Efficacy of fosfomycin in experimental osteomyelitis due to methicillin-resistant Staphylococcus aureus.

The activity of fosfomycin was evaluated in an experimental methicillin-resistant Staphylococcus aureus (MRSA) osteomyelitis model. Eighteen rats were treated for 4 weeks with 150 mg of fosfomycin/kg of body weight intraperitoneally once daily or with saline placebo. After treatment, animals were euthanized and the infected tibiae were processed for quantitative bacterial culture. Bone cultures were positive for methicillin-resistant S. aureus in all 9 (100%) untreated controls and in 2 of 9 (22.2%) fosfomycin-treated rats. Thus, fosfomycin treatment was significantly more efficacious than placebo. No development of resistance was observed after the 4-week treatment period.

Daptomycin, fosfomycin, or both for treatment of methicillin-resistant Staphylococcus aureus osteomyelitis in an experimental rat model.

The in vivo activities of daptomycin, fosfomycin, and a combination of both antibiotics against a clinical isolate of methicillin-resistant Staphylococcus aureus (daptomycin MIC, 0.25 µg/ml; fosfomycin MIC, 0.5 µg/ml) were evaluated in a rat model of osteomyelitis. A total of 37 rats with experimental osteomyelitis were treated for 4 weeks with either 60 mg/kg of body weight of daptomycin subcutaneously once daily, 75 mg/kg fosfomycin intraperitoneally once daily, a combination of both drugs, or a saline placebo. After the completion of treatment, animals were euthanized, and the infected tibiae were processed for quantitative bacterial culture. Bone cultures were found to be positive for methicillin-resistant S. aureus in 9 of 9 (100%) animals of the placebo group, in 9 of 9 (100%) animals treated with daptomycin, in 1 of 10 (10%) fosfomycin-treated rats, and in 1 of 9 (22.2%) rats comprising the combination group. Results of bacterial counts in the bone samples were expressed as log(10) CFU/g of bone and analyzed by using the Mann-Whitney U test followed by Bonferroni's multiple-comparison test. Based on bacterial counts, treatment with daptomycin was significantly superior to placebo, although it remained inferior to treatment with fosfomycin. No synergistic or antagonistic effect was observed for the combination therapy. No development of resistance against daptomycin or fosfomycin was observed after the 4-week treatment period.

Nonspecific resistance to bacterial infections. Enhancement by ubiquinone-8.

A lipid fraction from Escherichia coli was extracted with apolar solvents and was found to protect mice from a number of experimental bacterial infections. The benzoquinone, ubiquinone-8, was isolated from this extract by high pressure liquid chromatography and identified as such by nuclear magnetic resonance and mass spectrometry. At a dose of 25 mg/kg this substance was found to provide complete protection against otherwise lethal infections with gram-negative and gram-positive bacteria in mice. Treatment was most effective when given intravenously 24 h before infection. In comparative studies, ubiquinone-8 had a clearly higher activity than ubiquinones-4, Q6, and Q10. A highly significant increase in the clearance rate of bacteria from the blood by the spleen and the liver of treated animals, correlated well with the protective effect of ubiquinone-8. The compound stimulated the ability of mouse macrophages to incorporate sheep erythrocytes and significantly increased the number of antibody-producing cells in spleens of mice.

Visuomotor coordination in reaching and locomotion.

Locomotion and reaching have traditionally been regarded as separate motor activities. In fact, they may be closely connected both from an evolutionary and a neurophysiological viewpoint. Reaching seems to have evolved from the neural systems responsible for the active and precise positioning of the limb during locomotion; moreover, it seems to be organized in the spinal cord. The motor cortex and its corticospinal outflow are preferentially engaged when precise positioning of the limb is needed during locomotion and are also involved during reaching and active positioning of the hand near objects of interest. All of these motor activities require visuomotor coordination, and it is this coordination that could be achieved by the motor cortex and interconnected parietal and cerebellar areas.

Motor cortical activity in a context-recall task.

A monkey was trained to respond on the basis of the serial position of a test stimulus in a sequence. First, three stimuli were presented successively on a circle. Then one of them (except the last) changed color (test stimulus) and served as the go signal: The monkey was required to produce a motor response in the direction of the stimulus that followed the test stimulus. When the test stimulus was the second in the sequence, there was a change in motor cortical activity from a pattern reflecting the direction of this stimulus to the pattern associated with the direction of the motor response. This change was abrupt, occurred 100 to 150 milliseconds after the go signal, and was evident both in the activity of single cells and in the time-varying neuronal population vector. These findings identify the neural correlates of a switching process that is different from a mental rotation described previously.

