Accuracy of planar reaching movements

This study examined the variability in movement end points in a task in which human subjects reached to targets in different locations on a horizontal surface. The primary purpose was to determine whether patterns in the variable errors would reveal the nature and origin of the coordinate system in which the movements were planned. Six subjects moved a hand-held cursor on a digitizing tablet. Target and cursor positions were displayed on a computer screen, and vision of the hand and arm was blocked. The screen cursor was blanked during movement to prevent visual corrections. The paths of the movements were straight and thus directions were largely specified at the onset of movement. The velocity profiles were bell-shaped, and peak velocities and accelerations were scaled to target distance, implying that movement extent was also programmed in advance of the movement. The spatial distributions of movement end points were elliptical in shape. The major axes of these ellipses were systematically oriented in the direction of hand movement with respect to its initial position. This was true for both fast and slow movements, as well as for pointing movements involving rotations of the wrist joint. Using principal components analysis to compute the axes of these ellipses, we found that the eccentricity of the elliptical dispersions was uniformly greater for small than for large movements: variability along the axis of movement, representing extent variability, increased markedly but nonlinearly with distance. Variability perpendicular to the direction of movement, which results from directional errors, was generally smaller than extent variability, but it increased in proportion to the extent of the movement. Therefore, directional variability, in angular terms, was constant and independent of distance. Because the patterns of variability were similar for both slow and fast movements, as well as for movements involving different joints, we conclude that they result largely from errors in the planning process. We also argue that they cannot be simply explained as consequences of the inertial properties of the limb. Rather they provide evidence for an organizing mechanism that moves the limb along a straight path. We further conclude that reaching movements are planned in a hand-centered coordinate system, with direction and extent of hand movement as the planned parameters. Since the factors which influence directional variability are independent of those that influence extent errors, we propose that these two variables can be separately specified by the brain.     

Estimated daily energy expenditure and blood lipids in adolescents: the Québec Family Study.

PURPOSE: To examine the association between estimated daily energy expenditure and blood lipids in a sample of adolescents. METHODS: The sample consisted of 415 males and 356 females aged 10-19 years, mainly French Canadian, recruited from the greater Quebec City area through the media as part of Phase I of the Quebec Family Study. Estimates of daily energy expenditure (DEE) were obtained with a 3-day physical activity record. Blood lipids were measured by standard procedures. The sample was stratified into three activity groups (least active, less than 25th percentile of DEE; moderately active, 25-74th percentile of DEE; and most active, 75th percentile or greater of DEE), and also by clinical cutpoints for blood lipids. Analysis of covariance, controlling for age and fatness, was conducted to compare blood lipids within gender across activity groups. Logistic regression analysis, controlling for age and fatness, was used to estimate the relative risk of being classified with an undesirable level of a blood lipid parameter on the basis of the DEE. RESULTS: Total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) levels were not significantly different across activity groups in males or females. High-density lipoprotein cholesterol (HDL-C) was significantly different across activity groups in males (p <.05) and females (p <.05), but the pattern of variation was different between genders. In males, the TC/HDL-C and LDL-C/HDL-C ratios decreased between the moderately active and most active groups (p <.05). Significant differences remained when subcutaneous fatness was considered as a covariate. The results from logistic regression analysis indicated that the odds ratios for low HDL-C levels was significant only in low DEE girls (odds ratio 2.83) compared with high DEE girls. CONCLUSIONS: The results suggest that increased energy expenditure and physical activity are associated with higher levels of HDL-C in adolescents of both sexes.     

