| 1. |
- Ekström, Thommy, et al.
(författare)
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Dense single-phase β-sialon ceramics by glass-encapsulated hot isostatic pressing
- 1989
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Ingår i: Journal of Materials Science. - 0022-2461. ; 24:5, s. 1853-1861
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Tidskriftsartikel (refereegranskat)abstract
- Single phase-sialon ceramics, Si6–z Al z O z N8–z , have been prepared from carefully balanced powder mixtures, also taking account of any excess oxygen in the starting materials. Sintering powder compacts in a nitrogen atmosphere (0.1 MPa) at 1800° C or higher transforms the starting mixture into a-sialon solid solution atz-values up to about 4.3, but the sintered material has an open porosity. Addition of 1 wt% Y2O3 to the starting mix improved the sintering behaviour somewhat and the density of the sintered compacts reached 95% of the theoretical value. By glass-encapsulated hot isostatic pressing at 1825° C, however, sintered materials of virtually theoretical density could be obtained, with or without the 1 wt% Y2O3 addition. These latter samples have been studied by X-ray diffraction and electron microscopy, and their hardness and indentation fracture toughness have been measured. It was found that the maximum extension of the-sialon phase composition at 1825° C and 200 MPa pressure is slightly below 4,z 3.85 and about 4.1 at atmospheric pressure, and that the hexagonal unit cell parameters are linear functions of thez-value. The single-phase-sialon ceramics had no residual glassy grain-boundary phase. The grain shape was equi-axed and the grain size increased from about 1m at lowz-values to 5m at highz-values. At lowz-values the hardness at a 98 N load was 1700 and the fracture toughness 3, whereas an increase inz above 1 caused both the hardness and fracture toughness to decrease significantly. Addition of 1 wt % Y2O3 to the starting mix prior to the HIP-sintering gave rise to a small amount of amorphous intergranular phase, changes in grain size and shape, a clear increase in fracture toughness and a moderate decrease in hardness.
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| 2. |
- Ekström, Thommy, et al.
(författare)
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Mixed α- and β-(Si-Al-O-N) Materials with Yttria and Neodymia Additions
- 1988
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Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 105/106, s. 161-168
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Tidskriftsartikel (refereegranskat)abstract
- A number of ceramic materials have been fabricated on a semipilot plant scale at different overall compositions in the (Y, Nd)---Al---O---N system at 177°C. Constant molar amounts of oxide mixtures of Y2O3: Nd2O3 in the ratios 100:0, 75:25, 50:50, 25:75 or 0:100 have been added. Dense materials were obtained for all compositions except those corresponding to mixed α- and β-(Si---Al---O---N) with higher α-(Si---Al---O---N) contents and high Nd2O3 contents. At the preparation temperature used in this study, the formation of an α-(Nd---Si---Al---O---N) seems prohibited and, thus, with increasing Nd2O3 content the amount of α-(Si---Al---O---N) decreased. The Nd2O3 added mainly formed crystalline intergranular phases such as the N-melilite phase, which increased in amount with increasing Nd2O3 in the starting mix. Hardness and indentation fracture toughness measurements were made and are discussed in relation to the phase composition and the microstructure. Some of the high Nd2O3 content Si---Al---O---N materials have as high fracture toughness values as the pure Y2O3 Si---Al---O---N materials do.
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| 3. |
- Edström, Anders, et al.
(författare)
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The use of the regenerating frog sciatic nerve for pharmacological studies of orthograde and retrograde axonal transport
- 1987
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Ingår i: Brain Research. - : Elsevier BV. - 0006-8993. ; 401:1, s. 34-42
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Tidskriftsartikel (refereegranskat)abstract
- The outgrowth region of the regenerating frog sciatic nerve shows an increased permeability for various drugs, which has been utilized for pharmacological studies of axonal transport. Six days after a bilateral crush lesion, the nerves, including the spinal ganglia, were incubated in a compartmented chamber. Orthograde transport was assessed from the proximodistal distribution and the accumulation of labelled proteins in the nerve growth region. Retrograde transport was examined by allowing orthogradely transported materials to reverse at the regenerating region and then to accumulate at a ligature during a second incubation period. The distribution of radioactivity along the nerve was assayed by fluorography of whole-mount nerve preparations or by scintillation counting. Fluorography made it possible to increase the spatial resolution and to demonstrate effects in the elongating part of the regenerating nerve. Colchicine at low concentrations (10-100 μM) only inhibited axonal transport in the outgrowth region (6 mm long at 6 days after crush) and along some mm of the nerve proximal to the crush. Compound 48/80 (50 μg/ml), the most specific calmodulin inhibitor so far described, inhibited the transport along the same part of the nerve. Cytochalasin B (10 μg/ml) inhibited transport by effects limited to the outgrowth region. Both orthograde and retrograde transport showed sensitivity to these and some other drugs. The regenerating frog sciatic nerve seems to have significant advantages for pharmacological studies of axonal transport.
