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At least 793 records · Page 44Linked to original sources
PubMed2001

Neurosurgery for Parkinson's disease.

Medical therapy for Parkinson's disease (PD) often becomes inadequate over several years. Disability increases despite maximal medical management and many patients develop motor fluctuations and dyskinesia. In addition, medications provide good control of tremor in only 50% of cases. In appropriately selected cases, surgical therapies for PD provide benefit for medically refractory symptoms. Recent advances have provided a greater array of surgical options. Unilateral thalamotomy and thalamic stimulation are considered safe and effective procedures to treat contralateral tremor. Pallidotomy and pallidal stimulation primarily reduce contralateral dyskinesia, with lesser effects on bradykinesia and rigidity. Studies indicate that subthalamic nucleus (STN) stimulation improves "off" period function, decreases "off" time, and lessens dyskinesia. Fetal cell transplantation remains experimental, and studies are underway to evaluate the safety and efficacy of porcine fetal cell and human retinal pigment epithelial cell transplantation. This chapter reviews the history of surgical procedures for PD, describes current procedures, and offers a look into the future of neurosurgical options for PD.

Animals↗
PubMed1994

Luria-Delbrück fluctuation experiments: design and analysis.

Luria and Delbrück, in a seminal paper, introduced fluctuation analysis primarily as a means to elucidate the timing of mutation in relation to the imposition of selective conditions. Their work, and subsequently that of LEA and COULSON, established also a basis for measuring the frequency of mutational events. The several estimators proposed by these authors differ both in complexity and in efficiency, and the published literature relies mainly on the less efficient but computationally trivial estimators. The estimators as originally proposed assume that all mutants occurring in culture will be counted in the subsequent assay, but a relaxation of this assumption suggests an alternative experimental design and alternative estimators which offer advantages over those currently in common use.

Biometry↗
PubMed2000

Drastic enhancement of energy-loss straggling of relativistic heavy ions due to charge-state fluctuations

Stopping power and energy-loss straggling of 197Au, 208Pb, and 209Bi projectiles have been measured in different solids (4</=Z2</=82) in the energy range (100-1000) MeV/u. The experimental results clearly demonstrate the influence of the different charge states of the ions. Because of charge-state fluctuations the energy-loss straggling is up to 7 times larger than the pure collisional straggling. The selected energy domain in combination with the heavy projectiles allows for the first time an unambiguous interpretation of the long-standing problem of charge-changing collisions in energy-loss straggling.

Journal Article↗
PubMed2001

Spin dynamics in a frustrated magnet.

180 degrees spin flips have been identified as the dominant fluctuation mechanism at the transverse spin freezing transition in partially frustrated a-Fe92Zr8. The form of the selective excitation double Mössbauer spectra, coupled with the perfect agreement with zero-field muon spin relaxation data, eliminates other relaxation forms.

Journal Article↗
PubMed1992

Anoxia-induced extracellular ionic changes in CNS white matter: the role of glial cells.

The rapid changes in brain extracellular ion concentrations that occur with anoxia are important in understanding the pathophysiology of anoxic-ischemic brain injury. While previous studies have focused on the ionic changes that occur in gray matter areas of the brain, white matter (WM) is also damaged by anoxia. We describe the changes in extracellular K+ concentration ([K+]o) and extracellular pH (pHo) that accompany anoxia in WM, and present new results indicating that glial cells directly contribute to the observed fluctuations of these ions. Anoxia-induced changes in [K+]o and pHo were measured with ion-selective microelectrodes in the isolated rat optic nerve, a typical WM tract. To assess the contribution of glial cells, recordings were also made in optic nerves that contained only glial cells (produced by neonatal enucleation). Anoxia in WM produced less extreme changes in [K+]o and pHo than are known to occur in gray matter; in WM during anoxia, the average maximum [K+]o was 14 +/- 2.9 mM (bath [K+]o = 3 mM) and the average maximum acid shift was 0.31 +/- 0.07 pH unit. These extracellular ionic changes were accompanied by rapid shrinkage of extracellular space volume. The ability of optic nerve axons to conduct action potentials was lost in temporal association with the increase in [K+]o. Increasing bath glucose concentration from 10 to 20 mM resulted in a much larger acid shift during anoxia (0.58 +/- 0.08 pH unit) and a smaller average increase in [K+]o (9.2 +/- 2.6 mM). The increased glucose concentration presumably enhanced anaerobic metabolism, leading to extracellular lactate accumulation and a greater acid shift.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1987

A simple quantitative analysis system for coronary cineangiograms using a personal computer.