Motor cortical encoding of serial order in a context-recall task.

The neural encoding of serial order was studied in the motor cortex of monkeys performing a context-recall memory scanning task. Up to five visual stimuli were presented successively on a circle (list presentation phase), and then one of them (test stimulus) changed color; the monkeys had to make a single motor response toward the stimulus that immediately followed the test stimulus in the list. Correct performance in this task depends on memorization of the serial order of the stimuli during their presentation. It was found that changes in neural activity during the list presentation phase reflected the serial order of the stimuli; the effect on cell activity of the serial order of stimuli during their presentation was at least as strong as the effect of motor direction on cell activity during the execution of the motor response. This establishes the serial order of stimuli in a motor task as an important determinant of motor cortical activity during stimulus presentation and in the absence of changes in peripheral motor events, in contrast to the commonly held view of the motor cortex as just an "upper motor neuron."

Cognitive neurophysiology of the motor cortex.

A major challenge of current neuroscience is to elucidate the brain mechanisms that underlie cognitive function. There is no doubt that cognitive processing in the brain engages large populations of cells. This article explores the logic of investigating these problems by combining psychological studies in human subjects and neurophysiological studies of neuronal populations in the motor cortex of behaving monkeys. The results obtained show that time-varying psychological processes can be visualized in the time-varying activity of neuronal populations. Moreover, the functional interactions between cells in the motor cortex are very similar to those observed in a massively interconnected artificial network performing the same computation.

Neuronal population coding of movement direction.

Although individual neurons in the arm area of the primate motor cortex are only broadly tuned to a particular direction in three-dimensional space, the animal can very precisely control the movement of its arm. The direction of movement was found to be uniquely predicted by the action of a population of motor cortical neurons. When individual cells were represented as vectors that make weighted contributions along the axis of their preferred direction (according to changes in their activity during the movement under consideration) the resulting vector sum of all cell vectors (population vector) was in a direction congruent with the direction of movement. This population vector can be monitored during various tasks, and similar measures in other neuronal populations could be of heuristic value where there is a neural representation of variables with vectorial attributes.

The motor cortex and the coding of force.

The relation of cellular activity in the motor cortex to the direction of two-dimensional isometric force was investigated under dynamic conditions in monkeys. A task was designed so that three force variables were dissociated: the force exerted by the subject, the net force, and the change in force. Recordings of neuronal activity in the motor cortex revealed that the activity of single cells was directionally tuned and that this tuning was invariant across different directions of a bias force. Cell activity was not related to the direction of force exerted by the subject, which changed drastically as the bias force changed. In contrast, the direction of net force, the direction of force change, and the visually instructed direction all remained quite invariant and congruent and could be the directional variables, alone or in combination, to which cell activity might relate.

Mental rotation of the neuronal population vector.

A rhesus monkey was trained to move its arm in a direction that was perpendicular to and counterclockwise from the direction of a target light that changed in position from trial to trial. Solution of this problem was hypothesized to involve the creation and mental rotation of an imagined movement vector from the direction of the light to the direction of the movement. This hypothesis was tested directly by recording the activity of cells in the motor cortex during performance of the task and computing the neuronal population vector in successive time intervals during the reaction time. The population vector rotated gradually counterclockwise from the direction of the light to the direction of the movement at an average rate of 732 degrees per second. These results provide direct, neural evidence for the mental rotation hypothesis and indicate that the neuronal population vector is a useful tool for "reading out" and identifying cognitive operations of neuronal ensembles.

Functional magnetic resonance imaging of motor cortex: hemispheric asymmetry and handedness.

A hemispheric asymmetry in the functional activation of the human motor cortex during contralateral (C) and ipsilateral (I) finger movements, especially in right-handed subjects, was documented with nuclear magnetic resonance imaging at high field strength (4 tesla). Whereas the right motor cortex was activated mostly during contralateral finger movements in both right-handed (C/I mean area of activation = 36.8) and left-handed (C/I = 29.9) subjects, the left motor cortex was activated substantially during ipsilateral movements in left-handed subjects (C/I = 5.4) and even more so in right-handed subjects (C/I = 1.3).

Evidence for physiological importance of calcitonin in the regulation of plasma calcium in rats.