Pre-adaptation, adaptation and de-adaptation to high altitude in humans: hormonal and biochemical changes at sea level

High altitude residence is known to modify body biochemistry and hormone status. However, the effects of such a sojourn on these status observed at sea level both immediately and later after return are not as well established as are the effects of an intermittent acclimation. The aim of this study was therefore to investigate these changes. To achieve our objectives, nine subjects received intermittent acclimation at low pressure in a barometric chamber (8?h daily for 5 days, day 1 at 4500 m, day 5 at 8500 m) before an expedition to the Himalayas. Hormonal and biochemical changes were studied using samples of venous blood taken at sea level before and after acclimation, after return from the expedition and 1 and 2 months after descent. Concentrations of thyroid hormones, adrenaline, noradrenaline (NA), hormones of hydromineral metabolism (aldosterone, renin, arginine vasopressin, atrial natriuretic peptide) as well as prolactin, cortisol, insulin and endothelin 1 were measured. Biochemical measurements made were plasma osmolality, and concentrations of glucose, total cholesterol, total proteins, pre-albumin, transferrin, complement 3C, apolipoproteins A₁ and B and serum iron. Acclimation induced no alteration in hormone (except for NA with increases of about 1.5, fold P<0.05) and biochemistry data. After the expedition, hormone responses were characterized by a higher total triidothyronine concentration (+18%, P<0.05) while other hormones did not vary. A linear relationship was found between thyroid-stimulating-hormone and body mass changes after the expedition (r=0.67, P<0.05). The observed increased concentrations of plasma proteins and total cholesterol (P<0.05) could be related to the restoration of lean body mass. At 1 and 2 months after return, no changes in hormones were observed but a significant decrease in transferrin concentration was noticed. The higher serum iron concentration reported after 1 month (P<0.05) could have been the result of a physiological haemolysis. It was concluded that both acclimation and the expedition in the Himalayas affected hormone status and body biochemistry status even though the observed changes were slight and rapidly reversed.     

Differential apoptotic response of J774 macrophages to alumina and ultra-high-molecular-weight polyethylene particles.

We recently identified apoptosis in in vitro wear particle-stimulated macrophages. The recent explosion of interest in apoptosis lies in the fact that it is under positive and negative regulation through evolutionary conserved biochemical pathways. It may also be possible to modulate macrophage apoptosis in the treatment of periprosthetic osteolysis. The purpose of this study was to compare the macrophage response to identically sized particles of alumina ceramic (Al2O3) and ultra-high-molecular-weight polyethylene (UHMWPE) in terms of TNF-alpha release and induction of apoptosis. J774 mouse macrophages were incubated for 0-24 h in the presence of Al2O3 and UHMWPE particles. TNF-alpha release was measured by ELISA; Poly(ADP-ribose)polymerase (PARP) and caspase-3 expression was analyzed by Western blot; DNA fragmentation (DNA laddering) was visualized on agarose gel containing ethidium bromide. Al2O3 particles induced TNF-alpha release after 4 h incubation with concentrations reaching 483 and 800 pg/ml after 24 h with 125 and 250 particles/macrophage, respectively (control = 161 pg/ml) (P < 0.05 vs. control). The same concentrations of UHMWPE particles induced a much larger and significant TNF-alpha release after only 1 h incubation, increasing up to 6250 pg/ml after 24 h (P < 0.05 vs. control). Western blot analysis demonstrated that the active caspase-3 fragment (17 kDa) and the proteolytic PARP fragment (85 kDa) were expressed after 2 h incubation with 125 and 250 Al2O3 particles/macrophage. The active caspase-3 and the PARP fragment had lower expression and appeared after a longer incubation time (8 h) with 125 and 250 UHMWPE particles/macrophage. Finally, DNA fragmentation (DNA laddering) was observed after 16 h with 125 and 250 particles of Al2O3 per macrophage whereas no laddering was induced by UHMWPE particles even after 24 h incubation. This study shows that although both Al2O3 and UHMWPE particles induce TNF-alpha release, this stimulation was much greater (8-10 times higher) with UHMWPE than Al2O3 (P < 0.05 vs. control). As well, the induction of apoptosis, as measured by activation of caspase-3, PARP cleavage and DNA laddering, is different for these two particles, being faster and more important with Al2O3 than UHMWPE. We hypothesize that the ability of Al2O3 to induce macrophage apoptosis may explain the lower TNF-alpha release observed with these particles and explain the differences seen in osteolysis patterns of ceramic-ceramic (CC) vs. metal-polyethylene (Mpe) articulations. In conclusion, apoptosis may be a major internal mechanism to decrease macrophage activity and may be a desired therapeutic endpoint. The identification of an apoptosis-related pathway in the macrophage response to ceramic particles provides crucial data for a rational approach in the treatment and/or prevention of periprosthetic osteolysis.     