We have developed a simple quantitative analysis system for coronary cineangiograms using a personal computer and a standard projector-video camera system. The selected frame of cinefilm was projected onto the target area of a CCD video camera. To decrease spatial fluctuations due to quantum noise, the digital data were smoothed spatially by applying a moving averaged filter and a median filter. Following the smoothing process, the digital data with gray level were transformed to binary data by quantifying the threshold property of their gray level. To minimize the geometric influence, mainly pincushion effect, a cinefilm of a 1 cm grid was placed against the input screen of the image intensifier to correct the distortion by using 3rd degree polynomials. The accuracy of the contour detection procedure was validated on the basis of phantom models filled with a contrast medium. Despite the potential influence of many radiographic variables on computerized diameter measurements, the overall accuracy was found to be 0.26-0.33 mm over a wide range of clinically relevant artery diameters and radiographic conditions. Using this system we demonstrated one method of examining the effects of acetylcholine and nitroglycerin on coronary artery diameter in adult humans.

Acetylcholine↗
PubMedDate not supplied

Monitoring middle ear pressure by tympanometry. A study of middle ear pressure variation through seven hours.

The aim of this investigation was to monitor fluctuations in middle ear pressure, to study tympanometric signs of Eustachian tube functioning and to assess the validity of the tympanometric readings. In 20 patients with a low initial middle ear pressure (-150 daPa or lower) and 5 normals, impedance tympanometry was performed every 3 min through 7 h. Median pressure for the patients was -150 daPa (range 100 to -400 daPa) and for the normals 0 daPa (range 50 to -50 daPa). A remarkable pressure increase was seen after changing the body position to the supine. The patients were arranged into three groups according to the lowest middle ear pressure registered. Median pressures for the groups were running at a rather constant level. However, the individual pressure fluctuations in many patients were so great that a single tympanometric reading has to be considered unreliable when selecting patients for insertion of ventilation tubes. Thirteen patients never equalized their negative middle ear pressure, indicating that their Eustachian tube did not open during the test period. In spite of this the pressure did not decrease to lower values, indicating that maintaining a relative constant middle ear pressure is independent of opening of the Eustachian tube.

Acoustic Impedance Tests↗
PubMed1999

[Modern therapeutic possibilities in Parkinson disease].

Several new methods for the treatment of patients suffering from Parkinson's disease have been introduced during the last few years. COMT inhibitors are available in addition to levodopa with a decarboxylase inhibitor. COMT inhibitors enhance and prolong the effect of single levodopa doses. Severe side effects have been mentioned in connection with the COMT inhibitor tolcapone in recent months. Several new dopaminergic agonists now provide efficacious monotherapy in the early stages of the disease. This brings about a reduction in late problems of treatment such as dyskinesias and fluctuations. Stereotaxic operations in the pallidum and the subthalamic afford relief for these late complications of treatment in selected patients.

Antiparkinson Agents↗
PubMed1975

Monoamine oxidase. Its inhibition.

Some 50 years ago the enzyme MAO was discovered by Hare and in the early 1930s Blaschko suggested that MAO may play an important role in the catabolism of monoamines in the central nervous system. With the discovery of iproniazid as an inhibitor of MAO and its introduction as an anti-depressant, many aspects of MAO activity and biogenic amine metabolism in experimental animals and man were examined. Although many other inhibitors of MAO were discovered and used therapeutically as anti-depressants, these drugs fell into disrepute largely because of their side-effects. Furthermore, their anti-depressant properties were questioned. After some years of relative inactivity there is now a revival of interest in the functional role of MAO in the central nervous system and drugs that inhibit or stimulate its activity "specifically". The basic reason for the upsurge of interest is that the enzyme from many tissues, including the brain of animals as well as man, has been purified and characterised. The evidence that neuronal MAO exist with different substrate and inhibitor specificities has led to the suggestion that they have physiological function and that deamination of non-methylated biogenic monoamines can take place in neurons. These findings have led to the advent of new drugs (clorgyline and depranil) with "selective" inhibition of enzyme forms. Their possible usage in the chemotherapy of depressive illness should be considered seriously. Fluctuation in peripheral organs as well as brain MAO is well documented. Recently they have been associated with changes in naturally occurring steroids. Although a decrease in platelet and brain MAO activity has been reported in a number of affect disorders (schizophrenia and bipolar depression) the results of these findings have recently been questioned (20, 141). Obviously further study in this area of research discussed is badly needed.

