The design and conduct of clinical trials to limit missing data.

This article summarizes recommendations on the design and conduct of clinical trials of a National Research Council study on missing data in clinical trials. Key findings of the study are that (a) substantial missing data is a serious problem that undermines the scientific credibility of causal conclusions from clinical trials; (b) the assumption that analysis methods can compensate for substantial missing data is not justified; hence (c) clinical trial design, including the choice of key causal estimands, the target population, and the length of the study, should include limiting missing data as one of its goals; (d) missing-data procedures should be discussed explicitly in the clinical trial protocol; (e) clinical trial conduct should take steps to limit the extent of missing data; (f) there is no universal method for handling missing data in the analysis of clinical trials - methods should be justified on the plausibility of the underlying scientific assumptions; and (g) when alternative assumptions are plausible, sensitivity analysis should be conducted to assess robustness of findings to these alternatives. This article focuses on the panel's recommendations on the design and conduct of clinical trials to limit missing data. A companion paper addresses the panel's findings on analysis methods.

Neuronal binucleation in Alzheimer disease hippocampus.

AIMS: The literature and teachings instruct that neurones in the adult brain are fully differentiated, quiescent cells that never divide. Somewhat surprisingly, and counter to such dogma, susceptible neurones in Alzheimer disease display an activated cell cycle phenotype. However, whether this leads to a coordinated procession through the cell cycle is unclear, particularly whether neurones enter anaphase and beyond. To begin to address this issue, in this study we sought to determine whether nuclear division occurs in these neurones. METHODS: We examined a series of 101 archived, routinely stained hippocampal sections collected at post mortem for neuropathological evaluation for evidence of neuronal binucleation. RESULTS: We report for the first time, binucleated neurones within the hippocampus in cases of Alzheimer disease but not in control cases (P < 0.05). CONCLUSIONS: While a relatively rare event, occurring once every 20,000 neurones, this morphological evidence that neuronal cells within the cortical regions of the adult human brain in Alzheimer disease contain two nuclei supports the hypothesis that neuronal cells can re-enter into a coordinated cell cycle that culminates in nuclear division.

Rasmussen syndrome and CNS granulomatous disease with NOD2/CARD15 mutations.

Rasmussen syndrome (RS) is a clinical diagnosis characterized by persistent focal seizures in a previously healthy child. Occasionally, the typical features of RS may be followed by another diagnosis. We discuss the course of a 12-year-old girl who presented with RS but was later diagnosed with CNS granulomatous disease and NOD2/CARD15 mutations. Her response to infliximab suggests that it should be included in immune-modulatory therapies used to treat these refractory disorders.

Dextran 40 (Rheomacrodex) or Polygeline (Haemaccel) as an epidural patch for post dural puncture headache: a neurotoxicity study in a rat model of Dextran 40 and Polygeline injected intrathecally.

BACKGROUND AND OBJECTIVE: Although an epidural autologous blood patch is considered the most effective treatment for post dural puncture headache, which sometimes occurs following spinal or inadvertent spinal anaesthesia, there remains a need for alternative materials for epidural patches. We investigated the potential neurotoxicity of Dextran 40 (Rheomacrodex) and Polygeline (Haemaccel) used for this purpose in a rat model. METHODS: Repeated boluses of 10% Dextran 40, 3.5% Polygeline or 0.9% saline were injected intrathecally over a period of 1 month in three groups of rats. RESULTS: No behavioural or clinical derangements were observed in any of the three groups during this period. After sacrifice of the animals at the end of the experiment, no significant differences in the histopathological appearances of the spinal cords in the three groups were observed. No toxic effects diminishing viability of spinal cord cells were evident. Similarly, viability of renal, hepatic and peripheral blood mononuclear cells remained unaffected (98% +/- 2%). CONCLUSIONS: No deleterious effects, clinical or cellular, were evident in this rat model when Dextran 40 or Polygeline were injected intrathecally. Thus, both substances can be considered as possible alternative materials for epidural patches.

Fluid preload before spinal anaesthesia in Caesarean section: the effect on neonatal acid-base status.

BACKGROUND AND OBJECTIVE: We evaluated the effect of two different preload solutions: (i) Ringer's lactate (compound sodium lactate intravenous infusion BP) and (ii) 0.9% sodium chloride solution on the neonatal acid-base status of the newborn infants. The two standard regimens were compared to detect a possible difference. METHODS: A 2 L crystalloid fluid bolus was administered immediately before spinal anaesthesia for elective Caesarean section in two groups of 20 healthy parturients, while rigorously maintaining maternal normotension. RESULTS: No significant differences in the Apgar scores at 1 and 5 min, or infant well-being were demonstrated in either of the two groups. The data show that umbilical artery PCO2 is lower in the Ringer's lactate group and that pH is insignificantly higher by 0.03. CONCLUSIONS: The choice of Ringer's lactate or saline for fluid preload does not have any effect on neonatal well-being.