Anatomic variations of the spermatic vein and endovascular treatment of left varicoceles: a pediatric series]

OBJECTIVE: To report on the high incidence of anatomical variants of the origin and course of the internal spermatic vein (ISV) discovered at the time of percutaneous embolization of left varicoceles in a pediatric population. METHODS: We reviewed retrospectively the 65 cases of left varicocele treated by percutaneous embolization (grade II and III) in our institution between 1990 and 2000. The course of the left renal vein (LRV), the origin of the ISV, and the number of ISVs and their pathway were recorded in all cases, according to the B?hren classification. RESULTS: In 37/65 (57%), the ISV was single and arose from a normal LRV (type I). The following variants were encountered: type V--circumaortic LRV 9/65 (14%); type IVb--intrarenal origin of ISV 8/65 (12%); type II--multiple ISV 5/65 (8%); and pelvic collaterals 6/65 (9%). CONCLUSION: Venous anatomical variants are frequently encountered (43%) at the time of left varicocele embolization in children. Such variants often impose some adjustments to the technique of embolization and, at times, hamper the procedure.     

Quantification and pharmacological characterization of dialysate levels of noradrenaline in the striatum of freely-moving rats: release from adrenergic terminals and modulation by α2-autoreceptors

Information concerning striatal levels of noradrenaline (NA) remains inconsistent. Here we have addressed this issue using a sensitive method of HPLC coupled to amperometric detection. The NA reuptake-inhibitor, reboxetine, selectively elevated levels of NA versus dopamine (DA), and NA levels were also selectively elevated by the α₂-adrenoceptor (AR) antagonist, atipamezole. The actions of atipamezole were mimicked by the preferential α_2A-AR antagonist, BRL44408, while JO-1 and prazosin, preferential antagonists at α_2C-ARs, caused less marked elevations in NA levels. In contrast to antagonists, the α₂-AR agonist, S18616, decreased NA levels and likewise suppressed those of DA. Unilateral lesions of the substantia nigra with 6-hydroxydopamine depleted DA levels without affecting those of NA. Further, the D₃/D₂ receptor agonist, quinelorane, decreased levels of DA without modifying those of NA. However, the D₃/D₂ receptor antagonists, haloperidol and raclopride, and the DA reuptake-inhibitor, GBR12935, elevated levels of both DA and NA. Levels of 5-HT (but not of NA or DA) were increased only by the 5-HT reuptake-inhibitor, citalopram. They were decreased by S18616 and prazosin, reflecting the inhibitory and excitatory influence of α₂- and α₁-ARs, respectively, upon serotonergic pathways. In conclusion, NA in the striatum is derived from adrenergic terminals. Its release is subject to tonic, inhibitory control by α₂-ARs, possibly involving both α_2A- and α_2C-AR subtypes, though their respective contribution requires clarification. A role of dopaminergic terminals in the reuptake of NA likely explains the elevation in its levels elicited by DA reuptake-inhibitors and D₃/D₂ receptor antagonists.     