Bipolar Disorder↗
PubMed1984

Demography of sterilization: Indian experience.

Using program statistics and a few local studies, the paper examines the prevalence of sterilization in India and makes demographic analysis of the performance. Major points of note are that the prevalence rates expressed in terms of currently married women showed irregular fluctuations across time and the age pattern of acceptance hardly agreed with that of the married population. The selectivity of high fertility couples for sterilization had been fairly high, resulting in a low fertility impact. Estimates of births averted due to the program were derived by using a computerized microsimulation model CONVERSE. It appears that the path of fertility changes was not smooth in the last decade and the impact has been, as a rule, greatest 2 years after acceptance.

Age Factors↗
PubMed2002

[Parkinson disease: deep cerebral stimulation].

The effects of deep brain stimulation (DBS) of the subthalamic nucleus (STN) or the internal pallidum (GPi) on the parkinsonian triad and on levodopa-induced dyskinesias are very similar. The antiakinetic effect of STN DBS seems to be slightly better. On the contrary to pallidal DBS, stimulation of the STN allows to reduce dopaminergic treatment by more than 50 p. 100 on average. Moreover, the current drain is smaller in STN. Thus, the STN is a low budget target compared to the GPi. STN DBS seems to be as effective on PD tremor as stimulation of the classic thalamic target, the ventral intermediate nucleus (Vim), whereas Vim stimulation has no effect on akinesia and very little on levodopa-induced dyskinesias. Thus, the STN has become the main target nucleus for DBS in PD, which is most often performed bilaterally in one surgical procedure. There is a good correlation of the preoperative response to levodopa and postoperative effects of bilateral STN DBS and this defines the patient population. Given the large patient population, simple guidelines for patient selection are developed. The referring physician can preselect patients based mainly on age (less than 70), absence of dementia and presence of severe disability related to motor fluctuations or dyskinesias. It is the responsibility of the operating centre to determine the levodopa response, to confirm the diagnosis, to rule out contraindications and to make sure that the medical treatment cannot be further optimised. Severe surgical complications with permanent sequels are relatively rare, about 1 p. 100 per implanted side. The patient selection, the precision of the surgery and the quality of the postoperative follow-up are the three main determinants of success.

Adult↗
PubMed1977

International aspects of oral microbiology.

It appears that the bacteria of the mouth are remarkably similar throughout the world. There are differences, but they are mostly of a quantitative rather than a qualitative nature. Although much is yet to be learned on the regulation of the oral ecosystems, these quantitative fluctuations to a large extent seem to be induced by different dietary patterns: the food exerting a strong selective pressure on the oral microbiota.

Bacteria↗
PubMed1988

Comparison of associated heterophoria measurements using the Mallett test for near vision and the Sheedy Disparometer.

The Mallett test for near vision and the Sheedy Disparometer are compared in terms of their ability to measure associated heterophoria. Twenty-two asymptomatic subjects were used. With the Disparometer, ten of these subjects, familiar with making prism vergence measurements, exhibited stable forced vergence fixation disparity curves, and the associated heterophoria values using both instruments were not significantly different. However, the twelve subjects not familiar with making such measurements generated fluctuating, unstable fixation disparity curves, and the associated heterophoria values were significantly different. Repeated trials with the randomly selected naïve subjects led to flatter, more stable fixation disparity curves and lower values for the x- and y-intercepts when using the Disparometer. The Mallett test, however, produced identical values for associated heterophoria in each successive trial. Therefore, the validity of measurements using the Disparometer in a clinical setting is questioned.

Adolescent↗
PubMedDate not supplied

[Cation selectivity of a BLM in a state of "stress"].

In asymmetric conditions (by electrolyte concentration) cyclic voltage current curves of BLM were measured in a stress state initiated after a short -- time effect of a strong electric field. BLM from negatively charged lipids were shown to exhibit notable cation -- anion selectivity under these conditions. The result obtained agrees with the assumption to the effect that stress and preclamping fluctuations are related to the formation of through pores the inner face of which is lined with the polar heads of lipids.

Electric Conductivity↗
PubMed1996

[Change in sex ratio of a Drosophila population in relation to population size].