To determine the physiological importance of calcitonin in the regulation of plasma calcium, studies were carried out in fasting animals to (a) assess the acute effects of thyroparathyroidectomy (TPTX) and thyroidectomy (TX) on plasma and urinary calcium; (b) investigate whether the changes in plasma calcium produced by removal of the glands were dependent on the presence of the kidney; and (c) determine if the effect of TPTX on plasma calcium is affected by age. Except where otherwise indicated, all studies were carried out on fasting male Wistar rats weighing over 300 g. The following observations were made. (a) TPTX and TX caused an increase in plasma calcium in nephrectomized animals. (b) This increase was not dependent on nephrectomy since in intact animals bearing autoparathyroid transplants TX also caused a significant rise in the mean plasma calcium level (0.37 mg/100 ml at 1 1/2 h). (c) Urinary calcium increased twofold in the 3-h period immediately after TX. (d) In unnephrectomized immature (50-g) rats, TPTX caused a progressive decrease in plasma calcium in contrast to old (360-g) rats, where a significant fall observed at 6 h was preceded by an increase in plasma calcium (0.5 mg/100 ml at 1 1/2 h). From these observations we conclude that: (a) calcitonin must play an important physiological role in the regulation of plasma calcium since the termination of its basal secretion caused an immediate but transient increase in plasma calcium in old unfed rats; (b) the relative importance of calcitonin and parathyroid hormone in the acute regulation of plasma calcium is age-related; and (c) the action of parathyroid hormone on bone may be modified by changes in ambient calcitonin concentration.

Current issues in directional motor control.

Many studies during the past 15 years have shown that the direction of motor output (movement or isometric force) is an important factor for neuronal activity in the motor cortex, both at the level of single cells and at the level of neuronal populations. Recent studies have investigated several new aspects of this problem including the effect of posture, the relations to time-varying movement parameters (for example, position, velocity and acceleration) and the cortical representation of memorized simple movements and complex-movement trajectories. Furthermore, the neural correlates of directional operations, such as mental rotation and memory-scanning of visuomotor directions, have also been investigated. In addition, neural networks have been used to model dynamic, time-varying, spatial motor trajectories.

Neural aspects of cognitive motor control.

Traditionally, motor and cognitive functions were studied separately; however, the investigation of processes at the interface between cognition and action has become more and more popular recently. Typical research goals include the identification of the processes involved using experimental psychological methods, and understanding the neural mechanisms underlying these processes using neurophysiological and functional neuroimaging methods. Specifically, there has been a special emphasis during the past few years on timing mechanisms, practice effects, and the application of rules in guiding action. New information concerning the neural mechanisms involved is being acquired at a rapid pace, albeit mostly within a descriptive framework. With respect to specific brain areas, a key finding has been the clear involvement of the primary motor cortex in complex tasks engaging diverse motor and cognitive dimensions.

Cortical control of motor behavior at the cellular level.

The studies reviewed in this paper describe the relations of single-cell activity in central motor structures to complex visuomotor tasks and document the fact that various cortical areas process visuomotor information in parallel. Moreover, the studies provide clear evidence that the map in the motor cortex is modifiable and dynamically maintained.

In vitro antimicrobial activity of the novel polymeric guanidine Akacid plus.

The bactericidal and fungicidal activity of Akacid plus, a novel polymeric compound of the cationic family of disinfectants, was compared with chlorhexidine digluconate using quality control strains of Staphylococcus aureus, Enterococcus hirae, Escherichia coli, Pseudomonas aeruginosa, Candida albicans and Aspergillus niger. In vitro activity was determined using the quantitative suspension tests described by the European Committee for Standardization. These use concentrations of 0.01-0.5% against bacterial strains/C. albicans, with 0.5-4% against A. niger, and exposure times of 5, 15 and 60 min in the presence and absence of 0.3% bovine albumin and with dilution in distilled and hard water. In the basic quantitative suspension test, Akacid plus destroyed all bacterial pathogens at a concentration of 0.1% in < or =5 min. Chlorhexidine was also highly active against S. aureus, E. coli and P. aeruginosa, but failed to eliminate E. hirae within 5 min. A high organic load reduced the bactericidal activity of both disinfectants slightly. Akacid plus showed fungicidal activity against C. albicans within 15-60 min and eliminated A. niger at a concentration of 1% in 5 min of contact. Chlorhexidine was fungicidal against C. albicans, but not against A. niger.

A comparative study of the effects of cholesterol and sclareol, a bioactive labdane type diterpene, on phospholipid bilayers.