Orientation-dependent C60 electronic structures revealed by photoemission spectroscopy.

We observe, with angle-resolved photoemission, a dramatic change in the electronic structure of two C60 monolayers, deposited, respectively, on Ag (111) and (100) substrates, and similarly doped with potassium to half filling of the C60 lowest unoccupied molecular orbital. The Fermi surface symmetry, the bandwidth, and the curvature of the dispersion at Gamma point are different. Orientations of the C60 molecules on the two substrates are known to be the main structural difference between the two monolayers, and we present new band-structure calculations for some of these orientations. We conclude that orientations play a key role in the electronic structure of fullerides.

Leucoencephalopathy with neuroaxonal spheroids (LENAS) presenting as the cerebellar subtype of multiple system atrophy.

Leucoencephalopathy with neuroaxonal spheroids (LENAS) is a rare disease of cerebral and cerebellar white matter. LENAS usually presents as a disorder of cognition and behaviour, or with gait dysfunction and ataxia. This report describes a patient who had a 14 year course of progressive neurological decline consistent with a clinical diagnosis of probable multiple system atrophy, with prominent cerebellar dysfunction and dysautonomia. Formal autonomic laboratory testing was consistent with global autonomic dysfunction of central origin. However, magnetic resonance imaging showed extensive white matter signal abnormalities, in addition to moderate cerebral and cerebellar atrophy. On postmortem microscopic examination, there were numerous axonal spheroids throughout the white matter of both regions. This case of LENAS presented unique clinical characteristics, and typical pathological findings.

In vitro activity of LY393558, an inhibitor of the 5-hydroxytryptamine transporter with 5-HT(1B/1D/2) receptor antagonist properties.

1-[2-[4-(6-fluoro-1H-indol-3-yl)-3,6-dihydro-1(2H)-pyridinyl]ethyl]-3-isopropyl-6-(methylsulphonyl)-3,4-dihydro-1H-2,1,3-benzothiadiazine-2,2-dioxide (LY393558) is a potent inhibitor of [3H]5-hydroxytryptamine ([3H]5-HT) uptake into rat cortical synaptosomes (pIC(50)=8.48+/-0.12). It produces a dextral shift of the 5-HT dose-response curves for the binding of GTPgamma[35S] to human 5-HT(1B) (pK(b)=9.05+/-0.14) and 5-HT(1D) (pK(b)=8.98+/-0.07) receptors and inhibits the contractile response of the rabbit saphenous vein to the 5-HT(1B/D) receptor agonist, sumatriptan (pK(b)=8.4+/-0.2). In addition, it is an antagonist at the 5-HT(2A) (pK(i)=7.29+/-0.19) and 5-HT(2B) (pK(i)=7.35+/-0.11) receptors. Presynaptic autoreceptor antagonist activity was demonstrated by its ability to potentiate the K(+)-induced outflow of [3H]5-HT from guinea pig cortical slices (pEC(50)=7.74+/-0.05 nM) in which the 5-HT transporter had been inhibited by a maximally effective concentration of paroxetine. It is concluded that LY393558 should be an effective antidepressant with the potential to produce an earlier onset of efficacy than selective serotonin uptake inhibitors.

Potent antagonism of 5-HT(3) and 5-HT(6) receptors by olanzapine.

The interaction of the psychotropic agent olanzapine with serotonin 5-HT(3) and 5-HT(6) receptors was investigated. Olanzapine did not contract the isolated guinea pig ileum, but blocked contractions induced by the 5-HT(3) receptor agonist 2-methyl serotonin (2-CH(3) 5-HT) with a pK(B) value of 6.38+/-0.03, close to the affinity of the 5-HT(3) receptor antagonist ondansetron. The atypical antipsychotic risperidone (1 microM) did not significantly inhibit 2-CH(3) 5-HT-induced contractions. Olanzapine had high affinity (pK(i)=8.30+/-0.06) for human 5-HT(6) receptors in radioligand binding studies. Olanzapine did not stimulate [35S]guanosine-5'-O-(3-thio)triphosphate ([35S]GTPgammaS) binding to the G protein G(s) in cells containing human 5-HT(6) receptors, but inhibited 5-HT-stimulated [35S]GTPgammaS binding (pK(B)=7.38+/-0.16). Among other antipsychotics investigated, clozapine antagonized 5-HT(6) receptors with a pK(B)=7.42+/-0.15, ziprasidone was three-fold less potent, and risperidone, quetiapine and haloperidol were weak antagonists. Thus, olanzapine was not an agonist, but was a potent antagonist at 5-HT(6) receptors and had marked antagonism at 5-HT(3) receptors.