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| 4. |
- Ekström, Per A R, et al.
(författare)
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Impaired nerve regeneration in streptozotocin-diabetic rats. Effects of treatment with an aldose reductase inhibitor
- 1989
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Ingår i: Journal of the Neurological Sciences. - 0022-510X. ; 93:2-3, s. 231-237
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Forskningsöversikt (refereegranskat)abstract
- Rats with streptozotocin-induced diabetes have a decreased rate of sciatic nerve regeneration. We studied the effects on this defect of treatment with the aldose reductase inhibitor, ponalrestat (25 mg/kg per day via an endogastric tube). The nerves of diabetic rats were crush-injured at 5 weeks of diabetes and regeneration evaluated 7 days later with the pinch-reflex test. Ponalrestat treatment was started at day 3 after streptozotocin injection and was continued for the whole experimental period, i.e. until 6 weeks of diabetes. The treatment prevented effectively the accumulation of sorbitol and fructose in the nerves of diabetic rats, but was without effect on the sciatic nerve regeneration (controls 21.8 ± 1.2 mm/7 days (mean ± SEM, n = 6), untreated diabetics 15.8 ± 1.8 (n = 7), ponalrestat-treated diabetics 16.2 ± 1.0 (n = 10)). The results indicate that there is no connection between increased sorbitol pathway flux and impaired regeneration in streptozotocin diabetic rats.
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| 5. |
- Ekström, Per A R, et al.
(författare)
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Nerve regeneration and serum levels of insulin-like growth factor-I in rats with streptozotocin-induced insulin deficiency
- 1989
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Ingår i: Brain Research. - : Elsevier BV. - 0006-8993. ; 496:1-2, s. 141-147
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Tidskriftsartikel (refereegranskat)abstract
- Peripheral nerve regeneration was studied in female Sprague-Dawley rats with streptozotocin-induced insulin deficiency. Nerve regeneration was provoked by a crush lesion on the sciatic nerve 21 days after the streptozotocin injection. The regeneration was assessed by a pinch test at different time-points after injury. The rate ofregeneration in insulin-deficient animals, 2.5 mm/day, was significantly lower than in control animals, 2.9 mm/day(P < 0.05). There was no difference in the initial delay, i.e. the period before regeneration attains a constant velocity. One group of insulin-deficient rats was treated with insulin during the regeneration period by means of implanted osmotic mini-pumps. This treatment prevented the decrease in regenerationsw. After 6 days the sciatic nerves of insulin-deficient rats had regenerated 12.3 ±0.3 mm (mean ±S.E.M.), while the corresponding value for insulin-treated rats was 15.7 ±0.6 mm (P > 0.01). The streptozotocin-treated rats were found to have a 39% reduction in the serum level of insulin-like 1 growth factor-I (IGF-I)_compared to control rats (0.33 ± 0.22 μg/ml and 0.54 ± ml respectively, (P < 0.001). Insulin treatment 1830 1732 during the regeneration period completely restored the IGF-I level back to normal.
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| 6. |
- Ekström, Per, et al.
(författare)
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Calmodulin‐Binding Proteins Within the Slow Phase of Axonal Transport in the Rabbit Vagus Nerve Per Ekstrom and Martin Kanje
- 1987
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Ingår i: Journal of Neurochemistry. - : Wiley. - 0022-3042 .- 1471-4159. ; 49:1, s. 146-151
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: : Calmodulin‐binding proteins (CBPs) in the rabbit vagus nerve were studied by means of calmodulin‐Sepha‐rose affinity chromatography and polyacrylamide gel electrophoresis. The soluble fraction (105g supernatant) of a nerve homogenate contained four CBPs with molecular weights of 44, 55, 91, and 93 kD, respectively. Slowly transported proteins were recovered in the vagus 3 days after injection of [35S]methionine into the nodose ganglion. Four labelled CBPs with molecular weights of 44, 55, 69, and 83 kD, respectively were found. The nodose ganglion con tained two labelled CBPs, 44 and 55 kD. The 55‐kD CBP was identified as tubulin after immunoblotting. In separate experiments it was also shown that bovine brain tubulin bound to the calmodulin column.
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| 7. |
- Ekström, Per, et al.