Impact of photon energy recovery on the assessment of left ventricular volume using myocardial perfusion SPECT

BACKGROUND: Photon energy recovery (PER) is a spectral deconvolution technique validated for scatter removal in patients and phantom studies. The purpose of this study was to examine the impact of PER on left ventricular volume measurement based on myocardial perfusion single photon emission computed tomography (SPECT). METHODS AND RESULTS: SPECT acquisitions were performed by use of a static cardiac phantom and in 25 patients after a rest injection of technetium 99m sestamibi by use of multiple energy windows (126-136, 137-144, and 145-154 keV). Data were successively reconstructed with and without PER, by use of iterative reconstruction and post-processing filtering (Butterworth filter; order, 5; cutoff, 0.30 cycles/pixel). Image contrast was evaluated in reconstructed data, and volumes were calculated by use of QGS. PER increased reconstructed image contrast from 62% +/- 2.7% to 84.3% +/- 5.7% in the phantom studies (P <.0001) and from 49% +/- 2% to 73% +/- 2% in patients (P <.0001). Although it remained underestimated (P <.0001), phantom volume was higher after PER correction compared with uncorrected data (50.9 +/- 0.8 mL vs 44.6 +/- 1 mL, P <.0001). The error in volume measurement was decreased by PER correction (16.6% +/- 1.3% vs 27% +/- 1.7% [uncorrected data], P <.0001). In patients, left ventricular volume increased from 83 +/- 10 mL to 91 +/- 10 mL (P <.0001), and the PER-induced volume increase was correlated with the image contrast increase (r = 0.61, P =.001). Finally, the percentage of volume increase was higher in patients with small left ventricular volumes. CONCLUSIONS: PER has a significant impact on image contrast and left ventricular volume measurement by use of perfusion SPECT. PER improves the accuracy of phantom volume assessment. In patients, volume increase is correlated to image contrast increase and is higher in those with small ventricles.     

Effects on Behaviour and EEG of Single Chain Phospholipases A2 from Snake and Bee Venoms Injected into Rat Brain: Search for a Functional Antagonism

Abstract: Three phospholipase A₂ (PLA₂s), OS₁ and OS₁ purified from the taipan snake venom Oxyuranus scutellatus scutellatus and bee venom PLA₂ were injected to rats by the intracerebroventricular route. OS₁ showed no sign of neurotoxicity at doses at which OS₂ and bee venom PLA₂ produced multiform dose-dependent behavioural effects including motor disturbances (stereotyped movements), compulsive scratching, convulsions and breathing difficulties. EEG recordings showed at the very time when the animal was motionless the induction of several episodes of a low frequency hippocampal theta rhythm, index of long-term changes in synaptic neuroplasticity. Spike-wave discharges were also produced but the occurrence was not systematic. These seizures were often accompanied with behavioural convulsions. Blockers of NMDA receptors and drugs modifying the GABAergic transmission could not abolish the neurotoxic effects of PLA₂s except for diazepam (10 mg/kg intraperitoneally) that prevented only OS₂-induced disturbances. Blockers of L-type Ca²⁺ channels and K⁺ channel openers were also without effect. The toxicity of OS₂ and bee venom PLA₂ is probably due to their initial specific binding to their neuronal receptor sites.     

Direct evidence for the link between monoaminergic descending pathways and motor activity:: II. A study with microdialysis probes implanted in the ventral horn of the spinal cord

In order to define precisely the relation between descending monoaminergic systems and the motor system, we measured in the ventral horn of spinal cord of adult rats the variations of extracellular concentrations of 5-HT, 5-HIAA, DA and MHPG. Measurements were performed during rest, endurance running on a treadmill, and a post-exercise period, with microdialysis probes implanted permanently for 45 days. We found a slight decrease in both 5-HT and 5-HIAA during locomotion with a more marked decrease during the post-exercise period compared to the mean of rest values. In contrast, the concentration of DA and MHPG increased slightly during the exercise and decreased thereafter. These results, when compared with those of a previous study, which measured monoamines in the spinal cord white matter [C. Gerin, D. Bécquet, A. Privat, Direct evidence for the link between monoaminergic descending pathways and motor activity: I. A study with microdialysis probes implanted in the ventral funiculus of the spinal cord, Brain Res. 704 (1995) 191–201], highlight the complex regulation of the release of monoamines that occurs in the ventral horn.