Amplifying Sommerfeld precursors and producing a discontinuous index of refraction with gains and losses.

We show that for specially designed linear dispersive media with one absorption line and one gain line the Sommerfeld precursors of a pulse can be amplified leading to an earlier detection of the signal. Also, we show that in some systems with one strong absorption line, a carefully placed gain resonance must induce a discontinuity in the imaginary part of the frequency dependent index of refraction and in the first derivative of its real part.

Cigarette smoking and chewing gum: response to a laboratory-induced stressor.

The current study examined the anxiolytic effects of cigarette smoking and chewing gum on urge to smoke, withdrawal, and anxiety in response to a public speaking task in 45 undergraduate smokers. Participants were asked to smoke, chew gum, or do nothing in response to the stressor. Participants completed measures of anxiety, withdrawal symptoms, and urge to smoke pre- and poststressor. The smoke group reported fewer urges to smoke pre- and poststressor than the other groups. The smoke and gum groups reported fewer withdrawal symptoms than did the control group poststressor. Chewing gum was helpful in managing levels of withdrawal symptoms compared with the control group. Groups did not differ on measures of anxiety. Results suggest that smoking in response to a stressor may not reduce levels of affective stress. Furthermore, chewing gum may be helpful in managing withdrawal symptoms in response to a stressor.

Mechanical instability and ideal shear strength of transition metal carbides and nitrides.

The ideal shear strength of transition metal carbides and nitrides is calculated with the use of the ab initio pseudopotential density functional method. The microscopic mechanism that limits the ideal strength is studied using full atomic and structural relaxation and the results of electronic structure calculations. It is shown that plasticity in perfect crystals can be triggered by electronic instabilities at finite strains. Our study explicitly demonstrates that the ideal strength in these materials is limited by the elastic instability which is in turn initiated by electronic instabilities. The potential application of alloy hardening due to the onset of instabilities at different strains is also discussed.

Investigations into the physiological role of muscarinic M2 and M4 muscarinic and M4 receptor subtypes using receptor knockout mice.

Determination of muscarinic agonist-induced parasympathomimetic effects in wild type and M2 and M4 muscarinic receptor knockout mice revealed that M2 receptors mediated tremor and hypothermia, but not salivation. The M4 receptors seem to play a modest role in salivation, but did not alter hypothermia and tremor. In the M2 knockout mice, agonist-induced bradycardia in isolated spontaneously beating atria was completely absent compared to their wild type litter mates, whereas agonist-induced bradycardia was similar in the M4 knockout and wild type mice. The potency of carbachol to stimulate contraction of isolated stomach fundus, urinary bladder and trachea was reduced by a factor of about 2 in the M2 knockout mice, but was unaltered in the M4 knockout mice. The binding of the muscarinic agonist, [3H]-oxotremorine-M, was reduced in cortical tissue from the M2 knockout mice and to a lesser extent from the M4 knockout mice, and was reduced over 90% in the brain stem of M2 knockout mice. The data demonstrate the usefulness of knockout mice in determining the physiological function of peripheral and central muscarinic receptors.

Computational design of direct-bandgap semiconductors that lattice-match silicon.

Crystalline silicon is an indirect-bandgap semiconductor, making it an inefficient emitter of light. The successful integration of silicon-based electronics with optical components will therefore require optically active (for example, direct-bandgap) materials that can be grown on silicon with high-quality interfaces. For well ordered materials, this effectively translates into the requirement that such materials lattice-match silicon: lattice mismatch generally causes cracks and poor interface properties once the mismatched overlayer exceeds a very thin critical thickness. But no direct-bandgap semiconductor has yet been produced that can lattice-match silicon, and previously suggested structures pose formidable challenges for synthesis. Much recent work has therefore focused on introducing compliant transition layers between the mismatched components. Here we propose a more direct solution to integrating silicon electronics with optical components. We have computationally designed two hypothetical direct-bandgap semiconductor alloys, the synthesis of which should be possible through the deposition of specific group-IV precursor molecules and which lattice-match silicon to 0.5-1% along lattice planes with low Miller indices. The calculated bandgaps (and hence the frequency of emitted light) lie in the window of minimal absorption in current optical fibres.

Vacancy hardening and softening in transition metal carbides and nitrides.