(författare)
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The effects of trifluoperazine on fast and slow axonal transport in the rabbit vagus nerve
- 1987
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Ingår i: Journal of Neurobiology. - : Wiley. - 0022-3034. ; 18:3, s. 283-293
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Tidskriftsartikel (refereegranskat)abstract
- The effects of trifluoperazine (TFP) on fast and slow axonal transport (AXT) of labeled proteins were examined in the rabbit vagus nerve. Cuffs soaked in a 10 mM, but not 0.1 mM or 1 mM, concentration of TFP applied locally around the vagus nerve in vivo blocked both fast and slow AXT, as measured by the accumulation of 3H‐labeled proteins. In vitro, fast AXT was affected by 0.1 mM TFP. The TFP cuff treatment caused a reduction in the number of axonal microtubules (MT) whereas cuffs soaked in saline had no effect. The levels of ATP, ADP, and AMP were not significantly lowered by the TFP treatment. The results suggest that both fast and slow AXT are sensitive to TFP treatment, and that the axonal MT‐system may be the main target of the drug.
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| 8. |
- Kanje, Martin, et al.
(författare)
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Ca2+-activated protease activity in frog sciatic nerve : Characterization and effect on rapidly transported axonal proteins
- 1985
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Ingår i: Brain Research. - : Elsevier BV. - 0006-8993. ; 327:1-2, s. 29-36
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Tidskriftsartikel (refereegranskat)abstract
- Protease activity was studied in the frog sciatic nerve. The activity was measured as the release of TCA-soluble radioactivity from either 3H-labelled proteins transported by rapid axonal transport (AXT) or 3H-labelled ganglionic proteins. In nerve homogenates containing transported substrates, protease activity exhibited two peaks, one around pH 5 and one around pH 8. Ca2+ at 100 μM or higher concentrations only stimulated the latter, which was inhibited by 1 mM parachloromercuric benzoate, a sulphydryl reagent, but unaffected by ATP (1 mM). The proteolytic activity was recovered in the 105 g supernatant of the homogenate. In desheathed nerves containing 3H-labelled transported proteins, the protease activity could be activated by exposing the nerve to a Ca2+-ionophore, X-537 A, or to an elevated Ca2+-concentration (50 mM). These conditions were also shown to increase the influx and efflux of 45Ca2+ in the nerves. The results indicate the presence within axons of a Ca2+-activated soluble protease, which degrades rapidly transported proteins. The finding that the protease degraded ganglionic soluble proteins to about the same extent suggests a broad substrate specificity. The present system should be useful for further characterization of protease activity during various physiological conditions.
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| 9. |
- Kanje, Martin, et al.
(författare)
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Effect of Estramustine Phosphate on the Assembly of Isolated Bovine Brain Microtubules and Fast Axonal Transport in the Frog Sciatic Nerve
- 1985
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Ingår i: Cancer Research. - 0008-5472. ; 45:5, s. 2234-2239
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Tidskriftsartikel (refereegranskat)abstract
- Estramustine phosphate (0.01 to 0.5 nriM), an estradiol mustard derivative used in the therapy of prostatic carcinoma, inhibited the assembly of brain microtubule proteins in vitro and disassembled preformed microtubules. In the presence of estramustine phosphate, the minimum microtubule-protein concentration sufficient for the assembly of microtubules was increased. Low concentrations of taxoi (20 μM) completely reversed the inhibition of assembly by estramustine phosphate. The effects were specific to estramustine phosphate since neither estradiol 170-phosphate, the hormonal moiety of the drug, nor nornitrogen mustard, the alkylating moiety, had any effect on assembly. Estramustine phosphate (0.1 to 0.5 HIM) was also found to reversibly inhibit fast axonal transport in the frog sciatic nerve. The nerve content of adenosine triphosphate, adenosine diphosphate, and adenosine monophosphate was not significantly affected by estramustine phosphate. Our results suggest that the cytotoxic action of estramustine phosphate could be dependent partially on an interaction with microtubules, probably via the microtubule-associated proteins.
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| 10. |
- Kanje, Martin, et al.
(författare)
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The effect of gossypol on fast axonal transport and microtubule assembly
- 1986
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Ingår i: Biochimica et Biophysica Acta - Biomembranes. - : Elsevier BV. - 0005-2736. ; 856:3, s. 437-442
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Tidskriftsartikel (refereegranskat)abstract
- Gossypol at micromolar concentrations (2 μM) was found to inhibit axonal transport and a microsomal ATPase activity in the frog sciatic nerve, although axonal microtubules and the neuronal content of AMP, ADP and ATP were not affected. At slightly higher concentrations (30-40 μM), gossypol also inhibited microtubule assembly and neuronal energy metabolism. Gossypol accumulated in the nerve and the results indicate that gossypol may act as a potent neurotoxin.
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