Changes in sex ratio with population size fluctuations were studied in natural and cage populations of Drosophila. It was shown that the proportion of females decreased with an increase in population size both in natural and laboratory populations. If laboratory populations were maintained on a poor diet, this effect was absent. The amplitude of number fluctuation was shown to be higher in males than in females. The possible role of density-dependent selection on sex in the control of population size dynamics is discussed.

Animals↗
PubMed2003

Theoretical study of the structure and dynamic fluctuations of dioxolane-linked gramicidin channels.

Gramicidin is a hydrophobic peptide that assembles as a head-to-head dimer in lipid membranes to form water-filled channels selective to small monovalent cations. Two diastereoisomeric forms, respectively SS and RR, of chemically modified channels in which a dioxolane ring links the formylated N-termini of two gramicidin monomers, were shown to form ion channels. To investigate the structural basis underlying experimentally measured differences in proton conductance in the RR and SS channels, we construct atomic-resolution models of dioxolane-linked gramicidin dimers by analogy with the native dimer. A parametric description of the linker compatible with the CHARMM force field used for the peptide is derived by fitting geometry, vibrational frequencies, and energy to the results of ab initio calculations. The linker region of the modified gramicidin dimers is subjected to an extensive conformational search using high-temperature simulated annealing, and free-energy surfaces underlying the structural fluctuations of the channel backbone at 298K are computed from molecular dynamics simulations. The overall secondary structure of the beta-helical gramicidin pore is retained in both linked channels. The SS channel is found in a single conformation resembling that of the native dimer, with its peptide bonds undergoing rapid librations with respect to the channel axis. By contrast, its RR counterpart is characterized by local backbone distortions in which the two peptide bonds flanking the linker are markedly tilted in order to satisfy the pitch of the helix. In these distorted structures, each of the two carbonyl groups points either in or out of the lumen. Flipping these two peptides in and out involves thermally activated transitions, which results in four distinct conformational states at equilibrium with one another on a nanosecond time scale. This work opens the way to detailed comparative studies of structure-function relationships in biological proton ducts.

Computer Simulation↗
PubMed2006

Higher cortical deficits influence attentional processing in dementia with Lewy bodies, relative to patients with dementia of the Alzheimer's type and controls.

BACKGROUND: Attentional dysfunction is believed to be a prominent and distinguishing neuropsychological feature of dementia with Lewy bodies (DLB); yet, the specific nature of the attentional deficit and factors that can potentially influence attentional processing in DLB have not been fully defined. AIMS: To clarify the nature of the attentional deficit in early-stage DLB relative to patients with early-stage dementia of the Alzheimer's type (DAT) and elderly controls, and examine the effect of task complexity and type of cognitive load on attentional processing in DLB. METHODS: Attentional impairment and fluctuating attention were investigated in three groups of subjects--patients with clinical features of early probable DLB (n = 20), a group with early probable DAT (n = 19) and healthy elderly controls (n = 20)--using an experimental computerised reaction time paradigm. RESULTS: Patients with DLB showed greater attentional impairment and fluctuations in attention relative to patients with DAT and elderly controls. The attentional deficit was generalised in nature but increased in magnitude as greater demands were placed on attentional selectivity. Attentional deficits in DLB were most pronounced under task conditions that required more active recruitment of executive control and visuospatial cognitive processes. CONCLUSIONS: Attentional deficits in DLB are widespread and encompass all aspects of attentional function. Deficits in higher cortical function influence the degree of attentional impairment and fluctuating attention, suggesting that attentional processing in DLB is mediated by interacting cortical and subcortical mechanisms. These findings serve to clarify the nature of the attentional deficit in DLB and have potentially important ramifications for our understanding of the neurocognitive underpinnings of fluctuations.

Aged↗
PubMed2003

Refining diathesis-stress models of depression or introducing ptolemaic epicycles? Commentary on Santor.

Work guided by diathesis-stress models of depression has not been as productive or clinically relevant as hoped. Santor (this issue) suggests some promising refinements of these theories. He proposes more of a contextual focus and addresses temporal instability in presumed diatheses. However, if carelessly applied, the innovations he proposes risk being so accommodating of diverse findings as to be unfalsifiable. Santor also suggests that the selection of coping strategies may be the means by which personality mediates between life events and subsequent depression; though reasonable, this elaboration too can lead to formulations immune to data. Other issues are raised concerning the distinction between fluctuations and disturbances in mood, the role of a history of depression, and operationalization of life events. One immediate solution to some of the problems inherent in this research may be intensive study of more select samples.

Comment↗