Sclareol (labd-14-ene-8,13-diol) is a highly water-insoluble molecule that belongs to the labdane type diterpenes and is characterized as a biologically active molecule, due to its cytotoxic and cytostatic effects against human leukemic cell lines. A superimposition study between sclareol and cholesterol, based on their corresponding hydrophobic and polar molecular segments calculated from their lipophilic profiles, revealed their spatial similarities. This structural similarity between the two molecules prompted us to compare their effects on the structure and stability of phospholipid dipalmitoylphosphatidylcholine (DPPC) membranes. Differential scanning calorimetry (DSC) was applied to compare the thermal changes caused by either cholesterol or sclareol when are incorporated in DPPC bilayers. The results showed that sclareol is incorporated into phospholipid model membranes and mimics the thermal effects of cholesterol especially at concentrations up to X(sclareol)=9.1 mol%. These effects can be summarized as the abolition of pre-transition, lowering of the main phase transition and reduction of the enthalpy change (DeltaH) of the gel to liquid-crystalline phase transition of DPPC bilayers. At concentrations X> or =16.7 mol%, sclareol and cholesterol caused different heterogeneity in lipid bilayers or a reversible transition from a vesicular suspension to an extended peak bilayer network. This different fluidization, exerted by the two molecules at high concentration, may be related to their different stability and the z-average mean diameter of the liposomes they form. Small unilamellar vesicles, prepared by the thin film hydration method showed that DPPC bilayers containing a high concentration of sclareol in equimolar ratio sclareol:cholesterol were unstable, in contrast to the ones containing only cholesterol.

Development of simple thiol-reactive liposome formulations, one-step analysis and physicochemical characterization.

The aim of this study was to synthesize simple thiol-reactive conjugates from maleimide and lipoamines (stearylamine or oleylamine) and to develop a simple, fast and low-cost method for the preparation of lyophilized general-purpose thiol-reactive liposomes. A formulation of egg phosphatidylcholine-dipalmitoylphoshatidylglycerol (9:0.1 molar ratio) was developed and characterized. Freeze-drying methodology was established to produce a stock of liposomes and the physicochemical characteristics of the reconstituted liposomes were compared with those of the initial preparation. The physicochemical properties (size and zeta potential) of the new liposomal formulations were studied. High-performance thin-layer chromatography coupled to a flame ionization detector was applied for one-step analysis of the liposomal components and for determining the maleimide-lipoamine conjugates phospholipid molar ratio. The differences concerning the incorporation efficiency of the synthetic conjugates into liposomes were discussed on the basis of their conformational properties. The small difference in structure between the two thiol-reactive conjugates (i.e., the C18 alkyl chain double bond) causes a considerable difference in phospholipids packing of the resulting lipidic bilayers of the liposomes; the conformational bending of conjugate maleimide-oleylamine may contribute to the final architecture of liposomes.

Intraperitoneal insulin delivery decreases the levels of chylomicron remnants in patients with IDDM.

OBJECTIVE: To investigate whether intraperitoneal insulin (IPII) decreases the levels of circulating chylomicron remnants in patients with insulin-dependent diabetes mellitus (IDDM). RESEARCH DESIGN AND METHODS: Eight nonobese, normolipidemic IDDM patients were studied twice: before (while on subcutaneous insulin) and 6 months after initiation of IPII by a programmable implanted medication system. Fasting and mean blood glucose, HbA1, and lipid values were determined. Blood samples were also drawn before and every 2 h for 10 h after ingestion of a fat meal (corn oil + Vitamin A). Triglycerides (TGs), apolipoprotein B (apoB), and retinyl esters were determined over time in two TG-rich lipoprotein subfractions (Sf > 100 and Sf20-100) isolated from plasma by density-gradient ultracentrifugation. RESULTS: IPII slightly decreased the mean blood glucose from 7.8 +/- 1.1 to 7.4 +/- 1.1 mmol/l (mean +/- SD, P = 0.027, paired Student's t test) and the HbA1 from 9.4 +/- 1.5 to 8.7 +/- 1.2 (NS). TG and apoB levels in postprandial Sf > 100 and Sf20-100 were not changed by IPII. On IPII, however, retinyl ester levels in Sf > 100 decreased (P = 0.05, analysis of variance [ANOVA]) and tended to be lower in Sf20-100 (P = 0.075). In addition, following IPII, the retinyl ester:apoB ratio was lower in Sf > 100 (P = 0.0002) and marginally lower (P = 0.06) in Sf 20-100. CONCLUSIONS: IPII decreased chylomicron remnant levels, which might decrease the atherosclerotic risk in IDDM. Since glycemic control was only slightly improved, the effect was most likely due to the intraperitoneal route of delivery.