The effects of vacancies on mechanical properties of the transition metal carbides and nitrides are studied using the ab initio pseudopotential approach. Calculated shear elastic stiffness and electronic structures show that the vacancy produces entirely different effects on the mechanical strength of groups IVb nitrides and Vb carbides. It is found that the occupation of shear-unstable metallic dd bonding states changes essentially in an opposite way for the carbides and nitrides in the presence of vacancies, resulting in different responses to shear stress. Our study provides an atomistic understanding of the anomaly in hardness for these substoichiometric materials.

Intrathecal anaesthesia alters intracellular Ca2+/Mg2+ homeostasis in the spinal cord neurones of experimental rats.

BACKGROUND AND OBJECTIVE: The effect of anaesthesia induced by intrathecal injection of 6.3% MgSO4 or 4% lidocaine on intracellular electrolyte homeostasis in spinal cord neurones of a rat model was investigated. METHODS: Intracellular Ca2+, Mg2+, Na+ and K+ concentrations were determined at different times after intrathecal administration of NaCl (saline, a control group), MgSO4 or lidocaine. RESULTS: In both thoracic and lumbar spinal cord segments, Ca2+ concentrations rose significantly 30 min and 2 h after 6.3% MgSO4 injection, and after 24 h were still significantly increased compared with the values obtained from the control group which were subjected to sham 'anaesthesia' by saline injection (172, 121 and 108 ng mg-1 protein vs. control 23 ng mg-1 protein, respectively, in the thoracic segment and 222, 229 and 176 ng mg-1 protein vs. control 43 ng mg-1 protein, respectively, in the lumbar segment). Lidocaine injection also produced a significant increase in intracellular Ca2+ in the thoracic and lumbar spinal cord segments (69, 64 and 53 ng mg-1 protein vs. control 33.4 ng mg-1 protein and 26, 94 and 46 ng mg-1 protein vs. 23 ng mg-1 protein respectively). Only a modest rise in intracellular Mg2+ was observed after intrathecal MgSO4 or lidocaine injection (27 ng mg-1 protein vs. 23 ng mg-1 protein). Na+ and K+ concentrations decreased 24 h after MgSO4 and 1 h after lidocaine injection. CONCLUSION: Intrathecal anaesthesia by MgSO4 or lidocaine alters intracellular electrolyte homeostasis in spinal cord neurones of experimental rats. A possible common mechanism of action via Ca2+ ion channels is discussed.

Effect of LY287045, a thrombin/trypsin inhibitor, on thrombin and trypsin-induced aortic contraction and relaxation.

The active site tripeptide arginal inhibitor of thrombin, LY287045, was used to study thrombin-induced aortic relaxation and contraction, two responses that differ both pharmacologically and physiologically. Although thrombin (10(-7) M) and trypsin (10(-6) M) were tachyphylactic upon repeated administration, trypsin contracted the aorta following thrombin-induced contraction. LY287045 (10(-7) M) attenuated thrombin-induced vasorelaxation, but not vasoconstriction with -log K(B) of 8.4. LY287045 (10(-7) M) also attenuated vasorelaxation, but not vasoconstriction to trypsin, another serine-protease with a thrombin-like catalytic triad, with similar potency (-log K(B) = 8.6) to that for thrombin. Consistent with these vascular effects, LY287045 inhibited the protease activity of both thrombin and trypsin. To explore further the selective inhibitory effect of LY287045 on protease-induced relaxation, we examined the effect of LY287045 on the nitric oxide and prostacyclin pathways and found that LY287045 did not alter vascular responses mediated by nitric oxide or prostacyclin. Likewise, LY287045 did not exert a direct inhibitory effect on the relaxant protease-activated receptor (PAR) since relaxation to the PAR-2-activating peptide was not blocked. The selective effect of LY287045 to inhibit only protease-induced endothelial-dependent relaxation demonstrated that protease inhibition will not affect all protease responses equally. Furthermore, increases in trypsin and thrombin have been associated with inflammation and angiogenesis. To the extent that these findings suggest that LY287045 exhibit dual protease inhibition of endothelial responses, LY287045 may have specific utility in hypotensive inflammatory diseases and in cancer metastases where both trypsin and thrombin have been implicated as causative agents.

High accuracy many-body calculational approaches for excitations in molecules.

Two state-of-the-art computational approaches: quantum Monte Carlo and GW with exciton effects [GW-BSE (Bethe-Salpeter equation)] are employed to calculate ionization potentials, electron affinities, and first excited singlet and triplet energies for the silane and methane molecules. Results are in excellent agreement between these dramatically different approaches and with available experiment. The optically forbidden triplet excitation in silane is predicted to lie roughly 1 eV higher than previously reported. In the GW-BSE method, we demonstrate that inclusion of off-diagonal matrix elements in the self-energy operator is crucial for an accurate picture.