analysis, and the actual flux vs. enzyme concentration profile conforms closely to a hyperbolic relationship. It is concluded that it may not normally be feasible to obtain reliable experimental estimates of enzyme flux control coefficients in realistic systems by the examined direct approach. Arguments are presented to show that the error situation is unlikely to be more favourable as it concerns that indirect calculation of flux control coefficients from transient-state kinetic data or from experimental estimates of infinitesimally defined quantities such as elasticity coefficients and co-response coefficients.
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| 9. |
- Ryde, Ulf, et al.
(författare)
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The cupric geometry of blue copper proteins is not strained
- 1996
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Ingår i: Journal of Molecular Biology. - : Elsevier BV. - 0022-2836. ; 261:4, s. 586-596
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Tidskriftsartikel (refereegranskat)abstract
- The geometry of several realistic models of the metal coordination sphere in the blue copper proteins has been optimised using high-level quantum chemical methods. The results show that the optimal vacuum structure of the Cu(II) models is virtually identical to the crystal structure of oxidised blue copper proteins. For the reduced forms, the optimised structure seems to be more tetrahedral than the one found in the proteins, but the energy difference between the two geometries is less than 5 kJ/mol, i.e. within the error limits of the method. Thus, the results raise strong doubts against hypotheses (entatic state and the induced-rack theory) suggesting that blue copper proteins force the oxidised metal coordination sphere into a structure similar to that preferred by Cu(I) in order to minimise the reorganisation energy of the electron transfer reaction. Instead, a small reorganisation energy seems to be reached by an appropriate choice of metal ligands. In particular, the cysteine thiolate ligand appears to be crucial, changing the preferred geometry of the oxidised complexes from square-planar to a more trigonal geometry.
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| 10. |
- Weng, H-R, et al.
(författare)
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Cutaneous inhibitory receptive fields of withdrawal reflexes in the decerebrate spinal rat
- 1996
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Ingår i: Journal of Physiology. - : Wiley. - 1469-7793 .- 0022-3751. ; 493:1, s. 253-265
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Tidskriftsartikel (refereegranskat)abstract
- 1. The inhibitory cutaneous input to the withdrawal reflex pathways to single hindlimb muscles was investigated in decerebrate spinal rats (n = 53) using electromyography. 2. Withdrawal reflexes in the peronei, extensor digitorum longus and tibialis anterior muscles of the leg were strongly inhibited by conditioning mechanical, thermal (CO2 laser) and intracutaneous electrical stimulation of specific skin areas. By contrast, withdrawal reflexes in the biceps posterior-semitendinosus muscles of the thigh could only be weakly inhibited by conditioning skin stimulation. 3. Powerful inhibition of withdrawal reflexes in single lower leg muscles was elicited from the ipsilateral hindpaw plantar area, which would move towards the stimulation on contraction in the respective muscle. In addition, weak nociceptive inhibition was evoked from the corresponding skin areas on the contralateral hindlimb and, in some muscles, the tail. 4. The ipsilateral inhibitory and excitatory receptive fields of the withdrawal reflexes in single muscles overlapped somewhat. On stimulation of these transitional areas the reflex responses were preceded by a short-lasting inhibition. 5. Graded mechanical and thermal stimulation demonstrated prominent inhibitory effects from nociceptive receptors. Weak inhibitory effects were elicited by innocuous mechanical stimulation, suggesting a weak contribution from low threshold mechanoreceptors. Latency measurements indicated an inhibitory input from both myelinated and unmyelinated fibres. 6. In conclusion, the withdrawal reflex pathways receive a powerful nociceptive inhibitory input through spinal pathways. The movement-related organization of this input suggests that it serves to prevent inappropriate withdrawal reflexes.
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