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| 2. |
- Lindvall, O, et al.
(författare)
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Grafts of fetal dopamine neurons survive and improve motor function in Parkinson's disease
- 1990
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Ingår i: Science (New York, N.Y.). - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 247:4942, s. 7-574
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Tidskriftsartikel (refereegranskat)abstract
- Neural transplantation can restore striatal dopaminergic neurotransmission in animal models of Parkinson's disease. It has now been shown that mesencephalic dopamine neurons, obtained from human fetuses of 8 to 9 weeks gestational age, can survive in the human brain and produce marked and sustained symptomatic relief in a patient severely affected with idiopathic Parkinson's disease. The grafts, which were implanted unilaterally into the putamen by stereotactic surgery, restored dopamine synthesis and storage in the grafted area, as assessed by positron emission tomography with 6-L-[18F]fluorodopa. This neurochemical change was accompanied by a therapeutically significant reduction in the patient's severe rigidity and bradykinesia and a marked diminuation of the fluctuations in the patient's condition during optimum medication (the "on-off" phenomenon). The clinical improvement was most marked on the side contralateral to the transplant.
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| 3. |
- Lindvall, O, et al.
(författare)
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In reply : Fetal brain grafts and Parkinson's disease
- 1990
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Ingår i: Science (New York, N.Y.). - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 250:4986, s. 1435-1435
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Tidskriftsartikel (refereegranskat)
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| 4. |
- Lindvall, O, et al.
(författare)
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Transplantation of fetal dopamine neurons in Parkinson's disease : one-year clinical and neurophysiological observations in two patients with putaminal implants
- 1992
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Ingår i: Annals of Neurology. - : Wiley. - 0364-5134 .- 1531-8249. ; 31:2, s. 65-155
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Tidskriftsartikel (refereegranskat)abstract
- Ventral mesencephalic tissue from aborted human fetuses (age, 6-7 weeks' postconception) was implanted unilaterally into the putamen using stereotaxic surgery in 2 immunosuppressed patients (Patients 3 and 4 in our series) with advanced idiopathic Parkinson's disease. Tissue from 4 fetuses was grafted to each patient. Compared with our previous 2 patients, the following changes in the grafting procedure were introduced: the implantation instrument was thinner, more tissue was placed in the operated structure, and the time between abortion and grafting was shorter. There were no postoperative complications. Both patients showed a gradual and significant amelioration of parkinsonian symptoms (most marked in Patient 3) starting at 6 and 12 weeks after grafting, respectively, reaching maximum stability at approximately 4 to 5 months; patients remained relatively stable thereafter during the 1-year follow-up period. Clinical improvement was observed as a reduction of the time spent in the "off" phase and the number of daily "off" periods; a lessening of bradykinesia and rigidity during the "off" phase, mainly but not solely on the side contralateral to the graft; and a prolongation and change in the pattern of the effect of a single dose of L-dopa. Neurophysiological measurements revealed a more rapid performance of simple and complex arm and hand movements bilaterally, but primarily contralateral to the graft. The results indicate that patients with Parkinson's disease can show significant and sustained improvement of motor function after intrastriatal implantation of fetal dopamine-rich mesencephalic tissue. The accompanying paper by Sawle and colleagues describes the results of repeated positron emission tomography scans in these patients.
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| 5. |
- Rothwell, P.L., et al.
(författare)
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Acceleration and Stochastic Heating of Ions Drifting Through an Auroral Arc
- 1992
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 97, s. 19333-19339
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Tidskriftsartikel (refereegranskat)abstract
- We find that ions E x B drifting through an auroral arc can undergo transverse acceleration and stochastic heating. This result is very analogous to recent work regarding similar phenomena in the magnetotail (Buchner and Zelenyi, 1990; Chen and Palmadesso, 1986; Brittnacher and Whipple, 199 1). An analytic expression for the maximum arc width for which chaotic behavior is present is derived and numerically verified. We find, for example, that a 1.5-km-thick arc at LAMBDA = 65-degrees requires a minimum potential drop of 3 kV for transverse ion acceleration and heating to occur. Thicker arcs require higher potential drops for stochasticity to occur. This mechanism could be a source for conic ions.
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| 6. |
- Rothwell, P.L., et al.
(författare)
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O+ phase bunching and auroral arc structure
- 1994
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 99, s. 2461-2470
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Tidskriftsartikel (refereegranskat)abstract
- The equations of motion are solved for ions moving in a model electric field that corresponds to the nightside equatorial region df the magnetosphere. The model represents the poleward region of the Harang discontinuity mapped to the magnetosphere. Within this region the model electric field has a constant earthward gradient superimposed on a constant dawn-to-dusk electric field. In combination with the earthward drift motion due to the dawn-to-dusk field, the electric field gradient introduces an earthward inertia drift, which is proportional to the ion mass and therefore faster for O+ ions than for H+ ions or electrons. It is also found that the entry of the ions into the gradient region causes phase bunching and as a result ion density striations form. The striations are enhanced for more abrupt changes in the electric field gradient, a weaker magnetic field, a stronger cross-tail electric field and colder O+ ions. The first two conditions apply during the growth phase of a substorm. Using the Tsyganenko (1987) model a minimum electric field gradient value of 1 x 1O(-9) V/m(2) ((1 mV/m)/1000 km) at L = 6-7 is found. Charge neutrality requires coupling with the ionosphere through electrons moving along magnetic held lines, and such electrons may be the cause of multiple auroral arcs.
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| 7. |
- Rothwell, P.L., et al.
(författare)
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PREBREAKUP ARCS - A COMPARISON BETWEEN THEORY AND EXPERIMENT
- 1991
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 96, s. 13967-13975
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a model describing the structure of a prebreakup arc based on an ionospheric Cowling channel and its extension into the magnetosphere. A coupled two-circuit representation of the substorm current wedge is used which is locally superimposed on both westward and eastward electrojets. We find that brighter, more unstable prebreakup arcs are formed in the premidnight (southwest of the Harang Discontinuity) than in the postmidnight (northeast of the Harang Discontinuity) sector. This contributes to the observed prevalence of auroral activity in the premidnight sector. Also, our model predicts that the north-south dimensions of the current wedge in the ionosphere should vary from a few kilometers at an invariant latitude (LAMBDA) of 62-degrees to hundreds of kilometers above LAMBDA = 68-degrees. Comparison of the model results with the extensive observations of Marklund et al. (1983) for a specific arc observed just after onset shows good agreement, particularly for the magnitude of the polarization electric field and the arc size. We conclude that this agreement is further evidence that the substorm breakup arises from magnetosphere-ionosphere coupling in the near magnetosphere and that the steady state model developed here is descriptive of the breakup arc before inductive effects become dominant.
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